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Estimating Flood Limits in Large Riverine Systems Using Unsteady-State Hydraulic Modeling (HEC-RAS)

Estimating Flood Limits in Large Riverine Systems Using Unsteady-State Hydraulic Modeling (HEC-RAS). Brian Greathouse, P.E. Malcolm Pirnie, Inc. METHODOLOGIES. US ARMY CORP OF ENGINEERS HEC-RAS RIVER ANALYSIS SYSTEM STEADY STATE ANALYSIS UNSTEADY STATE ANALYSIS. HEC-RAS OVERVIEW.

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Estimating Flood Limits in Large Riverine Systems Using Unsteady-State Hydraulic Modeling (HEC-RAS)

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  1. Estimating Flood Limits in Large Riverine Systems Using Unsteady-State Hydraulic Modeling (HEC-RAS) Brian Greathouse, P.E. Malcolm Pirnie, Inc.

  2. METHODOLOGIES • US ARMY CORP OF ENGINEERS HEC-RAS RIVER ANALYSIS SYSTEM • STEADY STATE ANALYSIS • UNSTEADY STATE ANALYSIS

  3. HEC-RAS OVERVIEW • MODEL COMPONENTS • GEOMETRY DATA • FLOW DATA • BOUNDARY CONDITIONS

  4. GEOMETRY DATA • CROSS SECTION DATA • DEVELOPED FROM TOPOGRAPHIC DATA • SURVEY DATA • COMBINATION OF BOTH • LAND COVER DATA – MANINGS “N” VALUE • DEFINED FOR THE CHANNEL AND OVERBANK PORTION OF THE CROSS SECTION • STRUCTURE DATA • BRIDGES, CULVERTS, WEIRS

  5. FLOW DATA • STEADY STATE – UNIFORM FLOW • UNSTEADY STATE – NON-UNIFORM FLOW: FLOW HYDROGRAPH

  6. STEADY-STATE MODELING • APPLICATION OF A UNIFORM FLOW THROUGHOUT THE RIVER SYSTEM • TYPICALLY A PEAK FLOW TAKEN FROM THE FLOW HYDROGRAPH • COMMON APPLICATION IS FEMA FLOOD MAPPING

  7. UNSTEADY STATE MODELING • NON-UNIFORM FLOW • APPLICATION OF A FLOW HYDROGRAPH • BETTER REPRESENTATION OF THE HYDRAULIC CHARATERISTICS OF A RIVER SYSTEM

  8. CASE STUDY – TALLAPOOSA RIVER MODEL MODELED FROM THURLOW DAM TO THE DEAD RIVER AREA

  9. FLOW DATA • APPLIED ACTUAL DAM RELEASE RATES TO THE MODEL • APPLIED HYPOTHETICAL RELEASE RATES WERE APPLIED

  10. MODEL CALIBRATION • STREAM GAGE DATA USED FOR MODEL CALIBRATION • COMPARE FLOW AND STAGE (MODELED vs GAGE DATA) • APPLY A UNIFORM DISTRIBUTED FLOW • CALIBRATION COMPENSATES FOR FLOW ENTERING SYSTEM DOWNSTREAM FROM DAM AND OFFLINE STORAGE

  11. Model Flow vs. Gage Flow

  12. Model Flow vs. Gage Height

  13. Model Flow vs. Gage Height

  14. FLOOD LIMITS • MODEL PRODUCES WATER SURFACE ELEVATIONS AT EACH CROSS SECTION • WATER SURFACE ELEVATIONS ARE APPLIED TO TOPOGRPAHICAL DATA AND THE FLOOD LIMITS ARE DETRMINED.

  15. QUESTIONS????????

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