CAPACITY EXPANSION OF A WATER RESOURCES SYSTEM

Abstract

Comprehensive river basin water resources planning is a complex and very difficult task posing numerous social, economic, environmental, and engineering problems. While planning for the development of a big river basin it is always necessary to take into account the various aspects of long-term river basin planning. One such implied aspect is the determination of sequence of development of various reservoirs. The sequencing of various reservoirs should be such that the decisions taken on grounds of exigency and expediency do not lead to infructuous and wasteful investments in the long-run. Nowadays it is very much possible to carry out such studies using modern systems analysis techniques and computing facilities. The specific problem in question is of obtaining a sequence of development of the reservoirs for capacity expansion of a multipurpose, multifacility system on the Narmada river in Central India, to meet current and forecasting growth in demand of water for irrigation and hydropower. The system consists of 30 major reservoirs, out of which, 10 are situated on the main river, the remaining 20 on nineteen tributaries, which include 2 in series on a tributary, and the other 18 are independent of each other and are situated on eighteen tributaries. The development is proposed in two Phases spread over 45 years as IV stipulated in the Haste, Plan. The various alternative configurations are to be analysed, based on the various proposals and engineering considerations for obtaining the optimal water use targets fro. reservoirs and subsequently the optical sequencing of the reservoirs over alternative planning horizons is to be obtained. The approach is to arrive at a suitable methodology to identify the minimum cost sequencing of reservoirs in the river basin for its development subjected to technological, economical and policy constraints. In view of the large number of reservoirs being involved and the planning nature of the present study, the neighbouring similar reservoirs have been suitably clubbed. A oetailed flexible simulation model is effectively used for fixrng the annual irrigation targets of reservoirs with irrigation and also for quantifying the effect of upstream reservoir (.) on annual firm hydropower targets of reserved with hydropower on the basis of water use dependability criteria. For this 22 years =„a Further a deterministic backward dynamic flow data is used. Furtner, programming process for tackling the reservoir sequencing problem, has been evolved and used in both the Phases. For analysis afew system demand patterns and planning periods in both the Phases have been formulated on the basis of data available. Suitable computer programs have been developed for a for seauencing. These programs are efficient, simulation and for sequeiiLiny a ^pfni tools for obtaining sequencing of flexible, convenient and useful tools multipurpose, multireservoir system. Initially, assuming that all 30 reservoirs are existing in the system, the individual reservoir wise as well as combined imulation runs for all the 30 reservoirs were undertaken starting from upstream to downstream for fixing the final simulated irrigation targets of each of the irrigation reservoirs. Secondly for 14 Phase I reservoirs the initial and the final simulated firm hydropower targets of hydropower reservoirs were determined. In each case, the irrigation targets were kept constant as obtained in the previous para. Further, sequencing of the Phase I reservoirs was done using the sequencing model. Finally, 16 Phase II reservoirs were sequenced in similar fashion as in Phase I. Looking at the huge size of the problem due to the presence of a large number of reservoirs in both the Phases of development it was necessary to reduce the size of the problem by clubbing some of the small neighbouring reservoirs and calling the new system by projects. In this study an attempt was made to blend the major advances of systems analysis by using simulation and sequencing models for capacity expansion. Dynamic programming has been used as an optimization technique for sequencing owing to obvious reasons of multistage sequential decisions involved in such problems. These models were effectively used for capacity vi s expansion of the Narmada river water resources system. The large multipurpose reservoirs are found insensitive to sequencing parameters such as demand patterns, allowances for shortage and excess and corresponding penalties, etc. and tend assume almost a fixed position in sequencing over the recommended planning horizon of 14 periods. However, small and moderate size reservoirs are found sensitive to the sequencing parameters. Three categories of targets have been considered, namely mixed, simulation and master plan for analysis and the simulation target sequencing is preferred and suggested for implementation amongst the recommended sequences. Trend of existing development is found to be matching with recommended sequences. Tradeoff between irrigation supply area fulfilled and hydropower supply for recommended as well as no penalty sequences is also studied. The agroclimatic zonewise distribution of the sequenced projects for the preferred simulation category sequence indicated evenly spread and balanced development of the system with respect to space (three zones) and time (planning horizon). The use of proposed strategy of exhaustive analysis of all possible reservoir combinations by detailed simulation model and subsequently sequencing by optimization(DP) suggests a promising scheme for capacity expansion of a multipurpose, multireservoir system. Such a strategy is likely to guarantee an optimal capacity expansion path. The approach is feasible and efficient within a reasonable amount of computing time and efforts.