HomeMy WebLinkAboutCDP 2016-0006; MFD-01; HYDROLOGY CALCULATIONS; 2018-04-06•
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1 IlECORD COPY
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L lnitial
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Date
Victor Rodriguez-Fernandez, PE.
1283 E Main St., Ste 109, El Cajon, CA, 92021
en~ineervictorrlifvaol.com PH: (760) 357-2434
PRELII\IIN" AR'.{
HYDROLOGY CALCULATIONS
for
2637 JEFFERSON ST., CARLSBAD
CDP 2016-0006
Victor Rodriguez-Fernandez, RCE 35373
April 6, 2018
RECEIVED
APR O 9 2018
LAND DEVELOPMENT
ENGINEERING
cJ)P ~{.{) ~ooDy;
Description:
Existing property is a flat 0.25 Acre residential lot with an existing single family
residence to be demolished draining with about a I% slope towards the West towards an
existing multi-family development that is accepting the existing flows at natural grade
and then flowing towards and over an existing 5' retaining wall. Existing structures and
pool at the subject site are to be demolished. No offsite drainage flows toward our site
were observed.
The project proposes 4 Apartment Units structure with permeable surface
driveway and new landscaping. There will be an increase of 742 SF of impermeable
surface (from 4152 SF to 4894 SF).
The drainage proposed will be directed towards the same west property line.
There will be no increase of flows after mitigating the imperviousness surfaces increase
by providing permeable surface pavement storing storm flows and infiltrate through
existing Type "C' soils (Existing soils at the site were found to be Type "B"' as per
county soils map and specified as Type "B"/"C'' per soils engineer report) in order to
increase the Time of Concentration of the storm flows to decrease the peak flows.
The existing drainage sheet flow towards the the west side of the project is to be
similar by providing a proposed 3" Landscape pond and a proposed property line
retaining wall with level raised top of wall of 0.1' from proposed finish grade to provide
sheet flow when overflowing.
The expected proposed conditions maximum runoff towards the West along the
North side of 0.21 CFS will be less than the existing conditions runoff of 0.25 CFS and
along the South side, the proposed 0.09 CFS will be less than existing of 0.23 CFS,
furthermore. For the previous existing pool concrete areas draining to the back of the
property, similar conditions are proposed with a similar 0.0 I Acre tributary areas and
maximum peak flows of0.07 CFS.
In summary, the proposed project proposes to simulate existing conditions and
increase of runoff will not be expected. The portion of ground between the existing
retaining wall and the property line (about 6" wide area) will receive sheet flows the
same or less peak runoff from the site as before.
CALCULATIONS:
EXISTlNG CONDITIONS: (Methodology: Rational Method)
NORTH AREA
Impervious%= 4, I 52SF I 11,000SF = 38%
Roughness coefficient C = 0.53 (Per Table 3-1 for 38%)
Length L= 150' Slope S = (58.3-56.8)/150' = I%
Area A I = 0.11 Ac. Soil Type "'C" (per Soils Engineer Report)
1/2
1.8 X (1.1-C) X (L)
Tc -----------------------------(Fig. 3-3)
I /3
s
1/2
l.8 X ( 1.1-0.53) X (150)
Tc -----------------------------12.6 Min, l = 4.06 (Fig. 3-1)
1/3
( 1)
Q I 00 =CIA= 0.53 x 4.06 x 0.11 = 0.24 CFS (Sheet Flow)
SOUTH AREA
L=l90' S = (58.0-56.8)/190' = 0.6%
A2 = 0.12 Ac.
1/2
l.8 X (l.]-0.53) X (]90)
Tc -----------------------------16.8 Min, I= 3.38 (Fig. 3-1)
1/3
(0.6)
Q 100 =CIA= 0.53 x 3.38 x 0.12 = 0.22 CFS
CENTER AREA
EXISTING AND PROPOSED
A3 = 0.01 Ac Assume 1=7.0 in/hr (highest chart value for P=2.8)
C= 0.95 for I 00% impervious concrete area
Q I 00 =CIA= 0.95 x 7.0 x 0.0 I = 0.07 CFS sheet flow
PROPOSED CONDITIONS:
Total TributaQ' Area = 0.25 Ac P6 = 2.8 in.
C = 0.69 (Per Table 3-1 for 4 DU/0.25 Ac= MOR 16 DU/ Ac)
NORTH AREA
A3 = 0.07Ac
LO =20' S = 3%
To= 4.9/(90/20) = 1.1 min. (used value per Table 3-2 for MOR 24 DU/Ac)
LI= 110' S = (57.7-57.0)/110 = 0.6%
1/2
l.8 X (0.4)) X (l 10)
Tc l -----------------------------= 9.2 Min (Fig. 3-3) , I = 4.98 in/hr
l/3
(0.6)
Tc2 = Time to fi II r Landscape pond
Landscape Pond storage Area= (50+ 30)/2 x 0.3= 12 CF
Assume I = 4.4 in/hr
Q3 =CIA= 0.69 x 4.4 x 0.07 = 0.21 CFS
Tc2 = 12CF I 0.21 CFS= 57 Sec.= 0.9 min
Total Tc= 1.1 + 9.2 + 0.9 = 11.2 min. , Intensity= 4.36 in/hr (Fig. 3-l) OK
corrected Q3 = CIA = 0.69 x 4.36 x 0.07 = 0.21 CFS
Q l 00 = 0.21 CFS Sheet Flow over proposed Landscape Pond < 0.24 CFS ( existing) OK
SOUTH AREA
The initial A0=0.014 Ac,
To= 4.9/(90/30) = 1.6 min. (used value per Table 3-2 for MOR 24 DU/Ac)
C = 0.69 (Per Table 3-1 for MOR 24 DU/Ac)
Assumed minimum infiltration rate for type "C" soil= I" I hr
Storm Volume P6 = C x P6 x A=
0.69 x (2.6) x 0.19 = 0.34 Ac-in = 123 7 CF for 6hr storm
Proposed below Pavers Storage Area @40% voids= 3,738 SF x 0.5' x 0.4= 748 CF
Infiltration per hour@ I "/hr= (0.19 Ac x 43560)( 1 /12) = 690 CF I hr
Infiltration capacity at 6hrs = 4140 CY> 1237 CY
Permeable area pavement expected to infiltrate all of peak 100 yr 6 hr storm flows
ALL FLOWS EXPECTED TO INFILTRATE
CENTRAL WEST AREA
A3 = 0.0 I Ac Assume 1=7.0 in/hr (highest chart value for P=2.8)
Q 100 =CIA= 0.95 x 7.0 x 0.01 = 0.07 CFS sheet flow
~ ! "' ~
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GRAPH IC SCALE: 1 "= 1 O'
10 10 20 JO
d d z i'j cj
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Sl (58.3-56 .8)/150 1. 0%
S2 (58.0 -56 .8)/190 0.6%
EXISTING SOIL TYPE "C "
EXISTING TOTAL TRIBUTARY AREA
11,100 SF= 0.25 ACRES
SHEETS FLOWS TOWARDS THE WEST
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Note: Soil Data Source
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THIS MAP IS PROVIDED \/VITHOUT V'JI\RRANTY OF ANY KIND,
EITHER EXPRESS OR MPLIED, INCLUDING, BUT NOT LIMITED
TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
FITNESS FOR A PARTICULAR PURPOSE.
Copyright SanGIS. Al Rigtts Reserved.
This prodo..d may contain irionnation from the SANDAG Regional
lrtormation System which camot be reprcdJced wihout lhe written
permission of SANDAG.
This prodo..d may contain infonnation which has been reproduced
wilh permission granted by Thomas Brothers Maps.
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D = Duration (min)
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Intensity-Duration Design Chart -Template
Directions for Appllcatlon:
(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 \()0 year
(b) Ps = ~ in., P24 = ~ 'PPS = 516 %(2) 24 --
(c) Adjusted p6<2> = 2 ,l::) in.
(d) tx;::: 12.6 min. 16.8
(e) I= . 4.06 in./hr. 3.38
Note: This chart replaces the Intensity-Duration-Frequency
curves used since 1965.
P6 1 1.5 2 2.5 3 . 3.5 . 4 ' 4.5 5 S.5 6
Duration I I I I -, . I ' I • I I I I
----~ ?_&~ .~95(S.27.:_659J~,9.22!10.54;11.66,13.17,14.49 1561
. _ 7_ _2.,22 13-!8. 4.24~5.30_6.~. 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::io f 1.952.ssTl.2,T:i.89. 4,54' 5 19 . 5.84 "'6 49 . 7.13 . 7.76 -------=---··-··-·-. ·-..... 20 1.08 '1.62 2.15 2.69 3.23 3.77 4 31 4.65 5.39 5.93 6.46
25 0.93 '1.40· 1.87-2.33 :Z:sci'3.27 !3 .73-4.20 . ~:6i '. 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 .._ t ~ • \ -• ...... • • -• I · _40 _0#) ,_l,;_03~1.38~1.72,2.07:2.41, 2.76_ 3.10 . 3.45. 3.79 4.13
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120 o.3°4 ·o.s1'0.sa10.ss·1.02:1.19· 1.36 · 1.s3 · 1.10 · 1.67 · 2.04
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~OO _C!,.19 .0.~fijO.~l Q.47 :0ffi~0.~~0.75 _0.85 _0.94 . 1.03 .1.13
360 0.17 0.25 0.331 0.42 0.50 0.58 0.67 0.75 0..84 0.92 LOO
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P5 = 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 \OD year
(b) P5 = ~ in., P24 = 4 _ g .;s = S~ %(2)
24 --
(c) Adjusted p6<2) = 2.,e, in.
(d) Ix_;::~ min. 11. 2 min
{e)I= 4·.98 in./hr. 4.36 in/Hr
Note: This chart replaces the Intensity-Duration-Frequency
curves used since 1965 .
P6 1 1.5 2 2.5 3 3.5 , 4.5 5 5.5 6
Duration I I I I I I I I I I I
--~ -~~ J ,95; 5.27 S 6.59 T 7.90,9.22'. !0.54 • 11.86. 13.\7 14.49, 15.81
7 2.12 t3,18 4.2,•5.30 6.36 7.42 8.48 9.54 · 10.60, 11.66 12.72
10 -,.-68-2.53'.3.37' 4.21 ·s.05's.901674 ' 7.58 . 842' 9.27-10.11
15 1::io"1.952_59't3.2i7'fi9"4_5,4' 5 19 . 5.84~6<49 : 7.1-3 . 778 -~ ------·---·-.,._ ~-' --20 1.08 1.62 2.15 2.69 3,23 3.n 4.31 4.85 5.39 . 5.93 · 6.46
2s 0.93 '1.40· 1_57' 2.33'iaoT3_frf1.n 4.20 · 4.67 ' s:1a· 5.60
30 0.83 j.24;1.66:2.01:2.49;2.90; 3.32 ~ 3.73 : 4.15 : 4.56 . <4.98
I __ 40 0.6_9_,_1.03;!-38 .. 1.72,2.07.2.,1 2.76 .3.10 .3 45 ,3.79 <4.13
SO 0.60 0.90 1.19 1.49 1.79 2.09 2.39 2.69 2.98 , 3:28 3.58
__ 60 0~~3 [o.aof ui6; 1.33 :1.s(1.8( 2.12 : 2.39 · 2.65 : 2.92 : 3 18
90 0.41 '.0.611 0.82 1.02 1.23 1.43 1.63 1.84 2.04 . 2.25 2.45
1__ 20 o.~ £0.51 ; q,_68 ;_ o.85 : 1.02 i 1.19: 1.36 . 1.53 ~ 1.10 '. 1.81 : 2.04
150 0.29 0.44•0.59 0.73 [0._88 1.03,1.18 1.32 147 1.62 1.76 ~ ·~26j o)9[Q.§2 j"'o.ss.fo).f .ci.9}:_ 1.04 : 1.18~ 1.31 : 1.44 : 1.51 !..'° J>E... o.33!0-~3 Lo 54. o.s5. o.~6t o.87 . o.ss : 1.oa . 1_-19 , 30 ~ .QJ~ .0.2~!<>:.J!!l.~-·7 .0..:..56..,0.§6:Jl.75. 0.85_, 0.94 . 1,03 . 1.13
360 0.17 Q.25 0.33 J 0.42 0.50 0.58 0.67 0. 75 0.84 0.92 1.00
PROPOSED r I~•UlR El
A
San Diego County Hydrology Manual
Date: June 2003
Table 3-1
Section:
Page:
RUNOFF COEFFICIENTS FOR URBAN AREAS
Land Use I Runoff Coefficient "C"
Soil T~Ee
NRCS Elements Count Elements % fMPER A B C
Undisturbed Natural Terrain (Natural) Permanent Open Space O* 0.20 0.25 0.30
Low Density Residential (LOR) Residential, 1.0 DU/A or less 10 0.27 0.32 0.36
Low Density Residential (LOR) Residential, 2.0 DUA or less 20 0.34 0.38 0.42
Low Density Residential (LOR) Residential, 2.9 DU/A or less 25 0.38 0.41 0.45
Medium Density Residential (MDR) Residential, 4.3 DU/A or less "O 0.41 0.45 ~ is
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 0.57
Medium Density Residential (MDR) Residential, 14.5 DU/A or less 50 0.55 0.58 0.60
High Density Residential (HOR) Residential, 24.0 DU/A or less 65 0.66 0.67 ~
High Density Residential (HOR) Residential, 43 .0 DU/A or less 80 0.76 0.77 0.78
Commercial/Industrial (N. Com) Neighborhood Commercial 80 0.76 0.77 0.78
Commercial/lndustrial (G. Corn) General Commercial 85 0.80 0.80 O.&l
Commercialllndustrial (O.P. Com) Office Professional/Commercial 90 0.83 0.84 0.84
Commercial!Tndustrial (Limited f.) Limited Industrial 90 0.83 0.84 0.84
Commercial/Industrial (General I.) General Industrial 95 0.87 0.87 0.87
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
*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 Resomces Conservation Service
3-6
,.
Element* DU/ .5%
Acre LM T I
Natural 50 13.2
LOR 1 so 12.2
LOR 2 so 11.3
LOR 2.9 so 10.7
MOR 4.3 so 10.2
MOR 7.3 so 9.2
MOR 10.9 so 8.7
MOR 14.5 so 8.2
HOR 24 50 6.7
HOR 43 so 5.3
N.Com so 5.3
G.Com so 4.7
O.P/Com so 4.2
Limited I. so 4.2
General I. 50 3.7
Table 3-2
MAXIMUM OVERLAND FLOW LENGTH (LM)
& INITIAL TIME OF CONCENTRATION (Tl)
1% 2% 3%
LM T I LM T I LM Ti
70 12 .5 85 10.9 100 10.3
70 11.5 85 10 100 9.5
70 10.5 85 9.2 100 8.8
70 10 85 8.8 95 8.1
70 9.6 80 8.1 95 7.8
65 8.4 80 7.4 95 7
65 7.9 80 6.9 90 6.4
65 7.4 80 6.5 90 (6 )
65 6.1 75 5.1 90 ~
65 4.7 75 4 85 3.8
60 4.5 75 4 85 3.8
60 4.1 75 3.6 85 3.4
60 3.7 70 3.1 80 2.9
60 3.7 70 3.1 80 2.9
60 3.2 70 2.7 80 2.6
*See Table 3-1 for more detailed description
5% 10%
LM T I LM T I
100 8.7 100 6.9
100 8 100 6.4
100 7.4 100 5.8
100 7 100 5.6
100 6.7 100 5.3
100 6 100 4.8
100 5.7 100 4.5
100 5.4 100 4.3
95 4.3 100 3.5
95 3.4 100 2.7
95 3.4 100 2.7
90 2.9 100 2.4
90 2.6 100 2.2
90 2.6 100 2.2
90 2.3 100 1.9
I-UJ ~ z -w 0 ~ ti)
0
UJ en re ::,
8 re ~ ~
I 2.so,.. ~&lope~ 2.0 I ·
1001 1,s I V-A/-' ' , :Y ' .... >
0
EXAMPLE:
Q«\i-en Wfltercourse Dcs,tance (0) • 70 Feet
Stope (s) = 1. S %
Runoff Coefficient {C) = 0 41
Overtand FICtff Time (T) = 9•.5 MinulBs
SOURCE: Airport Drainage, Federal Aviation A.dministralion, 1985
°K .I ,I' 1 1 ,C. I 30 • ~ . > ~-
en UJ 5 z
20 S§
' 0
T • 1.8 (1 .1-C) Vo :1v;;-
z
w ~ I-
~ ..J u..
0
::.!
i
e5
FIGU R E
Rational Formula .. Overland Time of R ow Nomograph 3.3