HomeMy WebLinkAboutCT 10-01; Sea Breeze Villas; Hydrology Study; 2010-08-12Hydrology Study
RECORD COPY
Initial Date
Sea Breeze Villas
Project No. CT 10-01
Carlsbad, California
Prepared For:
TMS Development, LLC
32 Sylvan
Irvine, California 92603
Prepared By:
Surender Dewan, P.E.
DMS Consultants, Inc.
12371 Lewis Street, Suite 203
Garden Grove, California 92840
714.740.8840
August 12, 2010
DMS
CONSIJ l/r A NTS, INC.
c I V r 1. K N G 1 N E F; R S
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SEA BREEZE VILLAS
CARLSBAD
Site Description
The proposed project is located in tlie City of Carlsbad on the south side of Tamarack Avenue, at 391
Tamarack Avenue on a 0.70 acre site.
The proposed project is a 12-unit airspace condominium project.
Purpose
The purpose of this study is to determine the total runoff generated for a storm of six (6) hour duration
for one hundred (ICQ) year frequency and design an infiltration system to store the increase in volume
of runoff between the pre and post runoff condition. For overflow conditions a 12-inch diameter PVC
pipe has been installed, this overflow pipe connects to an existing catch basin located along the
southerly curb of Tamarack Avenue.
Section 1.0 100 Year Hydrology Calculations
1.1 Rainfall
The 100 year 6 hr rainfall depth was taken
from the San Diego County Hydrology Manual
isopluvial maps. Figure 1 below is an enlarged
copy of the applicable section of the map.
1.1.1 Existing Condition Rainfall
Rainfall for the existing condition was
taken from the Manual.
1.1.2 Proposed Condition Rainfall
The total 100 year storm depth forthe
proposed condition was calculated by
subtracting the Water Quality Depth (see
below) from the 100 year storm total total
from the Manual.
Figure 1100 Year 6hr Isopluvials
1.2 Soil Tvpe
The hydrologic soil type for the area of the proposed tract is listed as "B" in the Manual Appendix A.
Runoff Coefficients
Runoff coefficients for the pre and post project
condition were taken from Table 3-1 ofthe
Hydrology Manual. (See attached table 3-1.)
1.3 Time of Concentration (Tc)
1.3.1 Existing Condition Tc
The lot currently drains, via overland flow,
to the northwest with an average slope of
2%. The iniital time of concentration (Ti)
was estimated using Table 3-2 of the
Hydrology Manual (See attached Table 3-2).
CARLSBAD
Figure 2 Soil Type The Tt for the rest of the flow distance
was estimated Manning's equation
assuming a broad open swale with a 20:1 side slope to calculate the flow velocity. See the
attached hydraulic calculations for the swale travel time.
1.3.2 Proposed Condition Tc
In the proposed condition the lots drain to a paver swal in the center of the tract wnich conveys
the flows to the north east corner of the lot. The flows then enter a storm drain pipe and are
conveyed to the existing inlet in Tamarack Avenue. The initial Ti was estimated using Table 3-2
ofthe Hydrology Manual. The velocity in the swale was estimated using Manning's equation
and the velocity in the pipe was calculated using V = Q/A and assuming the pipe will be flowing
full.
Section 2.0 Storm Water Quality Calculations
2.1 Rainfall
The storm water quality treatment J
volume was taken from the Manual
Appendix E. Figure 3 is an enlarged
copy ofthe applicable section of
the map.
2.2 Storage
The required storage was
calculated using the pre and post
project runoff coefficients from the
Manual and determining the
incremental increase in the storm
water yeild for the water quality
depth. The size of the paver area
and the depth ofthe gravel
subbase were set so that the entire incremetal increase in the storm water quality runoff could be
stored in the gravel subbase. (See the attached storm water quality calculations)
2.3 Infiltration
The geotechnical evaluation of the site yielded a percolation rate of 15 gallons per day per square foot
or 2.003 cubic feet per day per square foot. The required infiltration time was calculated by dividing the
required storage by the area ofthe paver swale and the rate of percolation for the geotechnical analysis.
See the attached calculations for the results of the analysis.
Figure 3 Storm Water Quality Depth
Qioo~
VICINITY MAP
LEGEND
AREA DISCRIPTION
AREA IN ACRES
(joT) NODE NUMBER
SCALE: r=30' DMS CONSULTANTS. INC.
CIVIL ENGINEERS
12371 Lewis St. #203 Garden Grove CA. 92840 P. 7U-740-8840 F. 714-740-8842
HYDROLOGY PLAN
PROPOSED CONDITIONS
SEABREEZE VILLAS
CARLSBAD. CALIFORNIA
SCALE: r=30* DMS
, VICINITY MAP
NP NTS'
LEGEND
AREA DISCRIPTION
AREA IN ACRES
CjoT) NODE NUMBER
CONSULTANTS. INC.
CIVIL ENGINEERS
12371 Levis St. #203 Garden Grow CA. 92840 P. 714-740-8840 F. 714-740-8842
HYDROLOGY PLAN
EXISTING CONDITIONS
SEABREEZE VILLAS
CARLSBAD, CALIFORNIA
Site Data
Graded Area
85th Percentile Depth
Soil Group
Pre Project Runnoff Coefficient "C"
Post Project Project Runnoff Coefficient "C"
Storm Water Quality Volume
Storm Water Quality CalGulations for Seabreeze Villas
Pre Project 85th Percentile Runoff Volume
Post Project 85th Percentile Treatment Runoff Volume
Required Infiltration Volume (LID)
Design for Infiltration of Treatment Volume
Available Storage
Paver Length
Paver Width
Paver Area
Gravel Subbase Depth
Porosity
Total Storage Volume Available
Time for Complete Infiltration
Infiltration Area
Infiltration Rate
Infiltration Rate
Total Infiltration Per Day
Total Infiltration Per Hour
Required Infiltration Time
Value Units
30100 sf
0.61 in
B
0.25
0.58
382.52
887.45
504.9275
887.45
285
8
2280
12
0.4
912
2280
15
2.003
4566.09
190.25
4.66
ft'^3
ft'^3
ft'^3
ft'^S
ft
ft
ft'^2
in
ff^S > 887 OK
ft'^2
gal/day/square foot
cubic feet /day / square foot
cubic feet/ day
cubic feet/hour
hours < 72 Hours OK
site Data Value Units
Graded Area 30100 sf
Soil Group B
Pre Project Runnoff Coefficient "C" 0.25
Post Project Project Runnoff Coefficient "0" 0.58
Pre Proiect 100 vear 6hr Runoff
Pre Project Ti 10.90 min
Earth Swale Length 210.00 ft
Earth Slope 0.020 percent
Earth Swale Z 20.00
Earth Swale N 0.025
ft Earth Swale Flow Depth 0.210 ft
Earth Swale Velocity 0.56 ft/sec
Earth Swale Tt 6.24 min
Tc = Ti + Tt 17.14 min
100 year 6 hr Depth 2.50 in
100 year 6 hr intensity 2.98 in/hr
100 Year flow rate 0.51 cfs
Post Proiect 100 vear 6hr Runoff
Post Project Ti 8.20 min
Paver Swale Length 235.00 ft
Paver Slope 0.005 percent
Paver Swale Z 50.00
Paver Swale N 0.02
ft Paver Swale Flow Depth 0.155 ft
Paver Swale Velocity 0.75 fl/sec
Paver Swale Tt 5.24 min
Pipe Size 12.00 in
Pipe Length 275.00 ft
Pipe Velocity (Assume pipe flows full) 1.04 ft/sec.
Pipe Tt 4.39 min
Total Tt 9.63 min
Tc 17.83 min
100 year 6 hr Depth 2.50 in
Infiltration Depth (See Storm Water Calculations) 0.61 in
Effective 100 6hr Depth at ground surface 1.89 in
100 year 6 hr intensity 2.19 in/hr
Infiltration Area 2280.00 ft'^2
Graded Area Less Infiltration Area 27820.00 ft'^2
100 Year flow rate 0.81 cfs
too Year Swale Velocity Calculations for Seabreeze Villas
Paver Swale
I-A2/3 s s'^.5 q VbL L. 4 ,0 aroa WD f rV/.3 S o ..J M
'^"""m." 0 01-5 0 50 50 1.125 15.003 0,074985 0.177821 0.0018 0.042426 0.840813 0.747389 0,15 0.015 0 50
Natural Swale
,1 T9 arpa WD r r'^2/3 s s'^.5 q VEL
021" 0 025 0 20 20 0,882 8410493 0.104869 0.222381 0.0018 0.042426 0.494631 0.560807
Paver Swale
depth n b zl z2 area wp r r'^2/3 s s'^.5 q VEL
0.155 0.015 0 50 50 1.20125 15.5031 0.077485 0.181751 0.0018 0.042426 0.917643 0.763907
Natural Swale
depth n b zl z2 area wp r r'^2/3 s s'^.S q VEL
0.12 0.025 0 50 50 0.72 12.0024 0.059988 0.153241 0.0018 0.042426 0.278243 0.386448
SAN DIEGO HYDROLOGY MANUAL
(ATTACHMENTS)
Table 3.1 and Table 3.2
San Diego County Hydrology Manual
Date: June 2003 Section:
Page:
Table 3-1
RUNOFF COEFFICIENTS FOR URBAN AREAS
3
6 of 26
Land Use Runoff Coefficient "C"
Soil Type
NRCS Elements Counfy Elements % IMPER. A B C D
Undisturbed Natural Terrain (Natural) Permanent Open Space 0* 0.20 0.25 Pre Project 0.35
Low Density Residential (LDR) Residential, 1.0 DU/A or less 10 0.27 0.32 0.36 0.41
Low Density Residential (LDR) Residential, 2.0 DU/A or less 20 0.34 0.38 0.42 0.46
Low Density Residential (LDR) Residential, 2.9 DU/A or less 25 0.38 0.41 0.45 0.49
Medium Density Residential (MDR) Residential, 4,3 DU/A or less 30 0.41 0.45 0.48 0.52
Medium Density Residential (MDR) Residential, 7.3 DU/A or less 40 0.48 0.51 0.54 0.57
Medium Density Residential (MDR) Residential, 10.9 DU/A or less 45 0.52 0.54 0.57 0.60
Medium Density Residential (MDR) Residential, 14.5 DU/A or less 50 0.55 0.58 Post Project 0.63
High Density Residential (HDR) Residential, 24.0 DU/A or less 65 0.66 0.67 0.69 0.71
High Density Residential (HDR) Residential, 43.0 DU/A or less 80 0.76 0.77 0.78 0.79
Commercial/Industrial (N. Com) Neighborhood Commercial 80 0.76 0.77 0.78 0.79
Commercial/Industrial (G. Com) General Commercial 85 0.80 0.80 0.81 0.82
Commercial/Industrial (O.P. Com) Office Professional/Commercial 90 0.83 0.84 0.84 0.85
Commercial/Industrial (Limited I.) Limited Industrial 90 0.83 0.84 0.84 0.85
Commercial/Industrial (General L) General Industrial 95 0.87 0.87 0.87 0.87
•The values associated with 0% impervious may be used for direct calculation of the
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
runoff 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 Diego County Hydrology Manual
Date: June 2003 Section:
Page: 12 of 26
Note that the Initial Time of Concentration should be reflective 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 significant 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 in
hydrology studies. Initial Tj values based on average C values for the Land Use Element are
also included. These values can be used in planning and design applications as described
below. Exceptions may be approved by the "Regulating Agency" when submitted with a
detailed study.
Table 3-2
MAXIMUM OVERLAND FLOW LENGTH (LM)
Element* DU/
Acre
.5% 1% 2% 3% 5% 10% Element* DU/
Acre LM Ti LM Ti LM Ti LM Ti LM Ti LM Ti
Natural 50 13.2 70 12.5 85 10.9^ -mr -toe-Ti ^re Project
LDR 1 50 12.2 70 11.5 85 10.0 100 9.5 100 8.0 100 6 .4
LDR 2 50 11.3 70 10.5 85 9.2 100 8.8 100 7.4 100 5.8
LDR 2.9 50 10.7 70 10.0 85 8.8 95 8.1 100 7.0 100 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 -str -6.0--too 100 ~4 Ti Post Project
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 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 60 3.7 70 3.1 80 2.9 90 2.6 100 2.2
General I. 50 3.7 60 3.2 70 2.7 80 2.6 90 2.3 100 1.9
*See Table 3-1 for more detailed description
3-12