Modeling of Groundwater Flow in an Unconfined Aquifer

Analytical models of groundwater flow owing to artificial recharge from basins of different geometries were initially developed for constant rate of recharge by many workers such as Bauman (1952), Glover (1960) , Hantush (1967) , Marino (1974 a, b, c), Rao and Sarma (1981 a, b, 1983 , 1984). However, the rate of recharge, which is largely dependent on the infiltration rate, is known to vary with time like infiltration rate. Initially, soil compaction and resistance from the entrapped air beneath the recharge basin reduces the recharge rate. This is followed by an increase in the rate of recharge for some time due to displacement of the entrapped air. Then, the rate of recharge decreases with time due to sediment clogging of the pores beneath the basin. When the rate of recharge drops below a specified value, the use of the basin is discontinued for some time; by drying, cleaning, and if necessary, scraping the top of its silty bottom, the recharge rate is brought back to its initial value for the next phase of recharge operation ( Bear, 1979 ; Detay, 1995 ; Dickenson and Bachman, 1995 ; Huisman and Olsthoorn, 1983; Zomorodi, 1991 ). Such a complex nature of periodic variation in the recharge rate cannot be accurately approximated by simple mathematical functions such as exponential function representing exponentially decreasing recharge rate ( Rai and Singh, 1995 ). The solution for exponentially decreasing recharge rate can be used in case of one cycle of recharge operation only. Zomorodi (1991) has shown that the solutions, based on the assumption of constant rate of recharge, failed to predict the decline in the water table, which is due to decrease in the recharge rate.