HomeMy WebLinkAboutCDP 07-12; SEARS RESIDENCE; DRAINAGE STUDY; DWG 458-7A; 2008-11-18•
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DRAINAGE STUDY
FOR
CDP 07-12
4017 SUNNYHILL DRIVE
APN 207 -061 -54
PREPARED FOR
Tom and Wendy Sears
1387 Cynthia Lane
Carlsbad, CA 92008
PREPARED BY
Robert 0. Sukup
4322 Sea Bright Place
Carlsbad, CA 92008
November 18, 2008
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C The subject property is an irregularly shaped in-fill lot. It is almost bounded on
three sides by either a public street or private driveways on the north, east and
west. All of the water flows to the southwest corner of the property where it exits
on the surface, across an existing concrete driveway, and then through an
existing drainage outlet. This outlet is through a wall, where it then continues on
the surface to Alder Street.
The single lot grading plan has been designed for all the water to surface flow
around the house where it is strategically collected in a 4" drain pipe system that
discharges into the lower, non graded, back yard area. The lower back yard area
has 2 -50' long grass swales that will promote filtration and infiltration. The 2
grass swales converge to a small gravel pit. The gravel pit is meant to augment
the filter and infiltration process started by the upstream grass swales. It also
creates a small storage capacity of about 5.65 c.f. [assumes 30% voids in the
gravel]. Whatever water is not absorbed by the gravel pit and grass swales,
continues in a gravel swale downstream to the existing offsite driveway that has
been the "historic conveyance channel" for the immediate houses in the area,
including the subject lot. The combination of the grass swales, gravel pit and
gravel swales should contain all low flows and nuisance water on site. Additional
heavy storm flows not absorbed, will go down the aforementioned driveway,
through a storm drain opening in a block wall, and then continue down a
driveway to Alder Street where it eventually goes into the City Drainage System.
In my professional opinion, the project's drainage system, as proposed, should
function very well and not create any downstream erosion, flooding, or siltation.
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San Diego County Hydrology Manual
Date: June 2003
0
Section:
Page:
Table3-1
RUNOFF COEFFICIENTS FOR URBAN AREAS
Land Use I Runoff Coefficient "C"
Soil T e
'. . NRCS Elements Coun Elements %IMPER. A B
Undisturbed Natural Terrain (Natural) Pennanent Open Space PR. O* % 0~ 0.25 ---,. 6
Low Density Residential (LOR) Residential, 1.0 DU/A or less IO 0 :,7 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
Medium Density Residential (MOR) Residential, 4.3 DU/A or less -12.34% 0~ 0.45
Medium Density Residential (MDR) 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 (MDR) Residential, 14.5 DU/A or less 50 0.55 0.58
High Density Residential (HOR) 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
CommerciaVIndustrial (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_!.) 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
G
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
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SanD; ,CountyHydrologyManual _________________ ----~=--_______ J_ Date:-.~~~2003------~----------Page: . 12 of26
Note that the Initial Time of Concentration should be rerlective of the general land-use at the
upstream end of a drainage basin. A single lot with an area of two or less acres does not have
a significant effect wpere the drainage basin area is 20 to 600 acres.
Table 3-2 provides limits of the length (Maximum Length (LM)) of sheet flow to be used in
hydrology studies. Initial Ti values based on average C values for the I '.d Use Element are
also included. These values can be used in planning and design appiJ,_ations as desc~bed
below. Exceptions may be approved by the "Regulating Agency" when submitted with a
detailed study.
MAXIMUM OVERLAND FLOW LENGTH (LM)
& INITIAL TIME OF CONCENTRATION (T;)
Element* DU/ .5% 1% 2% 3% C 5% ~J 10%
Acre LM Ti LM Ti LM Ti LM Ti LM Ti LM Ti
Natural 50 13.2 70 12.5 85 10.9 100 10.3 100 8.7 100 6.9
LDR 1 50 12.2 70 11.5 85 10.0 100 9.5 100 8.0 100 6.4
T T\D 2 50 11.3 70 10.5 85 9.2 100 8.8 100 7.4 100 5.8 ---) 50 LDR 2.9 10.7 70 10.0 85 8.8 95 8.1 lQo( ~ ")00 5.6 -MDR 4.3 50 10.2 70 9.6 80 8.1 95 7.8 100 6.7 100 5.3
MDR 7.3 50 9.2 65 8.4 80 7.4 95 7.0 100 6.0 100 4.8
MDR 10.9 50 8.7 65 7.9 80 6.9 90 6.4 100 5.7 100 4.5
MDR 14.5 50 8.2 65 7.4 80 6.5 90 6.0 100 5.4 100 4.3
HDR 24 50 6.7 65 6.1 75 5.1 90 4.9 95 4.3 100 3.5
HDR 43 50 5.3 65 4.7 75 4.0 85 3.8 95 3.4 100 2.7
N.Com 50 5.3 60 4.5 75 4.0 85 3.8 95 3.4 100 2.7
G.Com I 50 4.7 60 4.1 75 3.6 85 3.4 90 2.9 100 2.4
O.P./Com 50 4.2 60. 3.7 70 3.1 80 2.9 90 2.6 100 2.2 -
Limited I. 50 4.2 6( ~-.7 70 3.1 80 2.9, 90 2.6 100 2.2
;
General I. 50 3.7 60 .L2 70 2.7 80 2.6 90 2.3 '.00 1.9 -....
*See Table 3-1 for more detailed description
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Minutes Duration
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Directions for Appllcatlon:
(1) From precipitation maps determine 6 hr and 24 hr amounts
for the selected frequency. These maps are Included In the
EQUATION County Hydrology Manual (10, 50, and 100 yr maps Included
I = 7.44 Pa o·0.645 In the Design and Procedure Manual).
(2) Adjust 6 hr precipitation (If necessary) so that It Is within I = Intensity (In/hr)
P6 = 6--Hour Precipitation (in) the range of 45% to 65% of the 24 hr precipitation (not
lo applicaple to Desert) . D = Duration (min) (3) Plot 6 hr precipitation on the right side of the chart.
(4) Draw a Une through the point parallel to the plotted fines .
(5) This line is the Intensity-duration curve for the location
'~ beii. . .:,:l~•zed.
~ ' .... , .... Application Fonn: 10;10o, ., ,' ... , ...... ~ ' ... .. (a) Selected frequency --~ear :S~ ... :r ' ... .. .... ~~ g i,, 3.1 p ~" (b) Ps = lz.to in .• p24 = ~ .~ = ~%(21 , .. I~ "'"' ~ .. ~ ~~ ..,
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24 ,.
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(d) tx = ~ min. Pl~: 'l / · PQS"r = I. 5.5 Ct.
~L ~"' 5.0 g ... ~ ~ ~ .. 4.5 -,:, (e) I =<--r-in./hr.110flli = !~5 l:,oo ,e.: 5. ?7
4.0 i ', ~ ~~~ ~ 11• ~ .. ;PJ tl40 fodT-: bO . ""' .... """' 3.5-Note: This chart replaces the Intensity-Duration-Frequency ... "', 3.0 curves used since 1965. ... .... ... ..... ~~ .. 2.5 ··~ ... , ............ < ····-~-~-· i .. -··---!.--·--.. -f :b _,,_ .. J._T __
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~ ·2.0 ·--.. 5 2.63 3.95 5.271 6.59 [!.9019.22 ::~:t¥:1i 14;49 16.81 '._ ........ -·-"1 .. ---· 'fi]ia [ID! 7 2.12 3.18 4.24 5.30 6.3@~ .... ····--· 10 . 1.68 ,!-53 3.37 4,gt .§:~~ -i:if 10.11
1.5 --,i 1.30 1.95 2.59 3.24 3.89 4.54 s.1i s:iii .... s.49 7.13 7.78 ---··-20 cT.oa• ·u2 2.15 _g.89 3.23 3.77 _ 4.31 ..1,!5 .. ""5,311, s:e iiAi ·····-25 .o.93_ uo 1.8~~-'ii> "3.27 3.73 4.20 4.67 It "Sc60' ·-~ 0.83 U4 1.88 2.07 2.49 2.90 .. 3.32 .. 3.73 4.1! ·m
.. .. -·-40 0.69 1.03 1.38 1.72 2.01 2.41 £@..J!!!tJH!, m: :·:.:~ 1.0 ............. 1$1) o.eo o.90 1.1e us t.791:00 2.39 2.69 2.98 au ~!~ ---80 ·:~:· ,~;1 ~ _;~ 1.59 1.84 2.12 U9 2.65 2.92· 3.18 ......... -90 1.23 1.43 .!,~ 1,M ...t..<t'! .. ur "'i4i
120 .O.:M 0.51 O.e&i0-85 t.02 1.19 ua .. 1.53 r+10. "fif "foi' ··1so .. o.29, 0.44 .9z59 0.73 ~,!! ~~~
1.18 ·'1'·"'· Im T.78
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2 3 4 5 6 0.22 0.33 0.43 0.54 0.65 0.76 1.19 1.30
Hours
-··--300 0.19 0.28,..0.38 _0.47 0.56 0:66 .. ~ JJ! .... -360 0.17 0.25 0.33 0.42 0.50 0,58 0.87 0.75 . 0.84 t.00
FIGURE I I Intensity-Duration Design Chart· Template 3-1