Big Creek Watershed GIS, Hydrologic/Water Quality Monitoring & Analysis

The Posey County Soil and Water Conservation District (SWCD) and Drainage Board contracted cbec to conduct a yearlong hydrologic and water quality monitoring study within the Big Creek Watershed in Posey County, Indiana. The hydrologic and water quality dataset generated from this study were used to prioritize the Big Creek subwatersheds based upon sediment, nutrient, and E. coli loads. These datasets and analysis are intended to assist the Posey County Drainage Board and the SWCD to target future conservation and stabilization efforts in specific subwatersheds with the goal of reducing pollutant loads and minimizing future maintenance expenditures.

For this study, stream gaging was conducted at 5 monitoring sites to develop of a continuous dataset of water level, streamflow and sediment discharge for a 1‐year period. This dataset was developed by rating/indexing continuous stage and turbidity data to event‐based measurements of streamflow and suspended sediment discharge. In addition, event‐based water quality sampling for nutrients and E. coli. was conducted at each monitoring site. The continuous and instantaneous datasets generated from this effort were analyzed to quantify the pollutant loads for each subwatershed. Each subwatershed was then ranked based upon these loadings to identify source areas for future conservation/stabilization efforts.

The monitoring data collected for this study provides insight into the pollutant source areas within the watershed. Comparing the collected data to reference values developed by the United States Environmental Protection Agency (EPA) for Big Creek’s ecoregion indicate that all sites exceed regional reference levels for all constituents measured. While all monitoring sites exhibited high levels of pollutant loads, the headwater drainages appeared to be disproportionate contributors of all pollutants that were monitored. Additionally, temporal variability indicate that seasonal land use practices, such as fertilizer application and tillage practices, are likely contributing to elevated pollutant loads.

Morphological analysis of the creek channels derived from a comparison between 2013 LiDAR and ground surveys indicate significant increases in channel size (with and depth) over the 7‐year timeframe, indicating channel degradation and bank erosion are another potential source for elevated sediment loads. Analysis prepared for this study provide opportunities for targeted management efforts to effectively address nonpoint sources of pollution within the Big Creek Watershed and help to understand the significance of sediment, nutrient, and bacteria loading from tributaries to the Wabash River, which has been shown to be one of the most significant sources of pollutants contributing to hypoxia in the Gulf of Mexico.

Waterbody / Watershed

Big Creek Watershed