HYDROLOGIC ANALYSIS OF GOOSE POND, COLUMBIA COUNTY, WISCONSIN

Goose Pond is located in a closed drainage basin in southern Columbia County, Wisconsin and provides habitat for numerous bird species including tundra swans and peregrine falcons. A hydrologic analysis of Goose Pond was completed to estimate changes in the hydrologic budget and pond elevation resulting from a proposed ethanol plant discharging approximately 62,000 gallons per day to a ditch that discharges to the pond. Because of the pending planning commission meeting, it was imperative that the analysis be completed in less than a month. Since direct long-term measurements could not be made or extensive field investigation of the 8 square mile watershed conducted, regional data were used to estimate an average annual water budget of Goose Pond approximately 60 acres in area. Isolated from the underlying water table by low permeability alluvial-colluvial sediments, the pond is expected to lose water via seepage throughout the year potentially recharging the groundwater system. The long-term annual seepage flow was calculated as a residual in the water balance equation since the long-term annual change in storage was assumed to be zero. The average unit seepage rate was estimated using the annual water balance results and by direct calculation using pond stage records from June 1988 when no rainfall occurred. The unit seepage rates and the pond elevation-area relations were then used to evaluate the potential pond stages.

Results indicated that the present water balance was dominated by surface water runoff inflow (88 per cent) and seepage outflow (91 per cent). The proposed ethanol plant discharge was estimated to contribute approximately 4 per cent of the inflows. Increases in pond levels based on unit seepage rates resulting from the proposed ethanol plant discharge ranged from 0.1 feet to 0.7 feet depending on the initial pond elevation. The analysis indicated that the extreme variability in the month-to-month and year-to-year runoff is what produced the prairie pothole condition allowing the pond to dry out in some years. Despite the fact that the pond is dominated by surface water runoff inflow and seepage outflow, the small ethanol plant discharge may significantly impact the hydroperiod and pond ecology by limiting the ability of the pond to dry out during drought conditions.