HomeMy WebLinkAboutPD 2020-0017; REAGAN ADU; LID/HYDROLOGY REPORT; 2020-10-21Page 1
LID/HYDROLOGY
REPORT
Carlsbad, CA
PREPARED FOR:
Jack Reagan
2451 Torrejon Place
Carlsbad, CA 92009
PREPARED BY:
Stewart Design and Engineering Inc
23535 Palomino Dr., Suite 303
Diamond Bar, CA 91765
(909) 301-1017
______________________________________________
Carl Stewart PE License #86681
STEwmilr
DESIGN & ENGINEERING
Page 2
Table of Contents
Section I
Introduction ______________________________________________________________________________________ 3
Purpose of Study _________________________________________________________________________________ 3
Section II
Proposed Analysis___________________________________________________________________________ _________5-6
Hydraulics________________________________________________________________________________________________7
Section III
Conculsion_______________________________________________________________________________________8
Appendices
Appendix 1: Vicinity Map
Appendix 2: Isohyet Map and Soils Information
Appendix 3: Proposed Analysis
Appendix 4: Hydraulic Calcs
Page 3
Section I
Introduction
The site of study is located in the City of Carlsbad, County of San Diego, California on Torrejon Place,
near Rancho La Costa Reserve. The property is located in a residential area surrounded by single-
family homes. The developed land will consist of an Accessory Dwelling Unit along with an existing
single family home on the property. The existing terrain of the property slopes to the public right of
way. Appendix 1 will illustrate the location of the proposed development.
Purpose of Study
The purpose of this report is to provide a run-off study based on San Diego County Flood and the City
of Carlsbad design criteria. The project is designed to maintain existing drainage patterns. Based on
the San Diego County Hydrology Manual, the goal is to provide protection for structures from the 50
year storm. This report will show that onsite drainage will safely convey a 50-year storm event. The
rational method was used to calculate the runoff values.
Page 4
Section II
Proposed Runoff Analysis
The rational method was utilized to determine the runoff values for the subject property. As seen in
Appendix 3, the proposed site conditions are a partially developed site with a soil type of D. The 25
yr, and 50 yr, storms were analyzed to define the runoff characteristic of the site. Below are the
values obtained from the rational analysis
PROPOSED CONDITIONS 25 YEAR STUDY
DMA Acres Time of Concentration (min) Flow
(cfs)
Disturbed
Area
0.053 5.0 0.12
PROPOSED CONDITIONS 50 YEAR STUDY
DMA Acres Time of Concentration (min) Flow
(cfs)
Disturbed
Area
0.053 5.0 0.13
Hydraulics Analysis
The onsite and offsite pipes were analyzed to determine if the 50 year storm can be transported
safety to the public right of way. The main pipe utilized onsite was a 4” pvc pipe with a slope of 1
percent minimum. The pipe transporting drainage to the curb and gutter is a 3” pipe with a slope of
2 percent. As seen in Appendix 4, the capacity of the 3” pipe is 0.15 cfs and the 4” pipe 0.23 cfs.
Page 5
Section III
Conclusion
As seen in the analysis above, the onsite and offsite drainage facilities can safely convey a 50 year
storm event.
Page 6
Appendix No. 1
Vicinity Map
r Google Maps La Costa Ave I,) I,) \!! 0 \ ~ !'!-Encinitas Creek I,) ,. ---"n Marcos Cr. ~--~k_____./ ~ Gelson's Market T Takeout• Delivery Leucadia~ Wastewater District T The Broken Yolk Cafe ~ Takeout• Delivery T ~ Chabad at La Costa ~~e ' Bank of America (with Drive-thru ATM) \..-a.co<::>'?:> • El 1,1 Equinox La Costa Takeout U.S. Bank Branch • Mimi's Alterations ft & Tailoring T La Costa Wine I,) • 9 The Beacon La Costa El Escenico Tenace La CosraAve I " LeYanteSt .. Go gl~ <,i La Costa p..ve j J ~.? 9 Costa Pointe Apartments ~aClr 2451 Torrejon Place I " LwanteSt BocaSt ~ f !/I LevantaSt ft Auto Appraisal Network T in San Diego, CA Navarra Dr f LevanteSt La Gran II;., : ~,t, ,.,, ~ ~$''I> .,,. ~,If '-o,.., ~ ~,t, ,1;• .If" ~
Page 7
Appendix No. 2
Isohyet Map and Soils Information
San Diego County Hydrology Manual Section: 3 Date: June 2003 Page: 6 of 26 Table 3-1 RUNOFF COEFFICIENTS FOR URBAN AREAS Land Use Runoff Coefficient “C” Soil TypeNRCS Elements County Elements % IMPER. A B C D Undisturbed Natural Terrain (Natural) Permanent Open Space 0* 0.200.250.300.35Low 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 0.60 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 I.) 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 I
Nomograph for Determination of
Time of Concentration (Tc) or Travel Time (Tt) for Natural Watersheds
SAY 5 MIN
.6. E
Feet
5000
4000
Tc
Tc
L
.6.E
"' -:
=
EQUATION
(1~t)°·385
Time of concentration (hours)
Watercourse Distance (miles)
Change in elevation along
effective slope line (See Figure 3-5) (feet)
3000
2000
400
300
30
20
10
.6.E
SOURCE: California Division of Highways (1941) and Kirpich (1940)
L Miles Feet
.
3000
0.5 '
2000
1800
1600
1400
1200
1000
900
800
700
600
500
400
300
200
L
' ' '
Tc
Hours Minutes
4
3
2
' ' '
Tc
50
40
30
20
18
16
14
12
10
9
8
7
6
5
4
3
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Duration
EQUATION
I = 7.44 P6 D-0.645
I = Intensity (in/hr)
p6 = 6-Hour Precipitation (in)
D = Duration (min)
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Intensity-Duration Design Chart -Template
Directions for Application:
(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 that it is within
the range of 45% to 65% of the 24 hr precipitation (not
applicaple to Desert).
(3) Plot 6 hr precipitation on the right side of the chart.
(4) Draw a line through the point parallel to the plotted lines.
(5) This line is the intensity-duration curve for the location
being analyzed.
Application Form:
(a) Selected frequency ___ year
p
(b) P5 = --in., P24 = --'P 6 = %(2)
24
(c) Adjusted P6<2) = __ in.
{d) Ix= __ min.
(e) I = __ in./hr.
Note: This chart replaces the Intensity-Duration-Frequency
curves used since 1965.
I
PG 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 ~---Duration I I I I I I I I 1 I I
5 2.63 3.95 5.27 6.59 7.90 9.22 10.54 11 .86 13.17 14.49 15.81
7 2.12 3.18 4.24 5.30 6.36 7.42 8.48 9.54 10.60 11.66 12.72
10 1.68 2.53 3.37 4.21 5.05 5.90 6.74 7.58 8.42 9.27 10.11
15 1.30 1.95 2.59 3.24 3.89 4.54 5.19 5.84 6.49 7.13 7.78
20 1.08 1.62 2.15 2.69 3.23 3.77 4.31 4.85 5.39 5.93 6.46
25 0.93 1.40 1.87 2.33 2.80 3.27 3.73 4.20 4.67 5.13 560
30 0.83 1.24 1.66 2.07 2.49 2.90 3.32 3.73 4.15 4.56 4.98
--;fa 0.69 1.03 1.38 1.72 207 2.41 2.76 3.10 3.45 3.79 4.13
1.19 1.49 1.79 2.09 2.39 2.69 ... 3.28 3.58 50 0.60 0.90 2.98 -60 0.53 0.80 1.06 1.33 1.59 1.86 2.12 2.39 2.65 2.92 3.18
90 0.41 0.61 "o.82 1.02 TI3 T43 1.63 1.84 2.04 T25 2 .45
120 0.34 0.51 0.68 0.85 1.02 1.19 1.36 1.53 1.70 1.87 2.04
0.29 0.59 0.73 -1.03 -1.32 ~ f--150 0.44 0.88 1.18 1.47 1.62 1,76
180 0.26 0.39 0.52 0,65 0.78 0.91 1.04 1.18 1,31 1.44 1.57
240 0.22 0.33 0.43 0.54 0.65 0.76 0.87 0.98 1.08 1.19 130
300 0.19 0.28 0.38 0,47 0.56 0.66 0.75 0.85 0.94 1.03 1.13
360 0.17 0.25 0.33 0.42 0.50 0.58 0.67 0.75 0.84 0.92 1.00
2.3
50
4.3 53
2.3
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40 50
Duration
EQUATION
I = 7.44 P6 D-0.645
I = Intensity (in/hr)
p6 = 6-Hour Precipitation (in)
D = Duration (min)
,,
....
'""' ,r--. ' ,r-. i"'i-,.
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2 3 4
Hours
5 6
9' I 0 !:;
"t)
al n
6.0 -g
5.5 ~
5.0 g
4.5 '§' n 4.o l
3.5 ~
3.0
2.5
2.0
1.5
1.0
Intensity-Duration Design Chart -Template
Directions for Application:
(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 that it is within
the range of 45% to 65% of the 24 hr precipitation (not
applicaple to Desert).
(3) Plot 6 hr precipitation on the right side of the chart.
(4) Draw a line through the point parallel to the plotted lines.
(5) This line is the intensity-duration curve for the location
being analyzed.
Application Form:
(a) Selected frequency ___ year
p
(b) P5 = --in., P24 = --'P 6 = %(2)
24
(c) Adjusted P6<2) = __ in.
{d) Ix = __ min.
(e) I = __ in./hr.
Note: This chart replaces the Intensity-Duration-Frequency
curves used since 1965.
I
PG 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 ~---Duration I I I I I I I I 1 I I
5 2.63 3.95 5.27 6.59 7.90 9.22 10.54 11 .86 13.17 14.49 15.81
7 2.12 3.18 4.24 5.30 6.36 7.42 8.48 9.54 10.60 11.66 12.72
10 1.68 2.53 3.37 4.21 5.05 5.90 6.74 7.58 8.42 9.27 10.11
15 1.30 1.95 2.59 3.24 3.89 4.54 5.19 5.84 6.49 7.13 7.78
20 1.08 1.62 2.15 2.69 3.23 3.77 4.31 4.85 5.39 5.93 6.46
25 0.93 1.40 1.87 2.33 2.80 3.27 3.73 4.20 4.67 5.13 560
30 0.83 1.24 1.66 2.07 2.49 2.90 3.32 3.73 4.15 4.56 4.98
--;fa 0.69 1.03 1.38 1.72 207 2.41 2.76 3.10 3.45 3.79 4.13
1.19 1.49 1.79 2.09 2.39 2.69 ... 3.28 3.58 50 0.60 0.90 2.98 -60 0.53 0.80 1.06 1.33 1.59 1.86 2.12 2.39 2.65 2.92 3.18
90 0.41 0.61 "o.82 1.02 TI3 T43 1.63 1.84 2.04 T25 2 .45
120 0.34 0.51 0.68 0.85 1.02 1.19 1.36 1.53 1.70 1.87 2.04
0.29 0.59 0.73 -1.03 -1.32 ~ f--150 0.44 0.88 1.18 1.47 1.62 1,76
180 0.26 0.39 0.52 0,65 0.78 0.91 1.04 1.18 1,31 1.44 1.57
240 0.22 0.33 0.43 0.54 0.65 0.76 0.87 0.98 1.08 1.19 130
300 0.19 0.28 0.38 0.47 0.56 0.66 0.75 0.85 0.94 1.03 1.13
360 0.17 0.25 0.33 0.42 0.50 0.58 0.67 0.75 0.84 0.92 1.00
Page 8
Appendix No. 3
Proposed Analysis
Rational Method Calculations
Q = CIA
Per the Runoff Coef Table - C = 0.41
Intensity for the 25 yr = 5.8 in/hr
Intensity for the 50 yr = 6.0 in/hr
Distrubed Area = 2344 sf = 0.054 Acres
Q = 0.41 X 6.0 X 0.054 = 0.13
Page 9
Appendix No. 4
Hydraulic Calculations
Channel Report
Hydraflow Express Extension for Autodesk® Civil 3D® by Autodesk, Inc.Wednesday, Oct 21 2020
3 INCH PIPE
Circular
Diameter (ft)= 0.25
Invert Elev (ft) = 100.00
Slope (%)= 2.00
N-Value = 0.011
Calculations
Compute by:Q vs Depth
No. Increments = 10
Highlighted
Depth (ft)= 0.23
Q (cfs)= 0.157
Area (sqft)= 0.05
Velocity (ft/s)= 3.38
Wetted Perim (ft) = 0.63
Crit Depth, Yc (ft) = 0.23
Top Width (ft)= 0.15
EGL (ft)= 0.40
0 1
Elev (ft)Section
99.75
100.00
100.25
100.50
100.75
101.00
Reach (ft)
--,-, -' I
Channel Report
Hydraflow Express Extension for Autodesk® Civil 3D® by Autodesk, Inc.Wednesday, Oct 21 2020
4 INCH PIPE
Circular
Diameter (ft)= 0.33
Invert Elev (ft) = 100.00
Slope (%)= 1.00
N-Value = 0.011
Calculations
Compute by:Q vs Depth
No. Increments = 10
Highlighted
Depth (ft)= 0.30
Q (cfs)= 0.233
Area (sqft)= 0.08
Velocity (ft/s)= 2.88
Wetted Perim (ft) = 0.83
Crit Depth, Yc (ft) = 0.28
Top Width (ft)= 0.20
EGL (ft)= 0.43
0 1
Elev (ft)Section
99.75
100.00
100.25
100.50
100.75
101.00
Reach (ft)
--.., ~
/ -" -' '
~ _/