An Innovative Model for Watershed Management and the Development of Narrative TMDLs

Abstract

The State of Georgia ’s water quality standards are intended to provide protection for designated uses. TMDL (Total Maximum Daily Load) targets are based on these water quality standards. In cases where numeric water quality standards are not available, narrative standards are used for developing TMDLs. These narrative standards cannot be allocated, hence, there is a need to link the narrative standards to pollutant loads generated from the watershed. The WISE (Watershed Improvements through Statistical Evaluations) Model was designed to link the watershed pollutant loads to narrative standards, i.e., biological indices. Specific biological standards based on biological indices such as Index of Biological Integrity (IBI), Fish Score, and Invertebrate Community Index (ICI) are used as measurement tools and are linked to various pollutant loads from the watershed. The WISE model allows users to view various scenarios based on desired goals in order to make technically sound decisions for developing narrative TMDLs. The “what-if” scenarios allow users to screen various combinations of best management practices (BMPs) and present a reality check by way of cost-benefit analyses. The model also allows local governments to track new developments and control the amount of pollutants carried by runoff from the site by using BMPs.