HomeMy WebLinkAboutPD 09-03; SHEPRO RESIDENCE; DRAINAGE REPORT; 2009-08-04RECORD COPY
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COFFEY ENGINEERING, INC. Initial Date
Drainage Report
Shepro Residence
7133 Obelisco Circle
Carlsbad, CA 92009
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Prepared For:
Shepro Family Trust
And
The City of Carlsbad
August 04, 2009
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10650 SCRIPPS RANCH BLVD, SUITE 210 SAN DIEGO, CA 92131 PHONE: (858)831-01 11 FAx: (855)831-0179
Table of Contents
Summary and Current Conditions .3
Proposed Project................................................................................................................................3
Purpose and Scope of Report ...........................................................
.
................................................. 3
Method of Calculations ................................................................................................................. 4,5
Results and Conclusions ..................................................................................................................... 5
Declaration of Responsible Charge...................................................................................................6
Appendix
Assessor Parcel Map-La Costa Meadows Unit 4.
Drainage Map 'A' - Existing Conditions
Drainage Map 'B' - Proposed Conditions
Table 'A' - Time of Concentration Flow Conditions
Table 'B' - Hydraulics Proposed Structures
Flow Evaluation Data -Sections
Soil Hydrology Groups
Table 2— Runoff Coefficients
Figure 3-1— Intensity-Duration Design Chart
100-year, 6-hour Isopluvial map
100-year, 24-hour Isopluvial map
Table 3-2 - Maximum Overland Flow Length (Lm)
Figure 3-3 - Overland Time of Flow Nomograph
Summary and Current Conditions
The 0.57-acre site, Lot 686 of PM 7367, is located between Obelisco Circle and Babilona St in the
La Costa Community of the City of Carlsbad. The site is currently a vacant lot surrounded by
custom developed home sites. The site slopes an average of 27% from Obelisco to Babilonia. The
majority of storm water runoff travels via sheet flow from east to west over the sloping terrain. A
brow ditch runs perpendicular to Babilonia and discharges over the curb of the street, but without a
well-defined brow ditch at the top of the Babilonia cut slope (parallel to the street), only a small
portion of runoff from the site actually concentrates in the brow ditch. The runoff from this
property is finally collected on a curb inlet located in front of the adjacent property to the north
along the Street. Refer to Drainage Map 'A', attached, for current conditions.
Proposed Project
Proposed project is the construction of a single family residence, new driveway from Obelisco, and
a rear patio and pool deck area. Refer to Drainage Map 'B', attached, for proposed conditions. A
new vegetated swale is proposed along the top of the Babilonia Street cut slope, to both channel the
flows so they don't continue to erode the slope, and also to provide a means of stormwater
filtration for higher-pollutant, lower-rate flows from the newly-developed portion of the site.
Purpose and Scope of Report
This report evaluates the adequacy of the proposed drainage features at the finished site in the
event of 100-year time-of-concentration flow conditions, analyzing
a.) Flow characteristics of proposed drain lines, channels, and other features.
Evaluations
The following flows will be evaluated for the purposes of this report (refer to Drainage Map 'B' for
flow area and Flow Evaluation Data for the Sections):
Upper pad discharge —6" PVC @5%- Section I.D. NO. A.1-2.
Lower pad discharge - 6" PVC @3•% Section I.D. NO. B.1
Rip-Rap@ Grass Swale -8"PVC @7% Section I.D. NO. A+B
6" Depth x 60" Wide Grass —Swale - Section I.D. NO. A+B+C
6" Depth x 60" Wide Grass —Swale (Low Flow)— Section I.D. NO. A+B+C
Flow rate Discharge- D-25 - Section I.D. NO. A+B+C
4. Method of Calculations
The Rational Method, as defined by the County of San Diego Hydrology Manual (2003), will be
used to calculate storm water flow rates. Where noted, the following calculations were used to
determine flow properties:
Rainfall Characteristics
QC* I*A,where
Q = Flow rate (ft3/sec)
C = Runoff coefficient
I = Rainfall intensity (in/hr)
A = Area (acres)
I = 7.44 * P6 * D 0645, where
I = Rainfall intensity (in/hr)
P6 = Adjusted 6-hour precipitation (inches)
D = Storm duration (mm), equal to T for time-of-concentration storms
Tc = Ti+Tt+Tp (time-of-concentration), where
Ti=Over land initial time.
TtTravel time on natural watersheds.
Tp=Travel time on drainage structures (pipes, brow ditch, gutter etc.)
Ti= 1.8(1.1-C) D°5° /( S033) (Overland initial time of concentration formula),where
D= Watercourse Distance (feet)(see table 3-2 for the max. overland flow length)
s = Slope (%)
C= Runoff Coefficient
Ti=Initial time of concentration (mm.)
T = (1 1.9*L3 / AH)°385 (formula for travel time for natural watersheds), where
Tc = Time of Concentration or Travel time (hours)
L = Length of watercourse (miles)
AH = Change in effective slope height (ft)
Pipe and Open Channel Flow Characteristics
V = 1/n * e * S"2 (from Manning), where
V = Average cross-sectional velocity (ft/sec)
n = Manning roughness coefficient
R = Hydraulic radius (ft)
S = Slope of water surface (ft height/ft length)
ply + V2/2g + Z1 + hL = ply + V2 /2g + z2 (from Bernoulli), where
p = pressure (lbs/&)
y = density (lbs/fl)
V = velocity (ft/sec)
g = gravity (ft/sec/sec)
z = height of fluid (ft)
hL = head loss (ft)
5. Results and Conclusions
The study concludes that the proposed drainage culverts, channels, swales, and structures are
adequate to handle flows in the event of a 100-year-storm. In addition to the proposed grass swale
near the west side of the property, a standard D-25 curb outlet is proposed at Babilonia Street to
discharge flows cleanly into the road. (See 'Flow Evaluation Data', attached).
6. Declaration of Responsible Charge
I hereby declare that I am the Civil Engineer of work for this project, that I have exercised
responsible charge over the design of the project as defined in section 6703 of the business and
professions code, and that the design is consistent with current design.
I understand that the check of project drawings and specifications by the City of Carlsbad is
confined to a review only and does not relieve me, as Engineer of Work, of my responsibilities for
project design.
John "
Date
RCE 62716
Exp. 06-30-10
I Ne.0062716 I
't Exp.063010 *
OF
Appendix
Flow Evaluation Data
611PVC @3.3% SECTION ID NO. A.1
(1) Diameter (inches) 6.
(3) slope (ft/ft) 0.0331
(5) depth (ft) ..........0.50
Velocity (fps) 5.19
Area (Sq. Ft.) 0.20
Critical Depth ......0.47
Critical Velocity 5.30
DATE: 08-04-2009
TIME: 09:24:03
(2) Mannings n .013
(4) Q (cfs) ..........1.02
(6) depth/Diameter 1.00
Velocity Head 0.42
Critical Slope ... 0.0286
Froude Number .... N/A
611PVC @5% SECTION ID NO. A.1-2 DATE: 08-04-2009
TIME: 09:38:08
(1) Diameter (inches) 6.
(3) slope (ft/ft) 0.0505
(5) depth (ft) ..........0.50
Velocity (fps) 6.42
Area (Sq. Ft.) 0.20
Critical Depth ......0.49
Critical Velocity 6.46
(2) Mannings n .013
(4) Q (cfs) ..........1.26
(6) depth/Diameter 1.00
Velocity Head 0.64
Critical Slope ... 0.0449
Froude Number .... N/A
6" PVC @3.4% SECTION ID NO. B.1
(1) Diameter (inches) ... 6.
(3) slope (ft/ft) 0.0337
(5) depth (ft) ..........0.50
Velocity (fps) 5.25
Area (Sq. Ft.) 0.20
Critical Depth ......0.48
Critical Velocity 5.35
DATE: 08-04-2009
TIME: 12:36:39
(2) Mannings n .013
(4) Q (cfs) ...........1.03
(6) depth/Diameter 1.00
Velocity Head 0.43
Critical Slope ... 0.0292
Froude Number .... N/A
8" PVC @7% & Rip-Rap SECTION ID NO. A+B
DATE: 08-04-2009
TIME: 14:07:44
(1) Diameter (inches) B.
(3) slope (ft/ft) .0700
(5) depth (ft) ..........0.42
Velocity (fps) 9.96
Area (Sq. Ft.) 0.23
Critical Depth ......0.64
Critical Velocity 6.64
(2) Mannings n .013
(4) Q (cfs) ...........2.29
(6) depth/Diameter 0.63
Velocity Head 1.54
Critical Slope ... 0.0314
Froude fquxriber .... 2.94
6" DEPTH x 60" WIDE GRASS SWALE SECTION - ID NO. A+B+C
DATE: 08-04-2009
TIME: 13:37:58
(1) INVERT WIDTH (feet) 0.00 (2) Mannings n .027
(3) SLOPE (ft/ft) ..........0100 (4) Q (cfs) ..........2.63
(5) LEFT SIDE (6) RIGHT SIDE
SLOPE (X to 1) ........5.00 SLOPE (X to 1) ... 5.00
(7) DEPTH (ft) ............0.50 TOP WIDTH (FT) ... 4.96
VELOCITY (fps) ........2.14 VEL. HEAD (ft) ... 0.07
AREA (sq. ft) .........1.23 P + M (pounds) ... 24
CRITICAL DEPTH ........0.44 CRITICAL SLOPE ... 0.0179
CRITICAL VELOCITY 2.67 FROUDE NUMBER .... 0.76
(LOW FLOW) 6" DEPTH x 60" WIDE GRASS SWALE SECTION - ID NO. A+B+C
DATE: 08-20-2009
TIME: 11:59:35
(1) INVERT WIDTH (feet) 0.00 (2) Mannings n .027
(3) SLOPE (ft/ft) ..........0100 (4) Q (cfs) ..........0.07
(5) LEFT SIDE (6) RIGHT SIDE
SLOPE (X to 1) .........5.00 SLOPE (X to 1) ... 5.00
(7) DEPTH (ft) ............0.13 TOP WIDTH (FT) ... 1.28
VELOCITY (fps) ........0.85 VEL. HEAD (ft) ... 0.01
AREA (sq. ft) .........0.08 P + M (pounds) ... 0
CRITICAL DEPTH ........0.11 CRITICAL SLOPE ... 0.0278
CRITICAL VELOCITY 1.27 FROUDE NUMBER .... 0.60
8" PVC @44% SECTION-ID NO. A+B+C
DATE: 08-04-2009
TIME: 13:49:47
(1) Diameter (inches) ... 8.
(3) slope (ft/ft) .4400
(5) depth (ft) ..........0.26
Velocity (fps) ......20.55
Area (Sq. Ft.) 0.13
Critical Depth ......0.65
Critical Velocity 7.58
(2) Mannings n .013
(4) Q (cfs) ..........2.63
(6) depth/Diameter 0.39
Velocity Head 6.56
Critical Slope ... 0.0423
Froude Number .... 8.17
D-25 CURB OUTLET SECTION-ID NO. A+B+c DATE: 08-04-2009
TIME: 13:53:37
(1) INVERT WIDTH (feet) 3.00
(3) SLOPE (ft/ft) ..........0200
(5) LEFT SIDE
SLOPE (X to 1) ........0.00
(7) DEPTH (ft) ............0.18
VELOCITY (fps) ........4.79
AREA (sq. ft) .........0.55
CRITICAL DEPTH ........0.29
CRITICAL VELOCITY 3.04
(2) Mannings n .013
(4) Q (cfs) ..........2.63
(6) RIGHT SIDE
SLOPE (X to 1) ... 0.00
TOP WIDTH (FT) ... 3.00
VEL. HEAD (ft) ... 0.36
P + M (pounds) ... 28
CRITICAL SLOPE ... 0.0047
FROUDE NUMBER .... 1.97
Soil Groups
Group A - Group B
Group C
EM Group D
Undetermined
Data Unavailable
Orange
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'S County of San Diego
Hydrology Manual
Soil Hydrologic Groups
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San Diego County Hydrology Manual Section: 3
Date: June 2003 Page: 6 of 26
Table 3-1
RUNOFF COEFFICIENTS FOR URBAN AREAS
NRCS
Land Use
Elements I % IMPER.
Runoff Coefficient "C"
Soil Type
A B C
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. Corn)
Commercial/Industrial (G. Corn)
Commercial/Industrial (O.P. Corn)
Commercial/Industrial (Limited. I.)
Commercial/Industrial (General I.)
Permanent Open Space 0* 0.20 0.25 0.30 0.35
Residential, 1.0 DU/A or less 10 0.27 0.32 0.36 0.41
Residential, 2.0 DU/A or less 20 0.34 0.38 0.42 0.46
Residential, 2.9 DU/A or less 25 0.38 0.41 0.45 0.49
Residential, 4.3 DU/A or less 30 0.41 0.45 0.48 0.52
Residential, 7.3 DU/A or less 40 0.48 0.51 0.54 0.57
Residential, 10.9 DU/A or less 45 0.52 0.54 0.57 0.60
Residential, 14.5 DU/A or less 50 0.55 0.58 0.60 0.63
Residential, 24.0 DU/A or less 65 0.66 0.67 0.69 0.71
Residential, 43.0 DU/A or less 80 0.76 0.77 0.78 0.79 /
Neighborhood Commercial 80 0.76 0.77 0.78 0.79
General Commercial 85 0.80 0.80 0.81 0.82
Office Professional/Commercial 90 0.83 0.84 0.84 0.85
Limited Industrial 90 0.83 0.84 0.84 0.85
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 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
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San Diego County Hydrology Manual Section: 3
Date: June 2003 Page: 12of26
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 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 T1 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)
& INITIAL TIME OF CONCENTRATION (Ti)
Element* DU/
Acre
.5% 1% 2% 3% 5% 10%
LM Tj LM Tj LM Tj LM Tj LM T1 LM T1
Natural 50 13.2 70 12.5 85 10.9 100 10.3 100 8.7 100 6.9
LDR 1 1 50 12.2 70 11 11.5 85 10.0 1 100 9.5 1 100 8.0 1 100 6.4
LDR 2 50 1 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 9.21 65 8.4 80 7.41 95 7.0 100 6.0 100 4.8
MDR 10.9 50 1 8.7 65 1 7.91 80 6.9 90 1 6.41 100 5.7 1 100 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 75.1 4.0 85 3.8 95 3.4 100 2.7
N. Corn 50 1 5.3 1 60 4.5 75 4.0 85 1 3.8 95 3.4 100 2.7
G. Corn 50 4.7 60 4.1 75 3.6 85 1 3.4 90 2.9 100 2.4
O.P.ICom 50 4.2 60 3.71 70 3.1 80 2.9 90 2.6 100 2.2
Limited I. 50 4.2 60 3.7 70 1 3.1 80 2.9 1 90 2.6 100 2.2
General I. ____ 50 3.7 60 3.2 70 1 2.7 1 80 2.6 1 90 2.3 100 1.9
*See Table 3-1 for more detailed description
3-12
100 30
U)
I- Ui I- Ui w z U 0 20
w z
- 0 2
Ui
Cl) 0 -J W Cl) Li.
Ir
Ui > 0
0
EXAMPLE:
Given: Watercourse Distance (0) = 70 Feet
Slope (s) = 1.3%
_____________ T 1.8 (1.1-C) '/5
Runoff Coefficient (C) = 0.41 3'/
Overland FlowTime (T) = 9.5 Minutes
SOURCE: Airport Drainage, Federal Aviation Administration, 1965
FIGURE
Rational Formula - Overland Time of Flow Nomograph
3w3
ir
VA4a
M
or'A
C).0010
I 10