HomeMy WebLinkAboutSDP 05-17; DONALD CONDOMINIUMS; DRAINAGE & HYDROLOGY STUDY; 2006-06-21I
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2497 Ocean Street Condominiums
Drainage & Hydrology Study
LMA W.0.#12295
Prepared for
The City of Carlsbad
Prepared by
Lintvedt, McColl & Associates
2810 Camino Del Rio South, Suite 200
San Diego, Ca 92108
(619) 294-4440
June 21, 2006
..iUN 28 200f
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TABLE OF CONTENTS
• Vicinity Map
• Introduction
• Purpose and Scope
• Existing Conditions
• Proposed Conditions
• Calculations
• Conclusions and Recommendations
• Works Cited
• Appendix I
Hydrology Calculations
Drainage Basin Maps
Figure 3-1
Intensity Duration Chart
lsophlivial Maps
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I Vicinity Map
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I SITE
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I PACIFIC OCEAN
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• Introduction
This hydrology study will analysis the run off characteristics of the project site before and
after the proposed project is completed. The proposed development, a 2 unit Condominium,
which will replace a single family residence. The site is located on Ocean Street at the intersection
of Pacific Avenue, in the City of Carlsbad. The project site is 0.23 acre in size within Lot 6 per
Map 1782.
• Purpose and Scope
The site is currently developed with a single-family residence. The site drains west to the
Pacific Ocean. There is no run-on from the adjacent properties or Ocean Street. The purpose of
this study is to quantify the 100 year flows for both existing and proposed conditions and assess
impacts that may result from the proposed development.
• Existing Conditions
A total of 0.23 acres (within Lot 6 per Map 1782) and 0.20 acre from the westerly line of
Lot 6 to the mean high tide line at elevation 2.3 drain to the Pacific Ocean to the west of the
property. No runoff from adjacent properties drains into the site. There are no storm drains within
the immediate area.
• Proposed Conditions
The proposed site grading is for the construction of a 2 unit condominium. There will be
new impervious areas including buildings, driveways, walkways and sidewalks. The perimeter of
the site and area between buildings and sidewalks will be landscaped.
The impervious area of the developed site approximates that of the existing conditions.
The proposed drainage system is designed to be contained onsite in a sump pump and pump
system. Storm water will be used for landscaping purposes. Overflow from the storage tank will be
pumped into Ocean Street via 2" pressure line to a 4" diameter curb outlet. Flow in Ocean Street
will continue as gutter flow to the north and south and outlet into the Pacific Ocean. Porous paving
will be used for the walkways to retain water onsite. The undisturbed area of the property which is
from the proposed patio wall to the mean high tide line which was delineated from a field survey
dated May 22, 2006 at elevation 2.3 will continue to drain to the ocean. The overflow from the
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storage tank will not cause a significant effect on the existing downstream storm drain system.
There will be decreased flow to the Pacific Ocean.
• Calculations
The hydrology calculations were prepared in accordance with the County of San Diego
Hydrology Manual dated 2003. Project topographic survey and preliminary grading plans were
used to define the basin areas.
Flow rates were calculated using the rational method, Q=CIA, with 'C' being the runoff
coefficient, 'I' being the intensity, and 'A' being the drainage area in acres. For existing conditions,
a 'C' value of 0.79 was used for Natural Terrain per Table 3-1, "Runoff Coefficients for Urban
Areas", page 3-6 of the County of San Diego Hydrology Manual. For proposed conditions, a 'C'
factor of 0.79 was used for High Density Residential (43.0 DU/A), soil type D. A copy of Table 3-1
is provided in Appendix I. Basin intensities ('I') were calculated using Figure 3-1, from the County
of San Diego Hydrology Manual. The building, hardscaping and landscaping occupies the
majority ( approx. 2/3) of the site. An analysis of the Tc using standard charts and graphs was not
done because the site runoff was complex and to use routing method over such a short distance
would not give reliable results. The Tc was therefore conservatively estimate to be 5 minutes.
This seemed reasonable since the elevation difference between the eastern side of the lot and the
western side is about 28'.
Since the runoff areas are the same and the runoff coefficients are the same, the existing
and proposed hydrology calculations are the same for 'any' duration storm. There will be
decreased flow to the Pacific Ocean because of the containment of the flow from the roofs,
driveways and walkways onsite.
• Conclusions & Recommendations
No increase in runoff from the development is anticipated. Since the immediate recipient
of the runoff is the Pacific Ocean, intuitively one can conclude that even if there was and increase
it would have no affect on the Pacific Ocean.
• Works Cited
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Brater and King. Handbook of Hydraulics, Sixth Edition. Pages 6-14-6-16. McGraw Hill, Inc.
1976.
County of San Diego. San Diego County Hydrology Manual. 2003.
APPENDIX I
HYDROLOGY CALCULATIONS
0100 = CIA
'C' value (before and after)= 0.79
A (before and after) = 0.24 ac
I= 6.5
0100 = (0. 79)(6.5)(0.24)
0100 = 1.23 cfs
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,;; "' Z:if, ::;~ ,.,.,., ;z;
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EX~SUllD'NC
\
LEGEND:
-DIRECTION OF FLOW
40 0 40 120
Scale 1''=40'
EXISTING CONDITIONS
12295 DRFT: MD CHK'D BY: TM
LlnTVEDT, m0COLL
A550C.IATE5
■PLANNING
■CIVIL ENGINEERING
■ LAND SURVEYING
2810 Camino Del Rio South, Suite 200, San Diego, CA 92108 ■{619)294-4440 ■Fox(619)294-4442
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LL u~
<(
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20
1 ', __ _
0 20
Scale 1''=20'
...
LEGEND:
-
60
: .!. ,'
STORM DRAIN SUMP-:' ,-·: ,___,
UMP AN0·,PUMP ' ~--'-, Y~Ti~M> ·,;
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·-,·. '.-'UNIT B
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F.F.=35.45 (/:i
DIRECTION OF FLOW
UNIT A
• ... !j
-~,.,;;;:;:==r:::,,1
', ,16.7%
ONC\OW
UNIT B
GARAGE
F.F.=38.2 1
TRs~~ttp~~JN, 1 I,, _ -
, .• __ -::··-~-, : I
( i'-!';._ '-·:· 1 __ 1
.... ' ... )
PROPOSED
DATE: 6-21-06 W.O. 12295
-1
CONDITIONS
DRFT: MD CHK'D BY: TM
■PLANNING
LlnTVEDT m0COLL ' ' ■CIVIL ENGINEERING
A-550CIATE5 ■ LAND SURVEYING
2810 Camino Del Rio South, Suite 200, Son Diego, CA 92108 ■(619)294-4440 ■Fox(619)294-4442
1..-----:::--------------:------~24~.R~CP;:;-i ~~----... -::::;;;~-~ ::,._:--... ~---~-_,__.z::r-z;,i.,-----;;.J.:-~~-r.,:-:::~~~, .. :•·~·· -~-..... 1_-1 ________ 7
• ·-----.... •.. .. ~ ~ ~4-RCP /1 ..
I BVLN A J\S The LAG0-::+1 ; f t~p, .. \: ·•··•·• •.·. ·~ ~ k.: ~/1 : .
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!PROJECT SITEI
'18.RCP /~62%
18,.RCP /_57% ·
36~
~24.RCP
2497 OCEAN STREET
EXISTING DRAINAGE FACILITIES
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San Diego County Hydrology Manual
Date: June 2003
-----------
Section:
Page:
Table 3-1
RUNOFF COEFFICIENTS FOR URBAN AREAS
Land Use Runoff Coefficient "C"
Soil Type
NRCS Elements Coun Elements %IMPER. A B
Undisturbed Natural Terrain (Natural) Permanent Open Space 0* 0.20 0.25
Low Density Residential (LDR) Residential, 1.0 DU/A or less 10 0.27 0.32
Low Density Residential (LDR) Residential, 2.0 DU/A or less 20 0.34 0.38
Low Density Residential (LDR) Residential, 2.9 DU/A or less 25 0.38 0.41
Medium Density Residential (MDR) Residential, 4.3 DU/A or less ' 30 0.41 0.45
Medium D_ensity Residential (MDR) Residential, 7.3 DU/A_orless 40 0.48 0.51
Medium Density Residential (MDR) Residential, 10.9 DU/A o~ less 45 0.52 :?-54
Medium Density Residential (MDR) Residential, 14.5 DU/A or less 50 0.55 ,(;).58
High Density Residential (Hi:>R) Residential, 24.0 DU/A or less 65 0.66 :_Q.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) Ge~eral 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 I. General Industrial 95 0.87 0.87
---
3
6 of26
C D
0.30 0.35
0.36 0.41
0.42 0.46
0.45 0.49
0.48 0.52
0.54 0.57
0.57 0.60
0.60 0.63
0.69 0.71
0.78 ~
0.78 0.79
0.81 0.82
0.84 0.85
0.84 0.85
0.87 0.87
*The values associated with 0% impervious may be used for direct calculation of ~e 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
,ii located in Cleveland National Forest). •
/iDU/ A = dwelling units per acre
/ NRCS = National Resources Conservation Service
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EQUATION
I = 7.44 Ps o·0.645
I I "'. _ Intensity (ln/hr)
Pa= $-Hour Precipitation (" m)
D = Duration (min)
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'/ Minutes --
lntensity-Duration-Des~gn Chart .. Template I
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Directions for Application:
(1) From preclpitalion maps determine 6 hr and 24 hr amounts
for the selected frequency. These maps are lne!Uded in the
County Hydrology Manual (10, 50, and 100 yr maps included
In the DesJgn and Procedure Manual).
(2) Adjust 6 hr precipitatioll (if necessary) so that it is. wltilin
the range of 45% to 65% or the 24 hr precipitation (not
appllcaple to Desert). •
(3) Plot 6 hr preciprtation oo the right side of the chart.
(4) Draw a fine through the point parallel lo the plotted lines.
(5) This line is the intensity-duration cwve for the location·
being analyzed. •
.Application Form:
(a) Selected frequency~ year
' -p (b) Pe= ~m .. P24 = 4.0 •p 6 = .Q; . %(~
(21 . 24 (c) Adjusted P6 , = Z...S in.
(d) tx = .§__ min.
(e) I= ~.S-in.Ill!'.
Note: Th~ chart repraces the h1lensily*Ouraffon-Frequency
curves userJ slnoe 1965, .,
PS~----1., 1.5 2 2
Duration I ' . l l -
5 2-&S 3.95 5.27 6
2tl 1.00 1.62 2.tS
25 0.93 1.40 -
a-45 8.79 4.13
2.9a s.2a 5:srt 2.39·. 2.65 2.92 3.18
1.'84 2.04 2.25 2.45
1.53 1.70 1.87 2.04
1.32 ·1.47 1.62 1.16
3-1
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County of San Diego
Hydrology Manual
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Rainfall Isopluvials
-------· Jsopluvial (Inches)