standardization and development of civil design framework for small hydropower project

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 designfrom 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 basinbasin 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 15fall 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 settlithat 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 withsize 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 withsize of 3mm, water temperature 150C and width of

Figure 13: Standardization chart on settling basin withparticle size of 0.2mm, water temperature 15

Figure 14: Standardization chart on settling basin withparticle 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 time1minutes to 4 minutes while the width of the basin is from 1m to 12m. Figure 15, 16 and 1standardization 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 arespecific 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 Masters 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 Bachelosr 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 Bachelors 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 for small hydropower project

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