Head, Alternate Hydro Energy Centre
Indian Institute of Technology Roorkee
Water Resources and Environment Division
Centre for Ecology & Hydrology, Wallingford, UK
T. K. Raghuvanshi
Fellow’C’ Alternate Hydro Energy Centre
Indian Institute of Technology Roorkee
In the recent times the non-renewable and exhaustible sources of energy are getting depleted at a very fast rate, which has focused attention to the non-exhaustible and renewable sources of energy. Hydropower is one of the most common renewable sources abundantly available in the hilly region. However, large hydro power plants are not being taken up for execution in sufficient number as these involve huge amount of funds and also the planning and construction period is very high. Therefore, with the increasing demand for power, the activities on small hydropower projects have accelerated in recent times. The small hydropower schemes are the appropriate solution to power demand as these require small capital investment and can be completed in a very short period of time.
For the development of any small hydropower scheme an essential first step is to determine whether there is sufficient and reliable amount of water is available to make the scheme economically viable. As a standard practice a gauging station should be set up and the discharge should be observed for at least two lean seasons. For planning purpose this period is too long therefore, there was a need to develop regional hydrological models that enable users to rapidly estimate the temporal variability of river flows at a potential site, from which the hydropower potential can be determined.
This paper presents some main highlights of the study and software developed for application in Himachal Pradesh for small hydropower assessment. The paper is presented to make aware about the software developed and is available for use by potential developers, consultants and related agencies
Regional Flow Estimation Model
Small hydropower projects are normally run-of-the-river schemes with no storage of water. For a project to be economically viable it is essential to know whether there will be sufficient discharge available or not. As a normal practice flow duration curves are used to determine the dependable flows. However, at many potential sites the discharge data of stream is not available and also the representative discharge of streams in the close vicinity with more or less similar topographical and physiographical conditions is not available upon which a reliable estimate could be made.
To determine the flow duration curve at such un gauged site, Hydra-HP software has been developed. Hydra-HP, a new and innovated PC based software package that provides a rapid means of estimating small hydropower potential at any location in Himachal Pradesh. The software incorporates a regional flow estimation model derived from extensive statistical analysis of state wide river flow data and catchment information. The minimum PC configuration required to run Hydra-HP software is; any IBM compatible PC with 386 processor, 2 MB RAM, 3.5″ DD and Windows 3.1 or above.
The Hydra-HP is a result of three year project ‘REFRESHA’ (Regional Flow Regime Estimation for Small scale Hydropower Assessment) that was funded by the UK Department for International Development (DFID). The project was undertaken by Center for Ecology and Hydrology (CEH), UK in collaboration with Alternate Hydro Energy Centre, Indian Institute of Technology, Roorkee (formerly University of Roorkee) and Himurja, the Himachal Pradesh Energy Development Agency of Govt of Himachal Pradesh.
Characteristics of the Region
For study purpose the area of Himachal Pradesh state was divided into three distinct hydrological homogeneous regions, following the north west to south west axis of the mountains, within which the river regimes were considered to be relatively homogeneous. The southern most region in the altitude regions below 2000 m, the catchments are mainly fed by rains only, thus the runoff is dependent on rainfall only, which means that rivers experience peak flows during the monsoon, but the discharge during lean season reduces considerably. In the central region between 2000 and 5000 m, the catchments are fed by rainfall and snow melt, resulting peak discharge during the monsoon, while discharge for the remaining period are resulted by snowmelt. In the higher altitude, region above 5000m altitude, discharge in streams is maximum during summers but tends to reduce to zero as it gets colder during winter. The central region is considered the potential region for the development of small hydropower, as the flows in the streams in this region are perennial in nature.
The regional flow estimation method is based on the criterion that the temporal variability of flows in a stream are controlled by the natural storage characteristics of the catchment. These characteristics are influenced by the geology and the soil cover present in the catchment. Moreover, at higher altitudes snow cover also contributes to this effect. If the flow duration curves of different catchments are standardised by the catchment mean flow, certain low flow statistics, such as Q95 can be used to describe the whole flow duration curve.
Using multi-variate regression to relate the observed Q95 (expressed as % MF) to the proportional extent of different soil types in selected gauged catchment, a map of standardised Q95 was developed for the whole of Himachal Pradesh. The map is included in the software as a grid at a resolution of 1 km by 1 km. Catchment estimate of Q95 may be obtained by overlaying any catchment boundary within the software.
Software also includes the family of flow duration ‘type’ curves. Flow duration curves of the selected catchments have been pooled to define the family of curves, this family of standardised curves represents the range of flow regimes that are likely to be encounter in Himachal Pradesh. Thus, if the Q95 is known for any catchment a flow duration curve can be derived.
The Hydra-HP software provides, a grid of average annual runoff, with a cell resolution of 1 km by 1 km grid, developed by relating observed runoff to catchment estimates of average annual precipitation and elevation. Simply by overlaying the catchment boundary, the average annual runoff and area of the un gauged catchment can be derived.
Small hydropower assessment – A solution through hydra-HP software
For statistical analysis, 10 daily discharge data for minimum two years was procured for 60 gauging stations within the rain and snow fed hydrological homogeneous region, area roughly defined between the elevations 2000m to 5000m. After the quality control checks it was found that 40 gauging station data is suitable for actual analysis. For these selected gauging stations catchments were delineated from 1:50,000 scale Survey of India toposheets and were digitized. In addition spatial data on geology, soil cover, land use, topography, drainage, precipitation, temperature and snow cover were also digitized. Fig. 1 shows the drainage theme of Himachal Pradesh.
The data analysis revealed that the distribution of land use clases are closely correlated with the geology and the soil cover in the study area. The soil cover map procured from Soil Survey of India describes total 96 units in Himachal Pradesh. On the basis of drainage property and depth these soil units were reclassified into 17 soil groups. The proportional extent of each soil group in the catchment was determined by the digitized catchment boundary. Step wise Multi-variat regression was applied, grouping soil types to give a parameter estimates of Q95 for each group. Nine groups of soils were defined in the final regression model. Using the parameter estimates for each soils group, grid of standardized Q95 were mapped at a 1 km by 1 km grid resolution for study area. Further, the standardized flow duration curves for the selected catchments were pooled into classes based on the Q95. For each class, the average curves were determined, resulting into flow duration type curves.
Small Hydropower Potential and details
In order to calculate the hydropower potential at a given potential site user is required to provide the dependable flow, the residual flow, the hydraulic head and the number of turbines. The Hydra-HP will provide the maximum power generation and net annual energy generation for a prospective site.
The Hydra-HP comprises of four key modules, these are;
- Catchment Characteristics Module: This requires the user to enter the catchment boundary of the proposed site, defined by a series of coordinate pairs. The software overlays the boundary onto 1 km by 1 km grid of average annual runoff and a standardised low flow statistic.
- Flow regime Estimation Module: This takes the output from the catchment characteristics module to determine a synthetic flow duration curve for the site. An interactive facility enables the interrogation of the flow duration curve providing value of flow from probability or vice versa. For gauged sites, ordinates of the flow duration curve may be entered manually.
- Turbine Selection Module: This requires the user to specify the design flow and head conditions for the site. The software automatically compares these with the operational envelopes of eight key turbine types to select which are operateble under the stated conditions. The turbine type supported are; Pelton, Turgo, Cross Flow, Francis Open Flume, Francis Spiral Case, Propeller, Semi-Kaplan and Kaplan.
- Power Potential Module: This calculates the power output for each selected turbine by relating the amount of available water to the manufacturers’ approved flow-efficiency relationship; the available water being defined by the flow duration curve, the design flow and the residual flow requirements of the stream.
With the increasing demand for power the activity in developing small hydropower projects has increased in an effort to promote the use of renewable energy technologies. The inclination towards small hydropower has resulted because of the acute power shortage, environmental concerns and the dependency of the fossil fuels. The Hydra-HP is a rapid solution to provide reliable estimation of small hydropower potential at any given potential site in Himachal Pradesh. It will help in reducing the expenditure on hydrological surveys. The software is a useful tool for preliminary design and turbine selection.
The contributions made by the staff of Alternate Hydro Energy Centre, Dr. A.K.Saraf of Department of Earth Sciences and Dr. N.K.Goel of Department of Hydrology, Indian Institute of Technology, Roorkee, National Institute of Hydrology, Roorkee and Himachal Pradesh Energy Development Agency (Himurja), Shimla in carrying out the study are appreciated by the project team lead by the authors. The financial sponsorship from DFID, UK for the study is acknowledged with thanks.
- AHEC, 1997 Development of Regional flow duration models for preparation of Zonal Plan for Small Hydro Power projects, UNDE-GEF Hilly Hydro Project of Ministry of Non Conventional Energy Sources, Govt of India.
- Gwyn Rees, et al ,2002, Application of the Regional flow Estimation Method in the Himalayas, accepted for presentation in the FRIEND Conference to be held in South Africa.
- CEH, 2001 Hydra-HP User guide and Technical Reference, Centre for Ecology and Hydrology, Wallingford, United Kingdom.
- Brochure on Hydra-HP 2001