Simulation of groundwater flow using visual MODFLOW: A case study for the command area of Chalakudy river diversion scheme

Numerical models are proper tools for studying the status of groundwater, the world's largest water resource. Among the various models developed, visual MODFLOW is a simple, reliable, user-friendly and widely used model. The present study was conducted to simulate groundwater levels and flow in the command area of the Chalakudy River Diversion Scheme (CRDS) that lies in the typical midland region of Kerala where the humid tropical climate is existing. The area is characterized by a welldrained lateritic unconfined aquifer above the weathered rocky aquifer. Hard rock is lying below these two layers of the unconfined aquifer. Considering all these, a numerical conceptual model was created in visual MODFLOW software. The model was calibrated against historical observed water level data from 1996 to 2010 and validated using observed water level data from 2011 to 2014. Calibration and validation created a model that was capable to generate measured groundwater levels and flow. Sensitivity analysis of the model showed that groundwater level of the area was more sensitive to groundwater recharge and hydraulic conductivity. Influence of the specific storage of the aquifer on groundwater level was comparatively less. The model was used to predict groundwater levels for10 years from 2015 to 2024 under two scenarios. The scenario I considered the existing rate of groundwater abstraction and recharge. An annual decrease in groundwater recharge at the rate of 5% and an increase in groundwater draft at the rate of 10% was considered in scenario II. Even though the model shows the impact of reduced recharge and increased pumping rate on groundwater levels, the decline of groundwater levels is not drastic. This showed the immense scope for conjunctive use of surface and groundwater in the command area.