HomeMy WebLinkAboutCT 13-06; La Costa Villas Development; Drainage Study; 2014-11-11PcOrcJ copy
DRAINAGE STUDY FOR
A.P.N. 216-300-04-00
Lot 401, Gibralter Street
Carlsbad, CA
For
Majid Mortazavi
Report by Rene Figueroa
Arrow Civil Engineering Incorporated
9467 Tropico Drive
La Mesa, CA 91941
619-750-5327
11/11/14
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Table of Contents
Vicinity IVlap
Background
Design Criteria
Design Runoff Method
Hydrology
Hydraulics (100 Year Recurrence)
Water Quality Calculations
Conclusions
Declaration of Responsible Charge
Appendix 1: Pre-Development Hydrology
Appendix 2: Post Development Hydrology Calculation & Post
Development Hydrology/Hydraulic Map
Appendix 3: Hydraulic Calculations
Vicinity Map
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BACKGROUND
The intended development consists of an approximately 16787 square foot lot with the owner proposing to build an
8 unit condominium complex. The site has 9393 square feet of roof & hardscape. The project is located in the City
of Carlsbad. The map used for the design of the drainage facilities for the property was from a topographic map
provided by CCH Design Group Inc. The purpose of this study is for the sizing ofthe drainage facilities for the
property.
DESIGN CRITERIA
The drainage design criteria for this project is based on the County of San Diego Hydrology Manual, Dated June
2003 and the San Diego County Drainage Design Manual, Dated July 2005.
DESIGN RUNOFF METHOD
The Rational Method was used for the design of this project along with the Rational Method Hydrograph Procedure.
The selected storm frequency used was 100 years as required by the City of Carlsbad.
The drainage system was designed to convey the water from a 100 year storm without damage to the proposed
building and to detain the flow so that it would not exceed the predevelopment flow.
Hydrologic characteristics for the project are as follows:
Located at 33° 05' 08"N , 117° 14' 52"W
The soil group is determined to be Group D based of Appendix A ofthe San Diego County Hydrology Manual.
The 100 year, 6 hour precipitation is 2.7 inches.
The 100 year, 24 hour precipitation is 4.8 inches.
These numbers are based on the isopluvial maps of Appendix B ofthe San Diego County Hydrology Manual.
The Rational Method is described as follows:
Q = CIA
Where
Q = Flow rate in cubic feet per second (cfs)
C = Coefficient of runoff
I = Rainfall intensity in inches per hour (in/hr)*
A = Area in acres
Rainfall intensity has been determined from the equation given on Figure 3-1 ofthe Hydrology Manual where:
Intensity "I" = 7.44P6Tc"''*^'
Where:
I = Rainfall intensity in inches per hour (in/hr)
Pe = 100 year 6 hour precipitation in inches (in)
Tc = Time of concentration on minutes (min.)
The time of concentration is based on the FAA equation given in Figure 3-3 ofthe County Hydrology Manual.
HYDROLOGY
Basin Calculations
Summary Rational Method Calculations 100 Year Recurrence Interval (Pre-Development & post
Development)
Based on Section 3 (Rational Method) and Section 6 (Rational Method
Hydrograph Procedure) of the San Diego County Hydrology Manual, June 2003
Pe hour = 2.7
P24 hour = 4.8
Predevelopment
Drainage Area's Tc Runoff Coefficient (C) Intensity Basin
Acres (A) Q
Pre Development Basin 1 10.9 0.35 4.3 0.35* 0.53
* Existing brow ditch captures offsite flow along with some onsite flow and directs away from property
reducing acreage from 0.39 to 0.35 for calculations.
Post development
Drainage Area's Tc
Runoff
Coefficient (
C)
Intensity
Basin
Acres (A
)
Q
Basin A 5 0.58 7.1 0.10* 0.41
Basin B 10.6 0.68 4.4 0.16 0.47
Basin C 5 0.75 7.1 0.09 0.47
Existing brow ditch captures offsite flow along with some onsite flow and directs away from property reducing
acreage from 0.14 to 0.10 for Basin A calculations.
Based on the junction equation the post development time of concentration is Tc= 9.3 min
and the flow is 1.10 cfs
Storage from the permeable pavement in the driveway reduces the volume of total flow exiting the basin during the
6 hour storm window by capturing and detaining the flow within the permeable pavement. The permeable pavement
will have a liner between the base and subgrade to prevent infilfration or weakening of the soils adjacent to the
building and also provide a underdrain to remove the accumulated precipitation.The relationship between increase in
volume and flow is linear as shown in the incremental hydrographs. So the total volume as a result ofthe storage in
the pavement increased 23.1%, this percentage was applied to the predevelopment flow for a final post development
peak flow of 0.66 cfs.
100 YEAR PEAK FLOW MITIGATION
The project results in a 0.13 cfs increase of peak flow. This has been mitigated by use of a detention basin. The
detention base holds the volume ofthe increase in flow generated during the time the peak flow is exceeds the
predevelopment flow. Orifices have been added to inlets prior to entering the basin to bypass 0.53 cfs (the
predevelopment flow so that the basin size is for only the increase in flow due to development.
HYDRAULICS (100 YEAR RECURRENCE)
The South Side drainage system is based on a flow of 0.41 cfs. The site uses a D-75 brow ditch to capture the flow
from the slope and directs it to a 12" corrugated HDPE to a 24" grated inlet. The flow then drops into the structure
and outlets to a 6" HDPE (TYPE S) pipe. The flow travels under the sidewalk and is used to capture the roof flows
which are captured by downspouts and directed by a 4" pipe to the 6" mainline pipe (detail in Appendix 3). The
maximum flow from the roof for any downspout is 0.08 CFS. The flow then is directed to a detention basin.
The flow from the driveway and the roofs, 0.47 cfs, is directed into the driveway via roof downspouts and are
allowed to flow on to the permeable pavement. The flow continues down the driveway where it is captured by a
trench drain and directed to the detention basin.
The north side drainage system, 0.47 cfs, captures the flow from the north side ofthe north building and the flow
from the roof is captured and directed to a 6" HDPE (Type S) in the same manner as the south side drainage system.
The flow is then directed toward the south side detention basin.
DETENTION OF PEAK FLOW
The predevelopment and post development peak flows and volumes generated were determined using Chapter 6 of
the San Diego County Hydrology Manual using the rational method hydrograph procedure. Hydrographs were
developed for both the predevelopment and post development flows. The difference in volume generated by the
rainfall between post development flows and predevelopment was determined. The volume captured by the
permeable pavement was subfracted from the post development volume generated. The percent increase in volume
was then determined due to development. This percentage was applied to the predevelopment flow to account for
the storage in the permeable pavement. The remaining increase in flow was detained in a basin and released through
an orifice so that the post development flow would not exceed the predevelopment flow.
PREDEVELOPMENT FLOW = 0.53CFS
POST DEVELOPMENT PEAK FLOW = 1.10 CFS
POST DEVELOPMENT FLOW AFTER STORAGE IN PERMEABLE PAVERS =0.66 CFS
POST DEVELOPMENT PEAK FLOW DETAINED = 0.20 CFS
ALLOWABLE PEAK ORIFICE FLOW = 0.46 CFS
CHECK: 0.66 CFS-0.20 CFS = 0.46 CFS, ORIFICE SIZED FOR 0.46 CFS WHICH IS LESS THAN THE
ALLOWABLE FLOW OF 0.53 CFS. Therefore the post development offsite flow 0.46 cfs which is less than
predevelopment flow of 0.53 cfs while the volume exceeding the difference between the predevelopment and post
development peak flows is detained in the detention basin and permeable pavement driveway.
CONCLUSIONS
No adverse impacts are anticipated provided that the drainage facilities are constructed as designed in the plans and
maintained with care.
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 STANDARDS.
I UNDERSTAND THAT THE CHECK OF THE PROJECT DRAWINGS AND SPECIFICATIONS BY THE
COUNTY OF SAN DIEGO IS CONFINED TO A REVIEW ONLY AND DOES NOT RELIEVE ME, AS
ENGINEER OF WORK. OF MY RESPONSIBILITES FOR PROJECT DESIGN.
<etie-Tigueroa, P.E. i
Arrow Civil Engine^^g Incorporated
9467 TropicolDrive
La Mesa, CA 91941
APPENDIX 1
• PRE DEVELOPMENT HYDROLOGY MAP
• PRE DEVELOPMENT CALCULATIONS
San Diego County Hydrology Manual
Date: June 2003 Section:
Page:
3
12 of 26
Note that lhe 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 T, values based on average C values for die 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 sutmitted with a
detailed study.
Table 3-2
MAXIMUM OVERLAND FLOW LENGTH (LM)
Element"* DU/
Acre
.5% 1% 2% \ 3% 5% 10% Element"* DU/
Acre LM Ti LM LM T, \LM Ti LM Ti LM T,
Natural 50 13.2 70 12.5 ^85 10.9/ 'lOO 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.P7Com 50 4.2 60 3.7 70 3.1 80 2.9 90 2.6 100 2.2
Limited I. 50 A2 60 3.7 70 3.1 80 2.9 90 2.6 100 2.2
General I. 50 3.7 60 32 70 2.7 80 2.6 90 2.3 100 1.9
*See Table 3-1 for more detailed description
3-12 -^^^--r^ 4-
: : PREDEVELOPMENT HYDROLOGY
APPENDIX 2
• POST HYDROLOGY/HYDRAULIC MAP
• POST HYDROLOGY CALCULATIONS
• HYDROGRAPHS
GIBRALTAR
Summary Rational Method Calculations (Urban Watershed) 100 Year Recurrence Interval (Post-Development)
Based on Section 3.2, San Diego County Hydrology Manual, June 2003
Pe hour = 2.7
P24 hour = 4.8
Drainage Area's Tc Runoff
Coefficient (C) Intensity Basin
Acres (A) Q
Basin A 5 0.58 7.1 0.10 0.41
Basin B 10.6 0.68 4.4 0.16 0.47
Basin C 5 0.75 7.1 0.09 0.47
Total = 1.35
Basin A
T2 = 5 Q2 = 0.41 12 = 7,1
Basin B
T3 = 10.6 Q3 = 0.47 13 = 4.4
Basin C
Tl = 5 Ql = 0.47 11 = 7.1
Junction Equation: Ti - T; Tj
Qtl =
Qt2:
Qt3 =
1.10
1.10
1.01
SoQ = 1.10
Tc = [d (CA)7.44 P«) Q] ' •'•
Tc = 9.2
100 Year recurrence Hydrology Calculation (Post-Development)
Drainage SubBasin A
P6 = 2.7
Soil Type = D
Zoned = RD M 8 DU
Sub Basin A 6150 SF
Pervious area= 3611
Roof and pavement area = 2539 SF
% Impervious = 0.41
Tlierefore according to Table 3-1 of the San Diego County Hydrology Manual (SDCHM) the Runoff Coefficient = 0.58
Basin Size = 0.10 acres
Maximum overland flow length = 100 ft
Intial Time of Concentration Ti = 3.5 min per table 3-2 (SDCHM)
Total length of flow = 268 feet
Assume Tc= 5 minTherefore i = 7.1 in/hr
Assumed Flow per Acre = CIA= 4.1 cfs
Assumed flow for 0.1 acres = 0.41 cfs
Assume all overland flow therefore travel time = 0
Assume travel time Tt, = 0.0 min (conservative)
Tc= Ti+Tt, = 3.5
Minimum Tc = 5 minutes Therefore Tc = 5
Therefore I = 7.1
Check Assumed Q
Q = CIA= 0.41 cfs
100 Year recurrence Hydrology Calculation (Post-Development)
Drainage SunBasin B
P6 = 2,7
Soil Type = D
Zoned = RD M 8 DU
Sub Basin A 6808 SF
Pervious Area = 2730
Roof Area = 4078 SF
% Impervious = 0.60
Therefore according to Table 3-1 of the San Diego County Hydrology Manual (SDCHM) the Runoff Coefficient = 0.68
Basin Size = 0,16 acres
Maximum overland flow length = 100 ft
Intial Time of Concentration Ti = 4.9 min per table 3-2 (SDCHM)
Total length of flow = 154 feet
Assume Tc = 11 minTherefore I = 4.4 in/hr
Assumed Flow per Acre = CIA= 3.0 cfs
Assumed flow for 0.15629 acres = 0.47 cfs
Node 1 to 2 (Slope)
Assume Tt1 = 0
Node 2-3 (Center of Driveway)
Tt2 = 5.7
Tc= 10.6
1= 4.4
Check Assumed Q
Q = CIA = 0.47 cfs
100 Year recurrence Hydrology Calculation (Post-Development)
Drainage SubBasin C
P6 = 2.7
Soil Type = D
Zoned = RD M 8 DU
Sub Basin A 3829 SF
Pervious Area = 1053
Roof Area and pavement = 2776 SF
% Impervious = 0.72
Therefore according to Table 3-1 of the San Diego County Hydrology Manual (SDCHM) the Runoff Coefficient •• 0.75
Basin Size = 0,09 acres
Maximum overland flow length = 100 ft
Intial Time of Concentration Tl = 3.5 min
Total length of flow = 268 feet
Assume Tc = 5 minTherefore 1 = 7.1 In/hr
Assumed Flow per Acre = CIA= 5,2 cfs
Assumed flow for 0.09 acres = 0.46 cfs
per table 3-2 (SDCHM)
Assume all overland flow therefore travel time = 0
Assume travel time Tt, = 0.0 min (conservative)
Check Assumed Q
Tc = Tl + Tti =
Minimum Tc = 5 minutes Therefore Tc =
Q = CIA:
3.5
Therefore I =
0.47 cfs
7.1
Summary of Hydrograph Analysis
Volumes
Basin A
Basin B
Basin C
Totals =
Total Increase =
Pre Post
475 cf 566 cf
542 cf 416 cf
305 cf 645 cf
Increase
91 cf
-126 cf
340 cf
1322 cf
305 cf
1627 cf
% Increase in Volume = 23,1%
*Linear relationship of volume to runoff, therefore adjust post development to 23,1% above pre development volume
to account for permeable paver storage in driveway
Note 72 hour lag for flow to migrate out of pavement through underdrains (typical). So out of 6 hour stomi window.
Flows
Time min Pre Post "Adjusted post Increase Route 30% of adjusted post fiow
0 0.00 0.00 cfs 0,00 cfs 0.00 cfs 0.00
30 0.04 0.09 cfs 0.05 cfs 0.01 cfs 0.02
60 0.05 0.10 cfs 0.06 cfs 0.01 cfs 0.02
90 0.05 0.11 cfs 0.06 cfs 0.01 cfs 0.02
120 0.06 0.13 cfs 0.08 cfs 0.01 cfs 0.02
150 0.07 0,15 cfs 0.09 cfs 0.02 cfs 0.03
180 0.11 0,22 cfs 0.13 cfs 0.02 cfs 0.04
210 0.15 0.31 cfs 0.18 cfs 0.03 cfs 0.05
240 0.53 1.11 cfs 0.66 cfs 0.12 cfs 0.20
270 0.08 0.18 cfs 0.10 cfs 0.02 cfs 0.03
300 0.06 0.12 cfs 0.07 cfs 0.01 cfs 0.02
330 0.04 0.09 cfs 0.05 cfs 0.01 cfs 0.02
360 0.00 0,00 cfs 0.00 cfs 0.00 cfs 0.00
Post Development Incremental Hydrograph Per Chapter 6, San Diego County Hydrology Manual
Basin A
Pe = 2.7 in Pervious Area = 3611.0 sf
Roof Area and Pavement= 2539,0 sf
Te = 5,0 min C„„,= 0,9
^Landscape ~ 0-35
Composite C = 0,58
A = 0.10 acres
IT,= 7.44P,D^"= =
PT(NI = 0.124 Ps (NTJ"'^" for N= 1 to 11
PN = PT(N) ~ PT{N-I)
INTC = 60 PN/T,
QN = 60CAPNAc(cfs)
7.1in/hr
Rainfall Inches for Tc = 5
Total Rainfall
Block N PT,N, = 0.124 P^NT/''^
1 0.593
2 0.758
3 0.876
4 0.970
5 1.050
6 1.120
7 1.183
8 1.240
9 1.293
10 1.343
11 1.389
Time QN Rainfall Block
0 0.00
30 0.03 11
60 0.04 9
90 0.04 8
120 0.05 6
150 0.06 5
180 0.08 3
210 0.11 2
240 0.41 1
270 0.07 4
300 0.04 7
330 0,03 10
360 0,00
Actual Rainfall
PN = P-T(N| - r-
0.593
0.165
0.117
0.094
0.080
0.070
0.063
0.057
0.053
0.049
0.046
WIKR:
1
VCH. = CPtA
VOL=vnboc of naoff (acre-iodies)
Pe - 6-how oafidi (iad»)
C = foaoff ooefficKOt
A=am of die mienfaed (aoet)
(Eq.6-1) Total Storm Volume -
Pre Storm Volume -
Volume Increase =
566 ft3
475 ft3
91 ft4
Peak Flow = 0.41 cfs
I 1
-4 >
PostDevelopment Volume
Predevelopment Volume
Increase in Volume
566
475
91
Post Development Incremental Hydrograph Per Chapter 6, San Diego County Hydrology Manual
Basin B
Pc = 2.7 in Pervious Area = 2730.0 sf
Roof Area = 4078.0 sf
Tc = 10.6 min C^,= 0.9
^Landsopt = 0,35
Composite C = 0.68
A = 0,16 acres
ITC = 7.44P6D-° 4,4 in/hr
01^ ) HV**) - Hie* <*V*«)
= 0.124 Ps (NTJ°'" for N= 1 to 11
I (MB'Mt - tab > (Hc/MI
4(heun|
PN = PT(N) - PT(N.I)
Im, = 60 PN/T,
Q„ = 60 CAPN/TC (cfs)
Rainfall Inches forTc = 10.6 0.4S
Total Rainfall Actual Rainfall 0.40
Block N PT|N) = 0.124 Pe(NTj"" PN - PT{N) ~ PT(N-I) 1N = 60P„/T. 0.35 1 0.774 0.774 4.4
2 0.990 0.216 1.2 0.30
3 1.143 0.153 0.9 0.25
4 1.266 0.123 0.7 0.20
5 1.371 0.104 0.6
6 1.462 0.092 0.5 QN 0.15
7 1,544 0,082 0.5 0.10
8 1.619 0.075 0.4 0.05
9 1.689 0.069 0.4 0.4 0.00 10 1.753 0.064 0.4
11 1.813 0.060 0.3
Time QN Rainfall Block
0 0.00
30 0.04 11
60 0.04 9
90 0.05 8
120 0.06 6
150 0.06 5
180 0.09 3
210 013 2
240 0.47 1
270 0.07 4
300 0.05 7
330 0.04 10
360 0.00
V0L=CP«A
Whoe: VOL = vofaiine of naoff (acn-mdiK)
P« = 6-hour na^iD (mdics)
C = naoff coefficical
A = area of die watcnlicd (acies)
(Eq6-1)
Total Storm Volume =
Pre Storm Volume -
Volume Increase =
1041 ft3
542 ft3
499 ft3
Peak Flow = 0.47 cfs
Note: Permeability of Permeable Pavers is l"per hour, Max actual rainfall per hour Pj = 0.73"
Storage Type Square Feet Gravel Depth ft Capacity (porosity 40%)*
Permeable Pavers Driveway 3125 0.5 625
Total Stored =
Volume Increase =
625
-126
'Assumes Open Graded Base Course
Post Development Incremental Hydrograph Per Chapter 6, San Diego County Hydrology Manual
Basin C
Pe = 2,7 in Pervious Area = 1053.0 sf
RoofArea = 2776.0 sf
I Tt - 5.0 min C,„of= 0.9
^Landscape ' 0-35
Composite C = 0.75
A = 0.09 acres
IT, = 7.44P,D-""' =
PT(N| = 0.124 Pe (NT^)"'" for N= 1 to 11
PN = PT(NI ~ PT|N-I)
INTC = 60 PJT,
QN = 60CAPN/T,(cfs)
7.1in/hr
Time QN Rainfall Block
0 0.00
30 0.04 11
60 0,04 9
90 0,05 8
120 0,06 6
150 0.06 5
180 0.09 3
210 0,13 2
240 0,47 1
270 0,07 4
300 0.05 7
330 0.04 10
360 0,00
i
1 CH
-4 (tioursi
Rainfall Inches for Tc = 5 0.45
Total Rainfall Actual Rainfall 0.40
Block N PT|„, = 0.124 Pe(NT,)"" PN - PT(N) ~ PT(N-I) IN = 60PN/T, 0.35 1 0.593 0.593 7.1 0.35
2 0.758 0.165 2,0 0.30
3 0.876 0.117 1,4 0.25
4 0,970 0.094 1,1 0.20
5 1,050 0.080 1,0
6 1,120 0.070 0,8 QN 0.15
7 1,183 0.063 0,8 0.10
8 1,240 0.057 0,7 0.05
9 1.293 0.053 0,6 0.00
10 1.343 0.049 0,6
11 1.389 0.046 0.6
VOL = CPsA
V/bae: VOL = volume of mnoff (aoe-indics)
P« = 6-hour lain&ll (incfaes)
C = nmoff coefficient
A = aiea of die watershed (acies)
(Eq.6-1)
Total Storm Volume =
Pre Storm Volume =
Volume Increase =
645 ft3
305 ftS
340 ft4
Peak Flow = 0.47 cfs
-4 J
Tim* (mlr>ut*s)
APPENDIX 3
• HYDRAULIC CALCULATIONS
• DRAINAGE DESIGN MAPS
VDRIVEWA>|
ROOF LINf
109.00 TW
106.50 BW
CITY ST'D
DWG. C-3
108.70 TW
105.70 BW
CITY STD
DWG. C-3
^E)DRtVENN
Storage Routing
Storage Routing Calculation Basin Area =
Time step (min) = 30
120
Storage
Time n = In Sn On (S„.i-S„)/Dt (ln+lnn)/2 (On+0„.i)/2
0 0.00 cfs 0 0
30 0.02 cfs 18.00 0.16 18.00 0.01 0.08
60 0.02 cfs 36.00 0.23 18.00 0.02 0.20
90 0.03 cfs 45.00 0.26 9.00 0.03 0.24
120 0.03 cfs 54.00 0.28 9.00 0.03 0.27
150 0.04 cfs 63.00 0.30 9.00 0.04 0.29
180 0.06 cfs 90.00 0.36 27.00 0.05 0.33
210 0.20 cfs 234.00 0.59 144.00 0.13 0.48
240 0.03 cfs 207.00 0.55 -27.00 0.12 0.57
270 0.02 cfs 45.00 0.26 -162.00 0.03 0.40
300 0.02 cfs 36.00 0.23 -9.00 0.02 0.24
330 0.02 cfs 36.00 0.23 0.00 0.02 0.23
360 0.00 cfs 18.00 0.16 -18.00 0.01 0.20
390 0.00 cfs 0.00 0 -18.00 0.00 0.08
Peak Flow Reduction = -0.54 cfs
Orifice
CdA(2gh)^''^
Cd = 0.6
A = 0.0872665 sf
g= 32.2 ft/s'
Diameter 4 in
Zo= 0.17 ft
h = D-Zo+Diameter/2/12
Sn D Zo Diameter/2/12 h
0 0 0.16666667 0.166666667 0
18 0.15 0.16666667 0.166666667 0.15
36 0.3 0.16666667 0.166666667 0.3
45 0.375 0.16666667 0.166666667 0.375
54 0.45 0.16666667 0.166666667 0.45
63 0.525 0.16666667 0.166666667 0.525
90 0.75 0.16666667 0.166666667 0.75
234 1.95 0.16666667 0.166666667 1.95
207 1.725 0.16666667 0.166666667 1.725
45 0.375 0.16666667 0.166666667 0.375
36 0.3 0.16666667 0.166666667 0.3
36 0.3 0.16666667 0.166666667 0.3
18 0.15 0.16666667 0.166666667 0.15
Max height
ORIFICE EQUATION
Q = n(DV4)(2gh)'''
force of gravity g= 32.2 fps
head =h= 1.691666667 ft
Allowable Q = 0.460 cfs
Solving for D:
D= 0.321 ft = 4 in
HDPE 8" @2.86% TYPE C SIZING CHECK
Enter Values in boxes:
Pipe Type: HDPEC Corrugated
Diameter = 8 inches
D = 0.666666667 ft (pipe diameter)
n = 0.024 Mannings Roughness Value
So = 0.0286 fim (Pipe Slope)
0.35 ff
R(u« = 014= 0.17 ft
Qfu« = 1.49Afu(|R^ftj(tSo^'^ 1,11 ft^/s
VfuB =Qful/Aful| -3.2 nis
Q= 0.55 ft^/s Post Design Flow
Q/Qfuir 0.50
1 Figure 3-6 San Diego County Drainage Design Manual
V= 3.2 ft/s
HDPE 6" @ 2% TYPE S SIZING CHECK
Enter Values in boxes:
MaxQ = 0.55
Pipe Type: HDPEC Conojgated
Diameter = 6 inches
D = 0.5 ft (pipe diameter)
n = 0.013 Mannings Roughness Value
So = 0.02 ft/ft (Pipe Slope)
0.20 ft'
Rfuii = D/4= 0.13 ft
Qfu« = 0.80 ft^/s
Vfull =Qful/Afui| =
n
4.1 ft/s
Q=
Q/Qfun=
0.55
0.69
ft^/s Post Design Flow
VA/,^r
V=
1,13
4.6
Figure 3-6 San Diego County Drainage Design Manual
ft/s
Max Q for 18" x 18" Grate = 1.58 CFS
Grated Inlet in Sag (County of San Diego 2.3.2.2)
Table 2-1 Weir CoefRcients for Inlets in Sag Locations
Inlet Type Coefficient Weir Length Equation Valid
Cw Lw
Grate Inlet Against Curb 3.00 d<1.79(Ao/Lw)
Grate Inlet Flow From All Sides 3.00 2(L+W)'" d<1.79(Ao/Lw)
Curb Opening inlet 3.00 U d<h
Depressed Curb Opening Inlets
Less Than L'=12ft'^' 3.00 L'*1.6W d<h
Slotted Inlets 2.48 Liv d<0.2ft
(1) Weir length shall be reduced to account for clogging. (2) "Depressed Curb Opening Inlets" refers to curb inlets with
depression larger the width of the gutter( for example , SD-RSD No. 20," Concrete Apron for Curb Inter). The width
(W) of the curb opening depression is measured perpendicular to the face of the curb opening.
Type Opening = Grate Inlet Flow From All Sides
Q= 1.17 ft^/s (Flow to capture)
P = 6 ft (Grate Perimeter)
g= 32.2 ft/s' (gravitational acceleration)
a= 0 ft (curb inlet depression)
6> =
CL =
CA =
0
0.50
0.50
° (Standard Drawing D-12 = 33.69°)
clogging factor
Clear Opening Clogging Factor
d = 0.33 flow depth (Figure 2-2, 6 inch curb), (Figure 2-3, 8 inch curb)
Weir Equation
weir discharge coefficient
Pe = (1-CJ'P 3 ft (effective perimeter)
1.71 ft^/s (Good)
Table 2-1 Weir Coefficients for Inlets In Sag Locations
Inlet Type Coefficient Orifice Area Equation Valid
Co Ao
Grate Inlet 0.67 Clear Opening Area d<1.79(Ao/Lw)
Curb Opening Inlet 0.67 hL d + (h/2) > 1.4h
Slotted Inlets 0.80 Lw'^' d<0.4ft
(1) Actual grate opening for SD-RSD No. 15 Drainage Structure Grate is Ao= 4.7 ft'
(2) Orifice area shall be reducd by 50 percent to account for clogging.
Orifice Equation
Ao = 4 (Actual Opening of grate inlet), D-15 grate = 4.7 ft'
Ae = (I-CA)AO = 2 ft'
Co = 0.67 Orifice coefficient
Q=CA(2gd)"' 6.2 ft^/s (Good)
Inlet to D-25
Enter Values in boxes:
Pipe Type: HDPE S Conjugated
Diameter = 10 inches
D = 0.833333333 ft (pipe diameter)
n = 0.024 Mannings Roughness Value
So = 0.02 ft/ft (Pipe Slope)
Ah,R = 7iD^/4= 0.55
RM = D/4= 0.21 ft
QfuK = 1.49A^R^^So"' 1.68 ft^/s
VfuU =Qful/Afu|| -3.1 ft/s
Q= 1.17 ft^/s Post Design Flow
0.70
VA/nnr 1.08 Figure 3-6 San Diego County Drainage Design Manual
V= 3.3 ft/s
Rectangular Channel Calculation
Channel Type ; CONCRETE (RSD D-25)
Based on Equation 19.15, Civil Engineering Reference Manual, 9th Edition, Michael R. Lindburgh, P.E.
Q = 1.17 ftVs
n = 0.016 Mannings Roughness Value
8 = 0.02 ft/ft (Slope)
w = 3.0 Channel Width (ft)
Normal Depth = dn = 0.79 nQ
wS
1/2 = 0.17 ft = 2.0 in.
Channel Area = A = 0.50 ft^
Channel Velocity = V = Q/A = 2.36 ft/s
DETENTION BASIN
SCALE: 9<.-»r-0"
W.i3-TW
WALL TYPE c-3
' leXIBGRATE,
91.96 TOG"
''WAlXTYFt c-3
B-HPOE TYPE
•CSKPLAN
FORItSLOf^
SECTION
SCALE: T-0-
FRONT ELEVATION
SCALE: s r-ir
DETENTION BASIN SECTIONS
SCALE: - l-,a'
I
M.33-TW 6e.66.BW
"WALL TYPE C-3 92.33-TW
89.00-BW
, ' wiiL TYPE C.3
92.00-TW
WALIITVPE C-3
c=j
CATCH BASIN
HrHPDETO
D-25 CURS
D«AW -• m
tb
SECTION Cl
SCALE: ){" = r-(r
SECTION C2
SCALE: ;5-=1--fr
DETENTION BASIN SECTION
%CAiS::li-.r<r
T FREEBOARD
r
O' HYPE PIPE
OUTLET TO
RSD-25
NOT USED NOT USED INLET @ DETENTION BASIN
"AS BUILT'
REVIEWED BY:
ENONEEn OF WORK REVISION OESCraPTlON
OTHER APPROVAL CITY APPROVAL
SHEET
7 CITY OF CARLSBAD
ENGHEEHNG OffARIMEf^
GRADING PLANS FOR:
LA COSTA VILLAS
DETENTION BASIN
SHEETS
8
Ef-KaNeEBMANAGER RCE439I2 EXP.9/30/i7
OWN BY:
CHKO BY:
RVWOBY:
PROJECT NO-
JASON S-GaOERT
EMAWINGNO.
483-2A