General Hydrologic Characteristics of Flow-Through Lakes & Wetlands
Original content source: Minnesota Metro Council, https://metrocouncil.org/Wastewater-Water/Publications-And-Resources/WATER-SUPPLY-PLANNING/Monitoring-Guidelines-Flow-Through-Lakes-and-Wetla.aspx
Flow-through lakes are surface expressions of the water table and are in direct hydraulic connection with the water-table aquifer. They receive inflows from groundwater along the upgradient shore of the lake and discharge flow to groundwater along the downgradient shore. In general, the net contribution of groundwater to the overall lake water balance is zero (although some net loss of groundwater from evaporation may take place). Flow-through lakes can have contributions of surface-water runoff into the lake but if that contribution is large, a flow-through lake might better be classified as a recharge lake. If the lake has an outlet of significance, a better classification would be a discharge lake.
Many lakes are flow-through lakes. The stage elevation of the lake moves up and down with the regional water table. During prolonged dry periods, the lake may drop a few feet. During extended wet periods, lake stage will rise. Depending upon lake bathymetry, these changes in lake stage (responding to water-table fluctuations) can be visually dramatic and can change the surface-water area of the lake. Because flow-through lakes are surface expressions of the water table, they are susceptible to regional groundwater pumping. Lakes have much higher storage properties than the surrounding aquifer media – therefore, lakes will dampen the effects of drawdown from pumping for a period of time and act as recharge sources to the aquifer. But over a longer period of time, the storage in the lake will be reduced in response to the overall lowering of the water table and the lake elevation will drop until a new hydraulic equilibrium is reached.
It is important to recognize that flow-through lakes are susceptible to climatic changes. A period of successive years of lower than average precipitation will tend to cause a drop in the water table and a corresponding drop in the lake stage. This drop in lake stage may have nothing to do with changes in regional pumping. However, regional pumping often increases in response to dry periods as more irrigation takes place. Differentiating the effects of pumping from climatic changes can be challenging.
Figure: Simulation graphic of a flow-through lake (regional scale and site scale).