DEVELOPING A TURBIDITY-SUSPENDED SEDIMENT RATING CURVE FOR BUCK CREEK, SPRINGFIELD, OHIO
Suspended sediment samples were collected adjacent a water quality station using an ISCO 3700 Flow Sampler during storm events, filtered using a Millipore funnel and Zefon 934-AH glass microfiber filters, and weighed to determine suspended sediment concentration. The relation between suspended sediment concentration (SSC), in mg/l, and turbidity (T) in nephalometric turbidity units (NTU) follows a power function SSC = 0.0018T0.95 (R2=0.85). This curve indicates a direct positive relationship, as the turbidity increases, so does the suspended sediment.
Hydrographs of storm events in the Buck Creek watershed are double-peaked, representing an initial influx of stormwater from an urbanized area of the watershed, which is located nearer the outlet, and a secondary influx of water from a predominantly agricultural part of the watershed. Turbidity parallels this response and exhibits hysteresis. Turbidity representing agricultural input displays a clockwise hysteresis as expected, higher on the rising limb of the hydrograph and lower on the falling limb. Turbidity associated with the urban part of the hydrograph shows a counter-clockwise hysteresis which we attribute to delayed contributions from combined sewer overflows.