standardization and development of civil design framework...

P. Khatri, S.S Khadka, U.Bhattarai & R. Prajapati: Standardization and Development of Civil Design Framework for Small…

Rentech Symposium Compendium, Volume 4, September 2014 66

Standardization and Development of Civil Design

Framework for Small Hydropower Project in Nepal Pawan Khatri*, Shyam Sundar Khadka, Utsav Bhattarai and Rashmila Prajapati

Department of Civil and Geomatics Engineering,SoE, KU and Cross Momentum Engineers Pvt. Ltd.,

Abstract - The presence of perennial rivers originating from the

Himalayas and a steep topography providesan ideal condition for the

generation of hydroelectricity in Nepal. However, due to many socio-

political, technical and financial reasons, hydropower development in

Nepal has been very slow. Design of civil structures is the most

important phase of hydropower development as they are expensive and

the entire project depends their proper functioning throughout the

project life.

In Nepal, there are many guidelines and standards for the design

of civil works of micro/mini/small hydro power projects. These

guidelines are prepared by different organizations and the design

methods, parameters and procedures explained in them vary; as a result

conflicts arise between designers. Hence, a research was carried out

with the main objective of developing a framework for the design

procedures of civil works of mini/micro/small hydropower projects and

standardization of the design procedure. This paper is part of the major

outcome of that research.

All national and international guidelines/codes of

practice/manuals/detail design reports used in Nepal have been

reviewed and analyzed extensively. Based on these documents, the

design framework has been developed and the procedures

standardized. The proposed design procedures have been validated and

verified by case studies.

Index Terms-Small hydropower project, civil work components,

design framework, standardization

I. INTRODUCTION

The first hydropower plant (HPP) constructed and

operated in Nepal was at Pharping with an installed capacity of

500KW in 1911, 29 years after the establishment of the world's

first hydel station in Wisconsin, USA and one year before the

Chinese [2]. Nepal has a technical hydropower potential of

40,000MW [15]. With such early start in hydropower

development, now more than a century later, Nepal has a total

installed capacity of 708MW while the demand reported in

2012 was 1094MW [2]. Despite having a century long history

of electricity generation, half of the Nepalese population is

deprived of electricity and the other half is facing long hours of

power cuts.

Depending upon the installed capacity, HPPs are classified

into pico, micro, mini, small, large and mega projects. The large

to mega scale HPPs are mainly storage type and grid connected

which supply energy to a large population of consumers. The

micro and small HPPs are mainly run-off-river type (grid

connected or isolated) and supply electricity to meet the local

energy demands. The micro, mini and small HPPs have proven

to be very effective and worthy because of their simple design,

* Corresponding author: [email protected]

low cost and short construction period. These could be the

reasons that in fiscal year 2012/13 nine HPPs were

commissioned in Nepal and all of them had installed capacities

below 10 MW [2].

Hydropower projects that have an installed capacity less

than 10MW are called small HPPs. A small HPP contains basic

components: intake structure, diversion weir, diversion canal or

pipe, gravel trap, settling basin, forebay, tunnel, penstock,

powerhouse and tailrace. In general, intake structures are built

to divert the required design discharge while diversion work

ensures it by maintaining the full supply level of water upstream

of intake. Canals, pipes and tunnels are water conveyance

structures diverting the water from intake to

forebay/powerhouse. Gravel trap and settling basin settles and

removes sediment and flushesit back to the river. Forebay

ensures the submergence and retention of water for the pressure

flow at penstock. At the powerhouse, electricity is generated by

interaction of turbine and generator before flowing into the river

downstream through the tailrace.

Figure 1: General civil works components of small hydropower

project.

Proper design of each hydropower component is very important

at all stages of its life starting from its construction to operation

and maintenance. The most important design parameter of civil

components of any HPP is design discharge. Other parameters

that play vital roles in design process are velocity, sediment

properties, slope and temperature, among others. In Nepal, there

are a number of design guidelines and codes in use, however,

lack of consistency among them is largely felt. Therefore, this

research was carried out with an objective of developing a very

clear and pragmatic design framework for civil works in HPPs.

The standardization of the civil components is done as the



function of the different design typical ready to use design

charts.

Figure 2: Standardization of civil work components of small

hydro power project.

II. METHODS

Although the bigger scope of this research had two parts

– the first one for micro and mini HPP (upto 1 MW) and the

second for small HPP (from 1 to 10 MW), this paper is

intended only for small HPPs. The methodology includes

literature review, case studies, field verification and analysis

of primary and secondary data.

A. Literature review and documentation

Available national and international level guidelines,

design aids, manuals, codes of practice, published design

reports, academic theses, and journal articles in use in Nepal

were compiled. They were thoroughly analyzed and the

design procedures were checked using different principles of

hydraulics. Any gaps and flaws prevalent in them were also

noted. These documents formed the foundation for

development of design framework based upon which the

design procedures were standardized.

B. Field visit, data collection and analysis

The existing design procedures and their implications in

theHPPs were assessed by a series of field visits from which

primary and secondary data were collected and analyzed. The

field visits were made to already constructedHPP sites below

10MW. The main aim of the field visitswas to check whether

the current design procedures and construction methodswere

successful in producing the hydro energy with high efficiency.

In order to achieve that, hydrological analysis, field study of

hydraulic structures and questionnaire survey were conducted.

The data collected for the civil structures were analyzed and

compared with the design requirements.

C. Problem identification and analysis

One of the objectives of this research was to compile all

available information in Nepal on design of civil structures for

HPPs and develop a database including all these information.

Analysis of the documents for civil works in hydropower

development in Nepal led to the identification of the existing

gaps in design procedures. These gaps were then addressed

using advanced methods and modifications were suggested on

the existing methods. Finally a comprehensive design

framework was developed choosing the most suitable and

applicable design procedures. Regular consultation with

experts was a very important activity during the research.

III. RESULTS AND DISCUSSION

Standardization of the HPP civil components was done

on the basis of the design framework.

A. Design framework

The design framework developed as a major outcome of

this research includes all the steps for the design of the HPPs

civil structures. The civil structures focused are of run-off-

river type small HPPs. The developed design framework has

clearly explained the design requirements, data required,

design parameters, design principles and equations. Five

sample flowcharts from the design framework for the design

of headworks, canal, gravel trap, settling basin and forebay

have been respectively presented in Figures 3 to 6.

Design

discharge

Continuity equation

Design

velocity

Flow area

Design coarse

trashrack

Calculation of

headloss at intake

and trashrack

Determination of

weir height

(if required)

Analysis of

discharge through

orifice:

-at normal flow

-at flood flow

Design of intake

canal

Figure 3: Flow chart for the design of headwork



Figure 4: Flow chart for the design of canal

Figure 5: Flow chart for the design of gravel trap/settling

basin

Design

discharge

Fix design

parameter

-Retention time, T

-Penstock Diameter

-Sill height

-Freeboard

Calculate

-Volume

required

Calculate

Submergence

required

Calculate:

-Surface area

Calculate depth

required

Check for

submergence

Dimension:

-Trial Width

-Calculate Length

Design

-spillway

-Fine trashrack

Figure 6: Flow chart for the design of forebay

Note: In case of gravel trap, generally the sediment storage criteria

is not considered since it is generally continuous flushing type.

Hence “Design of sediment storage step is generally excluded in

figure 5 for gravel trap.

B. Standardization chart

Standardization of the civil design procedures for HPPs

has been done by developing standard charts considering

different combination of the discharge and design parameters.

For small HPPs, the discharge variation is done upto 5 m3/s. It

is assumed that this limit of the discharge shall cover all types

of run-off-river type small HPPs in Nepal. These charts are

believed to be extremely helpful as a ready reference material

that directly provides the dimensions of the civil structures.

The basic principles, equations and constants used in

generating these charts have been selected as per the

developed design framework. Some typical sample charts

with their brief description are presented below.

Side Intake: Side intake is standardized as the function of

discharge and different combinations of design velocity,

number of orifice and width to depth ratio of orifice. The

design velocity is taken so as to minimize the headloss at

intake. The design velocity is varied from 0.8m/s to 1.5 m/s

while the width to depth ratio is kept constant 2 so as to obtain

P. Khatri, S.S Khadka, U.Bhattarai & R. Prajapati

Rentech Symposium Compendium, Volume 4, September 2014

maximum efficiency. Figure 7 & 8below show some of such

possible combinations.

Figure 7: Standardization chart of side intake with design

from orifice 1m/s, number of orifice is 1 and width to

2.

Figure 8: Standardization chart of side intake with design velocity

from orifice 1.2 m/s, number of orifice is 3 and width to

is 2.

Diversion canal: The diversion canal is standardized as the

function of discharge and different combinations of

longitudinal slope. The longitudinal slope is varied from 1 in

500 to 1in 1500. The ratio of width to depth is fixed at 2 so as

to obtain maximum efficiency (Figures 9 and 10).

Figure 9: Standardization chart on diversion canal with longitudinal

slope of 1/500; lining of cement mortar 1:3 and of rectangular shape

P. Khatri, S.S Khadka, U.Bhattarai & R. Prajapati: Standardization and Development of Civil Design Framework for S


maximum efficiency. Figure 7 & 8below show some of such

Standardization chart of side intake with design velocity

from orifice 1m/s, number of orifice is 1 and width to depth ratio is

Standardization chart of side intake with design velocity

from orifice 1.2 m/s, number of orifice is 3 and width to depth ratio

The diversion canal is standardized as the

function of discharge and different combinations of

longitudinal slope. The longitudinal slope is varied from 1 in

500 to 1in 1500. The ratio of width to depth is fixed at 2 so as

m efficiency (Figures 9 and 10).

Standardization chart on diversion canal with longitudinal

slope of 1/500; lining of cement mortar 1:3 and of rectangular shape

Figure 10: Standardization chart on diversion canal with

longitudinal slope of 1/1000; lining of cement mortar 1:3 and of

rectangular shape

Gravel trap and Settling basin

basin are standardized as the function of the design discharge

and the combination of design particle size, water temperature

and width of the basin. The design particle size for the gravel

traps taken are 1mm, 2mm, 3mm and 4mm while that for

settling basin is 0.1mm, 0.2mm, 0.3mm and 0.4mm. The

water temperature is fixed at 15

fall velocity. The basin width is varies from 1m to 4m for

gravel trap while that for settling basin is from 1m to 12m.

Figures 11, 12, 13 and 14 show some of the standardization

chart for the gravel trap and settli

that Figure 13 is suitable for the settling basin with higher

discharge and Figure 14 for lower value of discharge.

Figure 11: Standardization chart on gravel trap with

size of 2mm, water temperature 15

Standardization and Development of Civil Design Framework for Small…

69

Standardization chart on diversion canal with

longitudinal slope of 1/1000; lining of cement mortar 1:3 and of

rectangular shape

Gravel trap and Settling basin: The gravel trap and settling

basin are standardized as the function of the design discharge

and the combination of design particle size, water temperature

and width of the basin. The design particle size for the gravel

traps taken are 1mm, 2mm, 3mm and 4mm while that for

settling basin is 0.1mm, 0.2mm, 0.3mm and 0.4mm. The

xed at 150C for the calculation of the

fall velocity. The basin width is varies from 1m to 4m for

gravel trap while that for settling basin is from 1m to 12m.

Figures 11, 12, 13 and 14 show some of the standardization

chart for the gravel trap and settling basin. It is to be noted

that Figure 13 is suitable for the settling basin with higher

discharge and Figure 14 for lower value of discharge.

Standardization chart on gravel trap with-design particle

ater temperature 150C and width of 3m.

P. Khatri, S.S Khadka, U.Bhattarai & R. Prajapati


Figure 12: Standardization chart on gravel trap with

size of 3mm, water temperature 150C and width of

Figure 13: Standardization chart on settling basin with

particle size of 0.2mm, water temperature 15

Figure 14: Standardization chart on settling basin with

particle size of 0.2mm, water temperature 15

Forebay: The forebay is also standardized as the

the design discharge and the combinations

time and width of the basin. The retention time

1minutes to 4 minutes while the width of the basin is

from 1m to 12m. Figure 15, 16 and 1

standardization chart for forebay.

P. Khatri, S.S Khadka, U.Bhattarai & R. Prajapati: Standardization and Development of Civil Design Framework for S


gravel trap with-design particle

C and width of 3m.

Standardization chart on settling basin with-design

particle size of 0.2mm, water temperature 150C and width of 15m.

Standardization chart on settling basin with-design

particle size of 0.2mm, water temperature 150C and width of 3m.

: The forebay is also standardized as the function of

n discharge and the combinations of the retention

time and width of the basin. The retention time is varied from

1minutes to 4 minutes while the width of the basin is varied

and 17 show the typical

Figure 15: Standardization chart on forebay given surface area as

output with-retention time 4 minutes.

Figure 16: Standardization chart on forebay given

asoutput with-retention time 4 minutes and basin width fixed to 3m.

Figure 17: Standardization chart on forebay given depth &

output with-retention time 4 minutes and basin width fixed to 12m.

Note: The tunnel, surge tank and penstock design are

specific and inter-related. The design parameters like tunnel length,

penstock length, net-head,

widely from site to site. Hence, the standardization chart has not

developed for these civil structures.

been developed for all these civil structures.

Standardization and Development of Civil Design Framework for Small…

70

Standardization chart on forebay given surface area as

retention time 4 minutes.

Standardization chart on forebay given depth & length

retention time 4 minutes and basin width fixed to 3m.

Standardization chart on forebay given depth & length as

retention time 4 minutes and basin width fixed to 12m.

rge tank and penstock design are very site

related. The design parameters like tunnel length,

mean monthly discharge, etc. varies

widely from site to site. Hence, the standardization chart has not

developed for these civil structures. But the design framework has

been developed for all these civil structures.



IV. CONCLUSION

In Nepal very few guidelines and design documents are

available for the design of hydropower infrastructure and the

ones available are inconsistent and conflicting at times.

Therefore, the need of effective and complete design

framework and standardization of the design is of immense

importance. This research has been successful in the

development of correct, non-ambiguous, clear and effective

design procedures and their standardization for the civil works

of small HPPs. The developed framework and standardization

documents are believed to be extremely useful to practicing

engineers as well as other relevant stakeholders related to the

hydropower sector of Nepal.

ACKNOWLEDGEMENT

The authors would like to duly acknowledge Prof. Dr.

Ramesh K. Maskey and Mr. Kiran S. Yogacharya for their

valuable expert advice on the research. The authors are also

extremely thankful to Renewable Nepal Program and

NORAD in particular for funding the project. Authors' deep

gratitude goes to Kathmandu University, especially

Department of Civil and Geomatics Engineering and all the

staff of Cross Momentum Engineers Pvt. Ltd. for providing

the platform to conduct this research. The authors would also

like to thank REMREC, District Development Committee

(Dhulikhel), and all other who directly and indirectly

supported this research.

REFERENCE

[1] D. Adhikari, "Hydropower Development in Nepal,"

Economic Review, vol. 18.

[2] Nepal Electriciy Authority, "Annual Report 2012/13,"

NEA, Kathmandu, Nepal, 2013.

[3] Nepal Electricity Authority, "Annual Report 2010/11,"

NEA, Kathmandu, Nepal, 2011.

[4] ITDG, Kathmandu, Civil work guidelines for Micro

Hydropower in Nepal.

[5] JICA, Manual and Guidlines for development of Micro

Hydropower in Developing countries, Phillipines, 2009.

[6] Alternate Hydro Energy Center, Civil Works guidlines

for Hydraulic Design of SHP project, India, 2008.

[7] DOED, "Design guidelines for Water Conveyance

System of Hydropower project," Kathmandu, 2006.

[8] P. Novak, Hydraulic Structures.

[9] E. Mosonyi, Water Power Development, Volume A & B.

[10] E. Mosonyi, Low Head Hydro power, Volume-1.

[11] DOED, "Design Guidelines for Headworks of

Hydropower Project," Kathmandu, 2006.

[12] DOED, "Design guidelines for Water Conveyance

System of Hydropower Project," Kathmandu, 2006.

[13] A. Harvey, Micro Hydro Design Manaul, 1993.

[14] A. R. Inversin, Micro Hydro Power Source Book, A

Practical Guide to Design and Implementation in

Developing Countries.

[15] IPPAN, Independent Power Producer Associations'

Nepal, [Online]. Available:

http://www.ippan.org.np/HPinNepal.html.

[16] M. Andaroodi, "Standardization of civil engineering

works of small high-head hydro-power and development

of an optimization tool," LCH, Lausanne, 2006.

BIOGRAPHIES

Shyam Sundar Khadkahas obtained his

Master’s degree in Structural engineering from

Pulchowk Campus, Tribhuvan University. He is a

Ph.D. candidate and Assistant Professor at

Department of Civil and Geomatics Engineering

at Kathmandu University. He was the project

leader for the Renewable Nepal fundedproject.

Utsav Bhattarai obtained his Master's degree in

Water Resources Engineering from Pulchowk

Campus, Tribhuvan University. He is the

Executive Chairman of Cross Momentum

Engineers Pvt. Ltd. He was the activity leader for

this project.

Pawan Khatri obtained his Bachelo’sr degree in

Civil Engineering (with specialization in

hydropower) from School of Engineering,

Kathmandu University. Currently, he is working

as the research assistant at Kathmandu University

for Renewable Nepal funded project.

Rashmila Prajapatiobtained her Bachelor’s

degree in Civil Engineering from Khowpa

Engineering College, Tribhuvan University.

Currently, she is working as the research assistant

at Cross MomentumEngineers Pvt. Ltd for

Renewable Nepal funded project.

standardization and development of civil design framework...

Documents