R.C.E. 49302 P.L.S. 6368 STEVEN J. LAFRANCHI & ASSOCIATES, INC. CIVIL ENGINEERS ~ LAND SURVEYORS PETALUMA MARINA BUSINESS CENTER 775 BAYWOOD DRIVE, SUITE 312, PETALUMA, CA 94954 TEL 707-762-3122 FAX 707-762-3239 WETLANDS RUN-OFF REPORT BRODY RANCH SUBDIVISION 360 Corona Road Petaluma, California APN : 137-061-042 Job No.: 141680 October 2015 Prepared by: ADF
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WETLANDS RUN-OFF REPORT - City of Petaluma Plot Hydraflow Hydrographs Extension for AutoCAD® Civil 3D® 2009 by Autodesk, Inc. v6.066 Hyd. No. 1 Existing Area A Hydrograph type =
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R.C.E. 49302 P.L.S. 6368
STEVEN J. LAFRANCHI & ASSOCIATES, INC. CIVIL ENGINEERS ~ LAND SURVEYORS
PETALUMA MARINA BUSINESS CENTER 775 BAYWOOD DRIVE, SUITE 312, PETALUMA, CA 94954
TEL 707-762-3122 FAX 707-762-3239
WETLANDS RUN-OFF REPORT
BRODY RANCH SUBDIVISION 360 Corona Road Petaluma, California APN : 137-061-042 Job No.: 141680 October 2015 Prepared by: ADF
TABLE OF CONTENTS
General Statements ......................................................................................... 1-2
Existing Stormwater Run-Off to Wetlands Map ......................................... DM-1
Post Development Stormwater Run-Off to Wetlands Map ........................ DM-2
GENERAL STATEMENTS
The purpose of this report is to provide confirmation that the Proposed Project is preliminarily designed to support the existing wetlands with stormwater run‐off equal to the volume of water the onsite wetlands currently receive under the existing conditions. There are a couple of complicating issues with the above stated design. One complication is the removal of pollutants from the stormwater run‐off prior to it reaching the preserved and protected wetlands and the other being the transport of stormwater below grade in a piped network and then being able to discharge at a grade elevation that is constructible. The removal of pollutants is via Best Management Practices and the use of Bio‐Retention basins on each Lot and upstream of each catch basin. See the Stormwater Mitigation Plan prepared by this office for calculations and exhibits. We have chosen to discharge upstream of the wetlands through the use of a distribution trench with a concrete lip set at a constant elevation to evenly disperse stormwater across a wide area. Due to the way we propose to distribute the run‐off, there is a certain amount of volume loss due to storage in the distribution trench (this volume is calculated and shown as the total storage in cubic feet on the Pond Report for each distribution trench). This potential loos of volume has been accounted for in the post development area that is collected and directed in continued support of the existing wetlands. There are two hydrographs for each area that drains to the wetlands to be preserved. The hydrograph in red is the existing condition and represents a time of concentration (Tc) equal to fifteen minutes with a run‐off coefficient of C=0.32 which is from the Sonoma County Water Agencies(SCWA) Flood Control Design Criteria, Plate B‐1 for vegetated areas having a ground slope of approximately three percent. The blue hydrograph represents the post development condition with a Tc equal to ten minutes and a calculated composite run‐off coefficient of C=0.84. The intent of these calculations is to match the pre and post development run‐off volumes (excluding the trapped volume in the distribution trenches), not the peak discharge.
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Multi-Hydrograph PlotHydraflow Hydrographs Extension for AutoCAD® Civil 3D® 2009 by Autodesk, Inc. v6.066
Hyd. No. 1
Existing Area A
Hydrograph type = RationalPeak discharge = 0.272 cfsTime to peak = 15 minHyd. Volume = 245 cuft
Hyd. No. 2
Postdevelopment Area A
Hydrograph type = RationalPeak discharge = 0.74 cfsTime to peak = 10 minHyd. Volume = 441 cuft
0 5 10 15 20 25 30
Q (cfs)
0.00 0.00
0.10 0.10
0.20 0.20
0.30 0.30
0.40 0.40
0.50 0.50
0.60 0.60
0.70 0.70
0.80 0.80
0.90 0.90
1.00 1.00
Q (cfs)
Time (min)
Existing Area A through Postdevelopment Area A10-yr frequency
Hyd No. 1 Hyd No. 2
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Pond ReportHydraflow Hydrographs Extension for AutoCAD® Civil 3D® 2009 by Autodesk, Inc. v6.066 Monday, Oct 26, 2015
Pond No. 1 - Wetlands Swale A
Pond DataTrapezoid - Bottom L x W = 35.0 x 0.1 ft, Side slope = 2.00:1, Bottom elev. = 37.00 ft, Depth = 1.50 ft
Stage / Storage TableStage (ft) Elevation (ft) Contour area (sqft) Incr. Storage (cuft) Total storage (cuft)
Note: Culvert/Orifice outflows are analyzed under inlet (ic) and outlet (oc) control. Weir risers checked for orifice conditions (ic) and submergence (s).
Stage / Storage / Discharge TableStage Storage Elevation Clv A Clv B Clv C PrfRsr Wr A Wr B Wr C Wr D Exfil User Totalft cuft ft cfs cfs cfs cfs cfs cfs cfs cfs cfs cfs cfs
Note: Culvert/Orifice outflows are analyzed under inlet (ic) and outlet (oc) control. Weir risers checked for orifice conditions (ic) and submergence (s).
Stage / Storage / Discharge TableStage Storage Elevation Clv A Clv B Clv C PrfRsr Wr A Wr B Wr C Wr D Exfil User Totalft cuft ft cfs cfs cfs cfs cfs cfs cfs cfs cfs cfs cfs
Note: Culvert/Orifice outflows are analyzed under inlet (ic) and outlet (oc) control. Weir risers checked for orifice conditions (ic) and submergence (s).
Stage / Storage / Discharge TableStage Storage Elevation Clv A Clv B Clv C PrfRsr Wr A Wr B Wr C Wr D Exfil User Totalft cuft ft cfs cfs cfs cfs cfs cfs cfs cfs cfs cfs cfs