HomeMy WebLinkAboutPD 2022-0007; HAGUE RESIDENCE; DRAINAGE STUDY; 2022-06-07
DRAINAGE STUDY
HAGUE RESIDENCE
Cynthia Lane, APN 156-231-70-00
Carlsbad, California
PD 2022-0007
GR 2022-0011
City of Carlsbad DWG 536-9A
Dated 6-7-2022
Prepared By:
Erin Rist
RCE 65122
ENGINEERING
DESIGN GROUP
www.designgroupca.com
2121 Montiel Road, San Marcos, CA 92069
760.839.7302
SITE DESCRIPTION
The subject project consists of a single-family residence located at APN 156-231-70-00, Cynthia Lane, Carlsbad,
California. The front property fronts Cynthia Lane and for the purposes of this report the front of the property
faces north. The property descends from an approximate high point along the east side and descending across
the property to the west and to the east to the street below. The total acreage of the property is approximately
0.18 acres. The site is served by onsite wastewater treatment.
EXISTING DRAINAGE PATTERNS
At the time of this report the site is generally undeveloped with the exception of an existing concrete bad and
shed structure. Site runoff generally flows as sheet flow to the property to the west as well as the front of the
property flows to existing curb/gutter improvements at the improved street Cynthia Lane. The original tentative
parcel map, prepared as part of the development of the subject site parcel map, PM 19753, depicts developed
runoff to be routed to curb and gutter improvements at the street.
PROJECT SCOPE
The proposed site development includes the construction of a new single-family residence, with associated
flatwork and associated landscape improvements.
BASIN DESCRIPTION AND EXISTING FLOW PATTERNS
For this drainage analysis, the proposed pad area has been included as one main basin in the predeveloped
condition. As the design intent for the runoff, as part of the creation of the subject property intended for runoff
to be run to curb and gutter improvements at the street, the proposed design incorporates this design intent
into the overall drainage design. In the post developed condition, the main basin is divided into sub-basins B1A-
B1E for the purposes of pipe sizing. The post development condition utilizes a private storm drain, that collect
and direct runoff curb and gutter improvements at the street. See attached spreadsheet for quantities.
ANALYSIS & METHODS
The hydrologic analysis utilizes the Rational Method equation, Q = CIA, to calculate peak runoff rates, where
Q = flow (cfs)
C = Coefficient of Runoff, calculated for the amount of impervious surface
I = Intensity (in/hr) for specific Tc, see the attached isopluvial and County of San Diego Hydrology
Manual (2003) Figure 3-1, I = 7.44 x P6 x D -0.645, where P6 – 6 hour precipitation (in) and D = duration
wherein Tc is used
A = area (ac)
When calculating coefficient of runoff, C, both the soil type and the land use were considered. Soil type D was
utilized in the drainage design. The weighted C is calculated for both the pre-development and post
development condition, in the attached tables, utilizing the equation from the County of San Diego Hydrology
Manual section 3.1.2, C= 0.90 x (%Impervious) + Cp x (1-%Impervious), where Cp = pervious coefficient runoff
value for the soil type from Table 3-1. For the purposes of these calculations a Cp of 0.35 for natural ground was
utilized for soil type D, as underlined on the attached copy of Table 3-1.
When considering time of concentration (Tc), both initial time of concentration Ti as well as travel time Tt were
considered. Per the County of San Diego Hydrology Manual, Section 3.1.4.1, Ti can be calculated utilizing the
Overland time of Flow Equation, as noted in Figure 3-3. In the pre-development condition, the slope and
distance at the upper portion of the drainage in the direction of sheet flow is variable across the site. At the
most remote portion of the site, iterating for length of flow utilizing the equation from Figure 3-3, the Ti is
calculated to be 6.5 min
In the post-development condition, the Ti is calculated based upon Table 3-2, see attached, for a distance of 35
ft. as 4.8 min, plus negligible travel time in the pipe, for a Tc=5min. Attached are San Diego isopluvial maps for
100 year (Q100). The runoff coefficients for the various basins are calculated in the attached tables based upon
the percentage of impervious area.
BMPS
The project is considered a standard development project and implements site design and source control BMPs,
including the planned use of rainwater harvesting tanks, the dissipation of runoff across landscape areas,
minimize erosion on slope surfaces and conserving natural features. No treatment control BMPs are required
for the subject site.
CONCLUSIONS
As outlined on the attached spreadsheet, existing Q100 = 0.38 cfs. As a result of proposed development, the
total peak runoff from the site is calculated to increase by approximately 0.38 cfs, to Q100 = 0.76 cfs. In general,
the sub-basins consist of those basins on the west side of the site, the east side of the site and the driveway.
New private storm-drain will include a combination of 4-inch and 6-inch private storm drain within the private
property. In consideration of the curb height, the outlet of Basins B1A-B1C, and B1D will outlet with 3-inch pvc
pipe.
See the attached hydraulic sizing for 3 in pressure pipe, 4 & 6 inch private storm drain to sufficiently convey
runoff from the pad to dissipators below, as well as sizing of storm drainage systems on the pad.
HYDROLOGY PRE- DEVELOPMENTt DRAINAGE SUMMARY TABLE Basin Area (ac) Impervious Q (cfs) V (fps) Area (ac) 81 0.17 0.02 O.JB SHEET FLOW BASl 1 LEGEND - - - -PROJECT BOUNDARY ---HYDROLOGY SUB-BASIN ,I FLOW DIRECTION □ IMPERVIOUS CONG SURFACE -SITE 30 0 ~---30 60 90 I l;____-------=-,1 -;::::-,.....__ ~ ~ m '-..:. .,..... N --.-..~'~~~-~~-~~~--I-- - - -SCALE 1• = JO FT
HYDROLOGY POST DEVELOPMENTDRAINAGE SUMMARY TABLE Basin Area (ac) Impervious Q (cfs) Area (ac) B1A B1B B1C B1D B1E 0.08 0.07 0.44 0.01 0.01 0.02 0.04 0.002 0.09 O.OJ 0.01 0.11 0.01 0.01 0.09 LEGEND ----PROJECT BOUNDARY - - - - -FLOW DIRECTION □ HYDROLOGY BASIN C PRP. BLDG SURFACE-IMPERVIOUS LLLLl <l,:; LLLLl , tttti PRP. IMPERVIOUS CONC/PAVERS LLLLl SITE E O E W W -~~------~-------------1 ____ 1---~1 SCALE 1• = JO FT FF=1J0.25 17' 55'W 4'
HAGUE RESIDENCECynthia Lane, CarlsbadPRELIMINARY HYDROLOGY CALCULATIONSC(composite) C=0.90 x % impervious surfaces + Cp x (1‐%impervious)RATIONAL METHOD FOR TRIBUTARY < 0.5 SQ MILEQ = CIAI (in/hr) - 100 YR6.59=7.44 P6 D^(-0.645)P62.50SOIL TYPE DHYDROLOGIC & HYDRAULIC DESIGNBASIN NO.TOTAL AREA (sf)TOTAL AREA (ac)IMPERV AREA (sf)AREA IMPERV (ac)% IMPAREA PERV (sf)AREA PERV (ac)C Tc Ti Tt I Q100 (cfs)PRE‐DEVELOPMENT ONSITEB1 7,354 0.17 681 0.02 0.096,673 0.15 0.40 6.55.56 0.387,354 TOTAL Q 0.38POST DEVELOPMENT ONSITEB1A 3,395 0.08 3149 0.07 0.932460.01 0.86 5.06.59 0.44B1B 433 0.01 0 0.00 0.004330.01 0.35 5.06.59 0.02B1C 1,626 0.04 80 0.002 0.0515460.04 0.38 5.06.59 0.09Subtotal 0.56B1D 1,257 0.03 550 0.01 0.447070.02 0.59 5.06.59 0.11B1E 643 0.01 643 0.01 1.0000.00 0.90 5.06.59 0.097,354 4,422 2,932 TOTAL Q 0.760.62Delta Q0.38
HYDRAULICS
HAGUE RESIDENCEHYDRAULIC DESIGNPIPESLabel Solve For Friction MethodRoughness CoefficientChannel Slope (ft/ft)Normal Depth (in)Diameter (in)Discharge (ft³/s)Flow Area (ft²)Wetted Perimeter (ft)Hydraulic Radius (in)Top Width (ft)Critical Depth (ft)Percent Full (%)Critical Slope (ft/ft)Velocity (ft/s)Velocity Head (ft)Specific Energy (ft)Froude NumberMaximum Discharge (ft³/s)Discharge Full (ft³/s)Slope Full (ft/ft)Flow Type4" ‐ B1C, B1DFull Flow CapacityManning Formula0.01 0.01 0.33 4.0 0.25 0.09 1.05 0.08 0 0.28 100 0.01 2.8 0.12 0.46 0 0.27 0.25 0.01 SubCritical6" ‐ B1A, B1B, B1CFull Flow CapacityManning Formula0.01 0.01 0.5 6.0 0.73 0.20 1.57 0.13 0 0.43 100 0.01 3.7 0.21 0.71 0 0.78 0.73 0.01SubCritical3" ‐ B1D ROWFull Flow Manning 0.01 0.01 0.25 3.0 0.11 0.05 0.79 0.06 0 0.2 100 0.01 2.3 0.09 0.34 0 0.12 0.11 0.01SubCriticalLabel Solve For Friction MethodPressure at 1 (psi)Pressure at 2 (psi)Elevation at 1 (ft)Elevation at 2 (ft)Length (ft) Roughness CoefficientDiameter (in)Discharge (ft³/s)Energy Grade at 1 (ft)Energy Grade at 2 (ft)Hydraulic Grade at 1 (ft)Hydraulic Grade at 2 (ft)Flow Area (ft²)Wetted Perimeter (ft)Velocity (ft/s)Velocity Head (ft)Friction Slope (%)Notes Messages SuperCritical3" B1A‐C pressure D‐27 DischargeManning Formula4.2 0.0 125.5 125.1 17.00 0.01 3 0.6 132 127.4 129.7 125.10 0.1 0.79 12.17 2.3 0.27CHANNELSLabel Solve For Friction MethodRoughness CoefficientChannel Slope (ft/ft)Normal Depth (in)Left Side Slope (ft/ft (H:V))Right Side Slope (ft/ft (H:V))Discharge (ft³/s)Flow Area (ft²)Wetted Perimeter (ft)Hydraulic Radius (in)Top Width (ft)Critical Depth (ft)Critical Slope (ft/ft)Velocity (ft/s)Velocity Head (ft)Specific Energy (ft)Froude NumberFlow Type
HYDROLOGY
100
4.02.5 0.63
2.5
5
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15 20 30
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40 50
Duration
EQUATION
I = 7.44 P5 D-0.645
I = Intensity (in/hr)
P5 = 6-Hour Precipitation (in)
D = Duration (min)
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Intensity-Duration Design Chart -Template
Directions for Application:
(1) From precipitation maps determine 6 hr and 24 hr amounts
for the selected frequency. These maps are included in the
County Hydrology Manual (10, 50, and 100 yr maps included
in the Design and Procedure Manual).
(2) Adjust 6 hr precipitation {if necessary) so that it is within
the range of 45% to 65% of the 24 hr precipitation (not
applicaple to Desert).
(3) Plot 6 hr precipitation on the right side of the chart.
(4) Draw a line through the point parallel to the plotted lines.
(5) This line is the intensity-duration curve for the location
being analyzed .
Application Form:
(a) Selected frequency ___ year
p
(b) P6 = ___ in., P24 = ___ ,p2-= %(2)
24
(c) Adjusted P6<2) = ___ in .
{d) Ix= ___ min.
(e) I = __ in./hr.
Note: This chart replaces the Intensity-Duration-Frequency
curves used since 1965.
P6 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6
Duration I I I I I I I I I I I
5 2.63 3.95 5.27 6.59 7.90 9.22 10 5i 11.86 13.17 14.49 15.81
7 2.12 3.18 4.24 5.30 6.36 7.42 8.48 9.54 10.60 11.66 12.72
10 1.68 2.53 3.37 4.21 5.05 5.90 6.74 7.58 8.42 9.27 10.11
15 1.30 1.95 2.59 3.24 3.89 4.54 5.1 9 5.84 6.49 7.13 7.78
20 1.08 1.62 2.15 2.69 3.23 3.77 4.31 4.85 5.39 5.93 6.46
25 0.93-1.40 1.87 2.33 2.80 3.27 3.73 4.20 4.67 5.13 5.60
30 0.83 1.24 1.66 2.07 2.49 2.90 3.32 3.73 4.15 4.56 4.98 --40 0.69 1 .03 ~ 1.72 2.07 2.41 2.76 3.10 3.45 3.79 '4.13
50 0.60 0.90 1.19 1.49 1.79 2.09 2.39 2.69 2.98 328 -3.58
60 0.53 0.80 1.06 1.33 1.59 1.86 2.12 2.39 2.65 2.92 3.18
90 0.41 0.61 0.82 1.02 '1.23 1.43 1.63 1.84 2.04 2.25 '2.45
120 0.34 0.51 0.68 0.85 1.02 1.19 ,J_.36 1.53 1.70 1.87 .._2.04 150 0.29 ~~ 0.44 0.59 0.73 0.88 1.03 1.18 1.32 1.47 1.62 1.76
180 0.26 0.39 0.52 0.65 0.78 0.91 1.04 1.18 1.31 1.44 1.57
240 0.22 0.33 0.43 0.54 0.65 0.76 0.87 0.98 1.08 1.19 1.30
300 0.19 0.28 0.38 0.47 0.56 0.66 "0.75 0.85 0.94 1.03 1.13
360 0.17 0.25 0.33 0.42 0.50 0.58 0.67 0.75 0.84 0.92 1.00
FIGURE ~
SITE
33d10’03” ; 117d20’30”
County of San Diego
Hydrology Manual
Rairifa/1 Isopluvials
I lsopluvial (inches) I
----1
SITE
33"00:
County of San Diego
Hydrology Manual
• Rainfal/ lsop/uvia/s
100 Year Rainfall Event -24 Hours
I --------lsopluvial (illCMO) I
DPW *GIS ~.,,,_~ ...__,,,_,_, __
3 0 3Mlles
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~
S1tGIS 'if/c H:i.vc San Diego {Awcrcd!
SITE
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33•,
33• 15'
33•00:
32•
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Legend
County of San Diego
Hydrology Manual
Soil Hydrologic Groups
Soil Groups
D G10YpA -G10Yp B
D G10Yp C
D Gl0Yp D
D Undetermined
D Data Unavailable
DPW ~GIS ~o/P--_,,,,,__,__,.
N n1•-·PIW:MIJEDWIDOITWIIAlloWTY(FNlf-.~-BIPREM +~~~~~==~==--~ °""""" ....... _ ..... ~-n.~..,-~-"' ......... ...,._ ...._.,... ___ ...,..__,.. ----.-w). Thlopooll,ld. _______ _ ,._......,.,1-_,...
3 0 3 MIies
~
San Diego County Hydrology Manual
Date June 2003
Table 3-1
Section:
Page:
RUNOFF COEFFICIENTS FOR URBAN AREAS
Land Use Runoff Coefficient "C"
Soil Type
NRCS Elements County Elements %IMPER A B
Undisturbed Natural Terrain (Natural) Permanent Ooen Soace 0* 0.20 0.25
Low Density Residential (LDR) Residential, 1.0 DU/A or less 10 0.27 0.32
Low Density Residential (LDR) Residential, 2.0 DU/A or less 20 0.34 0.38
Low Density Residential (LDR) Residential, 2.9 DU/A or less 25 0.38 0.41
Medium Density Residential (MDR) Residential, 4.3 DU/A or less 30 0.41 0.45
Medium Density Residential (MDR) Residential, 7.3 DU/A or less 40 0.48 0.51
Medium Density Residential (MDR) Residential, 10.9 DU/A or less 45 0.52 0.54
Medium Density Residential (MDR) Residential, 14.5 DU/A or less 50 0.55 0.58
High Density Residential (HDR) Residential, 24.0 DU/A or less 65 0.66 0.67
High Density Residential (HDR) Residential, 43.0 DU/A or less 80 0.76 0.77
Commercial/Industrial (N. Com) Neighborhood Commercial 80 0.76 0.77
Commercial/Industrial (G. Com) General Commercial 85 0.80 0.80
Commercial/Industrial (O.P. Com) Office Professional/Commercial 90 0.83 0.84
Commercial/Industrial (Limited I.) Limited Industrial 90 0.83 0.84
Commercial/Industrial (General I.) General Industrial 95 0.87 0.87
C
0.30
0.36
0.42
0.45
0.48
0.54
0.57
0.60
0.69
0.78
0.78
0.81
0.84
0.84
0.87
3
6 of26
D
0.35
0.41
0.46
0.49
0.52
0.57
0.60
0.63
0.71
0.79
0.79
0.82
0.85
0.85
0.87
*The values associated with 0% impervious may be used for direct calculation of the runoff coefficient as described in Section 3.1.2 (representing the pervious runoff
coefficient, Cp, for the soil type), or for areas that will remain undisturbed in perpetuity. Justification must be given that the area will remain natural forever (e.g., the area
is located in Cleveland National Forest).
DU/A = dwelling units per acre
NRCS = National Resources Conservation Service
3-6
Element*
Natural
LDR
LDR
LDR
MDR
MDR
MDR
MDR
HDR
HDR
N.Com
G.Com
O.P ./Com
Limited I.
General I.
Table 3-2
MAXIMUM OVERLAND FLOW LENGTH (LM)
& INITIAL TIME OF CONCENTRATION (Ti)
DU/ .5 % 1% 2% 3% 5%
Acre LM Ti LM Ti LM Ti LM Ti LM Ti
50 13.2 70 12.5 85 10.9 100 10.3 100 8.7
1 50 12.2 70 11.5 85 10.0 100 9.5 100 8.0
2 50 11.3 70 10.5 85 9.2 100 8.8 100 7.4
2.9 50 10.7 70 10.0 85 8.8 95 8.1 100 7.0
41 .:;o 10?. 70 96 ~o ~ 1 9.:; 7~ 100 67
7.3 50 9.2 65 8.4 80 7.4 95 7.0 100 6.0
10.9 50 8.7 65 7.9 80 6.9 90 6.4 100 5.7
14.5 50 8.2 65 7.4 80 6.5 90 6.0 100 5.4
24 50 6.7 65 6.1 75 5.1 90 4.9 95 4.3
43 50 5.3 65 4.7 75 4.0 85 3.8 95 3.4
50 5.3 60 4.5 75 4.0 85 3.8 95 3.4
50 4.7 60 4.1 75 3.6 85 3.4 90 2.9
50 4.2 60 3.7 70 3.1 80 2.9 90 2.6
50 4.2 60 3.7 70 3.1 80 2.9 90 2.6
50 3.7 60 3.2 70 2.7 80 2.6 90 2.3
* See Table 3-1 for more detailed description
10%
LM Ti
100 6.9
100 6.4
100 5.8
100 5.6
100 .:; 1
100 4.8
100 4.5
100 4.3
100 3.5
100 2.7
100 2.7
100 2.4
100 2.2
100 2.2
100 1.9