HomeMy WebLinkAboutMS 2018-0013; REDWOOD BEACH HOMES; HYDROLOGY STUDY; 2019-06-19I
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HYDROLOGY STUDY
FOR
GRADING PERMIT
3861 GARFIELD STREET
PUD 2018-0009 I CDP 2018-0044 / MS 2019-0013 / GR 2019-0010 I DWG 517-1A
CITY OF CARLSBAD, CA
PREPARED FOR:
RREG INVESTMENTS SERIES, LLC SERIES 1033. A DELAWARE LIMITED
LIABILITY COMPANY
3005 S. EL CAMINO REAL
SAN CLEMENTE, CA 92672
PH: (949) 438-5494
PASCO LARET SUITER & ASSOCIATES, INC.
535 N. HIGHWAY 101, SUITE A
SOLANA BEACH, CA 92075
PH: (858) 259-8212
Prepared: June 19, 2019
RCE 80356 DATE
RCEW)
JUL 23 2019
LAN.i uEVELOPMj r
ENGINEERING
TABLE OF CONTENTS
Executive Summary
Introduction
Existing Conditions
Proposed Project
Conclusions
References
Methodology
Introduction
County of San Diego Criteria
Runoff Coefficient Determination
Hydrology & Hydraulic Model Output
Pre-Developed Hydrologic Calculations (100-Year Event)
Post-Developed Hydrologic Calculations (100-Year Event)
Supplemental Calculations
AES Streetfiow Analysis
Appendix
Isopluvial Maps
Intensity Duration Design Charts
Runoff Coefficients
Hydrologic Soil Group - USDA Web Soil Survey
Pre-Development Hydrology Node Map
Post-Development Hydrology Node Map
Street Flow Node Map
SECTION
1.0
1.1
1.2
1.3
1.4
1.5
2.0
2.1
2.2
2.3
3.0
3.1
3.2
3.3
4.0
I PLSA 2889-01
I 1.0 EXECUTIVE SUMMARY
1.1 Introduction
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This Hydrology Study for the proposed development at 3861 Garfield Street has been
prepared to analyze the hydrologic and hydraulic characteristics of the existing and
proposed project site. This report intends to present both the methodology and the
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calculations used for determining the runoff from the project site in both the pre-
developed (existing) conditions and the post-developed (proposed) conditions produced
by the 100-year, 6-hour storm.
1.2 Existing Conditions
The subject property is located along Redwood Avenue, west of the intersection of
Redwood Avenue and Garfield Street, in the City of Carlsbad. The site is bound by an
existing single-family residential development to the west, an existing multi-family
residential development to the south of the property, Redwood Avenue to the north, and
Garfield Avenue to the east of the property. The existing site consists of two (2) existing
multi-family residence developments, driveway, detached garage and associated
improvements. The project site is located in the Agua Hedionda Hydrologic Area, and,
more specifically, the Los Monos Hydrologic Sub-Area (904.31).
The existing site can be categorized into one drainage basin, and primarily drains from
the southeast to the northwest corner of the site and out to Redwood Avenue. The
existing drainage basin has an approximate area of 0.25 acres and is approximately 58%
impervious. Per the Web Soil Survey application available through the United States
Department of Agriculture, the basin is generally categorized to have group B soils.
Based on the existing impervious area, a pre-development runoff coefficient of 0.55 was
calculated using the methodology described in section 3.1.2 of the San Diego County
Hydrology Manual and the formula provided therein. Using the Rational Method
Procedure outlined in the San Diego County Hydrology Manual, a peak flow rate and
time of concentration were calculated for a 100-year, 6-hour storm event. For the
existing drainage basin, the peak flow rate for the 100-year, 6-hour storm was determined
to be 1.04 cfs at the point of discharge from the site with a time of concentration of 5.0
minutes. Refer to pre-development hydrology calculations included in Section 3.1 of this
report for a detailed analysis of the existing drainage basin, as well as a pre-development
hydrology node map included in the appendix of this report for pre-development drainage
basin delineation and discharge locations.
1.3 Proposed Project
The proposed project includes the demolition of all existing onsite improvements and the
construction of a 4-unit detached condo map with associated private landscaping and
hardscape improvements, a 20-foot-wide driveway, sidewalk improvements and a sewer
main extension in the public right-of-way. Site grading along with road, drainage and
utility improvements typical of residential developments will also be constructed. The
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I PLSA 2889-01
proposed building pad elevations range from 63.5 feet at the southeasterly unit to 62.9
feet at the northwesterly unit in an attempt to match the existing sloping terrain.
In an effort to comply with the City of Carlsbad storm water standards, the proposed site
has incorporated LID design techniques to optimize the site layout. Runoff from
proposed roofs and hardscape areas will be directed to vegetated swales in an effort to
disperse drainage to pervious surfaces. The swales will remove sediment and particulate-
bound pollutants from storm water and will assist in decreasing peak runoff by slightly
increasing the site's overall time of concentration. Using the Rational Method Procedure
outlined in the San Diego County Hydrology Manual, a peak flow rate and time of
concentration were calculated for a 100-year, 6-hour storm event. For the existing
drainage basin, the peak flow rate for the 100-year, 6-hour storm was determined to be
1.22 cfs at the point of discharge from the site with a time of concentration of 5.0
minutes. Refer to post-development hydrology calculations included in Section 3.1 of
this report for a detailed analysis of the proposed drainage basin, as well as a post-
development hydrology node map included in the appendix of this report for post-
development drainage basin delineation and discharge locations.
1.4 Conclusions
Based upon the analysis included in this report, there is an increase of 0.18 cfs in peak
runoff as a result of the proposed development. Similar to the existing condition, the
post-developed site will discharge onto Redwood Avenue into the proposed curb and
gutter system. Once in the gutter, drainage will be conveyed to an existing curb inlet
located approximately 550 feet southwest on Carlsbad Boulevard, and will enter the
buried pipe network. Water will not be diverted away from existing drainage patterns,
and the increase in proposed impervious area and resulting peak runoff will not have an
adverse effect on the downstream watershed.
A study of the larger drainage basin draining to the curb inlet along the east side of
Carlsbad Boulevard at the intersection of Tamarack Avenue and Carlsbad Boulevard was
performed to confirm the existing system was equipped to convey the slight increase in
peak runoff generated by the proposed development. The results of the peak runoff
occurring during the 100-year, 6-hour storm event, including checking the capacity of the
existing curb face and curb inlet, can be found in Section 3.3 as well as the Appendix of
this report. The analysis of the resulting depth of flow in the existing curb and gutter
along Carlsbad Boulevard - due to the slight increase in runoff leaving the subject
property - was performed using Hydraulic Elements - I and Advanced Engineering
Software (A.E.S.). The depth of flow was then used to calculate the resulting flow
capacity of the existing curb inlet using the Curb Inlets in Sag equation per San Diego
County Hydraulic Design Manual, Section 2.3.2.1. Based on the results of the analysis,
the existing curb inlet on Carlsbad Boulevard appears to be sized appropriately to
adequately intercept and convey the peak flows generated during the 100-year, 6-hour
storm event.
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PLSA 2889-01
The post-developed site will be exempt from hydromodification compliance requirements
as it does not qualify as a Priority Development Project as defined in the San Diego
County Model BMP Design Manual. Additional analysis and design may be required to
verify that the proposed project is in compliance with current stormwater quality
regulations.
1.5 References
"San Diego County Hydrology Manual ", revised June 2003, County of San Diego,
Department of Public Works, Flood Control Section.
"San Diego County Hydraulic Design Manual", revised October 2012, County of San
Diego, Department of Public Works, Flood Control Section
"Model BMP Design Manual San Diego Region ", adopted June 27, 2015, San Diego
Region
"Low Impact Development Handbook - Stormwater Management Strategies", revised
July 2014, County of San Diego, Department of Public Works
Soil Survey Staff, Natural Resources Conservation Service, United States Department of
Agriculture. Web Soil Survey. Available online at http://websoilsurvey.nrcs.usda.gov.
Accessed July 20, 2015
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PLSA 2889-01
2.0 METHODOLOGY
2.1 Introduction
The hydrologic model used to perform the hydrologic analysis presented in this report
utilizes the Rational Method (RM) equation, Q=CIA. The RM formula estimates the
peak rate of runoff based on the variables of area, runoff coefficient, and rainfall
intensity. The rainfall intensity (I) is equal to:
I = 7.44 x P6 x D °645
I Where:
I I = Intensity (in/hr)
P6 = 6-hour precipitation (inches)
D = duration (minutes - use Tc)
Using the Time of Concentration (Tc), which is the time required for a given element of
water that originates at the most remote point of the basin being analyzed to reach the
point at which the runoff from the basin is being analyzed. The RM equation determines
the storm water runoff rate (Q) for a given basin in terms of flow (typically in cubic feet
per second (cfs) but sometimes as gallons per minute (gpm)). The RM equation is as
follows:
Q=CIA
I Where:
Q = flow (in cfs)
C = runoff coefficient, ratio of rainfall that produces storm water
runoff (runoff vs. infiltration/evaporation/absorption/etc)
I = average rainfall intensity for a duration equal to the Tc for the
area, in inches per hour.
A = drainage area contributing to the basin in acres.
The RM equation assumes that the storm event being analyzed delivers precipitation to
the entire basin uniformly, and therefore the peak discharge rate will occur when a
raindrop that falls at the most remote portion of the basin arrives at the point of analysis.
The RIVI also assumes that the fraction of rainfall that becomes runoff or the runoff
coefficient C is not affected by the storm intensity, I, or the precipitation zone number.
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I PLSA 2889-01
2.2 County of San Diego Criteria
As defined by the County Hydrology Manual dated June 2003, the rational method is the
preferred equation for determining the hydrologic characteristics of basins up to
approximately one square mile in size. The County of San Diego has developed its own
tables, nomographs, and methodologies for analyzing storm water runoff for areas within
the county. The County has also developed precipitation isopluvial contour maps that
show even lines of rainfall anticipated from a given storm event (i.e. 100-year, 6-hour
storm).
One of the variables of the RM equation is the runoff coefficient, C. The runoff
coefficient is dependent only upon land use and soil type and the County of San Diego
has developed a table of Runoff Coefficients for Urban Areas to be applied to basin
located within the County of San Diego. The table categorizes the land use, the
associated development density (dwelling units per acre) and the percentage of
impervious area. Each of the categories listed has an associated runoff coefficient, C, for
each soil type class.
The County has also illustrated in detail the methodology for determining the time of
concentration, in particular the initial time of concentration. The County has adopted the
Federal Aviation Agency's (FAA) overland time of flow equation. This equation
essentially limits the flow path length for the initial time of concentration to lengths under
100 feet, and is dependent on land use and slope. The time of concentration minimum is
5 minutes per the County of San Diego requirements.
2.3 Runoff Coefficient Determination
As stated in section 2.2, the runoff coefficient is dependent only upon land use and soil
type and the County of San Diego has developed a table of Runoff Coefficients for Urban
Areas to be applied to basin located within the County of San Diego. The table, included
at the end of this section, categorizes the land use, the associated development density
(dwelling units per acre) and the percentage of impervious area.
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PLSA 2889-01
3.0 HYDROLOGY MODEL OUTPUT
3.1 Pre-Developed Hydrologic Model Output (100-Year Event)
Pre-Development:
Q=CIA
Pioo=2.5
Basin 1
Total Area = 10,811 sf4 0.25 Acres
Impervious Area = 6,389 sf4 0.15 Acres
Pervious Area = 4,422 sf4 0.10 Acres
Cn, Weighted Runoff Coefficient
- 0.25, Cn value for natural ground, Type B soils
* Per San Diego Hydrology Design Manual (SDHDM) Section 3.1.2
- 0.9, C value for developed / impervious surface
* Per SDHDM Section 3.1.2
Cn = 0.9 x 6,389 sf+ 0.25 x 4,422 sf= 0.63
10,811sf
Tc = 5.0 Mm (minimum for small areas
P6 = 2.5
I = 7.44 x P6 D 0645
I = 7.44 x 2.5 x 50-0.645 6.59 in/hr
liooz 6.59 in/hr
Qioo = 0.63 x 6.59 in/hr x 0.25 Ac = 1.04 cfs
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PLSA 2889-01
3.2 Post-Developed Hydrologic Model Output (100-Year Event)
Post-Development (without considering HMP/BMP treatment):
Q=CIA
P100=2.5
Basin A
Total Area= 10,811 sf4 0.25 Acres
Impervious Area = 8,227 sf4 0.19 Acres
Pervious Area = 2,584 sf 4 0.06 Acres
Cn, Weighted Runoff Coefficient
- 0.25, Cn value for natural ground, Type B soils
* Per San Diego Hydrology Design Manual (SDHDM) Section 3.1.2
- 0.9, C value for developed / impervious surface
* Per SDHDM Section 3.1.2
Cn = 0.9 x 8.227 sf+ 0.25 x 2.584 sf= 0.74
10,811sf
Tc = 5.0 Mm (mm. for small areas)
P6 = 2.5
I = 7.44 x Px D °'645
I = 7.44 x 2.5 x 5.0-0:645 z 6.59 in/hr
I iooz 6.59 in/hr
Qioo = 0.74 x 6.59 in/hr x 0.25 Ac = 1.22 cfs
Pre-Development vs. Post-Development (Discharge Leaving Site):
Pre-Development Post-Development Delta
Qioo = 1.04 cfs Qioo = 1.22 cfs 0.18 cfs
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PLSA 2889-01
3.3 Supplemental Calculations for Determination of Downstream Facilities Capacity
Basin Area= 252,297 sf= 5.792 Ac
C=0.58; value for Medium Density Residential (14.5 DU/A or less), Type 'B' soils
* Per San Diego Hydrology Design Manual (SDHDM) Section 3.1.2
TcTi+Tt Ti@100'=0.5%
R-23 per Land Use Element => 8.2 min from Table 3-2
Tt=>L=966' AE=23.8'
Tt= [{1 l.9(L/5,280)'3}/AE]"0.385
Tt= [{1 l.9(966/5,280)'3}/23.8]"0.385 = 0.725
0.725 x 60 = 43.5 Mm.
Tc = 8.2 + 43.5 = 51.7 Min
P6 = 2.5
I = 7.44 X P6 x D °645
I = 7.44 x 2.5 x 51.70645 1.46 in/hr
Qioo = C*I*A
Qioo = 0.58 x 1.46 in/hr x 5.792 Ac = 4.90 cfs
Total Qioo = Basin A + Delta (Pre vs. Post)
Total Qioo = 4.90 cfs + 0.18 cfs = 5.08 cfs
Results from AES:
Street Flow Depth (feet) = 0.36
Halfstreet Flood Width (feet) = 11.74
Average Flow Velocity (ft/s) = 1.70
Product of Depth & Velocity = 0.61
*See attached AES Streetfiow Analysis
Street Flow Depth (0.36') < Height of Curb Face (0.5')
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RER11111
Check CaDacitv at Curb Inlet:
Curb Inlets in Sag
*per San Diego County Hydraulic Design Manual Section 2.3.2.1
Q = C L d312
Where...
Q = inlet capacity (ft3/s);
weir discharge coefficient = 3.0 (per Table 2-1)
LW = weir length (feet) = 9 (per in-field measurement)
D = flow depth (feet) = 0.36 (per Street Flow Depth caic on previous page)
Q = 3.0 x 9 ft x (0.36 ft)312
Q = 5.83 cfs
Street Flow (5.08 cfs) < Downstream Curb Inlet Flow Capacity (5.83 cfs),
therefore, the downstream facilities are equipped to convey the slight increase in
peak Q100 flow.
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PLSA 2889-01
4.0 APPENDIX
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County of San Diego
Hydrology Manual
Rainfall Isopluvials
100 Year Rainfall Event - 6 Hours
IsopIuvial (inches)
GISSan"Is
F .. i . r
N THIS MAP IS PROVIDED WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESS * OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
Copyright SenGIS. WI Rights Resemed
This products may 0001001 intormebon from the SANDAG Regional
F Information System which cannot be reproduced wrthoat the
wiitterr pnlrorssoe of SANDAG
This product may 0001001 information which has been reproduced with
permission granted by Thomas Brothers Maps
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San Diego County Hydrology Manual Section: 3
Date: June 2003 Page: 6 of 26
Table 3-1
RUNOFF COEFFICIENTS FOR URBAN AREAS
Land Use Runoff Coefficient "C"
Soil Type
NRCS Elements County Elements % IMPER. A B C D
Undisturbed Natural Terrain (Natural) Permanent Open Space 0.20 0.25 0.30 0.35
Low Density Residential (LDR) Residential, 1.0 DU/A or less 10 0.27 0.32 0.36 0.41
Low Density Residential (LDR) Residential, 2.0 DU/A or less 20 0.34 0.38 0.42 0.46
Low Density Residential (LDR) Residential, 2.9 DU/A or less 25 0.38 0.41 0.45 0.49
Medium Density Residential (MDR) Residential, 4.3 DU/A or less 30 0.41 0.45 0.48 0.52
Medium Density Residential (MDR) Residential, 7.3 DU/A or less 40 0.48 0.51 0.54 0.57
Medium Density Residential (MDR) Residential, 10.9 DU/A or less 45 0.52 0.54 0.57 0.60
Medium Density Residential (MDR) Residential, 14.5 DU/A or less 50 0.55 0.58 0.60 0.63
High Density Residential (HDR) Residential, 24.0 DU/A or less 65 0.66 0.67 0.69 0.71
High Density Residential (HDR) Residential, 43.0 DU/A or less 80 0.76 0.77 0.78 0.79
Commercial/Industrial (N. Corn) Neighborhood Commercial 80 0.76 0.77 0.78 0.79
Commercial/Industrial (G. Corn) General Commercial 85 0.80 0.80 0.81 0.82
Commercial/Industrial (O.P. Com) Office Professional/Commercial 90 0.83 0.84 0.84 0.85
Commercial/Industrial (Limited I.) Limited Industrial 90 0.83 0.84 0.84 0.85
Commercial/Industrial (General I.) General Industrial 95 0.87 0.87 0.87 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 Resources Conservation Service
3-6 - - - - - - - - - - - - - - - - - - -
467824 - .
N
Hydrologic Soii Group San Diego County Area California
33o Br 54 N Ai 33u J 8 N
467824 4(TRi~' 41,841 467W 4 ~,j 467872 A-37.3 -
Map Scale. 1:371 if pnnted on A landscape (11" x 8.5") sheet.
N o 5 10
- Meters
Fee
30
0 15 3) 60 9)
Map projection Web Mercator Corner coordinates: WGS84 Edge tics LCM Zone uN WGS84
-ui-s NtiirM flnhIrr4I WLr SQil Suivwy
Conservation Service NitinnaI Coonrt,e Soil Siiruey 1Jge 1 ,8A
Hydrologic Soil Group—San Diego County Area, California
MAP LEGEND MAP INFORMATION
Area of Interest (AOl)
Area of Interest (AOl)
Soils
Soil Rating Polygons
AID
B/D
LIC
C/D
Not rated or not available
Soil Rating Lines
A
AID
. B
B/D
, C
C/D
D
, Not rated or not available
Soil Rating Points
A
D AID
B
BID
The soil surveys that comprise your AOl were mapped at
1 24000
Warning Soil Map may not be valid at this scale
Enlargement of maps beyond the scale of mapping can cause
misunderstanding of the detail of mapping and accuracy of soil
line placement The maps do not show the small areas of
contrasting soils that could have been shown at a more detailed
scale
Please rely on the bar scale on each map sheet for map
measurements
Source of Map: Natural Resources Conservation Service
Web Soil Survey URL
Coordinate System. Web Mercator (EPSG.3857)
Maps from the Web Soil Survey are based on the Web Mercator
projection, which preserves direction and shape but distorts
distance and area. A projection that preserves area, such as the
Albers equal-area conic projection. should be used if more
accurate calculations of distance or area are required
This product is generated from the USDA-NRCS certified data as
of the version date(s) listed below.
Soil Survey Area. San Diego County Area, California
Survey Area Data: Version 12, Sep 13, 2017
Soil map units are labeled (as space allows) for map scales
1 50,000 or larger
Date(s) aerial images were photographed. Nov 3, 2014—Nov
22, 2014
The orthophoto or other base map on which the soil lines were
compiled and digitized probably differs from the background
imagery displayed on these maps As a result, some minor
shifting of map unit boundaries may be evident.
DC
CID
•
Not rated or not available
Water Features
Streams and Canals
Transportation
--- Rails
Interstate Highways
US Routes
Major Roads
Local Roads
Background
Aerial Photography
IJSI)A Natural Resources Web Soil Survey 8/1 5/2U Id
Conservation Service National Coonrative Soil Siiruey qe 2 ,f A
Hydrologic Soil Group—San Diego County Area, California
Hydrologic Soil Group
Map unit symbol Map unit name Rating Acres in AOl Percent of AOl
1lC Marina loamy coarse B 0.3 100.00,
sand, 2 to 9 percent
slopes
Totals for Area of Interest 0.3 100.0%
- .--.- ---- -----...-- ---- - .- - ._J.___ .---------- ----
Description
Hydrologic soil groups are based on estimates of runoff potential. Soils are
assigned to one of four groups according to the rate of water infiltration when the
soils are not protected by vegetation, are thoroughly wet, and receive
precipitation from long-duration storms.
The soils in the United States are assigned to four groups (A, B, C, and D) and
three dual classes (ND, BID, and CID). The groups are defined as follows:
Group A. Soils having a high infiltration rate (low runoff potential) when
thoroughly wet. These consist mainly of deep, well drained to excessively
drained sands or gravelly sands. These soils have a high rate of water
transmission.
Group B. Soils having a moderate infiltration rate when thoroughly wet. These
consist chiefly of moderately deep or deep, moderately well drained or well
drained soils that have moderately fine texture to moderately coarse texture.
These soils have a moderate rate of water transmission.
Group C. Soils having a slow infiltration rate when thoroughly wet. These consist
chiefly of soils having a layer that impedes the downward movement of water or
soils of moderately fine texture or fine texture. These soils have a slow rate of
water transmission.
Group D. Soils having a very slow infiltration rate (high runoff potential) when
thoroughly wet. These consist chiefly of clays that have a high shrink-swell
potential, soils that have a high water table, soils that have a claypan or clay
layer at or near the surface, and soils that are shallow over nearly impervious
material. These soils have a very slow rate of water transmission.
If a soil is assigned to a dual hydrologic group (ND, BID, or CID), the first letter is
for drained areas and the second is for undrained areas. Only the soils that in
their natural condition are in group D are assigned to dual classes.
Rating Options
Aggregation Method: Dominant Condition
USDA Natural Resources Web Soil Survey 8/15/2018
Conservation Service National Cooperative Soil Survey Page 3 of 4
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EXISTING HYDROLOGY EXHIBIT
REDWOOD HOMES - 3861 GARFIELD STREET
LEGEND
PROPERTY BOUNDARY
CENTERLINE OF ROAD
ADJACENT PROPERTY LINE /
RIGHT-OF-WAY
EXISTING CONTOUR LINE
EXISTING PATH OF TRAVEL • • ______ •• ______
EXISTING MAJOR DRAINAGE
BASIN BOUNDARY
EXISTING IMPERVIOUS AREA V/V i//// >
BASIN -AREA CALCULATIONS
TOTAL BASIN AREA 10,811 SF(0.25AC)
BASIN EXISTING IMPERVIOUS AREA 6,389 SF (0. I5AC)
**BASIN EXISTING PERVIOUS PAVEMENT 0 SF
BASIN EXISTING PERVIOUS AREA 4,422 SF (0. IOAC)
% IMPERVIOUS 59.1%
Cn 0.63
EXISTING HYDROLOGY EXHIBIT
REDWOOD HOMES - 3861 GARFIELD STREET
CITY OF CARLSBAD
PASCO LARET SUITER
& A88OCIATE CML mernINs + LAND PLAISNIND + lAND IUlVtYlNS
MI Nwlh NDjb., ill. It. A. kls P..th. CL M171
pIIS.2I.M13 I ft.2fl.4S13 I t.
0
RED WOOD AVENUE
0
NODE 101
Q100=1.04 CFS
F
NODE 100
ELEV=640
/,•',, ///// -
PLAN VIEW - EXISTING NODE MAP
SCALE: 1=20'
PLSA 2889-01
PROPOSED HYDROLOGY EXHIBIT
REDWOOD HOMES — 3861 GARFIELD STREET
LEGEND
PROPERTY BOUNDARY —
CENTERLINE OF ROAD
ADJACENT PROPERTY LINE!
RIGHT-OF-WAY
EXISTING CONTOUR LINE
PROPOSED PATH OF TRAVEL • -•
PROPOSED MAJOR DRAINAGE
BASIN BOUNDARY
PROPOSED IMPERVIOUS AREA
BASIN A - AREA CALCULATIONS
TOTAL BASINAREA 10,811 SF (0.25AC)
BASIN PROPOSED IMPERVIOUSAREA 8,227 SF (0.19 AC)
**BASIN PROPOSED PERVIOUS PAVEMENT 0 SF
BASIN PROPOSED PER VIOUS AREA 2,584 SF (0.06 AC)
% IMPERVIOUS 76.1%
Cn 0.74
PROPOSED HYDROLOGY EXHIBIT
REDWOOD HOMES - 3861 GARFIELD STREET
CITY OF CARLSBAD
PLAN VIEW- PROPOSED NODE MAP
SCALE: 1"=20'
& ASSOCIATES
IL ThSINWINS + lAND PIANNINS + lAND DURYtYINS
Itk Hlvq ill. IN A. kki usa. C Sfl
SN.2.S212 I US.2I.4S12 I j't.r
PLSA 2889-01
/ /
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EV=65.6
/
100
65.8
'ECT
TI ! !1•J1I :xi ii:T
PROPERTY BOUNDARY - -
CENTERLINE OF ROAD
ADJACENT PROPERTY LINE /
RIGHT-OF-WAY
EXISTING CONTOUR LINE
PROPOSED PATH OF TRAVEL
PROPOSED MAJOR DRAINAGE
BASIN BOUNDARY
BASIN AREA
LIBASINA -AREA CALCULATIONS
TOTAL BASIN AREA 252,297 SF (5.792 AC)
Cn 0.58
STREET FLOW NODE MAP EXHIBIT
REDWOOD HOMES - 3861 GARFIELD STREET
CITY OF CARLSBAD
PLAN VIEW- STREETFLOWNODE MAP
SCALE: 1"=50'
'S
GRAPHIC SCALE: 1" = 50' PASCO IARET SUITER
& ASSOCIATES
YIL EMINERINU + LAND PIMNINQ + LAND IURVEYINO
UI Norik 1flk1, 101. No A lokas BnCb6 CL U075
ph IMi!I.I212 $ it 151.23L4$12 I
****************************************************************************
HYDRAULIC ELEMENTS
- I PROGRAM PACKAGE
(C) Copyright 1982-2016 Advanced Engineering Software (aes)
Ver. 23.0 Release Date: 07/01/2016 License ID 1452
Analysis prepared by:
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TIME/DATE OF STUDY: 10:20 06/19/2019
Problem Descriptions:
Check Depth of Flow in 0.5% Street
Q100 = 5.08 cfs
****************************************************************************
I >>>>STREETFLOW MODEL INPUT INFORMATION<<<<
----------------------------------------------------------------------------
CONSTANT STREET GRADE(FEET/FEET) = 0.005000
CONSTANT STREET FLOW(CFS) = 5.08 I AVERAGE STREETFLOW FRICTION FACTOR(MANNING) = 0.015000
CONSTANT SYMMETRICAL STREET HALF-WIDTH(FEET) = 30.00
DISTANCE FROM CROWN TO CROSSFALL GRADEBREAK(FEET) = 20.00 I INTERIOR STREET CROSSFALL(DECIMAL) = 0.020000
OUTSIDE STREET CROSSFALL(DECIMAL) = 0.020000
CONSTANT SYMMETRICAL CURB HEIGHT(FEET) = 0.50
I CONSTANT SYMMETRICAL GUTTER-WIDTH(FEET) 1.50
CONSTANT SYMMETRICAL GUTTER-LIP(FEET) = 0.03000
CONSTANT SYMMETRICAL GUTTER-HIKE(FEET) = 0.12500
I FLOW ASSUMED TO FILL STREET EVENLY ON BOTH SIDES
STREET FLOW MODEL RESULTS:
----------------------------------------------------------------------------
STREET FLOW DEPTH(FEET) = 0.36
HALFSTREET FLOOD WIDTH(FEET) = 11.74
AVERAGE FLOW VELOCITY(FEET/SEC.) = 1.70
PRODUCT OF DEPTH&VELOCITY = 0.61
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Chapter 2. Street Drainage and Inlets
LT = length of clear opening of inlet for total interception (ft).
For the minimum required efficiency of E=0.85, this general equation reduces to the following
expression:
L085 = 0.65LT (2-5)
Step 3. Calculate the amount of flow intercepted by the inlet and the bypass flow, and apply
to the bypass flow to the roadway flow calculations and inlet capacity calculations
downstream.
QJNTERCEPT = EQApPoAcH (2-6)
QBYPASS = QAPPROACH - QINTERCEPT = (1 - E) QAPPROACH (2-7)
I Curb Inlets in Sag
Curb inlets in sags or sump locations operate as weirs at shallow depths, and operate as orifices as
water depth increases. The designer shall estimate the capacity of the inlet under each condition
I and adopt a design capacity equal to the smaller of the two results. When designing the size of a
facility, the designer shall use the larger of the sizes obtained by solving for the two conditions.
I Inlets in sumps act as weirs for shallow depths, which can be described using Equation 2-8:
Q=CLd312 (2-8)
where.
Q = inlet capacity (fi3/s);
Cw = weir discharge coefficient (see Table 2-1)
Lw = weir length (ft); and
d = flow depth (ft).
Table 2-I presents appropriate weir coefficient values and lengths for various inlet types.
At higher flow depths, curb inlets operate in a manner more typical of an orifice (Equation 2-9).
Q = 0.67hL(2gd0)1/2 (2-9)
where
Q = inlet capacity (ft3/s);
h = curb opening height (ft);
L = curb opening length (ft);
g = gravitational acceleration (ft2/s); and
d0 = effective depth of flow at curb face (11).
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Page 2-6 San Diego County Hydraulic Design Manual
September 2014
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Chapter 2. Street Drainage and Inlets
Table 2-1 Weir Coefficients for Inlets in Sag Locations
Inlet Type Coefficient Weir Length Equation Valid
cw LW
Grate Inlet Against Curb 3.00 L + 2W (1) d <1.79(A0 /L)
Grate Inlet, Flow from All Sides 3.00 2(L + W) (1) d <1.79(4/Lw )
Curb Opening Inlet 3.00 L' d < h
Depressed Curb Opening Inlets Less
than L=12ft2 3.00 L +1.8W d<h
Slotted Inlets 2.48 L (1) d <0.2 ft
(1) Weir length shall be reduced by 50% 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 Inlet").
The width (W) of the curb opening depression is measured perpendicular to the face of the curb opening.
The effective depth of flow at the curb face includes the curb depression, and must be adjusted for
the curb inlet throat configuration. The San Diego Regional Standard curb inlet opening (SD-
RSD No. D-12) has an inclined throat, and therefore the effective depth of flow at the curb face is
given by the expression:
d0 =(y+a)— sin 9 (2-10)
where
y = depth of flow in adjacent gutter (ft);
a = curb inlet depression (ft);
(h/2) sin O= adjustment for curb inlet throat width (h) and angle of throat incline (0. For a
standard 6-inch curb inlet opening with a 4-inch depression (SD-RSD No. D-12),
(h/2) sin 9"3.l inches (0.26 ft).
Table 2-2 presents appropriate orifice coefficient values and lengths for various inlet types. In
general, if an inlet is functioning as an orifice, the depth of flow is very deep and it is
recommended that the design of the inlet be re-considered to avoid this condition.
2.3.2.2 Grated Inlets
Grated Inlets on Grade
The capture efficiency of grated inlets on grade depends on the width and length of the grate and
the velocity of the flow approaching the grate. When the approaching flow velocity is slow and
the flow width does not exceed the grate width, the grate inlet might be able to intercept all of the
approaching flow. In cases where the width of the approaching flow exceeds the grate width,
very little of the approaching flow that exceeds the grate width will be intercepted by the inlet.
When the velocity of the approaching flow is too high, the flow will "splash over" the grate.
Both these phenomena contribute to flow bypass of grate inlets, which is analogous to the bypass
flow discussed in relation to curb opening inlets on grade.
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San Diego County Hydraulic Design Manual Page 2-7
September 2014