drainage analysis – the weiss & lavine residence

“We’ll Get The Permit”1702 4th Street • Santa Rosa, CA 95404 • T 707.544.2104 • F 707.522.2105 • hoganls.com

Surveying • Civil & Structural Engineering • Construction Management • Violation Resolution

Drainage Analysis – The Weiss & Lavine Residence

Prepared December 1, 2020

Site: Owners:40 Montecito Road Tania Weiss & Rich LavineSan Rafael, California 40 Montecito RoadAPN: 016-054-10 San Rafael, CA 94901HLS Project # 3987 (415) 883-8000

Analysis Prepared by:Hogan Land Services, Inc.1702 4th StreetSanta Rosa, CA 95404 Jim Conklin, PE [email protected] 707-544-2104

http://www.hoganls.com/

The Weiss & Lavine Residence Preliminary Hydrology AnalysisJob # 3987 2

PREPARED: December 1, 2020

SUBJECT: 10-Year event hydrology calculations and reasoning for drainage network sizing

PROJECT: Drainage Analysis – The Weiss & Lavine Residence

ADDRESS: 40 Montecito Road, San Rafael, California

APN: 016-054-10

PROJECT DESCRIPTION:The subject parcel is located at 40 Montecito Road in San Rafael, California. Existing onsite infrastructure consists of a single-family dwelling, detached garage, concrete driveway, patio, and retaining walls. The proposed development under this permit includes a replacement main residence, detached garage, concrete driveway, concrete porch, wood deck, and site retaining walls. Only earthwork, grading, and drainage activities are covered under this preliminary civil plan set and preliminary drainage analysis. Topography of the area consists of moderate to steep slopes (10-30%) with the majority of the lot vegetated with native trees and grasses. This preliminary drainage analysis evaluates the potential drainage impacts of the proposed site redevelopment.

EXISTING AND PROPOSED DRAINAGE PATTERN:Runoff from the site and upslope watershed generally sheet flows diagonally across the subject parcel in a northeast direction before converging at an existing roadside ditch. Flow within the roadside concrete curb and gutter enter a public storm drain inlet along Point San Pedro

DESIGN REQUIREMENTS:The subject parcel is located within Marin County and is subject to BASMAA Post Construction requirements (See associated Preliminary Stormwater Control Plan). This analysis focuses strictly on the 10-year event sizing of the proposed drainage improvements. BASMAA Post Construction requirements are addressed within the Preliminary Stormwater Control Plan.

DESIGN CRITERIA & ASSUMPTIONS: This evaluation is based on the policies and procedures detailed in Flood Management Design Manual, by the Sonoma County Water Agency, Revised March 2020. The hydraulic design of the individual drainage improvements is based on the rational formula (Q = C i A ) and is based on the 10-year, 10-minute initial time of concentration storm. A precipitation intensity of 2.45 was used in the analysis and was derived from NOAA Atlas 14, Volume 6, Version 2. Minor downspout storm drain network was evaluated only for the worst case run within the network. The worst-case pipe sizing and slope is then conservatively used throughout the network. METHODOLOGIES USED:Rational Formula calculations for the 10-year storm are included based on the composite runoff coefficients for each tributary for sizing of the individual drainage improvements. The calculation spreadsheets are attached with this submittal. Pipe sizing and swale sizing were determined using Hydraflow Express, a design tool which uses Manning’s equations for circular channels to determine pipe sizing and triangular channels for swale sizing. 100 YEAR STORM IMPACT AND FLOODING CONCERNS:The parcel lies outside of the 100-year flood zone therefore flooding is not expected. A 100-year storm event would likely result in overflow of the culverts and swales and runoff returns to sheet flow downhill.

The Weiss & Lavine Residence Preliminary Hydrology AnalysisJob # 3987 3

CONCLUSION:The calculations and analysis provided herein is based upon the Sonoma County Water Agency Flood Management Design Manual and generally accepted engineering principles. The proposed drainage improvements for the development have been sized to accommodate the 10 year storm event. Drainage network calculations are based on free flow and should be routinely inspected by the property owner. The drainage pattern at a regional scale remains unchanged from pre to post development conditions.

ATTACHMENTS: Watershed Exhibit Rational Method Calculation Spreadsheet Hydraflow Express Calculations NDS Catch Basin Sizing Detail Other Supporting Tables & Figures

WATERSHED EXHIBIT

AREA OF DEVELOPMENT

SHEET FLOW

CONCRETE CURB & GUTTER

PUBLIC STORM DRAIN INLET

PUBLIC STORM DRAIN INLET

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3987- THE WEISS & LAVINE RESIDENCE

1

IntensityRunnoff

CoefficientFlow

Tributary Point of Conc. Area (ac.) Avg. Slope % Length Velocity fpsTravel Time

(sec.)Total Time I C_comp IAC Q (cfs)

1 POC 1 0.02 INITIAL 10 2.45 0.90 0.04 0.04

IntensityRunnoff

CoefficientFlow



2 POC 2 0.03 INITIAL 10 2.45 0.70 0.05 0.05

IntensityRunnoff

CoefficientFlow



3 POC 3 0.68 INITIAL 10 2.45 0.60 0.99 0.99

IntensityRunnoff

CoefficientFlow



4 POC 4 0.06 INITIAL 10 2.45 0.81 0.12 0.12

IntensityRunnoff

CoefficientFlow



5 POC 5 0.02 INITIAL 10 2.45 0.90 0.05 0.05

IntensityRunnoff

CoefficientFlow



6 POC 6 0.08 INITIAL 10 2.45 0.90 0.18 0.18

IntensityRunnoff

CoefficientFlow



7 POC 7 0.01 INITIAL 10 2.45 0.90 0.02 0.02

IntensityRunnoff

CoefficientFlow



8 POC 8 0.04 INITIAL 10 2.45 0.84 0.08 0.08

2

Post-Development - Tributary 7 Time of Concentration








Triburary AcresPost-Dev. Imp.

Acres

Post-Dev.

Vegitated

Acres

C_comp Total Q (cfs)

1 0.02 0.02 0.00 0.90 POC 1 4" PIPE 0.11

2 0.03 0.01 0.01 0.70 POC 2 SLOT DRAIN 0.05

3 0.68 0.16 0.52 0.60 POC 3 (E) PIPE NO CALC 0.99

4 0.06 0.05 0.01 0.81 POC 4 CATCH BASIN 0.12

5 0.02 0.02 0.00 0.90 POC 5 SLOT DRAIN 0.05

6 0.08 0.08 0.00 0.90 4" PIPE 0.18

7 0.01 0.01 0.00 0.90 6" PIPE 0.43

8 0.04 0.03 0.01 0.84 POC 7 SLOT DRAIN 0.02

Total Watershed 0.94 POC 8 6" SWALE 1.42

C_vegitated 0.50 C_impervious 0.90

POC / Design

5

6

7

3, 4, 5, 6, & 8

POC 64, 5, 6 & 8

Tributaries Receiving

1, 2 & 7

2

3

4

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Channel Report

Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. Wednesday, Dec 2 2020

4 INCH PIPE

CircularDiameter (ft) = 0.33

Invert Elev (ft) = 100.00Slope (%) = 5.00N-Value = 0.012

CalculationsCompute by: Known QKnown Q (cfs) = 0.16

HighlightedDepth (ft) = 0.14Q (cfs) = 0.160Area (sqft) = 0.03Velocity (ft/s) = 4.62Wetted Perim (ft) = 0.47Crit Depth, Yc (ft) = 0.23Top Width (ft) = 0.33EGL (ft) = 0.47

0 1

Elev (ft)Section

99.75

100.00

100.25

100.50

100.75

101.00

Reach (ft)

Channel Report


SLOT DRAIN

RectangularBottom Width (ft) = 0.17Total Depth (ft) = 0.50




0 .1 .2 .3 .4

Elev (ft) Depth (ft)Section

99.75 -0.25

100.00 0.00

100.25 0.25

100.50 0.50

100.75 0.75

101.00 1.00

Reach (ft)

Channel Report


4 INCH PIPE





0 1

Elev (ft)Section

99.75

100.00

100.25

100.50

100.75

101.00

Reach (ft)

Channel Report


6 INCH PIPE





0 1

Elev (ft)Section

99.75

100.00

100.25

100.50

100.75

101.00

Reach (ft)

Channel Report


6 INCH ROCK LINED SWALE

TriangularSide Slopes (z:1) = 2.00, 2.00Total Depth (ft) = 0.50




0 .5 1 1.5 2 2.5 3

Elev (ft) Depth (ft)Section

99.75 -0.25

100.00 0.00

100.25 0.25

100.50 0.50

100.75 0.75

101.00 1.00

Reach (ft)

3 of 7

12” CATCH BASIN

Part #: 1200, 1203, 1207

GRATE CAPACITIES

Grate Number(s) Description Flow Rate with ½” Head

1210, 1211, 1212,

1212S

12” x 12” Square Grate 155.28 GPM

1211* 12” x 12” Square Grate 157.79 GPM

1213 12” x 12” Square Cast Iron Grate 113.80 GPM

1215 12” x 12” Square Galvanized Steel

Grate

348.07 GPM

1280, 1290 12’ x 12” Atrium Grate 154.79 GPM

1218, 1218S,

1218GR, 1218GY

12” Botanical Plastic 74.77 GPM

1218CI 12” Botanical Cast Iron 76.60 GPM

1224, 1224S,

1224GR, 1224GY

12” Wave Plastic 78.53 GPM

1224CI 12” Wave Cast Iron 78.31 GPM

OUTLET FLOW CAPACITIES

Part # Flow Rate per Outlet

1242, 1243 78.10

1245 Top: 70.49 GPM

Middle: 76.30 GPM

Bottom: 83.41 GPM

1266 247.12 GPM

1889 238.20 GPM

6 INCH

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1215

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1266

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1200

NOAA Atlas 14, Volume 6, Version 2 Location name: San Rafael, California, USA*

Latitude: 37.9721°, Longitude: -122.502° Elevation: 75.03 ft**

* source: ESRI Maps ** source: USGS

POINT PRECIPITATION FREQUENCY ESTIMATES

Sanja Perica, Sarah Dietz, Sarah Heim, Lillian Hiner, Kazungu Maitaria, Deborah Martin, SandraPavlovic, Ishani Roy, Carl Trypaluk, Dale Unruh, Fenglin Yan, Michael Yekta, Tan Zhao, Geoffrey

Bonnin, Daniel Brewer, Li-Chuan Chen, Tye Parzybok, John Yarchoan

NOAA, National Weather Service, Silver Spring, Maryland

PF_tabular | PF_graphical | Maps_&_aerials

PF tabularPDS-based point precipitation frequency estimates with 90% confidence intervals (in inches/hour)1

DurationAverage recurrence interval (years)

1 2 5 10 25 50 100 200 500 1000

5-min 1.85(1.64‑2.09)

2.28(2.03‑2.59)

2.89(2.57‑3.30)

3.43(3.01‑3.94)

4.20(3.54‑5.03)

4.82(3.97‑5.93)

5.51(4.40‑6.97)

6.24(4.82‑8.16)

7.31(5.38‑10.0)

8.17(5.77‑11.7)

10-min 1.32(1.18‑1.50)

1.63(1.45‑1.85)

2.08(1.84‑2.36)

2.45(2.15‑2.83)

3.01(2.54‑3.61)

3.46(2.84‑4.25)

3.95(3.16‑4.99)

4.48(3.46‑5.85)

5.23(3.85‑7.19)

5.86(4.14‑8.38)

15-min 1.06(0.948‑1.21)

1.32(1.17‑1.50)

1.67(1.48‑1.90)

1.98(1.74‑2.28)

2.42(2.04‑2.90)

2.79(2.30‑3.43)

3.18(2.54‑4.02)

3.61(2.79‑4.72)

4.22(3.10‑5.80)

4.72(3.34‑6.75)

30-min 0.784(0.698‑0.888)

0.970(0.862‑1.10)

1.23(1.09‑1.40)

1.46(1.28‑1.68)

1.78(1.50‑2.14)

2.05(1.69‑2.52)

2.34(1.87‑2.96)

2.65(2.05‑3.47)

3.10(2.28‑4.26)

3.47(2.45‑4.97)

60-min 0.560(0.499‑0.635)

0.693(0.617‑0.787)

0.880(0.780‑1.00)

1.04(0.914‑1.20)

1.27(1.08‑1.53)

1.47(1.21‑1.80)

1.67(1.34‑2.12)

1.90(1.47‑2.48)

2.22(1.63‑3.05)

2.48(1.75‑3.55)

2-hr 0.420(0.374‑0.476)

0.520(0.462‑0.590)

0.661(0.586‑0.752)

0.782(0.687‑0.900)

0.958(0.808‑1.15)

1.10(0.907‑1.35)

1.26(1.00‑1.59)

1.42(1.10‑1.86)

1.67(1.22‑2.29)

1.86(1.32‑2.66)

3-hr 0.355(0.317‑0.403)

0.440(0.392‑0.500)

0.558(0.495‑0.636)

0.661(0.580‑0.760)

0.808(0.682‑0.968)

0.929(0.764‑1.14)

1.06(0.845‑1.34)

1.20(0.925‑1.57)

1.40(1.03‑1.92)

1.56(1.10‑2.23)

6-hr 0.262(0.233‑0.297)

0.325(0.289‑0.369)

0.411(0.365‑0.469)

0.486(0.427‑0.559)

0.592(0.499‑0.709)

0.678(0.558‑0.833)

0.769(0.615‑0.973)

0.868(0.670‑1.13)

1.01(0.741‑1.38)

1.12(0.792‑1.60)

12-hr 0.185(0.165‑0.209)

0.231(0.205‑0.262)

0.294(0.260‑0.334)

0.347(0.304‑0.399)

0.422(0.355‑0.505)

0.481(0.396‑0.591)

0.544(0.435‑0.688)

0.611(0.472‑0.798)

0.704(0.518‑0.967)

0.779(0.551‑1.12)

24-hr 0.126(0.113‑0.143)

0.159(0.143‑0.180)

0.203(0.182‑0.231)

0.240(0.214‑0.275)

0.291(0.252‑0.344)

0.332(0.281‑0.399)

0.374(0.310‑0.459)

0.418(0.338‑0.526)

0.479(0.373‑0.626)

0.527(0.398‑0.712)

2-day 0.084(0.076‑0.095)

0.106(0.096‑0.121)

0.136(0.122‑0.155)

0.160(0.143‑0.184)

0.194(0.168‑0.229)

0.220(0.186‑0.264)

0.247(0.205‑0.303)

0.274(0.222‑0.346)

0.312(0.244‑0.409)

0.342(0.259‑0.462)

3-day 0.064(0.058‑0.073)

0.081(0.073‑0.092)

0.104(0.093‑0.118)

0.122(0.109‑0.140)

0.147(0.127‑0.174)

0.166(0.141‑0.200)

0.186(0.155‑0.229)

0.207(0.167‑0.261)

0.234(0.183‑0.307)

0.256(0.194‑0.346)

4-day 0.053(0.048‑0.060)

0.067(0.060‑0.076)

0.086(0.077‑0.098)

0.101(0.090‑0.116)

0.121(0.105‑0.143)

0.137(0.116‑0.165)

0.153(0.127‑0.188)

0.170(0.137‑0.214)

0.192(0.150‑0.251)

0.209(0.158‑0.282)

7-day 0.037(0.033‑0.042)

0.047(0.042‑0.053)

0.060(0.053‑0.068)

0.070(0.062‑0.080)

0.084(0.073‑0.099)

0.095(0.080‑0.114)

0.105(0.087‑0.129)

0.116(0.094‑0.146)

0.131(0.102‑0.171)

0.142(0.107‑0.192)

10-day 0.030(0.027‑0.034)

0.038(0.034‑0.043)

0.049(0.044‑0.055)

0.057(0.051‑0.065)

0.068(0.059‑0.080)

0.077(0.065‑0.092)

0.085(0.070‑0.104)

0.093(0.076‑0.118)

0.104(0.081‑0.137)

0.113(0.085‑0.152)

20-day 0.020(0.018‑0.022)

0.025(0.023‑0.029)

0.032(0.029‑0.037)

0.037(0.033‑0.043)

0.044(0.038‑0.052)

0.049(0.042‑0.059)

0.054(0.045‑0.067)

0.059(0.048‑0.074)

0.065(0.051‑0.085)

0.069(0.052‑0.094)

30-day 0.016(0.014‑0.018)

0.020(0.018‑0.023)

0.026(0.023‑0.030)

0.030(0.027‑0.035)

0.035(0.031‑0.042)

0.039(0.033‑0.047)

0.043(0.036‑0.053)

0.046(0.038‑0.058)

0.051(0.039‑0.066)

0.054(0.041‑0.072)

45-day 0.013(0.012‑0.015)

0.017(0.015‑0.019)

0.021(0.019‑0.024)

0.025(0.022‑0.028)

0.029(0.025‑0.034)

0.032(0.027‑0.038)

0.034(0.028‑0.042)

0.037(0.030‑0.046)

0.040(0.031‑0.052)

0.042(0.032‑0.057)

60-day 0.012(0.011‑0.013)

0.015(0.014‑0.017)

0.019(0.017‑0.022)

0.022(0.019‑0.025)

0.025(0.022‑0.030)

0.028(0.024‑0.033)

0.030(0.025‑0.037)

0.032(0.026‑0.040)

0.034(0.027‑0.045)

0.036(0.027‑0.049)

1 Precipitation frequency (PF) estimates in this table are based on frequency analysis of partial duration series (PDS).Numbers in parenthesis are PF estimates at lower and upper bounds of the 90% confidence interval. The probability that precipitation frequency estimates (for agiven duration and average recurrence interval) will be greater than the upper bound (or less than the lower bound) is 5%. Estimates at upper bounds are notchecked against probable maximum precipitation (PMP) estimates and may be higher than currently valid PMP values.Please refer to NOAA Atlas 14 document for more information.

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DATE: 11/30/20

JOB: 3987

DRAWN BY: AC

HYDROLOGY MAP EXHIBIT - 10 YEAR STORM EVENT

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, 11/30/2020 3:39:57 P

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29,468.09 sf

3,598.88 sf

1,302.58 sf

2,542.72 sf

1,755.06 sf

985.47 sf

348.44 sf

786 sf

12

3 45 6

8

7

(P) ROCKLINED SWALE

(P) 4" PIPE

(P) 4" PIPE

(P) SLOT DRAIN

(P) 6" PIPE

(P) 4" PIPE

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drainage analysis – the weiss & lavine residence

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