WATERSHED DELINEATION FOR CONTAMINANTS IN THE PORTER CREEK WATERSHED

Porter Creek in Cuyahoga County, Ohio contains high densities of Escherichia coli and plays a major role in transporting bacteria pollution to Huntington Beach, on the Lake Erie shoreline. Closer inspection of the storm-sewershed showed high densities of E. coli draining from storm drains directly into Porter Creek, whose outlet is in close proximity to the beach.

To identify areas in the watershed which are significant contributors to concentrations in the creek, a GIS exercise was conducted to map drainages feeding into storm drains throughout the towns of Bay Village and Westlake. Using the TOPAZ delineation technique in the WMS software package and storm-sewer maps of each town, a combination of 2.5 and 10 foot LiDAR data from OSIP was used to map drainage patterns of 28 outfalls and determine the area drained by each outfall. The drainage areas were then used to identify the sub-watersheds responsible for providing the highest densities of E. coliper area.

Of the 28 outfalls sampled, 22 had storm-sewershed basins of sufficient size to allow further analysis, with the basins ranging from 25.06 square kilometers to 10 square meters in size. Within these areas, concentrations of E. coli were found to range between 0 and 1,687,308 colonies/ 100 ml/ in of rain/ square kilometer.

Policy makers may employ this method in areas facing high pollutant discharge in rivers and streams, allowing them to target problem areas when they have limited resources.