OPERATION OF A MULTIPURPOSE RESERVOIR

Abstract

Systems analysis is well accepted as a powerful tool for planning and management ofwater resources. It helps guide the decision makerin examining potential configurations and the sizing of project elements of a new project and for improving operating policies for existing projects. There are a multitude of examples, where systems techniques have been employed to formulate operating policies for multi-purpose reservoirs. These operating policies have clearly resulted in an improvement over the historic performance. For improving project performance, the reservoir operation studies are usually coupled with flow generation and forecast mechanisms the derivation of which often leads to undertaking the studies of rainfall-runoff modelling. The Soil Conservation Service(1956) Curve Number (SCS-CN) method- a one-parameter rainfall-runoff methodhas myriad applications. It has, however, been rarely employed for simulating daily flows. Therefore, there is a need to (i) examine critically and derive analytically the basic hypothesis of the SCS-CN method; (ii) develop an improved version of this method and derive its general form; (iii) develop SCS-CN-based infiltration and runoff models; (iv) provide a physical interpretation of the parameter Potential maximum retention; (iii) develop an SCS-CN method based daily flow simulation model for utilizing its results in generating daily flows 'hrough an error model; and (iv) develop a daily flow forecasting model.The whole reservoir operation mechanism can be explained within the frame-work of six basic operating questions of James and Lee(1971). The analysis of these questions has not appeared to have been reported in literature. Therefore, there is a need to analyse them and develop strategies for reservoir operation in both low and high flow seasons. (ii) Using the Ramganga Project, as an example, this thesis employs systems analysis toderive policies for improved project performance. The project is a multi-purpose storage scheme providing irrigation, power, and flood control benefits to the vast areas ofGanga- Yamuna Doab of the State of Uttar Pradesh, in addition to augmenting drinking water supply to Delhi. Acomprehensive study is carried out for developing reservoir operating policies/strategies for daily cperation ofthe Ramganga reservoir in both high and low flow seasons. This study is carried with the following objectives: 0 to develop operating policies for daily operation of the multi-purpose Ramganga Reservoir in both low and high flow seasons; 0 to examine and analyse the six basic operating questions of reservoir operation of James and Lee (1971); 0 to develop a daily flow simulation model and use its results in generating a sequence of daily flows through an error model and develop adaily flow forecasting model; 0 to derive an operation policy for flood control; 0 to derive a reservoir operation policy for flood control and conservation in the monsoon season; 0 to derive a reservoir operation policy for conservation in non-monsoon season; 0 to estimate monetary benefits which can be accrued if the developed reservoir operation policies are employed. In an attempt to apply the Soil Conservation Service(1956) Curve Number (SCSCN) method for daily flow simulation, the SCS-CN method is revisited. The basic underlying hypothesis of this method, which has not yet been critically analysed, is derived analytically. The derivation reveals its basis in the Mockus(1949) method, which has not appeared in literature so far. The modified and general forms of this method are (iii) presented. The SCS-CN method, the modified version of the SCS-CN method, and the Mockus method are compared using published data of four watersheds. For these data, the modified version is found to be more accurate than the current version. An SCS-CN method-based infiltration model is developed and compared with the Horton model. The former is found to simulate infiltration tests reasonably well. Furthermore, an SCS-CNbased runoff model is developed and employed to simulate the rainfall-runoff events ofa watershed of catchment area 600 sq. km. Its performance is found to be satisfactory. A mathematical expression is derived for physical interpretation of the SCS-CN parameter potential maximum retention, S. S is found to be a definite function of sorptivity and hydraulic conductivity of the soil. It is also found to be related with the parameters ofthe Horton model and the derived relationship is verified using 99 sets of infiltration data. Another model based on tank concept is also proposed. Employing these methods, daily flow simulation models are formulated and employed to a 16-year data set of Ramganga and compared with the results oflinear perturbation model. The SCS-CN-based simulation model is found to be superior to other models. Using these simulation results, an error model is developed for generating a sequence of daily flows. Furthermore, a daily flow forecasting model of the form of linear perturbation model is also proposed andemployed to the Ramganga data. The results of the error model and the forecasting model are used in deriving an operating policy for flood control and conservation in monsoon season. Besides describing the reservoir operation principles, the six basic reservoir operating questions of James and Lee(1971) are examined and analysed. The first three questions dealing respectively with the reservoir operation for flood control, flood control and conservation in the monsoon season, and conservation in non-monsoon season are found to be pertinent to the present study. For flood control operation of the Ramganga Reservoir, a strategy which accounts for the current storage and the characteristics of (iv) coming inflow, whether rising or receding, is developed and flood control benefits are derived. For flood control and conservation operation in the monsoon season, filling rule curves, based on historical flows and actual reservoir routing results of the major flood events occurred on different dates, are developed. An economic evaluation of generated streamflows is performed and the benefits are derived over historic performance of the reservoir. A strategy is proposed and employed for operating the Ramganga Reservoir using daily flow forecast. The proposed strategy improves significantly the performance of the reservoir operation for both flood control and conservation. For operating the Ramganga Reservoir in non-monsoon season, firm and normal rule curves are developed by trial and error through simulation and a multiple-zoning-based strategy is developed. Using this strategy, irrigation and hydropower benefits, which could be accrued over and above the historical performance of the reservoir, are derived. Finally, the present worth of the total net annual benefits is computed. The aggregated net annual benefits due to application of the developed policies for the Ramganga reservoir operation for flood control and conservation are estimated to be of the order of 92.84 million rupees which are over and above the historical benefits. The computer programs developed for performing these tasks are included along with their documentation.