SEDIMENT FLUXES FROM PITMAN CREEK, A TRIBUTARY OF THE GREEN RIVER IN WESTERN KENTUCKY

An analysis of suspended sediment flux from Pitman Creek was conducted in order to better understand the rates and patterns of sediment supply to the Green River. Water quality and sediment loads in the river are important concerns because Green River flows through Mammoth Cave National Park, and supports populations of threatened and endangered aquatic species. Water and sediment fluxes were estimated from data collected at a gauging station near the mouth of Pitman Creek. A water quality sonde provided records of turbidity and water temperature and river stage was measured with a pressure transducer and data logger. A rating curved based on discharge measurements at the site was used to convert stage records into discharge hydrographs. Turbidity readings were used to estimate suspended sediment concentrations based on data gathered by the USGS on the Green River in Mammoth Cave National Park and elsewhere. These data were then used to estimate instantaneous suspended sediment fluxes and total sediment loads for several storm events in 2006.

Preliminary analysis indicates that sediment load and discharge are related but are not simply proportional owing to the temporal variation in suspended sediment concentration. Sediment load increases at about the same rate as discharge but then sediment concentration and load decrease quickly while discharge decreases more gradually. So far 8 individual events have been analyzed that have had peak discharge ranging from 2.6 m3/sec to 45.6 m3/sec and total sediment flux per event ranging from 29,000 kg to 9,931,167 kg. The total sediment flux is directly related to the peak discharge and the duration of the event. For the first six months of 2006 total estimated sediment flux for Pitman Creek is 12.2 million kg. This sediment load amounts to 6% of the estimated historical average annual load of the Green River at Munfordville, consistent with the 10% ratio of Pitman Creek to Green River at Munfordville catchment areas.