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Quantifying Flow Reduction Benefit of the Miners Ravine Off-Channel Detention Basin Using HEC-HMS

Quantifying Flow Reduction Benefit of the Miners Ravine Off-Channel Detention Basin Using HEC-HMS. Or What Happens When a Project Requires Use of an HEC-1 Model to Evaluate Regional Benefits and an Unsteady HEC-RAS to Model Project Function. History of Miners Ravine Off-Channel Detention Basin.

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Quantifying Flow Reduction Benefit of the Miners Ravine Off-Channel Detention Basin Using HEC-HMS

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  1. Quantifying Flow Reduction Benefit of the Miners Ravine Off-Channel Detention Basin Using HEC-HMS Or What Happens When a Project Requires Use of an HEC-1 Model to Evaluate Regional Benefits and an Unsteady HEC-RAS to Model Project Function

  2. History of Miners Ravine Off-Channel Detention Basin • 1992: Flood Control Study called for on-channel basin • 1998: On-channel basin concept rejected • Off-channel basin concept pursued • 2006-2007: Off-channel basin constructed

  3. Sierra College Boulevard, 1995

  4. Project and Dry Creek Watersheds

  5. Project Site

  6. Available Models • HEC-1 models of the Dry Creek watershed • HEC-RAS models converted from HEC-2

  7. Modeling Challenges • HEC-1 models did not provide reasonable hydrographs necessary to evaluate basin function from 2- to 100-year events • HEC-RAS models did not reflect the pre-project flood attenuation function of the site

  8. HEC-1 Flow Hydrographs

  9. Pre-Project Site in the Floodplainprovided some Peak Flow Reduction

  10. Original HEC-RAS Modeled Project Area as Ineffective Flow

  11. Modeling Goals • Provide a consistent basis for evaluation of project alternative • Evaluate local flow and stage reduction • Estimate benefits at locations about 3.5 miles downstream, below major confluences.

  12. Steps to Make an Apples to Apples Assessment of Basin Benefit • Create HEC-HMS from HEC-1 • Use HMS results as input to RAS • Create detailed unsteady RAS model of existing site • Create unsteady RAS model of project alternative configurations • Use unsteady RAS results as input to HMS model • Use HMS model results and steady-state RAS rating curves to quantify downstream benefit

  13. HEC-HMSfrom HEC-1

  14. Miners Ravinein HEC-HMS

  15. HEC-1 Definition Typical on Miners Ravine KK MR30 ROUTE MRC6 TO MR30 RS 15 FLOW -1 SV 47 101 185 267 348 427 SQ 500 1000 2000 3000 4000 5000 KK MR30 BA 1.75 BF -23 -0.08 1.01 PT 8 PR 8 LU .10 .09 11 US 1.31 .60 KK MRC7 - COMBINE MR30 WITH ROUTED MRC6 HC 2 KK MR31 ROUTE MRC7 TO MR31 RS 15 FLOW -1 SV 31 66 133 210 283 330 SQ 500 1000 2000 3000 4000 5000

  16. Adding Zeros…

  17. Makes a Difference

  18. Detailed Baseline Unsteady Model

  19. Refined Model SimulatesPre-Project Weir Flow

  20. Detailed Proposed System Unsteady Model

  21. Hydraulic Model ShowsBenefit Near the Site

  22. HEC-RAS ResultsUsed in HEC-HMS

  23. HEC-HMS RoutingReplaced by Gage

  24. Each Run Required a Basin Model

  25. HEC-HMS Provided Results for Flow Reduction Calculation

  26. Compared Results for Numerous Options and Recurrence Intervals

  27. Stage Reduction from Rating Curves from Steady-State HEC-RAS

  28. Stage Reduction from HEC-HMS Flows and HEC-RAS Rating Curves

  29. Modeling Effort DemonstratedBenefit of Control Structure

  30. Process Led to Project Construction!

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