teaching aids in hydrology; technical papers in hydrology; vol.:27
TRANSCRIPT
. - Technical Papers in Hydrology ii 'L"
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Teaching aids in hydrology
Second edition
A contribution to the International Hydrological Programme
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27
Unesco
Technical Papers in Hydrology 27
In this series:
1. 2. 3. 4. 5.
6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27.
Perennial ice and snow masses. A guide for compilation and assemblage of data for a world inventory Seasonal snow cover. A guide for measurement, compilation and assemblage of data. Variations of existing glaciers. A guide to international practices for their measurement. Antartic glaciology in the International Hydrological Decade. Combined heat, ice and water balances at selected glacier basins. A guide for compilation and assemblage of data for glacier mass balance measurements. Textbooks on hydrology - analyses and synoptic tables of contents of selected textbooks. Scientific framework of world water balance. Flood studies - an international guide for collection and processing of data. Guide to world inventory of sea, lake, and river ice. Curricula and syllabi in hydrology. Teaching aids in hydrology. Ecology of water weeds in the netropics. The teaching of hydrology. Legends for geohydrochemical maps. Research on urban hydrology, vol. 1. Research on urban hydrology, vol. 2. Hydrological problems arising from the development of energy. Urban hydrological modelling and catchment research, international summary. Remote sensing of snow and ice. Predicting effects of power plant once-through cooling on aquatic systems. Research on urban hydrology, vol. 3. Curricula and syllabi in hydrology. Dispersion and self-purification of pollutants in surface water systems. Experimental facilities in water resources education. Teaching the systems approach to water resources development. Study of the relationship between water quality and sediment transport. Teaching aids in hydrology - Second edition.
A contribution to the International Hydrological Programme
Teaching ,’. I . d. aids in hydrology Second edition
A report by IHP Working Group “Teaching aids in hydrology”
Chairman : U. Maniak,
Editor : P.W. Jowitt, Federal Republic of Germany
United Kingdom
Unesco
The designations employed and the presentation of the material do not imply the expression of any opinion whatsoever on the part of Unesco concerning the legal status of any country or territory, or of its authorities, or concerning the frontiers of any country or territory.
Published in 1985 by the United Nations Educational, Scientific and Cultural Organization 7, place de Fontenoy, 75700 Paris Printed by Presses Universitaires de France, Vendbme
OUnesco 1985 Printed in France
ISBN 92-3-102304-7
Preface
Although the total amount of water on earth is generally assumed to have remained virtually constant, the rapid growth of population, together with the extension of irrigated agriculture and industrial development, are stressing the quantity and quality aspects of the natural system. Because of the increasing problems, man has begun to realize that he can no longer follow a "use and discard" philosophy - either with water resources or any other natural resource. As a result, the need for a consistent policy of rational management of water resources has become evident.
water availability and movement. Thus, as a contribution to the solution of the world's water problems, Unesco, in 1965, began the first world-wide programme of studies of the hydrological cycle - the International Hydrological Decade (IHD). The research programme was complemented by a major effort in the field of hydrological education and training. The activities under- taken during the Decade proved to be of great interest and value to Member States. By the end of that period, a majority of Unesco's Member States had formed IHD National Committees to carry out relevant national activities and to participate in regional and international co- operation within the IHD programme. The knowledge of the world's water resources had substan- tially improved. Hydrology became widely recognized as an independent professional option and facilities for the training of hydrologists had been developed.
logical Decade and following the recommendation of Member States, Unesco, in 1975, launched a new long-term intergovernmental programme, the International Hydrological Programme (IHP), to follow the Decade.
from the beginning of a need to direct its activities toward the practical solutions of the world's very real water resources problems. Accordingly, and in line with the recommendations of the 1977 United Nations Water Conference, the objectives of the International Hydrological Programme have been gradually expanded in order to cover not only hydrological processes con- sidered in interrelationship with the environment and human activities, but also the scientific aspects of multi-purpose utilization and conservation of water resources to meet the needs of economic and social development. Thus, while maintaining IHP's scientific concept, the objec- tives have shifted perceptibly towards a multidisciplinary approach to the assessment, planning, and rational management of water resources.
issued : "Studies and Reports in Hydrology" and "Technical Papers in Hydrology". In addition to these publications, and in order to expedite exchange of information in the areas in which it is most needed, works of a preliminary nature are issued in the form of Technical Documents.
The "Technical Papers in Hydrology" series, to which this volume belongs, is intended to provide a means for the exchange of information on hydrological techniques and for the coordi- nation of research and data collection. Unesco uses this series as a means of bringing together and making known the experience accumulated by hydrologists throughout the world.
Rational water management, however, should be founded upon a thorough understanding of
Conscious of the need to expand upon the efforts initiated during the International Hydro-
Although the IHP is basically a scientific and educational programme, Unesco,has been aware
As part of Unesco's contribution to the objectives of the IHP, two publication series are
Contents
I INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1 1.2 1.3 1.4
I1
2.1 2.1.1 2.1.2 2.1.3 2.2 2.2.1 2.2.2 2.2.3 2.2.4
111
3.1 3.2 3.3 3.4
IV
4.1 4.2 4.2.1
V
5.1 5.1.1 5.1.2 5.2 5.2.1 5.2.2 5.2.3 5.2.4 5.2.5 5.3 5.3.1 5.3.2 5.3.3
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Purpose 1 Origins 1 Scope and limitations 1
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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Content 2
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . TEACHINGHYDROLOGY 3
Improvement of the learning process Motivation of learning - - - . - Educational technology - - - - - Teaching methods . . . . . . . . . Organisation of teaching activities Organisation aspects . . . . . . . Teaching aspects . . . . . . . . . Evaluation of the teaching process Study tours . . . . . . . . . . .
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DATA AND DATA MANAGEMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Origin of data 14 Hydrological instruments 19 Transfer of data 19 Storing and cataloguing of data . . . . . . . . . . . . . . . . . . . . . . . . 20
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THE USE OF HYDROLOGICAL MODELLING . . . . . . . . . . . . . . . . . . . . . . . 25
. . . . . . . . . . . . . . . . . . . . . . . . . . . . Basic statistical analysis 25 Principles of hydrological models . . . . . . . . . . . . . . . . . . . . . . . 28 Basic deterministic concepts 31 . . . . . . . . . . . . . . . . . . . . . . . . . .
VISUAL PRGSENTATION OF HYDROLOGICAL INFORMATION - * - - * - - - - * - - - - - 43
Graphical representation of hydrological variables . . . . . . . . . . . . . . . 43 Coordinate dependent diagrams . . . . . . . . . . . . . . . . . . . . . . . . . 43 Line diagrams, area diagrams and isometric diagrams . . . . . . . . . . . . . . 52 Hydrologicalmaps 56 Introduction 56
General classification of hydrological maps . . . . . . . . . . . . . . . . . . 58 Classification of fields of interest . . . . . . . . . . . . . . . . . . . . . . 58 Records 62 Hydrological mapping and interpretation from aerial photographs . . . . . . . . . 63 Interpretation 63 Evaluation of results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 Materials 65
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. . . . . . . . . . . . . . . . . . . . . . . . . Technical points, cartography 57
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VI AUXILIARY AIDS AND EDUCATIONAL TECHNOLOGY . . . . . . . . . . . . . . . . . . . 67
6.1 6.2 6.3 6.3.1 6.3.2 6.4 6.4.1 6.4.2
Textbooks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 Visual aids 67 Audio-visual aids 67 Video equipment 67
68 Computers 69 Computational facilities 69 Computers as teaching aids 71
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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Video techniques in the teaching process . . . . . . . . . . . . . . . . . . .
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REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
I. Introduction
1.1 Purpose
This Technical Paper has been prepared by the International Hydrological Programme (IHP) Working Group on Teaching Aids; it serves several purposes, all of which are geared to the production of successful technology transfer between teacher and student to the benefit of hydrological practice and mankind.
serves as a guideline to these Papers and the many other publications produced by Unesco in the field of hydrological education.
Thus, illustrative examples are interspersed in the text for the purpose of demonstrating how particular ideas can be conveyed from the teacher to the student. These examples emphasise the benefit of appropriate didactic tools, accompanying more traditional teaching methods and making use of the panoply of hydrological models.
practice and teaching is also emphasised and dealt with at some length. The collection, processing and dissemination of hydrological information is aast against the requirements of hydrometry, statistics, hydraulic/hydrological models, systems analysis etc. Where possible, guidelines for teaching and practice are outlined.
A curricular description of the basic hydrological sciences (mathematics, physics, chemistry, computer science, the biological and earth sciences) is not attempted within this Paper but can be found in the relevant Unesco publications.
The Paper is a companion to other Technical Papers produced by the Working Group and
It is also intended that this paper should stimulate interest in hydrology and its teaching.
The parallel between the evaluation and presentation of hydrological information in both
1.2 Origins
The Council of the International Hydrological Decade (IHD) initiated the steps which led to this publication when it established the Working Group on Education and Training. This Group produced the first version of the Unesco publication 'Teaching Aids in Hydrology'. When this went out of print the Intergovernmental Council of the IHP declined to reprint it and decided instead to replace it with a more up-to-date publication.
The IHP Working Group on Teaching Aids was entrusted with this task and for this purpose established a team of Authors consisting of Messrs Maniak (Chairman), Gilbrich, Jowitt, Kovsr, Lecher and Lindh. Mr Meijerink of the Netherlands contributed the material on photohydrologi- cal mapping and interpretation. The team of Authors held three sessions between 1979 and 1981. The Federal Republic of Germany financed additional meetings and also the sheet of the International Hydrogeological Map of Europe annexed to this report.
1.3 Scope and Limitations
Hydrology is both a quantitative and qualitative science; it is multidisciplinary. In this Paper attention is concentrated on the quantitative aspects in the sense that qualitative methods are discussed only where they have a direct influence on the understanding of particular models of hydrological behaviour. earth sciences is broached only to the extent necessary to understand the water cycle and the hydrological processes within it. Topics which, traditionally at least, have not been regarded within the mainstream of hydrology are given only cursory attention. Water quality,
Thus descriptive hydrology as part of the
1
for example, is covered by several other Unesco publications. The hydrologist is usually just a part of an interdisciplinary team concerned with problems in which water is the integrating feature. It is necessary that the hydrologist is aware of the role played by international organisations such as WMO, WHO, FAO and Unesco in specific parts of the water cycle.
1.4 Content
Despite the fact the hydrological character, level of water resource development and data availability range from region to region, the methods of water resource planning and operat- ion, in which teaching has to be expressed, enjoy a common basis. Understanding the hydrology of an area and the resolution of its water resources problems is achieved by a progression from data reduction, statistical analysis, hydrological modelling and systems analysis. Correspond- ing to this is the requirement for the hydrologist to have equal facility with hand/graphical calculation methods and more sophisticated computer-orientated techniques. It is also vital for the hydrologist to understand how the principles of hydrology are connected and manifest within the hydrological cycle. This Paper is intended to reflect all of these aspects, pointing out the prerequisites necessary for the study of applied hydrology; it is meant to be a teaching aid to inspire both teacher and student and not merely a learning aid for the sole benefit of the student.
data management and its relevance and availability for the teaching process. logical modelling is detailed in Chapter 4. learning and practice is the effective communication of hydrological information in various visual forms and so Chapter 5 describes at some length the variety of visual presentation meth- ods, ranging from simple graphical procedures to the highly sophisticated methods of photo- hydrology and hydrological map interpretation. Finally, Chapter 6 describes the role of auxiliary teaching aids and educational technology.
Chapter 2 describes the philosophy of hydrological teaching. Chapter 3 discusses data and The role of hydro-
An important aspect of hydrological teaching,
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11. Teaching hydrology
Education undoubtedly plays a most important role in the advancement of our capabilities to resolve hydrological problems. Earlier teaching methods in hydrology and water resources management mostly contained elements of the so called 'component approach' - describing single hydrological components in relative isolation. The present advanced teaching methods in hydrology should include these components within the systems approach, integrating the mutual interactions between various hydrological processes; the multidisciplinary character of modern, advanced hydrology must be stressed.
Hydrological training should be broad enough to convey sufficient knowledge not only of the natural sciences but also of the social sciences, enabling the hydrologists to communicate effectively in an interdisciplinary environment. The hydrologist should have a sound knowledge of modern operational mathematics; he should have basic training in operations research, systems analysis, statistics and probability, computer technology and management science.
In completing this Technical Paper, the Team of Authors have made some use of the ideas of experts published in the earlier publication, 'Teaching Aids in Hydrology' (Unesco, 1972a), as well as material published in the Proceedings of the International Seminar on Water Resources Education, Unesco/IWRA, 1975), Papers on the International Workshop on Hydrological Education, (CSVH, 19811, and last but not least, the authors' own experience.
ledge are mentioned here for completeness and to draw attention to the fact that a definite strategy is needed. The successful use of water resources depends on the level of investment, the effectiveness of investments and the selection and application of appropriate technologies. The constraints which will be faced are financial, the availability of industrial infrastract- ure and the availability of trained and motivated manpower. Financial and infrastructure constraints can often be overcome by the use of appropriate technology combined with proper education, training and motivation. Thus, the training and motivation of persons working in the field of water is, without doubt, the most important topic to be considered in meeting the goals of the IHP. That is to say, even if adequate funds are made available, the efforts can- not be successful without proper education, training and motivation.
The transfer of knowledge subsumes all of the sub-topics such as the training of experts, education, transfer of information, and the preparation of teaching materials and instructional manuals. In other words, it is an hbrella term which describes at the most general level the objectives of the IHP. Progress in this transfer of knowledge has been substantial in recent years and shows what can be accomplished using modern communications technologies as opposed to old methods of teaching. the local level, it is believed that the problems of education and training can be overcome with great benefits for the achievement of the goals of IHP.
in general, hydrological science, educational technology, and the capability to make use of information (see Figure 2.1).
Whilst the teaching aspects have been dealt with above, aspects of the transfer of know-
By combining these modern technologies with well-planned training at
It is important to recognise the different rates of development associated with education
The figure tries to show that:
the art of teaching is older than the hydrological sciences but has been developing SO slowly that, at some point, hydrological education will no longer be able to cope with all the knowledge available;
C- the need for transferring hydrological knowledge to developing countries became apparent when they gained independence; technology transfer evolved slowly in the beginning; nowadays communication technology is developing more rapidly than science so that more information can be transferred that can be absorbed;
a. the hydrological sciences are still developing and no upper limit can be envisaged; b.
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c I
T - time
Fig. 2.1 - Development of education and science in hydrology.
d. although the developing countries have increased their capability to receive and digest more information, they cannot yet cope with the increase in information and the gap becomes ever wider and wider. The task of the future will be to harmonise the trends visualised in the four lines of
the graph and in particular, to increase the capability of the developing countries to make use of the information at their disposal.
2.1 Improvement of the Learning Process
The aim of all teaching/learning activities is to improve the state of knowledge and level of understanding, though it is recognised that 'Teaching should be intended to promote learning by an individual, rather than doing something to an individual' (Unesco/IWFW, 1975).
teacher's influence, then it is possible to say that relations shown in Figure 2.2 express their mutual abilities to make themselves understood. Communication is the transfer of a message from one to another. Feedback is a secondary message indicating how well the first message was understood (Unesco/IWRA, 1975).
important to consider those factors which substantially affect the degree of success of the teaching process: a. motivation of learning b. education technology c. teaching methods
When the teacher is the source of information, and the student is the object of the
Deliberating over the fundamental issue of how to improve the learning process, it is
COMMUNICATION f . r [ S o ~ ~ c E H EDUCATIONAL I -[ RECFIoPJ 1
INFORMATION IN FORMATI ON TECHNOLOGY
Fig. 2.2 - Diagram of the learning process.
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2.1.1 Motivation of Learning
One of the most important roles of the teacher is to inspire and motivate the student to learn. The relevance of motivation to learning must not be overlooked. First of all, i't is important to emphasise the professional motives in the teaching of hydrology compared with other disciplines. From the teaching point of view, the professional interest of civil engineering students is different from that of pure science students. Obtaining good grades, avoiding failure and satisfying sponsors are always present as partial motives in teaching institutions, but as primary motives these should be replaced by more realistic ones which link the learning activity to potential career success. Even so, students must have frequent opportunities to experience success in learning.
realise the following important factors in a teaching /learning process (Unesco/IWRA, 1975). - Repetition - Repetition is an important factor in the learning of information and skills. - concentration - Concentration of the student is necessary to learning and a situation must
be provided such that information is presented when the student is alert and attentive. - Association - Association of new material with other concepts known to the student is an
important aid to learning. Few people have the capacity to remember or understand facts and concepts that are unrelated to some previous knowledge.
size of the unit depends on the type of material studied and on the intellectual capacity of the ztudent.
- Use of a communication method appropriate to the objective - A complex subject requires a variety of learning activities and the same method of communication cannot be effective for all aspects of the subject. It would be a waste of time to lecture students on how to develop laboratory skills which can only be developed by practising them. Clearly defined course objectives give important guidance to the choice of the learning activities for each part of the course.
In seeking guidelines for the development of effective education, the starting point is to
- Unit Steps - Unit steps presented in a structured sequence have been found effective. The
- Use of a multiplicity of approaches - People differ in their response to different approaches to a subject. With the current emphasis on technology in education there is an unfortunate tendency to seize upon one device and use it to the exclusion of all others. Some people may learn best through a lecture approach, some through a video approach, and others through workshops or laboratories. It seems desirable that a variety of approaches be available so that students will have an opportunity to respond to the approach that most suits them.
2.1.2 Educational Technology
The principal communication medium, and so far the most efficient source of information available at any time to the students, is textbooks and reference books dealing with various topics in hydrology (see section 6.1).
incorporated into the teaching of hydrology. These include: - films - slide and overhead projection - closed circuit TV - audio techniques - interactive computer methods etc.
organised design and implementation of the learning system, taking advantage of, h t not ex- pecting miracles from, modern communication methods, visual aids, classroom organisation and teaching methods I . (Unesco/IWRA, 1975) .
subject and the purpose of the teaching. The follodng two tests have bePn proposed to deter- mine whether or not any advanced educational technology should be used (Unesco/IWRA, 1975) :
The use of other communication media resulting from rapid technological advances is being
Education technology is not only a set of communication media and instruments but 'the
The choice of modern teaching methods must be well received, taking into consideration the
- the teaching/learning task to be performed should be essential to the course of instruction to which it is applied;
- the task could not be performed as well as , if at all, by the students without the tech - nology considered. The application of these criteria will restrict the use of novel teaching methods to
situations where they are of real benefit. Experience has shown that teaching efficiency is not always enhanced by the use of the most advanced educational technology. A commonsense appraisal of the type and complexity of the problem to be discussed and the standard of the
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students will often suggest the most appropriate teaching medium. However, it is possible to recommend quite unequivocally, extensive use of slides, overhead projection and films. Over- head projection is a common and effective aid in teaching technology.
2.1.3 Teaching Methods
The starting point for considering the teaching methods used in hydrology should be a clear determination of the learning objectives; assess the efficiency of the learning process and helps the students to monitor their own progress.
able time to help the student comprehend the subject matter. The teaching methods used in hydrology are either conventional (based on classical learning psychology) or use various advanced experimental teaching methods. These will be outlined fuxther here.
studies), the common form of study consists of lectures, exercises and projects, group discuss- ions and tutorials. Lecture organisation is primarily influenced by the number of students, the subject matter, and the technical facilities available in the lecture room. A well-planned and well-delivered series of lectures should offer the student not merely the essential knowledge, but a modification of what they find in their textbooks; when the lectures touch upon recent developments, they should serve as a source of stimulation and inspiration.
Conventional lectures should make adequate use of visual teaching techniques (Section 6.2). A drawback here is that lectures usually do not allow for two-way communication or continuity of interaction. Compared to other forms of teaching, the degree of student activity in lectthres is usually very low. Exercises, group discussions, workshops, seminars and so on allow far more active forms of student participation in the teaching/learning process. The main objective of these activities is to encourage the students to identify the problems and recommend their solution. Such working sessions provide an opportunity for two-way communication and good learning experience. They undoubtedly require careful preparation and well-trained leaders.
The value of group discussion is well-proven, involving active student participation and with the advantages of good feedback between the teacher and his students. According to the authors' experience, the optimum number of students for a group discussion is usually between six and ten.
of tasks to be undertaken. However, the logical strucbure should grow from the same base: a. definition of the problem; b. identification of the possible solutions C. choice of the optimum solution d. implementation of the solution e. solution assessment and discussion
a statement of these objectives makes it possible to
A whole host of existing methods share a common goal: to use the best means in an accept-
Regardless of the categories of education (undergraduate, postgraduate or post-experience
The teaching procedures used during exercises and workshops will again depend on the type
Audio-tutorial approaches are detailed in Unesco/IWRA, 1975 and are briefly reviewed here. 'The program of learning should be organised in such a way that the students can proceed
at their own pace, filling in gaps in their background information and omitting the portions which they have covered at some previous time. available and attempt to align the exposure to these learning experiences in a sequence which will be most effective and efficient. The kind, the number, and nature of the devices involved will be dependent on the nature of the subject matter under consideration.
In the audio-tutorial system,the instructor's voice is available to the student to direct and supplement his study effort. This does not mean that a taped lecture is given. It refers to an audio programming of learning experiences, logically sequenced to produce the most effect- ive student response. Each study activity has been designed to provide information or a skill leading to a proper performance of the next activity or else to build on the foundation of knowledge previously laid. The overall set of integrated experiences includes lectures, reading of test or other appropriate material, making observations of demonstration set-ups, doing experiments, watching movies, and/or any other appropriate activities helpful in under- standing the subject matter.'
(PSI) method summarised in Unesco/IWRA (1975). To implement the PSI method, course material is divided into units, each containing a reading assignment, study questions, references, study problems and any necessary introductory or explanatory material. The student studies the units sequentially at the rate, time and place he prefers.
The basic features of the PSI method are: a, Self-pacing, which permits a student to move through the course at a speed commensurate
with his ability and other demands upon his time.
It should make use of every educational device
A particularly well-structured system of learning is the Personalised System of Instruction
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b.
C. d. e.
The unit-satisfaction requirement for advance, which lets the student go ahead to new material only after demonstrating mastery of that which preceded. The use of lectures as vehicles of motivation, rather than sources of critical information. The related strass upon the written word in teacher-student communication. The use of proctors (tutors), which permits repeated testing, immediate assessment, almost unavoidable tutoring, and a marked enhancement of the personal-social aspect of the education process. This system of instruction has been used in junior and senior level courses in some
universities with great success, as judged by student learning, motivation and enjoyment.
built upon established principles of learning theory. Examples of both the special teaching methods mentioned above and experience with their application are given in the literature (Unesco/IWRA, 1975).
but it is as well to remember that regardless of all the effort towards designed learning systems, communications technology and behavioural motivation, one should not overlook the personal influence of an outstanding teacher (Unesco/IWRA, 1975).
It is believed that the personalised system of instruction is successful because it is
A common goal of all these methods is improving the learning atmosphere for the students,
2.2 organisation of Teaching Activities
2.2.1 Organisation Aspects
Teaching activities in hydrology and water resources may be classified according to: a. the form used in the transfer of information b. educational status of the student.
- university and college level training, either for degree or non-degree programmes - short courses, for example domestic national courses oriented to specific needs, inter-
The commonly accepted methods of direct transfer of knowledge include:
national and regional courses seminars - conferences - study tours - workshops - technical assistance programmes - practical or field training.
student, i.e. undergraduate, postgraduate and professional training/post-experience studies. However, few universities offer education leading to a first degree in hydrology. In most in- stitutions hydrology is taught as a subsidiary subject within comprehensive courses such as: - civil engineering - forestry and agricultural engineering - geology - geography
As a result the multidisciplinary character and complex nature of hydrology is often suppressed. In postgraduate teaching, many universities or colleges offer courses leading to a Master of Sciences degree, or other diploma in hydrology. In these courses, the participants are taught the modern analytical methods used in the solution of hydrological and water resources problems and emphasis is placed on the interdisciplinary character of hydrology.
graduate courses in hydrology, which are organised by universities and other educational establishments. The participants are awarded either a diploma or certificate of attendance on the basis of their satisfactory progress.
There are also universities and various institutes which offer post-experience courses or workshop facilities for re-training or advanced education in the professions. Educational programmes in hydrology require cooperation with various research and operational institutes and outside agencies. Such cooperation can be of particular value in the professional development of the students.
Three categories of teaching of hydrology are considered which relate to the status of the
In addition, Unesco and several other international organisations sponsor special post-
2.2.2 Teaching Aspects
A comprehensive survey of teaching activities promoting learning was given by Unesco (1972a) and is presented in Table 2.1. The table can be used to: - show the individual forms of teaching/learning process in the light of an assessment of
the possibilities of their use as various teaching aids.
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3lassif ication Method
L a* Computer assisted learning b* Teaching machines and programmed learning
2 a* Lecturing in class b* Slides and overhead projection C* Films and film loops d* Laboratory and field demonstration e* Diagrams and charts
3 a Classroom exercises b Classroom discussion C* Laboratory exercises a* Field exercises e* Field trips f Reporting by students on special topics g Tutorials
1 a* b*
Study of textbooks and lecture notes Study of reference books
j a Homework assignments b*
C* Field and/or laboratory projects carried out by students
Solution of problems by students using computational facilities (in a computer centre)
5 a* Theoretical research b* Laboratory research C* Field research
* - this method may be thought of a teaching aid applicable to some aspects of teaching activity Table 2.1 : Methods to promote learning (modified after Unesco/IWRA, 1975)
- identify those forms of teaching which require more initiative and self-direction from the
- show the relative effort required of teacher and student. Some forms of teadhing place learner (listed towards the bottom of the table).
increasing requirements on the preparation and planning of the teaching by the teacher while reducing the requirements on the initiative and activity of the learner. The selection and application of a particular teaching method will first of all depend on
the subject or problem and the objective being addressed. It also depends on the students, their previous theoretical or practical foundations, knowledge etc. The choice is also affected by the technical equipment and the facilities available in the lecture room.
The methods included in the table under classification 1 are those used increasingly in the teaching of hydrology. They involve a form of interaction with the computer by way of a terminal located in the lecture room. Shown on the display are simulations of some hydrological processes and their changes resulting from varying the process parameters (Nemec, 1972).
depends on both the available technical facilities and on the subject matter.
which are controlled directly by the teacher. taught, lectures may be divided into: - introductorylectures - main lectures - application lectures
The objectives are formulated and the simple steps to achieve them are illustrated. lectures should be the means of motivation for personal study. They should contain the mater- ial for solving problems. matter including all important aspects.
The use of these methods is possible only after thorough teacher preparation and mainly
Classification 2 includes those activities which take place mostly in a classroom and According to the scope and depth of the matter
Introductory lectures relate the subject-matter to previous lectures and to other subjects. Main
These lectures have also to comprise an assessment of the subject The application lectures represent the advanced
8
teaching process and require good co-operation with the students. Previous knowledge is necessary to solve the more comprehensive problems and to outline the solution to them. These lectures place the acquired knowledge in context so that structured knowledge aimed at specific problems is obtained. Case studies showing the students the application of basic theory as well as the methodology for problem solving are also sometimes given. The problem can be resolved later, either in exercises, individually at home, or in a computer centre.
Slides and overhead projection are very effective lecturing aids;overhead projection is more convenient than slides; overhead transparencies are more easily made, updated, supple- mented and annotated during the lectures. Films have been promoted successfully as teaching aids for many years and can be used to show students complex or unusual events which they nor- mally would not have the opportunity to see otherwise.
Laboratory and field demonstrations may be shown either directly or on film. Special la- boratory apparatus has been made for teaching purposes. Demonstration equipment is used for quantitative and qualitative studies of various hydrological phenomena (Unesco/IWRA, 1975).
Diagrams and charts of plotted information enhance retention by a student. Graphical procedures based on the systems approach, or flowcharts explaining the algorithm of a discussed problem are indispensable teaching aids, especially in computational hydrology.
learning process requiring more or less the same contribution from students and teachers alike. In general, these activities are aimed at expanding the individual work of students.
Classification 4, incorporating textbook and reference book study, is undoubtedly the principal way of acquiring information and consolidating knowledge. This form is individual- istic; the method of study of printed (or written) material depends on the individual student, his study habits and capabilities. It is important that the sought information is available whenever required. Often it becomes important to compare information or approaches in order to understand the complex relationships between the fields of study.
Classification 5, the assignment of problems to be done by students individually as home- work, is widely used with good results by many teaching institutions. The nature of the pro- blems assigned as homework depends on the subject-matter of the course and may range from very simple examples to complex problems taken from professional practice. Students are often given problems to be solved individually with the use of a computer. Program and data inputs to the computer are undertaken in a variety of ways: - batch reception of a deck of cards, - user-operated card reader facility, - interactively from a terminal. Computerised problem-solving not only enhances the knowledge of students in the field of hydro- logy and related subjects but also stimulates their logical thinking in algorithm design and improves facility in computer programming.
The nature of hydrology itself also requires field and laboratory projects that can be performed by students. These establish the link between theory and practice. The main object- ive of field and laboratory studies is to acquaint students with the operation and maintenance of instruments and evaluation of experiments.
Classification 6 (research) can usually only be allocated to able students with special interest in the subject. For this reason it does not rate as a widely used method for teaching purposes.
the student's ability to grasp the subject-mattex. This control takes the form of tests, examinations and/or discussion of reports.
An outline of a typical postgraduate course is given in Figure 2.3 (CSVH, 1981). TWO phases of the study process are distinguished: a. acquisition of the necessary special knowledge of the discipline; b. demonstration of the acquired knowledge, application of the subject-matter in practical
The activities classified under item 3 of the table comprise various forms of the teaching/
Naturally, any teaching method must be accompanied by feedback and the teacher must judge
examples, discussion within a team. The basic elements of this study plan are those explained in the above text. The design of
the teaching/learning process is very general and may serve as a basis for the determination of teaching plans for postgraduate hydrological courses.
2.2.3 Evaluation of the Teaching Process
The previous text shows that it is often rather difficult to select an appropriate teaching method to match the hydrological topic under discussion, the level of understanding of previous topics and the facilities in the teaching rooms and laboratories.
It is possible though to state the general principles involved in the selection of teaching methods which allow students to achieve the expected results. Undoubtedly undergraduate and
9
t- 1 . P h a s e ( A c q u i s i t i o n ) 2. Phase (Demonstration o f proficiency, argumentation I -
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introductory 1 ecture main lecture application lecture readiness test defence o f the paper or design acquisition by personal study
TT tutoring, testing, supervision E exercises W workshops SP solving o f problems C consultation EN examination
General outline of the teaching/learning process (Modified after Dyck in CSVH, 1981).
postgraduate courses should both stimulate and guide students in independent work and study. The teaching process should be controlled so as to motivate and develop creative ability. In the planning and management of students' independent work, it is important to set out specific and appropriate objectives and related tasks, time schedules and the methods of supervision.
The PSI method outlined earlier has produced good results but not without some justified reservations, especially with regard to the keeping of a time schedule within a syllabus and the confusion between the roles of tutors and lecturers. Nonetheless the system may be recommended for application with the reservation that the study tasks are well-defined in terms of both time and structure.
unit, the level of prior knowledge required for its completion, a suggested study procedure and reference list, some means of self-assessment and, finally, an indication of how the lecturer will review and control the student's progress.
Each topic or sub-topic should be accompanied by an indication of the purpose of the study
2.2.4 Study Tours
Hydrological education is incomplete without study tours and field trips. These activities enable students to see various structures and processes in natural and existing conditions. The main aims of the hydrologically oriented study tour should be to: - acquaint students with new techniques and recent developments in hydrology at research
institutions and to see the results of research work and field experiments; - make students familiar with various aspects of the organisation of the hydrological services and their normal field practices; - show the multiple facets of water use by visiting various water resources structures and projects and to emphasise the interdisciplinary character of hydrology;
- make personal contacts promoting the exchange of practical experience, etc. The enormous advantage of study tours is the opportunity to observe the interrelationship
of hydrological practice and research, and to combine them with personal experience. other hand, in organising such study tours, the relatively high costs and long distances to be covered must be balanced against the educational benefits. programme, the following aspects should not be neglected: - professional orientation of the participants relative to the course; - the uniqueness or representativeness of the site or location to be visited; - interconnection of theoretical aspects in lecture courses with the practical applications; - duration of the study tour, distances to be travelled, and costs.
On the
In the planning of a study tour
10
Previous experience from field trips generally shows that participants are more receptive during a shorter trip (one or a few days only). An appropriate daily programme is equally important. In this respect, there can be no general advice on how field trips should be organised, but a realistic time schedule is a principal prerequisite for the success of any study tour or field trip.
The benefit of study tours can be enhanced when the participants play an active plart, as they should in any form of teaching/learning. A well-planned tour with clearly stated object- ives, together with a well-defined itinerary and time schedule(given to the participants in advance) brings positive results. The benefits are further increased if the participants write a report discussing the activities and hydrological problems of the sites visited.
11
111. Data and data management
The efficient and economic planning of water resources influences all aspects of national development. Satisfactory solutions to many water resources problems require readily access- ible and reliable observational data on the elements of the hydrological cycle and related factors. The collection, transfer and storage of such data is essential in providing inform- ation for developing and managing water resources.
This table shows the basic need for relevant data for the most frequent cases to be treated and resolved in water resources management. Figure 3.1 shows how the relative importance of different types of data may change with the degree of development of the country.
Table 3.1 gives the primary use of hydrological data for various water management projects.
Table 3.1 : Primary use of hydroloqical data in particular water management projects
13
" 1930 1940 1950 1960 1970
Fig. 3.1 - The changing pattern of data use for a developed country from 1928 to 1969. (After Unesco, 1972 C).
The growing significance of water resources management and planning makes it imperative to design and use more ingenious systems for the collection, transmission and processing of hydrological data. An example of such a sophisticated data system is given in Figure 3.2 (Unesco, 1972~). The data acquisition comprment of such a system presents two aspects: the network design and the instrumentation/sensor equipment. Both these aspects form the basic elements of the whole system and therefore should be kept at an interrelated technical level. Temporary data logging is usually a component of the instrumentation in the form of a field logger. It should be noted that the sensor and the local field logger often cannot be consider- ed separately from the transmission (communication) system. The following elements of both components must be considered (Nemec, 1972) :
Sensors : physical element-sensing units, their range and accuracy, timing of observation
output I digital (paper or magnetic tape), analogue (voltage, graphical, visual Transmission: automatic or non-automatic
and transmission, display, power supply
The processing and dissemination phases should be related and will often depend on a particular computer, its hardware and software system.
Mention should be made of the efforts undertaken by the World Meteorological Organisation within the framework of the HOMS project (Hydrological Operational Multipurpose Subprogramme), which is a uniform proceduxe 'providing an international systematic framework for the integrat- ion of the many techniques and procedures in the collection and processing of hydrological data for use in water resources systems' (WMO, 1981).
3.1 Origin of Data
Data are required to define the input and output from the hydrological system. In addition, the analysis and prediction of the response of a catchment to an input requires information on its physical characteristics, including relevant human influences.
It is not the purpose of this section to describe the observational procedures applied in the collection of basic and special hydrological data; these instructions are treated exhaust- ively by the World Meteorological Organisation (WO, 1971b).
these problems within the context of "aids for teachina data manaaement". Here, in line with the overall aim of the present treatise, the task is rather to place
14
REOUCTION SYNTHESIS 'A, m ANALYSIS L'A ,
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EXPLANATION
DATA FLOW I Cornrnuniation)
----- PLANNING A N D P R O G R A M M I N G
A R E A OF M U T U A L INTEREST TO THE DATA PROCESSING A N D DATA ACQUISITION ACTIVITIES
RESOURCE EVALUATION RESOURCE DEVELOPMENT RESOURCE M A N A G E M E N T
COMMUNI CAT1 ON D I SS E M IN AT1 0 N RADIO FlJBLl CAT1 O N MICROWAVE MlCROFl LM T E L E PH 0 NE DIGITAL TELEGRAPH O U T P U T MAIL
Fig. 3.2 - Diagram of the automatic data system. (After Unesco, 1972 c)
The appropriate classification of data depends on its intended purpose. In the teaching and modelling of hydrological processes it is often convenient to separate the data into those which measure the catchment inputs and outputs, the catchment's physical characteristics, and those that determine the nature and rate of processes within it.
in Table 3.2 (Fleming, 1975). Typical examples of the type of information contained within each classification are shown
Class 1: Hydrological and Meteorological Data monitor the changes in water mass and energy in the atmosphere, land and the sea. These include precipitation, evaporation, river stage and discharge, groundwater levels, radiation, temperature, air kmmidity, vapour pressure, wind speed and direction, cloud cover, sediment transport, ice phenomena, etc. Some of the data may come from stations in networks set up to meet the daily needs of hydrological forecasting and water management.
Since hydrological processes, like all natural processes, are evolutionary, any selected sampling interval should be consistent with the time variability of the individual processes and take into consideration the purpose of the acquired data. For example, pan evaporation rate may be satisEactorily measured on daily interval. However, runoff measurement from a small mountainous catchment will, most probably, require streamflow measurement at one-hour time intervals, or less, in order to provide adequate information on the response.
Quantitative and qualitative properties of the measured hydrological and meteorological data are also influenced by the density of the observation network. graphical conditions, together with the wide ranae of various water resources problems to be
Heterogeneity of physio-
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solved, render impossible the design of a universally valid observation network, especially for precipitation and streamflow. Furthermore it is now commonly accepted that any theoretical app- roach must be supplemented by an element of judgement (WM0,1972). In general, stations of such Observation networks should be located so that the collected data will be useful in developing re- lations between the hydrological and meteorological factors, and the significant physical para- meters such as the slope, elevation, morphology, geology, land use and soil types. The minimum density of both precipitation and streamflow networks are indicated in the literature (WM0,1972).
Class 2: Physiographical Parameters consist of information representing the physiographical conditions of the river basin and which can be defined analytically or in geometric terms. These data are required to define the retention characteristics of a catchment. Surveying the catchment to define the existing physical features of area, slope, drainage, network, vegetation, etc. will provide information on factors affecting its response. These data are incorporated into equations for calculating the rate at which water moves from the land surface. Table 3.2 shows examples of the physical parameters, which can be grouped as follows (Fleming, 1975): - land surface - natural drainage channel network - urban drainage channel network - reservoirs
Class 3: Process Parameters consist of information related to the processes influencing the movement and distribution of water in the land phase of the hydrological cycle. In many cases the data are difficult or impracticable to measure directly and have to be determined indirectly from other data. They represent the rates at which individual processes of the hydrological cycle take place (interception, infiltration, interflow, percolation and groundwater flow). They may be monitored at various points but integral values for a non-homogeneous catchment may be established only with the use of more complicated and advanced simulation techniques. Some examples of process parameters are shown in Table 3.2.
The collection and processing of all three groups of data using a sophisticated automatic system is shown in diagrammatic form in Figure 3.3
In all data handling operations it is necessary to consider and monitor data quality. Erroneous data can lead to errors of judgement or even cast doubt on inferences drawn from the more reliable parts of the record. In order to minimize sources of errors in sets of data collected from a network of stations, it is necessary to maintain (WMO, 1974): - proper instrumentation and network design - care in observation - quality control in data processing - data processing schedules.
station identification st or age time signal - - - - - - - - - - - I - ’
periodic
1 1 continuous data proces- - sing by
ondemand ~ com pu ter I
parameter identification
t feed back
process parameters
process analysis
Fig. 3.3 - Block diagram of the data system based on an automatic hydrometeorological station.
18
3.2 Hydrological Instruments
The hydrological equtpment listed fn Table 3.3 can be employed as a teaching aid in the classroom, the laboratory or in practical studies. Climate stations, lysimeters, flow measuring structures can usually be visited on study tours and are invaluable aids to teaching. Details of the particular instruments and observation techniques are given in the forthcoming Unesco publication 'Experimental Facilities in Water Resources Education'. The application of this equipment for different hydrological observations is described in many manuals and textbooks on hydrometry. In order to obtain comparable observations most of the observation techniques and types of instruments are standardised. Thus, the degree of instruction in instrumentation depends on the needs of the country and will reflect climatic conditions.
The accuracy, usefulness and operation of current meters, flumes weirs etc. is best appreciated by first-hand experience, just as the problems of sediment transport and sediment sampling are more easily understood by experimentation on a laboratory flume.
3.3 Transfer of Data
It is not always possible in the classroom to show the full spectrum of instrumentation, data collection and transfer. Thus, the demonstration of a measurement including data transfer and processing should be restricted to important hydrological variables, e.g. stage, discharge, rain and climatological data. By visiting meteorological stations and gauging stations, the major facets of data collection, transmission and storage can be appreciated. Experimental basins for water budget studies, erosion problems etc., together with lysimeters and further special hydrological equipment, should be visited either within the regular courses or occasion- ally during a study tour. An appreciation of measurement methods in the field can be supplement- ed by films, slides etc., in the classroom. It is of mutual benefit for the student and/or technician if he becomes well acquainted with the handling of the instruments, data collection and processing. This fieLd-oriented teaching is an important link between hydrometry and use of hydrological data.
instrumentation or transmission systems should be emphasised, and where possible can be demon= strated by appropriate instruction in the field.
Many hydrological networks have developed in response to particular local problems, without taking into account future data requirements. Although an immense amount of hydrometeorological data has been accumulated over the years, the quality, quantity and availability of hydrological data is generally inadequate for present development needs and particularly so for forecasting. The transfer and processing of data can be used as a teaching aid if it is considered as the step from pure hydrometry to the quantitative description of the hydrological problems under study. In this figurative sense, the hydrological stations may be broadly classified in the following four categories (WMO, 1973) : a. Non-recording stations, where manual observations are made occasionally or during selected
time intervals. b. Automatic hydrological observing stations, at which instruments make and record the observ-
ations automatically. c. Telemetering hydrolgical observing stations, where instruments make and transmit the
observation automatically without recording them. d. Telemetering automatic observing stations, at which instruments make, record and transmit
the observations automatically to the receiving centre. Stations in each of these categories are described in numerous textbooks on hydrometry or
hydrology and a variety of illustrative examples on the design and operation of hydrological networks, standards of observations, data quality control etc. is given in several manuals and guides (WMO, 1971b, 1974).
itself and its purpose. It is beneficial to the student if the acquisition, selection and evaluation of data forms a part of the learning process.
The transmission of hydrological data depends on the demand of the user and may become quite sophisticated (Figure 3.4). In general, the factors affecting the choice of a trans- mission system are the speed with which data are required (e.g. for planning or operational purposes) and the accessibility of the measurement site; transmission techniques are becoming important as special teaching aids if analogue or digital transmission is used together with digital computers for the evaluation of (laboratory ) experiments. This on-line data processing requires checking of the data for completeness, correctness, errors etc.
The consequences of data loss or corruption through systematic or occasional errors in the
The type of data required for a particular hydrological model obviously depends on the model
19
transmission of data by
Interrogation of ou to mat ic a Il y recording instruments at (regular) time intervals by Central Office
J I Automatically transmitted messages
Instantaneous Observations at spe - Observations at pre - observations cified unit of change determined time inter-
I Automatic transmission of continuous data I Analogue trans - Analogue trans - Digital transmission mission by wire mission with frequency
Fig. 3.4 - Data transmission systems.
3.4 Storina and Cataloauina of Data
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Standardised procedures for storing and cataloguing of meteorological data have been recommended internationally (WMO, 1973). Data banks of hydrological data are available in many countries. The compilation of the data depends on the particular needs of the country, which is why inter- national standards for the compilation of hydrological data are not widely practised. Hydrolog- ical data may also be available at regional or national hydrological agencies/centres; national statistical bureaux or information centres may also provide hydrological data.
Data stored in data banks will be fully corrected and it is seldom possible to reconstruct raw data or autographic records. Autographic records are useful in the early stages of a study but effective use of data, both in the class and in practice, really requires data in computer compatible form; hard copies or microfilms are inadequate and time-consuming substitutes. The data stored at a bank must be available for quick, effective and economic retrieval and analysis. In view of the fairly high costs of software development and data collection, most data banks serve the following objectives: - to standardise and make accessible the data derived from planning, construction and operat-
- to integrate the actual collection of statistical and related data in a homogeneous form,
The developing objectives are: - to expand and improve existing data files through the collection of complementary data -
ion of water resources systems, from control and administration etc.
to prevent misuse of 'confidential' data.
to organise new data files and homogeneous partial data bank systems for special applicat- ions to include these partial data systems within completely integrated water resources data banks.
-
20
The state of development of a national data bank dictates the extent to which its data can
For solving problems in the classroom a recourse to published data (year books etc) might be used as a teaching aid.
become necessary. The contents of such publications will depend on the need of the most important and numerous users of the data. Besides these official publications, unpublished data may be available which can be quite adequate for some teaching purposes.
becomes important; the data bank will usually store additional catchment and hydrological information. The familiarisation of the student with the infrastructure and practice of a data bank is important in relation to the work that will be encountered later in his career. Figures 3.5, 3.6, 3.7 show the relationship of the data bank to the monitoring network, the internal functions of the data bank, and the interrelation of the data bank and other organisations. It is beneficial to be able to show the students specific examples of data bank publications and hydrological information.
If a computer is used in the teaching of mathematical models, access to a national data bank
Fig. 3.5 - Data system for water resources management in the catchment of the River Vah. (courtesy of HMU, Bratislava).
2:
SPACE - TIME REFERENCE SYSTEM
1
- INFORMATION TRANSFER TECHNIQUES
CORRELATION TECHNl OUES I Regression 1
~
DATA STORAGE SYSTEM
PHYSIOGRAPHIC
FILES FILES FILES 1 1
I DATA PROCESSING SYSTEM
PHYSIOGRAPHIC METEOROLOGIC HYDROMETRIC
FILES FILES FILES
t INFORMATION RETRIEVAL FOR
PLANNING H Y D R O LOGY FORECASTING
Fig. 3.6 - Basic layout of the physiographic land use, land cover and hydrometeorological data bank of Canada (after Shen, 1976).
22
I
Regional water au thori ties State agencies
I I I
Municipal and other licensed users
I I
Fig. 3.7 - Data bank for water resources of the Federal Republic of Germany.
23
n! The use of hydrological modelling
Hydrological models are fundamental both to the teaching and professional practice of hydrology. The hydrological model represents an important link between hydrological data, their evaluation and the final presentation of the results of hydrological studies. Models of hydrological phenomena allow the whole or part of the hydrological cycle to be simulated. Hydrological models can be based on mathematical representations, physical experiments or electrical analogues
The main purpose of using hydrological models in the teaching process is not to duplicate the complicated hydrological process in detail by a sophisticated model, but to demonstrate the principal elements of the process, their combination into a simple or comprehensive model, and the importance of the model in solving typical problems of engineering hydrology.
parameters used in the model, and to the degree that the model structure represents the primary components of the hydrological process under study. It must be emphasised that the influence of the input data and model parameters on the output must be demonstrated, e.g. by the variation of parameters of a deterministic model or by the variation of time period of the observed data in a stochastic model. By these means, the student learns to use hydrological models and develop them into powerful tools in the process of decision making. The teaching of hydrological modelling as an end in itself must be avoided. The teacher must necessarily restrict attention to only a few of the large variety of hydrological models which have been developed in the past twenty years for different purposes.
The demonstration of particular elements of models may require only simple equipment, but the application of comprehensive models is dependent on the availability of suitable computers and/or experimental facilities for physical or electrical analogues. It must be stressed that several models may be able to solve a given problem, but the choice of a particular model is often highly dependent on factors such as the size of computer, computer programs, experimental facilities etc. It is often possible to adapt more complex models to illustrate salient features and allow the student to gain some experience of using the model.
which different types of models are taught is dependent on the depth of knowledge and ability of the students; the use of hydrological models as teaching aids in the training of technic- ians and students is similarly refined.
The verification of the output is inseparably connected to the quality of input data and
The following outline is commonly used in teaching hydrological models. The extent to
4.1 Basic Statistical Analysis
A preliminary statistical analysis of hydrological measurements is the first stage after the data collection and processing and precedes the application of hydrological models. At this stage, the input data and parameters of models are determined. A basic analysis may suffice for the solution of simple problems; for example the design of a hydraulic structure of minor importance may require only streamflow records over a sufficiently long period. When such a basic analysis can be done by hand or via simple computational facilities (e.g. pocket calculators, slide rules, planimeters etc.), it becomes a teaching aid both for technicians and students alike; this basic analysis forms the transition from the problems of data collect- ion to an understanding of process behaviour. basic statistical analysis of data series.
stochastic character of hydrological variables and of the correlation between variables. General statistical information is assembled about the hydrology of a river regime or a region. for the publication of hydrological yearbooks. These basic statistical analyses are also
Stochastic modelling has its origin in this
In general, basic statistical analysis is an important aid in the understanding of the
These analysos are also undertaken nationally and internationally, forming the base
25
used to prepare hydrological maps (see Chapter 51, in which the regional variability of hydro- logical variables is represented. All these forms of statistical summary and preliminary inter- pretation are useful teaching material.
which suits the proposed hydrological model and is compatible with the data. (e.g. stage, discharge, precipitation etc.) are then abstracted as discrete/instantaneous values or averages over the selected time interval.
applied hydrology, and numerous illustrative examples are shown in textbooks an hydrology, !WO, 1974; Yevjevich, 1972a,b; Nemec,l972),In general, the time-averaged or discrete values of discharge are ordered in the sequence of their occurrence over an observation period of a month, year, etc., to form the hydrograph (Figure 4.1). The integral of the hydrograph over
At the beginning of a hydrological study, a time interval (hour, day, month) is selected The observed data
Hydrographs, mass curves, and duration curves are employed in solving many problems of
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26
time is the mass curve, frequently used for designing storages or in water balance studies (Figure 4.1). In the special form of the double mass curve it can be used for testing the homogeneity of the data (Figure 4.2). tude is graphically represented by the histogram of empirical frequencies (see Figures 4.1 and 5.8). The cumulative frequency diagram forms the duration curve over the given observation period (month, half-year, year) (see Figures 4.1, 5.9 and 5.10). It is not primarily the simple routines of the computations in these basic analyses, but the critical evaluation of the observed data, the selection of suitable time intervals for discretisation and adequate graphical representation which become important in teaching and which demonstrate impressively the fluctuation, frequency and interdependence of hydrological variables.
a confusingly large number of outputs, tables and graphs which at first sight all look alike, with the increasing danger that the results are only readable by specialists. more and more important to present statistics in such a form that they are easily understand- able by students and by non-hydrologists.
to water resources management.
The distribution of discharges according to their magni-
The advent of digital computers has led to a situation where it is all too easy to produce
Thus it becomes
The following examples describe just a few techniques of basic statistical analysis applied
200
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Cumuiative runoff at control gauge G1
Application of double mass curve for testing of homogeneity of monthly discharges.
Example 4.1: Application of mass curves for designing the storage capacity of a reservoir
The mass curve of inflow, which is the cumulative flow volume versus time, is plotted at say monthly intervals over the period of discharge observations. any point denotes the discharge, a seasonally constant demand can be drawn as a straight line. The maximum vertical ordinate between the mass curve and the demand line gives the storage capacity that should be provided. If the storage capacity is limited, the volume of spill and the period of complete drawdown can be determined using parallel lines at an interval equal to the given storage (see Figure 4.1).
As the slope of the mass curve at
References: Linsley and Franzini, 1974; Nemec, 1972; Chow, 1964.
27
Example 4.2: Estimation of water power potential using flow duration curves
The water power potential plant of a river is proportional to the product of discharge and head. As the head Hi is dependent on the stage of the tailwater, which in turn, is a function of discharge Q the duration curve of stage and discharge can be used for estimation of the theoretical water power potential. For any discharge of the flow duration curve, the respective differences of stage in the upstream and downstream section are given by the stage duration curves. is the yearly water power potential (see Figure 4.3).
i'
The product QiHi is proportional to the daily water power. The integral over one year
References: Linsley and Franzini, 1974.
Fig. 4.3 - Estimation of hydro-power potential of a low head river power plant
4.2 Principles of Hydrological Models
The influence of different hydrological variables on the formulation of hydrological processes can be demonstrated to the students by physical, analogue or mathematical models. Recently mathematical models have taken over the most important tasks in problem solving in hydrology.
It should be noted that this chapter deals only with models to be used as teaching aids. The purpose here is not to engage in a critical discussion or to provide specialised commentary on individual models. In order to demonstrate their potential in the teaching of hydrology and other related subjects, It is necessary to give several explanatory definitions and a descript- ion of some of their basic features.
the system. Progress in computational facilities has changed the direction of emphasis in hydrology, and hcs radically changed the applications of mathematical models. Mathematical models in all aspects of hydrology have become more complex and more descriptive of the physic-
A model is a simplified representation of a complex hydrological system, or of a part of
al system. A hydrological system is defined as a set of physical, chemical and/or biological processes
acting upon input variables to convert them into output variables (Dooge, 1968). In this definition a variable is understood to be a characteristic of the system which may be measured, assuming different values when measured at different times. A parameter is a quantity characterising the hydrological system and which is usually assumed to remain constant in time.
If x(t) and y(t) denote the input and output variables, the mathematical model of the system may be described by the general equation (Clarke, 1973):
28
where f(.) is a function whose explicit form must be given; 8 , e2 ... are parameters (obtained by measuring the hydrological prototype or by optimization melhods) . es the model error (i.e. differences from the prototype) at time t.
distribution, then equation (4.1) is a stochastic model, otherwise it represents a deterministic model.
Another general qualitative characteristic of the model is its linearity or non-linearity. During the teaching process, it must be emphasised that the model is linear in the determinis- tic sense when it maintains the validity of the principle of superposition; however, it may be non-linear in the stochastic sense, when the relationships of parameters expressing the behaviour of the system are non-linear (Clarke, 1973). At this juncture, explanations should be accompanied by examples quoted from the literature.
An important aspect in the classification of models with a prevailing deterministic con- cept is the spatial classification of the input/output variables and parameters. Lumped models disregard any spatial dependency of these quantities, while geometrically distributed models do incorporate this dependency. Spatial changes of variables and parameters are solved at grid points of the selected geometric network. Probability distributed models represent a combination of the two previously mentioned types of models, deterministic and stochastic. They reflect spatial variability of the input variables or parameters. However, these are considered neither non-relative to the configuration of the grid points of the geometric network, nor relative to the prototype topography; rather, they are considered in the context of a probability distribution of the occurrence of these quantities. Good examples are given in many publications (Crawford and Linsley, 1966; Dawdy et al. 1972; Becker, 1972 etc.).
be stressed that not all aspects, approaches or methods are represented.
The variable E (t) express-
When any of the variables x(t), y(t) or &(t) is a random variable having some probability
A general classification of hydrological models is shown in Figure 4.4, though it should
Serial Markov Correlation Models
MATHEMATICAL MODELS IN HYDROLOGY . I
Monte Carlo Models
DETERM I N ISTIC MODELS ] i
r-----l Component models Integrated models
(Conceptual 1
Linear Non-linear
Linear or Lumped or Discrete or non-linear distributed continuous
I STATISTICAL MODELS AND METHODS I
Fig. 4.4 - Mathematical models hydrology (modified after Fleming, 1975).
Students, who as beginners are becoming acquainted with hydrological models, often ask why there are so many models and what criteria are best for their classification, comparison and evaluation. It is quite clear that for the wide range of hydrological processes, frequently influenced by specific conditions which often make the dynamics of the particular process unique, a multiplicity of models is required.
'The feature that all hydrological models have in common is that the observed output variable y(t) deviates from its fitted value f (.) by a residual amount E(t) (see eq. 4.1); the respects in which they differ are the assumptions made about the structure of a model f(.) and the assumptions made about a residual E(t)' (Clarke, 1973). The use of these residual errors in fitting mathematical models to prototype data is illustrated in Figure 4.5. intercomparison and evaluation of the best known conceptual models proposed for operational use in hydrology was made by the WMQ in the period 1968 to 1974 (WMO, 197533). This project involved the testing of ten operational conceptual hydrological models on six standard river catchment data sets and their usefulness in providing a short term forecast of streamflow in
An
data yc(t)
Parameter adjustment
Criterion or changes in of accuracy model structure
Fig. 4.5 - The mathematical model concept.
various forecasting situations. The details of the tested models including specifications of their purpose, data requirements, fitting criteria and references together with a description of the model structure are contained in the quoted WMO monograph, which in this sense may be used as a teaching aid. There are a number of other publications discussing mathematical models in hydrology, and serving well the needs of teaching in hydrology (Fleming,, 1975; Clarke, 1973; Kutchment, 1972 etc.).
However, not all models developed far use in operational hydrology or intended for scientific research are well suited as teaching aids. The use of the models in the teaching/ learning process will require the teacher to follow a set methodological approach relating to the model's computer implementation. This approach largely consists of: - the mathematical analysis of the problem (numerical or analytical solution) - the aonstruction of a flow-chart - the writing of the program for a digital or analogue computer
The procedure for the construction of a mathematical (simulation) model is illustrated by a flow chart such as that shown in Figure 4.6.
The mathematical simulation of hydrological phenomena shares the same phases of model development and implementation: - Identification phase is the primary phase of model work. Its aim is to identify the model
- Simulation phase is the secondary phase in model implementation, and may consist of short structure and estimate model parameters
term prediction in real-time for operational purposes, or long term prediction and data generation for planning and design.
Conceptual hydrological models can be used...
'to considerable advantage as teaching aids in integrating the interaction between hydrological processes, e.g. to demonstrate the effect of various hydrological phenomena on catchment response. Use of hydrological models in teaching, however, requires a sound understanding of
30
1
Formulate problem-examine system's behaviour, analyse real-world data
I
1 Define problem reauirina simulation I 1
Formulate mathematical model L .
Develop algorithms t Reject
Accept Program computer model
Reject 1 - Check program
Accept Reject
(Check para=\ - Accept
Conduct simulation experiments
Check results ?eject model I
Accept model Reject simulation { Compare p r e d i c w ) - -
Accept si m u la t i on I Apply sirnulation to solve problem 1
Fig. 4.6 - Phases in the construction of a mathematical model (modified after Hille, 1977).
the individual components of the whole system. Therefore, the use of models should be introduc- ed into a course only after basic hydrological principles have been already taught with a para- llel teaching of related subjects, such as hydraulics, soil science, geology and meteorology.' (Fleming, 1975).
4.2.1 Basic Deterministic Concepts
The degree of equivalence of the model and prototype response is dictated by the deterministic principles encompassed in a given approach. mination of physical parameters which describe the system, the deterministic approach is frequently called the parametric concept.
It is always difficult to classify deterministic models according to the principles governing their intrinsic structure or the simulation methods used.
'The formulation of a model is a continual process of modification, testing and remodification. The model may begin by being largely empirical; as more is learnt about the physical behaviour of the system under study, empirical components for the model will be replaced by others, more firmly based in theory, and modification must be tested, where possible, by comparison of forecast with observation'. (Clarke, 1973).
For this reason students must be told repeatedly that hydrological models must be considered as something subject to constant supplementation and improvement and that it is possible to combine both deterministic and stochastic approaches.
Since the model solution is rooted in the deter-
31
According to the implementation technique, deterministic models in hydrology are based on
Mathematical models in which the system behaviour is represented by a set of equations and statements expressing relations between the variables and parameters. Analogue models in which simulation of hydrological processes is based on the analogy between a response of the hydrological prototype (or its physical element), and its electric, hydraulic or thermal counterpart. Physical models which respect the scale similarity with the prototype.
or more principles:
4.2.1.1 Mathematical Models
Two basic approaches should be emphasised in the teaching process: a. Component Modelling representing a mathematical simulation of a small component in the hydrological cycle, while mutual interactions between other hydrological zones are substantially suppressed. the component. Such a major component might be infiltration, evapotranspiration, streamflow routing, etc. Modelling of streamflow routing was among the first means of introducing systems theory into hydrology (Dooge, 1959). In particular, linear systems theory substantiated the scigntific basis of the unit hydrograph method and its broad application in hydrological engineering, and also led to the rapid development of storage models. The superposition princ- iple, mathematically expressed by the convolution integral, forms the basis of these models. Different combinations of equal/unequal linear reservoirs in series or parallel can be introduc- ed, showing how more complex models may lead to better prediction of prototype behaviour but at the cost of an increasing number of estimated parameters. The students should be told emphatic- ally that the so-called black-box approach in simulation of a physical system results in the development of a relationship between the input and the output, without introducing any physical relevance to the equations and parameters of the model. A clear example is needed in any explanation of the structure and function of the black-box models (see examples 4.3 and 4.4).
Various structural schemes of linear and non-linear runoff and flood routing models are described in the literature (e.g. TNO, 1966; DFG,1975; Kutchment, 1972). Examples from the group of linear runoff models suitable for teaching purposes should include the Muskingum method, Nash model, Kalinin-Miljukov model, etc. Suitable non-linear rainfall-runoff models are the Kutchment-Borshevskij scheme, O'Donnell-Mandeville model, etc. (Kutchment, 1972; O'Donnell and Mandeville, 1975; Fleming, 1975).
The teaching of these component models should be concluded with the procedures required to determine the parameters using optimisation or estimation techniques followed by implementation procedures with actual hydrological data. The application of component models of surface runoff runs into the difficulties of mutual interaction between hydrological processes. This drawback is reflected in a problem common to this group of models, namely the determination of time and space development of effective (net) rainfall for individual isolated flood events. These draw- backs limit the application scope of the models. For these reasons there is a tendency to favour integrated (conceptual) modelling.
The development has been towards an understanding of the physical laws governing
b. Integrated System Modelling involves the simulation of the whole hydrological system. Here- in, the component theories are conceptually combined to represent a time-variant interaction of processes constituting the hydrological cycle. This approach is often referred to in various publications as conceptual modelling. An example of a conceptual system representation is given in Figure 4.7; continuous time basis.' (Fleming, 1975, see example 4.5).
set of analytical relationships between hydrological processes, and may never do so.
approach, is the representation of the hydrological cycle as a determinate system quantitatively expressed by mathematical functions governing the process. Model parameters are obtained either from direct measurement, analyses of measured records, by trial and error, or by an automatic optimisation procedure (see example 4.6). It is important to specify the criteria for model performance and accuracy. A common criterion of accuracy is to minimise the sum of squared errors between the recorded output from the catchment, and the simulated output from the model.
'The conceptual approach is an integration of the component theories on a
Empirical relationships are still necessary since the subject has not yet produced a complete
A necessary prerequisite of the deterministic approach, compared with the stochastic
Lack - - -
32
of fit might be caused by: errors resulting from an over-simplified description of the physical processes in the model, in contrast to the prototype, time and spatial variability of the input and the output data, errors in measurement of the input and output data.
Potential evaporation (daily, monthly) and lor relevant hydromet.data
Interception
’
I
1
Surface deten- tion stogare
I Upper soil zone
+ Total
. 1
Per colat ion
I I Inactive I
Fig. 4.7 - Example of conceptual representation.
Digital hydrological simulation used for teaching purposes requires a suitable computer with sophisticated software and well-experienced teaching staff capable of describing clearly the simulation techniques to the students.
Any well-functioning mathematical model inherently contains some notable features in its structure, and some of the principles on which such models are based can be demonstrated in the teaching process. It is impossible to say unequivocally which of the existing models are explicitly suitable for teaching use. From a number of existing conceptual models, those particularly suitable for teaching were chosen. Any choice will, of course, depend on the teacher and his practical experience.
Example 4.3:
Surface runoff formation may be schematically described in discrete time steps by a set of linear algebraic equations representing convolution of input to output function (unit hydrograph). Given a set of known inputs and outputs, the system of equations may be solved for the unknown transformation function of the catchment using matrix algebra. At this point, it is appropriate to illustrate common principles of the unit hydrograph method, and the methad of isochrones. By repeated iterations of the computation procedure, it is possible to show how the ordinates of net rainfall as well as the ordinates of the unit hydrograph can be refined to provide better model replication.
Solution of equations of surface runoff via matrix inversion (The Unit Hydrograph)
via an impulse response
Ref. Snyder, 1961; TNO, 1966.
33
Example 4.4: Linear and non-linear storage models as examples of component modelling of hydrological processes
Storage models are mostly applied to significant isolated rainfall-runoff events, particularly for design purposes. practical bydrological problems. particularly useful teaching aids. superposition principle and the derivation of the convolution integral. used to obtain parameters in linear cascade models can also be considered and attention can be given to the mutual overlap between the deterministic and statistical principles.
is possible to introduce non-linear models. linear models should be emphasised.
Linear storage models are a particularly good aid in the solution of Their conceptual and mathematical simplicity makes them With these models it becomes necessary to explain the
The method of moments
Once the students have become acquainted with the principles of linear storage models, it The principal differences between linear and non-
References: DFG, 1975; Kutchment, 1972; O'Donnell and Mandeville, 1975.
Example 4.5: The Stanford Model as an example of an integrated model of the hydrological cycle
Some conceptual hydrological models can be classified as general purpose with the remainder as special purpose models. former type remains the Stanford Watershed Model ram). instructive algorithm structure (see Figure 4.7). catchment water regimes and describes all significant processes of the hydrological cycle: Land surface processes: Interception, effects of impervious area, infiltration, overland flow,
Sub-surface processes:
Channel processes: Basin configuration and storage, channel flow and routing.
From the teaching point of view, the classical representative of the (version IV and the Hydrocomp Simulation Prog-
It gives an exhaustive description of the hydrological processes resulting in an The model may be used for a wide range of
detention storage, evaporation, snow accumulation and snowmelt. Interflow, soil moisture dynamics in both upper and lower zones, percolation, groundwater storage and flow.
The Stanford model contains over thirty parameters, at least four of which must be optimised. The remaining parameters are evaluated from maps, surveys, or existing hydrometeor- ological recorda. Instructions in its use are given in the Stanford Report (Crawford and Linsley, 1966).
the contribution of the Stanford Watershed Model to hydrological education (Linsley et a1.,1969): - Organising instruction around the flow chart (Figure 4.7) as a basic functional description
-
It is not the main purpose here to discuss the details of digital simulation, but rather
of the hydrological cycle. Providing greater opportunity for students to explore hydrological processes via digital simulation Providing for a variety of research projects in hydrology.
There are other conceptual models which can be used as instructive examples, and which are
-
listed in the following references.
References: Clarke, 1.973; Fleming, 1975; Kutchment, 1972.
Example 4.6: Automatic adjustment of parameters using the Rosenbrock technique.
In a catchment model context, an obvious parameter-dependent function to be optimised is the difference between the observed and computer output data from available input data. Other objective criteria could be used alone or in any combination. Among various optimisation techniques, the Rosenbrock method is most commonly applied for hydrological models. The students should be shown how to achieve the minimum value of the criteria, searching in an n-dimensional vector space (n being the number of parameters to be optimised) until some function F (i.e. the model function) is optimised. For the sake of simplicity, it is preferable to explain two parameter optimisation first. It is also important to emphasise that the number of parameters to be evaluated by calibration should be consistent with the complexity of model structure and the extent of the data set. If computational facilities are available, the sensitivity of the model response to parameter changes should be demonstrated. It is important that the student should appreciate the difference between the model's sensitivity to particular parameters per se and the sensitivity of the (optimal) set of parameters to a specif- ic data set.
References: Clarke, 1973; Fleming, 1975; Kutchment, 1972.
34
4.2.1.2 Analogue Models
-U,(O) & U,
Analogue models are most commonly based on an electrical analogy. The analogue model is programmed into an analogue computer. In this type of model, there exists a direct correspond- ence between the prototype system and the elements of the electrical network. The electrical network, composed o€ components capable of performing certain mathematical functions (integret- ion, differentiation and arithmetic operations), constitutes the main operational part of the analogue computer. Many processes occurring in the hydrologic system can be represented by time and/or space dependent differential equations. their solution as it can integrate problem variables on a continuous basis. With the analogue computer, the effect caused by a change in an input parameter or function is immediately observ- able. Output from the analogue computer is capable of graphical representation in the form of a continuous plot of the variable quantities involved. The student, as the operator of the analogue model, can readily and directly visualise results. The effect of different combinat- ions of the various components within the entire system can be explored easily to show the changes in specific processes that might be necessary to meet prototype conditions.
components of an analogue computer may be interconnected in such a way that the voltages in the resulting circuit are governed by the same equations, modified where necessary by scale factors. By monitoring or recording voltages in the computer, a solution to the problem is obtained. The basic components of a general purpose analogue computer are listed in Table 4.2.
mathematical expression of the system to the prototype and vice versa. E~wever, compared to digital computation, programming for an analogue computer is in some senses subject to a greater measure of lucidness. The flow chart for the analogue computer (using symbols listed in Table 4.1) is very clear, giving instant ideas about the interlinkage of computer units (see examples
The analogue computer is particularly suited to
Thus where a physical problem can be expressed by differential equations, the basic
In common with digital computation, the student often has difficulty in relating the
U,:-k, i;,dr+y(O)
k,= 1. 10 or H)o INTEGRATOR where: u,(O] .... initial cond..
I SYMBOL I C o ~ ~ ~ ~ N T I EXPLANATION
U1
u,=-~,(u,+u,) where; k, = 1 or 0.1 1 1 S U M M E R
U1
I
SUMMATION uo=-k, (U,+U1+lOU,)dT+U,(0) t INTEGRATOR (for several input voltages 1
FUNCT1oN CONVERTOR
U,= f(Ui) (for adjustment an output volt- age as some specified function of its input voltage )
1
MULTIPLIER
u,=a.u, (Osa'l) (for mult iplicat ion by any constant ) METER
U,= u,.u,/lOO (voltoge ?: 100) (for multiplication by another variable)
U,( t I generating (for generating o function
Table 4.1 : Some basic components of a general purpose analog computer.
35
4.7 and 4.8 below). Facility with analogue computation requires practice. The general sequence in model implementation is usually as follows(Christie, 1971):
1. Prepare a scaled computer diagram. 2. Label the components on this diagram (i.e. state the reference number of the actual
computer components to be used, and also state what the output voltage that each component represents).
3. Wire-up on patch panel 4. Set potentiometers, initial conditions and timer. 5. Carry out a static check and possibly a dynamic check. 6. Compute (if overload occurs, modify scaling and repeat).
The display or recording of solutions can be carried out as follows (Christie, a. In continuous time During the computation procedure (step 6) the output voltage from any component can to: - an oscilloscope - a high-speed pen recorder - a high-speed ultra-violet recorder - an X-Y plotter
1971) :
be connected
b. In discrete time At the end of the computing time any voltage may be monitored with a digital voltmeter and printed .
More complex hydrological models, even in teaching situations within specialised postgrad- uate courses, may be solved by using hybrid computers. of digital and analogue computers. However, hybrid computers are still rare, very expensive and difficult to program. Therefore they are very seldom used as teaching aids. shows a possible arrangement of analogue and digital computers for investigating a general rainfall-runoff model.
These computers combine the advantages
Table 4.2
Digital Part Interface Analogue Part I Data reading or generating logical operations
Result evaluation fitting criteria storing data
Digital to analogue data transfer
Analogue to digital data transfer
High speed solution of differential equations
Timing
Table 4.2 : Interfaced digital and analogue components
The above text shows the suitability of using analogue models for the demonstration of some hydrological problems, especially in modelling some components of the hydrological cycle. Analogue models are sometimes implemented for flood routing through a reservoir (see Example 4.7), structuring of various storage models (see Example 4.8), and a number of groundwater models (Bouver, 1967; Unesco, 1972a).
particularly those models simulating groundwater flow. Models based on a non-electrical analogy represent a special category of analogue models,
Groundwater flow through a soil mass follows the Laplace equation:
where $ is the head, and x, y, z are Cartesian coordinates
Equation 4.2, fundamental in groundwater flow models, describes steady potential flow. Its basic characteristics include the fact that flow lines and equipotential lines are mutually orthogonal. Good examples of their use as teaching aids are described by Klaasen (Unesco, 1972a).
Models which demonstrate this phenomenon simply to the students are very useful.
36
The parallel-plates model (Hele-Shaw model), involves the laminar flow of a viscous liquid between two parallel plates. particularly well-suited for teaching and demonstration in the class (see example 4.9).
The heat model is based on the analogy between heat flow through a conductor and ground- water flow. Only two-dimensional problems are dealt with in practice; the model is less suited to demonstration.
The electric model uses electric current passing through a conductor as the analogy. Where the transmissivity (or permeability) is relatively constant, two dimensional steady flow with complex boundary conditions can be easily demonstrated by using conducting paper (Tele- deltos paper) cut to the shape of the boundary.
flow for the solving of well flow problems.
which the groundwater flow is reproduced to scale. In this kind of model three-dimensional flow problems can also be solved but difficulties arise when the model is too small. Large models are often too expensive. (Capillary action, enclosed air and organic growths may be troublesome and require special treatment).
It is restricted to two-dimensional flow problems but
The membrane model, consisting of a tightly stretched membrane, simulates groundwater
The Sand-model consists of a trough filled with sand or any other coarse material, through
Example 4.7: Problem of flood routing through a reservoir
Reservoir lag occurs when the rate of outflow, Q, and the water level, h, in the reservoir are governed by some form of outlet weir and the reservoir is subjected to a variable rate of in- flow, I (the flood hydrograph). During any time interval, the change in storage equals the volume entering, minus the volume leaving the reservoir:
A dh (I-Q)dt
312 so that for a simple spillway where A = kbh
- dh - 1 (I(t) - kbh 3/2) dt A (4.3)
where A = surface area of reservoir h = depth of water above spillway crest at time t I = I(t) = rate of inflow k = spillway coefficient b = breadth of spillway
This problem can be easily solved by a general-purpose analogue computer. The unscaled computer diagram for solution of the equation above is given in Figure 4.8. Graphs of I, Q and h can be obtained by connecting a recorder to the appropriate point in the circuit. The effect of varying the breadth of spillway can be seen very clearly and quickly by adjusting the po- tentiometer representing kb (and perhaps also by adjusting the initial value of h). The effect of variations in A (as a function of h) can also be included.
References: Christie, 1971; IASH-Unesco, 1969.
I F G.
form Ut) -kbhf
s -hi
kb
d h dt
I
A- = I-kbh’
Fig. 4.8 - Simplified computer diagram for reservoir lag problems.
3 7
Example 4.8:
With the Kalinin-Miljukov method a river channel is divided into "characteristic reaches" (a catchment can also be divided into isochronal or other sub-areas); for each reach or sub-area following from the principle of linearity, the continuity equation holds
Flood-routing problem using the Kalinin-Miljukov approach
(4.4
where k is a constant having dimension of time, and the other variables are as in the previous example. By solving equation (4.4) for the initial conditions t = 0, Q = Po, then
etIk ltlI etIkldt + Q e -t/k 0 0 Qt = (4.5)
Equation (4.4) and its integrated form (4.5) hold only for one characteristic reach. For n reaches the recursive relations hold:
L
dQn 1 -- - (Qn-l - Qn) dt kn
The problem may be easily resolved on an analogue computer.
L I1.c. 1 F G.
Note: If n is odd number dQ 1 -- dt'-k,(I-Ql) - then Q. is negative and the sign changer should be connected
Fig. 4.9 - Simplified computer diagram for the Kalinin-Miljikov model.
Figure 4.9 shows a diagrammatic flow chart. From a mathematical viewpoint, the model is a system of n ordinary differential equationgh each of which is of the 1st order.
k on the potentiometers and by plugging in a continuous recording device (e.g. an oscilloscope) a? selected points, the routing effect of the system can be followed.
The final unknown Q is considered as being of the n order. By setting different values of k 1: k2 -.- n
References: Kutchment, 1972; IASH/Unesco, 1969.
These together with other single or multi-purpose models, partly overlap with the group of physical models.
38
4.2.1.3 Physical Models
Physical models have been applied to investigate hydraulic and hydrological phenomena for many years. For teaching purposes it is necessary to have models capable of simple demonstration of some of these phenomena. In contrast to hydraulic phenomena, there are a number of difficulties in the modelling of standard hydrological processes. These are caused by the fact that Newton's law of dynamic similarity (which also assumes geometric and kinematic similarities) between the model and the prototype is impossible to maintain. The difficulties encountered in trying to maintain scale similarities are made more acute when modelling surface runoff from artificial rainfall on a topograhic model of a catchment. Thus, the distortion of dynamic similarity can relegate physical models to a mere demonstration of the qualitative character of the phenomenon.
A number of single or multi-purpose physical models are used for teaching purposes by universities or other training institutions. Some of these models are mentioned below.
Single purpose physical models
For simulation of the rainfall-runoff process and compilation of the hydrograph, it is possible to use a surface runoff physical simulator, a catchment-topography model, and an outflow measuring device. Such models are described in the literature (e.g. Nemec in Unesco, 1972a; Grace and Eagleson, 1966). Despite difficulties arising from the impossibility of maintaining full-scale similarity, and despite the unwanted capillary effect, these models may be used successfully for high quality demonstrations of: - the effect of rainfall duration and its intensity on the hydrograph form, - non-linearity of the runoff process, - the effect of physiographical features of the catchment, - the effect of antecedent conditions on the runoff process.
Multi-purpose physical models
In the teaching of hydrology increasing use is made of multipurpose physical models or apparatus capable of demonstrating various hydrological phenomena. Sellin and Treleaven (Unesco/IWRA, 1975) described a simple self-contained laboratory facility. Successful experiments were reported on: - rainfall-runoff flood hydrographs for a number of surface or subsurface conditions, - single and multiple well abstractions with accompanying piezometric measurements, - aspects of fluvial mechanics including meander patterns and sediment transport.
holding up to a 200 mm depth of gravel, together with an overhead spray device accurate measurement devices for inflow to and outflow from the gravel bed, and a multi-tube manometer bank.
Other equipment which sets out to demonstrate hydrological processes on a small scale, has been developed (e.g. Armfield Eng., 1979, Figure 4.10). Such equipment can be used to show the relationship between rainfall and runoff from catchment areas of varying permeability and the abstraction of groundwater by wells both with and without surface recharge from rainfall.
The authors describe the apparatus consisting of a 2 m by 1 m shallow tray capable of (rain simulator),
Example 4.9: Simulation of groundwater flow through an aquifer (Hele-Shaw model)
In this analogue model viscous fluid flows between two parallel plates. For demonstration purposes, coloured glycerine can be used as the fluid, with perspex plates, 1.5 mm apart, for the model (see Figure 4.11).
Stokes has shown that the two-dimensional laminar flow of viscous fluid can be described by the equation:
1 gd2 d@ 12 v as v = - --- (4.7)
(for definition of symbols see below).
ally by tests carried out using the described physical model which can be used both vertically and horizontally. The vertical model represents flow in a vertical soil section. It is possible to simulate an unconfined aquifer, with seepage surface, free water table and rising storage levels (Verruijt, 1970)
Such flow also satisfies the Laplace equation (eq. 4.2). This can be confirmed experiment-
39
Fig. 4.10 -
Fig. 4.11 -
Basic
Scheme
4700 mm
cut view from left side
hydrology system.
fr
of the
AI
parallel-plates model.
CROSS SECTION A-A'
The horizontal model represents the flow through a certain layer of the aquifer. a case, a comparison is made not of velocities but of the total discharges. Thus
in the field
in the model
dO ds
Q = qBh -kHB -- 9dm3 dhm
m Q m = S n B d m m = - Bm 12v -- ds
In such
(4.8)
(4.9)
The value of transmissibility kH, obtained from the field as basic hydrogeological data representing the aquifer, is simulated by the model as:
sdm - 12v
40
Symbols used: v
g
dm (+
3. as
k
H
B
Q q
h
V
m
= velocity in the direction of flow = gravity acceleration = separation of parallel plates = potential head
= gradient in the direction of flow
= coefficient of permeability = thickness of aquifer = width of flow region in a vertical plane = discharge
= specific discharge
= height of groundwater table
= kinematic viscosity
= subscript denoting model
References: Verruijt, 1970; Thomas, 1973.
41
V Visual presentation of hydrological information
Graphic representation of the temporal and spatial variation of one or more hydrological variables is one of the well known and most important teaching aids. The purpose of diagram- matic presentation is to illustrate the essential features of complex phenomena and highlight those factors which are influential to decision-making. A good representation will influence decisions; the specialist can summarise a large quantity of data and inform the non-specialist in a graphic way, allowing him to grasp the hydrological phenomena under study and int.erpret the results accordingly. The teacher uses graphs, diagrams and maps to convey information to the student in much the same way as the hydrologist communicates to a non-hydrologist. In order that the student fully appreciates these methods it is of the utmost importance to explain them actively by selecting illustrative examples from different fields in hydrology. There should be sufficient time in the curriculum to encourage the presentation of results, using auxiliaries such as descriptive geometry, cartography, statistics etc.
The decision process is facilitated if this information is self-explanatory and understandable to the public. In contrast to a scale model test, which is illustrative in itself, the presentation of results in tabular form or by a mathematical model will often be too abstract for a non-expert with no adequate mathematical background. Thus, the preparation of information in an adequate graphic form must be emphasised as it becomes a powerful tool in practical work, and one which is often overlooked in many textbooks on hydrology.
The level of public information is often a decisive factor in water resources development.
5.1 Graphical Representation of Hydrological Variables
Graphical figures are invaluable in demonstrating the interdependence of two or more numerical variables. They can often reveal the relationships between variables that would otherwise be masked by the complexity of the relationship or even by the badly-ordered tabular form of the data. In some cases such figures have only a subsidiary function to fill, and serve only to supplement numerical tables and the accompanying text, not to replace them.
Data from a group of hydrometeorclgic measuring stations over a large catchment are usually given in tables, with the stations, possibly subdivided into those of primary and secondary importance, arranged alphabetically. Whilst graphical diagrams are usually used to portray local values of the median, mean value, quantile etc. or to display time variations, such diagrams are used increasingly in pertinent hydrological cartography to show spatial variations (see also section 5.2; Hydrological Maps).
5.1.1 Coordinate Dependent Diagrams
1 - Right-angle coordinates
The most useful form of illustration of a numerical time series is the plot in a right-angled two-axis coordinate system. In such time-dependent relationships both curvilinear plots as in Figure 5.1 and straight-line polygonal plots as in Figure 5.2 may be applicable. The most common example is the hydrograph which is often plotted in real-time as the analogue trace of self-registering measuring instruments. From digital recorders only discrete (time-sampled) values are available. Here the intervals between the measurements should be small enough so that a constant rate of change can be assumed between them (Figure 5.2) and interpolation errors kept small. If the sampling interval is increased the number of recorded data is reduced considerably but as shown in Figure 5.2 there would be loss of information on the peak. If a
43
Stage h lcml
Fig. 5.1 - Discharge rating curve.
At = 15 min
----- At = 6 hrr. -. -. - bt = 9 hrc.
1 1 1 1 1 1 1 1 1 1 l j
0 16 24 0 16 2L time in h
Fig. 5.2 - Representation of a hydrograph by discrete values.
hydrograph over months or years exhibits a marked variation, it is usually advisable to plot the trend-line at the same time in order to show the periodic, seasonal or random nature of the deviations; for this, many methods have been developed from mathematical statistics (mean value, ,weighted average value, moving average, method of least squares, approximation through second or higher order equations, asymptotic growth curve etc.).
Arithmetic axes are most preferred because they are understandable to all, but for certain variables, for instance low-water analysis, k-valuations by the Muskingum method (Figure 5.3), semi-logarithmic scales are advisable. On a semi-logarithmic scale system an ascending straight line represents an exponential rate of increase. The decision between arithmetic and logarithmic curve representations is not always made on the basis of available diagram space but sometimes to aid interpretation.
44
CO-axial graphs permit the display of the development of many events simultaneously. In Figure 5.4 for instance, the quantity of previous rainfall (AP 1 , the number of the week (W), the rainfall duration (D) and the amount of rainfall (PI are izterrelated.
@ K.29Eh @ K = 31.1 h @ K = 32.1 h @ K = 39.8h
1- 6-
5t * 0% 10 20 PI 30 LO tlhl
Fig. 5.3 - Determination of the storage coefficient K from the decreasing part of flood hydrographs.
Fig. 5.4 - Basin recharge (P-R,) = f(APs,W,D,P) relation for Wietze river determined by coaxial graphical method.
Time-series and spatial time-series
In hydrological statistics, special importance has been placed on the analysis of time-series. The simplest example of such a time-series is the hydrograph. The analysis of such time-series allows trends, periodic or seasonal or cyclic changes to be investigated. In addition, the variations of short duration can be emphasised or eliminated.
A spatial equivalent to time-series would be the land-profile line, in which the abscissa "time" is replaced by "location". Examples are elevation profiles that show river- length profiles, hydrological longitudinal sections (Figure 5.51, or channel/valley cross- sections for investigation of discharge characteristics. Temperature and precipitation profiles, derived from isothermal and isohyetal maps can be set in relation to the elevation profile. The time profile of a series is fixed as one-dimensional; the land profile line can be placed in all possible directions and on the map plane it is two-dimensional and as a spatial contin- uum, three-dimensional.
0 0
Disc harge L
9 IrnJ/sl < 6 000
2 000
1 000
0
- 0
c 0
Yt 2 2 a. Z C
0 CO c .- 0 3 6s E Mean high water discharge U L CO .; MHQ
l- ! I
I c
! I ! ! I ! I ! I I
3 000
1000
0
Unit discharge
t 6o q I l/skm21 60
LO 10
20 20
0 0
Fig. 5.5 - Longitudinal section of discharge (river Rhine).
The autocorrelation determines the correlation relationships within a single time-series. For instance, in a time-series of monthly precipitation or discharge, the value of one month is serially correlated with the next month in the series; month 2 with month 3 etcand it is straightforward to compute the lag-one correlation coeffic- ient rl i.e. the serial correlation coefficient with lag 1. (month 1 with month 3, month 2 with month 4) , to r are similarly ascertained. The grapi of rk versus k, where k = 1,2,3.. .n designatesr&e time lag, is called a correlogram (Figure 5.6). As well as autocorrelation, cross correlation diagrams can also be plotted to show the temporal relation between values of two time-series.
month 1 is correlated with month 2,
The correlation coefficients r
n
46
1.0
L 0.6
- 0.q
Fig. 5.6 - Correlogram of monthly precipitation. Frequency Diagrams
As a rule, arithmetic scales are used for simple frequency distributions. For instance, grouped classes of discharges are plotted on the abscissa, and the number of values assigned to single classes are plotted on the ordinate. The points of the diagram are joined by straight lines, or, for the most part, represented in the form of a histogram (Figure 5.7) in which the total area represents the total number of values or 100% frequency.
60
LO
20
0 60 100 0 IdhI LO 60 0 20
discharge
Fig. 5.7 - Frequency distribution of discharge.
Cumulative Frequency Diagram fSinyIe Mass Curve)
With the diagram of flood frequency, for instance,30ne no longer questions how many events belong to a specific class (e.g. from 200 to 300 m /second), but how many events are above or below a given value. The cumulative frequencies are plotted either directly or as a percentage of the total number. A graph shows the well-known S-shaped form. If the frequency distribut- ion has a central mode then such mass curves are often better suited for the matching of frequency distribution functions than the simple frequency curves (Figure 5.8).
plotted with arithmetically divided coordinate scales (Figure 5.9) the areas of low water and flood water discharges are ill-defined and are better measured if probabllity paper with log- noma1 divisions are used, as in Figure 5.10.
The well-known flow-duration curve is also a mass curve. If flow-duration curves are
Double Mass Curve
Cumulative data are plotted on both axes; one site to another, with time as the independent variable.
for example, Figuse 4.2 relates cumulative runoff at
47
Datum or class of data x
0 11.5 Datum or class of data x
Fig. 5.8 - Density function and cumulative frequency.
I m3/s 50C
LOO
300
200
100 80 60 LO 2(
100
River Marondava- Tsiandava / Madagascar 1968/69
a. 60.9 '-I--
K (non excedancr) 90 80 70 SO 5b LO 30 20 10 0% -lexcedancel
I 0 20 LO 60 80 100 200 300
Fig. 5.9 - Flow duration curve of Morondava river, Madagascar.
48
365 Days
Flow duration curve of mean ddly discharge(&) for River Momndaw- Tsiandava IMadagascar I M / 6 9 platted on log. normal paper
9897 95 90 80 70 64 Y) Lo 1) 20 10 5 4
Fig. 5.10 - Flow duration curve.
Climatological diagrams Diagrams are especially well suited for representing climatic data, and may, for example, facil- itate the identification of different climatic zones. Temporal variations are well illustrated. For example mean monthly temperature and precipitation values over the year can be set in relation (see Figure 5.11). The relationship between the scales for precipitation and temper- ature is arbitrary and based on climatic considerations which are not discussed here.
Manbus 27.1 O C 1771 m m /a
Precipitation P [mm] 3001
Temperature T ["C 1 100 50
80 40
60 30
/ **..:.::.*. .: . ..: .*:* t 2o LO 1" *.*..:.' T
2o 1 Po
Fig. 5.11 - Diagram showing mean monthly precipitation and temperature over the year
49
By using a ratio of 1:2 (or 1:3 in semi arid regions) for the temperature and precipitation scales, the year may be classified into dry, humid, super-humid periods (Walter and Lieth, 1960). In humid areas, the precipitation curve generally runs above the temperature curve; in arid areas the pattern is reversed. One must be sure that the diagram for the southern hemisphere begins with the month of January, in order to make possible a direct comparison between the two. The hatched areas, where the precipitation curve lies above the temperature curve, indicate hum- id months; stippled areas indicate arid months. At stations in the tropics and subtropics, when the precipitation exceeds 100 mm in a month, the scale ratio may be reduced to 1:lO (one scale division of the ordinate equals 200 mm precipitation). In the figure these super-humid months are especially emphasised through dark shading.
Precipitation diagrams
This may show the precipitation distribution within the year or the differences from year to year. For instance, the average number of days/month with at least 0.lmm precipitation (sub- divided into rain and snow) can be plotted against the month (Figure 5.12). Likewise, tempera- ture graphs, hydrographs and so on can be used to show annual and seasonal variations. Fpr many purposes, it is advisable to emphasise especially the deviations of precipitation, discharge etc. from the mean values computed over many years.
do s
snow - fall
.-.:.:. wi{h ..
Fig. 5.12 - Average number of days with precipitation and snow a.t IIannover, 1951-1970.
If climatological diagrams are plotted on maps, it is necessary to make sure that the diagrams refer to single stations and not to areas. Such climatological diagrams are not to be confused with real climatic maps (Walter and Lieth, 1960). The latter should show, through isopaths, the extent of the climatic variation over large areas and permit a comparison with other geographic phenomena over the same areas.
diagrams. However, here the actual successive years are plotted along the abscissa, and the individual monthly values are plotted on the ordinate (Figure 5.13). In this figure the occurrence of particular dry years is clearly defined. In the same way, precipitation can be compared to groundwater levels (Figure 5.14).
Climatic time-series diagrams are constructed in similar fashion to average climatological
50
SAN JOSk Precipitation P Imrnl
3001 Temperature T 1°C I
'JI A'S' O ' N I D I J I F ' M I A 'M ' J I ! I A'S' O ' N DI J ' F ' M ' A 'M J ' A ' S ' 0 ' N ' 0 I J ' F ' M ' A ' M 'J ' 1978 1979 1980 1977
Fig. 5.13 - Mean monthly temperature and precipitation from 1977 to 1980.
Rrcipitation mm 1LO-
120-
' 1970 I 71 L I 76 I 77 I 1978 '
Fig. 5.14 - Monthly values of precipitation at station Grasdorf and regional groundwater level in the Leine Valley.
51
2. Triaxial ordinates
If three variables sum to a constant value, their relative proportions can be graphically illustrated using triaxial ordinates. their components of clay, silt and sand (Figures 5.15). An alternative to counting outwards from the angular points of the triangle, is to consider each side as a base (zero line) for one of the three variables and measure the percentage value vertically to them; the highest value (100%) is then the angular point opposite to the respective base line.
Such figures are used to classify soils according to
100 80 60 LO 20 100
Sand S ( 6 0 ~ 1 - 2 m m l . X
Fig. 5.15 - Soil texture triangle of the USDA (Marshall/Holmes, 1976).
3. Polar coordinates
Polar coordinates and related radial coordinate systems are convenient for representing some types of data; for example, Figure 5.16 shows how an octagonal coordinate system can be used to describe the frequency distribution of wind direction in each of the eight principal compass bearings. The wind frequencies are represented in percentages, with the frequency of calm indicated at the origin (3.5% in the figure).
5.1.2 Line Diagrams, Area Diagrams and Isometric Diagrams
One of the common uses of the line diagram is to show the magnitude and time of occurrence of flood peaks, as shown in Figure 5.17. In essence, the top two diagrams, in which time is the abscissa and magnitude the ordinate, are a set of distinct points of the complete hydrograph. The lines joining each point to the abscissa are merely a visual device to aid connection of the ordinate value to the abscissa. The lower diagram in the figure has rank on the abscissa; the temporal distribution of the flood peaks is lost but a sense of the statistical distribution is gained. Linear scales are used in this example but in special cases, for instance in the presentation of very extreme flood values, geometric or logarithmic scales for the ordinate are advisable. Additionally, the use of a strict scale on the abscissa is not always necessary; for example, the annual maxima diagram in Figure 5.17 is often given with the events spaced evenly at yearly intervals.
Bar graphs differ from the pure line diagram only through the width of the lines. Thereby the figure is not changed in principle, but the impact is greater. (Figure 5.18). The basic difference between line and bar diagrams is merely one of presentation. Bar diagrams are suited for the comparison of quantities as well as the presentation of progressive series (climatolog- ical diagrams and time-series diagrams are often represented as bar graphs).
2 x I
Fig. 5.16 - Wind rose (% of year and distribution for each month (whole year = 100%) for Hannover from 1951 to 1970.
Band diagrams result from the segmentation of a complete quantity into smaller parts. These figures can be portrayed in the normal way with a coordinate system (Figure 5.19). but can also be plotted on both sides of a vertical or horizontal centre line. Such band diagrams are optically very impressive, but have the disadvantage that, to some extent, only the group lying next to the base line can be estimated accurately. The irregular base lines of the adjacent groups lead to optical distortion of the arrangement. Through suitable selection of cross-hatching, particular groups in these figures can be made to stand out.
resource systems) there is a need to represent visually the magnitude of various quantities (for example, populations, water demands, reservoir capacities etc.). Plane and isometric diagrams are ideally suited for this purpose. Both types of diagram permit a compact way of representing a wide range of values; for plane diagrams the area denotes magnitude and for isometric diagrams a trebling of the value of a variable can be achieved with only a doubling of the diagram area.
diagrams (see Figure 5.20) .
In many situations (such as in maps, map legends, or schematic representations of water
Circles, squares and triangles are the most commonly used form of plane and isometric
55
8
TIME IN YEARS
(PARTIAL SERIES DATA IN ORDER OF OCCURRENCE)
6
0 0 Z'
TIME IN YEARS
' DATA IN ORDER OF MAGNITUDE I T
10 20 RANKOFVALUE io
Fig. 5.17 - Flood peaks in the Danube, Vienna-Nussdorf, 1961-1970.
54
2oc n =,
2 2
a 0 U W CK a J 100 a 3 z e zu Q k
E 3
2 100
c
200
300
't I In 0 ul b e e
Fig. 5.18 - Deviation of annual precipitation from the mean at Hannover from 1951 to 1970.
I I 1970 1080 ' 1990
Fig. 5.19a - Band diagram of water demand.
Emmcrrdorf 4 Gail -River , 3( ~ i ~ l a c h ~
I \ Gaillitz
Fig. 5.19b - Band diagram of sediment size distribution of river Gail.
55
total asable part 0
a)
(L - scale foetor a) /total
W
C)
Use of groundwater Id m'l by different consumers
Scale tar drinking water demand I 106mJ1 in o mop legend
Triangle diagram showing reservoir capacity in a mop
Isometric diagram of regional oquifcr capacity ond exploited component Square diogram S h i n 9 wotcr demand
of different users in o region
Fig. 5.20 - Use of plabe and isometric figures to represent magnitudes.
5.2 Hydrological Maps
The following section is not intended to constitute a treatise on hydrological mapping in view of the availability of the Unesco/WMO publication "Hydrological Maps" (Unesco/WMO, 1977). For questions on cartography and mapping techniques, the reader is referred to this publication. Hydrological maps are treated here with regard to their value as a teaching aid.
5.2.1 Introduction
Whilst maps have always shown some hydrological information, such as river courses, swamps, lakes etc., they are not proper hydrologicalmaps. generally in use is still rather unsophisticated but the field of hydrological mapping is now in a phase of rapid development. required to compile hydrological maps but demonstrates very much that hydrologists in many cases have only just discovered the use of hydrological maps as a tool for their daily work and as a teaching aid.
and civil engineers often have not been trained in the art of mapping. why hydrologists often prefer descriptions, tables and graphs although a map is much more suitable for demonstrating phenomena and their quantitative aspects over an area. In contrast, hydrogeologists, again as a consequence of their education, are much more used to preparing and utilizing maps; geological mapping has a long tradition. Thus, it is not surprising that the first hydrogeological maps were clearly derived from geological maps; maps showing the dynamics of groundwater are, however, rather new. Sophisticated types of maps have been developed allowing the presentation of even three-dimensional phenomena such as generally occur in groundwater; even the existence of several aquifers does not create serious difficulties.
known tools of geographers. Permanent features are amenable to mapping, but hydrology, as a science of the hydrological cycle, deals with changing phenomena. A hydrological map, there- fore, is not necessarily permanently valid and needs an explanation as to its origin, its way
The type of hydrological map at present
This fact not only reflects the large amounts of data
Hydrological mapping is rarely found in the curricula and syllabi of hydrology courses, This perhaps explains
real hydrogeological
A physical map shows permanent features (rivers, mountains, etc.) and is one of the best-
56
of compilation and in some cases, even as to its purpose. Such an explanation would either be in the form of a printed note beneath the map or an accompanying booklet, and might concern the contents of the map, the reliability of data, the preparation of the map, its cartography, the interpretation of the method of presentation and its legend.
5.2.2 Technical Points, Cartography
Scales
The following classification has been introduced and is widely used:
large scales : up to 100,000; medium scales : 1 : 100,000 to 1 : 500,000; small scales : 1 : 500,000 and smaller.
Large-scale maps are generally prepared for or used in connection with special projects or programmes, whereas very small-scale maps are normally used for teaching, scientific and demons- tration purposes. For detailed studies or projects, large-scale maps (generally 1 : 25,000) are used; for a general overview, maps of 1 : 1,000,000 or much smaller are useful.
Cartography
In some cases hydrological maps call for specific requirements related to the character of the phenomena presented. Discharge and quality of water in rivers need special forms of present- ation since the phenomenon is not observed within an area but along the line of the river. Hydrological maps, therefore, usually have an outstandingly rich choice of cartographic tools such as:
symbols (points, triangles, etc.) lines (different thicknesses, dashed, coloured); curves (with symbols or other signs); Dands (different thicknesses, structures, coloured); diagrams (simple, compound, geometric figures); isolines or area markings (colours, bands, shading, screens, overlays, superimposed markings, area signs).
Base Maps
In general, hydrological maps are made using existing base maps on a given projection or scale. Depending on the purpose of the maps, outline maps (showing only main items such as rivers, towns, etc.) or normal topographical maps are used. Outline maps are preferred for small scales; the larger the scale the more valuable is a basic map showing more detail. In addition, in order to avoid confusion between the topographical detail of the base map and the superimposed hydrological detail, map-makers prefer the base map to be printed in light grey or brown rather than the customary black. Such maps are generally available at scales larger than 1 : 200,000 and in particular at 1 : 50,000, 1 : 25,000 and larger. Since these maps are very commonly used, they are normally inexpensive and have the advantage of being comparable with other maps.
Course organisers are advised to have a stock of base maps of the region in which the students are conducting their field work so that the students may map their results. Immediate mapping in the field facilitates the visualisation of the project and helps to identify mistakes on-the-spot; mapping irregularities are much more easily identified than errors in tables.
The International Hydrogeological Map of Europe (1 : 1,500,000) is being published on the same scale and with the same projection, background, sections etc., as the geological map, the tectonic map and the deposits map, etc. The same principle is generally applied to atlases - not only for economic reasons but also to facilitate comparison.
Legends
The choice of the scale may be regarded as the most important decision of the map-maker. The scale influences the quality of presentation and also determines the detail included in the legend.
ly in the field of climatic and geological maps. No recommendations exist for surface water. In many countries standardised legends have been developed for specific reasons, particular-
57
For hydrogeological maps, an international legend for hydrogeological maps (Unesco/IAHS, 1970) has been developed with a view to facilitating the preparation of maps. certain symbols and modes of presentation for several phenomena of groundwater hydrology.
5.2.3
It recommends
General Classification of Hydrological Maps
Network Maps
Network maps permit interpretation of the quality of the network, observations and the representativeness of data. They contain all gauges and observation stations for measurement of the chemical composition of water, temperature, discharge and biological parameters. An indication of the meteorological network is frequently omitted though this would be a very valuable addition for the hydrologist. Groundwater observation stations should also be shown in a network map, although very often they are to be found in maps compiled by different agencies. of water agencies or authorities and borders of administrative districts.
Maps Showing Hydrological Phenomena
the universality of
Network maps may also indicate the areal responsibilities
Due to the changing character of hydrological phenomena, many maps describe momentary conditions, averages, durations, variabilities, frequencies, intensities, etc. The first type of map deals with observed data. These data may concern properties and conditions existing at the moment of observation (examples: discharge 1.1.1970 7 am, borders of inundated area of the flood of ..., temperatures of water in a lake, etc.). These maps generally emerge from observations taken at various places at the same moment or for the same event. This type of map is a typical product of the field work of students. Maps such as these show data without any interpretation or evaluation. The same generally applies to any map of totals and absolute values, including the results of physical and chemical analyses.
A very common group of maps deals with evaluated data such as averages, maxima or minima. Most of the maps of water quality, discharges and temperatures have been drawn on the basis of a long series of data developed with rather simple mathematical processes (calculation of averages). years of data.
these data, a third group interprets the data. In this group all maps of duration, variability, frequencies, intensities, beginning or ending dates of a phenomenon, of tendencies and developments, are included. These maps require the existence of reliable and sufficient data and need careful treatment. Maps of this kind are absolutely indispensable for the work of hydrologists since they are most suitable for describing particular aspects of the hydrological cycle, especially changes in hydrological and hydraulic conditions.
For mean levels and discharges, averages are obtained from twenty or even thirty
Whereas the first group deals with the actual dataland the second group with averages of
Reliability
The considerations above are based on the assumption that sufficient and reliable data are available. In many cases the available data do not justify the preparation of a detailed map or they demand qualification on their representativeness and reliability. Lack of quantity or quality of data may only lead to schematic maps or to maps on such a small scale that the mapping requirements can be met by the amount of available data.
5.2.4 Classification of Fields of Interest
A very important aspect of classification is the place of the phenomenon within the hydrological cycle.
5.2.4.1 Atmospheric Water
The hydrologist should be familiar with the most important climatic maps (precipitation, wind, temperature, air pressure, sunshine, etc.) and he should pay particular attention to learning to read and interpret daily weather charts and even to making an attempt at prediction. Each syllabus of a hydrology course should include the study of weather charts, explanation of their symbols, description of the element presented, and exercises on how to read charts. Consider- ation of three ar more consecutive charts will help students to understand the development of the weather. Precipitation intensity maps are of particular importance. Details may be obtained from the WMO Guide to Climatological Practices (WMO, 1960). Precipitation maps are easily obtained - they are in all good atlases, in publications of national weather boards,
58
and are obtainable from school equipment suppliers. with data on a given heavy rainfall and should develop for himself a map of rain intensities as a basis for the computation of a flood. be acquainted with maps on evaporation.
The hydrology student should be supplied
Besides precipitation maps, the hydrologist should
5.2.4.2 Surface Water
The description of surface water phenomena often poses immense difficulties and leads to tables, graphs or maps being prepared. can only be presented on maps. River problems can be presented on a map but only in relation to the river itself and not in relation to the surface they drain. ping is often the easiest way to present data in a comprehensive and instructive way.
The most generally used surface water map is the physical map showing the boundaries of the catchment areas and their sub-catchments. The map would show rivers, canals, lakes, swamps, deserts, etc., and may be supplemented with details of the hydrological network. This type of map is more geographical than hydrological.
are concerned, the maps exist only on rather large scales, whereas large lakes may be shown on a smaller scale. Maps of deltas, valleys with remainders of unregulated river systems, inundat- ed areas and changes of river beds belong to this group. Engineers in particular use these maps, since hardly any plans for construction in rivers or lakes can be drawn without a concise geomorphological map. Hydrologists and civil engineers should be able to compile, or at least interpret, maps of this kind, detailing river beds and banks for use in streamflow studies, for studies on erosion and sedimentation and for construction purposes.
Streamflow maps deal with the distribution of streamflow in a river and flow of river water through a lake.
Chemical properties and water quality maps generally show chemical concentrations or alkalinity and acidity levels anly at the spot where the sample was taken, since it is almost impossible to extrapolate chemical properties in order to describe the situation between two distant measuring points.
chemical composition of the dissolved materials. The biological component generally is the most important factor which influences the quality of surface water and the possibilities of its use. The quality of water may be divided into five categories in decreasing order of water quality:
Lakes often have three-dimensional problems which in some cases
In spite of all this, map-
Geomorphological maps deal with the geomorphology of rivers and lakes. As far as rivers
The quality of water is not only a question of the solid matter in the water and the
oligo-saprobe zone (1) B-meso-saprobe zone (11) a-meso-saprobe zone (111) poly-saprobe zone (IV) excessive pollution zone (v). If sufficient data are available, sub-categories may be introduced. Maps on water quality
are based on observations made over a set period. Water quality maps show pollution, the in- fluence of polluted tributaries or of tributaries with relatively pure water. It is very instructive for students to see the influence of human activities (factories, cities with or without purification plants, recovery of river water, influence of water quantity, relation between pollution and population density, influence of new or overloaded purification plants). The ecologist and planner may see from these maps how far man has exhausted the natural water resources and, in collaboration with engineers, chemists and town and country planners, can discuss whether reserves are still available, whether these reserves can be used and whether measures are necessary to improve the situation.
Simple discharge maps. One type of such maps shows the average discharge along the river, the data being obtained over a long period. Maps are available for
mean discharge; mean high water discharge; mean low water discharge;
and occasionally for winter, summer, rainy or dry seasons. The thickness of the line tracing the river's path denotes the runoff. The maps show very clearly the development of a river, the influence of tributaries and of important factors such as evaporation, infiltration or retention. The hydrologist will note the difference between rivers in flat swampy areas with little seasonal variation in the discharge and mountain minimum and maximum discharge.
Classical examples of rivers losing water on their way are the Nile and the Niger.
rivers with a great variation between the
59
An important type of discharge map is ralated to the drained area. The water which has passed on observation station during a given period (e.g. one year) is converted into a theoret- ical layer of constant thickness over the whole drained area according to:
1 R = -CQ at A where Q = discharge; t = time; A = drained area; R = depth of the theoretical water layer;
This sort of map can be superimposed on and compared with precipitation maps. Whereas these maps are based on the idea of the discharge over a period of time (monthly or
yearly), another group of maps can show the discharge per unit of area and time. For this purpose the discharge is divided by the size of the area drained
where Q = discharge; A = catchment area; q = unit discharge, dimension generally 1s”m2
The value q is most advantageous since it permits direct comparisons with the production of other river systems.
Complex discharge maps. In principle, complex regime maps describe the situation with relation to as many hydrological phenomena as possible.
If maps of precipitation P and runoff R (related to the drained area) are available, it is easy to develop a map showing the percentage of the discharge of precipitation and to show the isolines of the value R
c1 = - 100 P This relation may be regarded as a runoff factor and should be studied by hydrologists in connection with a topographical map, a geological map and possibly with a map on soil and vegetation.
run dry,be covered with ice or be open for navigation. Maps of this type are generally called ‘simple regime maps’.
monthly discharge and the mean discharge. On the map the river is, therefore, accompanied by two bands. One of them represents the ratio of the lowest of the twelve mean monthly discharges and the mean annual discharge. The other band represents the corresponding ratio for the highest of the twelve mean monthly discharges.
pluvial, pluvionival, nivo-pluvial, nival (in mountains), glacial or influenced by underground karst layers. For more detailed studies, the reader is referred to Unesco/WMO, 1977.
have been omitted, the possibilities of presenting various hydrological phenomena in one map and of demonstrating their interrelation can be seen. The value of these maps for hydrology students stems from the potential of being able to show possible interaction of parameters and to introduce the student to various hydrological regimes.
A further description of the regime deals with the length of period in which a river may
Another type of complex regime map shows the relation between the minimum and maximum mean
These ratios and their relations represent the type of river discharge regime, e.g.
Although this list of complex maps is not complete and the more sophisticated possibilities
Snow and ice. Maps of snowfall have been mentioned already under Atmospheric Water. Maps of glaciers, however, deserve special mention here. One type of such maps deals with the balance of the glacier. Besides showing the contours of the underlying ground, the thickness of the glacier is indicated in isolines. Special signs show the reduction of ice masses in periods of melting as well as the amount of new ice formation from snow or water.
Papers in Hydrology’, Paris, Unesco, 1970, numbers 1 to 5, entitled: 1. Perennial ice and snow masses. 2. Seasonal snow cover. 3. Variations of existing glaciers. 4. Antarctic glaciology in the International Hydrological Decade. 5. Combined heat, ice and water balances at selected glacial basins.
Further information on the mapping of glaciers is available in the series ‘Technical
5.2.4.3 Groundwater Maps, Hydrogeological Maps
The International Hydrogeological Map of Europe. In collaboration with the International
60
Association of Hydrogeologists, the Commission for the Geological Map of the World (Sub- commission for Hydrogeological Maps) and Unesco,a set of maps at the scale 1 : 1,500,000 is being prepared and is partly available. The legend is based on: - groundwater in porous rocks (colour); - groundwater in jointed massive rocks (colour); - regions generally with no or only local groundwater (colour); - particular notes on groundwater and springs (signs); - particular notes on surface water (signs); - particular notes on artificial works (signs); - particular notes on geological outarops (signs).
map restricts its practical value; it is mainly intended for use in teaching and for demonstration purposes. The map is strongly recommended for hydrology courses since nearly all aspects of hydrogeological mapping can be demonstrated. A sample sheet (Annex 1) is to be found inside the back cover of this book. Maps for other regions of the world are in preparation.
This example has been chosen since this map is internationally available. The scale of the
Approaches for Making Hydrogeological Maps
Differences between hydrogeological maps consist of the different methods of presenting hydro- geological elements and, to a greater extent, the subject to be mapped and the scientific approach. Therefore, the legends and the presentation of data vary much more than in maps of surface water. Since technical possibilities for combining symbols on a map are limited and someeimes three-dimensional problems have to be shown, much information is given in the text of the legend or in small diagrams and cross-sections in the margin of the map. Five different approaches have been developed with the aim of introducing to hydrology students the complex relations existing between geological, lithological and hydraulic features connected with the occurrence of groundwater.
Geological approach. The geological approach can be considered as the first phase of development of hydrogeological mapping. A coloured background represents the distribution and the litho- logical composition of the geological formations, mostly in full analogy to a geological map or even by using it. A text may indicate the properties and the availability of groundwater and may also show the stratum in which it appears, as well as the conditions of recharge. Isolines may represent the relief of the piezometric surface and the thickness of the zone of aeration.
Since groundwater and the geological conditions are always very closely related, the geological approach is of much importance and should be given high priority by hydrology teachers. The student hydrologist should be acquainted with the geological aspects of ground- water hydrology. Maps of this type are an excellent tool to show these relations under practical conditions.
Hydraulic approach. In this group of maps, hydrophysical properties of the rocks and the underground formations are the principal subjects of mapping. The rocks are described according to the conditions of water accumulation in them (porous, fractured, anhydrous, complex formations or aquifers in the shape of a lens). The colour of the map still relates to the geological formations with a cartographic presentation of the lithological composition of the rocks by hatchings covering the coloured background.
This type of map classifies the rocks according to their permeability. The degree of permeability does not necessarily correspond to the genesis, composition and age of strata or geological formation. The dynamics of the aquifer are indicated by a system of hydro-isohypses.
Resources approach. In this type of map areas of distribution of 'useful waters' are outlined by contours. Regions with aquifers which are being exploited or are expected to be exploited are shown. The conditions of groundwater occurrence, their dynamics, the quality and quantity of water are not generally represented.
Hydrogeological approach. This group of maps is based on the selection of aquifers of complexes in their geological relation, taking into account the formation and lithological composition of the rocks, the interrelation between water-resistant and water-bearing rocks, their thickness and permeability and their hydrodynamic characteristics.
One section of the legend is devoted to aspects of the hydraulic approach including aspects of porosity etc. Other sections of the legend deal with the description of the groundwater, its dynamics, quantity, quality and temperature. These data have a cartographic reflection in the form of isolines, etc.
Modern hydrogeological maps are quite universal and give an understanding of hydrogeological
61
conditions and of the interrelations between groundwater and geology, geomorphology and the mechanics of the water moving under the ground. least contain information on - surface elevation; - -
A large-scale hydrogeological map should at
distance of the aquifer from the surface or contour lines of the surface of the aquifer; indication of the transmissivity of the aquifers or of the productivity or possible yield; and, if possible
Generally, only the main aquifer will be mapped. Where several aquifers exist, the other However, this method of presentation is often
Groundwater is an essential element of the occurrence of water in the hydrological cycle.
- the quality of the groundwater.
aquifers can be indicated in different colours. confusing and the use of transparent overlying sheets, one for each aquifer, is recommended.
The complex maps which have been discussed above are a means of identifying areas of deficit or surplus in groundwater formation and they should be compared with geological maps in order to control the precision of the surface water maps (discharge, etc.). In particular, they may also be used to adjust the computation of the actual evaporation.
A special feature of groundwater maps is hydrochemistry, and information on the availabil- ity of groundwater is often sup lemegied by2$solines on different aspects of the water quality, particularly the contents of Na , Ca + Mg , Cl-, SO4 , Fe, Mn, hardness, etc. Special maps on salinity, salt water intrusion, brines, hot springs for medical waters, etc., should also be mentioned.
A rather new field of hydrogeological mapping is of interest in areas where industrial and household waste is deposited. These areas require an impermeable underground layer for the prevention of infiltration into neighbouring water-bearing layers. These maps are developed from geological maps and soil maps in connection with maps showing the permanent use of groundwater as well as future plans for the use of the water resources and for urbanization.
? 2-
5.2.5 Records
To conclude discussion of the subject dealt withlin this chapter, the importance of records must also be mentioned briefly. Records form the basis of most hydrological maps, and are the source of data for nearly every element of the hydrological cycle. They exist on:
- meteorological phenomena: air pressure, wind direction and velocity, air temperature, air
- surface water measurements:water level, discharge, temperature, data on water quality,
- groundwater measurements: level, temperature, chemical composition.
With regard to the compilation of data, the following principles can be observed:
humidity, precipitation, sunshine duration and intensity;
ice conditions, physical data;
- records cover one year (in some countries, the 'water year' differs from the calendar year);
- records exist for a country as a whole or for a catchment area.
carefully the yearbook of their country and compare it with yearbooks of other countries. They should learn to read the records (abbreviations, ways in which the tables, charts and diagrams are composed, subject contents, references, competence of water boards, etc.). A hydrology student should be charged with interpreting the situation at a given data by sorting out all necessary data from the yearbook in order to describe the hydrological (and if available, the meteorological) circumstances. In doing this, the student will see that a conscientious compilation of data is absolutely necessary for any work in hydrology, and he will learn that data collection and processing is the indispensable basis of every hydrological service.
While yearbooks on surface water observatlon generally contain data by station and time, groundwater data are generally stored in special groundwater archives.
The yearbook is the source of data for a map, but it cannot replace a map nor can a map replace the records. The hydrologist will always base his work on the data contained in records and he will express his ideas in the map, maps being extremely adaptable for showing relations between data and their area of origin and the dynamics of the data. Maps re-animate a past situation, demonstrate impressively situations and developments, and open many possibilities of presenting and interpreting data even of different character, origin and subject. maps data are converted into a picture which facilitates the understanding of events and situations.
exceptionally they cover shorter or longer periods;
Yearbooks exist for almost all countries. Hydrology students should, therefore, study very
Through
62
5.3 Hydrological Mapping and Interpretation from Aerial Photographs
Any kind of aerial photograph might be practicable for teaching purposes but vertical photographs varying in scales between 1 : 15,000 and 1 : 50,000 are to be preferred. Large-scale photographs may provide extra detail but a less general view; they are more time consuming to elaborate and the number of photographs to cover a certain area is large. On the other hand, small-scale photographs may be deficient in showing recognisable details.
Infra-red pictures may be useful for hydrological purposes as they clearly mark the differences between wet and dry soils. The use of colour or false-colour photographs for both teaching hydrology and in practice depends on the objectives of the studies and the area itself.
identify different hydrological conditions. These photographs, accompanied by some explanatory notes, should be interpreted on a sketch-map of the area, drawn on a transparent sheet covering the photograph. The student should mark the relevant features, distinguish and delineate the units in which the area has to be divided and draw hydrogeological conclusions resulting from them.
Normal black-and-white photographs (panchromatic-minus-blue) are the most commonly used.
Stereo pairs of photographs for a variety of landscapes can be examined by the student to
5.3.1 Interpretation
Since hydrological processes as such cannot be interpreted from the imagery, the emphasis is on the analysis and mapping of the physical terrain attributes which influence hydrological process- es. The attributes are seen in a unique way in the stereomodels created by two overlapping photographs, and their mutual relationships can be studied. The interrelationships between physical terrain factors on the one hand and their influence on the hydrological processes on the other, is reflected in the methodology of interpretation and outlined below. Proficiency at this interpretation develops only with practice. Short field trips are strongly recommended to visualise at first hand these features of terrain interpreted from photographs and to check the nature of rock types, soils, groundwater tables, and so on.
In the vast range of terrain attributes, ranging from geological to vegetational factors, and the varied nature of hydrological themes, there is an obvious need to structure the inter- pretation exercise. The structuring could be done by:
- Providing background hydrological data, such as graphs showing rainfall and evaporation on a monthly basis, rainfall intensity data, regional effective precipitation and tables relating lithology with permeability, specific yield. In this way, each exercise is viewed against the main hydrological setting.
- Discussion of the hydrological theme(s) of intesest to be analysed, for example: ranking of small catchments according to their relative peak runoff, relative sediment production, site location of small reservoirs, location and recharge of shallow aquifers or possible deeper aquifers, factors to be used in estimates of the water budget and so on. A list of suitable questions is of great assistance.
- Adherence to a strict sequence of thematic interpretations (see below).
- Evaluation of the results (see below).
Each terrain, shown in a stereomodel, is composed of geological, geomorphological, soil and vegetal attributes.
The Draina qe Net work
The image interpretation should start with the main frame of the terrain, the geology (surface geology and subsurface extrapolations) and gradually work upward to the geomorphology, physio- graphy and related soils, finishing with the vegetation and land use.
the nature of the area and the hydrologic theme.
description can be made. Where necessary, published information or local field knowledge should be consulted.
drainage tracing will focus attention on the hydrological characteristics.
Not all steps in the sequence may have equal weight as this depends on the interpretability,
However, the sequence should be adhered to strictly, even if not much more than a sketchy
A simple tracing of the drainage network provides an introduction to the area;
Flood limits and areas with inundation in relative terms of duration and frequency may be
a thematic
63
related to a detailed interpretation of the flood plain geomorphology. listed aspects may require in-depth interpretations and data on groundwater levels. There- fore the thematic drainage mapping may be finalised at a later stage. useful exercise in itself is to ask the students to list the unknown factors required to complete the analysis and interpretation.
Several of the
It may be noted that a
Geol o yical Interpretation
Proper photo-geological results can only be expected from experienced field geologists. However, the interpretation of stereomodels is an excellent way of teaching geology to the inexperienced. The geological interpretation should attempt to define the lithology and structure The order of magnitude of the quantities of water in the located aquifers may be assessed in an approximate way with the aid of the regional hydrological data and empirical tables. preparation to the interpretation of geomorphology and soils, questions on the non-baseflow component and the recharge of aquifers may be posed.
Geomorphological Interpretation
As a
The geomorphological classification should incorporate the lithological and geological inform- ation, as well as describe associations of internal relief, slope steepness and degree of dis- section. Just two hierarchical levels are sufficient for most hydrological interpretations, a broad genetical grouping indicative of the lithology and a physiographic sub-differentiation, adjusted to requirements and nature of the terrain studied.
agriculture and natural vegetation, whereas the soils succession may be placed in the physio- graphical framework.
Soils
The resulting mapping units usually coincide with broad land use classes in traditional
Soil taxonomy and physical soil factors cannot be interpreted from imagery. A detailed analysis of the terrain on stereomodels, as an aid in a soil survey, is a specialist task. The soil aspects in hydrological interpretation have to be assessed in an indirect way, by relating the soil successions and associations to the physiographical factors.
hydrological survey are: Examples which can be identified and singled out as separate mapping units in a photo-
- areas with salt efflorescence (the high reflectivity is well visible on black and white (BW) , infra-red (IRC) and on LANDSAT (all bands)) ,
- wetlands, which have usually high depression and detention storage, and which may indicate seasonal groundwater emergence zones.
- areas with crusts, which impede infiltration.
Veyetation
In the last stage of the interpretation sequence the attention concentrates on the vegetation and land use.
Broad classes of vegetation and traditional land use tend to be associated with the physio- graphic units, and their patterns may have been used for the delineation of those units already.
When no such coincidence is apparent, a separate mapping may be necessary. Here again, the students should be instructed that the mapping effort, and thus the legend, should tally with the hydrological data available.
pretation may be directed to identify and make an inventory of the acreage under the various types of crops. The recognition of individual crop types depends on the scale of the photo- graphs, when they were taken and the type of film.
LANDSAT finds its most general application in water resources studies in the domain of vegetation and land use inventory, particularly if the satellite images are used in conjunction and not in competition with aerial photography. TCJ teach the potentialities of LANDSAT, a sequential set of images at characteristic moments in the cropping calendar should be available. The strong seasonal effects of broad-leafed vegetation are adequately recorded as well as the response of vegetation to rainfall or irrigation in the drier parts of the world.
If reliable crop water use coefficients are available for the area of interest, the inter-
64
Special interpretations of vegetation patterns could be of interest when a direct link with groundwater exists, such as: - density and extent of phreatophytes along streams; - alignment of tall trees, bushes along inferred faults, fractures, outcrops with seepage,
clusters of dense vegetation around springs.
5.3.2 Evaluation of Results
Photo-hydrological interpretation is not an end in itself, but a means of assisting hydrological work. The students will gain much experience when some of the exercises are treated as case histories, however simple they may be. Exercises dealing with more complex terrain could be restricted to the following aspects: - interpretationof results which are fairly straightforward and need little fieldwork or
other information (acreages with broad land use classes, outcrop areas of hard rock, certain geomorpholoqical units, etc.).
- delineation of units where field investigations are required to determine their lithology, soils, depth, as well as an assessment of their hydrologic behaviour.
- determination of hydrological data required to answer the hydrological questions posed, but whlch cannot be solved by the use of imagery. Attention can also be devoted to some of the more specialised applications of remote
sensing data. For example: - Thermal Infrared (TIR) for studies of thermal pollution in water bodies, or thermal
- Use of False Colour (FC), Infrared Colour (IRC), LANDSAT in studies of wetlands, tidal
- Use of LANDSAT in analysing patterns of relative concentrations of suspended sediment. - Use of LANDSAT in monitoring vegetation and land use. - Digital image processing and computer assisted classification techniques and their
anomalies caused by groundwater effusion into the sea.
areas.
applications.
5.3.3 Materials
In order to teach hydrology students the basic principles of aerial photography and its interpretation the following material is needed: - an ample collection oE photographs and maps related to a variety of hydrological
conditions. The photographs should reflect different film/filter combinations and LANDSAT images;
- tracing paper (Kodatrace or other transparent film: - compasses for fiducial marking- - transparent rulers; - working tables; - pocket stereoscopes for field use; - mirror stereoscope with magnifiers; - parallax bars.
exercise. It should be noted that a good illumination of the exercise room is required.
Geological aspects: Mekel, 1970; Miller & Miller, 1961 Geomorphology, Physiography, Soils: Verstappen, 1977; Way, 1973 Vegetation: Howard, 1970 Hydrology: Meijerink, 1974; Nefedo 8, Popova, 1969; Thomson et a1.,1973; General : Fraysse, 1980; Lillesand & Keifer, 1979; Schanda, 1976.
One set of each of the above-mentioned material is required for each student doing the
Suitable references are as follows:
65
VI. Auxiliary aids and educational technology
6.1 Textbooks
For most effective teaching and learning it is important that full information be at hand on available textbooks and reference books dealing with topics in hydrology. A monograph on textbooks in hydrology prepared during the International Hydrological Decade (THD) includes information on a limited number of textbooks in hydrology available in various languages (Unesco, 1970, 1974). It contains information such as chapter headings and sub-headings, the number of pages, figures, tables, references cited for each chapter and a general comment on the book. A tabular comparison gives the amount of space devoted by each book to various topics. Such information was prepared for books classified as general hydrology, groundwater hydrology or hydrometry. These monographs shculd be helpful to teachers of hydrol- ogy in locating books with which they might not otherwise be familiar. Now the Unesco periodical 'Nature and Resources' contains such descriptions of newly publish& textbooks.
6.2 Visual Aids
Among the visual aids, slides and overhead transparencies play a predominant role. In view of the numerous individual collections at universities and other training institutions, it is difficult to assess their value hut they undoubtedly constitute first-class teaching aids.
pictures; showing physical phenomena to the student which he ordinarily would not have an opportunity to see and appreciate. Motion pictures showing the wide variations in streamflow certainly give the student a better appreciation for the extremes that occur. Film loops of cloud formation and types of storms also are useful.
appreciation for the field problems he will encounter; films on fluvial channels can show the student the importance of bed fcrms and their interaction with sediment and streamflow.
during a short period or where fast processes can he extended to permit comprehension by the students.
to the showing of films. Films of about half-hour length are frequently shown at universities at times other than the regular class period; they can be scheduled in advance and students requested to attend the showings as a non-classroom activity.
limited, though films dealing with water quality aspects, specific water resource development projects, or hydraulic engineering are often available.
There are a number of aspects of hydrology which lend themselves to presentation in motion
Films of actual precipitation and streamflow measurements give the student a realistic
Films are particularly valuable where either slow hydrological processes can be shown
Experience has shown that many instructors are reluctant to give an entire classroom period
The number of motion pictures dealing specifically with hydrological subjects is quite
6.3 Audio-Visual Aids
6.3.1 Video Equipment
The use of video equipment in hydrology teaching is likely to increase. fundamentally different to cinematography; electronically.
transmission, storage and reproduction of pictures and sound.
The video technique is the pictures are produced, stored and transmitted
Figure 6.1 is a sketch of the principal structure of a video system including recording, The video technique has the
67
microphone \
vi deo camera videorecorder television set
record storage reproduction
Fig. 6.1 - A simple video system.
following advantages over other techniques: - The synchronisation of picture and sound remains even after revision or editing of the
- recording. There is no delay between making a video recording and examining the result: recorded can be immediately reproduced to check the lighting, the camera angles, the logical transition of one scene to another, etc.
- The pictures can be transmitted over cable or radio. The principal elements of the video system shown in Figure 6.1 are
what is
Video recorder
For storage of video or televisicn picture signals, a video recorder is used. this is quite similar to the tape recorder. replay and the facility to re-use the tape to record different phenomena.
In principle The magnetic tape storage medium allows unlimited
Video cameia
Video cameras and/or television cameras are used for recording. film cameras, but (at present) are much heavier. Hand cameras are lighter and are connected to portable video recorders.
They are outwardly similar to
Television set
For control and transmission of the recording most commercial-size televisions can be used. set is connected to the video recorder through the antenna-input connection.
The
Microphone
Sound may be recorded at the same time as the picture or added at a later date.
6.3.2 Video Techniques in the Teaching Process
The video technique offers the teaching process a series of new and following, a few typical possibilities for the application of video process are indicated.
a. Recording of television transmissions and reproduction in teac-.
unique features. In the techniques in the teaching
ing
All suitable video cassette recorders have the advantage that they are easy to operate and their operating elements are exceptionally similar to the well-known tape cassette recorders.
68
The advantages of video recording are: - The reproduction of the TV transmission can take place at the most favourable time. - Single segments can be used for several purposes. - The application of the video technique can be planned in advance. - The teacher can familiarise himself with the recording prior to transmission to the
- The operation of the video recorder is simpler than a film projector.
b. Video transmission in the classroom
students.
'A live video transmission' can be made by connecting a video camera directly to a TV set. This technique can be useful in showing an entire class some small detail of apparatus.
c. Making recordings in the class, laboratory or during fieldwork
Portable video cameras and microphones enable the teacher to make his own video films. This allows several possibilities for teaching, which were hitherto unrealisable. Recordings of particular lessons or demonstrations are available for student revision purposes or for the teacher to examine and improve his teaching technique.
tory or experiment or fieldwork, particularly where a live demonstration is time-consuming, difficult to set up, in a remote or awkward location, or only possible at inconvenient times. For example, a class visit to a discharge measuring station at times of flood would be valuable but inconvenient to all concerned. Recordings could also be made of pumping tests, dilution gauging and so on, allowing detailed pictures to be projected to a great number of students in a relatively short time. This permits the more intensive use of the actual teaching time and particular phases of the work can be shown any number of times if they have been stored on video tape. Barely visible details can be enlarged by the video camera. Moreover, some video recorders permit a slowed-down projection of a rapid sequence of events and a speed-up of a slow sequence of events; this is useful, for instance, in showing ground- water flow.
Video equipment is still expensive, but will become less so in relative terms. An extensive range of equipment is available for purchase or hire, and care must be exercised in selecting suitable and compatible, though not necessarily the most expensive, equipment for teaching purposes. Even so the costs of video equipment and tapes can be offset against costs in time and travel and shared with other departments. Although an actual experiement may be regarded as better than a recording of it, one must consider that, throqgh the video technique a greater number of experiments can be made available for discussion at the same time. In the most favourable case, the video technique will not replace the direct performance of laboratory and field experiments, but will complement them in valuable ways.
Video equipment can be used to great advantage for demonstrating certain types of labora-
6.4 Computers
6.4.1 Computational Facilities
Computers can be divided into three broad categories: - pocket calculators - microcomputers/minicomputers - mainframe computers
Pocket calculators
These are single-user, hand-held calculating devices which perform sequences of arithmetic calculations (including trigonometrical and exponential functions) and store intermediate and final values. The more advanced types can store (either internally or in external memory) sequences of instructions for repetitive calculations.
Microcomputers/minicomputers
These are desk-top computers, generally consisting of a keyboard, visual d printer, microprocessor and permanent storage devices (e.g. magnetic tape, disc, hard disc units etc.). They are operated using a system language to devices and manipulate and access program and data files. Programs can be
splay unit and/or cassette, floppy control the various written in high
69
level languages such as Fortran. Microprocessors are readily linked to sensing/measuring apparatus and so they find application not just as computing devices but for process monitoring and control.
standard business accounting software etc. Extensive proprietary software is usually available, for example graphics packages,
pocket-calculator
microcomputer mini-computer
Mainframe computers
hydrological calculations in the field, small statistical investigations substitute for slide-rule, mathematical and statistical tables
book-keeping in engineering bureaux, data-recording and data analysis for programming of small simulation models, can be connected to a large storage computer (on- and off-line) , process monitoring/control
Mainframe computers are usually large, very powerful machines, intended for several users (either in batch or interat.tive/time-sharing modes). They have large central core memory as well as auxiliary storage (magnetic tape etc.). The input and output devices can take a variety of forms, including plotters, visual display units, printers, punched card readers, paper tape readers etc. Control of mainframe computers is usually exercised by a complex operating system and supervised by computer specialists. The typical configuration of a mainframe computer is shown in Figure 6.2.
mainframe computer
n
~~~
large data recording and data analysis, for programming of most of the hydrological simulation, rainfall-prediction and flood-forecast models
I rat el I i te console computer I
CPU control I host computer) consoIe
I
I rat el I i te computer I
6-1 fJ & paper tape unch
Fig. 6.2 - Configuration of a main frame computer.
It is often rather difficult to decide to which class a
high speed printer
card reader card punch
active termiml
inter- active terminal
single machine belongs.
IClass of Computer I possible usage in hydrological research I
Table 6.1 : Classes of computers and their possible usage in hydroloqical research
70
The use of computer programs for the numerical solution of common hydrological problems has been publicised in the literature (e.g. Clarke, 1973; Bugliarello et all 1974). An extensive summary of available computer software, giving a general description of the program, its purpose, availability, hardware and data requirements, has been compiled (WMO, 1981); further details of the WMO publication and its contents are available from IHP National Committees.
Real objects
6.4.2 Computers as Teaching Aids
Printed texts (e.g textbooks)
In contrast to visual and audio-visual auxiliaries, which are only capable of one-way communication, computers are adaptive auxiliaries in the teaching process and involve two-way communication between the user and the machine. Computer assisted instruction has been used since 1960 in the USA and other countries. are stored in the computer together with programs which all-ow interaction between the students and the computer. By this means, the simulation of hydrological processes (e.g. watershed models, time-series generation) can be performed which could not be solved numerically in a conventional teaching situation (for examples see Chidley and Wood, 1981).
the hydrological problem under study. are determining factors for the type of computer.
table 6.2. The possibilities and advantages of the various media in presenting information are evident; in some cases, it appears that the repertoire of presentation of technical teaching aids is superior to that of the teacher. Some hydrologic phenomena (precipitation, infiltration, sediment transport, turbulences, etc.) can be visualised more effectively by means of motion pictures which can slow down or speed up the process. In giving directives for processing new information and reacting to student feedback, the efficiency of the technical media is lower than that of the teacher, but in comparison with other auxiliary teaching aids, the computer is a powerful aid in hydrology.
Programs for controlling the learning process
For small groups of students or for research purposes the type of computer may depend on Both the hydrological problem and the available data
The benefits of computers and other media as teaching aids are compared to the teacher in
Yes
limited
Media
limited
yes
present information
offer models of expected achievement
direct attention
off er teaching aids
offer transfer of knowledge
feed back information
no
limited
I
Yes
yes
I
Static Pictures (e.g slides)
Limited
10
Limited
Limited
Limited
3ynamic Pictures (e.g. films)
yes
limited
no
limited
limited
limited
~~
Teaching machines (e.g computers)
limited
Teache. (oral)
limitei
Yes
Yes
Yes
Yes
Yes
Table 6.2 : Comparison of didactic functions between different teaching aids and the teacher
71
References
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Becker, A., 1972. Applied principles of catchment simulation. Proc. Symp. I.A.S.H., Warsaw, Poland.
Bouver, H., 1967. Electric analogue groundwater model. Water Resources Res., Vol. 3.
Bugliarello, G.; Gunther, F.J., 1974. Computer systems and water resources development in water science. Elsevier Comp., Amsterdam.
Chidley, T.R.; Wood, S.R. , 1981. Electronic Data Processing Systems for Land and Water Data. Vol. 1, FAO, Rome.
Chow, V.T., 1964. Handbook of applied hydrology. McGraw Hill, New York.
Christie, I.F., 1971. Analogue computation. Lecture notes of the Int. courses in hydraulics, Delft.
Clarke, R.T., 1973. Mathematical models in hydrology. FAO Irrigation and Drainage Paper No.19, Rome.
Crawford, N.H.; Linsley, R.K., 1966. Digital simulation in hydrology, Stanford,, Watershed Model IV, TR 39, Stanford, Calif., USA.
CSVH, 1981. Proceedings of the International Workshop on Hydrological Education 1980, Smolenice, Czechoslovakia .
Dawdy, D.R.; Lichty, R.W.; Bergmann, J.M., 19'12. A rainfall-runoff simulation model for estimation of flood peaks from small drainage basins. US Geol. Survey, professional paper 50 6-B.
DFG, 1975. Theoretische Hydrologie. (Theoretical Hydrology). Heft 2. Boldt-Verlag, Boppard, FRG.
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Dooge, J.C.I., 1968. The hydrologic cycle as a closed system. Bull. Int. Ass. Scient. Hydrol., 13. (1).
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Fraysse, G. (ea.), 1980. Remote sensing applications in agriculture and hydrology (ISPRA). A.A. Balkema, Rotterdam.
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Hillel, D., 1977. Computer simulation of soil-water dynamics. IDRC, Ottawa, Canada.
Howard, J., 1970. Aerial photo-ecology. Faber and Faber.
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Lillesand, T.M.; Kiefer, R.W., 1979. Remote sensing and image interpretation. John Wiley and Sons.
Linsley, R.K.; Kohler, M.A.; Paulhus, J.L.M., 1969. Hydrology for engineers. McGraw Hill, New York.
Linsley, R.K.; Franzini, J.B., 1974. Water resources engineering, McGraw Hill, New York.
Marshall, T. J.; J.W. Holmes, 1976: Soil Physics. Cambridge bniversity Press, Cambridge, England.
Meijerink, A.M.J., 1974. Photo-hydrological reconnaissance surveys. ITC Enschede, The Netherlands.
Mekel, J.F.M., 1970 . The use of aerial photographs in geologic mapping. ITC Enschede, The Netherlands.
Miller, V.C.; Miller, C.F., 1961. Photogeology. McGraw Hill, New York.
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