irrigation engineering unit v

IRRIGATION ENGINEERING

5th Semester – III Year

Department of Civil Engineering

Lecture Slides by SARAVANAN.J B.E – Anna University

UNIT VIRRIGATION WATER MANAGEMENT

Need for optimization of water use – Minimizing irrigation water losses – On farm development works – Participatory irrigation management – Water users association – Changing paradigms in water management – Performance evaluation

INTRODUCTION

• Management of irrigation water gets special importance because, Irrigation alone needs about 75% of the total water requirement.

• The main objective of irrigation water management is to supply and apply the right amount of water at the right place and at the right time.

• The performance of any irrigation project is gauged by the following factors:– Area irrigated as proportion of the area planned to be irrigated.– Water logging– Tail end deprivation– yield

OPTIMUM USE OF WATER

• Optimum water requirement of a crop is the quality of water required during its growth period that results in maximum yield.

• The optimum quantity of water include water supplied by precipitation as well as water delivered by irrigation.

• The supply of water more than optimum requirement may not result in increase in yield of most crops but also decreases the quality of the product.

Need of irrigation water should be at optimum level because,

• If the supply of water to the crop is more (or) less than its optimum requirement, it will adversely affect the crop yield supply.

• Supply of less water will cause the plant to spend extra energy to get moisture from the soil, which would otherwise has been used in its growth.

• Supply of surplus water will expel the air from soil pores and will prevent free circulation of fresh air, which is essential for food preparation of the plant.

NEED FOR OPTIMUM USE OF WATER

• Depth of ground water table

• Slope of the ground

• Climatic conditions of that regions

• Intensity of irrigation

• Texture and structure of the soil

• Moisture storage capacity of the soil

• Type and quantity of manure applied

• System of irrigation used

FACTORS AFFECTING CROP WATER REQUIREMENT

• Water enters the main canal at the head works through the head regulator and flows through the distributors and the water courses & finally reaches the field.

• Throughout this journey, there is continuous water losses which have to be accounted for the design of channels.

• These losses are especially in unlined canals, the losses may be as high as one quarter to one half of water diverted.

• In North India, the water losses are usually found in practice are as follows:

(a) Losses in main canal & branches : 15 to 20%

(b) Losses in the major & minor distributaries : 6 to 8%

(c) Losses in the field channels : 20 to 22%

(d) Losses in the application of water : 25 to 27%

(e) Water actually utilized by crops as consumptive use : 28 to 29%

The main categories of irrigation losses are as follows:

IRRIGATION WATER LOSSES

Absorption Losses:• Absorption losses occurs because of absorption of water by soil

surface canal’s wetted perimeter.• Absorption losses are independent of the seepage head.• These losses depend upon the water head ‘h’ from water level of

the canal to the bottom of the saturated zone.

• And also dependent on the capillary head ‘hc’ at the boundary of the saturated zone.

• Generally, absorption depends upon the depth of the water and type of soil.


Percolation (or) Seepage Losses:• Percolation losses are usually much greater than absorption losses.

They may be as high as 3 times or more of the absorption losses.• Both absorption and percolation losses are initially high because

the water is utilized for filling the pores of the soil.

• With the passage of time, the losses decreases and an equilibrium is finally reached. Absorption & percolation losses depends on:

- Permeability of soil

- Depth of water

- Velocity of water

- Amount of silt

- Temperature of water

- Age of the channel


Evaporation Losses:• Evaporation losses mainly depends upon the water surface area

of canal, relative humidity, wind velocity, temperature & various factors.

• In hot & dry summer months, evaporation losses are high but they don’t exceed 10% of the total losses.

• Generally, evaporation losses is less than 1% of the total water entering the canal head.

• There are no suitable practical measures to reduce the evaporation losses from the canal.

• For design issue, no separate consideration is made.


Transpiration Losses: • Transpiration losses occur through the vegetation & weeds in the

canal.• Losses are usually a small percentage of the total losses in an un

lined channel.• These losses can considerably decreased by keeping the canal

banks free of vegetation.


• The main objective of an On Farm Development is to develop a proper water distribution system to obtain maximum crop production per unit of water from a unit of land in unit time.

• At farmer’s level, the major aspects of wasteful use of irrigation waters are:– Wastage arising due to practicing field to field irrigation in the absence

of field channels– Wastage due to escape of water to drains during transit from the outlet

to the field because of lack of supervision of flow of water in field channels

– Wastage due to surface run off of irrigation water because of lack of proper field leveling

– Wastage due to over irrigation

ON FARM DEVELOPEMENT

• The items of works pertaining to on farm water management are

termed as “ On farm development works”.

• The on farm development works comprise of following,

a) Field channels for conveyance of water

b) Control structures

c) Crossings

d) Surface drainage system

e) Farm roads

f) Field channel protection works and

g) Land forming (Smoothening / grading / leveling).

ON FARM DEVELOPMENT – INVOLVING STAGES

• Participatory Natural Resource Management is based on the concept of communities having very close relationship with resources provided by nature.

• Local communities have their own emotions and attachments with these resources.

• Such knowledge can be revealed through participatory interactions for learning & action.

• Provisions made in the National Water Policy of 1987 were as under:

“Efforts should be made to involve farmers progressively in various aspects of management of irrigation systems, particularly in water distribution and collection of water rates. Assistance of voluntary agencies should be enlisted in educating the farmers in efficient water-use and water management.”

PARTICIPATORY IRRIGATION MANAGEMENT

• To promote and secure equitable distribution of water among its users, adequate maintenance of irrigation system, efficient and economical utilization of water to optimize agricultural production.

• To protect the environment and to ensure ecological balance inculcating sense of ownership of the irrigation system in accordance with the water budget and the operational plan.

• To Bridge the gap between potential created and potential utilized.

• For Prompt attention to problems and resolutions of disputes.• For Collective involvement in better application &

management of agricultural extension services.

OBJECTIVES OF PIM

Optimal Ignorance:• The principle of optimal ignorance is to minimize cost & time.

It is applied by investigation to know what is worth to know.• The matter not desirable, should be ignored to the possible

extent to avoid confusion.

Seeking Diversity:• PIM is to look for different analysis through diverse events.• Various processes and deliberating relationships in local

communities explore the facts in local situation.

PRINCIPLES OF PIM

• The participatory approach is an informal way of learning from local people about the problems, & opportunities in the given area.

• PIM is both an attitude & methodology which produces authentic information of the village.

PIM requires for:

- Sustained change & the need for accurate & timely information

- Advocating that people themselves are ‘solution agents’ for their need & problems

- Reducing ‘normal professional bias’ & ‘anti-poverty bias’ towards people

- Cutting down time consuming long methods of surveying

NEED FOR PIM

• Lack of legal back up and policy changes

• System deficiency

• Uncertainty of water availability

• Fear of financial viability

• Lack of technical knowledge

• Lack of leadership

• Lack of publicity and training

• WUAs v/s Panchayats

Constraints in Implementation of PIM

• A Water User Association (WUA) is a co-operative association of individual water users who wish to undertake water-related activities for their mutual benefit.

• The specific nature of the service that a WUA provides will differ from case to case, as the name suggests, a water user association is an institution that serves its members.

• Because member needs will differ from one area to another.

WATER USERS ASSOCIATION

• A number of issues are important in considering the differences between various tiers of water management, namely:

1.The function that the institution has been established to perform. Four key functions of water institutions can be identified, namely:

• Operational functions, related to the management of a service;

•Bulk supply functions, related to the management of a bulk water supply system

•Resource management functions, related to the management of the resource;

•Representation functions, related to the representation of stakeholder needs at higher institutions of water management

2. The functions mentioned above each require a certain nature and frequency of the communication between members or sub-aggregate units.

3. The commonality of vision and purpose amongst members or sub-aggregate units

Functions of WUAs

WATER USER ASSOCIATION

Establishment of Water User Associations

• Information sharing and awareness raising • The facilitation of a community visioning process• Financial and technical support • Model constitution of WUAs

Advantages of Water Users Association:• Better maintenance of the distributary leading to better water

availability• Possibility of getting irrigation frequency suitable for crops, soil

& crop water requirements• Better access to information about water availability & other

irrigation policies

• From the point of view of performance, the management of the canal irrigation systems in India is far from satisfactory. The major deficiencies are:– In sufficient planning & preparation at the stage of execution of the

project which results in longer construction time– Involvement of more than one ministry (or) poor coordination– Non-responsive (or) poor administration– Lack of interactions between engineering and agricultural experts– Lag between creation of potential and its utilization– Higher conveyance losses– Poor On-farm management– Lack of communication facilities in command area– Absence of conjuctive use of ground water and surface water

CHANGING PARADIGMS OF IRRIGATION MANAGEMENT IN INDIA

Various methods available to improve the canal irrigation system are:• Cropping patterns• Conjuctive use• Channel capacity• Canal lining• Canal regulators and Escapes• Water logging• Water delivery system• Soil reclamation• Farmer’s participation

METHODS OF IMPROVING CANAL IRRIGATION MANAGEMENT

Cropping Patterns:

- Cropping pattern is described in terms of the area under various crops at different periods of a year

- An optimum cropping patterns for an area can ideally be determined by using System Analysis

Conjuctive Use:

- Conjuctive use means that water lifted from below the ground is used in conjuction with canal water.

- It results in the coordinated, combined, and creative exploitation of ground water & surface water so as to minimise the dislocation of water.


Channel Capacity:

- The discharge capacity of the channel should be decided on the concept of evapo-transpiration rather than kor period.

Canal Lining:

- Lining of canals is a mean to reduce the seepage losses from canals.

- So, the lining of field channel is the most beneficial.

- In order to prevent damage to lining, the slope of lined channel is reduced.

- This reduce the sediment carrying capacity of an existing channel which is being lined.


Canal Regulators & Escapes:

- For ensuring proper distribution of irrigation water according to the adopted management policy, a suitable number of regulators & escapes must be provided on the canal network.

- Canal escapes are needed for the safety as well as for regulating canal supplies in areas which have received excess rainfall.

Water Logging:

- To eliminate the water logging, one or more of the following is usually been used.

(i) Reducing inflow through lining of canals

(ii) Removing ground water through pumping

(iii) Removing surface & ground water through drainage

(iv) Educating farmers in water management

(v) Conjuctive Use


• The most common criteria generally accepted for judging the performance of an irrigation system are:

- Productivity

- Equity

- Stability

Productivity:

- Its defined as the ratio of output & input.

- Output can be: Area irrigated, Yield or Income

- Input can be: Water in the root zone, Water at farm gate, including the points of diverting and storage.

- Improved water supply influences the adoption of high yielding agricultural practices by farmers which justified the productivity criterion of performance

PERFORMANCE EVALUATION

Equity:

- Equity in canal irrigation systems implies equality, fairness and even-handed dealing in matters of allocation and appropriation of irrigation water.

- Equity can be achieved by several methods in the supplying to different farmers.

- In the method of Prior Appropriation, whoever first exploits in resource establishes a right to continue to do so. Thus less water or no water to tail end farmers or late comers.

- In the second method of Proportionate Equality, the supply of water is in proportion to the size of the land holding.

- Attempts to improve equity are usually limited to achieving the supply of water in proportion to the size of the land.


Stability:

- Stability of productivity or equity are important. Stability can be either short term stability & long term stability.

- The short term (or) inter-seasonal stability refers to the variations in productivity and equity between irrigation seasons.

- It depends on climate, water supply, storage and control, system management. It can be measured by comparing the performance between seasons.

- Long term sustainability refers to the prevention (or) minimizing of adverse physical changes such as water logging, leaching of nutrients, salinity, erosion.

- It can be measured by monitoring the ground water levels, salinity through inspection works.


irrigation engineering unit v

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