HomeMy WebLinkAboutCT 06-27; Muroya; Storm Water Management Plan; 2011-07-14STORM WATER MANAGEMENT PLAN
FOR
CARLSBAD TRACT NO. 06-27, MUROYA
(SWMP 11-05)
July 14, 2011
Preparedfor:
Taylor Morrison of California, LLC
Southern California Division
15 Gushing
Irvine, CA 92618-4220
Wayne W. Chang, MS, PE 46548 o
Civil Engineering ° Hydrology - Hydraulics ° Sedimentation
P.O. Box 9496
Rancho Santa Fe, CA 92067
(858) 692-0760 RD COPY
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-TABLE OF CONTENTS -
1.0 Introduction 1
1.1 Vicinity Map 1
1.2 Project Description 2
1.3 Site Map 2
1.4 Constraints and Opportunities 2
2.0 Water Quality Environment 3
2.1 Beneficial Uses 3
2.1.1 Inland Surface Waters 3
2.1.2 Groundwater 4
3.0 Pollutants and Conditions of Concern 4
3.1 Pollutants from Project Area 4
3.2 Pollutants of Concern in Receiving Waters 5
4.0 Permanent Storm Water Best Management Practices 5
4.1 Standard Site Design BMPs 6
4.2 Source Control BMPs 7
4.3 Low Impact Development Site Design BMPs 8
4.4 Hydromodification 10
5.0 Storm Water BMP Maintenance 11
6.0 Summary/Conclusions 11
7.0 Certification 12
Storm Water Standards Questionnaire, E-34
Site Map
APPENDIX
A. Low Impact Development and Hydromodification Analyses
B. SCCWRP Channel Screening Analysis
1.0 INTRODUCTION
This Storm Water Management Plan (SWMP) addresses water quality requirements
associated with final engineering for Carlsbad Tract 06-27, Muroya, located along the west
side of Black Rail Road at Songbird Avenue in the city of Carlsbad. A preliminary SWMP
was prepared for the tentative map on July 8, 2009 by Hunsaker & Associates, San Diego,
Inc. This SWMP is for final engineering and follows the criteria outlined in the City of
Carlsbad's January 14, 2011, Standard Urban Storm Water Management Plan (SUSMP).
The January 14 SUSMP contains additional requirements that were not present when the
preliminary SWMP was prepared. The additional requirements are addressed in this final
SWMP.
According to the City's Storm Water Standards Questionnaire E-34 (attached following this
report text), the development is in the following priority project categories: housing
subdivision, streets/roads, and more than 1-acre of disturbance. The SUSMP outlines the
SWMP objectives, which are to identify site opportunities and constraints, identify pollutants
and conditions of concern, follow low impact development design objectives, describe best
management practices (BMPs), and outline maintenance requirements. BMPs will be utilized
to the maximum extent practicable to provide a long-term solution for addressing runoff
water quality. BMPs were selected that meet the current regulations and also fit within the
entitled project.
1.1 Vicinity Map
CITY OF
SAN MARCOS
CITY OF ENCINITAS
VICINITY MAP
NO SCALE
1.2 Project Description
The Carlsbad Tract No 06-27, Muroya project is a proposed residential subdivision that will
consist of 37 detached single-family residences along with associated driveways, sidewalks,
landscaping, drainage facilities, and outdoor recreation areas. The development will be
constructed within a 20.27 acre parcel along the west side of Black Rail Road at Songbird
Avenue. Approximately 9.8 acres of the site will become an open space preserve. Adjacent
uses consist of residential development.
Under pre-project conditions, the site is mostly pervious. The northeasterly portion of the site
historically supported agricultural uses. The remainder of the site contains undisturbed
natural terrain. A 150-foot wide SDG&E easement containing utility lines is aligned in a
northwest to southeast direction near the middle of the site.
The site slopes towards the west and southwest. Storm runoff from the northerly portion of
the site is collected by an existing storm drain system just beyond the northwest corner of the
site along Nightshade Road. Runoff from the remainder of the site flows into an existing
storm drain system near the southwesterly corner of the site. There is minimal run-on from
off-site areas to the north. The existing storm drains convey the runoff generally towards the
south where it ultimately enters Batiquitos Lagoon.
Under post-project conditions, two underground storm drain systems will convey runoff
through the site and discharge towards the receiving storm drain systems at the northwest and
southwest. A proposed detention basin will ensure that the peak 100-year runoff from the site
will not be increased and bio-retention basins will be used to meet hydromodification criteria.
1.3 Site Map
A Site Map is included following this report text.
1.4 Constraints and Opportunities
As shown on the site map, the development is being clustered along the northeasterly portion
of the parcel in order to preserve an undisturbed natural area along the southwesterly portion
of the site. The clustering provides the ability to preserve over 48 percent of the site in its
natural state.
The development will consist of detached single-family residences surrounded by gently
sloping landscape areas and some shared driveways. The landscape areas provide
opportunities to treat runoff through contact and bio-filtration by vegetation. For several of
the residences, shared driveways will be used to minimize impervious surfaces. Bioretention
basins are proposed at the northwesterly and southerly portions of the development area. The
bioretention basins will be used to meet both treatment and hydromodification requirements.
The geotechnical engineer is requiring an impervious liner at the bioretention basins. As a
result, the basins were sized based on the flow through planter criteria, which assumes an
impervious liner.
2.0 WATER QUALITY ENVIRONMENT
2.1 Beneficial Uses
The beneficial uses for the hydrologic unit are included in Tables 1 and 2. These tables were
obtained from the April 25, 2007 amended Water Quality Control Plan for the San Diego
Basin (9). The following contains definitions of the beneficial uses in the tables:
MUN - Municipal and Domestic Supply: Includes uses of water for community,
military, or individual water supply systems including, but not limited to, drinking
water supply.
AGR - Agricultural Supply (AGR): Includes uses of water for farming,
horticulture, or ranching including, but not limited to, irrigation, stock watering, or
support of vegetation for range grazing.
REC1 - Contact Recreation: 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 - Non-Contact Recreation: 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.
WARM - Warm Freshwater Habitat: 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.
WILD - Wildlife Habitat: Includes uses of water that support terrestrial 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.
2.1.1 Inland Surface Waters
Inland surface waters for the San Marcos Hydrologic Area have the beneficial uses shown in
Table 1:
Table 1. Beneficial Uses for Inland Surface Waters
Hydrologic
Unit
Code
904.51
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• Existing Beneficial Use
2.1.2 Groundwater
Groundwater beneficial uses for the El Salto Hydrologic Subarea are shown in Table 2:
Table 2. Beneficial Uses for Groundwater
Hydrologic
Unit
Code
904.51
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Potential Beneficial Use
3.0 POLLUTANTS AND CONDITIONS OF CONCERN
3.1 Pollutants from Project Area
The project is located within the Batiquitos Hydrologic Subarea (904.51) of the San Marcos
Hydrologic Area (904.50), which is within the Carlsbad Hydrologic Unit (904.00). The total
drainage area of the hydrologic unit is approximately 210 square miles. Runoff from portions
of the hydrologic subarea ultimately drains to Batiquitos Lagoon, which is south of the
project site. All of the project runoff will ultimately enter Batiquitos Lagoon. The project site
represents less than one percent of the overall watershed.
The following table lists pollutants of concern that are anticipated or can potentially exist at
proposed priority development project sites. The pollutants are from the city of Carlsbad's
SUSMP. The project falls within the detached residential development and streets, highways
& freeways priority project categories (highlighted yellow in the table). All of the listed
pollutants are either anticipated or can potentially exist at the developed site.
Table 3. Priority Project Pollutants
Priority
Project
Categories
Detached
Residential
Development
Attached
Residential
Development
Commercial
Development
> one acre
Heavy
Industry
Automotive
Repair Shops
Restaurants
Hillside
Development
>5,000 ft2
Parking Lots
Retail
Gasoline
Outlets
Streets,
Highways &
Freeways
Sediments
X
X
pdi
X
X
p(I)
X
Nutrients
X
X
p(0
X
pin
p(l)
Heavy
Metals
X
X
X
X
X
X
Organic
Compounds
p(2)
X
X(4X5)
X
X(4)
Trash
&
Debris
X
X
X
X
X
X
X
X
X
X
Oxygen
Demanding
Substances
X
pd)
p(5)
X
X
X
p(l)
X
p(5)
Oil
&
Grease
X
pO)
X
X
X
X
X
X
X
X
Bacteria
&
Viruses
X
P
p(3)
X
X
Pesticides
X
X
p<5)
p(D
X
pdi
p(i)
X = Anticipated
P = Potential
(1) A potential pollutant if landscaping exists on-site
(2) A potential pollutant if the project includes uncovered parking areas
(3) A potential pollutant if land use involves food or animal waste products
(4) Including petroleum hydrocarbons
(5) Including solvents
3.2 Pollutants of Concern in Receiving Waters
According to the 2008 303(d) list approved by the State Water Resources Control Board (and
by the US EPA in November 2010), the receiving water body closest to the project vicinity,
Batiquitos Lagoon, is not 303(d) listed and is not subject to total maximum daily loads
(TMDLs). Therefore, the project does not generate pollutants of concern in the receiving
waters.
4.0 PERMANENT STORM WATER BEST MANAGEMENT PRACTICES
To address water quality for the project, best management practices (BMPs) will be
implemented. The following discusses the Standard Site Design, Source Control, and Low
Impact Development design BMPs for the project.
4.1 Standard Site Design BMPs
The City of Carlsbad's standard objectives are required for all projects. The project will
accomplish these goals through the following BMPs, which are from the Carlsbad SUSMP:
Standard Stormwater Requirements
Minimize Impervious Surfaces. The project will include pervious surfaces (landscaping
within the development area and no disturbance along the southwesterly portion of the site,
which is over 48 percent of the site).
Disconnect Discharges. Roof drains will discharge to adjacent landscape areas, where
feasible. Most of the proposed sidewalks are being designed with a landscaped parkway
between the sidewalks and curbs to allow runoff to drain over adjacent landscape areas.
Conserve Natural Areas. The southern portion of the site, which covers over 48 percent of
the site including a natural hillside, will not be disturbed. The development is being clustered
along the northeasterly portion of the site.
Stenciling Inlets and Signage. The curb inlets along the main drive will be stenciled with
prohibitive language such as "No Dumping -1 live downstream" or approved similar.
Landscape Design. A landscape plan will be prepared that uses drought-tolerant species in
accordance with the City's landscape manual. Native trees and shrubs will be preserved over
the majority of the parcel in order to maximize canopy interception and promote water
conservation. The project will only use water as needed to support the landscaping.
Water Efficient Irrigation. The irrigation systems will be designed to each landscaped areas
water requirements to avoid over irrigation. Rain shutoff devices will be used to prevent
irrigation after rain events.
Protect Slopes And Channels. The grading design does not include large slopes or channels.
The design will prevent runoff from flowing uncontrolled over the tops of manufactured
slopes. The proposed slopes will be landscaped. Riprap energy dissipaters will be used at
storm drain outfalls.
Vegetate slopes with native or drought tolerant vegetation. Native and drought tolerant
vegetation will be used to the extent allowed by the resource agencies.
Trash Receptacles. Each residence will have personal, covered trash receptacles.
Material Storage Areas. The project does not propose outdoor material storage areas. Any
required material storage shall be kept under cover.
4.2 Source Control BMPs
Source control BMPs will consist of measures to prevent polluted runoff. The following
addresses the source control BMPs from Appendix 1 of the Carlsbad SUSMP:
Table 4. Pollutant Sources and Source Control Checklist
Potential Source
of Runoff Pollutants
Permanent Source
Control BMPs
Operational Source
Control BMPs
On-site storm drain
inlets
Mark all inlets with "No
Dumping -1 live downstream"
Maintain and periodically
repaint inlet markings
Provide stormwater pollution
information to owners, lessees,
and operators (Fact sheet SC-
44 from the CASQA
Stormwater Quality Handbook
at www.cabmphandbooks.com)
Owner/lessee agreements shall
state "Tenant shall not allow
anyone to discharge anything to
storm drains or to store or
deposit materials so as to create
a potential discharge to storm
drains.
Need for future
indoor & structural
pest control
Buildings shall be designed to
avoid openings that would
encourage entry of pests.
Integrated Pest Management (e.g.,
the EPA's Citizen's Guide to Pest
Control and Pesticide Safety)
information shall be provided to
owners, lessees, and operators.
Landscape/Outdoor
Pesticide Use
Final landscape plans will
accomplish all of the
following.
• Preserve existing native trees,
shrubs, and ground cover to
the maximum extent possible.
• Design landscaping to
minimize irrigation and
runoff, to promote surface
infiltration where
appropriate, and to minimize
the use of fertilizers and
pesticides that can contribute
to stormwater pollution.
• Where landscaped areas can
Maintain landscaping using
minimum or no pesticides.
See applicable operational BMPs
in Fact Sheet SC-41, "Building and
Grounds Maintenance," and TC-
30, "Vegetated Swale," in the
CASQA Stormwater Quality
Handbooks at
www.cabmphandbooks.com
Integrated Pest Management (e.g.,
the EPA's Citizen's Guide to Pest
Control and Pesticide Safety)
information shall be provided to
owners, lessees, and operators.
retain or detain stormwater,
specify plants that are
tolerant of saturated soil
conditions.
1 Consider using pest-resistant
plants, especially adjacent to
hardscape.
1 To ensure successful
establishment, select plants
appropriate to site soils,
slopes, climate, sun, wind,
rain, land use, air movement,
ecological consistency, and
plant interactions
Vehicle and
equipment cleaning
The CC&Rs will prohibit car
washing at the site. The HO A
will be responsible for
enforcing this requirement.
Vehicle/Equipment
Repair and
Maintenance
The CC&Rs will prohibit
repair and maintenance
activities in areas exposed to
precipitation and storm flows.
The HOA will be responsible
for enforcing this requirement.
Roofing, gutters, and
trim
The architectural design will
avoid roofing, gutters, and trim
made of copper or other
unprotected metals that may
leach into runoff.
Plazas, sidewalks,
and parking lots.
Plazas, sidewalks, and parking lots
shall be swept regularly to prevent
the accumulation of litter and
debris. Debris from pressure
washing shall be collected to
prevent entry into the storm drain
system. Wash water containing
any cleaning agent or degreaser
shall be collected and discharged
to the sanitary sewer and not
discharged to a storm drain.
4.3 Low Impact Development Site Design BMPs
The preliminary SWMP by Hunsaker and Associates approved during the entitlement
process was based on the regulations at the time of preparation in July 2009. Since then, the
City of Carlsbad updated the SUSMP in March 24, 2010 and January 14, 2011. For final
engineering design, the Low Impact Development (LID) BMPs have been updated and sized
to meet the January 14, 2011 LID requirements. The integrated LID outlines four strategies:
1. Optimize the site layout by preserving natural drainage features and designing
buildings and circulation to minimize the amount of roofs and paving.
2. Use pervious surfaces such as turf, gravel, or pervious pavement—or use surfaces that
retain rainfall. All drainage from these surfaces is considered to be "self-retained".
3. Disperse runoff from impervious surfaces on to adjacent pervious surfaces (e.g.,
direct a roof downspout to disperse runoff onto a lawn).
4. Drain impervious surfaces to engineered Integrated Management Practices (IMPs),
such as bioretention facilities, planter boxes, cisterns, or dry wells. IMPs infiltrate
runoff to groundwater and/or percolate runoff through engineered soil and allow it to
drain away slowly.
The project design is in compliance with these strategies. The site layout has been designed
to preserve over 48 percent of the lot in open space including the majority of the natural,
undisturbed portions of the site. Shared driveways will provide access to many of the units
and the on-site streets are being designed with minimal widths.
Runoff from the roofs will flow towards pervious landscape areas, where possible.
Bioretention basins will also be used to treat the on-site runoff and to meet
hydromodification requirements (discussed in next section). Bioretention basins provide high
to medium removal effectiveness for the pollutants generated by the project, which are listed
in Table 3. The bioretention basins were sized using County of San Diego's BMP Sizing
Calculator. The bioretention basins will have an impervious liner so they were sized using
the flow-through planter criteria, which has a slightly higher sizing factor. Other than this,
the ponding depths and material layers are the same between a bioretention basin and flow-
through planter. The development site was divided into the following drainage management
areas (see DMA exhibit):
• Paving (streets, driveways)
• Sidewalks
• Roofs
• Drainage ditch (concrete)
• Landscape areas
Bioretention will be provided for the narrow strip of improvements along Black Rail Road.
The improvements include a small amount of paving as well as curb, gutter, and sidewalk.
The runoff from these areas will be captured by a 3-inch PVC pipe in the curb face, then
conveyed by the pipe to the southerly-most on-site bioretention basin. The basin was sized
for the both the tributary on-site runoff and the off-site runoff from Black Rail Road.
4.4 Hydromodification
The January 14, 2011 SUSMP requires hydromodification (flow control) for priority
development projects to ensure that post-development peak flows do not exceed pre-
development peak flows. Muroya is a priority development project and must meet the
hydromodification requirement. This can be accomplished by sizing bioretention facilities
using the County of San Diego's online BMP Sizing Calculator (Calculator). The Calculator
was used for this project.
The proposed project will have two major drainage areas. One area flows towards the
northwest and one flows towards the south. Consequently, a bioretention basin will be
included at the northwest in the same vicinity as the basin shown on the tentative map. The
outflow from this basin will enter the storm drain system near the northwest corner of the site
in Nightshade Road. Another series of interconnected bio-retention basins will be included at
the south. This will include a deeper basin in the same vicinity as the basin shown on the
tentative map as well as shallower basins on either side of the south end of private street C.
The outflow from these basins will outfall towards the west and ultimately enter an existing
storm drain system near the westerly property line.
The data entry into the Calculator was as follows. The site is within the Oceanside rainfall
basin and contains soil group D. The area tributary to the northwest basin has slopes ranging
up to 20 to 40 percent, which are classified as steep slopes. The area tributary to the southerly
basins has slopes in the 5 to 8 percent range, which are classified as moderate slopes. The
receiving water characteristics were entered based on a detailed site investigation of the
areas. The mean annual precipitation is 12.5 inches. The drainage management areas were
divided into roofs, landscaping, sidewalks, paving, and ditches. An analysis was performed
based on the Southern California Coastal Water Research Project's (SCCWRP)
hydromodification screening tool (see Appendix B). The analysis shows that the downstream
receiving channels meet the low (O.SCh) threshold. Appendix A contains the DMA exhibit
and Calculator results. Since the bioretention basins will contain an impervious liner, they
were modeled as a flow-through planter. The Calculator provides the surface area sizing,
surface volume sizing, and subsurface volume sizing, which are summarized in Table 5. The
bio-retention basins will be sized based on these results. Besides the larger sizing, the
ponding depths and material layers are the same between a bioretention basin and flow
through planter.
Table 5. Summary of Bioretention Sizing
Bioretention
Basin1
Northwest Basin
Southerly Basins
Surface
Area, sf
5,856
4,516
Surface
Volume, cf
4,884
3,761
Subsurface
Volume, cf
3,514
2,709
Sized based on flow-through planter option.
10
5.0 STORM WATER BMP MAINTENANCE
The developer will be responsible for funding and implementing the operations and
maintenance of the project BMPs. Provisions will be made to transfer operations and
maintenance to the new owner in the event of a change in ownership. The homeowner's
association will ultimately be responsible for ongoing operations and maintenance. The
following describes the specific BMP maintenance.
Bioretention basins
The drainage outlet from the basins shall be inspected monthly and after large storm events.
Debris, sediment, and other obstructions shall be removed immediately from the outlet. The
habitat shall also be inspected annually and replanted as needed to maintain an adequate
cover.
Landscaping and Vegetated Swales
Maintenance will be performed by landscaping personnel. The vegetation will be maintained
and inspected on a monthly basis by landscape maintenance staff and will be replaced or
replanted, as necessary, to maintain a dense, healthy cover. The vegetation will also be
inspected after major storm events. Maintenance shall include periodic mowing, weed
control, irrigation, reseeding/replanting of bare areas, and clearing of debris. A design grass
height of 6 inches is recommended. Grass clippings shall not be left in grass swales. The
private drainage system will shall be kept clear of debris and inspect prior to and during the
rainy season to ensure it is free-flowing.
Efficient Irrigation
The landscaping personnel shall inspect and maintain the irrigation system on a regular basis.
This will occur during the routine maintenance activities. All valves, heads, shutoff devices,
lines, etc. shall be kept in a properly functioning condition. Any defective parts shall be
replaced immediately. The irrigation system shall be adjusted to prevent excessive runoff
from landscape areas. The irrigation schedule shall be adjusted based on seasonal needs.
Inlet Stenciling
Any stenciling shall be inspected at the beginning and end of each rainy season and repaired
or replaced, as needed.
Hazardous Wastes
Suspected hazardous wastes will be analyzed to determine disposal options. Hazardous
materials are not expected to be generated on-site; however, if discovered, hazardous
materials will be handled and disposed of according to local, state, and federal regulations. A
solid or liquid waste is considered a hazardous waste if it exceeds the criteria listed in the
California Code of Federal Regulations, Title 22, Article 11 (State of California, 1985).
6.0 SUMMARY/CONCLUSIONS
This final SWMP has been prepared in accordance with the City of Carlsbad's January 14,
2011, Standard Urban Storm Water Management Plan, and has evaluated and addressed
potential pollutants associated with the Muroya project and its effects on water quality. This
11
SWMP has been based on the final engineering plans. A summary of the facts and findings
associated with the project and the measures addressed by this SWMP are as follows:
• The beneficial uses for the receiving waters have been identified. BMPs will be used
to protect the beneficial uses as outlined by the SUSMP.
• The project will not significantly alter drainage patterns and will meet
hydromodification requirements.
• A Storm Water Pollution Prevention Plan for construction activities has been
prepared to address construction-related water quality objectives.
• Permanent BMPs will be incorporated into the project design in the form of site
design, source control, and LID treatment control.
• The proposed BMPs address mitigation measures to protect water quality and
beneficial uses to the maximum extent practicable.
7.0 CERTIFICATION
The selection, sizing, and preliminary design of stormwater treatment and other control
measures in this plan meet the requirements of Regional Water Quality Control Board Order
R9-2007-0001 and subsequent amendments.
July 14,2011
Wayne W. Chang, RCE 46548 Date
12
CITY OF
CARLSBAD
STORM WATER
STANDARDS
QUESTIONNAIRE
E-34
Development Services
Land Development Engineering
1635 Faraday Avenue
760-602-2750
www.carlsbadca.gov
To address post-development pollutants that may be generated from development projects, the City requires that new
development and significant redevelopment priority projects incorporate Permanent Storm Water Best Management
Practices (BMP's) into the project design per the City's Standard Urban Stormwater Management Plan (SUSMP). To
view the SUSMP, refer to the Engineering Standards (Volume 4, Chapter 2) at www.carlsbadca.gov/standards.
Initially this questionnaire must be completed by the applicant in advance of submitting for a development application
(subdivision, discretionary permits and/or construction permits). The results of the questionnaire determine the level of
storm water standards that must be applied to a proposed development or redevelopment project. Depending on the
outcome, your project will either be subject to 'Standard Stormwater Requirements' or be subject to additional criteria
called 'Priority Development Project Requirements'. Many aspects of project site design are dependent upon the
storm water standards applied to a project.
Your responses to the questionnaire represent an initial assessment of the proposed project conditions and impacts.
City staff has responsibility for making the final assessment after submission of the development application. If staff
determines that the questionnaire was incorrectly filled out and is subject to more stringent storm water standards than
initially assessed by you, this will result in the return of the development application as incomplete. In this case, please
make the changes to the questionnaire and resubmit to the City.
If you are unsure about the meaning of a question or need help in determining how to respond to one or more of the
questions, please seek assistance from Land Development Engineering staff.
A separate completed and signed questionnaire must be submitted for each new development application submission.
Only one completed and signed questionnaire is required when multiple development applications for the same project
are submitted concurrently. In addition to this questionnaire, you must also complete, sign and submit a Project Threat
Assessment Form with construction permits for the project.
Please start by completing Section 1 and follow the instructions. When completed, sign the form at the end and submit
this with your application to the city.
Does your project meet one or more of the following criteria:
1. Housing subdivisions of 10 or more dwelling units. Examples: sinqle family homes, multi-family homes.
condominium and apartments
2. Commercial - greater than 1-acre. Any development other than heavy industry or residential. Examples: hospitals;
laboratories and other medical facilities; educational institutions; recreational facilities; municipal facilities; commercial
nurseries; multi-apartment buildings; car wash facilities; mini-malls and other business complexes; shopping malls;
hotels; office buildings; public warehouses; automotive dealerships; airfields; and other light industrial facilities.
3. Heavy Industrial / Industry- areater than 1 acre. Examples: manufacturing plants, food processing plants, metal
working facilities, printing plants, and fleet storage areas (bus, truck, etc.).
4. Automotive repair shoo. A facility categorized in any one of Standard Industrial Classification (SIC) codes 5013,
5014, 5541, 7532-7534, and 7536-7539
5. Restaurants. Any facility that sells prepared foods and drinks for consumption, including stationary lunch counters
and refreshment stands selling prepared foods and drinks for immediate consumption (SIC code 5812), where the
land area for development is greater than 5,000 square feet. Restaurants where land development is less than 5,000
square feet shall meet all SUSMP requirements except for structural treatment BMP and numeric sizing criteria
requirements and hydromodification requirements.
YES
X
NO
X
X
X
X
E-34 Page 1 of 3 REV 1/14/11
CARLSBAD
CITY OF
STORM WATER
STANDARDS
QUESTIONNAIRE
E-34
Development Services
Land Development Engineering
1635 Faraday Avenue
760-602-2750
www.carlsbadca.gov
6. Hillside development. Any development that creates more than 5,000 square feet of impervious surface and is
located in an area with known erosive soil conditions, where the development will grade on any natural slope that is
twenty-five percent (25%) or greater.
x
Environmentally Sensitive Area (ESA)1. All development located within or directly adjacent2 to or discharging
directly3 to an ESA (where discharges from the development or redevelopment will enter receiving waters within the
ESA), which either creates 2,500 square feet or more of impervious surface on a proposed project site or increases
the area of imperviousness of a proposed project site 10% or more of its naturally occurring condition.
X
8. Parking lot. Area of 5,000 square feet or more, or with 15 or more parking spaces, and potentially exposed to urban
runoff X
9. Streets, roads, highways, and freeways. Any paved surface that is 5,000 square feet or greater used for the
transportation of automobiles, trucks, motorcycles, and other vehicles X
10. Retail Gasoline Outlets. Serving more than 100 vehicles per day and greater than 5,000 square feet
11. Coastal Development Zone. Any project located within 200 feet of the Pacific Ocean and (1) creates more than
2500 square feet of impervious surface or (2) increases impervious surface on property by more than 10%.
12. More than 1-acre of disturbance. Project results in the disturbance of 1-acre or more of land and is considered a
Pollutant-generating Development Project4.
1 Environmentally Sensitive Areas include but are not limited to all Clean Water Act Section 303(d) impaired water bodies; areas designated as Areas of Special
Biological Significance by the State Water Resources Control Board (Water Quality Control Plan for the San Diego Basin (1994) and amendments); water bodies
designated with the RARE beneficial use by the State Water Resources Control Board (Water Quality Control Plan for the San Diego Basin (1994) and amendments);
areas designated as preserves or their equivalent under the Multi Species Conservation Program within the Cities and County of San Diego; and any other equivalent
environmentally sensitive areas which have been identified by the Copermittees.
2 "Directly adjacent" means situated within 200 feet of the Environmentally Sensitive Area.
3 "Discharging directly to" means outflow from a drainage conveyance system that is composed entirely of flows from the subject development or redevelopment site, and
not commingled with flow from adjacent lands.
4 Pollutant-generating Development Projects are those projects that generate pollutants at levels greater than background levels. In general, these include all projects
that contribute to an exceedance to an impaired water body or which create new impervious surfaces greater than 5000 square feet and/or introduce new landscaping
areas that require routine use of fertilizers and pesticides. In most cases linear pathway projects that are for infrequent vehicle use, such as emergency or maintenance
access, or for pedestrian or bicycle use, are not considered Pollutant-generating Development Projects if they are built with pervious surfaces or if they sheet flow to
surrounding pervious surfaces.
INSTRUCTIONS:
Section 1 Results:
If you answered YES to ANY of the questions above, your project is subject to Priority Development Project requirements. Skip Section 2 and
please proceed to Section 3. Check the "meets PRIORITY DEVELOPMENT PROJECT requirements" box in Section 3. Additional storm water
requirements will apply per the SUSMP.
If you answered NO to ALL of the questions above, then please proceed to Section 2 and follow the instructions.
E-34 Page 2 of 3 REV 1/14/11
<«
CITY OF
CARLSBAD
STORM WATER
STANDARDS
QUESTIONNAIRE
E-34
Development Services
Land Development Engineering
1635 Faraday Avenue
760-602-2750
www.carlsbadca.gov
INSTRUCTIONS: Complete the questions below regarding your project YES NO
1. Project results in the disturbance of 1 -acre or more of land and is considered a Pollutant-generating Development
Project *?
INSTRUCTIONS: If you answered NO, please proceed to question 2.
If you answered YES, then you ARE a significant redevelopment and you ARE subject to PRIORITY DEVELOPMENT PROJECT
requirements. Please check the "meets PRIORITY DEVELOPMENT PROJECT requirements" box in Section 3 below.
2. Is the project redeveloping an existing priority project type? (Priority projects are defined in Section 1)
INSTRUCTIONS: If you answered YES, please proceed to question 3.
If you answered NO, then you ARE NOT a significant redevelopment and your project is subject to STANDARD STORMWATER
REQUIREMENTS. Please check the "does not meet PDP requirements" box in Section 3 below.
3. Is the work limited to trenching and resurfacing associated with utility work; resurfacing and reconfiguring surface
parking lots and existing roadways; new sidewalk; bike lane on existing road and/or routine maintenance of damaged
pavement such as pothole repair? Resurfacing/reconfiguring parking lots is where the work does not expose underlying soil
during construction.
INSTRUCTIONS: If you answered NO, then proceed to question 4.
If you answered YES, then you ARE NOT a significant redevelopment and your project is subject to STANDARD STORMWATER
REQUIREMENTS. Please check the "does not meet PDP requirements" box in Section 3 below.
4. Will your redevelopment project create, replace, or add at least 5,000 square feet of impervious surfaces on existing
developed property or will your project be located within 200 feet of the Pacific Ocean and (1) create 2500 square feet or
more of impervious surface or (2) increases impervious surface on the property by more than 10%? Replacement of
existing impervious surfaces includes any activity that is not part of routine maintenance where impervious material(s) are
removed, exposing underlying soil during construction.
INSTRUCTIONS: If you answered YES, you ARE a significant redevelopment, and you ARE subject to PRIORITY DEVELOPMENT
PROJECT requirements. Please check the "meets PRIORITY DEVELOPMENT PROJECT requirements" box in Section 3 below. Review
SUSMP to find out if SUSMP requirements apply to your project envelope or the entire project site.
If you answered NO, then you ARE NOT a significant redevelopment and your project is subject to STANDARD STORMWATER
REQUIREMENTS. Please check the "does not meet PDP requirements" box in Section 3 below.
*for definition see Footnote 4 on page 2
My project meets PRIORITY DEVELOPMENT PROJECT (PDP) requirements and must comply with additional stormwater criteria
per the SUSMP and I understand I must prepare a Storm Water Management Plan for submittal at time of application. I understand
flow control (hydromodification) requirements may apply to my project. Refer to SUSMP for details.
My project does not meet PDP requirements and must only comply with STANDARD STORMWATER REQUIREMENTS per the
SUSMP. As part of these requirements, I will incorporate low impact development strategies throughout my project.
Applicant Information and Signature Box This Box for City Use Only
Address: West of B,ack Rgi| Rd
at Songbird Avenue
Applicant Name:
Wayne W. Chang
Apnlfca/ft Signature: /]rmrt C*-?,-
Assessor's Parcel Number(s):
214-040-03
Applicant Title:
Principal
Date:
July 14, 2011
City Concurrence:YES NO
By:
Date:
Project ID:
E-34 Page 3 of 3 REV 1/14/11
D
SITE MAP
C.T. NO. 06-27, MUROYA
0 50 100
1 INCH = 100 FEET
r!y
APPENDIX A
APPENDIX A
LOW IMPACT DEVELOPMENT
AND HYDROMODIFICATION ANALYSES
SUMMARY
The SUSMP requires that Drainage Management Areas (DMA) be delineated for various
surface types. DMAs were determined for roofs, landscaping, sidewalks, paving, and a
concrete drainage ditch. These are shown on the DMA Exhibit in this appendix. The attached
table summarizes the DMAs to each of the bioretention basin areas. The bioretention basins
have been sized using the BMP Sizing Calculator. Since the basins will have an impervious
lining, the flow-through planter option was used. This will result in larger storage
requirements than the bioretention option. The ponding depth and subsurface growing
medium and gravel layer are the same between a flow-through planter and bioretention basin.
The calculator results are attached and summarized below.
Bioretention
Basin1
Northwest Basin
Southerly Basins
Surface
Area, sf
5,856
4,516
Surface
Volume, cf
4,884
3,761
Subsurface
Volume, cf
3,514
2,709
>ized based on flow-through planter option.
Table 1. Summary of Bio-retention Sizing
The southerly basins have been sized to treat the additional off-site development area along
Black Rail Road (curb, gutter, sidewalk, and transition paving). A 3-inch PVC pipe will be
installed in the curb to direct low flow to the southerly bioretention area. An analysis was
performed to determine the water quality flow rate that needs to be conveyed by the 3-inch
PVC pipe. The water quality flow rate is based on the rational method equation, and
determined by multiplying the runoff coefficient, rainfall intensity (0.2 inches per hour for
water quality), and tributary area or:
Q=CIA where Q is the water quality flow rate, cfs
C is the runoff coefficient = 0.87 for impervious areas
I is the rainfall intensity = 0.2 inches per hour
A is the tributary area = 0.21 acres of development along
Black Rail Road
Based on the equation, the water quality flow rate from the proposed off-site development
area is 0.04 cubic feet per second (0.87X0.2x0.21 = 0.04). A normal depth analysis was
performed and attached, which shows that a single 3-inch PVC pipe at a 1 percent slope can
convey 0.1 cfs, which is more than the water quality flow rate. Consequently, a 3-inch PVC
pipe will be sufficient to convey the water quality runoff from Black Rail Road to the
southerly bioretention area.
i t i i i
Project Summary
Project Name
Project Applicant
Jurisdiction
Parcel (APN)
Hydrologic Unit
Muroya Hydromodifcation
Taylor Morrison
City of Carlsbad
215-040-03
Carlsbad
Compliance Basin Summary
Basin Name:
Receiving Water:
Rainfall Basin
Mean Annual Precipitation (inches)
Project Basin Area (acres):
Watershed Area (acres):
SCCWRP Lateral Channel Susceptiblity (H, M, L):
SCCWRP Vertifical Channel Susceptiblity (H, M, L):
Overall Channel Susceptibility (H, M, L):
Lower Flow Threshold (% of 2-Year Flow):
North Drainage Area
Night Shade Rd Storm Drain
Oceanside
12.5
4.74
26.47
Low (Lateral)
Low (Vertical)
LOW
0.5
Drainage Management Area Summary
ID
5807
5808
5809
5811
5812
Type
Drains to LID
Drains to LID
Drains to LID
Drains to LID
Drains to LID
BMP ID
BMP 1
BMP1
BMP1
BMP1
BMP1
Description
Roofs
Streets and Driveways
Sidewalks
Drainage Ditch
Landscaping
Area (ac)
1.3
0.9
0.1
0.0
2.2
Pre-Project Cover
Pervious (Pre)
Pervious (Pre)
Pervious (Pre)
Pervious (Pre)
Pervious (Pre)
Post Surface Type
Roofs
Concrete or asphalt
Concrete or asphalt
Concrete or asphalt
Landscaping
Drainage Soil
Type D (high runoff - clay
soi...
Type D (high runoff - clay
soi...
Type D (high runoff - clay
soi...
Type D (high runoff - clay
soi...
Type D (high runoff - clay
soi...
Slope
Steep (greater 10%)
Steep (greater 10%)
Steep (greater 10%)
Steep (greater 10%)
Steep (greater 10%)
LID Facility Summary
BMP ID
BMP1
Type
Flow-Through Planter
Description
North - Flow Through Planter
Plan Area (sqft)
5856
Volume 1(cft)
4884
Volume 2(cft)
3514
Orifice Flow (cfs)
0.580
Orifice Size (inch)
4.00
f i I i I I
Project Summary
Project Name
Project Applicant
Jurisdiction
Parcel (APN)
Hydrologic Unit
Muroya Hydromodification
Taylor Morrison
City of Carlsbad
215-040-03
Carlsbad
Compliance Basin Summary
Basin Name:
Receiving Water:
Rainfall Basin
Mean Annual Precipitation (inches)
Project Basin Area (acres):
Watershed Area (acres):
SCCWRP Lateral Channel Susceptiblity (H, M, L):
SCCWRP Vertifical Channel Susceptiblity (H, M, L):
Overall Channel Susceptibility (H, M, L):
Lower Flow Threshold (% of 2-Year Flow):
South Drainage Area
Southerly Discharge Location
Oceanside
12.5
2.66
6.78
Low (Lateral)
Low (Vertical)
LOW
0.5
Drainage Management Area Summary
ID
8219
8220
8221
8222
Type
Drains to LID
Drains to LID
Drains to LID
Drains to LID
BMP ID
BMP1
BMP1
BMP 1
BMP1
Description
Roofs
Streets and Driveways
Sidewalks
Landscaping
Area (ac)
0.5
0.6
0.2
1.3
Pre-Project Cover
Pervious (Pre)
Pervious (Pre)
Pervious (Pre)
Pervious (Pre)
Post Surface Type
Roofs
Concrete or asphalt
Concrete or asphalt
Landscaping
Drainage Soil
Type D (high runoff - clay
soi...
Type D (high runoff - clay
soi...
Type D (high runoff - clay
soi...
Type D (high runoff - clay
soi...
Slope
Moderate (5 -10%)
Moderate (5 -10%)
Moderate (5 -10%)
Moderate (5- 10%)
LID Facility Summary
BMP ID
BMP1
Type
Flow-Through Planter
Description
South - Bioretention Basin
Plan Area (sqft)
4516
Volume 1 (eft)
3761
Volume 2(cft)
2709
Orifice Flow (cfs)
0.281
Orifice Size (inch)
3.00
fill I i I i
HYDROMODIFICATION (DMA Summary)
Bio-Retention Basin
1 (North)
DMA Name
Roofs
Streets and driveways
Sidewalks
Ditch
Landscape
Total
Area, sf
57,972
42,496
4,759
1,592
99,565
206,384
Area, ac I
1.33
0.98
0.11
0.04
2.29
4.74
Runoff F
1.0
1.0
1.0
1.0
0.1
Runoff Factor Area x Runoff Factor, sf
57,972
42,496
4,759
1,592
9,957
116,776
2 (South) Roofs
Streets and driveways
Sidewalks
Landscape
Total
23,457
26,357
8,736
57,246
115,796
0.54
0.61
0.20
1.31
2.66
1.0
1.0
1.0
0.1
23,457
26,357
8,736
5,725
64,275
Note: The BMP Sizing Calculator truncates the area to the tenth, For instance, an entry of 0.98 is shown as 0.9 in the Calculator output
GRAPHIC SCALE
0 50 100
BLACK RAH ROAD*1 INCH = 100 FEET
DRAINAGE MANAGEMENT AREA EXHIBIT
PROPOSED CONDITION DRAINAGE BASIN BOUNDARY
2.44 AC DRAINAGE BASIN AREA
BIORETENTION BASIN
INFILTRATION TRENCH
ROOFS
PAVING (STREETS AND DRIVEWAYS)
SIDEWALK
CONCRETE DRAINAGE DITCH
LANDSCAPING—i
NOTE:
THE NORTHWESTERLY BIORETENTION BASIN HAS A SURFACE AREA OF
OVER 6,080 SF AND THE SOUTHERLY HAS A SURFACE AREA OF 4,960
SF. A PVC PIPE WILL BE USED TO DIRECT FLOW FROM THE GUTTER IN
BLACK RAIL ROAD TO THE SOUTHERLY BIORETENTION BASIN. THE
SOUTHERLY BIORETENTION BASIN HAS BEEN SIZED TO TREAT THIS
OFF-SITE FLOW ALONG BLACK RAIL ROAD AND THE TRIBUTARY
ON-SITE FLOW.
Worksheet for 3" PVC at Black Rail
Project Description
Friction Method
Solve For
Input Data
Roughness Coefficient
Channel Slope
Diameter
Discharge
Results
Normal Depth
Flow Area
Wetted Perimeter
Hydraulic Radius
Top Width
Critical Depth
Percent Full
Critical Slope
Velocity
Velocity Head
Specific Energy
Froude Number
Maximum Discharge
Discharge Full
Slope Full
Flow Type
GVF Input Data
Downstream Depth
Length
Number Of Steps
GVF Output Data
Upstream Depth
Profile Description
Profile Headloss
Average End Depth Over Rise
Normal Depth Over Rise
Downstream Velocity
Manning Formula
Normal Depth
SubCritical
0.011
0.01000 ft/ft
0.25 ft
0.10 fp/s
0.20 ft
0.04 ft2
0.54 ft
0.08 ft
0.21 ft
0.19 ft
78.5 %
0.01052 ft/ft
2.42 ft/s
0.09 ft
0.29 ft
0.95
0.11 ft3/s
0.10 ft3/s
0.00917 ft/ft
0.00 ft
0.00 ft
0
0.00 ft
0.00 ft
0.00 %
78.47 %
Infinity ft/s
6/7/2011 10:17:56 PM
Bentley Systems, Inc. Haestad Methods SaBdntte£EhluMaster V8i (SELECTseries 1) [08.11.01.03]
27 Siemens Company Drive Suite 200 W Watertown, CT 06795 USA +1-203-755-1666 Page 1of 2
APPENDIX B
APPENDIX B
SCCWRP CHANNEL
SCREENING ANALYSIS
INTRODUCTION
The City of Carlsbad's January 14, 2011, Standard Urban Storm Water Management Plan
(SUSMP) outlines low flow thresholds for hydromodification analyses. The thresholds are based
on a percentage of the pre-project 2-year flow (Ch), i.e., O.lQa (low), 0.3Q2 (medium), or O.SQi
(high). A threshold of 0.1 Ch represents a downstream receiving conveyance system with a high
susceptibility to erosion. This is the default value used for hydromodification analyses and will
result in the most conservative (greatest) on-site facility sizing. A threshold of 0.3Q2 or O.SCh
represents downstream receiving conveyance systems with a medium or low susceptibility to
erosion, respectively. In order to qualify for a medium or low susceptibility threshold, a project
must perform a channel screening analysis based on a "hydromodification screening tool"
procedure developed by the Southern California Coastal Water Research Project (SCCWRP).
The SCCWRP results are compared with the critical shear stress calculator results from the
County of San Diego's BMP Sizing Calculator to establish the appropriate susceptibility
threshold of low, medium, or high.
The SCCWRP screening tool requires both office and field work to establish the vertical and
lateral susceptibility of a downstream receiving channel to erosion. The vertical and lateral
assessments are performed independently of each other although the lateral results can be
affected by the vertical rating. The Muroya project discharges to two downstream locations (see
Figure 1). The screening was performed to assess the natural channel at both locations, which are
referred to as the North Screening Area (NSA) and South Screening Area (SSA).
The on-site runoff reaches the NSA as follows. Storm runoff from the northerly portion of the
project is collected by an existing 24-inch RCP storm drain system (Drawing No. 387-1 A) within
Nightshade Readjust beyond the northwest corner of the site. This storm drain system continues
north to northwest along Nightshade Road then discharges into the NSA natural canyon
approximately 500 feet west of the site. Runoff in the canyon flows approximately 600 feet west
to the bottom of the NSA where it is collected by a 48-inch RCP (Drawing No. 322-2A). This
storm drain system continues several thousand feet in Alga Road, Kestrel Drive, and Rockrose
Terrace then ultimately discharges into the Aviara golf course before entering Batiquitos
Lagoon.
The on-site runoff reaches the SSA as follows. Storm runoff from the southerly portion of the
project discharges from the proposed bioretention basin at the southwest corner to the upper end
of the SSA natural canyon. Runoff in the canyon flows approximately 500 feet westerly to the
bottom of the SSA where it is collected by a 36-inch RCP (Drawing No. 322-2A). This storm
drain system continues over 600 feet to the south then discharges into the Aviara golf course
before entering Batiquitos Lagoon.
The initial step in performing the SCCWRP screening analysis is to establish the domain of
analysis. This is followed by office and field components of the screening tool along with the
associated analyses and results. The following sections cover these procedures in sequence.
DOMAIN OF ANALYSIS
SCCWRP defines an upstream and downstream domain of analysis, which establishes the
required study area. The downstream limit is defined when one of these is reached:
• at least one reach downstream of the first grade-control point
• tidal backwater/lentic waterbody
• equal order tributary
• accumulation of 50% drainage area for stream systems and 100 percent drainage area for
urban conveyance systems.
The upstream limit is defined as:
• extend the domain upstream for a distance equal to 20 channel widths or to grade control
in good condition - whichever comes first. Within that reach, identify hard points that
could check headward migration, evidence that headcutting is active or could propagate
unchecked upstream.
NSA Downstream Domain of Analysis
The downstream domain of analysis for the NSA has been determined according to the bullet
items above. Storm runoff from the project discharges into the NSA at the outlet of the
abovementioned 24-inch RCP storm drain. The first permanent grade control below the outlet is
the existing 48-inch RCP (with headwall and concrete apron) at the bottom of the natural canyon
(see Figure 2). Since the storm drain containing this RCP continues for several thousand feet,
one reach downstream of the grade control will be within a non-erodible pipe. Therefore, the
downstream domain of analysis based on the first bullet item will be the grade control created at
the 48-inch RCP entrance.
Since the grade control created by the 48-inch RCP is readily located, it was used to establish the
downstream domain of analysis. This is also closer than the tidal backwater/lentic waterbody
(Batiquitos Lagoon) and other bullet criteria, so it meets the criteria established by SCCWRP.
NSA Upstream Domain of Analysis
A concrete drainage ditch was constructed immediately upstream of the 24-inch RCP outlet into
the NSA. The ditch is shown on Drawing No. 322-2A and verified during a field inspection.
Headcutting has not occurred upstream of the outlet due to the presence of the non-erodible
ditch. Therefore, the upstream domain of analysis is the 24-inch RCP outlet.
SSA Downstream Domain of Analysis
The downstream domain of analysis for the SSA has been determined according to the bullet
items above. Storm runoff will outlet the southerly project area in the proposed 18-inch RCP
storm drain from the proposed southerly bioretention basin. The first permanent grade control
below the outlet is the existing 36-inch RCP (with headwall and concrete apron) at the bottom of
the natural canyon (a photograph was not taken of this facility due to dense brush). The natural
channel reach between the 18-inch RCP outlet and 36-inch RCP inlet is approximately 500 feet.
Since the storm drain below the 36-inch RCP continues for approximately 800 feet (this is
greater than the channel reach), one reach downstream of the grade control will be within a non-
erodible pipe. Therefore, the downstream domain of analysis based on the first bullet item will
be the grade control created at the 36-inch RCP entrance.
m Since the grade control created by the 36-inch RCP is readily located, it was used to establish the
downstream domain of analysis. This is also closer than the tidal backwater/lentic waterbody
(Batiquitos Lagoon) and other bullet criteria, so it meets the criteria established by SCCWRP.
SSA Upstream Domain of Analysis
The area upstream of the proposed 18-inch RCP outlet will be a graded 2:1 fill slope with
m landscaping. The only storm runoff on the slope will be from direct precipitation. Consequently,
the slope is not anticipated to erode and the upstream domain of analysis for the SSA will be at
m the 18-inch RCP outlet, i.e., the 18-inch RCP outlet establishes the headwater of the SSA.
«•
Summary of Domain of Analysis
— The domain of analysis for the NSA is in the natural canyon northwest of the site, and extends
^ from the existing 24-inch RCP outlet down to the existing 48-inch inlet. The flow length covers
approximately 615 feet (see Figure 1). The domain of analysis for the SSA is the natural canyon
"*• from the southwest of the site, and extends from the proposed 18-inch RCP down to the existing
36-inch RCP. The flow length is approximately 509 feet. SCCWRP defines the maximum spatial
"" unit (i.e., channel length) within the domain of analysis to be 200 meters (656 feet). If the
<* domain of analysis is greater than 200 meters, the study reach must be subdivided into smaller
units for study. The domain of analysis for the NSA and SSA are both less than 200 meters.
"** Therefore, the NSA and SSA were each analyzed as a single reach.
m
INITIAL DESKTOP ANALYSIS
After the domain of analysis is established, SCCWRP requires an "initial desktop analysis" that
~" involves office work. The initial desktop analysis establishes the watershed area, mean annual
M precipitation, valley slope, and valley width. These terms are defined in Form 1 included in
Attachment 1. SCCWRP recommends the use of National Elevation Data (NED) to determine
the watershed area, valley slope, and valley width. A review of the NED for Carlsbad determined
that it is equivalent to USGS quadrangle maps. The topographic resolution on USGS maps is low
and typically on a 25-foot contour interval. For this report, the site topography and topography
shown on adjacent as-built grading plans was used because the topography is at a much higher
detail than NED. There is a small area in the NSA watershed with no available topographic
mapping. A site visit was used to determine the watershed boundary in this area.
Figure 1 shows the existing watershed area tributary to the NSA and SSA. The total watershed
areas are 29.11 (0.046 square miles) and 6.78 acres (0.011 square miles), respectively. The mean
annual precipitation is provided in the County of San Diego's BMP Sizing Calculator (see
Appendix A) and is 12.5 inches. The NSA and SSA valley slopes were determined from the
topographic mapping and are 0.048 and 0.159 (meters/meter or feet/feet), respectively. The
„ valley width was estimated from the topographic mapping and site investigation. This is the
portion of the valley that conveys the hydromodification flows. The NSA and SSA valley widths
are approximately 20 feet (6.10 meters) and 10 feet (3.05 meters), respectively.
These values were input to a spreadsheet to calculate the simulated peak flow, screening index,
and valley width index in Form 1. The input data and results are included in Attachment 1.
FIELD SCREENING
After the initial desktop analysis is done, a field assessment must be performed. The field
assessment is used to establish a natural channel's vertical and lateral susceptibility to erosion.
SCCWRP states that although they are admittedly linked, vertical and lateral susceptibility are
assessed separately for several reasons. First, vertical and lateral responses are primarily
controlled by different types of resistance, which, when assessed separately, may improve ease
of use and lead to increased repeatability compared to an integrated, cross-dimensional
assessment. Second, the mechanistic differences between vertical and lateral responses point to
different modeling tools and potentially-different management strategies. Having separate
screening ratings may better direct users and managers to the most appropriate tools for
subsequent analyses.
The field screening tool uses combinations of decision trees and checklists. Decision trees are
typically used when a question can be answered fairly definitively and/or quantitatively (e.g., dso
< 16 mm). Checklists are used where answers are relatively qualitative (e.g., the condition of a
grade control). Low, medium, high, and very high ratings are applied separately to the vertical
and lateral analyses. When the vertical and lateral analyses return divergent values, the most
conservative value shall be selected as the flow threshold for the hydromodification analyses.
Visual observation of the NSA and SSA reveals densely vegetated, natural canyons (see Figures
3 to 6). The vegetative cover extends fairly uniformly across the canyon bottoms and sides. The
cover was so dense that most areas in the NSA and SSA were very difficult to access by foot,
and some areas were only possible to access if the vegetation was trimmed. Due to the dense
cover and relatively low 10-year flows calculated through Form 1 (8.7 cfs for the NSA and 2.4
cfs for the SSA per Attachment 1), the vertical and lateral stability was anticipated to have a
limited susceptibility to erosion.
Vertical Stability
The purpose of the vertical stability decision tree (Figure 2-4 in the City of Carlsbad SUSMP) is
to assess the state of the channel bed with a particular focus on the risk of incision (i.e., down
cutting). The decision tree is included in Figure 16. The first step is to assess the channel bed
material. There are three categories defined as follows:
1. Labile Bed - sand-dominated bed, little resistant substrate.
2. Transitional/Intermediate Bed - bed typically characterized by gravel/small cobble,
Intermediate level of resistance of the substrate and uncertain potential for armoring.
3. Threshold Bed (Coarse/Armored Bed) - armored with large cobbles or larger bed
material or highly-resistant bed substrate (i.e., bedrock).
Figures 7 through 10 shows photographs of the bed material for the NSA and SSA. A
gravelometer is included in the photographs for reference. Each square on the gravelometer
indicates grain size in millimeters (The squares range from 2 mm to 180 mm). Based on the
photographs and site investigation, the bed material and resistance is generally within the
transitional/intermediate bed category. There was no evidence of a threshold bed condition.
Some bed areas contained smaller grain sizes found in a labile bed. Dr. Eric Stein from
SCCWRP, who co-authored the Hydromodification Screening Tool in the Final
Hydromodification Management Plan (HMP), indicated that it would be appropriate to analyze
the channel as a transitional/intermediate bed. This requires the most rigorous steps and will
generate the appropriate results for the size range.
Transitional/intermediate beds cover a wide susceptibility/potential response range and need to
be assessed in greater detail to develop a weight of evidence for the appropriate screening rating.
The three primary risk factors used to assess vertical susceptibility for channels with
transitional/intermediate bed materials are:
1. Armoring potential - three states (Checklist 1)
2. Grade control - three states (Checklist 2)
3. Proximity to regionally-calibrated incision/braiding threshold (Mobility Index Threshold
- Probability Diagram)
These three risk factors are assessed using checklists and a diagram (see Attachment 2), and are
combined to provide a final vertical susceptibility rating for the intermediate/transitional bed-
material group. Each checklist and diagram contains a Category A, B, or C rating. Category A is
the most resistant to vertical changes while Category C is the most susceptible.
Checklist 1 determines the armoring potential of the channel bed. The channel bed of the NSA
and SSA fall in Category B, which represents intermediate bed material within unknown
armoring potential due to a surface veneer and dense vegetation. The soil was probed with a
shovel. Penetration was difficult through the underlying layer. Due to the dense vegetative
growth, the armoring potential could have been rated higher, but Category B was conservatively
(i.e., more potential for channel incision) chosen.
Checklist 2 determines the grade control characteristics of the channel bed. Grade controls can
be man-made such as the pipes, headwalls, and concrete aprons at the downstream end of the
NSA and SSA. SCCWRP also states that grade controls can be natural. Examples are vegetation
or confluences with a larger waterbody. As indicated above and verified with photographs, the
NSA and SSA both contain dense vegetation (see Figures 11 through 14). The plant roots and
fallen tree trunks serve as natural grade control. The spacing of these is much closer than the 50
meters identified in the checklist. Further evidence of the effectiveness of the natural grade
controls is the absence of headcutting, mass wasting (large vertical erosion of a channel bank), or
undercutting of existing drainage facilities. Based on this information, both the NSA and SSA
are within Category A on Checklist 2.
The Mobility Index Threshold is a probability diagram that depicts the risk of incising or
braiding based on the potential stream power of the valley relative to the median particle
diameter. The threshold is based on regional data from Dr. Howard Chang of Chang Consultants
and others. The probability diagram is based on dso as well as the Screening Index determined in
the initial desktop analysis (see Attachment 1). dso is derived from a pebble count in which a
minimum of 100 particles are obtained along transects at the site. SCCRWP states that if fines
less than ya-inch thick are at a sample point, it is appropriate to sample the coarser buried
substrate. The dso value is the particle size in which 50 percent of the particles are smaller and 50
percent are larger. The pebble count results for the NSA and SSA are included in Attachment 2.
The results show a dso of 16 millimeters for each area. The screening index for the NSA and SSA
and included in Attachment 1. Plotting the dso and screening index values on the Mobility Index
Threshold diagram shows that the NSA and SSA have a less than 50 percent probability of
incising or braiding, which falls within Category A.
The overall vertical rating is determined from Checklist 1, Checklist 2, and the Mobility Index
Threshold. The scoring is based on the following values:
Category A = -1, Category B = 0, Category C = 1
The vertical rating score is the sum of the armoring potential score, grade control score, and
Mobility Index Threshold score (0 + -1 + -1 = -2). The combined score of-2 is considered a low
threshold for vertical susceptibility.
Lateral Stability
The purpose of the lateral decision tree (Figure 2-5 from City of Carlsbad SUSMP is included in
Figure 17) is to assess the state of the channel banks with a particular focus on the risk of
widening. Channels can widen from either bank failure or through fluvial avulsions such as chute
cutoffs and braiding. Widening through fluvial avulsions/active braiding is a relatively
straightforward observation. If braiding is not already occurring, the next logical question is to
assess the condition of the banks. Banks fail through a variety of mechanism; however, one of
the most important distinctions is whether they fail in mass (as many particles) or by fluvial
detachment of individual particles. Although much research is dedicated to the combined effects
of weakening, fluvial erosion, and mass failure, SCCWRP found it valuable to segregate bank
types based on the inference of the dominant failure mechanism (as the management approach
may vary based on the dominant failure mechanism). A decision tree (Form 4 in Attachment 2)
is used in conducting the lateral susceptibility assessment. Definitions and photographic
examples are also provided below for terms used in the lateral susceptibility assessment.
The first step in the decision tree is if lateral adjustments are occurring. The adjustments can take
the form of extensive mass wasting (greater than 50 percent of the banks are exhibiting planar,
slab, or rotational failures and/or scalloping, undermining, and/or tension cracks). The
adjustments can also involve extensive fluvial erosion (significant and frequent bank cuts on
over 50 percent of the banks). Neither mass wasting nor extensive fluvial erosion was evident at
the NSA or SSA. The banks are intact (see Figures 3 through 6 and 15). Due to the dense
vegetation in both areas, photographs representative of the banks were difficult to take.
Nonetheless, the dense vegetation supports the absence of large lateral adjustments.
The next step is to assess the consolidation of the bank material. The banks were moderate to
well-consolidated. This determination was made because the banks were difficult to penetrate
with a shovel. In addition, the banks showed limited evidence of crumbling and were composed
of tightly-packed particles (see Figure 15).
Form 6 (see Attachment 2) is used to assess the probability of mass wasting. Form 6 identifies a
10, 50, and 90 percent probability based on the bank angle and bank height. Hydromodification
is based on flow rates up to the 10-year event. The 10-year flows calculated through Form lin
Attachment 1 are 8.7 cfs for the NSA and 2.4 cfs for the SSA. The bank height associated with
these flows will be small and certainly less than 5 feet. Even during the 100-year flow, the NSA
and SSA tributary areas in Figure 1 indicate that the associated bank height will only be a few
feet high. In addition, the topographic mapping and site visit reveals that the bank angles are
primarily in the 40 degree or less range. Using these values in Form 6 yields a less than 10
percent risk of bank failure.
The final step is based on the braiding risk determined from the Mobility Index Threshold in the
vertical rating. The braiding risk for the NSA and SSA were both less than 50 percent per the
Vertical Stability analysis above. From this, the lateral susceptibility rating is low (red circles are
included on the Form 4 Decision Tree in Attachment 2 showing the decision path).
CONCLUSION
The SCCWRP channel screening tools were used to assess the downstream channel
susceptibility. The assessment was made for both downstream receiving channels identified as
the North Screening Area and South Screening Area. The assessment was performed based on
office analyses and field work. The results indicate a low threshold for vertical and lateral
susceptibilities. The HMP requires that these results be compared with the critical stress
calculator results incorporated in the County of San Diego's BMP Sizing Calculator. The BMP
Sizing Calculator results are included in Appendix A. The critical stress calculator in the
Calculator also returned a low threshold. Therefore, the SCCWRP analyses and critical stress
calculator demonstrate that the project can be designed assuming a low susceptibility, i.e., 0.5Q2.
The SCCWRP results are consistent with the physical condition of the NSA and SSA. Both areas
support dense vegetative growth. The growth is so dense that travel by foot was very difficult in
most areas. Neither area has exhibited signs of extensive, ongoing erosion. Finally, the tributary
area to each area is relatively small so the storm runoff will not be significant.
^^^^2^LZ.;"":XT*'.: \ * -':;.;
a -rtSt :\s ••' . • ~£* t'/ J 'i V-.j.. '' •- "'S-ill1 5$ m- - «?! :!•]»- r^ \ '•" / *ps*«^r>^5%;r ^ "s" *n 4 -Vr.- - ^-tu^t • ^.-ty ]*r it- Cm i /ili, 1, — — "1V4JI a 1T-Eite-V^ f
WH,a, - p-'J-M
^^"--w4,,m
EXIST. 36" RCP
GRAPHIC SCALE
0 100 200
LEGEND:
1 INCH = 200 FEET
EXISTING WATERSHED BOUNDARY
FLOW PATH WITHIN DOMAIN OF ANALYSIS
NSA NORTH SCREENING AREA
BSA SOUTH SCREENING AREA
6.78 AC WATERSHED AREA
• PEBBLE COUNT LOCATION
PHOTO LOCATION (MATCHES FIGURE NUMBERS
FROM REPORT)
FIGURE 1. SCCWRP EXHIBIT
Figure 2. Existing 48-inch RCP, Headwall, and Concrete Apron
(i.e., Grade Control) at Downstream End of NSA
Figure 3. Looking Upstream at the NSA from the Downstream End
9
Figure 4. Looking Downstream at the NSA from the Upstream End
Figure 5. Looking Upstream at the SSA from the Downstream End
10
Figure 6. Looking Downstream at the SSA from the Upstream End
Figure 7. Channel Material in NSA
11
Figure 8. Channel Material in NSA
Figure 9. Channel Material in SSA
12
Figure 10. Channel Material in SSA
Figure 11. Dense Vegetation in the NSA
13
Figure 12. Dense Grasses and Trees in the NSA
Figure 13. Dense Vegetation in the SSA
14
Figure 14. Fallen Tree Trunks Form Grade Control on Channel Bed
Figure 15. Typical Channel Bank with Well-Consolidated Material
15
CHANNEL BED RESISTANCE
LAB I IE BED
•Sand- Dominated
•i < 16 mm
•1 Surface Sand > 25%
•Loosely-Packed
INTERMEDIATE BED
•Woderatelyto Loosely-
Packed Cobble / Gravel
• Hardpan of Uncertain
Depth, Extent Erodibility
COARSE/ARMORED BED
•d > 128 mm
•Boulder/Large Cobble
•Tightly-Packed
•<5% Sand
•Continuous Bedrock
•Contirvuous Concrete
EXAMINE RISK FACTORS
•Grade Control
•Armoring Potential
•Proximftyto Incision Threshold
Goto Bed ErodibiWy
Checklists and Incision
Diagram Checklist
Fill out SCCWRP Scoring
Omens to Determine if the
Receiving Channel has a HIGH,
MEDIUM, or LOW Susceptibility
Figure 16. SCCWRP Vertical Channel Susceptibility Matrix
LOW
•Fully Amored / Bedrock Bank
Estabilization in Good Condition
•No Evidence of Chute
Formation / Avulsions
•Fully Confined, Directly
Connected to Hillside. VWI-1
ArERAU.Y ADJUSTABLE?^
<r •"
/ AeLa
1 AJjusti
V 6«a«
I
teral ~\ |B
ting? J
NO
None, or Flu «ial Only Limited to
Bends and Constrictions
ir
Mass wasting or
Extensive Fluvial
" Erosion or Chute
Cutoff Formation
\
4 i
MED HIGH
VWI <= 2 VWI > 2
1 I
/GotoX
/ Figure 2 3 \
1 ofthe J
V Decision /
xMatrix/
Moderately or Wed-Consolidated Poorly or Unconsolidated
Goto
Figure 2.3
ofthe
Decision
Matrix
Figure 17. SCCWRP Lateral Channel Susceptibility Matrix
Attachment 1
ATTACHMENT 1
SCCWRP INITIAL DESKTOP ANALYSIS
November, 2009 Revised Draff for Field Tesfing/TAC Review 6
Note: This form is reproduced exactly from the HMP except for the red text.
FORM 1: INITIAL DESKTOP ANALYSIS
IF required at multiple locations, circle one (applicant site, upstream extent, downstream
extent)NSA: 33.1100 degrees
Location: Latitude: SSA: 33.1074 degrees
-117.2921
Longitude: -117.2893
Description (river name, crossing streets, etc.): Unnamed natural canyons.
GIS Parameters: US Customary units used for contributing drainage area (A) and
mean annual precipitation (P) to apply regional flow equations after the USGS
Table 2.1: Initial desktop analysis in GIS
Symbol
Aen"O 05 .-t±
<D d) C
<D Q. ^ p
^ 2 "5i
g Q_ CLJJ_
Sv
_0
B "Q-'cO =j
°~<n W
^ "(/)
Variable
(units)
Area
0(rni )
Mean annual
precipitation
(iri \in.)
Valley slope
(m/m)
• •
Valley width
(m)V "/
Value Description and Source
contributing drainage area to location via published Hydrologic
Unit Codes (HUCs) and/or < 30 m National Elevation Data (NED),
USGS seamless server
area-averaged annual precipitation via USGS delineated
polygons using records from 1900 to 1960 (Natural Resources
Conservation Service (NRCS) shape file using records from 1961
to 1990 was less accurate in hydrologic models)
geomorphically-defined valley slope at site via NED, dictated by
watershed configuration, confluences, consistent valley widths,
etc., over a distance of up to -500 m or 10% of the main-channel
length from site to drainage divide (whichever is smaller)
valley bottom width at site from natural valley wall to valley wall,
dictated by clear breaks in surface slope on NED raster,
irrespective of potential armoring from floodplain encroachment,
levees, etc.
See the following page for the above values for the NSA and SSA.
Table 2.2: Simplified peak flow (Hawley and Bledsoe, In review), screening index,
and valley width index
Symbol Dependent Variable
(units)
Value Equation Required
units
Qiocfs 10-yr peak flow (ft7s)
Q10 10-yr peak flow (m3/s)
INDEX 10-yr screening index (m15/s°5
Wref Reference width (m)
VWI Valley width index (m/m)
Q10cfs=18.2*A087*P077
Q10 = 0.0283 * Q10cfs
INDEX = SV*Q10 °'5
Wref = 6.99 * Q10 °438
VWI = Wv/Wfel
A (mr)
QlOcfs
Sv (m/m)
Qio (m3/s)
Qio (m3/s)
W¥(m)
Wref(m)
Note: Gray highlighting indicates values directly used in field assessments
See the following page for the calculations associated with Table 2.2. (Sheet 1 of 1)
The * in the equations indicates multiplication.
SCCWRP FORM 1 ANALYSES
Study Area
NSA
SSA
Area
A, sq. mi.
0.041
0.011
Mean Annual Precip.
P, inches
12.5
12.5
Valley Slope
Sv, m/m
0.048
0.159
Valley Width
Wv, m
6.10
3.05
Study Area
NSA
SSA
10-Year Flow
QlOcfs, cfs
8.65
2.43
10-Year Flow
Q10, cms
0.245
0.069
10-Year Screening
Index
INDEX
0.024
0.042
Reference Width
Wref, m
3.77
2.17
Valley Width Index
VWI, m/m
1.62
1.41
Note:
The areas were obtained from the watershed delineations shown on the SCCWRP Exhibit.
The mean annual precipitation was obtained from the County of San Diego's BMP Calculator (see Appendix A).
The valley slope was determined from the elevations and flow lengths from the SCCWRP Exhibit.
The valley width was estimated from the topographic mapping on the SCCWRP Exhibit and site investigation.
The 10-year flow, screening index, reference width, and valley width index are calculated from the equations in Table 2.2 on Form 1.
Attachment 2
ATTACHMENT 2
SCCWRP FIELD SCREENING DATA
November, 2009 Revised Draft for Field Testing/TAC Review 15
Checklists and diagram for assessing potential bed erodibility - transitional/
intermediate bed material:
Checklist 1: Armoring Potential
A.D
NSA & SSA
D
A mix of coarse gravels and cobbles that are tightly packed with
< 5% surface material of diameter < 2 mm
B. Intermediate to A. and C. or hardpan of unknown resistance, spatial extent
(longitudinal and depth), or unknown armoring potential due to surface
veneer covering gravel or coarser layer encountered with probe
C. Gravels/cobbles that are loosely packed and/or > 25% surface material of
diameter < 2 mm
Figure 2.3: Armoring potential photographic supplement for assessing
intermediate beds (16 < d50 < 128 mm) in conjunction with Checklist 1
(Sheet 2 of 5)
November, 2009 Revised Draff for Field Testing/TAC Review 16
Checklist 2: Grade Control
NSA & SSA
D
D
A. Grade control is present with spacing < 50 m or every 2/Sv
• No evidence of failure/ineffectiveness, e.g., no headcutting (> 30
cm), no active mass wasting (analyst cannot say grade control
sufficient if mass-wasting checklist indicates presence), no exposed
bridge pilings, no culverts/structures undermined
• Hard points in serviceable condition at decadal time scale, e.g., no
apparent undermining, flanking, failing grout
• If geologic grade control, rock should be resistant igneous and/or
metamorphic or if sedimentary/hardpan should be subjected to
hammer test/borings before placing in this category (criteria TBD)
B. Intermediate to A. and C. - artificial or geologic grade control present
but spaced 2/Sv to 4/Sv or potential evidence of failure or hardpan of
uncertain resistance
C. Grade control absent, spaced > 100 m or > 4/Sv, or clear evidence of
ineffectiveness
most resistant least resistant
8) Intermediate
Figure 2.4: Grade-control (condition) photographic supplement for assessing
intermediate beds (16 < d50 < 128 mm) in conjunction with Checklist 2
Diagram - Regionally-calibrated screening index threshold for incising/braiding
For transitional bed channels where the bed material dsn is between 16 and 128 mm, use the
diagram and table (Figure 2.5 and Table 2.3, respectively) to determine if the risk of incision is >
50%.
(Sheet 3 of 5)
Mobility Index Threshold —
probability of incising or braiding
1
SSA
NSA
0.001
• Stable
10% risk
1d50(mm) 10 10°
Braided + Incising
50% risk 90% risk
(mm)
o
'to
£ EQJ f-»
ra
<T *~
£ "0
I-0
g> E
0 ^.1 VOS o
128
96
80
64
48
32
16
8
4
2
1
0.5
0.145
0.125
0.114
0.101
0.087
0.070
0.049
0.031
0.026
0.022
0.018
0.015
zo;
CD
3...
OO
(B
-a
(Da
:5a:
n
ns,-rj
•>
«
'
GIS-derived: 10-yr flow & valley slope
Field-derived: ci50 (100-pebble count)
Figure 2.5: Probability of incising/braiding based on logistic regression of Screening Index and dso
(Sheet 4 of 5) -
d50 is 16 mm from field work. For 16 mm, the table on the left indicates that the risk of incising or braiding is less than 50% if the
screening index is less than 0.049. The Form 1 analyses in Attachment 1 shows that the screen index for the NSA and SSA are
0.024 and 0.042, respectively. Therefore, the table and the chart show the risk is less than 50%.
Pebble Count
NSA diameter, mm SSA Diameter, mm
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2.8
2.8
2.8
2.8
2.8
2.8
2.8
2.8
4
4
4
4
4
4
4
8
8
8
8
8
8
8
8
8
8
11
11
11
11
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2.8
2.8
2.8
2.8
2.8
2.8
2.8
2.8
2.8
4
4
4
4
4
4
4
4
4
8
8
8
8
8
8
8
11
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
11
11
11
11
11
16
16
16
16
16
16
16
16
16
16
22.6
22.6
22.6
22.6
22.6
22.6
32
32
32
32
32
32
32
32
45
45
45
45
45
45
45
45
45
45
45
64
64
64
64
64
90
90
11
11
11
16
16
16
16
16
16
16
16
16
16
22.6
22.6
22.6
22.6
22.6
22.6
32
32
32
32
32
32
32
45
45
45
45
45
45
45
45
45
45
64
64
64
64
16
64
90
90
90
11
90
D50
92
93
94
95
96
97
98
99
100
90
90
90
90
128
128
128
180
180
90
90
128
128
128
128
180
180
180
FORM 4: LATERAL SUSCEPTIBILTY FIELD SHEET
Circle appropriate nodes/pathway for proposed site or use sequence of questions provided below (Form 5).
FORM 6: Probabilistic bank stability using height & angle
Figure 2.10: Lateral Susceptibility decision tree
Zo<
CD
.'
•
oo
c(D5•Via
-o
O""*
r
2o-«
(8
(Sheet 1of1) MCn
November, 2009 Revised Draff for field Testing/JAC Review 27
FORM 6: LATERAL SUSCEPTIBILTY
If mass wasting is not currently extensive and the banks are moderately- to well-consolidated,
measure bank height and angle at several locations (i.e., at least three locations that capture
the range of conditions present in the study reach) to estimate representative values for the
reach. Use diagram/table below to determine if risk of bank failure is > 10%. Support your
results with photographs that include a protractor/rod/tape/person for scale reference.
50 60 70
Bank Angle (degrees)
Figure 2.11: Lateral probability of bank-failure diagram
Table 2.6: Applicant-determined values for Lateral probability of bank failure
Bank Corresponding Bank
Bank Angle Height (m) Height for 10% Risk of
(degrees) (from Mass Wasting (m)
(from Field)
(from
Field)(from Table)
Rating
(LOW-VERY HIGH
depending on other
decision-tree
components)
Left Bank
Right Bank
(Sheet 1 of 1)