Dewatering Example Model
Review this model, download it, and play with it to learn how to apply AnAqSim to dewatering problems. This is a model of a complex dewatering system that includes a partially-penetrating circular sheet pile barrier, three shallow wells pumping inside the barrier, and a shallow recharge trench outside the barrier, where the discharge of the wells is put back into the aquifer. The aquifer is unconfined and sandy, with about 120 ft of saturated thickness. The system will allow excavation 10 ft below the ambient water table within the barrier to install a tank. The figure at right shows a map of the system elements. The sheet pile wall is 63 ft in diameter and it penetrates 30 ft below the water table. The pumping wells are screened in the upper 20 ft of saturated thickness and are 6 inches in diameter. The recharge trench introduces water into the uppermost part of the saturated zone and is 116 ft long.
The upper 30 ft of saturated thickness in the aquifer is more conductive (20 ft/d) than the lower 90 ft (6 ft/day), so the barrier cuts off flow in the more conductive part. The model is set up just to model drawdowns – all initial heads are zero (water table) and deviations from zero are simulated.
Near the system, there are 7 layers, with thinner layers near the bottom of the barrier where there are important vertical flows (see below). Far away from the system, there is only one layer, with an interdomain boundary linking the 7 layers within to the single layer without. At the interdomain boundary, the total normal components of discharge are matched over intervals and heads are matched at points. The topmost layers (1) are unconfined and layers 2-7 are confined (fixed transmissivity).