S Mohan

A combined optimization-simulation approach was used to develop and evaluate the alternate priority-based policies for operation of surface and groundwater systems and is demonstrated with a case study. An optimization model was used to find optimal cropping pattern with and without the conjunctive use of surface and groundwater, as well as with and without socio-economic constraints. The optimization model, based on linear programming, maximizes the net benefit from irrigation activities subject to various physical, economical, and social constraints. A simulation model was used to evaluate the conjunctive operation of the system using the optimal cropping pattern derived from the optimization model. The developed policies have been verified with long-generated stream flow sequences. Three alternate priority-based policies differing in level of groundwater pumping and area of cultivation of rice crop have been evaluated: (1) irrigation with surface water only (Policy-1); (2) irrigation with conjunctive use of surface and groundwater, without socio-economic constraints (Policy-2); and (3) irrigation with conjunctive use operation and with socio-economic constraints (Policy-3). It was found that the use of available groundwater within three meters below ground level (Policy-2) to be optimal, and these results were used in simulation for further evaluation of policies. It was also found that the policy-3 of conjunctive use operation with a priority of 75 percent of maximum possible rice area (using groundwater available within four meters below ground level) resulted in a better scenario. Thus the conjunctive use Policy-2 and Policy-3 with 75 percent of maximum possible rice crop area can be used as better policies for the system studied. © 2003 Taylor & Francis Group, LLC.

Population growth and higher living standards have resulted in ever-increasing demand for water. For the present study natural recharge was computed from a water balance model and daily water level fluctuations were measured to study the increase in water level due to artificial recharge. Numerical models were developed using MODFLOW to analyze the feasibility of different artificial recharge arrangements such as check dam and percolation pond with percolation wells individually and in combination and evaluate the effectiveness of the structures in recharging the aquifer. The maximum increase in water level was found to be 3.46 m, 2.54 m and 4.7 m respectively for the check dam, percolation pond with three percolation wells and combined structure arrangement after 2 years of artificial recharge. The zone of influence was obtained as 400 m, 600 m and 500 m respectively for the check dam, percolation pond and combined structure system. Water level fluctuations also proved the same. Water level increase obtained from the natural recharge study was only of the order of 0.2 m. Artificial recharge is found to be very effective for sustainable development of water resources and the percolation pond was found to be the most appropriate structure for groundwater recharge for the study area.

Long-term Groundwater pumping alters the environment and groundwater availability and thus affecting both the local and regional environment in a significant way. There are many purposes for which the groundwater has been abstracted in large quantity thus creating an unscientific way of management of the groundwater, leading to jeopardizing the sustainability of groundwater availability on a long-term basis. In this paper, we would be discussing one case study dealing with the groundwater modeling of open-cast mines with the development of an Integrated groundwater model to evaluate the impact of mining and the irrigated agriculture in the surrounding environs, on the groundwater status as well as to determine the time-period/year when the newly proposed mines without any increase in total pumping of groundwater. The study includes estimating groundwater recharge and developing a three‐dimensional steady‐state groundwater flow model exclusively for mine pumping simulation. The model has been utilized to evaluate the impacts of changes in groundwater pumping under the mine expansion scenario. In addition, simulation runs were made with the developed model to assess the impacts of recharging into the aquifer systems through the proposed recharge structures on groundwater and the surrounding environments and for various scenarios that vary depending upon the current as well as on the future conditions of water use. The other case study was in connection with the dewatering optimization in a metro rail tunneling construction. The requirement of maximum allowable drawdown necessitates the need for pumping and injection simultaneously and the optimal pumping wells and recharge wells location as well as the quantum of pumping and injection have been arrived at for 5 typical tunnel construction locations in a metro city of India. The engineering lessons learned, and the environment-friendly groundwater pumping plans are the major outcomes of these research works, which would be highlighted.

The laboratory scale tracer experiments on homogenous and heterogeneous porous media have been increasingly used to study the dispersion phenomenon of contaminants in saturated and un-saturated groundwater system. The present study is concerned with the estimation of scale effect of dispersion coefficient of conservative tracer solute. Tracer test in soil column is one of the reliable techniques for the estimation of dispersion coefficient. Soil samples were collected from different locations in a contaminated area and five different sets of experiments were conducted by varying the dimensions of the column and head in-order to arrive at optimal size of column and the minimum head required. The raw textile effluent considered as conservative tracer was characterized. During the column study, the effluent samples were collected in regular intervals at the bottom of column and its quality parameters were tested. The results reveal that the absorbance rate of various salts by the various soil columns goes on decreasing with length and at a certain point the concentration becomes negligible or zero. The Break through Curve (BTC) was obtained for the concentration difference with time. The longitudinal dispersion coefficient (αL) and transverse dispersion coefficient (αT) are estimated using the sigmoidal curve method. It is found that αT is one tenth of αL and was verified by summation distribution graph approach and the results are found to be more or less same. The scale effect of dispersion coefficient was estimated for different length versus diameter (L/D) ratios. In this paper, a new approach of estimation of dispersion coefficient using BTC has been proposed and evaluated its estimation with that of estimate from Summation Distribution (SD) and Sigmoidal Curve (SC) methods, and these scale effect has been quantified by all these methods. It is found that the estimation of dispersion coefficient and its scale effect from all these methods were matching well. The results also established that the scale effect of dispersion coefficient was predominantly due to the inappropriate L/D ratio. It is recommended that the optimal L/D ratio of 4 to 20 is acceptable without any pronounced scale effect.