Behaviour and significance of reservoir evaporation and seepage losses – an experience of four reservoirs in Damodar River Valley, India

Abstract

ABSTRACT More knowledge on spatial and temporal behaviour of losses is needed due to increased utilizable water demand and space constraint for building new reservoir. Tilaiya, Maithon, Konar, and Panchet reservoirs in Damodar Valley, India were considered for this study. Evaporation and seepage losses were estimated using pan coefficient and reviewing water balance equation, respectively. Besides exploratory data analyses, non-stationarity and statistical trend (Mann–Kendall test) analyses were performed to establish the behaviour of losses. Long-term mean dry period evaporation loss was 60% of the long-term mean water-year evaporation loss. Annual seepage loss and its mean rate increased gradually for a considerable period during initial operation stage; later, both decreased and stabilized. Monsoon seepage rate was more compared to dry periods. Annual pattern of both monthly (non-monsoon) and water-year mean seepage rates was similar. Frequency of seepage varied significantly with the season or month. It increased noticeably with rise of operating level. While formulation of gauge-seepage model, best linear relation was between their log transformed values. Both correlation and Nash–Sutcliffe efficiency values indicated satisfactory performance of the gauge-seepage model. During non-monsoon months, seepage and evaporation losses were significant, which indicated necessity of consideration of losses in water balance equation for estimation of inflow.