HomeMy WebLinkAboutSDP 96-14C; LEGOLAND HOTEL CALIFORNIA; PRELIMINARY DRAINAGE STUDY; 2008-04-14PRELIMINARY DRAINAGE STUDY
For
LEGOLAND HOTEL CALIFORNIA
Carlsbad, CA
Date:
April 14, 2008
Prepared By:
Hofman Planning & Engineering
3152 Lionshead Avenue
Carlsbad, CA 92010
RCE 58873
RECEIVED
APR 1 ' "
CITY OF Cl'
PLANI I ,_,
Prepared by: jc
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• Legoland Hotel California Drainage Study
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TABLE OF CONTENTS
Section 1 . Certification . . . . .. . . . . . . . . . . . .. .. . . .. . .. . .. . . .. . .. .. . . . . . . . . . .. . . .. .. . . . . . . . .. . .. . .. . . . . . 1
Section 2. Project . .. ... . .. . .. .. . .. .. .... .. ... ... . .. .. .. ... ... ... .. .. . ... . . . .. . . .. ... ... ... .. .. . ... . ... ..... 2
Section 2 .. 1 Objective ............................................................................. 2
Section 2 .. 2 Description ............................................................................. 2
Section 2 .. 3 Existing Condition ...... ............ ... ... ... ............ ...... ... ...... .......... 2
Section 2 .. 4 Proposed Condition ....... ..... ...... ...... ... ...... ......... ... ...... 2
Section 3. Methodology .......... ..... ... ...... ... ...... ... . .. ...... ...... ...... ...... ... ......... ... 3
Section 3. 1 Rational Method ...... ......... ............ ... ......... ...... ... ...... .......... 3
Section 4. Summary............................................................................................. 4
Section 5. Hydrology Calculations ......... ...... ......... ... ... . .. ...... ...... ............ .. 5
Section 5. 1 Pre-Developed .... ..... ...... .... ........ ... ... ...... ... ... ... .. .... ... . ..... ... ... . . 5
Section 5.2 Post-Developed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1
Attachment A
Attachment B
Attachment C
Attachment D
Attachment E
Vicinity Map
Pre-Developed Hydrology Map
Post-Developed Hydrology Map
Node Analyses
Tables & Charts
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• Legoland Hotel california Drainage Study
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Section 1 . Certification
DECLARATION OF RESPONSIBLE CHARGE
I hereby declare that I am the 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.
\ '
EXP. 06-30-09
·'>'-,~ ..•
l-·"
C 58873
p. G·W-rf-J
.l
~rLi-o&
DATE
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• Legoland Hotel California Drainage Study
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Section 2. Project
Section 2 .. 1 Oqjective
The objective of this study is to determine the stormwater runoff generated in a 100-
year event for both the existing and proposed conditions on the site and to determine
the need for hydraulic structures. Moreover, this study will also design the proposed
storm drain system to effectively control the runoff while mitigating impacts to the
downstream storm drain facilities.
Section 2 .. 2 Description
As shown in attachment A, the site is wholly within the parking lot of Legoland California
in the city of Carlsbad (APN 211-100-14). The site is bordered by the park to the north
and the parking lot to the east west and south. The site is presently a paved parking lot
and decorative paving which will be removed .
Section 2 .. 3 Existing Condition
As shown on attachment B, the site currently drains to the south, into an existing private
36" PVC storm drain. The runoff enters the storm drain through a series of curb inlets in
the existing parking islands.
Section 2 .. 4 Proposed Condition
A new 3-story hotel building as well as incidental utilities, and hardscape improvements
is proposed within the parking lot at will span over the existing pedestrian park
entrance. As indicated on attachment C, a new private subsurface drainage system will
convey the runoff around the hotel building into the existing storm drain system .
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Legoland Hotel California Drainage Study
Section 3. Methodology .............................................................. .
Section 3.1 Rational Method
The Rational Method as described in the San Diego County Hydrology Manual, Section 3,
(Revised June 2003) shall be used to determine storm runoff .
The Rational Method formula is expressed as follows:
Q = CIA
Where:
Q = peak discharge, in cubic feet per second (ds)
C = runoff coefficient, proportion of the rainfall that runs off the surface.
The coefficient C has no units and is based on the soil group and the
percentage of impervious area for the drainage sub-area. Attachment E
includes calculations for the percent of impervious area for each drainage
sub-area.
I = average rainfall intensity for a duration equal to the Tc for the area, (in/Hr.)
A = drainage area contributing to the design location, in acres
The following values are used in the calculations:
Soil Group D from San Diego County Soils Group Map. (See Attachment E)
C (Coefficient of Runoff) from Table 3-1. (See Attachment E)
100 year 6 Hr. Rainfall = 2.6" (See Attachment E)
100 year 24 Hr. Rainfall = 4.5" (See Attachment E)
The site has be divided into drainage sub-areas as shown on the On-Site Hydrology
Maps in Attachments B and C. Basin areas and invert elevations were calculated from
the proposed grading plans and the existing topography. Given that the soil around the
site is type B and the proposed site is general commercial, the runoff coefficient C is
assumed to be 0.80 throughout the site in accordance with table 3-1 of the manual .
The time of concentration, Tc, for each sub-area along the drainage path is computed
based on the initial time of concentration for the initial area and the travel time to reach
the next node. We based the times of concentration on overland flow nomograph
shown on figures 3-3 through 3-7 and/or table 3-2 of the manual. The 100-year rainfall
intensity was calculated with the intensity duration design chart template (figure 3.1 of
the manual). Then, applying the rational method equation, the peak runoff is
determined at each node along the drainage path. Q's are tabulated for each sub-area
along the drainage path. The node analyses are shown in Attachment D .
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-Legoland Hotel california Drainage Study
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Section 4. Summary
The proposed project will not significantly alter drainage patterns on the site or the
surrounding area. Placement of the hotel requires minimal flow diversion. There will be
no net an increase to the amount of impervious area.
As shown on the results in Attachment D, the existing site runoff is at 72.90 cfs, while
the proposed project will increase the volume of runoff to 73.59 cfs. The increase in
runoff is negligible and due solely to the diversion around the existing hotel as well as a
slight increase in area to the west of the site.
A capacity analysis of the existing 36" PVC storm drain shows that the pipe is currently
at 58% capacity and is able to handle the increase in volume resulting from this project.
(See attachment D)
We have determined that the inlet capacities of the proposed storm drain system are
sufficient to prevent any ponding during a 100-year storm event. Moreover, we have
designed the storm drain system so that the 100-year runoff generated from the
proposed development does not significantly impact the downstream facilities any more
than the existing condition .
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4f> ACIFIC -OCEAN ---.. .. .. .. .. ---
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ATTACHMENT A
VICINITY MAP
CITY OF OCEANSIDE
CITY OF ENCINITAS
■
NOT TO
SCALE
CITY OF VISTA
ITY OF
N MARCOS
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BASIN
NOOE
DRAINAGE OIR£CnON
STORM DRAIN PIP£
-LEGEND
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(780)~·
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CCN■ULTIN■
!he contents d . NOTICE
information of LE ths document constit related entities. ~LANO California :e proprietary
~m',;',:, oonfiden~: ~-:v;ng .,;:":uo:'nt
in whole or i~o:ined herein s:i~ ~ the
~;'"' ... prio, ";.:.~~sdosed to oth':.":"" ornia coosent of LEGOLAND
~ S1 E " t-f ~ 1:i
AMENDMENT g
EGOLAND HOTE SDP # 96-14(C) ~ PRE L CALIFORNIA ~
HYDR8E~EGL YO PED :c MAP
Scale: as shown
April 14, 2008
Sheet Number
ATTACHMENT B
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240
LEGOL:Jll
CALIFORNIA
1 LEGOLAND DRIVE
CARLSBAD, CA 92008
(760) 918-5300
Prepared by:
NICHOLS BROWN WEBBER
AJ.OilTECTS AND 1.ANDSCAP1! PlANNl!RS
,ctCDl&'.Jm8,~NBl«.ln'4'.1'MAlml,,(lll]N ... &G,, tx
Tl!l.i'TUaVlI.LBHBATH(++41....i"9.IJC).PA%(+4414'1812aJ
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571-11 HygoloA-,uo
Leucadia, CA IIZ024
(780) 943-071!0
IWltl)8l2Qcox.n
CA-il:2825
NOTICE
The contents of this document constitute proprietary
information of LEGOLAND Califorria and/or other
related entities. Any party receiving this document
does so in confidence and agrees that the
information contained herein shall not be duplicated
in ¥mole or in part, nor disclosed to others without
the express prior written consent of LEGOLAND
California.
Key Plan
CITY SUBMITTALS
Description Date
r "' i;: ~ t t f ~ I;\ SITE DEVELOPMENT PLAN -
AMENDMENT i
SDP # 96-14(C) EJ
LEGOLAND HOTEL CALIFORNIA §?
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-Existing Node Analysis
Carrying -Capacity
... Node Basins Area Ac C Tc Min I In/Hr Q100 cfs cfs Conveyance
1 1 18.87 0.82 14.4 3.46 53.59 66.70 36" PVC @. 1.0% .. 2 1,2 19.97 0.82 16.0 3.24 52.97 66.70 36" PVC @. 1.0%
3 3 4.56 0.82 5.0 6.85 25.59 22.62 24" RCP @ 1.0% .. 4 1 Thru 4 28.55 0.82 17.0 3.11 72.90 123.00 36" RCP @ 3.4% -
Proposed Node Analysis -Carrying
Capacity ¥
Node Basins Area Ac C Tc Min I In/Hr Q100 cfs cfs Conveyance
1 1 18.87 0.82 14.4 3.46 53.59 66.70 36" PVC@ 1.0% -2 2 1.24 0.82 5.0 6.85 6.97 10.50 18" PVC@ 1.0% .. 3 2,3 5.44 0.82 8.0 5.06 22.55 22.62 24" RCP @. 1.0%
4 4 2.71 0.82 6.0 6.09 13.52 14.40 18" PVC@. 2.0% -5 1 thru 5 28.85 0.82 17.0 3.11 73.59 123.00 36" RCP @ 3.4%
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County of San Diego
Hydrology Manual
Soil Hydrologic Groups
Legend
Soil Groups
D GroupA
-Groups
D Data Unavailable
DPW ~GIS s1iiGIS
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THIS MAP IS PROVIDED WrTHOVTWARRANTY OF ANY KIND, EITHER EXPRESS
OR l~ED. INQ.UOING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
OF MERCHANTABILITY ANO FITNESS FOR A PARTICULAR PURPOSE. Copyright SanGIS. All Rights ReseM,d.
This products may oontaln Information from the SANOAG Regional
Information System wNch C&Mot be ,epn,ducad without tt1e
written permission d SANDAG.
Thia product may ccntarn lnfonnatkln which has been reproduced ,.;tt,
permission granted by Thomas Brothers Maps.
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Hydrology Manual
Rainfall lsopluvials
100 Year Rainfall Event-6 Hours
lsopluvial (inches)
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THIS MAP IS PROvtOED WITHOUT WARRANTY OF ANf KIND, EITHER EXPRESS
OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
OF MERCHANT.ABIUTY ~O FITNESS FOR A PARTICULAR PURPOSE.
Cowtghl SanGIS. All Rights Rel8N9d.
Thts products may contain Information from the SANOAG Regional
Information System which..-be reproduced without the
wrtttsn pennlsalon ol SANDAG.
This product may oontafn Information which haa been reproduced -.1th
pennlsalon granted by Thomas 8-Mapo.
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Hydrology Manual
Rainfall lsop/uvials
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THIS MAP IS PROV10EO WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESS OR IMPLIED, INQ..UOING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
OF MERCHANTABILITY ANO FITNESS FOR A PARTICULAR PURPOSE.
Copyright S..GIS. All Rights --
This products may oontaln lnfoonatlon from the SAND,_G Regional Information System which cannot be reproduced wtthout the wrttten permission ol SAND.-\G.
This product may contain Information which has been reproduced wtth
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.u ;:::1'. ,..._ ..., ...... ,..._ ,._, ""...,.._ •._ "".. EQUATION
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4.o N. .... ..._ :-... "' · I .. D = Duration (min) I f' l"'r-,., •~"" to.., " I • i-... ..., ' "' " r-.,... i,. I',! . "~
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6 7 8 9 10 15 20 30
Minutes
40 50 2 3
Hours
4 5 6 5
Duration
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.
{S) This line is the intensity.cturation curve for the location
being analyzed.
Application Fonn:
(a) Selected frequency loo year
{b) p6 = ~ in., P24 = ~ .:6 = ~7 7 %(2)
24
(c) Adjusted p6<2> = ~ in.
(d) tx = __ min.
(e) I = ___ in./hr .
Note: This chart replaces the Intensity-Duration-Frequency
curves used since 1965.
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25 0.93 I 1.40 1:a1 ! 2~33 °2.801
1 3.271 3.73 4.20 r<J:67 15:i:f 5.60
30 .... -.o.·.03 1.2-i1.1.u j 2.01 ;2.49 ).9()[ 3,32 t· 3.73 [ 4 !5 4.56 4.98
'-----~ .. 0~69 ' .. ·.03 .. 1.38J 1.7.2,2.07.2.411 .. 2.76 ···3.10 ; 3.45. 3.7·9 · "_ ... 1.3 50 o.oo o._90 U9: 1.49, 1.79~2_.09 2.39 i 2,6~, 2.sa_ 3,~~ 3,~
---60 0.53 0.80 Ul6! 133 j 159, 1.86i 2.12 1 2.39 j 2.65 2.92 3.18
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.... _!!!(.! .!?:fil _o~4 00~_9 OJ~. o.~, 103: 1. t 8 1.32 1 1.41 1 1,e2 ;_1.76_
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FIGURE
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I I I I I I I I
San Diego County Hydrology Manual
Date: June 2003
• I I I i I I f I • i i I a l
Section:
Page:
Table 3-1
RUNOFF COEFFICIENTS FOR URBAN AREAS
Land Use I Runoff Coefficient "C"
Soil Type
NRCS Elements Coun Elements %IMPER. A B
Undisturbed Natural Terrain (Natural) Permanent Open Space 0* 0.20 0.25
Low Density Residential (LDR) Residential, 1.0 DU/A or less IO 0.27 0.32
Low Density Residential (LDR) Residential, 2.0 DU/A or less 20 0.34 0.38
Low Density Residential (LDR) 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 Density Residential (MDR) Residential, 7.3 DU/A or less 40 0.48 0.51
Medium Density Residential (MDR) Residential, 10.9 DU/A or less 45 0.52 0.54
Medium Density Residential (MDR) Residential, 14.5 DU/A or less 50 0.55 0.58
High Density Residential (HDR) Residential, 24.0 DU/ A or less 65 0.66 0.67
High Density Residential (HDR) 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. Com) General Commercial 85 0.80 0.80
Commercial/Industrial (O.P. Com) Office Professional/Commercial 90 0.83 0.84
Commercial/Industrial (Limited I.) Limited Industrial 90 0.83 0.84
Commercial/Industrial (General I.) General Industrial 95 0.87 0.87
I I
C
0.30
0.36
0.42
0.45
0.48
0.54
0.57
0.60
0.69
0.78
0.78
0.81
0.84
0.84
0.87
I t
3
6 of26
D
0.35
0.41
0.46
0.49
0.52
0.57
0.60
0.63
0.71
0.79
0.79
0.82
0.85
0.85
0.87
t I
*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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' ' • t I I .I i 1 l 4 I j • I i I j •
100 I 1,5 I U./'i// / I ~JJ' § § ✓I .....-"F 130
(/J
~ z I» I ■ I I I I~ -' 41"" v~ I .....,..,.-1 I ~ 20 ~ 0 y~,--,-., ,-~
w :E
i=
~ u.
10 ~
~ a: w ~
-0
EXAMPLE:
Given: Watercourse Distance (D) = 70 Feet
Slope (s) = 1.3 %
Runoff Coefficient (C) = 0.41
Overland Flow Time (T) = 9.5 Minutes
T= 1.8(1.1-C)VD
3\fs
SOURCE: Airport Drainage, Federal Aviation Administration, 1965
F'IGURE
Rational Formula -Overland Time of Flow Nomograph 3-3
. ' i l i I
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..
....
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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 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)
Element* DU/ .5% 1% 2% 3% 5% 10%
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
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~E
Feet
5000
4000
EQUATION
Tc = (1~!3)0.385
Tc
L
~E
= Time of concentration (hours)
= Watercourse Distance (miles)
= Change In elevation along
effective slope line (See Figure 3-5)(feet)
3000
2000
1000
' soo' ' 400 '
JOO
200
100
30
20
10
5
'~ ,~?),
~/4>
' ' ' ' ' ' ' '
SOURCE: California Division of Highways (1941) and Kirpich (1940)
L
MIies Feet
'1
.
3000
0.5 '
2000
1800
1600
1400
JOO
200
L
'
Nomograph for Determination of
' '
Tc
Hours Minutes
' ' '
Tc
50
40
30
20
18
16
14
12
10
9
8
7
6
5
4
3
Time of Concen1ration (Tc) or Travel Time (Tt) for Natural watersheds
FIGURE
3-4
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---/ ----i------------------L--------------------1
Watershed
Divide
-r
.6.E
I Effective Slope Line
Design Point
(Watershed Outlet)
•-----------------L-----------------
Area "A" = Area "B"
SOURCE: California Division of Highways (1941) and Kirpich (1940)
FIGURE
Computation of Effective Slope for Natural Watersheds 3-5
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Q) a. 0 en
Q)
~ u5
0
l.--1B--+I
1
..-n = .015-+-~---2% _ -n = .0175 -----....::..::... ____ _,! 2%
Concrete
Gutter Paved RESIDENTIAL STREET
ONE SIDE ONLY
20 -;-------1---.... --+---+--+~r+--t-➔~~"""-------1-----+----+----t-...-
18--f-------t----j ..... -+----+---++➔--f-➔--IHf--..;::,,,,._
16 ~-------+-#---,+;::::a.-::1----1~-+-+--+--l~I----.....;:...._,;
14 ~--------t,----;----+-+P.....t~+-t-illHl--------==-t~+----,l-----i--#-1----+
10 ...,. ______ ,_-+-------11----1---4---4--4-,j~-'--.,__..;::,,~
9 -+----J~=t===----=::~--l-+---l~+-1:........i---1--+------=::::....~~----J---l-+-.:::::..i--1-
8 -t----
7----
5
1.0 ~---,,-----+--1-'----+-;;:,,,,,,:c;
0.9 --f....;::""#<o:=-----t-#---+----+-..;:,,.~-+--f-➔--IHt-~~----+if----~.
0.8 ~"""".l~--....;:: ..... ::---fljf------11----+---+-l-::o+o::---+--+-+-.... +--...... ::-----, ..... -------------+-
0.7 ~#---------j~;;:,,,,,"-
0.5
2 3 4 5 6 7 8 9 10 20 30 40 50
Discharge (C.F.S.)
EXAMPLE:
Given: Q = 10 S = 2.5%
Chart gives: Depth= 0.4, Velocity= 4.4 f.p.s.
SOURCE: San Diego County Department of Special District Services Design Manual
FIGURE
Gutter and Roadway Discharge -Velocity Chart 3-6