Most lakes and streams exchange water with the groundwater system. However, wetlands underlain by low permeability hydric soils can be disconnected from groundwater in settings dominated by surface runoff, precipitation, and high evaporation and evapotranspiration (Figure 48).
Disconnected wetlands occur when precipitation and surface runoff fill topographic depressions with water. These water-filled depressions promote wetland vegetation and soil development. Percolation to an underlying groundwater system is inhibited by the low permeability soils and high rates of direct evaporation and evapotranspiration (Figure 48).
Figure 48 – Schematic cross section and map view of a disconnected wetland. Hydric soil saturation and the wetland water level varies seasonally. Equipotential lines and relative head values are in black. Groundwater flow lines are in blue. Isotropic and homogeneous conditions are assumed. A disconnected wetland occurs when direct evaporation and evapotranspiration exceeds downward movement of wetland water. Monitoring wells are open at the bottom. The water table remains below the wetland soils. In this setting no exchange occurs. a) Cross sectional view of a disconnected wetland. Blue dashed arrow represents groundwater flow beneath the wetland. b) Map view of a disconnected wetland (Woessner, 2020).
