HomeMy WebLinkAboutCDP 07-12; Sears Residence; Drainage Study; 2008-11-18DRAINAGE STUDY
FOR
CDP07-12
4017SUNNYHILLDRIVE
APN 207 - 061 - 54
PREPARED FOR
Tom and Wendy Sears
1387 Cynthia Lane
Carlsbad, CA 92008
PREPARED BY
Robert O. Sukup
4322 Sea Bright Place
Carlsbad, CA 92008
November 18, 2008
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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
Section:
Page:
3
6 of 26
Table 3-1
RUNOFF COEFFICIENTS FOR URBAN AREAS
Land
NRCS Elements
Undisturbed Natural Terrain (Natural)
Low Density Residential (LDR)
Low Density Residential (LDR)
Low Density Residential (LDR)
Medium Density Residential (MDR)
Medium Density Residential (MDR)
Medium Density Residential (MDR)
Medium Density Residential (MDR)
High Density Residential (HDR)
High Density Residential (HDR)
Commercial/Industrial (N. Com)
Commercial/Industrial (G. Com)
Commercial/Industrial (O.P. Com)
Commercial/Industrial (Limited I.)
Commercial/Industrial (General I.)
Use
County Elements
Permanent Open 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 p^.
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"
Soil Type
% IMPER.
: -StX10
20
25
r -^34%
40
45
50
65
80
80
85
90
90
95
S^^e*
( A ,
0.20,
^0?7
0.34
0.38
0.41/<s-C,
0.48
0.52
0.55
0.66
0.76
0.76
0.80
0.83
0.83
0.87
> B
^ °'25
^— ^ 0.32
0.38
0.41
3D °45
^-^ 0.51
0.54
0.58
0.67
0.77
0.77
0.80
0.84
0.84
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
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 SEARS
SanD. County Hydrology Manual
Date: : 2003
Section:
Page:
3
12 of 26
Note that the Initial Time of Concentration should be reilective 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 where the drainage basin area is 20 to 600 acres.
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Table 3-2 provides limits of the length (Maximum Length (LM)) of sheet flow to be used in
hydrology studies. Initial Tj values based on average C values for the 1 d Use Element are
also included. These values can be used in planning and design apparitions as described
below. Exceptions may be approved by the "Regulating Agency" when submitted with a
detailed study.
MAXIMUM OVERLAND FLOW LENGTH (LM)
& INITIAL TIME OF CONCENTRATION QY
Element*
Natural
LDR
-LDB
LDR- " 'MDR
MDR
MDR
MDR
HDR
HDR
N. Com
G. Com ,
O.P./Com
Limited I.
General I.
DU/
Acre
1
2
^»s2.9_~*~~^
4.3
7.3
10.9
14.5
24
43
.5
LM
50
50
50
>50
50
50
50
50
50
50
50
50
50
50
50
%
TJ
13.2
12.2
11.3
10.7
10.2
9.2
8.7
8.2
6.7
5.3
5.3
4.7
4.2
4.2
3.7
1
LM
70
70
70
70
70
65
65
65
65
65
60
60
60
6(
60
%
Ti
12.5
11.5
10.5
10.0
9.6
8.4
7.9
7.4
6.1
4.7
4.5
4.1
3.7
•,7
3.2
2
LM
85
85
85
85
80
80
80
80
75
75
75
75
70
70
70
%
T,
10.9
10.0
9.2
8.8
8.1
7.4
6.9
6.5
5.1
4.0
4.0
3.6
3.1
3.1
2.7
3(
LM
100
100
100
95
95
95
90
90
90
85
85
85
80
80
80
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Ti
10.3
9.5
8.8
8.1
7.8
7.0
6.4
6.0
4.9
3.8
3.8
3.4
2.9
2.9
2.6
v 5 .
LM
100
100
100
100(
100
100
100
100
95
95
95
90
90
90
90
4*^)
Ti
8.7
8.0
7.4
^TXT
Tf
6.0
5.7
5.4
4.3
3.4
3.4
2.9
2.6
2.6
2.3
10
LM
100
100
100
^00
100
100
100
100
100
100
100
100
100
100
.00
%
Ti
6.9
6.4
5.8
5.6
5.3
4.8
4.5
4.3
3.5
2.7
2.7
2.4
2.2
2.2
1.9
*See Table 3-1 for more detailed description
3-12
l'1 M i:I r.County of San Diego
Hydrology Manual
(;./V«*.
Rainfall Isophivials
10 Year Rainfall Event- 6 Hours
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County of San Diego
Hydrology Manual
a-~t-p-;... •->.fo-
Rainfall Isopluvials
10 Year Rainfall Event- 24 Hours
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County of San Diego
Hydrology Manual
Rainfall Isopluvials
100 Year Rainfall Event - 6 Hours
INS MAP IS PROVIDED WI1HOUT WMVUNTY tf ANT WHO. EJTHtR EXPRESS, maucww. BUI NOT LIMITED 10. TitE IMPLIED WARRAHHES
OF MERCWMTABlOrv AMD FITNESS FOR A PARDCUlAft PUHPOSE.
SmGIS. Al Ft^liu H«
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rtyaroiogy ivianuai
Rivefsidd fcotihly
Kifep''
Rainfall Isopluvials
100 Year Rainfall Event - 24 Hours
;n!?' t •. • •. '••! 1 *•' K V • <
IMS MAP IS PHOV1DEO WITHOUT WARRAMTT OF AN* MND. CITVCH UPME&S
OR IMPLIeD. kClUOMG, Bin HD1 tMITEO TO, THE WPLIEO WARRAHDESMERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
i.rtahl S*nGIS. 01 Riohli FU»rvcl
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Intensity (in/hr)
6-Hour Precipitation (in)
Duration (min)
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
bei: !
Application Form: .. t....,
(a) Selected frequency
(b)P6=' '2,(a |n..P24«
(c) Adjusted Pg(2> =''_
(d)tx =
(e)l
Note: This chart replaces the Intensity-Duration-Frequency
curves used since 1965.
pa" "
Duration
5
7
10
15
20
25
30
40
SO
60
90
120
150
160
"240
300
360
1 i 1.5
1 I 1
2.63
212
tea
f.30
1.08
093
083
069
060
053
041
0.34
029
026
395
318
253
1.95
162
1.40
124
1.03
0.90
080
061
051
0.44
039
0.22 j 0.33
019 1028
0.17 1 0.25
T-'2.5
i
527.659
4 24' 5 30
337!421
259J324
215)269
187!233
166
1.38
1.19
106
207
1.72
1.49
1.33
082 102o.ea
059
052
0.43
038
033
0.85
073
065
054
047
042
3"4'3.5i i i
7.90
636
SOS
389
323
2.80
249
207
1.79
1.S9
123
1.02
0.88
078
0.65
056
0.50
9,22
742
5.90
454
377
327
290
2.41
2.09
1.86
143
J.19
1.03
091
076
066
058
""4"'j:"4.S 5"i I i I J
10.54
848
6.74
5.19
4.31
3.73
332
2.76
2.39
2 12
1 63
136
1.1 fl
104
087
075
0.67
11.86 j 13.17
9.54 i 10.60
7 58 ! 8.42
5.84 649
4.85 i 5.39
420 467
3.73 i 4.15
310 ! 345
2.69 i 2.98
239 2.6S
184
1.53
132
1 18
0.98
204
1.70
147
1.31
1.08
0 85 0 94
0.75 ! 0.84
..._,
j
14.49
11.66
927
713
593
513
456
379
3.28
2.92
225
187
162
144
1 19
103
092
af
15,81
12.72
1011
778
6.46
5.60
498
413
3.58
318
245
2.04
1.76
167
1.30
1 13
100
Intensity-Duration Design Chart - Template
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FIGURE
3-1