HomeMy WebLinkAboutPD 2020-0027; 3481 SEACREST DRIVE SLOPE REHABILITATION; DRAINAGE REPORT; 2020-10-213481 SEA CREST DRIVE &
3470 CHARTER OAK DRIVE
PREPARED FOR
Tim Carroll
City of Carlsbad
1635 Faraday Avenue
Carlsbad CA, 92008
PROPERTY LOCATION
3481 Seacrest Drive
Carlsbad CA, 92008
APN: 167-122-13-00
PD 2020-0027
GR2020-0021/DWG 526-4A
DRAINAGE REPORT
triad/holmes ossoci OteS
civil engifleering
land surveying
Mammoth lakes . bhQp • redwood dty
OCT 23 ZRO
LAND DLVEiLOPMENT
ENLELKJNG
777 Woodside Rd., Suite 2A
REDWOOD CITY, CA 94061
Phone (650) 366-0216
Fax (650) 366-0298
Email sfthainc.com
October 21, 2020
THA #01-4310
SURFACE TYPE
ROOF
CONCRETE /DRIVEWAY
HARDSCAPE
LANDSCAPE/NATURAL
1,787 0.95
3,108 0.9
813 0.9
6,575 0.30
AREA(SF) COEFFICIENT
S
PURPOSE:
The purpose of this report is to determine pre- and post-development runoff and velocity.
PROJECT DESCRIPTION:
The project consists of two sites. The first site (3481 Seacrest) is 0.28 acre, and the second
(3470 Charter Oak Drive) is 0.28 acre. The proposed project is a slope restoration of the
lower site (3470 Charter Oak Drive) due to a failed french drain under an excessive rain
event. The french drain originally ran parallel between the two sites and will now be removed
and replaced with a 4" solid drain. The runoff from the slope will be intercepted by a new
concrete swale to direct flow into a new 1 8"x 18" inlet. The existing piping will remain that
conveys the stormwater to an inlet in the backyard of 3470 Charter Oak Dr. where the
existing 4" drain line will be replaced with a 6" line (due to slope of drain line) in order to
convey the runoff out to Charter Oak Drive. The sloped area that was affected by the damage
will be replaced with fill and decreased from a 1.6:1 slope to a 2:1 slope-max with retaining
walls to maintain original site flow. NO additional impervious surface will be constructed
besides the swale to create excess flow from pre-developed conditions.
ASSUMPTIONS:
The pre-development area is to provide the same amount of flow directed to the south-west
property line of 3481 Seacrest Drive. There is no significant off-site tributary area to the
project. The recurrence interval for design purposes is a 100-year storm. Runoff coefficient,
rainfall intensity and intensity factor are from San Diego County Hydrology Manual.
Rational Method with an additional intensity factor per San Diego County Hydrology
Manual Data Figure 3-1, attached appendix A, is used to determine runoff.
HYDROLOGIC CALCULATIONS for 3481 Seacrest Drive:
DETERMINE PRE-DEVELOPMENT RUNOFF, Onre
Rational Method (modified): Q=CIAF
AVERAGE COEFFICIENT (C) = WEIGHTED COEFFICIENT 0.76
TOTAL AREA (A) 12,283 SQ. FT.
TOTAL AREA CAPTURED BY SOUTH INLETS
SURFACE TYPE AREA(SF) COEFFICIENT
ROOF 1,018 0.95
CONCRETE /DRIVEWAY 1,191 0.9
HARDSCAPE 0 0.9
LANDSCAPE/NATURAL 4,796 0.30
TOTAL AREA (A) 7,005 SQ. FT.
0.16 ACRE
Time of Concentration = 0-10 minutes (small single family lot)
INTENSITY (I) Based on Figure 3-1 (see attached) T=8 mm
5.0 IN/HR
San Diego Rainfall Runoff Data
Q = CIA 0.60 CF
Based on the data from the Hydraulic Manual from San Diego county, and the calcs
produced from Hydraflow Express program, Appendix A, a 6" SDR 35 will be able
to handle a looyr storm event occurring on the site 3481 Seacrest Drive from the
drain inlet in the backyard of 3470 Charter Oak to the street outfall. The 4" PVC
line from the inlet down the slope will be adequate as shown due to the steepness of
the grade the line was installed at.
PROJECT LOCATION MAP
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1 LANDSCAPE AREA
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TO SOUTH/ WEST
SUBDRAIN,
4,796 SF
17.31 N23°14W9ft6T (IN 23°33WW 966CFR1&R2)—
N 23°14'38" W 100.00' (N 233300" W 100fR1) 13.94'
[ 1 4" DRAIN
FAILURE
LOCATION
EX. 4" PVC
DRAINPIPE
TO REMAIN
b Q q
C) (N C) (N
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p CD p N- (N N-(N
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3.37' (N 23-33-00" W 3.37' R
LOT 84
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EX. 4" PVC
DRAI"J PIPE
REPLACE
W/ 6" DVC
PIPE FROM
INLE
N 23014'38' W 100.00' (N 23°3300 W 100.00' Ri) 1
CHARTER
481 SEACREST DR DRAINAGE AREA
EXHIBIT
APPENDIX A
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Channel Report S
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc.
3481 Seacrest 4 inch in Slope
Circular Highlighted
Diameter (ft) = 0.33 Depth (ft)
Q (cfs)
Area (sqft)
Invert Elev (ft) = 282.00 Velocity (ftls)
Slope (°7o) = 40.00 Wetted Perim (ft)
N-Value = 0.013 Crit Depth, Yc (ft)
Top Width (ft)
Calculations EGL (ft)
Compute by: Known Q
Known Q (cfs) = 0.60
Wednesday, Oct 21 2020
= 0.17
= 0.600
= 0.04
= 13.44
= 0.53
= 0.33
= 0.33
= 2.98
Elev (ft) Section
282.75
282.50
282.25
281.75
0 1
Reach (ft)
0 1 .2
Elev (ft)
281.00
Section
280.50
279.50
279.00
Channel Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. Tuesday, Sep 12020
01.4310 Seacrest Pipe Caic.
Circular
Diameter (ft) = 0.50
Invert Elev (ft) = 279.87
Slope (%) = 1.00
N-Value = 0.012
Calculations
Compute by: Known Q
Known Q (cfs) = 0.60
Highlighted
Depth (ft)
0 (cfs)
Area (sqft)
Velocity (ft/s)
Wetted Perim (ft)
Crit Depth, Yc (ft)
Top Width (ft)
EGL (ft)
= 0.41
= 0.600
= 0.17
= 3.47
= 1.14
= 0.40
= 0.38
= 0.60
Reach (ft)