Stockley Branch flows into Cow Bridge Branch watershed, which spans 28,676 acres and is located in the Indian River watershed in southeastern Sussex County. The Indian River Bay watershed makes up one of three of Delaware’s interconnected Inland Bays (Rehoboth Bay, Indian River Bay, and Little Assawoman Bay).
Runoff from agricultural and residential areas caused high bacteria levels in Delaware’s Stockley Branch. As a result, DNREC added Stockley Branch to the 303(d) List for bacteria. Watershed stakeholders provided technical assistance and installed agricultural BMPs in the watershed, causing bacteria levels to decline in the stream. As a result, DNREC removed the Stockley Branch from the state’s 2008 list of impaired waters for bacteria.
Monitoring data collected in the late 1990s indicated that Stockley Branch failed to meet the state’s Enterococcus bacteria numeric criterion, which requires the annual geometric mean to be less than 100 colony-forming units per 100 milliliters. Stockley Branch did not support its freshwater primary contact designated use, prompting the state to add it to Delaware’s 303(d) List for bacteria and nutrients.
In 1998 and 2006, the EPA developed TMDLs to address the nutrients and bacteria loading, respectively, throughout the Indian River watershed. The 1998 TMDL required an 85% reduction in nitrogen and a 65% reduction in phosphorus loadings. The 2006 TMDL required that the overall bacteria loading be reduced by 42% from the 2000–2005 baseline levels in freshwater regions of the Inland Bays drainage basin, which includes the Indian River basin.
Primary sources of NPS pollution in the watershed likely include runoff from agricultural activities (e.g., fertilizer and manure application), concentrated areas of animal production, and urban activities.
The Sussex Conservation District offered technical assistance to the farming community by providing nutrient management planning and cost-share funding for agricultural BMPs.
Conservation Reserve Enhancement Program BMPs:
Urban BMPs installed between 2011 and 2016:
Bacteria levels have decreased in response to the more than 10 years of water quality protection and restoration efforts. DNREC collected monitoring data at STORET Station 308281 in Cow Bridge Branch between September 2002 and August 2007. The geometric mean of the 31 samples collected over the 5-year period was 59 colony-forming units per 100 milliliters. This was well below Delaware’s freshwater bacteria water quality standard, so DNREC removed the 8.23 mile segment of Stockley Branch (DE-140-006) from the state’s list of impaired waters in 2008 per its Assessment and Listing Methodology. The Draft 2018 Integrated Report showed that the segment continued to meet the applicable water quality standards for bacteria.