Amite River Basin Numerical Model March 25, 2019 Project Report PREPARED BY: Dewberry Engineers Inc. Louisiana Department of Transportation & 1615 Poydras Street, Suite 650 Development (LA DOTD) New Orleans, LA 70112 1201 Capital Access Road Baton Rouge, LA 70802 Page intentionally left blank. 2 | Amite River Basin Numerical Model TABLE OF CONTENTS Introduction ............................................................................................................................................................................. 14 Numerical Model Purpose and Selection ......................................................................................................................................17 HEC Software Used to Develop the ARBNM ................................................................................................................................. 18 Tiered Modeling Approach ..................................................................................................................................................................20 The 6-tiers: .......................................................................................................................................................................................................................... 20 Application of Modeling Approaches ...................................................................................................................................................................... 21 Data Gap Analysis and Collection .................................................................................................................................... 23 LiDAR, Bathymetry, and Ground Survey Collection ................................................................................................ 26 2018 LA DOTD ARB LiDAR ..................................................................................................................................................................26 2017/18 LA DOTD ARB Survey and Bathymetry Collection ................................................................................................28 Survey Methodologies .................................................................................................................................................................................................... 28 Cross Section Survey ....................................................................................................................................................................................................... 28 Detailed Bridge Surveys ................................................................................................................................................................................................ 30 Limited Detail Survey ..................................................................................................................................................................................................... 30 High Water Mark (HWM) and Observed Data Collection ..................................................................................... 31 August 2016 Flood HWM Data ...........................................................................................................................................................32 Review of ARBC HWM Data ........................................................................................................................................................................................ 32 Other Sources of HWMs for the August 2016 Flood ......................................................................................................................................... 35 March 2016 Flood HWM Data ............................................................................................................................................................36 October 2017 Flood HWM Data ........................................................................................................................................................36 August 2017 Flood HWM Data ...........................................................................................................................................................36 Hydrologic Model .................................................................................................................................................................. 37 Model Geometry, Input, and Parameters ......................................................................................................................................38 Subbasins............................................................................................................................................................................................................................. 38 Routing ................................................................................................................................................................................................................................. 40 Meteorological Models .................................................................................................................................................................................................. 41 Hydraulic Model ..................................................................................................................................................................... 42 Dynamic HEC-RAS Hydraulic Model ...............................................................................................................................................42 Computation Methods ................................................................................................................................................................................................... 43 Model Geometry ............................................................................................................................................................................................................... 43 Model Parameters ........................................................................................................................................................................................................... 51 HEC-RAS Model Stability ......................................................................................................................................................................58 1D Flow Stability .............................................................................................................................................................................................................. 58 2D Flow Stability .............................................................................................................................................................................................................. 61 Steady State ARB HEC-RAS Hydraulic Models ............................................................................................................................68 Computation Methods ................................................................................................................................................................................................... 70 Model Geometry ............................................................................................................................................................................................................... 70 Hydrologic Flows ............................................................................................................................................................................................................. 70 Calibration ................................................................................................................................................................................71 Historic Precipitation Reconstruction for Floods ......................................................................................................................75 August 2017 Precipitation Event .............................................................................................................................................................................. 77 October 2017 Precipitation Event ............................................................................................................................................................................ 80 Amite River Basin Numerical Model | 3 March 2016 Precipitation Event ............................................................................................................................................................................... 82 August 2016 Precipitation Event .............................................................................................................................................................................. 84 HEC-HMS Calibration .............................................................................................................................................................................86 Validation of Excess Precipitation Observations ............................................................................................................................................... 92 HEC-RAS Calibration ...........................................................................................................................................................