The hydrogeology of a degraded, invasive species dominated, wetland in Liberty Park, Twinsburg, Ohio, located within the glaciated Allegheny Plateau region was investigated. This wetland, along with Pond Brook, the major stream draining the park, has been selected for a comprehensive restoration. Recent hydrologic modifications such as ditching, dredging, and channelization of Pond Brook adversely affected the hydrology of the natural riparian wetlands.
Fifteen shallow monitoring wells were installed in the 39-acre wetland cell. Continuous water-level data loggers with an interface for data-downloading to a host computer were installed in Pond Brook and five monitoring wells in the degraded wetland. The remaining wells were hand-monitored with a water-level probe. Average depth to water in May, 2006 was 94 cm. Hydrographs show that immediately after a precipitation event, the water level of Pond Brook rises rapidly, and then returns to normal base flow in approximately two days. Rapid fluctuations in water level were also observed in the monitoring wells, which reflect those of the stream. The geology and hydrologic setting of Wetland Cell 1 suggests that treated effluent water released into Ditch 1 (which is at hydraulic upgradient) flows through preferential high permeability units (peat and sand units) into Cell 1 and finally into Pond Brook which acts as a sink to the Ditch 1 source. These results suggest that the wetland is hydrologically linked directly to Pond Brook.
Analysis of a 17.1m (56 ft) sediment boring from the degraded wetland cell shows that there are two main stratigraphic layers, organic-rich deposits (0-1.8 m) and lacustrine clays and diamicts (1.8-17.1 m). Discontinuous lenses of peat and sand were observed in the top 1. 8 m. Statistical analysis of the upper (1.8-8.5 m) and lower (8.5-17.1 m) parts of the lacustrine clays and diamicts show significant differences in their clay, silt, calcite and dolomite contents at the 5% level of significance whereas the sand and total carbonate (calcite plus dolomite) contents are same. The hydrologic connection is attributed to the permeable sand and peat intercalations and fractures in the clays and diamicts. The near surface geology of the area is interpreted to be a glacial topography that was drowned in a post-glacial lake. The design of the restoration constructional works should take into account the direct hydrologic connection between Pond Brook and the modified wetland.