Catchment hydrology and ground water modeling of the Osmansagar and Himayathsagar reservoirs

Abstract

Hard rock region is tremendously witnessing a growing demand for ground water resources, since adequate surface water resources are not available. The decreased ground water level has considerable effect in decreasing the surface runoff. Hence, it is necessary to know the quantitative response of the aquifer system vis-à-vis surface runoff for proper water management in the catchments. Therefore an attempt is made in this thesis to understand the catchment hydrology of both Osmansagar and Himayathsagar catchments, which are supplying drinking water to Hyderabad city - a capital city for the state of Andhra Pradesh, India, with an intention of developing a ground water flow model for the catchments.For this purpose Inflows to the Osmansagar and Himayathsagar reservoirs are calculated using daily water levels at the reservoir sites. From this record it has been observed that inflows to Osmansagar and Himayathsagar reservoirs are decreasing continuously for the past 49 years inspite of normal rainfall over the period. This may be due to the fact that over the years, there is an increased usage of surface and ground water in the catchment areas resulting in the reduction of inflows. Because of the above fact whatever the rainfall that occurs in the upper catchment, is simply percolating down to recharge the depleted ground water table, to meet the soil moisture deficiency and to meet the storage of water in smaller or bigger water conservation structures leaving little or no runoff that could reach the downstream. The above fact is proved by NDVI analysis indicating that the total cropping area has been increased by 25.84% in kharif and 55.55% during rabi from the year 1989 to 2008. This has lead to the excessive usage of ground water in the catchment. A ground water flow model is also developed under steady and transient conditions using visual MODFLOW software for the period 2005 to 2009.