wetlands run-off report - city of petaluma plot hydraflow hydrographs extension for autocad® civil...

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

Vicinity Map ......................................................................................................... 3

SCWA Plate B-1 thru B-4 ................................................................................ 4-7

Post Development Run-Off Coefficient Calculations ....................................... 8

10-year Stormwater Hydrographs ................................................................ 9-17

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


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)

0.00 37.00 03 0 00.15 37.15 24 2 20.30 37.30 46 5 70.45 37.45 69 9 160.60 37.60 93 12 280.75 37.75 117 16 440.90 37.90 142 19 631.05 38.05 168 23 861.20 38.20 194 27 1141.35 38.35 221 31 1451.50 38.50 249 35 180

Culvert / Orifice Structures Weir Structures

[A] [B] [C] [PrfRsr] [A] [B] [C] [D]

Rise (in) = 0.00 0.00 0.00 0.00

Span (in) = 0.00 0.00 0.00 0.00

No. Barrels = 0 0 0 0

Invert El. (ft) = 0.00 0.00 0.00 0.00

Length (ft) = 0.00 0.00 0.00 0.00

Slope (%) = 0.00 0.00 0.00 n/a

N-Value = .013 .013 .013 n/a

Orifice Coeff. = 0.60 0.60 0.60 0.60

Multi-Stage = n/a No No No

Crest Len (ft) = 220.00 0.00 0.00 0.00

Crest El. (ft) = 38.50 0.00 0.00 0.00

Weir Coeff. = 3.33 3.33 3.33 3.33

Weir Type = Broad --- --- ---

Multi-Stage = No No No No

Exfil.(in/hr) = 0.000 (by Contour)

TW Elev. (ft) = 0.00

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

0.00 0 37.00 --- --- --- --- 0.00 --- --- --- --- --- 0.0000.15 2 37.15 --- --- --- --- 0.00 --- --- --- --- --- 0.0000.30 7 37.30 --- --- --- --- 0.00 --- --- --- --- --- 0.0000.45 16 37.45 --- --- --- --- 0.00 --- --- --- --- --- 0.0000.60 28 37.60 --- --- --- --- 0.00 --- --- --- --- --- 0.0000.75 44 37.75 --- --- --- --- 0.00 --- --- --- --- --- 0.0000.90 63 37.90 --- --- --- --- 0.00 --- --- --- --- --- 0.0001.05 86 38.05 --- --- --- --- 0.00 --- --- --- --- --- 0.0001.20 114 38.20 --- --- --- --- 0.00 --- --- --- --- --- 0.0001.35 145 38.35 --- --- --- --- 0.00 --- --- --- --- --- 0.0001.50 180 38.50 --- --- --- --- 0.00 --- --- --- --- --- 0.000

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Hyd. No. 4

Existing Area 'B'

Hydrograph type = RationalPeak discharge = 2.128 cfsTime to peak = 15 minHyd. Volume = 1,915 cuft

Hyd. No. 5

Post Development Area B


0 5 10 15 20 25 30

Q (cfs)

0.00 0.00

1.00 1.00

2.00 2.00

3.00 3.00

4.00 4.00

5.00 5.00

6.00 6.00

Q (cfs)

Time (min)

Existing Area 'B' through Post Development Area B10-yr frequency

Hyd No. 4 Hyd No. 5

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Pond No. 2 - Wetlands Swale B



0.00 37.00 17 0 00.15 37.15 147 12 120.30 37.30 277 32 440.45 37.45 408 51 950.60 37.60 539 71 1660.75 37.75 671 91 2570.90 37.90 804 111 3681.05 38.05 938 131 4981.20 38.20 1,073 151 6491.35 38.35 1,208 171 8201.50 38.50 1,344 191 1,012


[A] [B] [C] [PrfRsr] [A] [B] [C] [D]

Rise (in) = 0.00 0.00 0.00 0.00

Span (in) = 0.00 0.00 0.00 0.00


Invert El. (ft) = 0.00 0.00 0.00 0.00

Length (ft) = 0.00 0.00 0.00 0.00

Slope (%) = 0.00 0.00 0.00 n/a

N-Value = .013 .013 .013 n/a

Orifice Coeff. = 0.60 0.60 0.60 0.60


Crest Len (ft) = 220.00 0.00 0.00 0.00

Crest El. (ft) = 38.50 0.00 0.00 0.00

Weir Coeff. = 3.33 3.33 3.33 3.33







0.00 0 37.00 --- --- --- --- 0.00 --- --- --- --- --- 0.0000.15 12 37.15 --- --- --- --- 0.00 --- --- --- --- --- 0.0000.30 44 37.30 --- --- --- --- 0.00 --- --- --- --- --- 0.0000.45 95 37.45 --- --- --- --- 0.00 --- --- --- --- --- 0.0000.60 166 37.60 --- --- --- --- 0.00 --- --- --- --- --- 0.0000.75 257 37.75 --- --- --- --- 0.00 --- --- --- --- --- 0.0000.90 368 37.90 --- --- --- --- 0.00 --- --- --- --- --- 0.0001.05 498 38.05 --- --- --- --- 0.00 --- --- --- --- --- 0.0001.20 649 38.20 --- --- --- --- 0.00 --- --- --- --- --- 0.0001.35 820 38.35 --- --- --- --- 0.00 --- --- --- --- --- 0.0001.50 1,012 38.50 --- --- --- --- 0.00 --- --- --- --- --- 0.000

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Hyd. No. 7

Existing Area C


Hyd. No. 8

Post Development Area 'C'


0 5 10 15 20 25 30

Q (cfs)

0.00 0.00

1.00 1.00

2.00 2.00

3.00 3.00

Q (cfs)

Time (min)

Existing Area C through Post Development Area 'C'10-yr frequency

Hyd No. 7 Hyd No. 8

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Pond No. 3 - Wetlands Swale C



0.00 37.00 14 0 00.15 37.15 116 10 100.30 37.30 219 25 350.45 37.45 323 41 750.60 37.60 428 56 1320.75 37.75 533 72 2040.90 37.90 639 88 2921.05 38.05 746 104 3951.20 38.20 853 120 5151.35 38.35 961 136 6511.50 38.50 1,070 152 804


[A] [B] [C] [PrfRsr] [A] [B] [C] [D]

Rise (in) = 0.00 0.00 0.00 0.00

Span (in) = 0.00 0.00 0.00 0.00


Invert El. (ft) = 0.00 0.00 0.00 0.00

Length (ft) = 0.00 0.00 0.00 0.00

Slope (%) = 0.00 0.00 0.00 n/a

N-Value = .013 .013 .013 n/a

Orifice Coeff. = 0.60 0.60 0.60 0.60


Crest Len (ft) = 220.00 0.00 0.00 0.00

Crest El. (ft) = 38.50 0.00 0.00 0.00

Weir Coeff. = 3.33 3.33 3.33 3.33







0.00 0 37.00 --- --- --- --- 0.00 --- --- --- --- --- 0.0000.15 10 37.15 --- --- --- --- 0.00 --- --- --- --- --- 0.0000.30 35 37.30 --- --- --- --- 0.00 --- --- --- --- --- 0.0000.45 75 37.45 --- --- --- --- 0.00 --- --- --- --- --- 0.0000.60 132 37.60 --- --- --- --- 0.00 --- --- --- --- --- 0.0000.75 204 37.75 --- --- --- --- 0.00 --- --- --- --- --- 0.0000.90 292 37.90 --- --- --- --- 0.00 --- --- --- --- --- 0.0001.05 395 38.05 --- --- --- --- 0.00 --- --- --- --- --- 0.0001.20 515 38.20 --- --- --- --- 0.00 --- --- --- --- --- 0.0001.35 651 38.35 --- --- --- --- 0.00 --- --- --- --- --- 0.0001.50 804 38.50 --- --- --- --- 0.00 --- --- --- --- --- 0.000

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