Utilizing Watershed-Based Planning as a Tool to Protect Source Water: A Case Study from the Lower Caw Caw Swamp

Abstract

A watershed-based plan (WBP) is an example of a management tool that addresses nonpoint sources of pollution that affect surface water quality. We apply a simple spreadsheet tool to the Lower Caw Caw Swamp watershed in Orangeburg, South Carolina, to quantify the impact of modest management practices on water quality, and to examine how climate and land-use change could affect water quality in future decades. Three separate climate and land use scenarios are used to measure annual pollutant loads in the basin. Our analysis shows that E. coli loads in current conditions are largely attributed to anthropogenic sources of bacteria and have the potential to be reduced by about 15% with the implementation of structural stormwater best management practices (such as stormwater ponds and bioretention) and non-structural strategies (programmatic changes such as rooftop disconnection in residential areas and improving on-site sewage disposal systems). Modeled E. coli loads in future scenarios were almost twice the current loads as a result of a warmer climate and greater volumes of stormwater runoff generated by additional impervious surfaces and increased annual precipitation. These findings are consistent with others investigating water quality using future climate and land-use scenarios. We demonstrate that a simple watershed model can provide the basis for a watershed-based plan (WBP) to address nonpoint sources of pollution that affect surface water quality. This specific WBP analysis will be used to make recommendations to protect the City of Orangeburg’s source of drinking water along the North Fork of the Edisto River.