Groundwater Flow Modeling for Evaluating Specific Yield Sensitivity of a Sandstone Aquifer System in Gunderu Sub-basin

Abstract

Gunderu is an important minor stream in West Godavari district and drains through upland region. It finally joins the Kolleru Lake, a freshwater lake sandwiched between Krishna and Godavari deltas. Gunderu sub-basin considered has an aerial extent of 297 km2 with stream length 35 km. Intensive irrigation with ground water is prevailing in the study area, and the long term water levels are in depleting nature. The overall rates and magnitude of groundwater depletion in most of the aquifers are not well characterized. To understand the groundwater flow in the study area, modeling is carried using FREEWAT based on QGIS and MODFLOW to simulate the effect of different stress conditions of pumping and recharge. In this paper, an attempt is made to determine the sensitivity of specific yield of the model in satisfying continuity of groundwater flow for variation of pumping to simulate the different groundwater developments in the aquifer. The analysis helped to understand the existing behavior of ground water flow, and various scenarios are performed to observe the sensitivity of model by taking different specific yield conditions such as 3, 4, 5, 10, and 15% to determine its influence under various stress conditions such as wells, river, recharge due to rainfall, and tanks. Any change in volume of water in the aquifer due to pumping and recharge is associated with the specific yield of the aquifer. From the model same is analyzed for different specific yield values. Thus, with pumping, for different specific yield of aquifer formation, the change in aquifer volume and hydraulic heads changes differently in the aquifer system. The sensitivity of aquifer system to spatial variation in specific yield and thus variation in piezometric heads in the study area is presented in the paper.