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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. - PowerPoint PPT Presentation
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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• 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
Sierra College Boulevard, 1995
Project and Dry Creek
Watersheds
Project Site
Available Models
• HEC-1 models of the Dry Creek watershed
• HEC-RAS models converted from HEC-2
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
HEC-1 Flow Hydrographs
Pre-Project Site in the Floodplain
provided some Peak Flow Reduction
Original HEC-RAS Modeled Project Area as
Ineffective Flow
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.
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
HEC-HMSfrom HEC-1
Miners Ravinein HEC-HMS
HEC-1 Definition Typical on Miners
RavineKK MR30 ROUTE MRC6 TO MR30RS 15 FLOW -1SV 47 101 185 267 348 427SQ 500 1000 2000 3000 4000 5000KK MR30BA 1.75BF -23 -0.08 1.01PT 8PR 8LU .10 .09 11US 1.31 .60KK MRC7 - COMBINE MR30 WITH ROUTED MRC6HC 2KK MR31 ROUTE MRC7 TO MR31RS 15 FLOW -1SV 31 66 133 210 283 330SQ 500 1000 2000 3000 4000 5000
Adding Zeros…
Makes a Difference
Detailed Baseline Unsteady Model
Refined Model Simulates
Pre-Project Weir Flow
Detailed Proposed System Unsteady
Model
Hydraulic Model Shows
Benefit Near the Site
HEC-RAS ResultsUsed in HEC-HMS
HEC-HMS RoutingReplaced by Gage
Each Run Required
a Basin Model
Table A: Baseline Discharges (cubic feet per second)
Recurrence Interval (years) Location 2 5 10 25 50 100
Secret Ravine 757 1,277 1,680 2,544 3,385 3,788 Harding Blvd 1,654 2,875 3,872 5,595 7,012 8,024 Folsom Rd 2,390 4,267 5,125 7,465 9,699 10,718 Vernon St 3,371 5,828 6,974 10,013 13,004 14,344 Table B: Design Configuration Discharges (cubic feet per second)
Recurrence Interval (years) Location 2 5 10 25 50 100
Secret Ravine 749 1202 1594 2496 3148 3374 Harding Blvd 1654 2769 3778 5535 6747 7587 Folsom Rd 2389 4161 5044 7381 9422 10475 Vernon St 3370 5701 6884 9934 12731 14081 Table C: Design Configuration Flow Reduction (cubic feet per second)
Recurrence Interval (years) Location 2 5 10 25 50 100
Secret Ravine 8 75 86 49 236 414 Harding Blvd 1 106 94 60 265 437 Folsom Rd 0 106 81 84 277 243 Vernon St 1 127 90 80 273 263
HEC-HMS Provided Results for Flow
Reduction Calculation
Table A: Option A
Recurrence Interval (years) Location 2 5 10 25 50 100
Secret Ravine 5 91 98 25 26 85 Harding Blvd -1 59 108 25 83 138 Folsom Rd 0 67 69 31 207 197 Vernon St -1 89 93 34 151 126 Table B: Option B
Recurrence Interval (years) Location 2 5 10 25 50 100
Secret Ravine 8 6 49 118 328 347 Harding Blvd 4 8 45 131 303 395 Folsom Rd 0 7 48 182 147 104 Vernon St 2 9 44 171 271 203 Table C: Option C
Recurrence Interval (years) Location 2 5 10 25 50 100
Secret Ravine 8 39 68 13 227 396 Harding Blvd 4 46 53 29 258 449 Folsom Rd 0 47 78 78 288 245 Vernon St 2 49 60 73 280 269
Compared Results for Numerous Options and Recurrence Intervals
Stage Reduction from Rating Curves from Steady-
State HEC-RASRating Curve Upstream from Folsom Street
130
135
140
145
150
155
0 4000 8000 12000 16000
Discharge (cfs)
Sta
ge
(fee
t)
Table D: Design Configuration Stage Reduction (feet) Recurrence Interval (years) Location
2 5 10 25 50 100 Secret Ravine 0.03 0.09 0.09 0.04 0.16 0.28 Harding Blvd 0.00 0.11 0.09 0.05 0.27 0.44 Folsom Rd 0.00 0.14 0.07 0.08 0.23 0.20 Vernon St 0.00 0.11 0.06 0.05 0.18 0.18
Stage Reduction from HEC-HMS Flows and HEC-
RAS Rating Curves
Modeling Effort Demonstrated
Benefit of Control Structure
Process Led to Project Construction!
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