HomeMy WebLinkAboutCDP 06-16; Matsubara Residence; Drainage Report; 2007-04-09DRAINAGE REPORT
FOR
MATSUBARA RESIDENCE
APN 206 - 262 -11
PREPARED FOR
Ernie Matsubara
3560 Windsor Road
Oceanside, CA 92056
PREPARED BY
Robert O. Sukup
4322 Sea Bright Place
Carlsbad, CA 92008
September 27, 2007
The proposed project is to construct a new single family house on a vacant lot
on the north side of Chinquapin Avenue. The entire lot is about .26 acres. This is
an infill lot and one of the last lots to be built on. The existing neighborhood is all
built out. There are houses to the north, east, and west of the lot.
At present the lot sheet flows to the southwest. All of the drainage water goes
into the existing lot. I do not know how the water from the existing lot gets out.
Based on the topo we shot along the existing properties, there is a low point
about two thirds of the way back from Chinquapin Avenue on the developed lot. I
do not know of any drainage problems with the lot.
I cannot continue to drain into the existing lot. I have set up a combination of
swales and drain pipes on the proposed grading plan that takes the drainage
water back to Chinquapin Avenue. Prior to exiting to the street, the drainage
water goes through 30' of a gravel swale for filtration, absorption and velocity
reduction. Whatever water leaves the gravel swale at the R.O.W. line, I have
provided a small concrete swale to convey the drainage to the street. This will
prevent erosion over the earthen R.O.W. Once in Chinquapin Avenue, the
drainage goes "westerly" down a good grade in the street's curb and gutter,
across Adams Avenue via a concrete cross gutter, then into a 15' long catch
basin which also has a 2'x3' grate inlet.
My calculations show the projected increase in flow for the 100 year storm to be
about .6 cfs [.24 cfs to .84 cfs]. The drainage from this lot is staying entirely
within the existing drainage basin. The proposed house is consistent with
development in the area and its contribution to the area drainage would have
been accounted for when the City did the stonn drain improvements. It is the
intent of my design that the combination of grass swales around the house and
the gravel swale before exiting the property, will allow onsite inflitration to occur
and thus reduce the possible projected runoff from the site.
The projected drainage from the lot will not alter the pre determined and
designed drainage regime for the area. No down stream erosion or siltation will
take place because of all the non erodible improvements already in place.
VICINITY MAP
NO SCALE
THOM. BROS. PG. 1106 G6
Pf^Peill,TV 5 FRO|V\ e^AST TO UOeST 1NT6
AO:rA(eBK)T pROFeRXy TO TUB uOeST.
FOR. T(^Te 1 UseJD TABV-.e ^-Z- U;ITW. A C?P
Aloo A GftAD^ OF 6% TO oer A roT/)t r/Me oF-S/hm
?Rm TAHPLE -5-1 . = , ZO
FROM RGOR£ 3-1 . X ^
Q^C.xXvA-- ,zy^>1x.t4.- . c f 5 . Q p^g- ^^^^^^
fo^ CoH:sTROe.TlQN
460 " ^^^'^ iMPeilvious
T-Y - Tc +Tc ; Foe. li 1 g^eo A 2o' SWALEQ* l*?^- pe^P\(^URe 3>-S
THROUGH P\P6-5 t^O' OF GR/^VEL. Pen FlOJRE U3£ Z ^l^;-
ABOUT -700' POUJKJ WILL FROM T^IE LOT
0N\ Cl^lWGfeOAPlM AVISNUE
INSTAa NBT jSgWER-tATER
EXISTOJO--4-SB»ER V«l
CP,
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San Diego County Hydrology Manual
Date; June 2003 Section:
Page:
Table 3-1
RUNOFF COEFFICIENTS FOR URBAN AREAS
Land Use
. NRCS Elements
Undisturtied Natural Terrain (Natural)
Low Density Residential (LDR)
Low Datsity Residential (LDR)
Low Density Residential (LDR)
Medium Density Residential (MDR)
Medium Density Residential (MDR)
Medhnn Density Residential (MDR)
Medium Density Residential (MDR)
Hi^ Density Residential (HDR)
High Density Residential (HDR)
Commercial/Industrial (N, Com)
Commercial/Industrial (G, Com)
Commercial/Industrial (0,P. Com)
Commercial/Industrial (Limited L)
Commerciat/Industriai (General L)
Countv Elemqits
Permanent Opwi Space
Residential, 1.0 DU/A or less
Residential, 2.0 DU/A or less
Residential, 2,9 DU/A or less
Residential, 4.3 DU/A or less
Residential, 7.3 DU/A or less
Residential, 10.9 DU/A or less
Residential, 14.5 DU/A or less
ResidentiaL 24.0 DU/A or less
Residential, 43.0 DU/A or less
Neighborhood Commercial
General Commercial
Office Professional/Commercial
Limited Industrial
General Industrial
Runoff Coefficient "C"
% IMPER.
Soil Type
0*
10
20
25
30
40
45
50
65
80
80
85
90
90
95
*The values associated with 0% impervious may be used for direct calculation of tfie
coefficient, Cp, for the soil type), or for areas that will remain undisturbed in perpetuity
IS located in Cleveland National Forest).
DU/A = dwelling units per acre
NRCS = National Resources Conservation Service
0 27
0.34
0.38
0.41
0.48
0.52
0.66
0.76
0.76
0.80
0.83
0.83
0.87
B
0.25
0.32
0.38
0.41
0.45
0.51
0.54
0.58
0.67
0.77
0.77
0.80
0.84
0.84
0.87
0.30
0.36
0.42
0.45
0.48
0.54
0,57
0,60
0,69
0.?8
0.78
0.81
0.84
0,84
0.87
3
6 of 26
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
ranoff coefficient as described in Section 3.1.2 (representing the pervious runoff
Justification must be given that the area will remain natural forever (e.g., the area
3-6
San D. County Hydrology Manual
Date: .-2003
Section:
Page:
3
12 of 26
Note that the Initial Time of Concentration should be retlective ofthe 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 sie ignificant effect where 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 m
hydrology studies. Initial T, values based on average C values for the I d Use Element are
also included These values can be used in planning and design appu.ations as descnbed
below. Exceptions may be approved by the ''Regulating Agency" when submitted with a
detailed study.
Table 3-2
MAXIMUM OVERLAND FLOW LENGTH (LM)
& INITIAL TIME QF CONCENTRATION
*See Table 3-1 for more detailed description
3-12
100
UJ
Ill o z
w a
tu
V)
8 cc Ui
I
EXAMPLE:
Gwen: Watercourse Distance (D) = 70 Feet
Slope (s) =1.3%
Runoff Coefficient (C) - 0.41
Overland Flow Time (T) = 9.5 Minutes
SOURCE: Airport Drainage. Federal Aviation Administration. 1965
1.6 (1.1-C) VD
FIGURE
Rational Formula - Overiand Time of Flow Nomograpii
AE
Feet
.5000
.4000
Tc
Tc
L
AE
EQUATION
^11.9L^y-385
Time of concentration (houi^)
Watercourse Distance (miles)
Change In elevation along
effective slope line (See Figure 3-5)(feet)
• 3000
.2000
-1000
900
800
• "WO
60^ \
•500 ^^
.400 \
• 300
-200
• 100
•50
40
•30
.20
10
Tc
Hours Minutes
• 240
•180
120
— 100
— 90
— ao
— 70
\ L
\ Miles Feet
\
^1-
0.5-
. 4000
\
- 3000
N
.2000
1800
1600
• 1400
•
-1(H]0 • 900 -800
-700
-600
-500
— 400
— 300
s
• 60
-50
— 40
— 30
20
\—^a
16
— 14
— 12
•10
—9
8
—r
— 6
— 4
—3
• 200
AE
fcoURCE; California Division of Highways (1941) and Kirpich (1940)
FIGURE
Nomograph for Defenmination of
Time of Concentration (Tc) or Travel Time (Tt) for Natural Watersheds
.-1
County of San Diego
Hydrology Manual
Rciinfall Isopluvials
100 Year Rainfall Event - 6 Hours
Isopluvial (inches)
GIS GIS
IHIS IMP IS F'RovKiEr) v<|iitouT wAn<UNrr of AIIY KINO. uiitER EXPRESS URiMPUto mauunc. BCIKOI LNIIEOIO THEIMWIEDwARfwores OF MERrMW4r«niurr «txi FIIMESS FOM APARIKIAAR KWPOSE.
Cspfr^ SmCIS. M n•<t^% niianrtii.
TMs ftaiutn mty can*fi Inhniniijcin liom Aa SANOAO fiafinit
0 3 Miles
2 3 4
Houra
OlFBctlons for AppHeation:
(1) From precipitation maps determine 8 hr and 24 hr amourtts
fbr the selected frequericy. These maps are Induded in the
County Hydrology Manual (10,50, and 100 yr maps IrK^jded
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 (nol
applicaple to Desert).
(3) Plot 6 hr precipitation on ths right side of the chart.
(4) Draw a line through tha point parallel to the plotted lines,
(5) This line la the Intensity-duration curve for the location
beii r-:.tyzed.
Application Form:
(a) Selected frequency year
(b) Pfi = 2i5S_in., P24 = = 55L_%<^'
_ r- 24
(o) Adjusted PQ'-^ = ^-bt) in.
(d)t^= min. Vt^ 3.1 ^ i - ^.7
{e)I= in./hr, f<^'^' ^'^ ,
Note: This chart replaces ttie Intensity-Duratlon-Frequancy
curves used since 196S.
pa"• '"2"" "878 " '•*JS ' a' 5.8 8
Oursion ._.p.. ' "i" 1 r ^ ....
"878
III 1 1 i
• 5 2.63 3.95 izi i.w 10.54111.88113,17 ^^:40 HM
7 2.12 3.18 4.24 B.30 6.36 8.48 ! S,64 10.60 1166
10 l.sa 2.S3 337 4.ar sM Sm 674 'TSB' M2 "9.27 '»o.if
"•"TS 1.30 1.86 259 3.24 3.80 4,64 5.19 5.84 6.49 7.13 7.78
ftM 1.6S' TM 2lS TM' 3.23 3,77 IW 465 "5.39 "ass
7.78
ftM
as 0.93 U6 187 2.80 3,Z7 3.73 4.20 1.67 J 6.13 s!so
30 0.83 1.84 ise a.07 1,49 2.90 3.32 3,'73 4.iii 4;56 4.9|
36 aei 1.03 IW 2.07 2.4i 2'7B JIG 3 45 179
fii) 0.80 0.80 i.ift 1.4S T.7B ~£Sa 2:39 2.69" ~2,98' 558'
"iid 0.G3 080 i.iis i.33 1.69 ties '2.12 i2M s:sz ai8;
6.61 6.82' 1.02 ila i,43 i;63 i84 2.04 2;25 2.46
oi'i bisi 0.68 0.8S 1.19 1.36 i.S3 'll7 2,04
ISO 0.iZ9 0.44 O.SS o.n aes i.03 1.18
\M
i,32 1.47 IW TTS'
iici oie aM 9M 0,65 0.78 O.iM
1.18
\M 1,18 -,.„.
TU 1.67
iuo 0,22" 035 OM 054 O.iK 076 oW 0,98 1.08 1.18 1.30
300 0.1fl 0.38 t}.4i 0.S6 0.66 0.&S OJ94 1.03
ied 0.1T o^s 0.33 0.42 ¥50 6.58 0.67 0.76 a84 a02 ilo
p I g y R K,
Intensity-Duration Design Chart - Template