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Small hydropower assessment - A solution through hydra-HP software

Arun Kumar
Head, Alternate Hydro Energy Centre
Indian Institute of Technology Roorkee

G. Rees
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

Introduction
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.



Model Development
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.

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