HomeMy WebLinkAboutCT 01-16; CASA LAGUNA; HYDROLOGY & DETENTION CALCUALTIONS; 2002-03-08Casa Laguna Preliminary Hydrology and Detention Calculations
Carlsbad, Califomia
3/08/02
PREPARED FOR: PREPARED BY:
LAGUNA CARLSBAD LLC
31225 La Baya Drive, Ste 103
Westlake Village, CA 91362
(818) 991-1040
PACIFIC COAST CIVIL, INC.
30141 Agoura Court, Suite 200
Agoura Hills, CA 91301-4311
(818) 865-4168
Page 1 of2
Randall A. Greenwood
From: "Randall A. Greenwood" <rag@pacificcoastcivil.com>
To: "John Maashoff" <jmaas@ci.carlsbad.ca.us>
Sent: Friday, March 08, 2002 5:05 PM
Subject: Re: Storm Drain at Casa Laguna Project
John,
We've prepareci some preliminary hydrology calculations for this project and
have concluded the following:
The 10-year, 6-hour stonn is the control in designing the detention. Using
the side yard area bounded by the walkway to Unit 1, the driveway, Laguna
Drive and the wall at the easteriy boundary, and the 18" HDPE storm drain
pipe, there is sufficient storage to limit the outflow from the development
to predevelopment conditions. The catch basin (C.B.#2) adjacent to Unit 1
will have a top of grate elevation of 40.0', which will allow ponding in
this turf area up to 0.5'. Water ponding higher than 40.5' will flow back
out into the driveway and/or over the street right of way and into the
proposed catch basin (C.B.#3) in Laguna Drive. Unit I's finished floor
elevation is 42.9', so it will not be Impacted by this detention. Detention
will occur by the Installation of 2-4" diameter HDPE pipes between C.B.#2
and C.B.#3, which limit the outflow to pre-development conditions.
Note that C.B.#1 (serving the adjacent lot) has a top of grate elevation of
41.1', so no ponding will occur In this property as a result of the
detention on this lot.
Some of the data supporting this design is as follows:
P6=1.7 In.
1=4.48 in./hr.
A=1.18ac.
c(undeveloped)=0.33 c(developed)=0.70
Q(undeveloped)=1.74 cfs Q(developed)=4.48 cfs
Detention volume required: 749.5 cf
Detention volume provided: 942.4 cf
Maximum outflow from 2-4" pipes is 1.73 cfs.
Developed Q was calculated using the County's single hydrograph fomi and
detention storage computation worksheet.
P24=2.9 in
CN(undeveloped)=78 CN(developed)=90
Q(undeveloped)=0.4 cfs Q(developed)=0.5 cfs
Developed Q was calculated using the County's peak flow computation
3/8/02
Page 2 of2
worksheet and by using the hydrograph method and both yield the same result.
My calculations are preliminary in the sense that they are not accompanied
by final design plans. I will fon«^ard them to you for review on March 11.
Based upon these calculations and proposed storm drain design, runoff from
this development will not exceed predevelopment conditions.
Randy Greenwood
Pacific Coast Civil
818-865-4168
3/8/02
3
Current Map
Map Image Created Using Precision Mapping Streets 4 0 Copyright 1999. Chicago Map Corporation
COUNTY OF SAN DIEGO
DEPARTMENT OF SANITATION &
FLOOD CONTROL
10-YEAR 6-H0U[i PRECIPITATiOf^
^5'
30'
15'
10'
33'
45'
Pr«pi
16- iSGFLUViaiS OF 10-YEAR 6-ii3Un
PRECIPITATIOr^ IfJ TEfjlllS OF fiN INCH
rtd by
U.S. DEPARTMENfr OF COMMERCE
NATIONAt. OCEANIC AND AT OTSI'IIERJC AOXnNISTHATIOIt
SPECIAL STUDIES DPANCH. omCE Or .f D.OLOOV.rrN" WIA^HER SERVICE
30'
I >
I
118' 45' 30'
2020
15' 117° ^5' 30' 15' 116'
COUNTY OF SAN DIEGO .
DEPARTMENT OF SANITATION &
FLOOD CONTROL 10-YEAR 24-}]0UR PRECiPITATlOP^
^2W^ ISOPLUVIALS
PP.ECIPITATlOfJ in
33*
45'
]F 10-YEAR 24-HOUR
EWTliS OF Arj Viim
d by
T OF COMMERCE
lOSPKF.RIC ADMINISTRATION
Pr»p.
U.S. DEPARTMEr
NATIONAL OCEANIC AND AT
SPECIAL STUDIES DRA.VCII, OKFICE OK ijvDKOLOCy, NATIONAL WEATHER SERVICE
30'.
•-4
I
I
o • ^
INTENSITY^DU1V\TI0N DESIGN CHART
TTri'^llllillllillll I N >"""""'"""'"^ 1 i . T i'.'i.u.i Li-L-n inirliTii
[1 Equation: I « 7.44 D "'^'^^
I = Intensity (In./Hr.)
Pg «• 6 Hr, Precipitation (In.)
., D B Duration (Min.)
15 20
Minutes
40 50 1
0«v«Atf on
Directions for Application:
1) From precipitation naps determine 6 hr. and
24 hr. amounts for the selected frequency.
These maps are printed in the County Hydrology
Manual (10, 50 and 100 yr. maps included in tl
Design and Procedure Manual).
2)
3)
Adjust 6 hr. precipitation (if necessary) so
that it is within the range of 45« to 65% of
the 24 hr. precipitation. (Not {applicable
to Desert)
Plot 6 hr. precipitation on the right siW
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:
0) Selected Frequency P yr.
1) Pfi'-LI-ln-. P24=-^'!!6 = ^**
P,
2) Adjusted *Pg« 11
24
in.
3) \
4) I
s min.
tMft in/hr.
*Not Applicable to Desert Region
Revised 1/85 APPENDIX XI-A
03/01/2002 11:18 FAI 121052/054
• . • •]
DETEHTZON STORAGE COHPUTATION FROCEDtmE '
SINGLE HYDROGRAPH FORM
Input Variables (Urban Conditions)
\oirSix hour precipitation amount (inches) 1.7 _
Time of concentration (min.) b
Coefficient of runoff C -10
Basin area (acres] A (. jfi
ComtJutation
Time to peak
Tp = 2.0T^o/(l + Kp) = 1.1072T, -04072.7?;) T 5.63
Time of hydrograph to begin '
• \ 1" ~- ^-^'^5 T, mi
Time of hydrograph to end ^ .
TE = 20 + 1.5 T,--^otCl.'5X5.53) TB Zfe 30
= CIA . . ^ 5.70cl3
ITC = 7.44 P,/T,«^ = in./hr, ^
(7-MM) i.y^.''^^
Surrounding flow (Qg)
Depth of precipitation for 2 hours
Di2o = 7.44 P5/120'»^(2 hr.)
Dijo = 0,6785 Pe = |-I5 in.
l-l
Depth of precipitation for hydroqraph
DH = (P«T,<^**)/5.83 = 0.52. L, ^ ^
Surrounding Intensity .
Is « eOiDjM - PH)/(120 - 2,5TJ tO(Mb-.5ZK|20-2,5(5))
I5 — t/« >o m. /hr.
Qs - CIsA r C-7o)C35)0.ife) ^.^3
Plot Hydrograph and Surrounding flow
Outflow / Basin Size (Natural Conditions)
Outflow
C = -33 T. = |y/ min.
I = 7.44 Ps/T.»f ="Z335^ in./hr. (H4Xn/5<^'^'' ,
Q« = CIA C.2>^XM.M6)0.lg>) QK /-T^
1. Plot on Hydrograph
a. Draw line frora surrounding flow intercept with
beginning hydrograph limb to Q„
2. Estimate volume needed for reservoir
a. Determine preliminary reservoir dimensions
b. Surrounding flow discharges directly through
reservoir without detaining any storage
3. size outlet works
a. Outlet flow, Q, less than or equal to Q^,
b. Stay within the limits of the reservoir
4. Rout
a. Refine reservoir dimensions and/or outflow
facility
••ft PACIFIC COAS'TCIYIL, INC.
|z| 30141 AGOURA COURT, SUITE 200
mil AGOURA HILLS, CA 91301-4334
Si^min^/ PH: (818) 865-4168 FAX: (818) 865-41 98
DATE
PROJECT.
ENGINEER.
SHEET NO. C_j OF
. WORKORDER.
.CHECK BY
Ix
o
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7 , —tr*
Q 11 17 4 c-
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X
1 -\ \ —rr d
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<— >• -
TB n
1
// ^ I" rf • IO in = ( • Cf
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r I
QutFfooi Q-,,Ca
-Ek^^ b^|)Q^ Ql Q?. QT 6W AH
O o ^.Oh' 01^ ^.W] - l.^o
37.3 1.%' 0:46 i-Q36. ^ ^O.o ^'03' 0.%\ t .7^ (.GL
7 ^.05> O.UD-iQ.5Z. -^0.^ ^^9^ OfflH Q.gH • 1.7^
IO
storage (^Ic^ -fcr Dgfentitan Arm
Area i^e'Ueen Un>t L U:Q1IU>^V| , ptlo /:^rvj rAf: lo^-Sfcef
IG, P. C.P>i^.^ u:>;ll be, A 4o.^ ^ toKick 1.3 Q.s'IOOAQ^ d^/^
Coainutgd by: |2arj^ '• II
DEPARTMENT OF SANITATION ANl) F[/)Ol) CONTROL SAN PIEGO COUNTY
PEAK FF.OW CO.MFUTATION WORKSHEET (For use with Peak Flow Ch.-irts; Westem Drainage,
Precipitation Zones 1.0 to 5.5 only.)
REFERENCE IN
HYDROLOGY
MANUAL
1. Sec. IV-A
2. Fig. I-A-2,
p. I-A-23
3. Sec. II-B
Basin Nane (jaO|U NX^
si^uare miles.
4. Sec. I-A,
p. I-A-16
5. Sec. II-A
6. Fig. II-B-2a,
p. II-B-4
Geographic location of center of basin: Long, {{'("lj' Lat. 'i)^''[o'
Storm Frequency |0 year. Basin Area .QOt-
i 2.0 3^ AA.
AMC ( 5-35 yr) = 1^ 2.5 — 2.0 — 1.5
3.C 3.0 2.C
Precipitation Zone Number (PZN)
Antecedent Moisture
Condition
(interpolate basin AMC ANK (35-150yr) - 2_^
for basin PZN)
Runoff Curve Numbers CN2
(interpolate basin CN for basin AMC;
CN2 and CN3 are for AMC's = 2 and 5)
CN Q)0 CN3
Precipitation for Storm Duration: 6 hr (P^) |-7 inches
24 hr (P24) Z-^ inches
P5 X RJ = " inches
3Tir.hcs
Area Rainfall Reduction Ratio (Rj.)
(for areas greater than
10 souare sui Icsi
7. Sec. I-B ,
Sec. I-C
8. Enter Peak Flow Charts with ?„,
Tine to Peak eak (Tp) .03>7 hours (T = 0.862 x Lag time) ^^^^'^\~rr
^ L :=.0(p55mi. L =.037^ mi. S =55^ ft/mi.
P(j and P24; select two nearest T„'s available:
(For Tpa<Tpi,):
8a. From Peak Flow Charts: T„„
pa
For 10 sq. mi. basin : Tp " •'•
8b. From Peak Flow Charts: T pb
hr
hr
hr
6 hr storm
Qa6 cfs
Q'6 i- cfs
Qb6 cfs
Q'6 = %6
Q'24 = Qb24 +
Tpb - Tp
(Qa6 - Qb6)
Tpb - Tp
-Tpb " Tpa
24 hr storm
Qa24 <^<^50 cfs
Q'24 cfs
Qb24 cfs
(Qa24 - Qb24)
'pb
Tpb " Tpa
10. Greater of Q'(j and Q'24 » for 10 sq. mile basin, (Q' ) = Z^UQ cfs
11. Basin Area Ratio (Rg) = (ba.^in area) / (10 sq. miles) = •OC'Ol^M'-j
12. Peak Flow (Qp) = (Q') x (Rg) = 0.^^ cfs
13. SUMMARY : PtAK FLOW OH^ cfs , FRIZQUCNCY jQ year , DUIVVTION hr
CASA LAGUNA PROJECT - Developed Conditions
lO-YEAR, 24 HOUR STORM - B DISTRIBUTION AREA
AREA: 1.18 BASE FLOW: 0.12
P24: 2.9 CN: 90 S: 1.111 Ia=0.2S= 0.222
1 2 3 4 5 6 7 8 9
TIME P/P24 P PDELTA I Q QDELTA QDELTV QA
(Hr.) (In.) (In.) (In./Hr.) (In.) (In.) PDELTA cfs
2.0 0.034 0.099 0.015
0.058 0.058 0.011 0.20 0.2
3.0 0.054 0.157 0.004
0.067 0.067 0.004 0.06 0.1
4.0 0.077 0.223 0.000
0.078 0.078 0.005 0.07 0.1
5.0 0.104 0.302 0.005
0.096 0.096 0.019 0.19 0.2
6.0 0.137 0.397 0.024
0.058 0.116 0.017 0.29 0.2
6.5 0.157 0.455 0.040
0.067 0.133 0.023 0.35 0.2
7.0 0.180 0.522 0.064
0.087 0.174 0.036 0.42 0.2
7.5 0.210 0.609 0.100
0.131 0.261 0.064 0.49 0.3
8.0 0.255 0.740 0.164
0.194 0.389 0.113 0.58 0.3
8.5 0.322 0.934 0.278
0.255 0.510 0.172 0.67 0.4
9.0 0.410 1.189 0.450
0.278 0.557 0.208 0.75 0.4
9.5 0.506 1.467 0.658
0.238 0.476 0.190 0.80 0.5
10.0 0.588 1.705 0.848
0.119 0.238 0.098 0.82 0.5
10.5 0.629 1.824 0.946
0.078 0.157 0.066 0.84 0.5
11.0 0.656 1.902 1.011
0.067 0.133 0.056 0.85 0.5
11.5 0.679 1.969 1.068
0.061 0.122 0.052 0.85 0.5
12.0 0.700 2.030 1.120
0.058 0.116 0.050 0.86 0.5
12.5 0.720 2.088 1.169
0.055 0.110 0.048 0.86 0.5
13.0 0.739 2.143 1.217
0.049 0.099 0.043 0.87 0.5
13.5 0.756 2.192 1.260
13
1 2 3 4 5 6 7 8 9
TIME P/P24 P PDELTA I Q QDELTA QDELTA/ QA
(Hr.) (In.) (In.) (In./Hr.) (In.) (In.) PDELTA cfs
13.5 0.756 2.192 1.260
0.046 0.093 0.040 0.87 0.5
14.0 0.772 2.239 1.300
0.041 0.081 0.036 0.88 0.5
14.5 0.786 2.279 1.336
0.041 0.081 0.036 0.88 0.5
15.0 0.800 2.320 1.371
0.046 0.093 0.041 0.88 0.5
15.5 0.816 2.366 1.412
Column 1 -Time Intervals, in hours
Column 2-Precipitation Ratio per Table II-B-2, San Diego Countv Hvdrologv Manual
Column 3-Rainfall Depth, in inches (P24 x Col. 2)
Column 4-Change in Precipitation Depth between time intervals, in inches
Column 5-Intensity, in inches per hour (Col. 4 / Col. 1)
Column 6-Total Runoff Depth, in inches (Col. 3 - 0.2S)^/(Col. 3 + 0.8S)
Column 7-Change in Runoff Depth during time increment, in inches
Column 8-Runoff to Precipitation Ratio, (Col. 4 / Col. 7)
Column 9-Runoff, in cfs (60.5 x Col. 7 x Area)/Time increment in minutes)
S = 1000/CN - 10
CN is runoff curve number per Table I-A-1, San Diego Countv Hvdrologv Manual
CASA LAGUNA PROJECT - Pre-Development Conditions
10-YEAR, 24 HOUR STORM - B DISTRIBUTION AREA
AREA: 1.18 BASE FLOW: 0.12
P24: 2.9 CN: 82 S: 2.195 h=0.2S= 0.439
1 2 3 4 5 6 7 8 9
TIME P/P24 P PDELTA I Q QDELTA QDELTV QA
(Hr.) (In.) (In.) (InTHr.) (In.) (In.) PDELTA cfs
2.0 0.034 0.099 0.062
0.058 0.058 0.021 0.36 0.4
3.0 0.054 0.157 0.042
0.067 0.067 0.018 0.27 0.3
4.0 0.077 0.223 0.024
0.078 0.078 0.014 0.18 0.2
5.0 0.104 0.302 0.009
0.096 0.096 0.008 0.09 0.1
6.0 0.137 0.397 0.001
0.058 0.116 0.001 0.01 0.0
6.5 0.157 0.455 0.000
0.067 0.133 0.003 0.04 0.0
7.0 0.180 0.522 0.003
0.087 0.174 0.009 0.11 0.1
7.5 0.210 0.609 0.012
0.131 0.261 0.024 0.18 0.1
8.0 0.255 0.740 0.036
0.194 0.389 0.055 0.28 0.2
8.5 0.322 0.934 0.091
0.255 0.510 0.100 0.39 0.2
9.0 0.410 1.189 0.191
0.278 0.557 0.137 0.49 0.3
9.5 0.506 1.467 0.328
0.238 0.476 0.135 0.57 0.3
lO.O 0.588 1.705 0.463
0.119 0.238 0.073 0.61 0.4
10.5 0.629 1.824 0.536
0.078 0.157 0.049 0.63 0.4
11.0 0.656 1.902 0.585
0.067 0.133 0.043 0.65 0.4
11.5 0.679 1.969 0.628
0.061 0.122 0.040 0.66 0.4
12.0 0.700 2.030 0.669
0.058 0.116 0.039 0.67 0.4
12.5 0.720 2.088 0.707
0.055 0.110 0.037 0.68 0.4
13.0 0.739 2.143 0.745
0.049 0.099 0.034 0.69 0.4
13.5 0.756 2.192 0.779
15
1 2 3 4 5 6 7 8 9
TIME P/P24 P PDELTA I Q QDELTA QDELTA/ QA
(Hr.) (In.) (In.) (InTHr.) (In.) (In.) PDELTA cfs
13.5 0.756 2.192 0.779
0.046 0.093 0.032 0.69 0.4
14.0 0.772 2.239 0.811
0.041 0.081 0.028 0.70 0.4
14.5 0.786 2.279 0.839
0.041 0.081 0.029 0.71 0.4
15.0 0.800 2.320 0.868
0.046 0.093 0.033 0.71 0.4
15.5 0.816 2.366 0.901
Column 1-Time Intervals, in hours
Column 2-Precipitation Ratio per Table II-B-2, San Diego Countv Hvdrologv Manual
Column 3-Rainfall Depth, in inches (P24 x Col. 2)
Column 4-Change in Precipitation Depth between time intervals, in inches
Column 5-Intensity, in inches per hour (Col. 4 / Col. 1)
Column 6-Total Runoff Depth, in inches (Col. 3 - 0.2S)^/(Col. 3 + 0.8S)
Column 7-Change in Runoff Depth during time increment, in inches
Column 8-Runoff to Precipitation Ratio, (Col. 4 / Col. 7)
Column 9-Runoff, in cfs (60.5 x Col. 7 x Area)/Time increment in minutes)
S = 1000/CN - 10
CN is runoff curve number per Table I-A-1, San Diego Countv Hvdrologv Manual
TABLE II-B-2
CUMULATIVE RAINFALL TABLE, ONE-DAY WATERSHED EVALUATION STORf-l-TYPE B
Time 24 Tirae r/ r
24
0 .000 12.0 .700
•
.5 .009 12.5 .720
1.0 .016 13.0 .739
1.5 .025 13.5 .756
2.0 .034 14.0 .772
2.5 .045 14.5 .790
3.0 .054 15.0 .800
3.5 .065 15.5 .816
4.0 .077 16.0 .831
4.5 .090 16.5 .845
5.0 .104 17.0 .860
5.5 .120 17.5 .872
6.0 .137 18.0 .885
6.5 .157 18.5 .895
7.0 .180 19.0 .905
7.5 .210 19.5 .914
8.0 .255 20.0 .924
% *• '* 8.5 .322 20.5 .935
9.0 .410 21.0 .945
9.5 .506 21.5 .954
10.0 .588 22.0 .963
10.5 .629 22.5 .972
U.O .656 23.0 .981
11.5 .679 23.5 .991
24.0 1.000
Rev 11/75 II-
RUNOFF CURVE NUMBERS FOR HYDROLOGIC SOIL-COVER COMPLEXES (CN)
TABLE I-A-1
AMC 2
la = 0.2S
Cover Hydro log ic
Soil Groups
, . ,, Treatment Land Use „ ..-3 or Practice-'
Hydro log ic
Cond it ron^ A B c D
Water Surfaces
(during floods) 97 98 99 99
Urban
Commerciai-industrial 89 90 91 92
High density residential. 75 82 88 90
Medium density residential 73 80 86 88
Low density residential 70 78 m 87
Barren 78 86 91 93
Fallow Straight row 76 85 90 92
Vineyards (see accompanying land-use description)
disked 76 85 90 92
annual grass or
legume cover
Poor
Fair
65
50
78
69
85
79
89
84
Good 38 61 7k 80
5
Roads (hard surface) 7k 8k 90 92
(dirt) 72 82 87 89
Row crops Straight row Poor 72 81 88 91
Good 67 78 85 89
Contoured Poor 70 79 8k 88
Good 65 75 82 86
Narrowleaf chaparral Poor 71 82 88 91
Fair 55 72 81 86
I-A-5
RUNOFF CURVE NUMBERS (CN)
AMC 2
I&
Cover Hydrolog ic
Soil Groups
Land Use Treatment .
or Practice
Hydrolog ic
Condit ion^ A B C D
Perennial grass Poor 67 79 86 89
Fair 50 69 79 84
Good 38 61 7k 80
Annual grass Poor 67 78 86 89
Fair 50 69 79 84
Good 38 61 7k 80'
Close-seeded Straight row Poor 66 77 85 89
legumes or
rotated pasture Good 58 72 81 85
Contoured Poor Sk 75 83 85
Good 55 69 78 83
Small grain Straight row • Poor 65 76 8k 88
Good 63 75 83 87
Contoured Poor 63 7k 82 85
Good 61 73 81 84
Meadow Poor 63 77 85 88
Fair 51 70 80 84
Good 30 58 72 78
Open brush Poor 62 76 84 88
Fair k6 66 77 83
Good k\ 63 75 81
Farmsteads 59 7k 82 86
Irrigated pasture Poor 58 7k 83 87
Fair kk 65 77 82
Good 33 58 72 79
I-A-6