A hydrogeologic characterization of a sedge meadow, Van Patten Woods, Lake County, Illinois
Reid, Rebecca J.
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Delineating the controls of wetland hydrology for different hydrogeologic settings improves the success of wetland restoration and mitigation. This study examines a flow-through sedge meadow in Van Patten Woods Forest Preserve. The sedge meadow is located in a northward-sloping topographic low and overlies permeable fluvial sediments. To the west, a ridge composed mainly of silt and silty sand separates the wetland from the Des Plaines River flood plain. Lowpermeability till, forming a local topographic high, creates a no-flow boundary directly east of the wetland. The sedge meadow maintains high water levels in the spring and summer months from precipitation and transient local ground-water flow. During wet seasons, precipitation saturates the surrounding permeable units, increasing the hydraulic gradient and creating a new ground-water divide. Resulting local ground-water flow mimics the topography. When evapotranspiration exceeds precipitation, groundwater mounds dissipate and the water table drops; intermediate or regional ground-water flow is not significant enough to support high water levels. Calculations of ground-water flux using Darcy’s law with flow nets and a hydrologic budget produced inconsistent results. The main sources of errors were derived from hydraulic conductivity and the underestimation of evapotranspiration by the Thomthwaite method. In addition, calculations could not account for ground-water input from short-term rises of the water table in the surrounding upland area.