Modelling of Irrigation Return Flow in Unconfined Aquifer of Dharoi Command in Mehsana District of Gujarat, India

Surface water flow and subsurface flow have traditionally been investigated separately and simulators have been developed over the years, to model each of these systems. Growing interest in conjunctive water management, and need for simulations of surface/subsurface flow and their interactions has lead to the linking of models of the respective domains. This study from Dharoi command area, using MODFLOW, showed pertaining to the second layer of the calibrated model. The first layer is a thin soil cover layer of about 3 m uniform thickness. Top layer is kept under unconfined water table condition, where as the next layer is given the scope of transforming between water table to confined state and vice versa depending upon the fluctuation of the computed water level with respect to the bottom boundary of the top layer. No recharge and discharge options other than a single boundary condition of average May water level in the extreme north-east grid has been allowed. This calibration is based upon matching the observed and computed average gradient of the water table (hydraulic gradient) and nothing to do with matching the point to point values of the observation wells as that could lead to misappropriation in respect of hydrologic condition. Over all gradient of the water table in the area of interest is computed as 0.23 m per km in comparison to an observed hydraulic gradient of 0.3 m per km. The rivers such as Sabarmati downstream of Dharoi dam and up to Bijapur, Rupen and Pushpawati are activated in the transient run. Conductance value is considered as 0.0001 m/sec for all the rivers. proximity of the second layer under unconfined state. Comparisons of water levels in selected locations. Overall match between the trends and the point values indicate that the calibrated model transient run can be considered as base case and various options can be studied with this model. Visual MODFLOW is very effective to know the present scenario of ground water flow, water level of aquifer, wells, also point values indicate that the calibrated model transient run can be considered as base case and various options can be studied with this model. Visual MODFLOW is very effective to know the present scenario of ground water flow, water level of aquifer, wells, also distribution of spatial recharge, specific yield distribution. It gives very close result to the observed value.