Mission and Aransas Rivers Watershed Protection Plan - Draft Mission and Aransas River Watersheds Watershed Protection Plan A document developed by the stakeholders of the Mission and Aransas Rivers watersheds to restore and protect water quality in Mission River Tidal (Segment 2001), Aransas River Tidal (Segment 2003), Mission River Above Tidal (Segment 2002), Aransas River Above Tidal (Segment 2004), and Poesta Creek (Segment 2004B). Mission and Aransas Rivers Watershed Protection Plan Mission and Aransas Rivers Watershed Protection Plan Authored and prepared by: Texas Water Resources Institute Texas Water Resources Institute Technical Report 2019 Funding support for this project provided by the Texas Commission on Environmental Quality through a grant from the United States Environmental Protection Agency. i Mission and Aransas Rivers Watershed Protection Plan Acknowledgements This document presents the strategy developed by the stakeholders of the Mission and Aransas Rivers watersheds to restore and protect water quality in the Mission and Aransas Rivers and the waterbodies that flow into them. Local stakeholders dedicated considerable time and effort in discussing the watershed, influences on water quality, and developing management measures to address water quality concerns. The ultimate success of the Mission and Aransas Rivers Watershed Protection Plan depends on the current and continued engagement of local stakeholders with technical and financial support from regional, state, and federal agencies. Special appreciation is extended to the many watershed landowners and residents who attended the numerous meetings and events to provide direct input to the plan. The direct involvement of landowners and residents was critical to ensuring the plan included feasible management measures that address sources of water quality impairment in the watershed. The time and effort of landowners and residents are greatly appreciated and are reflected in the contents of this plan. Agency support and input was an integral part of the Watershed Protection Plan (WPP) development process. In particular, the following agencies provided technical guidance and willingness to provide specialized knowledge on several topics: Bee Soil and Water Conservation District Goliad Soil and Water Conservation District Copano Bay Soil and Water Conservation District San Patricio Soil and Water Conservation District Texas A&M AgriLife Research and Extension Service Texas Commission on Environmental Quality Texas General Land Office Texas Parks and Wildlife Department Coastal Bend Bays and Estuaries Program Texas State Soil and Water Conservation Board USDA Natural Resources Conservation Service ii Mission and Aransas Rivers Watershed Protection Plan Contents Acknowledgements .................................................................................................................................... ii Table of Figures ........................................................................................................................................ vii Table of Tables .......................................................................................................................................... ix Abbreviations ............................................................................................................................................. xi Executive Summary ................................................................................................................................... 1 Problem Statement ................................................................................................................................ 1 Action Taken ........................................................................................................................................... 1 Watershed Protection Plan Overview ................................................................................................. 1 Pollutant Reductions .......................................................................................................................... 2 Recommended Actions ..................................................................................................................... 2 Goals .................................................................................................................................................... 4 1 Watershed Management ................................................................................................................. 5 1.1 Introduction .................................................................................................................................. 5 1.1 Watersheds and Water Quality ................................................................................................ 5 1.2 The Watershed Approach ......................................................................................................... 5 1.3 Watershed Protection Plan ....................................................................................................... 6 1.4 Adaptive Management ............................................................................................................... 6 1.5 Education and Outreach ........................................................................................................... 6 2 Characterization of the Mission and Aransas Rivers Watersheds ..................................... 7 2.1 Introduction .................................................................................................................................. 7 2.2 Description of the Watershed and Waterbodies .................................................................... 7 2.3 Soils and Topography ................................................................................................................ 8 2.4 Ecoregion................................................................................................................................... 11 2.5 Land Use and Land Cover ...................................................................................................... 12 2.6 Climate ....................................................................................................................................... 13 2.7 Demographics ........................................................................................................................... 15 3 Water Quality ................................................................................................................................... 18 3.1 Introduction ................................................................................................................................ 18 3.2 Bacteria ...................................................................................................................................... 21 3.3 Water Quality Concerns .......................................................................................................... 23 3.3.1 Dissolved Oxygen ............................................................................................................ 23 3.3.2 Nutrients ............................................................................................................................. 24 iii Mission and Aransas Rivers Watershed Protection Plan 3.4 Flow ............................................................................................................................................ 24 3.5 Potential Sources of Water Quality Issues ........................................................................... 26 3.5.1 Domestic Livestock .......................................................................................................... 26 3.5.2 Wildlife and Feral Hogs ................................................................................................... 27 3.5.3 Domestic Pets ................................................................................................................... 27 3.5.4 On-Site Sewage Facilities ............................................................................................... 28 3.5.5 Permitted Discharges ...................................................................................................... 30 3.5.6 Unauthorized Discharges ................................................................................................ 37 3.5.7 Illicit Discharges ................................................................................................................ 41 3.6 Water Quality Summary .......................................................................................................... 41 4 Pollutant Source Assessment .................................................................................................... 43 4.1 Introduction ................................................................................................................................ 43 4.2 Source and Load Determination ............................................................................................ 43 4.2.1 Modified Load Duration Curves ...................................................................................... 43 4.2.2 Traditional Load Duration Curves .................................................................................. 46 4.3 Pollutant Source Load Estimates ........................................................................................... 49 4.3.1 GIS Analysis