HomeMy WebLinkAboutDEV 2016-0043; Vaughn Residence; Drainage Study; 2017-09-06I RECORD coP)'--
COFFEY ENGINEERING, INC. --··--
September 6, 201 7
Engineering Department
City of Carlsbad
1635 Faraday Ave
Carlsbad, CA 92008
Re: Drainage Summary
Vaughn Residence
2605 Crest Drive, Carlsbad, CA 92008
Dear Sir or Madam:
SE? 0 3 '''.J!7
LAN C ' ~ \ ,. '"' } • 1 ,-0 C... ,/ ::_ L .... I v :..... ,\; T
ENGia .. c.c..i,11-..G
The existing site consists of a vacant 0.28 AC lot located at 2605 Crest Drive in Carlsbad, CA.
Drainage on the vacant lot can best be described as sheet fl ow with runoff flowing from the eastern
corner of the site in a westerly direction. The grade falls in elevation approximately 9 ft. over a
distance of approximately 200 ft.
{o /)/,7J
~.,te --_ ..
The drainage area tributary to the site consists of the site itself (12,344 ft2), a portion of the fronting
road (apprx. 3,000 ft2), and a portion of the neighboring lot to the southeast (apprx. 9,200 ft2). Attached
to this letter is an exhibit depicting the extent of the drainage area tributary to the site.
Runoff from the area tributary to the subject property exits the site at the western property corner
where is continues westerly for approximately 90 ft. where the terrain begins to fall in a southwesterly
direction and runoff continues to the next street over (Wilson Street).
Current discharge from the tributary area containing the project has been calculated to be 1.34 cfs for a
100-year storm.
The proposed construction consists of a new single family residence with a footprint of approximately
2,600 ft, car port, driveway as well as landscaping and minor hardscape. Drainage for the proposed
site will be accomplished by surface sheet flow only. No subsurface drainage system is proposed. The
proposed development will require minor grading (30 CY -balanced) to create a pad for the proposed
home and to fi ne grade the driveway. No significant changes in overall topography are necessary or
proposed from the existing conditions.
Rainwater from the house will be collected at the downspouts and routed to a cistern to be used for
irrigation purposes. Runoff fro m the driveway and offsite tributary area will be intercepted by a
vegetated swale along the southern edge of the subject property where it will flow westerly then
northerly, ultimately discharging to an existing riprap pad at the westernmost corner of the site. Runoff
from the remainder of the site (landscaping areas and perimeter of the house) will flow along the
9666 BUSINESSPARK AVENUE, SUITE 2 10. SAN DIEGO. CA 9213 1 PHONE: (858) 83 1-0 111 FAX: (858) 831-0 179
surface to a vegetated swale along the northern edge of the subject property where it will then flow
westerly, ultimately discharging to the existing riprap at the westernmost comer of the site.
Calculated discharge from the developed condition of the tributary area containing the project has been
calculated to be 1.48 cfs for a 100-year storm. The calculated maximum discharge velocity of the
proposed vegetated swales to the exiting riprap at the rear of the site is 1.90 fps. The existing riprap
(No. 2 Backing per Dwg. No. 485-4A) is an appropriate size for this velocity.
If we can be of further assistance in providing any additional information, please feel free to contact
us. Thank you.
Sp¥~/
Daniel Vaid~ PE
Coffey Engineering, Inc.
Page 2 of2
~ COFFEY ENGINEERING, INC.
Table A -Weighted Runoff Coefficients ('C')
Impervious/ Percent
Developed Area Pervious Area Impervious/De
OMA (SF) (SF) Total (SF) Total (AC) C-Value* veloped
Pre 12,200 12,344 24,544 0.56 0.35 49.71%
Post 16,470 8,074 24,544 0.56 0.38 67.10%
*Impervious Areas C=0.45; Perv1ous Areas C=0.25; Perv1ous Pavers C=0.40
Table B -Project Runoff Calculations
Natural Watercouse (Qer Fig. 3-4} Urban Overland {Sheet) Flow {Qer Fig. 3-3) Pipe/Channel Flow Summary 100-yr P6 = 2.60
minimum)
Natural Urban Total time-
Element & Change in watercouse watercours Maximum Initial Ttime of Average Pipe travel of-
Flow ID Dwelling Watercourse Elevation, H duration, Dn e distance, Overland Flow Runoff Concentration Overland Flow Pipe Length, velocity, V time, TP concentrati Runoff Coefficient, Rainfall Intensity, I Basin Area, A Q(ds) =
(Basin) Unit/Acre distance, L (ft) Elev. 1 Elev. 2 (ft) (min) Ti (ft) (s LM) Length Watercourse slope, s (%) Coefficient, C (per Fig. 3-2) Time, Tt (min) l p (ft) (fps) (min) on, Tc (min) C (in/hr) (acres) C*l*A
Pre MOR· 4.3 228 186 177 9 1.77 0.00 0.00 5.00 0.35 6.85 0.56 1.34
Post MOR-4.3 0 0.00 0.00 228 1.4 2.81 5.00 0.38 6.85 0.56 1.48
10.0
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0.6
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0.4
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0.2
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1=6. 85"/hr
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111 111111111
30
Minutes
40 50
Duration
I =
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1111 11111
EQUATION
7.44 P6 D-0.645
Intensity (in/hr)
6-Hour Precipitation (in)
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:
100 (a) Selected frequency ___ year
(b) P = 2.6 in. p = 4. 7 ~ = 55 %(2) 6 --• 24 --•p24
(c) Adjusted P6<2l = ~ in.
(d) tx = 5 __ min.
(e) I = ___ in./hr.
Note: This chart replaces the Intensity-Duration-Frequency
curves used since 1965.
P6 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 10.54 11.86 13.17 14.49 15.81
1 2.12-3.18°4.24 5.30-6.36 7.42 8.48 · 9.54 ·10.so·11.66·12.12
10 1.68 ).53: 3.37_j.21 . 5.0( 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 5.19 5.84 6.49 7.13 7.78
20 1.08-1.62.2.152 .69-3.2f3.77. 4.31 . 4.85 -5.39 ' 5.936.46
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).4(2.00; 3.32: 3.73 : 4.15 : 4.56 ] 4.98
40 0.69 1.03 1.38 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 3.28 . 3.58
60 o.53 o.80· 1.oo· 1.33·1.s9 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 o.34 :o.s1 ;0.68: o.8s:1.02 1.1( 1.36 : 1.53 : 1.10 · 1.87 i 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
JOO 0.19 ·0.28·0.38'0.41·0.ss·o.66· o.75 · o.85 · o.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 ~
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 Coun Elements %IMPER A B
I Undisturbed Natural Terrain Q:!aturall Permanent QEen Sl?ace I o• 0.20 mI1
Low Density Residential (LOR) Residential, 1.0 DU/A or less 10 0.27 0.32
Low Density Residential (LOR) Residential, 2.0 DU/A or less 20 0.34 0.38
Low Density Residential (LOR) Residential, 2.9 DU/A or less 25 0.38 0.41
I Medium Densi!i'. Residential (MDR2 Residential, 4.3 DU/A or less I 30 0.41 ~
Medium Density Residential (MOR) Residential, 7.3 DU/A or less 40 0.48 0.51
Medium Density Residential (MOR) Residential, 10.9 DU/A or less 45 0.52 0.54
Medium Density Residential (MOR) 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 ProfessionaVCommercial 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
.6E
Feet
5000
4000
EQUATION
Tc = (1~~3)0.385
Tc
L
.6E
= Time of concentration (hours)
.. Watercourse Distance (miles)
= Change in elevation along
effective slope line (See Figure 3-5)(feet)
3000 Tc
Hours Minutes
4
3
2
400
60
300
50
200 40
L
MIies Feet 30
100
20
18 .
3000 16 ' ' 14
' ' 12
' 30 ' 10
' 9
8
20 7
6
5
10 4
3
SOURCE: California Division of Highways (1941) and Kirpich (1940)
Nomograph for Determination of
Time of Concentration (Tc) or Travel Time (Tt) for Natural watersheds
F IG U R E
3-4
C"nnh, "f ~~n n1POQ
Hydrology Manual
• Rainfall Isopluvials
100 Year Rainfall Event -6 Bonn
lsopluvtal (Inches)
~
SltGIS We H:ivc S-..n l>iq.((1 Col"Crcd!
t ~...+-+-'
-t r+ I-+ +e1+ i,~I
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Hydrology Manual
• Rainfall Isop/uvials
100 Year Rainfall Event -24 Hours
lsopluvfal (Inches)
DPW ~GIS
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S~GIS ~-~ .... ~..........,.. ...... We H:h-C S:.n Dii.~"O Covt"rcd.!
+N ~:.:_=-~~~.:= r»'~MUT'l'MmllfflrEIIINlRA~~ ~ ...... ,._. ..........
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3 0 3 MIias ~
33" ta23'N
33" IC121'N
N
A
Map Saile: 1 :441 f printed on A landscape (11" X 8.5") sheet
Hydrologic Soil Group-San Diego County Area, California
(Vaughn Residence - Hydrologic Soil Group)
-------=======-------------=============Metes 0 5 10 20 3)
--------========---------------=============:::=:,Feet o 20 ~ oo m
Map projectx)n: Web Mescator Comer roordinates: WGS84 Edge tics: VTM ZOre llN WGS84
USDA Natural Resources Web Soil Survey
National Cooperative Soil Survey -1ifiF Conservation Service
9/1/2017
Page 1 of 4
33" IC123'N
33" IC121'N
Hydrologic Soil Group-San Diego County Area, California
(Vaughn Residence - Hydrologic Soil Group)
MAP LEGEND MAP INFORMATION
Area of Interest (AOI)
Area of Interest (AOI)
Soils
Soil Rating Polygons
D A
D AID
D B
D BID
D C
D CID
D D
D Not rated or not available
Soil Rating Lines
_,, A
_,, AID
_,, B
_,, B/D
.,...,, C
_,, CID
_,, D
.. " Not rated or not available
Soil Rating Points
Iii A
• AID
• B
• B/D
USDA Natural Resources
:iiiliiii Conservation Service
C
C
C
CID
• D
C Not rated or not available
Water Features
Streams and Canals
Transportation
++t Rails
,,.,,., Interstate Highways
US Routes
Major Roads
Local Roads
Background
• Aerial Photography
Web Soil Survey
National Cooperative Soil Survey
The soil surveys that comprise your AOI were mapped at
1:24,000.
Warning: Soil Map may not be valid at this scale.
Enlargement of maps beyond the scale of mapping can cause
misunderstanding of the detail of mapping and accuracy of soil
line placement. The maps do not show the small areas of
contrasting soils that could have been shown at a more detailed
scale.
Please rely on the bar scale on each map sheet for map
measurements.
Source of Map: Natural Resources Conservation Service
Web Soil Survey URL:
Coordinate System: Web Mercator (EPSG:3857)
Maps from the Web Soil Survey are based on the Web Mercator
projection, which preserves direction and shape but distorts
distance and area. A projection that preserves area, such as the
Albers equal-area conic projection, should be used if more
accurate calculations of distance or area are required.
This product is generated from the USDA-NRCS certified data as
of the version date( s) listed below.
Soil Survey Area: San Diego County Area, California
Survey Area Data: Version 10, Sep 12, 2016
Soil map units are labeled (as space allows) for map scales
1 :50,000 or larger.
Date(s) aerial images were photographed: Nov 3, 2014-Nov
22,2014
The orthophoto or other base map on which the soil lines were
compiled and digitized probably differs from the background
imagery displayed on these maps. As a result, some minor
shifting of map unit boundaries may be evident.
9/1/2017
Page 2 of 4
Hydrologic Soil Group-San Diego County Area, California Vaughn Residence -Hydrologic Soil
Group
Hydrologic Soil Group
Hydrologlc Soll Group-Summary by Map Unit-San Diego County Area, California (CA638)
Map unit symbol Map unit name Rating Acres In AOI Percent of AOI
CbC Carlsbad gravelly loamy B 0.2
sand, 5 to 9 percent
slopes
MIE Marina loamy coarse B 0.1
sand, 9 to 30 percent
slopes
Totals for Area of Interest 0.3
Description
Hydrologic soil groups are based on estimates of runoff potential. Soils are
assigned to one of four groups according to the rate of water infiltration when the
soils are not protected by vegetation, are thoroughly wet, and receive
precipitation from long-duration storms.
The soils in the United States are assigned to four groups (A, B, C, and D) and
three dual classes (AID, 8/D, and C/D). The groups are defined as follows:
Group A. Soils having a high infiltration rate (low runoff potential) when
thoroughly wet. These consist mainly of deep, well drained to excessively
drained sands or gravelly sands. These soils have a high rate of water
transmission.
Group 8. Soils having a moderate infiltration rate when thoroughly wet. These
consist chiefly of moderately deep or deep, moderately well drained or well
drained soils that have moderately fine texture to moderately coarse texture.
These soils have a moderate rate of water transmission.
Group C. Soils having a slow infiltration rate when thoroughly wet. These consist
chiefly of soils having a layer that impedes the downward movement of water or
soils of moderately fine texture or fine texture. These soils have a slow rate of
water transmission.
Group D. Soi ls having a very slow infiltration rate (high runoff potential) when
thoroughly wet. These consist chiefly of clays that have a high shrink-swell
potential, soils that have a high water table, soils that have a claypan or clay
layer at or near the surface, and soils that are shallow over nearly impervious
material. These soils have a very slow rate of water transmission.
If a soil is assigned to a dual hydrologic group (AID, B/D, or C/D), the first letter is
for drained areas and the second is for undrained areas. Only the soils that in
their natural condition are in group D are assigned to dual classes.
USDA Natural Resources
~-Conservation Service
Web Soil Survey
National Cooperative Soil Survey
81.1%
18.9%
100.0%
9/1/2017
Page 3 of 4
•
Hydrologic Soil Group-San Diego County Area, California
Rating Options
Aggregatiqn Method: Dominant Condition
Component Percent Cutoff: None Specified
Tie-break Rule: Higher
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
Vaughn Residence -Hydrologic Soil
Group
9/1/2017
Page 4 of 4