Simulating the influence of two shallow, flow-through lakes on a groundwater system: implications for groundwater mounds and hinge lines

Groundwater mounds and hinge lines are important features related to the in teraction of groundwater and takes. In contrast to the transient formation of groundwater mounds, numerical simulations indicate that permanent ground water mounds form between closely spaced lakes as the natural consequence o f adding two net sinks to a groundwater flow system. The location of the gr oundwater mound and the position of the hinge lines between the two lakes a re intimately related. As the position of the mound changes there is a corr esponding shift in the position of the hinge line. This results in a change in the ratio of groundwater inflow to outflow (Q(i)/Q(o)) for the lake. Th e response of the lake is an increase or decrease in the take level. Our si mulations indicate that the movement of the hinge line in a natural system is a consequence of the dynamic interrelationships between recharge, the sl ope of the water table upgradient and downgradient of the lake, and the los s of water from the lake by evaporation. The extent of the seasonal movemen t of the hinge line will vary from one year to the next depending on local changes in the magnitude of the hydrologic variables.