TN-13 : Regional aquifer simulation

Abstract

Over the past two decades ground water has become topic of discussion and investigation and as a result the knowledge and understanding of ground water conditions have radically improved. The ground water in a basin is in a state of continuous movement. Its volume decreases by processes like discharge into natural streams or springs or evaporation or abstraction from wells, etc., causing the water table to go down. At the same time, its volume increases by recharge from rainfall or from surface water bodies causing the water table to rise. When considered over a long period of time, the water table will be nearly stationary indicating a state of hydrological equilibrium, the average recharge equalling the average discharge from the system. For a short duration observations, seasonal fluctuations around the average water table conditions may be noticed and at times these fluctuations may be significant and important.

The flow of groundwater is governed by certain laws. Solutions for the groundwater flow problems are obtained by solving the differential equation that can describe hydrological relationship within an aquifer. However, it is pre-requisite to have knowledge about geometry of the study area, hydraulic characteristics, initial and boundary conditions. It is attempted in this report to identify these various parameters that are required to be specified.

Mathematical models of ground water systems are primarily intended as means of investigating and predicting flow processes within an aquifer. A review on the models which have been developed to solve the groundwater problems is presented. Data which are obtained from various ,sources form the basis for building a model. Other information required for a model, boundary conditions, the recharge abstraction components, the historical data are discussed. Methods for estimating the aquifer parameters using inverse methods are indicated. Some of the commonly used solution techniques are also given. The formulation of a mathematical model and using a specific numerical technique for solving such a mathematical model is also presented. A specific case study using one of the finite difference schemes, conducted for one of the doabs in India is also described.