HomeMy WebLinkAboutCDP 2022-0067; LABOUNTY RESIDENCE -3950; DRAINAGE STUDY - LABOUNTY RESIDENCE; 2024-06-17
9666 BUSINESSPARK AVENUE, Suite 210 San Diego, CA 92131 Phone: (858) 831-0111 Fax: (858) 831-0179
Drainage Study
Labounty Residence
3950 Garfield Street
Carlsbad, CA 92008
APN: 206-012-06
Project No. CDP2022-0067
Dwg. No. 545-7A
Prepared For:
Paul & Judith Labounty Family Trust 07-30-02
And
The City of Carlsbad
June 17, 2024
8a
COFFEY ENGINEERING, INC.
2
Table of Contents
1. Existing Conditions ........................................................................................................................... 3
2. Proposed Project ................................................................................................................................ 3
3. Purpose and Scope of Report ............................................................................................................ 3
4. Method of Calculations ..................................................................................................................... 3
5. Results and Conclusions: .................................................................................................................. 5
6. Declaration of Responsible Charge ................................................................................................... 6
Appendix A – Referenced Plans & Drainage Maps
Grading Plan (Reduced Size Copy)
Drainage Map ‘A.1’ – Existing Drainage Conditions
Drainage Map ‘B.1’ – Proposed Drainage Conditions
Appendix B – Calculations/Evaluations
Table ‘A’ - Weighted Runoff Coefficients
Table ‘B’ - Pre Construction Flow Characteristics
Table ‘C’ - Post Construction Flow Characteristics
Appendix C – Reference Tables & Figures (County of San Diego Hydrology Manual)
Soil Hydrology Groups
Table 3-1 – Runoff Coefficients
Figure 3-1– Intensity-Duration Design Chart
Table 3-2 – Maximum Overland Flow Length and Initial Time of Concentration
Figure 3-3 – Overland Time of Flow Nomograph
Figure 3-4 – Nomograph for the Determination of Time of Concentration or Travel
Time for Natural Watersheds
100-year, 6-hour Isopluvial map
100-year, 24-hour Isopluvial map
3
1. Existing Conditions
The proposed project area consists of a 6,770 ft2 lot developed with a single family residence and
detached garage. Runoff tributary to the westerly 23% of the lot (of which 1,530 ft2 is impervious
surfaces) sheet flows toward the fronting street (Garfield Street). The remaining 77% (of which
3,437 ft2 is impervious surfaces) sheet flows to the east, to the residential property to the east.
There are no storm drain facilities or concentrated points of discharge from the subject property.
Refer to Drainage Map ‘A.1’ found in Appendix A of this report for a site map of the existing
conditions. A complete evaluation of the runoff quantities from the existing conditions are found in
Table A of Appendix B.
2. Proposed Project
Proposed is the demolition of the existing single family residence and the construction of a new
single family residence with plans for a future detached accessory dwelling unit. Frontage
improvements consisting of curb, gutter and sidewalk are also proposed. The site has been
designed to maintain existing drainage patterns with runoff from the front half of the property sheet
flowing west to the street and runoff from the rear half sheet flowing to the east. The total amount
of impervious surfaces proposed is less than the existing with 1,307 ft2 of impervious surfaces
being tributary to the street and another 3,477 ft2 of impervious surfaces being tributary to the rest
of the lot.
Refer to Drainage Map ‘B.1’ found in Appendix A for a site map of the proposed drainage
conditions. A complete evaluation of the proposed tributary areas evaluated are found in Table C of
Appendix B.
3. Purpose and Scope of Report
This report will evaluate the pre-construction hydrologic conditions as well as the post-construction
conditions to quantify increases or decreases in runoff from the project. Runoff conditions for a
100-yr design storm were evaluated for this purpose.
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
Q = C * I * A, where
Q = Flow rate (ft3/sec)
C = Runoff coefficient
(Runoff coefficient per County of San Diego Hydrology Manual Table 3-1 reproduced in
Appendix C. Soil type D determined from the Soil Hydrologic Groups map from the County of
San Diego Hydrology Manual reproduced in Appendix C also.)
I = Rainfall intensity (in/hr)
A = Area (acres)
4
Rainfall Intensity (per County of San Diego Hydrology Manual Figure 3-1 reproduced in
Appendix C)
I = 7.44 * P6 * D-0.645, where
I = Rainfall intensity (in/hr)
P6 = Adjusted 6-hour precipitation (inches)
D = Storm duration (min), equal to Tc for time-of-concentration storms
Tc = Ti+Tt+Tp (time-of-concentration), where
Ti=Over land initial time.
Tt=Travel time on natural watersheds.
Tp=Travel time on drainage structures (pipes, brow ditch, gutter etc.)
Overland Time of Flow (per County of San Diego Hydrology Manual Figure 3-3 reproduced in
Appendix C)
Ti= 1.8(1.1-C) D0.50 /( s0.33 ) (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 (min.)
Time of Concentration (TC) or Travel Time (Tt) for Natural Watersheds (per County of San Diego
Hydrology Manual Figure 3-4 reproduced in Appendix C)
Tt = (11.9*L3 / ΔH)0.385 ( formula for travel time for natural watersheds), where
Tc = Time of Concentration or Travel time (hours)
L = Length of watercourse (miles)
ΔH = Change in effective slope height (ft)
5
5. Results and Conclusions:
The below table summarizes the existing and proposed drainage conditions of the site.
Point of Existing Proposed‐
Existing
Tributary
Area
Proposed
Tributary
Area
Weighted
Runoff
Weighted
Runoff
Compliance Q100
(ft3/sec)
Q100
(ft3/sec) Acres Acres Coeff.
(Pre) Coeff. (Post)
Area C
(Front) 0.21 0.19 0.058 0.056 0.63 0.58
Area D
(Back) 0.48 0.48 0.098 0.099 0.75 0.75
The decrease in runoff from Area C (0.21 cfs to 0.19 cfs) can be explained by a decrease in
impervious areas of approximately 213 ft2. This decrease will not be detrimental to down stream
properties.
Regarding runoff directed to the back of the lot (Area D), there is a slight increase in impervious
areas tributary to the rear of the lot of approximately 40 ft2. This slight increase in impervious area
was calculated to not result in an increase in runoff directed to the neighboring private property.
The flattening out of the back of the lot will also aid in the dispersion to sheet flow, mimicking the
existing conditions.
Review of FEMA flood map # 06073C0764H shows that the site and surrounding area is in “an
area of minimal flood hazard” (Zone X). The site (and immediately adjacent properties) does not
show as being within a county mapped flood way or county mapped flood plain. Therefore the
project will not place housing within these mapped flood hazard areas nor would the proposed
project place structures within a 100-year flood hazard area which would impede or redirect flood
flows.
Full runoff calculations are included in Appendix B of this report.
Bibliography
County of San Diego. 2005. Drainage Design Manual
http://www.sdcounty.ca.gov/dpw/floodcontrol/drainage.html
County of San Diego. 2003. Hydrology Manual
http://www.sdcounty.ca.gov/dpw/floodcontrol/hydrologymanual.html
I
EX GRAVEL EX. AC
ow APRON I DRIVEWAY I
..---.'-. --------\---'------;:;--7r EX. MOW --------------------------------------=-:c---:-:::-::-::------1 . ~ CURB TW=66.66 TW=67.25
>.,~ ~(Ji TRW=66.32 TRW=66.92
q,~ 6 I ''===''====i ___ BRW=66.32 BRW=64.97 ~ """''-"\,'---!,-~,..,., ~
__. iiiiil -- - - -1------1----t---1 7. 5' ULTIMATE € _ ______,1-------t
3: TO CURB FACE :r:
.q q <l ISO-Kl
LANDSCAPE AR A
,1
I
I
I
I
I
I
I rJo. s::
CURB PER
SDRSD G-2 -0~ ·-Y OH-
OVERHEAD ELECTRICAL
SERVING PROPERTY TO
BE UNDERGROUNDED LAWN
OH --,-~C7"T77"'.ff,1"'7';"'7777""f7o/77o/ff'rrn-:~'"7i'7'77'!7-7777-7 ~'TT7'T,~'1777777-7TT77T77':T,T,i"j";F77~~~
II /'";7Y'J:L--m----
,-• 21.3'--IGIL--------'--'l"'I
I
---ii:--11-/
LAWN
I
II
I
I
I
I
EX. VINYL
FENCE ON
CMU WALL.
I
I
I
0,
I co
Vt:
• co
Vl
"" I
3:
I
REFER TO DWG NO.
545-7 FOR OFFS/TE
PUBLIC IMPROVEMENTS
I
3:
EX. EDGE
OF PVMT
:r:
0~-....,Zlr t-4 --
• ,1
CURB PER
SDRSD G-2-t----f--,--.J • 0 l w w --+-W t+--➔W. < ---,'IW ~ f/1~
~ISO-Kl l
3:
P.C.C. MOW
CURB
-------oN'-NfJSCAPE
.-:, AREA
56.e
PLANTER
_P.C.C. MOW
CURB
ISC-AI
,1
ISO-Kl
I
5 0 5 10 ~ ------
SCALE: 1"=5'
L
0 0 0 0 0 0 Q Q Q ~~ 0 0 0 0 0
DURING GRADING. TEST DATA, RESULTS AND
RECOMMENDATIONS WILL BE PROVIDED TO THE
CITY FOR REVIEW AND APPROVAL PRIOR TO
APN: 206-012-06
PROPOSED RESIDENCE
FF 67.07' FOOT/ RINT OF )I
EX. t USE (TO_/ I
BER MOVED) I
15
I
(
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
- - --~--;r-.J...__-+-+---------t-__,,..
4
4 ,1
4.0'
2 2 2 Mo a a g@o
5.5_2.Z.:QO '.'.W 120.
0
I
I
I
I
I
I
ol
I S 0
0
~
E
FOOTPRINT OF tl EX. HOUSE (TO
BE REMOVED) ---
~":
I I
DETACHED ADU
II I :
II----1 o. o' --sc:'t-+----tt#irll ________ I RYSB
I 4.0' ADU,-+-rl=IIHc,I
RYSB ' 10,5' (TO BE PROCESSED
UNDER SEPARATE CDP)
FF 62.52' (P) 6' WOOD EX. VINYL
FENCE 1---FENCE ON
ii-----:"'.li--'''-----J=r=il,-lll g CMU WALL
I g
I ,!.w la .,:, I 8
<5'_,. ~
I l
I l
l
r--
I
I
I
I ~--~ ::C====t'---~-----'-,.,.-,...,-.. -_ 1...,-_ tt--, .,..--,_ -_ ....,_ ":~
4 4 I 4-. · -. T----
Ll .1 5.0 1
<5' SYSB
0 0 0 0 0
0
~a o oo-e,O :J ■ ;ru 00 uo
ROCKLINEO
SWALE PER _;
10.0· !SD-Kl
P.C.C.
MOW
CURB
I
I
I
I
PUBLIC IMPROVEMENT NOTE EX. CMU
FENCE/WALL
<o <o
\ -----........ =------------_l __ -OETA~ ~·--l --
SPLASH BLOCK PER
COUNTY OF SD GREEN
STREETS STD. NO.
GS-5.06 TYPE 1
Oroa=0.18 CFS -7
V100=1.89 FPS
I
I IMPROVEMENTS WITHIN PUBLIC RIGHT-OF-WAY TO BE CONSTRUCTED PER
PUBLIC IMPROVEMENT PLANS. NOTE, ALL REFERENCES TO PUBIC IMPROVEMENT
PLANS DO NOT IMPLY APPROVAL THEREOF. THESE PLANS ARE SUBJECT TO
CHANGE.
SITE DESIGN {LID) BMPs SOURCE CONTROL BMPS
DESCRIPTION
IMPERVIOUS AREA DISPERSION
SUSTAINABLE LANDSCAPING
SYMBOL
I SD-Bl
I SD-Kl
DESCRIPTION
PROTECT TRASH STORAGE AREAS
SYMBOL
I SC-A I
EASEMENTS
THIS SURVEY WAS PREPARED WITH THE BENEFIT OF A PRELIMINARY TITLE REPORT FROM FIRST
AMERICAN TITLE COMPANY, ORDER NO. OIV-6930240, DATED 11/23/22. SAID REPORTS INDICATE THE
FOLLOWING EASEMENTS FOR THE SUBJECT PROPERTY:
(3) THE RECITAL ON MAP 1787 WHICH AGREES TO ALLOW THE CROSSARMS OF POLES
OR SIMILAR STRUCTURES PLACED ALONG THE RIGHT OF WAY OF HIGHWAYS LESS THAN
SIXTY (60) FEET IN WIDTH TO HANG OVER THE ABUTTING LAND.
(4) AN EASEMENT FOR RIGHTS OF WAY FOR TELEPHONE AND/OR ELECTRIC POLES AND
LINES, AND FOR SEWER, WATER AND/OR GAS MAINS AND PIPE LINES, IN UNDER, OVER
AND ACROSS SAID PROPERTY, TOGETHER WITH THE RIGHT TO ENTER ON SAID PROPERTY
FOR PURPOSES OF CONSTRUCT/ON, RECONSTRUCT/ON, REPAIRING AND/OR ALTERING ANY
OF THE SAME ANO INCIDENTAL PURPOSES IN THE DOCUMENT RECORDED
DECEMBER 24, 1937 AS BOOK 729, PAGE 313 OF OFFICIAL RECORDS.
(THE LOCATION OF THE EASEMENT CANNOT BE DETERMINED FROM RECORD INFORMATION.)
NOTE: DISINTEGRATED GRANITE (D.G.)
PER TABLE 200-2. 7.2(A) OF THE
STANDARD SPECIFICATIONS FOR
PUBLIC WORKS CONSTRUCTION 1 '
CONCRETE WALKWAY
(@ 2%)
SWALE
3"
MIN.
5.8"(TYP.)
9 EA. STEPS
14"
#3 NOSE_-,.
BAR -TYP.
•
1·-2· DIA. ANcuLAR=111 m 1 11 m 111
1111l11, rn
/J O 18· o.c.
EA.CH WAY.
LANDSCAPE ROCK -_" -'I I_,.... ,ill'"I I _ 111=11 ,-, •
2" THICK (COBBLE IS D.G. FILTER BLANKET
NOT ACCEPTABLE) (SEE NOTE AT LEFT)
DETAIL A' -
o---+-1-/4 T&EI
MIN. 12" ma INTO
UND/STllRBED SOIL 1 2 •
DETAIL 'B' -
ROCKLINED SWALE CONCRETE STAIRS
NOT TO SCALE
D: \DRAWING FILES\llllE SHEElS\GRADING TlllE SHEET.DWG REVISED: 01/05/16
I • r
70
68
66
64
62
' .
'"
t--- -. . ..
I -r
6-
60
58
5
4 ...
..
5
52
50
0+00
,-
FINISH
GROUND~
5%. -~
HOUSE
FOUNDATION
RAILING
2% -u-
"'-EX.
6' WOOD FENCE ON
"'1NIJIY.UIJJJS_GOJ;J,r
FOOTING (REPLACES EX. 6;\
VINYL FENCE)
DETACHED ADU FOUNDATION
(SEPARATE CDP)-
FF=62.52' FG=61.30'
~ i---o.5' ------li -~rl
EG-
...
...
70
68
66
64
62
GROUND 18" SOIL MEDIA IN
1.5.J I
I -..
60
58
56
54
52
PLANTER AREA*
• SOIL MEDIA TO BE PER APPENDIX F.J OF THE CITY OF CARLSBAD BMP
DESIGN MANUAL CONSISTING OF 70% TO 85% BY VOLUME WASHED SAND
AND 15% TO JO% BY VOLUME COMPOST OR ALTERNATNE ORGNvlC
AMENDMENT. Sff APPENDIX F.J OF THE BMP DESIGN MANU/.J.. FOR
SPECIFIC GRADAllONS Af/D COMPOSITIONS OF SAND AND COMPOST.
EX. CMU
WALL
SECTION 'G'
SCALE: 1 "=5'
il
ii
I .,.__ ~~ _/J "=-EG
50
0+48
72
70
68
66
64
62
SECTION A'
SCALE: 1 "=5'
70 -+------<r: -1-------------------------------·---------;----~--EX. 6' I 1 MAX CMU
68
66 --L2'
64
62
FG
2% FF=67.07'
HOUSE
FOUNDATION
---------\_ , ____ _
HOUSE
FOUNDATION
(p, PCC l, WALL / •I I WALKWAY 11 ,
2%. I: i 1.9' EX. ~ i: f DIFFERENTIAL
\ ·iv-
Ex . .l,./-
56
SECTION 'B'
SCALE: 1 "=5'
68
66
6' WOOD FENCE ON CONTINUOUS CONC.
FOOTING (REPLACES EX. 6' VINYL FENCE~
DETACHED ADU FOUNDATION t----61.30'-H ----l
(SEPARATE CDP) 1, SPLASH
FF=62.52'54 BLOCK PER f
SAFETY
RAILING
HOUSE
FOUNDATION
FF=67.07'
FG
2%
GS-5.06
62
s; 60 -I --\--~
1 '
70
68
58
56
66 54
18" SOIL MEDIA IN
PLANTER AREA (SEE
SEC. G FOR MIX)
I
I
11
64 52 EX. CMU _/-j
WALL
0.
64
60
58
56
54
EG
52
I
6//1/2"/
70 -+------t----+-70
68
BLDG. FOUNDATION PER
ARCHITECTURAL PLANS
66
64
62
60 -I---'-EG
0+00
FG
66
64
2%.
r--"'-"""""""",....~62
HOUSE
FOUNOAT/0 60
0+10
SECTION 'E'
SCALE: 1 "=5' 50-+----------1~50 ~-----------------, 0+00 0+10 "AS BUILT"
SECTION 'C' SECTION 'D'
SCALE: 1 "=5' SCALE: 1 "=5'
RCE __ _ EXP. ___ _ DATE
REVIE'v/ED BY:
INSPECTOR DATE
70 t----t----+------------------t---+--+---;-----1 I S2ET I CITY OF CARLSBAD I SH4ETS I
68 ENGINEERING DEPARTMENT
GRADING PLANS FOR:
66 LABOUNTY RESIDENCE
64 3950 GARFIELD STREET
GR2023-0040 GRADING & DRAINAGE PLAN
62 APPROVED: JASON S. GELDERT
60-+-----------------,-------------------,-------,; GROUND------~---t-60 t----+-----+~-----------------1---+--+---t-----1
~oo ~~ ~~ ~D=w=N~B~~~-o~v==~-
ENGINEERING MANAGER RCE 63912 EXPIRES 9 /30 /2 4 DATE
SECTION 'F' si~~ILP~ DATE 1N1r1AL DATE INITIAL DATE INITIAL CHKD BY: __ _
ENGINEER OF WORK REVISION DESCRIPTION OTHER APPROVAL CITY APPROVAL RVWD BY:
SCALE: 1 "=5'
PROJECT NO. DRAWING NO.
CDP2022-0067 545-7 A
LABOUNTY -DRAINAGE MAP A. I -EXISTING CONDITIONS
DESCRIPTION
PROPERTY LINE
EXISTING CONTOUR
BASIN LIMITS
DIRECTION OF FLOW
IMPERVIOUS AREA
PERVIOUS AREA
DRAINAGE MANAGEMENT
AREA (DMA) ID
N
I
50'
LEGEND
SYMBOL
N45" 45 '45 "W ---90---
■-------■
,......____,..-,......____,..-
IA. ,1
f8
0
0
0
!:§ COFFEY ENGINEERING, INC.
9666 BUSINESSPARK AVENUE, SUITE 210, SAN DIEGO, CA 92131 PH {858)831-0111 FAX {858)831-0179
Drainage
Management
Area
C.0 (Front)
D.0 (Back)
Impervious Pervious Total Runoff Percent
Area-ft2 Area-ft2 Soil Type Total (SF) (AC) Coefficient
(C) Impervious
1,530 983 B 2,513 0.06 0.63 60.88%
3,437 820 B 4,257 0.10 0.75 80.74%
LABOUNTY -DRAINAGE MAP 8. 1 -PROPOSED CONDITIONS
DESCRIPTION
PROPERTY LINE
EXISTING CONTOUR
PROPOSED CONTOUR
BASIN LIMITS
SUB-BASIN LIMITS
DIRECTION OF FLOW
IMPERVIOUS AREA
PERVIOUS AREA
DRAINAGE MANAGEMENT
AREA (DMA) ID
N
I
LEGEND
SYMBOL
N45. 45 '45 'W ----------90------90------------
I
o O I
I
I
I
I
I
1
0
0
!a COFFEY ENGINEERING, INC.
9666 BUSINESSPARK AVENUE, SUITE 210, SAN DIEGO, CA 92131 PH (858)831-011 l FAX (858)831-0179
__ oH
Drainage Management Impervious
Area Area -ft2
C.1 (Front) 1,703
D.1 (Back) 2,727
D.1.1 (to rock swale -
subarea of D.1) 1,866
Pervious Total
Area -ft2
Soil Type Total (SF) (AC)
1,147 B 2,850 0.065
1,193 B 3,920 0.080
484 B 2,350 0.050
0100=0.48 CFS
V10o=SHEET FLOW
Runoff
Coefficient (C)
0.62
0.68
0.74
CFS
FPS
Percent
Impervious
59.75%
69.57%
79.40%
Table A ‐ Area Tabulations & Runoff Coefficients ('C')
Drainage Management
Area
Impervious
Area ‐ ft2
Pervious Area ‐
ft2 Soil Type Total (SF) Total (AC)
Runoff
Coefficient
(C)
Percent
Impervious
C.0 (Front)1,530 983 B 2,513 0.058 0.63 60.88%
D.0 (Back)3,437 820 B 4,257 0.098 0.75 80.74%
C.1 (Front)1,317 1,124 B 2,441 0.056 0.58 53.95%
D.1 (Back)3,477 853 B 4,330 0.099 0.75 80.30%
D.1.1 (to rock swale)1,866 484 B 2,350 0.050 0.74 79.40%
Table B ‐ Pre Construction Flow Characteristics 100 ‐yr P6 =2.50
Pipe/Channel Flow Summary
Flow ID (Basin) Element &
Dwelling
Unit/Acre
Watercourse
distance, L (ft)
Elev. 1 Elev. 2 Change in
Elevation, H
(ft)
Natural
watercouse
duration, Dn
(min)
Urban
watercourse
distance, Ti (ft)
(≤ LM)
Maximum
Overland Flow
Length
Watercourse
slope, s (%)
Runoff
Coefficient, C
Initial Ttime of
Concentration
(per Fig. 3‐2)
Overland
Flow Time,
Tt (min)
Pipe Length, Lp
(ft)
Average
velocity, V
(fps)
Pipe travel
time, Tp
(min)
Total time‐of‐
concentration, Tc
(min) ‐
(5 min minimum)
Runoff
Coefficient, C
Rainfall
Intensity, I
(in/hr)
Basin Area, A (acres)Q (cfs) =
C*I*A
C.0 (Front)MDR ‐ 7.3 0 0.00 50 65 1.00 0.63 0.00 6.01 0.00 6.01 0.63 5.85 0.06 0.21
D.0 (Back)MDR ‐ 7.3 84 68 63 5 0.70 0.00 0.00 0.00 5.00 0.75 6.59 0.10 0.48
Table C ‐ Post Construction Flow Characteristics
Pipe/Channel Flow Summary 100 ‐yr P6 =2.50
Flow ID (Basin) Element &
Dwelling
Unit/Acre
Watercourse
distance, L (ft)
Elev. 1 Elev. 2 Change in
Elevation, H
(ft)
Natural
watercouse
duration, Dn
(min)
Urban
watercourse
distance, Ti (ft)
(≤ LM)
Maximum
Overland Flow
Length
Watercourse
slope, s (%)
Runoff
Coefficient, C
Initial Ttime of
Concentration
(per Fig. 3‐2)
Overland
Flow Time,
Tt (min)
Pipe Length, Lp
(ft)
Average
velocity, V
(fps)
Pipe travel
time, Tp
(min)
Total time‐of‐
concentration, Tc
(min) ‐
(5 min minimum)
Runoff
Coefficient, C
Rainfall
Intensity, I
(in/hr)
Basin Area, A (acres)Q (cfs) =
C*I*A
C.1 (Front)MDR ‐ 7.3 0 0.00 56 80 1.50 0.58 0.00 6.07 0.00 6.07 0.58 5.81 0.06 0.19
D.1 (Back)MDR ‐ 7.3 0 0.00 78 80 1.50 0.75 0.00 4.89 0.00 5.00 0.75 6.59 0.10 0.48
D.1.1 (to rock swale)MDR ‐ 7.3 0 0.00 91 80 1.50 0.74 7.40 7.51 0.00 7.51 0.74 5.07 0.05 0.18
Ex
i
s
t
i
n
g
Co
n
d
i
t
i
o
n
s
Natural Watercouse (per Fig. 3‐4Urban Overland (Sheet) Flow (per Fig. 3‐3)
Natural Watercouse (per Fig. 3‐4Urban Overland (Sheet) Flow (per Fig. 3‐3)
Pr
o
p
o
s
e
d
Co
n
d
i
t
i
o
n
s
100
2.5 4.5 55
2.5
varies
10.0
9.0
8.0
7.0
:5 0 .c <ii Q) .c
6.0
5.0
4.0
3.0
2.0
g 1.0
~09
-~08
Q) :§07
0.6
0.5
0.4
0.3
0.2
0.1
' ' " .... ' ... r-..
' ' .... :, .... ....
' • ' ..... , ........ ""r-,. 'r-. r-,,
' ... ...
'r-.. ' ' .....
..... , .... ,.
... • ' ' ' .... ---i-,.. ' ' ' ...
' .... ,
' ' • ' 'r-.. ...
.....
' .... ,.
' ' ..... ,
' ......
' 5 6 7 8 9 10
.. ,
....
..
r-..,
.. ,
... ,
.. ,
.... ,
r-.r-. .. r-r-' ~ ..
.. I"
I'-"-'""
r-.. .. ~ ~
r-.r-, "'i-. '~ ~ .. .. .. , ... , ..
'i-. ~ ~ r-.,. '~ .. ..
r-. i"r-.. ..
'r-~
....... ..
,.
'r-..
... ..
~
.. 1'-i-,. ,,
"", ..
15 20 30
Minutes
..
..
'""
.... ..
.... ..
~r-.. ..
~
~ .. ..
.. ..
~ ..
..
..
~
'"" ....
..
..
""~
40 50
Duration
I =
I =
p6 =
D =
EQUATION
7.44 P6 D-0.645
Intensity (in/hr)
6-Hour Precipitation (in)
Duration (min)
'r-,. ... ' .... , .... i', ..._I'-1 ... I',
i', .... ,,
' 'i-.. 'r--
....
... , , ...
'i-..
' I'-,
'r-,. '-i-..
2
', '' .. ' ....
'' ' .. .. "", ', ', r-..
"" ', .
.... ,
..
.... ,
.. ,
'
I"' ',
'"" I"
I"
3
Hours
..
..
..
..
..
..
..
~
~
..
..
..
4 5 6
"' ::'.c 0
~
-u iil 0
6.o -g;
5.5 ~
5.0 g
4.5 5'
0
4.0 ~
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) p6 = --in., P24 = --'P 6 = %(2J
24
(c) Adjusted p6<2l = ___ in.
(d) tx = __ min .
(e) I = __ in./hr .
Note: This chart replaces the Intensity-Duration-Frequency
curves used since 1965.
I
P6 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 I 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 5.60
30 0.83 1.24 1.66 2.07 2.49 2.90 3.32 3.73 4.15 4.56 4.98 ~ 0.69 1.03 1.38 1.E_ 2.07 2.41 2.76_ 3.10 3.45 3.79 4.13 ~-50 0.60 0.90 1.19 1.49 1.79 2.09 2.39 2.69 2.98 3.28 3.58
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 0.82 1.02 1.23 , .43 1.63 1.84 2.04 2.25 2 .45
120 0.34 0.51 0.613_ 0.8§_ ~ 1.19 1.36 1.53 1.70 1.87 2.04
150 0.29 0.44 0.59 0.73 0.88 1.03 1.18 1.32 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 1.30
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
F I GURE ~
Table 3-1
RUNOFF COEFFICIENTS FOR URBAN AREAS
San Diego County Hydrology Manual
Date: June 2003
Land Use
NRCS Elements County Elements
Undisturbed Natural Terrain (Natural) Permanent Open Space
Low Density Residential (LDR) Residential, 1.0 DU/A or less
Low Density Residential (LDR) Residential, 2.0 DU/A or less
Low Density Residential (LDR) Residential, 2.9 DU/A or less
Medium Density Residential (MDR) Residential, 4.3 DU/A or less
Medium Density Residential (MDR) Residential, 7.3 DU/A or less
Medium Density Residential (MDR) Residential, 10.9 DU/A or less
Medium Density Residential (MDR) Residential, 14.5 DU/A or less
High Density Residential (HDR) Residential, 24.0 DU/A or less
High Density Residential (HDR) Residential, 43.0 DU/A or less
Commercial/lndustrial (N. Com) Neighborhood Commercial
Commercial/lndustrial (G. Com) General Commercial
Commercial/lndustrial (O.P. Com) Office Professional/Commercial
Commercial/lndustrial (Limited I.) Limited Industrial
Commercial/lndustrial (General I.) General Industrial
%IMPER.
O*
10
20
25
30
40
45
50
65
80
80
85
90
90
95
Section: 3
Page: 6 of26
Runoff Coefficient "C"
' ,il Type
A B C D
0.20 0.25 0.30 0.35
0.27 0.32 0.36 0.41
0.34 0.38 0.42 0.46
0.38 0.41 0.45 0.49
0.41 0.45 0.48 0.52
0.48 0.51 0.54 0.57
0.52 0.54 0.57 0.60
0.55 0.58 0.60 0.63
0.66 0.67 0.69 0.71
0.76 0.77 0.78 0.79
0.76 0.77 0.78 0.79
0.80 0.80 0.81 0.82
0.83 0.84 0.84 0.85
0.83 0.84 0.84 0.85
0.87 fl R7 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
San Diego County Hydrology Manual Section: 3
Date: June 2003 Page: 12 of 26
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 Ti 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)
.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 10.9 100 10.3 100 8.7 100 6.9
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 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 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
I-w w u.
z
w () z <( I-(f)
0
w (f)
0:::
::J 0 ()
0::: w
i
2.50% slope--1, 2,Q--+-----1-#l#
100 1---_J1..J.5q===="-::h-~£J~L__I
0
EXAMPLE:
Given: Watercourse Distance (D) = 70 Feet
Slope (s) = 1.3%
Runoff Coefficient (C) = 0.41
Overland Flow Time (T) = 9.5 Minutes
SOURCE: Airport Drainage, Federal Aviation Administration, 1965
T= 1.8(1.1-C)VO
3\fs
(/) w I-::J z
20 ~
z
w
~
i==
~ 0 ...J u.
0 z <(
...J
0::: w > 0
FIGURE
Rational Formula -Overland Time of Flow Nomograph 3-3
.6. E
Feet
5000
4000
Tc
Tc
L
.6.E
=
=
=
=
EQUATION
(1~~3)0.385
Time of concentration (hours)
Watercourse Distance (miles)
Change in elevation along
effective slope line (See Figure 3-S)(feet)
3000
2000
400
300
200
30
20
10
5
.6. E
SOURCE: California Division of Highways (1941) and Kirpich (1940)
L
MIies Feet
4000
' .
3000
0.5 '
2000
1800
1600
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
FIGURE
~
Site
Cnnntv nf~~n n-iPOQ
Hydrology Manual
• Co
Soil Hydrologic Groups
Legend
Soil Groups D GroupA
-GroupB D Groupe
D GroupD
D Undetermined LJ Data Unavailable
DPW
*GIS ~/Xf'ts/;,'ic Wal<• ~i,clr,fom,;tlior,&.,n.,\'.;~
TI-MMAPIIIPlll"Mlll'nwTTWl"lllnW&All&tff¥'t-.:1.1,NIDIIID RIM'Rn'PRE58 + ~~~:~=~~~~Ell ~s.no&s.Mllgl!ifll~. n.-------~~ w =-~at~-:C-111,~Mta;tk
.... __ _.. ......... ~ ... IINl,~--
~9"'MGW,nio-.111ut.a ... . s
3 0 3 MIies I&-
P6=2.5
I I I I g /_ J_ -' g ·' 9 u') ~
~ .
~ ::: ~ ~ ~ -
--33°31~)''-+-t-±t1 c=t''-11.,~''"+Fl=!==i=+J.::;t· =4= 0,'.:>. r H---HH-+-t+H +t-++-,H-+-t+H +H-+-tH-+-t+H +!-++-IH-+-l++-++!-++-t!-++-l++-+-!--!-++-l!-++-l++-+-!--f-l.+-l+-l--l+-l--l3•3)•,...,...
• • 1--r:>t"l<::t---t-t-H ·---t-t---t-t---t-t--H--H--H--H-H --H--H--H--H--H--H--H--H--H--H--H--H--H--Hl-l-l-l-l-l-l-l-l-l-l-l-l-l-l-l-l-l-l-l-l-l-l-l--l-l--l-l--l-l-l If
V
3 .;;; jr) ~,.;
I I l I\ ... DEL LIAD \ ill. ,,,~ ,.
..
),I ·,.
'/
;) ,.
/It )I I ·•.
(-' ~
-~•~-~1 1111tttt tttttttt++++-++-++-+++++++-!+-!+-l+-l+-ll-+-l-+-l-+-l-+-l-+-l-+-l-+-+-+--+-+---l-l--l-l--l-l-UU--l---++-i-+-i-+-i---l--+--l--+--l--+--+-l--+-l--+-l--+-l--+-l~2•3r -~
' • -+-+-+-+-+-+-+-+-+-+-+-+-+-+'!!.-+-+->-+-+->-+-+-+-+-+-+-+-+-o-+-+-+-+-+-+-+-+-+-+-+-+-+-,■
H -+-+-t-+-+-t-+-H-+-He-4-~'--t-+-t-+-+-t-+-+-t-+-+--l-+-+~,-i---+-t-+-+--l-+-+--l-+-+-r+-tc~:-+-+-t-++--l-++--l-+-+--lf-++:~,-+-+-t-+-+-t-+-+-t-++--l-+--t-i!a-:a-++-r++-+--++-+--+-+-+--+-+-~r-t-++-t-++--l-+-+--l-+-+-HI
Crn1nh.r n-f ~~n n1 P OQ
Hydrology Manual
• Rainfall Isopluvials
100 Year Rainfall Event- 6 Hours
lsopluvial (inches)
DPW ~GIS
~
S1TiGIS {),op-(1(('-.;t;,';c~t,,;. &."W'-'Pficlr:fo,,T,.-W,s,,,,,;,,.,. We Ha\'t San Dil:go Ccw<:rtd!
'naWAP IIIPllrMOEDwrn«JUJWARA.UrllYC'S-AM'IICIIIID EffHEREXPRE58 + M .... Jft)..0.1JON1 11UTI011.JMffffiTOTNIU'l.lff)WAll!IIAHT1E8 rY-MEIIOaNTARllJlY......,RDa:I.IIIFQA/1.PAR'TlCllMPUJIPOSE. Cow\flSanOIS.M,..."-'IIKI. Tl,;J,---------~~ W ~S-Wtil~N~Vllto.t--Wllllln~d8AND,l,O . .,. __ ~........,~-'-"'~--~V--,0,TI'lllmllllllhn ....
3 0 jL_ 3 MIies
P24=4.5
~t=tt~=tj=tt~ttj=t:t=tsjH-++H+-H-++H++-• :i---t--HH+H+-t-1H+H1+-+-1-++H++-1-++-H-ro-+-1++-H++-1+-J.-j1-1----1---if:,..J.+-J.-j1-1---1-w++-11-1---1-1-,b,+-+-+-+-+--+-+-+-1--+-+-1----i.
~
I I I .,I_ In L ,!. J_
~ f ~ ... i'I ~ ~ ~ ~ --
---3 0
rt---t-H---t-+-H+t-+-++-H ++-1-'l-'1+-H-•SO
H--t-tiH-+H++-,-++H+-Hl-+-1!.l"'ll----l+-1-1--oeL
1, .. , ..
I-+-I-3?" ,_ 2'.3)' I -~ I ~ ~ ;: r., ~ !!: I "j" 'i "j" :;= 'i "j"
Crn1nh, of ~~n n1POO
Hydrology Manual
Rainfall Isopluvials
100 Year Rainfall Event-24 Hours
lsopluvial (Inches)
DPW
*GIS ~'l>f Pu!,IC Wc•l<• ~:,clr,fom ,;tlior,5';,,w:crs
n.dMA#llllt~flwm«'ril'l'W&filAAN"'l\'~UltllDllll".l~llil~ + DAIIY'UED.N'.liJOarO.BUTN:ITUMrl'EDTnn-=M'IJEDWARR.l«TIEll ~ ~TAAi rlY l,N"l m,,ai:lt_1 ~QA APAAl'ICUNt PUAPOSE. ~s.iola.M .... ~. Tllil,------... -~ W .___S--,,,,~bll~wllo.tlw .....,~dBANWJ.
'IMl!llm.ld _ _.,........,,.~ ... bNII~ .... ~,....,lllr""-~---s
3 0 3 Miles
I