HomeMy WebLinkAboutMS 01-15; THOMPSON SUBDIVISION; DRAINAGE ANALYSIS FOR THOMPSON TENTATIVE PARCEL MAP; 2002-12-23DRAINAGE ANALYSIS
FOR
THOMPSON TENTATIVE PARCEL MAP
MS 01-15
CDPO1-43
HDP 02-12
PREPARED BY:
Aquaterra Engineering Inc.
1843 Cámpesino Place
Oceanside, CA 92054
Kristin Lipska Borer, PE
C 57860 Exp. 6/30/06
(760) 439-2802
December 23, 2002
INTRODUCTION
The City of Carlsbad has requested a Drainage Analysis be completed in order to determine the
effect of development for the Thompson Tentative Parcel Map, creation of new lot, for the 10
year design storm atthe 6 hour interval.
The pre-Developed condition and post-developed condition will be analyzed for the area know as
Parcel Two. Parcel One will not be analyzed as there is no new development proposed for Parcel
1.
Drainage Reference Material
The following criteria and design manuals will be used for this drainage analysis:
- San Diego County Hydrology Manual, August 2001
Drainage Design Criteria
Design Storm: - 10 year
Hydrolo2y Calculations (Existing Condition)
Total Site Area: A=15400/43560 = 0.35 ac.
Coefficient of Runoffi
The Coefficient of Runoff for residential areas is determined by the density or dwelling units per
acre. The density of the existing condition of this property is 1.41 du/ac? Therefore from Table
3-1 of the Hydrology Manual, the Land Use Designator for the Existing Condition is Low,
Residential, 2.0 DU/A or less, for Soil Type C,
(C=.42
To Determine, I or the Intensity, we use (from FIG 3-1, & 3-5, attached)
Q10 =CxI10 xA
Where Q10 = 100 year runoff (cfs)
C = 0.42
I =l.41n/hr.
A =.35 ac.
Q10 =.42X 1.4X.35
CQ1OEXISrING 0.206 CfS 0
Hydrology Calculations (Developed Condition)
The Coefficient of Runoff for residential areas is determined by the density or dwelling units per
acre. The density of the developed condition of this property is82 du/ai. Therefore from Table
3-1 of the Hydrology Manual, the Land Use Designator for the Existing Condition is Low,
Residential, 2.9 DU/A or less, for Soil Type C,
C=.45
Total Site Area: A=15400/43560 = 0.35 ac.
To Determine, I or the Intensity, we use (from FIG 3-1 & 3-5, attached)
Q10 =CxI10 xA
Where Q10
C
I
A
Q10 =.45 X 1.25 X.35
LQ-iovEIthió =o. 197 cf
= 10 year runoff (cfs)
= 0.45
= 1.25 in/hr.
=.35 ac.
,Results 7TTJ
' -jResults of this Drainage Analysis show the that,Q10 for thédevëloódöñdiiion(QIoDEVEwpED
= 0197 cfs) is actually less than the Q existing (QIO EXISTING = 0.206 c1) due to the increase in Ic,
Time of concentration. The effective slope of the proposed condition is reduced, therefore
decreasing the Intensity, and thus creating a decrease in the Q10 for the proposed project.
Undisturbed Natural Terrain
LOW
Low
Low
Medium Density Residential
Medium Density Residential
Medium Density Residential
Medium Density Residential
I ugh Density Residential
High Density Residential
Commercial/Industrial
Commercial/Industrial
Commercial/Industrial
Commercial/Industrial
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
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
0.30
0.36
i 0. iO
2J&o p.
0.48
0.54
0.57
0.60
0.69
0.78
0.78
0.81
0.84
0.84
0.95
0
10
20
25
30
40
45
50
65
80
80
85
90
90
0.20
0.27
0.34
0.38
0.41
0.48
0.52
- 0.95
0.55
0.66
0.76
0.76
0.80
0.83
0.83
0.95
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
ri
Table 3-1
RUNOFF cOEFFICIENTS FOR URBAN AREAS
Land Use
- Runoff Coellicient "C"
Soil Type
NRCS Elements County Elements % IMPER. A B
-
C 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
*The values associated with 0% impervious may be u.ccd for direct calculation of the runoff coefficient as described in Section 3.1.2 (representing the pervious
runoff cooflicient, (7p, 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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FIGURE
Rational Formula - Overland Time of Flow Nomograph
35
HazMaUCounty Hydrcgea4ogy ManualiOve,Iand Flow.FH8
O,nnijn —
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T ' Poti.t*i5 3.0 4)IA
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County of San Diego
Hydrology Manual
Rainfall IsopIiit.MIs
10 Year Rainfall Evenl -6 Hours
Isopluvial (inches)
Map Notes
%4,$ato Nrdiin. 70w1,. NAIJS3
CjiIW Annfl.ltXtt
NOrtO Fit D FOR flHCQctJIJ5
MILES ameO-