Table of Contents 1. Executive Summary ................................................................................................................ 9 2. Introduction ........................................................................................................................... 14 2.1 General ........................................................................................................................... 14 2.2 Objective and Scope ....................................................................................................... 15 2.2.1 Report Organization ................................................................................................ 16 2.3 Watershed Description ................................................................................................... 17 2.3.1 Topography ............................................................................................................. 17 2.3.2 Soil Characteristics ................................................................................................. 17 2.3.3 Climate .................................................................................................................... 17 2.4 History of Flooding ........................................................................................................ 17 2.4.1 Southeast Texas Hurricane History ........................................................................ 17 2.4.2 Response to Hurricane Carla .................................................................................. 19 2.5 Information Collection ................................................................................................... 19 2.5.1 General .................................................................................................................... 19 2.5.2 Public Meetings ...................................................................................................... 20 2.5.3 Stakeholder Process ................................................................................................ 20 3. Design Parameter Identification ........................................................................................... 21 3.1 Surveying ....................................................................................................................... 21 3.2 System-wide Level of Protection ................................................................................... 21 3.2.1 Protection Level for Feasibility Study .................................................................... 21 3.2.2 Design Event for Storm Surge Protection ............................................................... 22 3.2.3 Sea Level Rise......................................................................................................... 26 3.3 Hydrologic & Hydraulic Parameters for Internal Drainage Systems ............................. 27 3.3.1 Design rainfall ......................................................................................................... 27 3.3.2 Coincidental rainfall................................................................................................ 28 3.3.3 Drainage Analysis (large basins) ............................................................................ 28 3.3.4 Pump Stations ......................................................................................................... 29 3.3.5 Tidal Boundary Conditions ..................................................................................... 29 3.4 Levee Cross Section Design ........................................................................................... 29 3.5 Flood Wall Design ......................................................................................................... 31 3.6 Transportation Considerations ....................................................................................... 32 3.6.1 Raised-Profile Crossings ......................................................................................... 32 3.6.2 Gated Closures ........................................................................................................ 33 2 3.6.3 TxDOT Coordination .............................................................................................. 34 3.6.4 County and City Coordination ................................................................................ 34 3.6.5 Private Street and Driveway Owner Coordination ................................................. 34 3.6.6 Railroad Coordination ............................................................................................. 35 3.7 Right-of-Way Considerations ........................................................................................ 35 3.8 Geotechnical ................................................................................................................... 35 3.9 Coastal Processes ........................................................................................................... 36 3.9.1 Coastal Design Parameters ..................................................................................... 37 3.10 Environmental Considerations ................................................................................... 39 3.11 System Design Life .................................................................................................... 39 3.12 Navigation Considerations ......................................................................................... 39 3.13 Potential Floodplain Fill and Floodway Encroachments ............................................ 41 3.13.1 Floodplain Fill ......................................................................................................... 41 3.13.2 Floodway Encroachments ....................................................................................... 41 3.13.3 Impact Analysis ...................................................................................................... 42 3.13.4 CLOMR/LOMR ...................................................................................................... 42 4. Project Alternatives and Evaluations .................................................................................... 44 4.1 Preliminary Considerations ............................................................................................ 44 4.1.1 Alternatives ............................................................................................................. 44 4.1.2 Protection System Features/Strategies .................................................................... 44 4.2 Description of Alternatives Investigated ........................................................................ 45 4.2.1 No-Action Alternative ............................................................................................ 45 4.2.2 County-Wide Protection Sabine River and East Bank of Neches River ................ 45 4.2.3 Protection System on the East and West Bank of the Neches River ...................... 46 4.2.4 County-Wide Protection with DD7 System Tie-in ................................................. 47 4.2.5 Sabine River Crossing............................................................................................. 47 4.2.6 Industrial Complex Protection System ................................................................... 48 4.3 Description and discussion of Alternatives Evaluation Process .................................... 50 5. Preliminary Design ............................................................................................................... 51 5.1 Levee and Floodwall Design .......................................................................................... 51 5.1.1 Height Determination.............................................................................................. 51 5.1.2 Earthen Levee Locations and Design ..................................................................... 52 5.1.3 Flood Wall Locations and Design........................................................................... 52 5.1.4 Right of Way Requirements.................................................................................... 52 5.2 Major channel / river crossings ...................................................................................... 53 3 5.2.1 Neches River ........................................................................................................... 53 5.2.2 Cow Bayou.............................................................................................................. 54 5.2.3 Adams Bayou .......................................................................................................... 54 5.2.4 Little Cypress Bayou............................................................................................... 55 5.2.5 Sabine Station Intake Canal .................................................................................... 55 5.2.6 Sabine Station Discharge Canal .............................................................................. 56 5.3 Preliminary pump station sizes and locations ................................................................ 56 5.3.1 Pump Stations ......................................................................................................... 56 5.3.2 Gravity Drainage Analysis ...................................................................................... 58 5.4 Major utility conflicts ....................................................................................................