CS(AR)-2/2000-2001 : Water balance study of Krishnai river basin according to Thornthwaite's concept of potential evapotranspiration

Abstract

The estimation of water balance is necessary in water resources development not only for economic appraisal of the project but also for checking the reliability and general pattern of availability of water from month to month. The planning, development and operation of water resources projects is very much dependent upon the availability of water in required quantity. Study of water balance of a river basin is necessary for various water resources development activities. Water balance study is an essential part to be carried out before deciding an irrigation project. The current work involves the study to see the feasibility of available water for Krishnai river basin in Goalpara district, Assam. The catchment area under study is 953.88 square km and extends on both the banks of river Krishnai.

For the study of climatological water balance for Krishnai river basin, 9 years (1986-1994) of mean monthly required climatological data like temperature etc. have been collected from the state irrigation department, Assam and Indian Meteorological Department, Borjhar and used for the analysis of various components of water balance like prediction of water surplus, water deficit etc. Thornthwaiters method has been used to find out the required essential input data named potential evapotranspiration. Mean monthly rainfall data for different months over the basin were computed using Isohyetal method.

The study reveals that, on normal annual basis, the basin has a water need of 1476.56 mm, the rainfall is 1844.14 mm and actual evapotranspiration is 1406.13 mm. Water surplus is 388 mm, and deficit is 70.43 mm. Since annual water surplus is more then water deficit, Basin is free from drought.