HomeMy WebLinkAboutCDP 2017-0021; OCEAN STREET RESIDENCE; HYDROLOGY STUDY; 2017-03-24John P. Strohminger
HYDROLOGY STUDY
2680 Ocean Street
Carlsbad, CA 92008
Shafran Coastal Residence
CDP 17-
Prepared for:
Alan Shafran
1673 Amante Court
Carlsbad, CA 92011
Prepared By:
John P. Strohminger RCE 55187
dba Pacific Overland Engineering & Surveying
635 Via Columbia
Vista, CA 92081
Date: March 24, 2017
Date
TABLE OF CONTENTS
1 P . D .. . roJect escnpt1on ............................................................................................................. 2
1.1. Existing Condition .................................................................................................. 2
I .2 . Proposed Condition ................................................................................................ 2
I .3. Soil Characteristics ................................................................................................. 3
2. Rational Method Description .............................................................................................. 3
3. Hydrology Analysis ............................................................................................................ 4
4. Water Quality ..................................................................................................................... 4
5. Hydromodification .............................................................................................................. 4
6. Attachments .......................................................................................... 5
7. References .......................................................................................................................... 6
1. Project Description
This project is a 0.08 acre residential parcel located at 2680 Ocean Street in the City of Carlsbad.
Ocean Street is a public street that connects with Cypress A venue to the north and Beech A venue
to the south. An existing single family residence and detached garage are currently onsite.
Proposed improvements consist of a single-family detached dwelling unit, driveway, and
replacement retaining wall along the rear property line. The site's APN number is 203-141-10-
00. The legal description is Lot 84 of Map 2037. Attachment 1 shows the Vicinity Map.
1.1. Existing Condition
The existing site has a single-family residence, detached garage and driveway at an average
elevation of 44 feet above Mean Sea Level (MSL). The elevation of the street fronting the
property is slightly lower at 42 MSL. There is a 6 foot high retain wall along the rear property
line. To each side of the project are single family residences at the same elevation. To the rear is
a parking lot for a condominium project 4 feet higher than the project's rear yard.
Storm water from the site surface flows to the street, continues on the surface north along the
east side of Ocean Street and on to an inlet 150 feet away. From there the water is conveyed to
the Pacific Ocean in an underground conduit.
1.2. Proposed Condition
The proposed project proposes to demolish the existing residence, garage, rear wall, fences and
hardscape and replacing them. The improvements and grading will disturb 0.09 acres. The new
drainage pattern is virtually the same as the existing drainage pattern. There is a high point in the
rear yard; storm flows around both sides of the house and joins at the street. Flows then continue
on the surface to the existing inlet mentioned above .
2
1.3. Soil Characteristics
The following soil group definitions come from Technical Release 55 (TR-55) by the United
States Department of Agriculture:
Group A soils have low runoff potential and high infiltration rates even when thoroughly wetted.
They consist chiefly of deep, well to excessively drained sand or gravel and have a high rate of
water transmission (greater than 0.30 in/hr).
Group B soils have moderate infiltration rates when thoroughly wetted and consist chiefly of
moderately deep to deep, moderately well to well drained soils with moderately fme to
moderately course textures. These soils have a moderate rate of water transmission (0.15-0.30
in/hr).
Group C soils have low infiltration rates when thoroughly wetted and consist chiefly of soils
with a layer that impedes downward movement of water and soils with moderately fine to fine
texture. These soils have a low rate of water transmission (0.05-0.15 in/hr).
Group D soils have high runoff potential. They have very low infiltration rates when thoroughly
wetted and consist chiefly of clay soils with a high swelling potential, soils with a permanent
high water table, soils with a clay pan or clay layer at or near the surface, and shallow soils over
nearly impervious material. These soils have a very low rate of water transmission (0-0.05 in/hr).
The conservative approach is assuming Group D soils for the site.
2. Rational Method Description
The rational method, as described in the 2003 San Diego County Hydrology Manual, was used to
generate surface runoff flows, which were then used to size the drainage facilities.
The basic equation: Q = CiA
C = runoff coefficient (varies with land use)
i = Intensity (in/hr)
A = Area (acres)
The 6 hour and 24 hour rainfall isopluvial maps are found in the 2003 San Diego County
Hydrology Manual. Adjusted P6 calculations can be found in the Attachments. Initial travel time
calculations (Ti) are based on the overland flow equation given in Figure 3-3 of the County's
Hydrology Manual and is limited to the maximum overland flow length in Table 3-2 of the
County's Hydrology Manual
3
3. Hydrology Analysis
The Zoning for the project is R-15 with a maximum density of 15 dwelling units per acre. Table
3-1 shows the MDR with 14.5 du/ac coupled with a soil type D to have a runoff coefficient "C"
of 0.63. From the County Rainfall Isopluvials P6 is 2.5 and P24 is 4.2. The adjusted value for P6
remains 2.5. From Figure 3-1 the resultant rainfall is 5.5 inches per hour. From Table 3-2 MDR
coupled with a slope of 2% warrants a maximum overland distance of 80 feet and a Time of
Concentration equal to 6.5 minutes.
Per the equation in Section 2, Q=CiA, Q=(0.63)(5.5)(0.09) = 0.31 cubic feet per second for both
the existing and proposed condition.
4. Water Quality
The project is a Standard Development Project per the completed Storm Water Standards
Questionnaire (E-34) provided in the attachments. The project is therefore not required to submit
a Stormwater Quality Management Plan (SWQMP).
The project is required to incorporate Source Control and Site Design BMP's. The Standard
Project Requirement Checklist (E-36) address these BMP's and is included in the attachments.
5. Hydromodification
This project is exempt from hydromodification requirements since it is not a Priority
Development Project.
4
6. Attachments
Includes Vicinity Map, Table 3-1, Isopluvials, Figure 3-1, Table 3-2, E-34 and E-36.
5
0
Ar y an · Novy
Acaoemy Boo store
2680 Ocean Street
Beach Terrace C
Inn Cnrtsbad
Mvgcc Park
Mel oir Properties 0
Swn·ni's Cofe Carlsbud
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SHEET T!TlE
~PN JOJ-1-1'-C.i
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Exist & Proposed Drainage
2680 Ocean Street, Carlsbad, CA 92008
John P Strohmin9er Engineering
/
/
0ATE:3-26-2017
San Diego County Hydrology Manual
Date: June 2003
Table 3-1
Section:
Page:
RUNOFF COEFFICIENTS FOR URBAN AREAS
Land Use Runoff Coefficient "C"
Soil Type
NRCS Elements County Elcmc11ts %IMPER. A B
Undist"ltrbed Nat11ral Terrnin (Natural) Permanent Open S11ace 0"' 0.20 0.25
Low Density Residential (LDR) Residential, 1.0 DU/A or less I 0 0.27 U.32
Low Density Residential (LDR) Rcsidc11lial, 2.0 DU/A or less 20 0.34 0.38
Low Density Residential (I .DR) 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 [)ensity Residential (MDR) Residential, 7.3 OlJ/J\ or less 40 0.48 0.51
Medium Density Residentinl (MDR) Residential, I 0.9 DU/ A or less 45 0.52 0.54
Medium Density Residential (MOR) Residential, 14.5 DU/A or less 50 0.55 0.58
High Density Resi lcntial (IIDR) Residential, 24.0 DU/A or less 65 0.66 0.67
IJigh Density Residential (II DR) 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. om) General Commercial 85 0.80 0.80
Commen:ial/lndustrial (O.P. Com) Orfiee Professional/Commercial 90 0.83 0.84
Commercial/Industrial (Limited l.) Limited Jndustrial 90 0.83 0.84
Commercial/Industrial (General I.) General Industriill 95 0.&7 0.87
C
0.JO
0.36
0.42
0.45
0.48
0.54
0.57
0.60
0.69
().'.78
0.78
0.81
0.X4
0.84
0.87
3
6 of26
D
0.35
0.41
0.46
0.49
0.52
0.57
0.60
\of>Jl
0.71
0.79
0.79
U.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 J.1 .2 (rqJrcscnting the pcrvious runoff
coefficient, Cp, for the soil type), or for areas that will rcmnin undisturbed in perpetuity. Justification must he given that the area will remain nalurnl forever (e.g., the area
is located in Cleveland Nalional Forest).
OU/ A = dwelling units per acre
NRCS = National Resources Conservation Service
3-6
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Intensity-Duration Design Chart -Template
Directions for Appllcatlon:
(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 u,at it is within
the range of 45°/4, to 65% of the 24 hr precipitation (not
applicaple to Desert) .
(3) Plot 6 hr precipitation on t110 right side of the chart .
(4) Draw a line through the point parallel to the plotted ·1ines.
(5) This line lg the Intensity-duration curve for the location
being analyzed .
Appllcatlon Form:
(a) Selected frequency !DO year
2 -4 2. p._ r-1 (b) P6 = ~ in., P24 ::: _, __ .~ = _:> ___ %(2)
z ~ 24 (c) Adjusted Pl?l = · in.
(d) t = U '1? min. X ---
(e) I = ~ in./hr.
Note: This chart replaces the Intensity-Duration-Frequency
curves used since 1965.
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F I
3-1
San Diego County Hydrology Manual
Date: June 2003
Section:
Page:
3
12 of26
Note that the Initial Time of Concentration should be reflective 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 ,vl1ere 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 Ti values based on average C values for the Land Use Element are
also included. The6e Yalues can be used in planning and design applications as described
belov,1. Exceptions may be approved by the "Regulating Agency'· when submitted \vith a
detailed study.
Table 3-2
MAXIMUM OVERLA.ND FLO"' LENGTH (LM)
& INITIAL TIME OF CONCENTR.I\..TION (Ti)
Element* DU/ .5 % 1% 2% 3% 5% 10%
Acre LM Ti LM Ti LM Ti L'-1 Ti L t-.1 Ti LM Ti
Natural 50 13.2 70 12.5 85 10.9 100 10.3 100 8.7 100 6.9
LDR I 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 8.2 65 7.4 80 6.5 90 6.0 100 5.4 100 4.3
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 1 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