STORAGE YIELD ,EVALUATION AND OPERATION OF RESERVOIR FOR WATER CONSERVATION

Abstract

An interactive computer simulation model has been developed for multipurpose reservoir operation for water supply and irrigation with application to the Mula dam in the state of Maharashtra, India. The methodology consists of two phases of computer modeling. In the first phase, monthly reservoir operation is performed with the historical river inflows, known demands and initial storage using the model through standard operating policy. The reservoir spills experienced by the reservoir operation are dressed (removed) from the river inflows of the corresponding periods and thus the river inflows are converted ' into dressed inflows. The final storage of end period is carried over to the initial storage of starting period so that the system is brought into a closed network. The reservoir operation is once again repeated through standard operating policy and the outputs of the model such as reservoir storage yield, % deficits, no. of deficit periods, shortage index, refill storage, carry over storage and vacuum storage resulting from the reservoir operation, are studied thoroughly to know about the reservoir system behaviours and regulation required for achieving a better performance.. In the second phase, monthly reservoir operation is simulated with the dressed inflows and the knowledge gained upon the reservoir system behaviours, using the model through 4 set of rules(no-spill rule, trial rules, primary rule and secondary rule). The upper bound of monthly target level which does not cause any excess spill is found out by no-spill rule and three trial rules are derived one by one, to bring down the % deficits gradually to zero or possible lower level. Monthly target level is fixed by simulating monthly reservoir operation by continuously bisecting the upper bound (which satisfies the required conditions) and the lower bound (which does not satisfy the conditions) through numerous iterations. The adjustment (increasing or lowering monthly target level) is also done in backward or forward direction (along the months of a water year) repeatedly until the satisfactory performance is achieved. The trial rule no.3 is further refined with primary rule to maximize the firm releases by minimizing the excess reservoir spills and the % deficits. Simulation is then continued to refine the primary rule with the secondary rule, in order to re-distribute the heavier irrigation deficits of shorter region into no-deficit or permissible deficits of possible larger regions. The comparative performances of primary and secondary rules with respect to that of standard operating policy are then studied in detail and the best one out of the two is chosen as the required new operating rule for efficient reservoir operation. The two special features of the model are instantaneous simulation results and hydraulic state diagrams. Both are automatically updated by the model with the user inputs of monthly target levels and provide the interactive system response to the user for deciding further input values. The model does not require any comprehensive procedure or technological background for its run by the user, to derive a new rule curve for this complex problem. The operating procedure of the model is very simple such that the user needs only the ability to change the cell fill colours, from red colours (negative values) to green (positive values) or yellow (permissible values) by continuously bisecting the upper and lower bounds of the target level of each month and/or moving forward or backward direction, like equalizers control in a music player system.