Evaluation of Natural Channel Design Versus Traditional Stormwater Infrastructure in Texas

Table of Contents 1. Executive Summary ............................................................................................................................ 1 2. Introduction ......................................................................................................................................... 7 2.1. Background ................................................................................................................................... 7 2.2. Study Goals and Objectives ........................................................................................................... 8 2.3. Channel Evolution and Erosion Processes .................................................................................... 9 2.4. Rosgen Classification System Guide ............................................................................................ 12 2.5. The Spectrum of Channel Management Options ....................................................................... 12 2.5.1. Priority 1: Establish Bankfull Stage at the Historical Floodplain Elevation ........................ 13 2.5.2. Priority 2: Create a New Floodplain and Stream Pattern with the Stream Bed Remaining at the Present Elevation ...................................................................................................................... 14 2.5.3. Priority 3: Widen the Floodplain at the Existing Bankfull Elevation .................................. 15 2.5.4. Priority 4: Stabilize Existing Streambanks in Place .............................................................. 15 2.6. Overview of Traditional Stormwater Infrastructure ................................................................... 15 2.7. Overview of Low Impact Development (LID) .............................................................................. 17 2.8. Regulatory Drivers ....................................................................................................................... 21 3. Study Methodology ........................................................................................................................... 24 3.1. Literature Review ........................................................................................................................ 24 3.2. Recent Experiences in Texas ....................................................................................................... 24 3.2.1. Houston Area ...................................................................................................................... 24 3.2.2. Dallas/Ft Worth and North Texas ....................................................................................... 28 3.2.3. San Antonio ......................................................................................................................... 29 3.2.4. Austin .................................................................................................................................. 30 4. Objective 1: Are NCD Techniques appropriate for use in Texas? ............................................... 35 4.1. Methodology ............................................................................................................................... 35 4.2. Texas Physiographic Provinces and Use of NCD in Similar Physiographic Provinces of the US .. 36 4.2.1. Texas Coastal Plains with Gulf and Atlantic Coast Regions ................................................. 37 4.2.2. West Texas (Basin and Range and High Plains) with Southwest US ................................... 39 4.2.3. North Texas (North Central Plains and Grand Prairie) with Midwest ................................. 40 4.2.4. Central Texas Uplift and Edwards Plateau with Karst areas ............................................... 42 4.3. Applicability of NCD in Texas ...................................................................................................... 43 I 4.3.1. Urban vs. Rural .................................................................................................................... 43 4.3.2. Flowchart (Applicability Tree) ............................................................................................. 46 5. Objective 2: How does NCD and traditional stormwater practices compare regarding ecological and water quality benefits? .................................................................................................... 48 5.1. TMDLs in Texas Metropolitan Areas ........................................................................................... 49 5.2. Processes or Mechanisms of Removal ........................................................................................ 50 5.3. Pollutant Removal Performance ................................................................................................. 50 5.3.1. Nutrients ............................................................................................................................. 50 5.3.2. Total Suspended Solids (TSS) .............................................................................................. 52 5.3.3. Bacteria ............................................................................................................................... 53 5.4. Ecological Considerations ........................................................................................................... 54 5.4.1. Riffle/Run/Pool/Glide and Fish Habitat .............................................................................. 54 5.4.2. Macroinvertebrates ............................................................................................................ 55 5.4.3. Riparian Wildlife Habitat and Corridor ............................................................................... 56 6. Objective 3: What is the difference in cost between NCD and more traditional stormwater conveyance projects? ................................................................................................................................ 57 6.1. Cost Comparison of Channel Management Options .................................................................. 57 6.1.1. Right‐of‐Way/Easement Acquisition ................................................................................... 59 6.1.2. Design and Total Construction Costs .................................................................................. 60 6.2. Direct Comparison of Costs ......................................................................................................... 62 6.2.1. NCD vs Traditional Costs for Stream Order 4 or Greater .................................................... 65 6.2.2. NCD Versus Traditional Cost for Stream Order 3 or Less .................................................... 66 6.2.3. NCD versus Traditional Methods Comparative Conclusions .............................................. 66 6.3. Economic Benefits of NCD Projects ............................................................................................ 66 6.3.1. Economic Framework for Stream Restoration .................................................................... 66 6.3.2. Methods of Quantification of Economic Benefits of Stream Restoration Projects ............ 67 6.3.3. Case Studies of the Evaluation of the Economic Benefits of NCD ...................................... 69 7. Potential Funding Mechanisms for NCD ........................................................................................ 74 8. Conclusions and Recommendations ................................................................................................ 75 8.1. Applicability for Use of NCD Techniques in Texas ...................................................................... 75 8.2. Ecological and Water Quality Benefits of NCD Techniques over Traditional Stormwater Practices .................................................................................................................................................. 76 II 8.3. Cost Difference between NCD and Traditional Stormwater Projects ......................................... 77 8.4. Recommendations ...................................................................................................................... 78 8.5. Webinar ....................................................................................................................................... 79 9. Acknowledgments ............................................................................................................................. 80 10. References .......................................................................................................................................... 81 LIST OF APPENDICES Appendix A – EPA Regulatory Programs Appendix B – NCD in the Houston Area Appendix C – Landscape-based BMP Summary Table from Watershed Protection for Texas Reservoirs: Addressing Sedimentation and Water Quality Risks (TWDB contract #:1004831120) Appendix D – Cost Trend Analysis of NCD Versus Appendix E – Rosgen Classification System Appendix F – Draft Report Comments and Responses LIST OF TABLES Table 1: Four Priority Approaches to Stream Restoration Objectives ........................................................ 13 Table 2: Summary of LID Removal Performance ...................................................................................... 20 Table 3: Summary of NCD Projects in the Houston Area .......................................................................... 26 Table 4: Summary of Priority

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