Pumping Impact
The town of Hubertville is planning to expand its
water supply by constructing a pumping well in an unconfined aquifer. The well
is designed to pump constantly at a rate of 20,000 m3/day. Well
construction was halted by the State Fish and Game Service who manage the Green
Swamp Conservation area. The agency claimed that pumping would “significantly
reduce” groundwater discharge to the swamp and damage a waterfowl habitat. The
town claimed the fully penetrating river boundary to the north and the
groundwater divide located near the center of the valley would prevent any
change in flow to the swamp.
1. You are hired to offer your professional opinion on this controversy. In particular, you are asked to construct a 2D areal steady state model of the aquifer between the river and swamp and use the model quantify the impact of the proposed water withdrawal.
Based on a previous study, mean long-term recharge is estimated to be 0.001 m/d and the hydraulic conductivity of the sand and gravel aquifer is estimated to be 50 m/d. The leakance (hydraulic conductivity per unit thickness) of the river sediments is estimated to be 5 day-1. The average depth of the river is 1m.
Hints/Suggestions:
- Use 'Synthetic Mode' to set up your flow model ( 'Other Tools' > 'Utilities' > 'Go to Synthetic Case Area')
- Use the ‘Distance Display’ capabilities when editing geometric features and/or the ‘Ruler’ tool to properly represent distances between model features.
- Represent the River as a two-way, head-dependent flux boundary, and the Swamp as a prescribed head boundary.
- Assume an aquifer bottom elevation of 980m
- Assume an average aquifer top elevation of 1015m
- Consider using a large grid size (NX=100)
2. Optional: Apply an analytical approach and compare the results to those of the numerical model.