HomeMy WebLinkAboutCT 02-25; TOUCHSTONE COMMUNITY; HYDROLOGY HYDRAULIC ANALYSIS; 2002-08-23HYDROLOGY/HYDRAULIC ANALYSIS
FOR
Touchstone Community Tentative Parcel Map
Lot 227 and 228 of La Costa Vale Unit No.1, Map No. 7457
-
R.C.E. 50477
-
TOUCHSTONE COMMU. TM
SUMMARY
PROJECT DESCRIPTION:
• File: CA1131
8/23/2002
THE PROJECT PROPOSES TO DEVELOP 14 LOTS TO INCLUDE 12 LOTS WITH
DWELLING UNITS AND 2 COMMON LOTS FOR ACCESS PRIVEWA Y AND
LANDSCAPE COMMON AREA ONTO TWO (2) VACANT LOTS, LOT 227 AND 228 OF
SUBDIVISION MAP NO. 7457.
CURRENT SITE CONDITIONS:
THE SUBJECT SITE IS LOCATED ON AN ELEVATED PAD WITH THE
TOPOGRAPHY SLOPING AWAY IN ALL DIRECTIONS. IT IS BOUND TO THE EAST
AND THE SOUTH BY LA COSTA AVENUE AND LEVANTE STREET, RESPECT/VEL Y;
TO THE WEST, IT IS BOUND BY MUL TI-FAMIL Y RESIDENTIAL AND SINGLE-
FA MIL Y RESIDETIAL TO THE NORTH. THE RUNOFF FROM THE PROPERTY
SHEET-FLOWS SOUTHERLY DISCHARGING INTO PUBLIC RIGHT-OF-WA Y,
LEVANTE STREET. NO OFF-SITE RUNOFF DISCHARGES ONTO THE SUBJECT
SITE.
EXISTING RUNOFF:
THE SUBJECT SITE HAS PREVIOUSL Y GRADED INTO 2 PADS AND FLOWS FROM
THE NORTHEAST CORNER OF THE SITE TO THE SOUTHWEST CORNER OF THE
SITE, WHICH IS THE LOW POINT. THE RUNOFF FROM THE SUBJECT SITE IN THE
CURRENT CONDITION IS 4.04 CFS IN THE 100-YEAR, B-HOUR STORM.
POST-DEVELOPMENT RUNOFF:
THE POST-DEVELOPED SITE DIVIDES THE SITE INTO 2 DRAINAGE BASINS,
NORTHERL Y BASIN AND SOUTHERLY BASIN, 0.92 ACRES AND 0.55 ACRES,
RESPECTIVEL Y. THE NORTHERLY HALF OF THE SITE INCLUDES THE
PROPOSED LOTS 1 TO 7, 14 AND PORTION OF LOT 13 OF THE PROPOSED
TENTATIVE MAP. SURFACE DRAINAGE FROM THE NORTHERLY BASIN SHEET
FLOWS TO A DETENTION BASIN, WHICH IS LOCA TED AT THE SOUTHWEST
CORNER OF THE PROJECT SITE THEN DISCHARGING TO THE PUBLIC RIGHT-
OF-WA Y, LEVANTE STREET, BY A CURB OUTLET. THE SOUTHEASTERL Y HALF
OF THE SITE INCLUDES LOTS 8 TO 12 AND PORTION OF LOT 13 OF THE
PROPOSED TENTATIVE MAP. SURFACE DRAINAGE SHEET FLOWS TO PUBLIC
RIGHT-OF-WAY, LEVANTE STREET.
THE ATTACHED DETENTION BASIN DESIGN CALCULATIONS SHOW THAT THE
POST DEVELOPMENT RUNOFF DISCHARGE SHALL NOT EXCEED THE PRE-
DEVELOPMENT RUNOFF DISCHARGE IN THE 100-YEAR, 6-HOUR STORM.
Prepared By: Drainage-Summary.doc
Snipes-Dye Associates
•
'TOUCHSTONE COMMUNITY TM • •
SITE PEAK FLOW DETENTION (100-yt;AR)
File: CA1131
8/27/2002
DETERMINE VOLUME OF INCREASED RUNOFF FROM THE DEVELOPED SITE IN THE 6-HOUR, 100-YEAR
STORM:
1. DETERMINE WEIGHTED SITE RUNOFF COEFFICIENT FOR CURRENT SITE.
2. DETERMINE WEIGHTED SITE RUNOFF COEFFICIENT FOR DEVELOPED SITE.
3. DETERMINE PEAK RUNOFF FROM THE CURRENT SITE AND THE DEVELOPED
SITE IN THE 6-HOURI 100-YEAR STORM.
4. PREPARE SITE HYDROGRAPH FOR THE DEVELOPED SITE.
5. DETERMINE VOLUME FOR INCREASED RUNOFF FROM THE DEVELOPED SITE.
6. DETERMINE RETENTION BASIN WITH INCREASED RUNOFF VOLUME:
1. CALCULATE WEIGHTED RUNOFF COEFFICIENT fCI FOR THE CURRENT SITE:
D= 1.37 ACRES
D=0.18ACRES
A =A1 +A2
C = (A 1 (C1) + A2(C2)}/A
(A 1 = 1.37 ACRES, ASSUME C1 = O.SS)
(A2 = 0.18 ACRES, ASSUME C2 = 0.70)
C = (1.37(0.55) + 0.18(0. 70)} + 1.54
C = 0.57
2. CALCULATE WEIGHTED RUNOFF COEFFICIENT eCI FOR THE DEVELOPED SITE:
D=0.S8ACRES
0= 0.06 ACRES
~= 0.91 ACRES
A =A3 +A4+A5
(A3 = 0.S8ACRES, ASSUME C3 = 0.40)
(A4 = 0.06 ACRES, ASSUME C4 = 0.70)
(AS = 0.91 ACRES, ASSUME CS = 0.9S)
C = (A3(C3) + A4(C4) + AS(C5)}/A
C = (0.S8(0.40) + 0.06(0.70) + 0.91(0.9S)} + 1.S4
C= 0.74
Prepared by:
Snipes-Dye Associates 100-YR Calculations
•
'TOUCHSTONE COMMUNITY TM • •
3. CALCULATE PEAK DISCHARGE OF CURRENT SITE:
ASSUME T c = 10 MINUTES FOR CURRENT AND DEVELOPED SITE.
UTILIZE FIGURE 3-1 INTENSITY/DURATION CURVE
AND ISOPLUVIALS OF 100-YEAR 6-HOUR PRECIPITATION
READ INTENSITY (I) = 4.6 INCH/HOUR
Q= CIA
C = 0.57, I::; 4.6 inihr, A = 1.54 acres
Q = 0.57(4.6)1.54
Q = 4.04 cfs
4. CALCULATE PEAK DISCHARGE OF DEVELOPED SITE:
Q = CIA
C::; 0.74, I::; 4.6 in/hr, A = 1.54 acres
Q::; 0.74(4.6)1.54
Q = 5.24cfs
Prepared by:
Snipes-Dye Associates 2
File: CA1131
8/2712002
100-YR Calculations
•
,
TOUCHSTONE COMMUNITY TM • •
5. CALCULATE VOLUME OF INCREASED RUNOFF FROM DEVELOPED SITE:
DEVELOPED SITE HYDROGRAPH
Q (efs) x=1.15
T c (MINUTES)
AREA UNDER SHADED AREA = VOLUME OF DISCHARGE FROM DEVELOPED SlTE
VOLUME = 1.15(1.20)(60) = 82.80 Cu. FT. (MIN. VOLUME OF STORMWATER TO RETAIN)
TOTAL PRE-DEVELOPMENT DISCHARGE FROM SITE (Qex):
Q ex = 4.04 cfs
TOTAL POST-DEVELOPMENT DISCHARGE FROM SITE (Q prj:
Q pr = 5.24 cfs
THE POST-DEVELOPMENT DISCHARGE RUNOFF THROUGH RETENTION BASIN (Qin):
Q in = 2.91 cfs (See attached calculations)
THE POST-DEVELOPMENT DISCHARGE RUNOFF NOT THROUGH RETENTION BASIN (Q nr):
Qnr = Qpr -Qin = 5.24 cfs -2.91 cfs
Q nr = 2.33 cfs
THE MAX. ALLOWABLE POST-DEVELOPMENT DISCHARGE RUNOFF PRIOR TO RJETAIN (Qr):
Qr = Qex -Qnr =4.04 cfs -2.33 cfs
Qr = 1.71 cfs
Utilize 2-4 inch PVC pipes for the proposed retention basin outlet:
4" pipe's discharge capacity = 0.84 cfs (See attached calculations)
2-4" pipes = 2xO.84 = 1.68 cfs < Qr
THE TOTAL POST-DEVELOPMENT RUNOFF = Q nr+Q (two 4" pipes) = 2.33 cfs 'I-1.68 cfs :: 4.01 cfs
4.01 cfs (the total post-development runoff) is less than 4.04 cfs (the totalpre-deve/opment:runoff)
Prepared by:
File: CAi131
8/2712.002
Snipes-Dye Associates 3 100-YR Calculations
•
TOUCHSTONE COMMUNITY TM • •
6. DESIGN RETENTION STRUCTURE WITH MINIMUM VOLUME OF 82 CUBIC FEET:
attached detail)
(See
RETENTION VOLUME (V) = CROSS-SECTION BASIN AREA (A) X WIDTH OF BASIN (W)
A = 1/2 X WATER LEVEL HEIGHT (H) X LENGTH OF WATER SURFACE (L)
6"OVERFLOW
PIPE
RETENTION BASIN DIMENSIONS:
W=4.17 FEET
H = 0.67 FEET
H/L = 1/100
L = 100(H) = 67 FEET
V=A(W) = 112 L(H)(W)
V = (67 FT)(O.67 FT)(4.17 FT)12
V = 94 CU. FT. > 82 CU. FT •
DETERMINE THE OVERFLOW PIPE:
Utilize one 6"pipe for the retention basin overflow pipe
6" overflow pipe's discharge capacity = 2.55 cfs (See attached calculations)
Q( enter) -Q (two 4" pipes) = Q( min. overflow pipe)
2.91 cfs -1.68 cfs = 1.23 cfs < 2.55 cfs
(The capacity of a 6" overflow pipe is greater than the require" runoff dischargeJ
CONCLUSION:
. THE TWO 4" PVC PIPE OUTLET AT THE BOTTOM OF THE LOW-
I, END OF THE PROPOSED RETENTION BASIN AND ONE 6" PVC
OVERFLOW PIPE, WHICH HAS AN INVERT ELEVATION AT 8" I
ABOVE THE BOTTOM OF THE LOW-END ARE SUFFICIENT TO .
RETAIN THE REQUIRED VOLUME OF STORM WATER AND DRAIN I
THE DEVELOPED SITE DURING A PEAK FLOW, 10o-YEAR STORM
EVENT.
Prepared by:
File: CA1131
8/27/2002
Snipes-Dye Associates 4 100-YR ·Calculations
67'
~~~~J. ~ ----g-----WiW~\Ai~!M~\~~1W\~\AI\~~\NJlm\~~~\I~~/~
/~/ ~o
.// ././ z/
'( :4" PVC PIPES
DISCHARGE
RETENTION VOLUME (V) = 105 Cu. FT.
RETAINING WALL • PER GRADING PLAN (TYP.)
TO CURB OUTLET
QotSCWJ<ee -1.68 CPS . SECTION A-A
NO SCALE
DRAINAGE PIPES DISCHARGE t--
TO CURB OUTLET PER 'Q
IMPROVEMENT PLANS (TYP') 0
0.67'
A -~. pv~ PIPE:rii-~J~~LOW !
• [-= 1i PIPE
.--C------
4" PVC-PIPE~-
RETAINING WALL
PER GRADING PLAN (TYP')
PLAN VIEW -RETENTION BASIN DETAIL
NO SCALE
e ...... • e
• •
****************************************************************************
HYDRAULIC ELEMENTS -I PROGRAM PACKAGE
(C) Copyright 1982-99 Advanced Engineering Software (aes)
Ver. 8.0 Release Date: 01/01/99 License ID 1305
Analysis prepared by:
Snipes-Dye Associates
8348 Center Drive, Suite G
La Mesa, CA 91942-2910
Fax (619)460-2033 Phone (619)697-9234
TIME/DATE OF STUDY: 11:52 8/ 7/2002
~==~===============~==========================~=============.===~====~==~=~=
DISCHARGE CAPACITY OF A 4" PIPE.
****************************************************************************
»»PIPEFLOW HYDRAULIC INPUT INFORMATION««
PIPE DIAMETER(FEET) = 0.330
FLOWDEPTH(FEET) = 0.330
PIPE SLOPE(FEET/FEET) = 0.4900
MANNINGS FRICTION FACTOR = 0.020000
»»> NORMAL DEPTH FLOW (CFS) = 0.84 CFS
~===============~==============~=====~======~========~===~====~======~======
• 1
• •
****************************************************************************
HYDRAULIC ELEMENTS - I PROGRAM PACKAGE
(C) Copyright 1982-99 Advanced Engineering Software (aes)
Ver. 8.0 Release Date: 01/01/99 License ID 1305
Analysis prepared by:
Snipes-Dye Associates
8348 Center Drive, Suite G
La Mesa, CA 91942-2910
Fax (619)460-2033 Phone (619)697-9234
TIME/DATE OF STUDY: 8:11 8/ 8/2002
=======================================================================~====
DISCHARGE CAPACITY OF A 6" PIPE
****************************************************************************
»»PIPEFLOW HYDRAULIC INPUT INFORMATION««
PIPE DIAMETER(FEET) = 0.500
FLOWDEPTH(FEET) = 0.500
PIPE SLOPE(FEET/FEET) = 0.4900
MANNINGS FRICTION FACTOR = 0.020000
»»> NORMAL DEPTH FLOW (CFS) = 2.55
=======~=~==========================================~======================= .1
• TOUCHSTONE COMMUNITY • • File: CA1l31
8127/2002
RATIONAL METHOD HYDROLOGY COMPUTER PROGRAM PACKAGE
Reference: SAN DIEGO COUNTY FLOOD CONTROL DISTRICT
1985,1981 HYDROLOGY MANUAL
(c) Copyright 1982-99 Advanced Engineeri~g Software (aes)
Ver. 1.SA Release Date: 01/01/99 License ID 130S
Analysis prepared by:
Snipes-Dye Associates
8348 ~enter Drive, Suite G
La Mesa, CA 91942-2910
Fax (619)460-2033 Phone (619)691-9234
LEVANTE STREET TENTATIVE MAP
POST~DEVELOPMENT CONDITIONS
TOUCHSTONE COMMUNITY
FILE NAME: CAl131.DAT
TIME/DATE OF STUDY: 14:49 8/27/2002
USER SPECIFIED HYDROLOGY AND HYDRAULIC MODEL INFORMATION:
1985 SAN DIEGO MANUAL CRITERIA
USER SPECIFIED STORM EVENT (YEAR) = 100.00
6-HOUR DURATION PRECIPITATION (INCHES) = 2.700
SPECIFIED MINIMUM PIPE SIZE(INCH) = 3.00
SPECIFIED PERCENT OF GRADIENTS (DECIMAL) TO USE FOR FRICTION SLOPE 0.95
SAN DIEGO HYDROLOGY MANUAL "C"-VALUES USED
NOTE: ONLY PEAK CONFLUENCE VALUES CONSIDERED
****************************************************************************
FLOW PROCESS FROM NODE 1. 00 TO NODE 2.00 IS CODE = 21
»»>RATIONAL METHOD INITIAL SUBAREA ANALYSIS««<
=======~================================~=================================~=
*USER SPECIFIED (SUBAREA) :
MULTI-UNITS DEVELOPMENT RUNOFF COEFFICIENT = .7400
INITIAL SUBAREA FLOW-LENGTH = 495.00
UPSTREAM ELEVATION = 295.45
DOWNSTREAM ELEVATION = 284.33
ELEVATION DIFFERENCE = 11.12
URBAN SUBAREA OVERLAND TIME OF FLOW (MINUTES) = 11.008
100 YEAR RAINFALL INTENSITY (INCH/HOUR) = 4.276
SUBAREA RUNOFF(CFS) 2.91
TOTAL AREA(ACRES) = 0.92 TOTAL RUNOFF (CFS) = 2.91
1 Post~Dev.doc
TOUCHSTONE COMMUNITY • • File: CA1l31
8/27/2002
***************************************************************************.*
FLOW PROCESS FROM NODE 2.00 TO NODE 3.00 IS CODE ::;:
»»>COMPUTE PIPEFLOW TRAVELTIME THRU SUBAREA««<
»»>USING USER-SPECIFIED PIPESIZE««<
4
~=====~=========================================================~===========
DEPTH OF FLOW IN 6.0 INCH PIPE IS 3.9 INCHES
PIPEFLOW VELOCITY(FEET/SEC.) = 21.5
UPSTREAM NODE ELEVATION = 287.00
DOWNSTREAM NODE ELEVATION = 279.60
FLOWLENGTH(FEET) = 15.00 MANNING'S N = 0.013
GIVEN PIPE DIAMETER(INCH) = 6.00 NUMBER OF PIPES 1
PIPEFLOW THRU SUBAREA (CFS) 2.91
TRAVEL TIME(MIN.) = 0.01 TC(MIN.) = 11.02
****************************************************************************
FLOW PROCESS FROM NODE 4.00 TO NODE 5.00 IS CODE::;: 21
»»>RATIONAL METHOD INITIAL SUBAREA ANALYSIS««<
;=========;;;=========================;======~==============================
*USER SPECIFIED (SUBAREA) :
MULTI-UNITS DEVELOPMENT RUNOFF
INITIAL SUBAREA FLOW-LENGTH =
COEFFICIENT = .7400
200.00
UPSTREAM ELEVATION = 294.00
DOWNSTREAM ELEVATION =
ELEVATION DIFFERENCE =
286.78
7.22
URBAN SUBAREA OVERLAND TIME OF FLOW(MINUTES} 5.974
*CAUTION: SUBAREA SLOPE EXCEEDS COUNTY NOMOGRAPH
DEFINITION. EXTRAPOLATION OF NOMOGRAPH USED.
TIME OF CONCENTRATION ASSUMED AS 6-MINUTES
100 YEAR RAINFALL INTENSITY(INCH/HOUR} = 6.325
SUBAREA RUNOFF(CFS) 1.17
TOTAL AREA(ACRES} = 0.25 TOTAL RUNOFF (CFS) 1.17
****************************************************************************
FLOW PROCESS FROM NODE 6.00 TO NODE 7.00 IS CODE::;: 21
»»>RATIONAL METHOD INITIAL SUBAREA ANALYSIS««<
===========================~================================================
*USER SPECIFIED (SUBAREA) :
MULTI-UNITS DEVELOPMENT RUNOFF COEFFICIENT = .740a
INITIAL SUBAREA FLOW-LENGTH = 100.00
UPSTREAM ELEVATION = 291.00
DOWNSTREAM ELEVATION = 285.00
ELEVATION DIFFERENCE = 6.00
URBAN SUBAREA OVERLAND TIME OF FLOW (MINUTES) 3.566
*CAUTION: SUBAREA SLOPE EXCEEDS COUNTY NOMOGRAPH
DEFINITION. EXTRAPOLATION OF NOMOGRAPH USED.
TIME OF CONCENTRATION ASSUMED AS 6-MINUTES
100 YEAR RAINFALL INTENSITY(INCH/HOUR) = 6.325
SUBAREA RUNOFF (CFS) = 1.40
TOTAL AREA (ACRES) = 0.30 TOTAL RUNOFF (CFS) = 1. 40
=======================================================~====================
END OF RATIONAL METHOD ANALYSIS
2 Post-Dev.doc
------------~--~e e
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Minutes Hours
Duration
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 cU/ve for the location
being analyzed.
Application Form:
(a) Selected frequency JQ 0 _ year
,.., "7 1.1. ~ 60 (b) P6 = A_LL_ in., P24 = .:T..!.""z,_ "p-= ______ %(2)
24
(c) Adjusted P6(2) = 2.._::L in.
(d) tx = _10 __ min.
(e) I = _____ in.!hr.
Note: This chart replaces the Intensity-Duration-Frequency
curves used since 1965.
pi>' 1" ,·l,:S·;'-2"h'.ir'''·3· h~5-:-'4"';' .(5·· .. 5 5.5: 6
Duralion", .... 1-: (.;. j''';'''j'' '1 .. ; .(";' 1 . 1 : I I!' I
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.... 20 1.08 ;1.6~.12.15:.~:69}.~~~.3?7: 4.31.: 1:~5. 5.39: 5.93 1 25 0.9311.40; 1.87, 2.33 .2.8013.27; 3.73 , 4.20 ; 4.67 i 5.13:
1
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.. _ •. 56 ~:~Q Iq'!?0i.1,)9.il.~9.,.1..:?9'L?:09,.2.39 : 2.6~ ,2.~8 I 3.28,3.58
........... ~ 0:53.,0.8011.0611:33;.1.5911:8612.12 i 2.39 i 2.65: 2.92: 3.18
___ .. ~_Q:4.1_LO.61! ~:82] 1.02: 1.2~ll:43;. 1.63 ! 1.84 ; 2.04 i 2.25 : 2.45
120 0.34 l'O.51:0.68i 0.85: 1.02 1.19' 1.36 i 1.53 1.70: 1.87; 2.04 ~ .. 5.~ J!,gp=,.q:4~10:~9r.6.73.·~<>,.88· (03;' 1.18 i 1.32: 1.47]1.62: 1.76
....... J!O _9:..~6.10c39iO.521 0.6510.78)0:91 i 1.01j 1,.18. 1.31 l1.44; 1.57
_._24!l...Q~~.~.2:.~~1.Q:~aj':..9.:~J.Q:~.5.;.Q.:!.~19:87 i 0.9~ .!.O~.~ 1:.19 ...... 1:?.q -.... -~~ -g~~hg:m,~:~~ rK!Hg:~~'I~:~~l g~~; I g:~; g:~:·l ~~~~ ll~
FJGURE
_'__ Intensity-Duration Design Chart -Template ~.
HazMaVCounty.. "geology ManualllhCDur Qesign Chal1.FHB
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Co.L", Y OF SAN D1 EGO
DEPARTMENT OF SAN ITATION &
flDOO CONTRDl
115 '
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lOO-YE/H1 14-l-Im,n PI1ECIPITATION
/"""2 OJ ISOPlUVIAlS ar-100 -Y[An 24-Houn
Ef·JTUS OF AtJ IfJCt-I
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33°
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45 1
Pr<f1"f,"J by
u.s. DEPAHTMENlr OF COMMERCE
N .... TJOI'ML oct::II,:'ac "'iD "',I':'\O:;PIIEHIC AO~tlNISTRATION
I. ,
SPECIAl. STUDIES l'~A:-ICII, Ofl'IC£ ot' lI'iUIWLOGY. N!.-nONAL WJ::ATIIEH SERVICE
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DErMRTMENT OF SANITATION &
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Prep" J:d by
U,S. DEPARnlENil' OF COMMERCE
NATIONAL OCEANIC AND AT~OSPIIE'RIC ADWHISTRATION
SPECIAL STUDIES URANCII, OFFICE OF lit UROLOGY, NATIONAL WEATHER SERVlCE
30' .1 . I
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