Methodology to deal with computed negative inflows in Indian reservoirs

Abstract

For developing the operation policies for a reservoir for conservation or flood control purpose, historical inflows into the reservoir forms an important input. In most of the Indian reservoirs, the inflows into the reservoir are not directly measured. Rather, continuous observations of reservoir levels at the dam site are made and reservoir inflows are computed indirectly using the water balance equation along with recorded outflows from the reservoir, precipitation inputs and evaporation losses from the reservoir water spread area. These computations, sometimes, result in negative inflow estimations which may be because of several reasons, such as a small error in the measurement of reservoir level, wrong consideration of reservoir storage at any elevation, error in recording of outflows or other variables etc. This inconsistency of inflow data needs to be handled before using the flow data for further analysis. This paper describes a few methodologies which can be used to adjust such computed negative inflows for a reservoir. Generalized computer program has been developed for this purpose and embedded in the NIH_ReSyP software so that it is easy for the field officials to use the program and adjust the negative inflows.