A thesis submitted in partial fulfilment of the requirement for the degree of Master of Engineering

Thesis (M.Eng.) - Asian Institute of Technology, 1991

In semi-arid tropics (SAT) timely availability of water to the crops is a major problem. As a consequence, crops suffer a low and unstable yields. In this study a hydrological model suitable for simulating runoff storage has been developed. The model integrates the processes of watershed runoff inflow, rain water, seepage and evaporation losses to and from tank respectively and gives the output as net storage in the tank and overflow from the tank for a particular day. A procedure of estimating seepage and evaporation losses from the reservoir was adopted by estimating water surface area and wetted area of the tank. The model is validated against the observed tank storage values which is being calculated from observed tank levels for three different tanks at International Crops Research Institute for Semi-Arid Tropics (ICRISAT) center, India. A close agreement between observed and predicted tank storage is found for all the test years. A water balance is done for all the study tanks for all the test years to investigate the relative inflows and losses to and from the tank. A probability analysis is done to have an idea of available water in tank for supplemental irrigation. A crop growth model is used to see the response of supplemental irrigation in rainy season sorghum. It is found that from the study tanks it is not possible to provide supplemental irrigation to rainy season crop, although the tank water can be used for pre sowing irrigation in post rainy season crops. By virtue of its simplicity and physical concept, it is convenient to use the model for various other purposes besides the prediction of tank storage. It can be used for scheduling irrigation, determining effective rainfall and determining the overflow from tank.