HomeMy WebLinkAboutMS 04-07; 952 PINE AVENUE CONDOMINIUMS; STORMWATER MANAGEMENT PLAN AND STORMWATER MAINTENANCE PLAN; 2004-09-28STORMWATER MANAGEMENT PLAN
STORMWATER MAINTENANCE PLAN
952 PINE AVENUE CONDOMINIUMS
CITY OF CARLSBAD
Prepared for:
4 Design Architecture & Planning
719 Pier View Way
Oceanside, CA 92054
Prepared by:
bkA. Inc.
land planning, civil engineering, surveying
5115 Avenida Encinas, Suite L
Carlsbad, CA 92008-4387
(760) 931-8700
September 28, 2004
W.O. 710-0964-400, BR
TABLE OF CONTENTS
1. INTRODUCTION ..........................................1
1.1 Project Description ............................................1
1.1.1. Hydrologic Unit Contribution ...............................1
1.1.2. BENEFICIAL USES ........................................1
1.1.2.1.Ground Water Uses .......................................3.
2.CHARACTERIZATION OF P ROJECT RUNOFF .................3
2.1. Expected Discharges .........................................3
IDENIFY CONDITIONS OF CONCERN........................3
Mitigation Measures to Protect Water Quality .....................4
4.1. Construction BMPs .........................................4
4.2 Post-construction BMPs .....................................4
5.Ope ration and Maintenance Program ..............................5
6.REFERENCES ................................................6
ATTACHMENTS
Location Map
Water Quality Standards Inventory Database
Numeric Sizing of BMPS
Storm Water Requirements Applicability Checklist
Site Map
Hydrology and Hydraulic Report
1. INTRODUCTION
A Standard Urban Storm Water Mitigation Plan (SUSMP) is required under the City of
Carlsbad ordinances. The purpose of this SUSMP is to address the water quality impacts from
the proposed condominium conversion for 952 Pine Avenue in the City of Carlsbad. The goal
of the SUSMP is to develop and implement practicable policies to ensure to the maximum
extent practicable that development does not increase pollutant loads from the project site and
considers urban runoff flow rates and velocities. Best Management Practices (BMPs) will be
utilized to provide a long-term solution to water quality. The SUSMP identifies appropriate
BMPs for certain designated project types to achieve this goal. This SUSMP is intended to
ensure the effectiveness of the BMPs through maintenance that is based on long-term
planning.
1.1 Project Description
The property is in the City of Carlsbad, at 952 Pine Avenue, west of Harding Street.
The existing site has a four-unit apartment building located on-site. The four unit apartment
building is being converted to condominiums. Runoff from the site sheet flows toward the
southwesterly corner, via an existing concrete swale, where an existing catch basin intercepts
the runoff. The runoff is then conveyed into the street gutter of Pine Avenue via two 3-inch
sidewalk underdrain pipes. A portion of the property to the east drains onto the subject
property, crossing an existing wooden fence.
After the apartment building is to condominiums, runoff from the site will surface drains in a
similar manner to the existing drainage runoff. The existing catch basin will be replaced with
a Swalegard swale filter by Kristar Enterprises Inc. The runoff will then be conveyed to the
street gutter via the existing two 3-inch sidewalk underdrain pipes. The condominium
conversion will not affect the existing drainage pattern from the property to the east. The
portion of the property to the east will continue to drain on-site.
1.1.1. Hydrologic Unit Contribution
The project falls within the Buena Vista Lagoon Coastal Outfall Hydrologic Unit Basin
Number 904.21. The total watershed size for Buena Vista Lagoon Basin is approximately 21.8
square miles or 13,926 acres, of which the site is composed of 0.43 acres, or 0.003 percent.
1.1.2. Beneficial Uses
The beneficial uses for the Buena Vista Lagoon Coastal Outfall Hydrologic Unit Basin
Number 904.21 are included in Table 1.2.3. This table has been extracted from the Water
Quality Control Plan for the San Diego Basin.
REC1 - Includes uses of water for recreational activities involving body contact with water,
where ingestion of water is reasonably possible. These uses include, but are not limited to,
swimming, wading, water-skiing, skin and scuba diving, surfing, white water activities, fishing,
or use of natural hot springs.
REC2 - Includes the uses of water for recreational involving proximity to water, but not
normally involving body contact with water, where ingestion of water is reasonably possible.
These uses include, but are not limited to, picnicking, sunbathing, hiking, camping, boating,
tide pool and marine life study, hunting, sightseeing, or aesthetic enjoyment in conjunction
with the above activities.
BIOL - Includes uses of water that support designated areas or habitats, such as established
refuges, parks, sanctuaries, ecological reserves, or areas of special biological significance, where
the preservation or enhancement of natural resources requires special protection.
EST - Includes uses of water that support estuarine ecosystems including, but not limited to,
preservation or enhancement or estuarine habitats, vegetation, fish, shellfish, or wildlife (e.g.,
estuarine mammals, waterfowl, shorebirds).
WILD - Includes uses of water that support warm water ecosystems including, but not limited
to, preservation and enhancement of terrestrial habitats, vegetation, wildlife, (e.g., mammals,
birds, reptiles, amphibians, invertebrates), or wildlife water and food sources.
RARE - Includes uses of water that support habitats necessary, at least in part, for the survival
and successful maintenance of plant or animal species established under state or federal law
as rare, threatened or endangered.
MAR - Includes uses Of water that support marine ecosystems including, but not limited to,
preservation or enhancement of marine habitats, vegetation such as kelp, fish, shellfish, or
wildlife (e.g., marine mammals, shorebirds).
WARM - Includes uses of water that support warm water ecosystems including, but not limited
to, preservation or enhancement of aquatic habitats, vegetation, fish or wildlife, including
invertebrates.
Table 1.1.2 Beneficial Uses for Coastal Surface Waters
Hydrologic
Unit
Number
0
ri E
cc
904.21
Buena Vista Lagoon X X X X X 0 X X
Coastal Outfall
X = Existing Beneficial Use
0 = Potential Beneficial Use
2
1.1.2.1. Ground Waters
There are no beneficial uses of ground water in Buena Vista Lagoon Coastal Outfall
Hydrologic Unit Basin Number 904.21. S
2. CHARACTERIZATION OF PROJECT RUNOFF
According to the 2002 CWA section 303(d) List of Water Quality Limited, Buena Vista
Lagoon Coastal Outfall Hydrologic Unit Basin Number 904.21 is impaired by Bacteria
Indicators, Nutrients, and Sedimentation/Siltation. See Attachment "B" for the 2002 CWA
Section 303(d) List of Water Quality Limited Segment List. Buena Vista Lagoon is located
approximately 1.4 miles downstream from the project site.
2.1 Expected Discharges
There is no sampling data available for the existing site condition. In addition, the project is
not expected to generate significant amounts of non-visible pollutants. However, the following
constituents listed in Table 2.1 below are commonly found on similar developments and could
contribute to impairment of Buena Vista Lagoon:
Table 2.1 - Pollutants from Pine Avenue Condominium Project
General Pollutants Categories
Project Categories to
a)
U)
. a)
. E
a i5 ti . .
00 -
C,) Z 00 H 0c' 0
Attached Residential X X X X X X X
X - Anticipated
3. IDENTIFY CONDITIONS OF CONCERN
The conversion of the apartments to condominiums at 952 Pine Avenue will not impact the
downstream water body of the Buena Vista Lagoon, or it's habitat integrity. There will be no
change in the vicinities priority hydrologic regime that would be considered a condition of
concern for the downstream water bodies and habitat integrity. The existing facilities (e.g.,
storm drain) and source control BMPs (e.g., landscaping) remove sediment and pollutants of
concern to the maximum extent practicable. See Attachment "D" for hydrologic and hydraulic
analysis of existing and proposed project site.
ki
4. MITIGATION MEASURES TO PROTECT WATER QUALITY
4.1 Construction BMPs
A detailed description of the construction BMPs will be developed during the Grading Plan
and Improvement Plan Engineering. Since the project is in the preliminary development
phase, only a listing of potential types of temporary BMPs are available. This includes the
following:
. Silt fence
Stockpile management
. Solid Waste management
Stabilized construction entrance/exit
Vehicle and equipment maintenance
Desilting basin
Gravel bag berm
Gravelbag barrier
Material spill prevention and Control
Spill prevention and control
Concrete waste management
Water conservation practices
Dust controls
Permanent revegetation of all disturbed
areas
Material delivery and storage . Sediment traps on graded building pads
Scheduling construction project to reduce the amount and duration of soil exposed to
erosion by wind, rain, runoff and vehicle parking.
Construction BMPs for this project will be selected, constructed, and maintained so as to
comply with all applicable ordinances and guidance documents. The Contractor on site will
be responsible for implementing and maintaining the BMPs.
4.2 Post-construction BMPs
952 Pine Avenue is an Attached Residential Development Priority Project. Storm Water
BMPs requirements are as follows:
(1) Site Design BMPs
Control post-development peak storm runoff discharge rates and velocities to maintain or
reduce pre-development downstream erosion by applying the following BMPs.
Minimize impervious footprints (See Site Map).
Minimize directly connected impervious areas by draining roof tops and patios
into adjacent landscaping. (See Site Map).
Maximize canopy interception and water conservation by planting additional
native or drought tolerant trees and large shrubs.
Convey runoff safely from tops of slopes (See Site Map).
Vegetate slopes with native or drought tolerant vegetation (See Site Map).
(2) Source Control BMPs:
4
Use efficient irrigation systems.
Trash enclosures will be paved with impervious surface and designed not to allow
run-on from adjoining areas. Walled enclosures will prevent off-site transport of
trash. Lids on all trash enclosures will exclude rain, or a roof or awning to
minimize direct precipitation.
BMPs Applicable to Individual Priority Project Categories:
A. Runoff from the 952 Pine Avenue Condominium project will be treated with a
Swalegard grassy swale filter by Kristal Enterprises Inc. See Treatment Control
BMPs for discussion of Swalegard grassy swale filter.
Treatment Control BMPs:
A. Runoff from the 952 Pine Avenue will be treated with a Swalegard grassy swale
filter by Kristar Enterprises Inc. The Swalegard grassy swale filter is a self-
contained filter designed to collect sediment, debris and petroleum hydrocarbons
from stormwater runoff. The unit is sized based on a rainfall intensity of 0.2 inches
of rainfall per hour for each hour of a storm event. See Attachment "C" for sizing
of Treatment Control BMPs and removal efficiency.
Placement of the Post-Construction BMPs are noted on Attachment "D" - Site Map.
The conversion of the apartments buildings to condominiums at 952 Pine Avenue will not
impact the downstream water bodies and habitat integrity. There will be no change in the
vicinities priority hydrologic regime that would be considered a condition of concern for the
downstream water bodies and habitat integrity. The proposed BMPs will remove sediment and
pollutants of concern to the maximum extent practicable.
5. OPERATION AND MAINTENANCE PROGRAM
A stormwater facilities maintenance agreement with the proponent of 952 Pine Avenue will
be used to maintain and repair the stormwater management facilities mention in this SUSMP.
The stenciling and signage of the existing public storm water conveyance system will be the
responsibility of the City of Carlsbad. The average annual cost for installation and
maintenance of landscaping will be $300 per acre. Landscaping, seeding and mulching will cost
$1,100 per acre. Trees, shrubs, vines and ground cover costs are based on species used.
Annual operation and maintenance cost for the Swalegard filter is $300.00.
6. REFERENCES.
Water Quality Control Plan for the San Diego Basin (9) California Regional Water Quality
Control Board, San Diego Region, September 8, 1994
County of San Diego Stormwater Management Requirements and Guidelines 2000-2001
California Stormwater Best Management Practice Handbook, Municipal, March 1993
1998 California 303 (d) List and TMDL Schedule approved by USEPA, May 12, 1999
City of Carlsbad, Standard Urban Storm Water Mitigation Plan, November 2003
ATTACHMENT "A"
LOCATION MAP
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WATER QUALITY STANDARDS INVENTORY DATABASE
ATTACHMENT "C"
NUMERIC SIZING OF BMPS
85TH PERCENTILE STORM WATER RUNOFFF
Pine Avenue Condominiums
City of Carlsbad
Where:
Q = Flow rate per cubic feet (cfs)
C = weighted runoff coefficient of drainage area
= Rainfall intensity in Inches per hour (0.2 lnhr)
= Drainage area (acres)
0.5
See Grassy Swale Hydraulic Calculations or 85th Percentile Storm Event and
100 Year Storm Event after this sheet.
Page 1 of I
AFACHMENT "D"
STORM WATER REQUIREMENTS APPLICABILITY CHECKLIST
Storm Water Standards
4/03/03
VI. RESOURCES & REFERENCES
APPENDIX A
STORM WATER REQUIREMENTS APPLICABILITY CHECKLIST
Complete Sections 1 and 2 of the following checklist to determine your project's
permanent and construction storm water best management practices requirements.
This form must be completed and submitted with your permit application.
Section 1. Permanent Storm Water BMP Requirements:
If any answers to Part A are answered "Yes," your project is subject to the "Priority
Project Permanent Storm Water BMP Requirements," and "Standard Permanent Storm
Water BMP Requirements" in Section III, "Permanent Storm Water BMP Selection
Procedure" in the Storm Water Standards manual.
If all answers to Part A are "No," and any answers to Part B are "Yes," your project is
only subject to the "Standard Permanent Storm Water BMP Requirements". If every
question in Part A and B is answered "No," your project is exempt from permanent
storm water requirements.
Part A: Determine Priority Project Permanent Storm Water BMP Requirements.
Does the project meet the definition of one or more of the priority project
categories?* es N 0
Detached residential development of 10 or more units . -
Attached residential development of 10 or more units . _><
3., Commercial development greater than 100,000 square feet
Automotive repair shop -
Restaurant
Steep hillside development greater than 5,000 square feet -
Project discharging to receiving waters within Environmentally Sensitive Areas - -
Parking lots greater than or equal to 5,000 ft' or with at least 15 parking spaces, and
potentially exposed to urban runoff -
Streets, roads, highways, and freeways which would create a new paved surface that is
5,000 square feet or greater
* Refer to the definitions section in the Storm Water Standards for expanded definitions of the priority
project categories.
Limited Exclusion: Trenching and resurfacing work associated with utility projects are not considered
priority projects. Parking lots, buildings and other structures associated with utility projects are
priority projects if one or more of the criteria in Pan A is met. If all answers to Part A are "No",
continue to Part B.
30
Storm Water Standards
4/03/03
Part B: Determine Standard Permanent Storm Water Requirements.
Does the project propose: Yes No
New impervious areas, such as rooftops, roads, parking lots, driveways, paths and
sidewalks?
- -
New pervious landscape areas and irrigation systems?
Permanent structures within 100 feet of any natural water body?
Trash storage areas? -
Liquid or solid material loading and unloading areas? -
Vehicle or equipment fueling, washing, or maintenance areas? -
Require a General NPDES Permit for Storm Water Discharges Associated with
Industrial Activities (Except construction)?
Commercial or industrial waste handling or storage, excluding typical office or
household waste?
-
Any grading or ground disturbance during construction?
Any new storm drains, or alteration to existing storm drains? - -
'To find out if your project is required to obtain an individual General NPDES Permit for Storm Water
Discharges Associated with Industrial Activities, visit the State Water Resources Control Board web site
at, www.swrcb.ca.gov/stormwtr/industrial.html
Section 2. Construction Storm Water BMP Requirements:
If the answer to question I of Part C is answered "Yes," your project is subject to
Section IV, "Construction Storm Water BMP Performance Standards," and must prepare
a Storm Water Pollution Prevention Plan (SWPPP). If the answer to question I is "No,"
but the answer to any of the remaining questions is "Yes," your project is subject to
Section IV, "Construction Storm Water BMP Performance Standards," and must prepare
a Water Pollution Control Plan (WPCP). If every question in Part C is answered "No,"
your project is exempt from any construction storm water BMP requirements. If any of
the answers to the questions in Part C are "Yes," complete the construction site
prioritization in Part D, below.
C. r)ptprminp Cnnstrtution Phase Storm Water Requirements.
Would the project meet any of these criteria during construction? Yes No
Is the project subject to California's statewide General NPDES Permit for Storm Water -
Discharges Associated With Construction Activities? -
Does the project propose grading or soil disturbance? -
Would storm water or urban runoff have the potential to contact any portion of the
construction area, including washing and staging areas? - -
Would the project use any construction materials that could negatively affect water
quality if discharged from the site (such as, paints, solvents, concrete, and
stucco)?
31
Storm Water Standards
4/03/03
Part D: Determine Construction Site Priority
In accordance with the Municipal Permit, each construction site with construction storm
water BMP requireme.nts must be designated with a priority: high, medium or low.
This prioritization must be completed with this form, noted on the plans, and included in
the SWPPP or WPCP. Indicate the project's priority in one of the check boxes using the
criteria below, and existing and surrounding conditions of the project, the type of
activities necessary to complete the construction and any other extenuating
circumstances that may pose a threat to water quality. The City reserves the right to
adjust the priority of the projects both before and during construction. [Note:
The construction priority does NOT change construction BMP requirements that apply
to projects; all construction BMP requirements must be identified on a case-by-case
basis. The construction priority does affect the frequency of inspections that will be
conducted by City staff. See Section lV.1 for more details on construction BMP
requirements.]
Li A) High Priority
Projects where the site is 50 acres or more and grading will occur during the
rainy season
Projects 5 acres or more. 3) Projects 5 acres or more within or directly
adjacent to or discharging directly to a coastal lagoon or other receiving water
within an environmentally sensitive area
Projects, active or inactive, adjacent or tributary to sensitive water bodies
,' B) Medium Priority
• •• 1). Capital Improvement Projects where grading occurs, however a Storm Water
Pollution Prevention Plan (SWPPP) is not required under the State General
Construction Permit (i.e., water and sewer replacement projects, intersection
and street re-alignments, widening, comfort stations, etc.)
2) Permit projects in the public right-of-way where grading occurs, such as
installation of sidewalk, substantial retaining walls, curb and gutter for an
entire street frontage, etc. , however SWPPPs are not required.
3) Permit projects on private property where grading permits are required,
however, Notice Of Intents (NOls) and SWPPPs are not required.
Li C) Low Priority
Capital Projects where minimal to no grading occurs, such as signal light and
loop installations, street light installations, etc.
Permit projects in the public right-of-way where minimal to no grading occurs,
• such as pedestrian ramps, driveway additions, small retaining walls, etc.
3) Permit projects on private property where grading permits are not required,
such as small retaining walls, single-family homes, small tenant
improvements, etc. •
32
ATTACHMENT "E"
SITE MAP
\-
20 10 0 20 40 60
SCALE: 1" = 20'
SITE MAJP
952 PINE A VENUE
CITY OF CARLSBAD
LEGEND
(TYPICAL LOCATION OF BMPs SHOWN ON PLAN)
CONSTRUCTION BMPS POST-DEVELOPMENT BMPS
GRA VEL BAGS (E5C52) ---- ® SWALEGARD S WALE FILTER 0
STABILIZED ENTRANCE (ESc24) çscg
(3 SILT FENCES (ESC50) ° 0- MAINTENANCE AND EDUCATION PROGRAMS NOT SHOWN ON PLAN
\ \ LANDSCAPE MAINTENANCE
STORM DRAIN INLET PROTEC77ON (ESC54) 41142 HOMEOWNER EDUCA liON
NON POLLUTANT FERTILIZER
DESIGNATED CONSTRUCTION MATERIAL MANAGEMENT
________71 __
7 AREA AND CONTRACTOR TRAINING (CA20 & CA21) SURFACE NODE PER PROPOSED HYDROLOGY MAP 30
7 STORM WA TER TREA TMEN T (cFs) 01
'7 RUNOFF PRODUCED FROM A RAINFALL INTENSITY
OF 02 INCH OF RAINFALL PER HOUR FOR EACH
HOUR OF A STORM EVENT
xz-
'7
0011
17'
7'
'77 '7 '7
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SITE MAP
Inc.
land planning, cMl engineering, surveying
5115 AVENIDA ENCINAS
SUITE "L"
CARLSBAD, CA. 92008-4387
(760) 931-8700
;1 7 i 0-5957 400 0 1'F \ .5 WM \ 7 0 0.564 - S 75)70. ciwq 09j29/5)70 00: 5 70 A F F) I
ATTACHMENT "F"
HYDROLOGY AND HYDRAULIC REPORT
HYDROLOGY and HYDRAULIC REPORT
952 PINE AVENUE CONDOMINIUMS
, CITY OF CARLSBAD
Prepared for:
4 Design Architecture & Planning
719 Pier View Way
Oceanside, CA 92054
Prepared by:
bhA, Inc.
land planning, civil engineering, surveying
5115 Avenida Encinas, Suite L
Carlsbad, CA 92008-4387
(760) 931-8700
September 28, 2004
W.O. 710-0964-400, BR
TABLE OF CONTENTS
Discussion: Purpose and Scope
Project Description
Study Method
Conditions of Concern
Conclusions
H. Calculations
Existing Hydrology
Proposed Hydrology
Ill. Exhibits
Existing Hydrology Map
Proposed Hydrology Map
IV. References
I. DISCUSSION
PURPOSE AND SCOPE:
The purpose of this report is to publish the results of hydrology and hydraulic computer
analysis for the proposed condominium conversion for 952 Pine Avenue. The scope is to study
the existing and proposed hydrology and hydraulics as it influences existing storm drain
facilities in the vicinity during a 100-year frequency storm event.
PROJECT DESCRIPTION:
The existing site has a four-unit apartment building located on-site. The four unit apartment
building is being converted to condominiums. Runoff from the site sheet flows toward the
southwesterly corner, via an existing concrete swale, where an existing catch basin intercepts
the runoff. The runoff is then conveyed into the street gutter of Pine Avenue via two 3-inch
sidewalk underdrain pipes. A portion of the property to the east drains onto the subject
property, crossing .an existing wooden fence. See Exhibit "A" for existing hydrology.
After the apartment building is to condominiums, runoff from the site will surface drains in a
similar manner to the existing drainage runoff. The existing catch basin will be replaced with
a Swalegard swale filter by Kristar Enterprises Inc. The runoff will then be conveyed to the
street gutter via the existing two 3-inch sidewalk underdrain pipes. The, condominium
conversion will not affect the existing drainage pattern from the property to the east. The
portion of the property to the east will continue to drain on-site. See Exhibit "B" for proposed
hydrology.
STUDY METHOD:
The method of analysis was based on the Rational Method according to the San Diego County
Hydrology Manual. The Hydrology and Hydraulic Analysis were done on HydroSoft by
Advanced Engineering Software.
Drainage basin areas were determined from the proposed grades shown on the Tentative
Parcel Map for the property.
The Rational MethOd provided the following variable coefficients:
Soil group B will be used for a composite runoff coefficient for the existing and proposed
hydrology analyses. The runoff coefficient (C=0.51) for attached residential land use reflects
a composite value of landscaping, roof and street runoff per County of San Diego Hydrology
Manual County.
Initial Time of concentration (in minutes) = Ti = 60x(11.9x(L'' 3)/H) ^ 0.385
Rainfall Intensity = I = 7.44x(P6)x(Tc) " 0.645
P6 for 100 year storm = 2.5
CONDITIONS OF CONCERN:
The conversion of the four apartment units to condominiums at 952 Pine Avenue will not
impact the downstream water bodies or their habitat integrity. There will be no change in-the
vicinities priority hydrologic regime that would be considered a condition of concern for the
downstream water bodies and habitat integrity.
See Table 1.1 below comparing existing and proposed storm drain flows.
Table 1.1
Existing and Proposed Storm Drain Flows
I Cumulative Nodes
Flow (cfs)
Existing Condition 1.3 50.1
See Exhibit "A"
Proposed Condition 1.3 50.1
See Exhibit "B"
CONCLUSION:
The existing and proposed storm drain system for 912 Pine Avenue Condominiums adequately
convey a 100-year frequency storm event, and will not affect the existing drainage patterns.
II. CALCULATIONS
II. CALCULATIONS
A. EXISTING HYDROLOGY
************************************************************************* ***
RATIONAL METHOD HYDROLOGY COMPUTER PROGRAM PACKAGE
Reference: SAN DIEGO COUNTY FLOOD CONTROL DISTRICT
2003, 1985, 1981 HYDROLOGY MANUAL
(c) Copyright 1982-2003 Advanced Engineering Software (aes)
Ver. 1.5A Release Date: 01/01/2003. License ID 1459
Analysis prepared by:
bHA, Inc.
5115 Avenida Encinas, Suite L
Carlsbad, Calif 92008
************************** DESCRIPTION OF STUDY **************************
* EXISTING HYDROLOGY . *
* *
* . *
FILE NAME: 964-E1.DAT
TIME/DATE OF STUDY: 08:47 09/28/2004
USER SPECIFIED HYDROLOGY AND HYDRAULIC MODEL INFORMATION: ----------------------------------------------------------------------------
2003 SAN DIEGO MANUAL CRITERIA
USER SPECIFIED STORM EVENT(YEAR) = 100.00
6-HOUR DURATION PRECIPITATION (INCHES) = 2.500
SPECIFIED MINIMUM PIPE SIZE(INCH) = 3.00
SPECIFIED PERCENT OF GRADIENTS (DECIMAL) TO USE FOR FRICTION SLOPE = 0.90
SAN DIEGO HYDROLOGY MANUAL "C"-VALUES USED FOR RATIONAL METHOD
NOTE: USE MODIFIED RATIONAL METHOD PROCEDURES FOR CONFLUENCE ANALYSIS
*USER_DEFINED STREET-SECTIONS FOR COUPLED PIPEFLOW AND STREETFLOW MODEL*
HALF-* CROWN TO STREET-CROSSFALL: CURB GUTTER-GEOMETRIES: MANNING
WIDTH CROSSFALL IN- / OUT-/PARK-. HEIGHT WIDTH LIP HIKE FACTOR
NO. (FT) (FT) SIDE / SIDE/ WAY (FT) (FT) (FT) (FT) (n)
1 30.0 20..0 0.018/0.018/0.020 . 0.67 2.00 0.0313 0.167 0.0150
GLOBAL STREET FLOW-DEPTH CONSTRAINTS:
Relative Flow-Depth = 0.00 FEET
as (Maximum Allowable Street Flow Depth) - (Top-of-Curb)
(Depth)* (Velocity) Constraint = 6.0 (FT*FT/S)
*SIZE PIPE WITH A FLOW CAPACITY GREATER THAN
OR EQUAL TO THE UPSTREAM TRIBUTARY PIPE.*
****** ********************************+* ****************************** ******
FLOW PROCESS FROM NODE 10.00 TO NODE 20.00 IS CODE = 21 ------------------------------------------------------------------------
>>>>>RATIONAL. METHOD INITIAL SUBAREA ANALYSIS<<<(< .
RESIDENTAIL (7.3 DU/AC OR LESS) RUNOFF COEFFICIENT .5100
SOIL CLASSIFICATION IS "B"
S.C.S. CURVE NUMBER (AMC II) = 76
1
INITIAL SUBAREA FLOW-LENGTH(FEET) = 78.00
UPSTREAM ELEVATION(FEET) = 65.30
DOWNSTREAM ELEVATION(FEET) = 64.90
ELEVATION DIFFERENCE(FEET) = 0.40
SUBAREA OVERLAND TIME OF FLOW(MIN.) = 9.418
WARNING: INITIAL SUBAREA FLOW PATH LENGTH IS GREATER THAN
THE MAXIMUM OVERLAND FLOW LENGTH = 50.38
(Reference: Table 3-15 of Hydrology Manual)
THE MAXIMUM OVERLAND FLOW LENGTH IS USED IN Tc CALCULATION!
100 YEAR RAINFALL INTENSITY(INCH/HOUR) = 4.378
SUBAREA RUNOFF(CFS) = 0.11
TOTAL AREA(ACRES) = 0.05 TOTAL RUNOFF(CFS) 0.11
FLOW PROCESS FROM NODE 20.00 TO NODE 50.00 IS CODE = 53.
>>>>>COMPUTE TRAPEZOIDAL CHANNEL FLOW<<<(<
>>>>>TRAVELTIME THRU SUBAREA (EXISTING ELEMENT)<<<<<
ELEVATION DATA: UPSTREAM(FEET) = 64.90 DOWNSTREAM(FEET) = 64.00
CHANNEL LENGTH THRU SUBAREA(FEET) = 192.00 CHANNEL SLOPE = 0.0047
CHANNEL BASE(FEET) = 0.00 "Z" FACTOR = 10.000
MANNING'S FACTOR = 0.015 MAXIMUM DEPTH(FEET) = 0.50
100 YEAR RAINFALL INTENSITY(INCH/HOUR) = 3.691
RESIDENTAIL (7.3 DO/AC OR LESS) RUNOFF COEFFICIENT = .5100
SOIL CLASSIFICATION IS "B"
S.C.S. CURVE NUMBER (AMC II) = 76
TRAVEL TIME COMPUTED USING ESTIMATED FLOW(CFS) = 0.20
TRAVEL TIME .THRU SUBAREA BASED ON VELOCITY(FEET/SEC.) = 1.12
AVERAGE FLOW DEPTH(FEET) = 0.13 TRAVEL TIME(MIN.) = 2.86
Tc(MIN.) = 12.27
SUBAREA AREA(ACRES) = 0.09 SUBAREA RUNOFF(CFS) = 0.17
AREA-AVERAGE RUNOFF COEFFICIENT = 0.510
TOTAL AREA(ACRES) = 0.14 PEAK FLOW RATE(CFS) = 0.26
END OF SUBAREA CHANNEL FLOW HYDRAULICS:
DEPTH(FEET) = 0.15 FLOW VELOCITY(FEET/SEC.) = 1.21
LONGEST FLOWPATH FROM NODE 10.90 TO NODE 50.00 = 270.00 FEET.
FLOW PROCESS FROM NODE 50.00 TO NODE 50.00 IS CODE = 1 ----------------------------------------------------------------------------
>>>>>DESIGNATE INDEPENDENT STREAM FOR CONFLUENCE<<<<<
TOTAL NUMBER OF STREAMS = 2 S
CONFLUENCE VALUES USED FOR INDEPENDENT STREAM 1 ARE:
TIME OF CONCENTRATION(MIN.) = 12.27
RAINFALL INTENSITY(INCH/HR) = 3.69
TOTAL STREAM AREA(ACRES) = 0.14
PEAK FLOW RATE(CFS) AT CONFLUENCE = 0.26
*S•* * * * * ** * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
FLOW PROCESS FROM NODE 30.00 TO NODE 40.00 IS CODE = 21
>>>>>RATIONAL METHOD INITIAL SUBAREA ANALYSIS<<<<<
RESIDENTAIL (7.3 DO/AC OR LESS) RUNOFF COEFFICIENT = .5100
2.
SOIL CLASSIFICATION IS "B"
S.C.S. CURVE NUMBER (AMC II) = 76
INITIAL SUBAREA FLOW-LENGTH(FEET) = 43.00
UPSTREAM ELEVATION(FEET) = 66.10
DOWNSTREAM ELEVATION(FEET) = 65.30
ELEVATION DIFFERENCE(FEET) = 0.80
SUBAREA OVERLAND TIME OF FLOW(MIN.) = 5.662
100 YEAR RAINFALL INTENSITY(INCH/HOUR) = 6.079
SUBAREA RUNOFF(CFS) = 0.12
TOTAL AREA(ACRES) = 0.04 TOTAL RUNOFF(CFS) = 0.12
******* ****************** ***************************************************
FLOW PROCESS FROM NODE 40.00 TO NODE 50.00 IS CODE = 51 ----------------------------------------------------------------------------
>>>>>COMPUTE TRAPEZOIDAL CHANNEL FLOW<<<<<
>>>>>TRAVELTIME THRU SUBAREA (EXISTING ELEMENT)<<<<<
ELEVATION DATA: UPSTREAM(FEET) = 65.30 DOWNSTREAM(FEET) = 64.00
CHANNEL LENGTH THRU SUBAREA(FEET) = 220.00 CHANNEL SLOPE = 0.0059
CHANNEL BASE(FEET) = 1.00 "Z" FACTOR = 50.000
MANNING'S FACTOR = 0.015 MAXIMUM DEPTH(FEET) = 0.50
100 YEAR RAINFALL INTENSITY(INCH/HOUR) = 4.516
RESIDENTAIL (7.3 DU/AC OR LESS) RUNOFF COEFFICIENT = .5100
SOIL CLASSIFICATION IS "B"
S.C.S. CURVE NUMBER (AMC II) = .76
TRAVEL TIME COMPUTED USING ESTIMATED FLOW(CFS) = 0-.62
TRAVEL TIME THRU SUBAREA BASED ON VELOCITY(FEET/SEC.) = 1.11
AVERAGE FLOW DEPTH(FEET) = 0.10 TRAVEL TIME(MIN.) = 3.31
Tc(MIN.) = 8.98
SUBAREA AREA(ACRES) = 0.43 SUBAREA RUNOFF(CFS) = 0.99
AREA-AVERAGE RUNOFF COEFFICIENT = 0.510
TOTAL AREA(ACRES) = 0.47 PEAK FLOW RATE(CFS) = 1.08
END OF SUBAREA CHANNEL FLOW HYDRAULICS:
DEPTH(FEET) = 0.12 FLOW VELOCITY(FEET/SEC.) = 1.20
LONGEST FLOWPATH FROM NODE 30.00 TO NODE 50.00 = 263.00 FEET.
FLOW PROCESS FROM NODE 50.00 TO NODE 50.00 IS CODE = 1
>>>>>DESIGNATE INDEPENDENT STREAM FOR CONFLUENCE<(<<<
>>>>>AND COMPUTE VARIOUS CONFLUENCED STREAM VALUES<<<<<
TOTAL NUMBER OF STREAMS = 2
CONFLUENCE VALUES USED FOR INDEPENDENT STREAM 2 ARE:
TIME OF CONCENTRATION (MIN.) = 8.98
RAINFALL INTENSITY(INCH/HR) = 4.52
TOTAL STREAM AREA(ACRES) = 0.47
PEAK FLOW RATE(CFS) AT CONFLUENCE = 1.08
** CONFLUENCE DATA **
STREAM RUNOFF Tc INTENSITY AREA
NUMBER (CFS) (MIN.) (INCH/HOUR) (ACRE)
1 0.26 12.27 3.691 0.14
2 1.08 8.98 4.516 0.47
RAINFALL INTENSITY AND TIME OF CONCENTRATION RATIO
CONFLUENCE FORMULA USED FOR 2 STREAMS.
** PEAK FLOW RATE TABLE **
STREAM RUNOFF Tc INTENSITY
NUMBER (CFS) (MIN.) (INCH/HOUR)
1 1.28 8.98 4:516
2 1.15 12.27 3.691
COMPUTED CONFLUENCE ESTIMATES ARE AS FOLLOWS:
PEAK FLOW RATE(CFS) = 1.28 Tc(MIN.) = 8.98
TOTAL AREA(ACRES) = 0.61
LONGEST FLOWPATH FROM NODE 10.00 TO NODE 50.00 = 270.00 FEET.
FLOW PROCESS FROM NODE 50.00 TO NODE 50.10 IS CODE = 41
>>>>>COMPUTE PIPE-FLOW TRAVEL TIME THRU SUBAREA<<<<<
>>>>>USING USER-SPECIFIED PIPESIZE (EXISTING ELEMENT)<<<<<
ELEVATION DATA: UPSTREAM(FEET) = 63.00 DOWNSTREAM (FEET) = 62.80
FLOW LENGTH(FEET) = 20.00 MANNING'S N = 0.010
ASSUME FULL-FLOWING PIPELINE
PIPE-FLOW VELOCITY(FEET/SEC.) = 2.45.
(PIPE FLOW VELOCITY CORRESPONDING TO NORMAL-DEPTH FLOW
AT DEPTH = 0.94 * DIAMETER)
GIVEN PIPE DIAMETER(INCH) = 3.00 NUMBER OF PIPES = 2
PIPE-FLOW(CFS) = 1.28
PIPE TRAVEL TIME(MIN.) = 0.14 Tc(MIN.) = 9.11
LONGEST FLOWPATH FROM NODE 10.00 TO NODE 50.10 = 290.00 FEET.
END OF STUDY SUMMARY:
TOTAL AREA(ACRES) = 0.61 TC(MIN.) = 9.11
PEAK FLOW RATE(CFS) = 1.28
END OF RATIONAL METHOD ANALYSIS
4
II. CALCULATIONS
B. PROPOSED HYDROLOGY
RATIONAL METHOD HYDROLOGY COMPUTER PROGRAM PACKAGE
Reference: SAN DIEGO COUNTY FLOOD CONTROL DISTRICT
2003,1985, 1981 HYDROLOGY MANUAL
(c) Copyright 1982-2003 Advanced Engineering Software (aes)
Ver. 1.5A Release Date: 01/01/2003 License ID 1459
Analysis prepared by:
bHA, Inc.
5115 Avenida Encinas, Suite L
Carlsbad, Calif 92008
************************** DESCRIPTION OF STUDY
* PROPOSED HYDROLOGY
*
*
FILE NAME: 964-P1.DAT
TIME/DATE OF STUDY: 17:24 09/28/2004 ----------------------------------------------------------------------------
USER SPECIFIED HYDROLOGY AND HYDRAULIC MODEL INFORMATION: ----------------------------------------------------------------------------
2003 SAN DIEGO MANUAL CRITERIA
USER SPECIFIED STORM EVENT(YEAR) = 100.00
6-HOUR DURATION PRECIPITATION (INCHES) = 2.500
SPECIFIED MINIMUM PIPE SIZE(INCH) = 3.00
SPECIFIED PERCENT OF GRADIENTS(DECIMAL) TO USE FOR FRICTION SLOPE = 0.90
SAN DIEGO HYDROLOGY MANUAL "C"-VALUES USED FOR RATIONAL METHOD
NOTE: USE MODIFIED RATIONAL METHOD PROCEDURES FOR CONFLUENCE ANALYSIS
*USER_DEFINED STREET-SECTIONS FOR COUPLED PIPEFLOW AND STREETFLOW MODEL*
HALF- CROWN TO STREET-CROSSFALL: CURB GUTTER-GEOMETRIES: MANNING
WIDTH CROSSFALL IN- / OUT-/PARK- HEIGHT WIDTH LIP HIKE FACTOR
NO. (FT) (FT) SIDE / SIDE/ WAY (FT) (FT) (FT) (FT) (n)
1 30.0 20.0 0.018/0.018/0.020 0.67 2.00 0.0313 0.167 0.0150
GLOBAL STREET FLOW-DEPTH CONSTRAINTS:
Relative Flow-Depth = 0.00 FEET
as (Maximum Allowable Street Flow Depth) - (Top-of-Curb)
(Depth)*(Velocity) Constraint = 6.0 (FT*FT/S)
*SIZE PIPE WITH A FLOW CAPACITY GREATER THAN
OR EQUAL TO THE UPSTREAM TRIBUTARY PIPE.*
*********************************************************************** *****
FLOW PROCESS FROM NODE 10.00 TO NODE 20.00 IS CODE = 21 ----------------------------------------------------------------------------
>>>>>RATIONAL METHOD INITIAL SUBAREA ANALYSIS<<<<<
RESIDENTAIL (7.3 DU/AC OR LESS) RUNOFF COEFFICIENT = .5100
SOIL CLASSIFICATION IS "B"
S.C.S. CURVE NUMBER (AMC II) = 76
1
INITIAL SUBAREA FLOW-LENGTH(FEET) = 78.00
UPSTREAM ELEVATION(FEET) = 65.30
DOWNSTREAM ELEVATION(FEET) = 64.90
ELEVATION DIFFERENCE(FEET) = 0.40
SUBAREA OVERLAND TIME OF FLOW(MIN.) = 9.418
WARNING: INITIAL SUBAREA FLOW PATH LENGTH IS GREATER THAN
THE MAXIMUM OVERLAND FLOW LENGTH = 50.38
(Reference: Table 3-1B of Hydrology Manual)
THE MAXIMUM OVERLAND FLOW LENGTH IS USED IN Tc CALCULATION!
100 YEAR RAINFALL INTENSITY(INCH/HOUR) = 4.378
SUBAREA RUNOFF(CFS) = 0.11
TOTAL AREA(ACRES) = 0.05 TOTAL RUNOFF(CFS) = 0.11
FLOW PROCESS FROM NODE 20.00 TO NODE 50.00 IS CODE = 51 ----------------------------------------------------------------------------
>>>>>COMPUTE TRAPEZOIDAL CHANNEL FLOW<(<<<
>>>>>TRAVELTIME THRU SUBAREA (EXISTING ELEMENT)<<<<<
ELEVATION DATA: UPSTREAM(FEET) = 64.90 DOWNSTREAM(FEET) = 64.00
CHANNEL LENGTH THRU SUBAREA(FEET) = 192.00 CHANNEL SLOPE = 0.0047
CHANNEL BASE(FEET) = 0.00 "Z" FACTOR = 10.000
MANNING'S FACTOR = 0.015 MAXIMUM DEPTH(FEET) = 0.50
100 YEAR RAINFALL INTENSITY(INCH/HOUR) = 3.691
RESIDENTAIL (7.3 DU/AC-OR LESS) RUNOFF COEFFICIENT = .5100
SOIL CLASSIFICATION IS "B"
S.C.S. CURVE NUMBER (AMC II) = 76
TRAVEL TIME COMPUTED USING ESTIMATED FLOW(CFS) = 0.20
TRAVEL TIME THRU SUBAREA BASED ON VELOCITY(FEET/SEC.) = 1.12
AVERAGE FLOW DEPTH(FEET) = 0.13 TRAVEL TIME(MIN.) = 2.86
Tc(MIN.) = 12.27
SUBAREA AREA(ACRES) = 0.09 SUBAREA RUNOFF(CFS) = 0.17
AREA-AVERAGE RUNOFF COEFFICIENT = 0.510
TOTAL AREA(ACRES) = 0.14 PEAK.FLOW RATE(CFS) = 0.26
END OF SUBAREA CHANNEL FLOW HYDRAULICS:
DEPTH(FEET) 0.15 FLOW VELOCITY(FEET/SEC.) = 1.21
LONGEST FLOWPATH FROM NODE 10.00 TO NODE 50.00 = 270.00 FEET.
FLOW PROCESS FROM NODE 50.00 TO NODE 50.00 IS CODE = ----------------------------------------------------------------------------
>>>>>DESIGNATE INDEPENDENT STREAM FOR CONFLUENCE<<<<<
TOTAL NUMBER OF STREAMS = 2
CONFLUENCE VALUES USED FOR INDEPENDENT STREAM 1 ARE:
TIME OF CONCENTRATION(MIN.) = 12.27
RAINFALL INTENSITY(INCH/HR) = 3.69
TOTAL STREAM AREA(ACRES) = 0.14
PEAK FLOW RATE(CFS) AT CONFLUENCE = 0.26
FLOW PROCESS FROM NODE 30.00 TO NODE 40.00 IS CODE = 21 ----------------------------------------------------------------------------
>>>>>RATIONAL METHOD INITIAL SUBAREA ANALYSIS<<<<<
RESIDENTAIL (7.3 DU/AC OR LESS) RUNOFF COEFFICIENT = .5100
2
SOIL CLASSIFICATION IS "B"
S.C.S. CURVE NUMBER (AMC II) = 76
INITIAL SUBAREA FLOW-LENGTH(FEET) = 43.00
UPSTREAM ELEVATION(FEET) = 66.10
DOWNSTREAM ELEVATION(FEET) = 65.30
ELEVATION DIFFERENCE(FEET) = 0.80
SUBAREA OVERLAND TIME OF FLOW(MIN.) = 5.662
100 YEAR RAINFALL INTENSITY(INCH/HOUR) = 6.079
SUBAREA RUNOFF(CFS) = 0.12
TOTAL AREA(ACRES) = 0.04 TOTAL RUNOFF(CFS) = 0.12
FLOW PROCESS FROM NODE 40.00 TO NODE 50.00 IS CODE = 51 ----------------------------------------------------------------------------
>>>>>COMPUTE TRAPEZOIDAL CHANNEL FLOW<<<<<
>>>>>TRAVELTIME THRU SUBAREA (EXISTING ELEMENT)<<<<<
ELEVATION DATA: UPSTREAM(FEET) = 65.30 DOWNSTREAM(FEET) = 64.00
CHANNEL LENGTH THRU SUBAREA(FEET) = 220.00 CHANNEL SLOPE = 0;0059
CHANNEL BASE(FEET) = 1.00 "Z" FACTOR = 50.000
MANNING'S FACTOR = 0.015 MAXIMUM DEPTH(FEET) = 0.50
100 YEAR RAINFALL INTENSITY(INCH/HOUR) = 4.516
RESIDENTAIL (7.3 DU/AC OR LESS) RUNOFF COEFFICIENT = .5100
SOIL CLASSIFICATION IS "B"
S.C.S. CURVE NUMBER (AMC II) = 76
TRAVEL TIME COMPUTED USING ESTIMATED FLOW(CFS) = 0.62
TRAVEL TIME THRU SUBAREA BASED ON VELOCITY(FEET/SEC.) = 1.11
AVERAGE FLOW DEPTH(FEET) = 0.10 TRAVEL TIME(MIN.) = 3.31
Tc(MIN.) = 8.98
SUBAREA AREA(ACRES) = 0.43 SUBAREA RUNOFF(CFS) = 0.99
AREA-AVERAGE RUNOFF COEFFICIENT = 0,510
TOTAL AREA(ACRES) = 0.47 PEAK FLOW RATE(CFS) = 1.08
END OF SUBAREA CHANNEL FLOW HYDRAULICS:
DEPTH(FEET) = 0.12 FLOW VELOCITY(FEET/SEC.) = 1.20
LONGEST FLOWPATH FROM NODE 30.00 TO NODE 50.00 = 263.00 FEET.
FLOW PROCESS FROM NODE 50.00 TO NODE 50.00 IS CODE = 1 ----------------------------------------------------------------------------
>>>>>DESIGNATE INDEPENDENT STREAM FOR CONFLUENCE<<<<<
>>>>>AND COMPUTE VARIOUS CONFLUENCED STREAM VALUES<<<<<
TOTAL NUMBER OF STREAMS = 2
CONFLUENCE VALUES USED FOR INDEPENDENT STREAM 2 ARE:
TIME OF CONCENTRATION(MIN.) = 8.98
RAINFALL INTENSITY(INCH/HR) = 4.52
TOTAL STREAM AREA(ACRES) = 0.47
PEAK FLOW RATE(CFS) AT CONFLUENCE = 1.08
** CONFLUENCE DATA **
STREAM RUNOFF Tc INTENSITY AREA
NUMBER (CFS) (MIN.) (INCH/HOUR) (ACRE)
1 0.26 12.27 3.691 0.14
2 1.08 8.98 4.516 0.47
RAINFALL INTENSITY AND TIME OF CONCENTRATION RATIO
3
CONFLUENCE FORMULA USED FOR 2 STREAMS.
** PEAK FLOW RATE TABLE **
STREAM RUNOFF Tc INTENSITY
NUMBER (CFS) (MIN.) (INCH/HOUR)
1 1.28 8.98 4.516
2 1.15 12.27 3.691
COMPUTED CONFLUENCE ESTIMATES ARE AS FOLLOWS:
PEAK FLOW RATE(CFS)= 1.28 .Tc(MIN.) = 8.98
TOTAL AREA(ACRES) 0.61
LONGEST FLOWPATH FROM NODE 10.00 TO NODE 50.00 = 270.00 FEET.
* * * * * * * * * * * * ** * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
FLOW PROCESS FROM NODE 50.00 TO NODE 50.10 IS CODE = 41 ----------------------------------------------------------------------------
>>>>>COMPUTE PIPE-FLOW TRAVEL TIME THRU SUBAREA<<<<<
>>>>>USING USER-SPECIFIED PIPESIZE (EXISTING ELEMENT)<<<<<
ELEVATION DATA: UPSTREAM(FEET) = 63.00 DOWNSTREAM(FEET) = 62.80
FLOW LENGTH(FEET) = 20.00 MANNING'S N = 0.010
ASSUME FULL-FLOWING PIPELINE
PIPE-FLOW VELOCITY(FEET/SEC.) = 2.45
(PIPE FLOW VELOCITY CORRESPONDING TO NORMAL-DEPTH FLOW
AT DEPTH = 0.94 * DIAMETER)
GIVEN PIPE DIAMETER(INCH) = 3.00 NUMBER OF PIPES = 2
PIPE-FLOW(CFS) = 1.28
PIPE TRAVEL TIME(MIN.) = 0.14 Tc(MIN.) = 9.11
LONGEST FLOWPATH FROM NODE 10.00 TO NODE 50.10 = 290.00 FEET.
END OF STUDY SUMMARY:
TOTAL AREA(ACRES) = 0.61. TC(MIN.) = 9.11
PEAK FLOW RATE(CFS) = 1.28
END OF RATIONAL METHOD ANALYSIS
4
III. EXHIBITS
'N
N I I LEGEND
20 10 0 20 40 60
1
SCALE: 1" = 20' \.
N N
62,
62,
I
SUBAREA (ACRES)
SURFACE NODE
SURFACE RUNOFF (CFS)
20 10 0 20 40 60
SCALE: 1" = 20
710
7
7
7
I
IS
'7
S
30,1
04
40
1
II
- 20
\ N N
I
.2
'
I \
INN
ps.- 50 'S
Sss
V çc
777" N'7'
N
!
U
/ Sj •5•5 S 1 7//) //f//Si 4s;s/s \ 7 i P!?P.S—/)/?/'5S/ iiWI
IV. REFERENCES
San Diego County Hydrology Manual
Date: June 2003 Section: 3 Page: 12of26
Note that the 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 were 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 the 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 submitted with a.
detailed study.
Table 3-2
MAXIMUM OVERLAND FLOW LENGTH (L 1)
& INITIAL TIME OF CONCENTRATION (T'
Element* DU/
Acre
.5% 1% 2% 3% 5% 10%
LM Ti LNI T1 LM Ti L,1 T1 L 1 Ti L 4 T
Natural 50 13.2 70 12.5 85 10.9 100 10.3 100 8.7 100 6.9
LDR, 1 50 12.2 70 11.5 1 85 10.0 1 100 9.5 1 100 8.01 100 6.4
LDR 2 50. 11.3 70 1 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 1 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 1 100 4.8
MDR 10.9 50 8.7 65 1 7.9 80 6.9 90 6.4 100 5.7 100 4.5
MDR 1 14.5 50 8.2 65 7.4 80 6.5 90 6.0 100 5.4 100 4.3
HDR 24 50 1 6.7 65 6.1 75 5.1 1 90 49 1 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. Corn 50 5.3 601 4.5 75 4.0 85 3.8 95 3.4 100 2.7
G. Corn 50 4.7 60 4.1 1 75 3.6 85 3.4 90 2.9 1 100 2.4
O.P./Com 50 4.2 60 3.7 70 3.1 80 2.9 90 2.6 100 2.2
Limited L. . 50 4.2 60 3.7 70 3.1 80 2.9 90 2.6 100 2.2
General .1. . 5Ø137 60 3.2 70 2.7 80 2.6 90 2.3 100 1 1.9
*See Table 3-1 for more detailed description
i'A9 •"
3-12
San Diego County Hydrology Manual Section: 3 Date: June 2003 Page: 6 of 26
Table 3-1
RUNOFF COEFFICIENTS FOR URBAN AREAS
Runoff Coefficient "C"
Soil Type
NRCS Elements County Elements % IMPER. A B C D
Undisturbed Natural Terrain (Natural) Permanent Open Space 0* 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 DTJ/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 (0. Corn) General Commercial 85 0.80 0.80 0.81 0.82
Commercial/Industrial (O.P. Corn) Office Professional/Commercial 90 0.83 0.84 0.84 0.85
Commercial/Industrial (Limited 1.) 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 fordirect calculation of the ñinoff 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