Statewide Decision Support System for Potential E. Coli Load Management in Texas Watersheds

Section 303(d) of the Federal Clean Water Act cites bacterial pathogens as one of the most common cause of impairment in the streams and other water bodies in the state of Texas and the number of bacteria impaired water bodies in Texas have been on the rise with a 57 percent increase in the number between 2004 and 2006. As development of Total Maximum Daily Loads (TMDLs) are mandatory to be prepared for each impaired water body by the United States Environmental Protection Agency (USEPA) regulations, the Texas Commission on Environmental Quality (TCEQ) and other institutions in Texas work together to develop TMDLs and Watershed Protection Plans (WPPs) for these impaired water bodies to identify potential sources of bacteria and provide strategies and best management practices to reduce bacterial pathogens in water. The GIS based Spatially Explicit Load Enrichment Calculation Tool (SELECT) is used in most TMDL reports to identify potential sources of bacteria in a watershed and high priority areas affected by bacterial contamination. However, the tool requires tedious process of collecting data from various sources, developing model in ArcGIS and running the model several times during the development of TMDL reports and watershed protection plans. The process can be time consuming and requires sufficient knowledge of GIS software. The Texas Watershed Characterization System (TWCS), a web-based user-friendly interface was developed using R Studio and R Shiny application, for estimation of potential sources of fecal coliform and develop management scenarios in Texas watersheds through pre-loaded datasets and user-editable inputs. The tool allows users to work on three spatial resolutions (HUC 8, HUC 10, and HUC 12) to calculate total potential Escherichia coli in HUC 12 sub-watersheds within the selected watershed and produce interactive charts and maps within a few minutes. Along with the calculation of E. coli loads, users can also develop management scenarios to look at load reduction strategies in the high priority sub-watersheds. This study was done to demonstrate the workflow of TWCS and estimate potential E. coli loads for the La Nana Bayou watershed in Texas using the TWCS web-interface