Watershed Characterization Report for Indicator Bacteria in the Cotton Bayou Watershed Cotton Bayou Segment: 0801C Cotton Bayou November 2020 Cotton Bayou Watershed Characterization November 2020 Watershed Characterization Report for Indicator Bacteria in the Cotton Bayou Watershed Cotton Bayou Segment: 0801C Prepared For: Total Maximum Daily Load Program Texas Commission on Environmental Quality MC-203 P.O. Box 13087 Austin, Texas 78711-3087 Prepared By: Rachel Windham William Hoffman Thushara Ranatunga Houston-Galveston Area Council P.O. Box 22777 Houston, Texas 77227 November 2020 Cotton Bayou Watershed Characterization November 2020 Acknowledgements Funding for this study was provided by the United States Environmental Protection Agency through a grant to the Texas Commission on Environmental Quality. The Texas Commission on Environmental Quality is the lead agency for this study. Local stakeholders provided insights including historical background, technical advice and feedback as part of the preliminary outreach conducted for this project. i | P a g e Cotton Bayou Watershed Characterization November 2020 Table of Contents Watershed Characterization Report for Indicator Bacteria in the Cotton Bayou Watershed ............................................................................................................................ 1 Acknowledgements .............................................................................................................. i Table of Contents................................................................................................................. ii List of Figures ..................................................................................................................... iv List of Tables ....................................................................................................................... v List of Acronyms and Abbreviations .................................................................................. vi Section 1: Introduction ........................................................................................................ 1 1.1 Background ................................................................................................................. 1 1.2 Water Quality Standards ........................................................................................... 3 1.3 Contact Recreation and Bacteria ............................................................................... 5 1.4 Total Maximum Daily Load Program ........................................................................ 6 1.5 Characterization Report Purpose and Organization ................................................. 6 Section 2: Watershed Description ...................................................................................... 7 2.1 Description of the Cotton Bayou System ................................................................... 7 Segment Description .................................................................................................... 7 Stream Network ........................................................................................................... 9 Primary Tributary .................................................................................................... 9 Drainage Area/Watershed Delineation ....................................................................... 9 2.2 Watershed Climate and Environmental Characteristics ........................................ 12 Precipitation and Temperature ................................................................................. 12 Elevation .................................................................................................................... 13 Water Usage ............................................................................................................... 15 Soils ............................................................................................................................ 15 Ecoregions .................................................................................................................. 15 Local Political Geography .......................................................................................... 18 2.3 Watershed Population and Population Projections ................................................ 18 2.4 Land Cover ............................................................................................................... 20 Section 3: Review of Historical Data................................................................................. 22 3.1 Historical Data Sources Overview ........................................................................... 22 3.2 Wastewater Treatment Facility Discharge Monitoring Reports ............................ 22 Data Acquisition......................................................................................................... 22 DMR Data Review – Bacteria .................................................................................... 23 DMR Data Review – Other Parameters .................................................................... 23 ii | P a g e Cotton Bayou Watershed Characterization November 2020 3.3 Sanitary Sewer Overflow Reports ........................................................................... 25 Data Acquisition......................................................................................................... 25 3.4 Ambient Monitoring Data ....................................................................................... 25 Analysis of Enterococci Data ..................................................................................... 25 Analysis of Other Parameters .................................................................................... 29 3.5 Evaluating Flow and Enterococci Loading.............................................................. 29 Data Acquisition......................................................................................................... 30 Load Duration Curves for Cotton Bayou ................................................................... 30 Section 4: Potential Sources of Contamination ................................................................ 34 4.1 Identifying Potential Sources .................................................................................. 34 4.2 Regulated Sources ................................................................................................... 35 Domestic and Industrial Wastewater Treatment Facilities ...................................... 35 Sanitary Sewer Overflows .......................................................................................... 35 Dry Weather Discharges/Illicit Discharges ............................................................... 36 TCEQ/TPDES Water Quality General Permits ......................................................... 36 TPDES-Regulated Stormwater .................................................................................. 36 4.3 Unregulated Sources ............................................................................................... 37 Onsite Sewage Facilities............................................................................................. 37 Agriculture ................................................................................................................. 39 Domestic Pets ............................................................................................................. 39 Wildlife and Invasive Animals ................................................................................... 40 Section 5: Findings and Recommendations ..................................................................... 41 5.1 Summary .................................................................................................................. 41 5.2 Findings and Recommendations ............................................................................. 41 Data Analyses ............................................................................................................. 41 Stakeholder Involvement ........................................................................................... 41 Conclusions ................................................................................................................ 42 iii | P a g e Cotton Bayou Watershed Characterization November 2020 List of Figures Figure 1. Cotton Bayou Watershed ........................................................................... 2 Figure 2. Cotton Bayou and the Trinity River Basin ............................................ 8 Figure 3. Stream Network Diagram for Cotton Bayou ...................................... 10 Figure 4. Cotton Bayou Watershed Delineation .................................................. 11 Figure 5. Mean Monthly Temperature and Precipitation, NOAA Station GHCND:USC00410586 (1981 through 2010) ........................................................ 12 Figure 6. Elevation Change in the Cotton Bayou Watershed ........................... 14 Figure 7. Soils in the Cotton Bayou Watershed ................................................... 16 Figure 8. Cotton Bayou Watershed, Level IV Ecoregions .................................. 17 Figure 9. Political Geography of the Cotton Bayou Watershed ....................... 19 Figure 10. Land Cover in the Cotton Bayou Watershed .................................... 21 Figure 11. Wastewater