HomeMy WebLinkAboutCT 04-21; CARLSBAD VILLAGE TOWNHOMES; DRAINAGE STUDY; 2005-05-02DRAINAGE STUDY
for
Carlsbad Village Townhomes
2683 & 2687 Roosevelt St
Carlsbad, CA
prepared by:
Tim Graves, P.E.
27003 (exp 3/31/01)
9373 Hazard Way, #101
San Diego, CA 92123
858.565.9512
5/2/05
I
METHOD
This drainage study was performed using the San Diego County Rational Method, as established
by the San Diego County department of Pubic Works, Flood Control Division, Hydrology Manual, 2003.
TIME PERIOD
The time periods for calculation of design flows is: EXISTING CONDlTlONS(PRE-DEVELOPMENT) AND
PROPOSED CONDITIONS (POST DEVELOPMENT)
RATIONAL METHOD
Theftational Method Formula is Q = C x I x A
Q is the peak design discharge in cubic feet per second
C Is the coefficient of runoff
I is the rainfall intensity in inches per hour
A is the tributary drainage area in acres
Run-off Coefficients - Soil Group D
Native 0.45
Landscaped Areas 0.45
Pavement 0.90
Roof Surfaces 0.90
DRAINAGE TABLE
Summary of Results
Area Existing Proposed
"Pre-Development" "Post-Development'
Q100 QIOO
(CFS) (CFS)
CHANGE
%
Sub-Basin "A:
Drainage Area
Run-Off Coef.
D (Tc)
QI 00
0.46 Ac
0.88
7.0 mm
5.30 in/hr
1.70 CFS
0.46 Ac
0.86
5.0 mm
6.59 in/hr
2.64 CFS +55.3%
Note: Flow attenuation is proposed which will decrease the rate of discharge from the
project area to 1.70 CFS.
[]
Narative: The proposed project is located on the west side of Roosevelt Street, between
Laguna Drive and Beach Ave. Street drainage on Roosevelt flows in the gutter is conveyed past
the site. The site has very mild slope. Runoff from existing roofs, hardscape & landscape is
conveyed as sheet flow and in a gentle swale and discharged to private property to the west.
The point of discharge for the proposed development will be maintained. Surface waters are
convyed in a private storm drain system to the westerly boundary, filtered and discharged across
the property line through a discharge manifold.
The discharge manifold is 18" diameter PVC Win length with (45) 1-1/4" diameter outlet orifices
distributed along its length (at approximately 16" o/c). Outlet orifices penetrate the base of the
proposed retaining wall at the westerly boundary resulting in a dissipated discharge. The discharge
from each orifice at the limiting head is 0.042 CFS (1.70 CFS Total) with a maximum discharge
velocity of 4.9 FPS. In addition to resulting in a distributive discharge, the manifold's volume (160
CF) also serves as storage for peak flow attenuation.
The project boundaries are coterminus with the existing drainage sub-basins: no alteration are
proposed.
Conclusion:
The proposed project will result is a slight decrease in the peak run-off from thre project site (2.2%
reduction) due to the increase in the amount of proposed landscapings +€.+t'ot&. mnA p14S4
COYdO tv dJa5iY. (mo-i iv40 ta.t41i3 orec*.S
44- ivh y&rd dsLiv.)
Attachments:
Hydrology - Existing
Hydrology - Proposed
100 Yr -6 Hr Isopluvial
100 Yr -24 Hr Isopluvial
Soil Classification Map
Hydraulic Calculation of Private Storm Drain System
Calculation of Travel Time (existing)
Overland Flow Nomograph
Open Channel (Swale) caic
Hydraulic Analysis of Discharge Manifold
Orifice Calculation
Attenuation Volume Calculation
Sub-Basin "An - Existing
Runoff Coefficient
Ci:= 0.9
Cp := 0.45
A=0.46
Run-off Coefficient - Soil Type 0
Al 6721 + 4163 Area of Impervious Surfaces (Roof, Patio, Pave, etc)
Ap 800 + 8537 Area of Pervious Surfaces (Landscaping, natural, etc)
A (Al + AP).AC Total area - Ac
Al-Ac % Impervious Percentl := ---
Ap.Ac
% Pervious Percentp A
C Cl.Percentl + Cp.Percentp
Hydrology Manual
100 Year 6-Hour Precipitation lsopluvial Map
100 Year 24-Hour Precipitation Isopluvial Map
Check for Mm/Max
P6
0.45< - 0.56 <0.60 ..............Okay
P24
Time of Concentration
See Attached Nomograph - Overland Flow - 75' 6.40 minutes
See attached Calc - Open Channel Flow - mild swale 0.60 minutes
Total Travel Time 7.00 minutes
Intensity -Duration Equation
Design Intensity inches per hour
Design Runoff
Qioo cubic feet per second
Percenti = 0.54
Percentp = 0.46
C = 0.69
P6:= 2.5
P24:= 4.5
P6:= P6
D:= 7.0
7.44 P6.0 0.645
= 5.30
Qtoo:= C.I.A
Q1 0O = 1.70
Run-off Coefficient - Soil Type D
Al 13895+ 4486 Area of Impervious Surfaces (Roof, Patio, Pave, etc)
Ap := 1840 Area of Pervious Surfaces (Landscaping, natural, etc)
A:= (Al + AP). AC Total area - Ac
A1.Ac
% Impervious Percentl
Ap-Ac
% Pervious Percentp A
C Cl.Percentl + CpPercentp
Hydrology Manual
100 Year 6-Hour Precipitation lsopluvial Map
100 Year 24-Hour Precipitation Isopluvial Map
Check for Mm/Max
0.45< P6
= 0.56 <0.60 ..............Okay
Time of Concentration
See Hydraulic calculation of transit time in storm drain
Use Tc = 5 minutes per Section 3.3.2 of Hydrology Maunal
D:= if(D<5,5,D)
Intensity -Duration Equation
Design Intensity inches per hour
Design Runoff
0100 cubic feet per second
Sub-Basin "A" -_Proposed
Runoff Coefficient
Cl:= 0.9
Cp := 0.45
A = 0.46
Percefltl = 0.91
Percentp = 0.09
C = 0.86
P6= 2.5
P24:= 4.5
P6:= P6
49 Tc := - 60
D:= Tc
D = 5.00
:= 7.44 P6. D_
= 6.59
Q100:= C.I.A
Qioo= 2.63
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Hydrology Manual
County
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Rainfall Isopluvials
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Analysis of Circular Sec •Number...of_Pipes 3
dia
Given
[1r2(O - sin(0))l
(2)
1.486 ri 2 (8))] I 2 Q •I—.r •(0—sin n[2 [ r.8 ]
d1a1 := nj:= S1:=
0.50 6 0.013 0.01 Upper Reach of Private Storm Drain
1.20 8 0.013 0.01 Middle Reach
1.32 12 0.013 0.01 Lower Reach
Results:
0.5 1.2 1.32 '
0.561 1.208 3.563 "Qfull"
0.891 0.993 0.37 'Q/Qfull"
Output = 3.23 3.947 4.198
4.413 6.507 5.057
0.736 0.813 0.421 "d/D"
Time of concentration.
Length of system L 185 Vav := 3.23 + 3.947 + 4.198Vav = 3.792 3
Tc:=_L Tc=48.791 sec
Vav
fps
2.50% slope
2.0 4zo 4z,
1.5 çS - 100 // 30
L:" 1,0 C,
.75
.50
C,
w
LU c z t.0 LL-0 I 20
I
LU o z I O' w
I-U)
rJ
'I Li
0
- LU C,)
D - -
10 z
o 0 of W LU F-
0
EXAMPLE:
Given: Watercourse Distance (D) = 70 Feet
Slope (s) =1.3% T = 1.8 (11.1-C)VD
Runoff Coefficient (C)= 0.41
Overland Flow Time (T) = 9.5 Minutes
SOURCE: Airport Drainage, Federal Aviation Administration, 1965
I" I G 1: R E
Rational Formula - Overland Time of Flow Nomograph
Open Channel: Flow
Sections := 2 Number of Cross Sections for Analysis
Section No. I At head of flow path
Section No. 2 At bottom of flow path
Basic Equation:
(2)
d
[2.b+d.(cot((x)+cot(3))]1 Q = 1.486[d[2bd cot(a) .(--)
)]][2 b+df_1 + I n (+ cot
sin(a) sin (0) I
Input:
Flow Rate "n" Slope Bottom Left Bank Right Bank
[CFS] Width Slope (V/H) Slope (V/H)
Si := b1
P
0.01 0.02 0 0.02 0.02
0.01 0.02 0.02 0.02
Summary:
1.468 + 3.293
- = 2.381 Vav - fps ("No 1" "No 2")
0.1 2.6
0.037 0.107 "d (ft)"
Output = 0.068 0.789 "Area (SF)"
3.691 14.723 "W (ft)"
1.468 3.293 'V (fps)"
160-75. 1 = 0.59 travel time - mm
2.381 60
g:= 32.2
H:= 1.5
V2 h:= H+ - 2-g
Q:= C.A.Th
N:= 54.12
16
N.Q = 1.7
Outlet Orifices -Entrance Control
S
.2 = 4.9 A
Outlet pipe, square end, projecting into Manifold
I.D. of outlet pipe (orifice)
A=8.522x 10 ft2 - area oforifice
ft/sec - Velocity Head
ft/sec2
Static head on orifice
h = 1.5 Height of Water Surface above Center of Entranc
Q = 0.042 CFS
N = 40.5 Number of Outlet Orifices
(@ 16" 0/c - over 54 LF of maniflod)
Combined discharge rate
(Less than 1.7 cfs Q100 (existing)
Maximum discharge velocity - FPS
C:= 0.5
ID:= 1.25
2ID 7r
A:= 144
1
S
Attenuation Volume Required
:= 7
Qioo_existing 1.70
5
Q1ooproposed := 2.63
AQ := Qioo_proposed - QiOOexistin
Qioo_existing
-
-60
00-proposed
Time of Concentration (E)dsting) - minutes
CFS
Time of Concentration (Proposed) - minutes
CFS
zQ=0.93 CFS
V=98.7 CF
Lenath of 18'6 Pine Required for Attenuation
L:= L=55.8 LF
1.5
1