Simulation the Shift in Position of Hinge Lines between Two, Shallow, Flow-through Lakes

Groundwater flow between two hypothetical, shallow, flow-through lakes was numerically simulated in steady state and transient conditions for two cases. In the first case the lakes are at identical surface water elevations and in the second case there is a small difference in surface water elevations between them. Simulation results from both cases indicate a direct relation between movement of hinge lines, which indicate changes in the direction of groundwater-lake seepage components, and the seasonal persistence and decline of a groundwater mound that exists between the two lakes. A comparison between steady-state simulation results for both cases indicates that a small difference in surface water elevation between two lakes results in differences between the relative proportions of groundwater-lake seepage components of the two lakes and is reflected in the difference in position of hinge line locations between the two lakes. A comparison between transient simulation results for both cases shows that the small difference in surface water elevations between two lakes results in a fairly constant difference in the rates of groundwater-lake seepage components. Hinge line positions between the two lakes also maintain a fairly constant difference in position during the course of the simulation. Lake level fluctuations produced by the model compare well with the range and seasonality of actual lake level fluctuations on which the modeled system is based. Simulation results establish the usefulness of the lake package addition to MODFLOW in simulating groundwaterlake interactions involving multiple lakes. Further, these results provide guidance in locating sampling wells because the bounds of hinge line traverse, for each lake, delineates a zone of transition characterized by groundwater-lake flow reversals. Advisor: David C. Gosselin