Hydrogeology of Hanging Bog State Preserve: The Role of Hillside Seeps in Draining the Iowan Surface

Along the margin of the Cedar River Valley, groundwater discharges from eroded and weathered glacial materials of the Iowan Surface to modern alluvial deposits of the valley floor. Hanging Bog State Preserve, located along this topographic, geologic, and hydrologic boundary, represents one such groundwater discharge location, in the form of a perennial hillside seep. Based on detailed monitoring of surface water and groundwater levels within the preserve for a one-year period, it is shown that a significant quantity of groundwater, collected from a disproportionately large recharge area, is funneled to the valley wall at this site and subsequently carried to the flood plain. The size of the recharge area presents a challenge to land owners in terms of protecting water quality in the preserve. More broadly, the hydrologic data from this study allow quantitative testing of previous assumptions about groundwater flow to bog and fen environments on the Iowan Surface that were based on geology and qualitative observation. Theoretical considerations and the limited occurrence of fens both locally and in the region both support the conclusion that the type of groundwater discharge seen at Hanging Bog State Preserve represents only a small piece of a continuum that exists along this and similar glacial-fluvial interfaces