This shapefile represents the delineation of the Christina Basin, HUC 02040205, into 70 subbasins that can be grouped into four larger watersheds: Brandywine Creek, Red Clay Creek, White Clay Creek, and Christina River. These subbasins were created and used as an input to the Hydrological Simulation Program - Fortran (HSPF) model by the USGS for the purpose of simulating hydrologic and water quality conditions in the Christina Basin (Pennsylvania and Delaware). The US Environmental Protection Agency assigned baseline loads and locations for nitrogen, phosphorus, sediment, and bacteria for these subbasins in the Christina Basin TMDLs.

This shapefile was transmitted to Chester County Water Resources Authority (CCWRA) by USGS in June, 2009. The features contained in this shapefile retain all geometric attributes as the source shapefile, however several extraneous fields were deleted. The four fields at the end of the attribute table have been added based on whether there is a pollutant reduction requirement based on tables presented in the following 2 TMDL reports:

1. Revisions to Total Maximum Daily Loads for Nutrient and Low Dissolved Oxygen Under High-Flow Conditions Christina River Basin, Pennsylvania, Delaware, and Maryland, Section 4. TMDL Methodology and Calculation, September 2006.

2. Total Maximum Daily Loads for Bacteria and Sediment in the Christina River Basin, Pennsylvania, Delaware, and Maryland, Section 4. TMDL Methodology and Calculation", September 2006

For more information about this data refer to the USGS documents listed in the Credits, below.

Additional information about the Christina River Basin, including links to the Christina Basin TMDL reports, can be found at the following website:

http://www.chesco.org/index.aspx?NID=2121

The text below is from the abstract and introduction of the USGS reports cited in the Credits-

The Christina River Basin, which includes White Clay Creek (drainage area of 108 mi2), Red Clay Creek (54 mi2), and Brandywine Creek (327 mi2), drains approximately 565 mi2 in southeastern Pennsylvania, northern Delaware, and a small part of northeastern Maryland. The Christina River and its tributaries provide drinking water for more than 40 percent of the residents of Chester County, Pa., and more than 50 percent of the residents of New Castle County, Del.

The HSPF model may be used to evaluate options for managing contaminants from nonpoint and point sources and can provide a comprehensive method of calculating nonpoint-source loads to meet total maximum daily load (TMDL) requirements.

For the HSPF model...Brandywine Creek ...was subdivided into 35 reaches draining areas that ranged from 0.6 to 18 mi2.; White Clay Creek was subdivided into 17 reaches draining areas that ranged from 1.37 to 13 mi2; Red ClayCreek was subdivided into 9 reaches draining areas that ranged from 1.7to 10 mi2.