HYDROLOGIC AND WATER-QUALITY IMPACTS OF URBANIZATION ON TRIBUTARY STREAMS

We quantified hydrologic and water-quality impacts to Hamilton Ditch (HD) and Clover Groft Ditch (CGD), two adjacent streams tributary to Big Darby Creek (BDC) in central Ohio. The two areas are similar in topography, precipitation and drainage, however the HD watershed is dominantly agricultural and CGD watershed is undergoing development. Our hydrologic data consist of stream discharge, storm recurrence intervals, and groundwater levels. The water-quality data consist of major ion and nitrate concentrations from samples we collected from the streams. Analysis of hydrologic and water-quality data indicates that increased peak stream discharges and increased runoff at the expense of baseflow accompany increased watershed urbanization. The shape of the discharge hydrographs during peak flow events distinguishes the two streams: CGD reflects storms with a sharper rise and fall of peak discharges than in HD. In addition, overall stream discharge in HD is lower than in CGD. Total alkalinity and calcium concentrations in stream water serve as a proxy for the amount of baseflow. Stream water in the agricultural watershed, HD, has higher concentrations of calcium and total alkalinity than in the developed CGD watershed. In addition, the nitrate concentrations are higher in HD than CGD. Thus the water-quality data confirm that the developed watershed has an increased runoff component to streamflow.