CC RES 2015-024 RESOLUTION NO. 2015-24
A RESOLUTION OF THE CITY COUNCIL OF THE CITY OF RANCHO PALOS VERDES,
CALIFORNIA, APPROVING A GREEN STREETS POLICY.
THE CITY COUNCIL OF THE CITY OF RANCHO PALOS VERDES, CALIFORNIA, HEREBY
RESOLVES, DETERMINES AND ORDERS AS FOLLOWS:
SECTION 1: The Municipal Separate Storm Sewer System (MS4) Permit (Order
No. R-2012-0175)was adopted by the California Regional Water Quality Control Board, Los Angeles
Region on November 8, 2012. Municipalities electing to prepare a Watershed Management Program
or an Enhanced Watershed Management Program under this Permit are required to demonstrate
that Green Street policies are in place that specify the use of green street strategies for transportation
corridors.
SECTION 2: Green Streets are enhancements to street and road projects to
improve the quality of storm water and urban runoff through the implementation of infiltration, bio-
treatment, xeriscaping parkways and tree lined streets.
SECTION 3: The City Council of the City of Rancho Palos Verdes, California,
hereby adopts the City of Rancho Palos Verdes Green Streets Manual shown in Exhibit"A,"attached
hereto and incorporated by reference, and directs the Director of Public Works, or his designee, to
implement green streets strategies for transportation corridors as described in the City of Rancho
Palos Verdes Green Streets Manual to the maximum extent practicable.
SECTION 4: Routine maintenance including but not limited to: slurry seals, grind and
overlay and reconstruction to maintain original line are grade are excluded from the Green Street
Policy.
PASSED, APPROVED, AND ADOPTED this 7th day Jo A pril, 2015.
r
'May•r
ATTEST: . /'
6C iilk
City Clerk
STATE OF CALIFORNIA )
COUNTY OF LOS ANGELES ) ss.
CITY OF RANCHO PALOS VERDES )
I, Carla Morreale, City Clerk of the City of Rancho Palos Verdes, California, hereby
certify that the above Resolution No. 2015-24 was duly and regularly passed and adopted by the
said City Council at a regular meeting thereof held on April 7, 201.5-:
City Clerk
i; ; Resolution No.2015-24
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Resolution No.2015-24
Exhibit A
Page 2 of 23
Green Streets Manual
April 2015
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Prepared for:
City of Rancho Palos Verdes
Department of Public Works
30940 Hawthorne Blvd.
Rancho Palos Verdes, CA 90275
(310) 544-5252
Resolution No.2015-24
Exhibit A
Page 3 of 23
Green Streets Manual
TABLE OF CONTENTS
Section 1—Introduction 1
1.1 What are Green Streets? 1
1.2 Why are Green Streets being required? 1
1.3 Planning and Development 3
1.3.1 Site Considerations 3
1.3.2 Design Considerations 4
1.3.3 BMP Sizing for Applicable Green Streets Projects 4
1.3.4 Alternative Compliance Options for Applicable Green Streets Projects 5
1.3.5 Infiltration Considerations 5
Section 2—Infiltration 9
2.1 Infiltration Trenches and Dry Wells 9
2.2 Rain Gardens 10
2.3 Permeable Pavement 11
Section 3—Biotreatment 13
3.1 Bioretention 13
3.2 Flow-Through Planters 14
3.3 Vegetated Swales 15
3.4 Vegetated Buffer Strips 16
Section 4—Treatment BMPs 17
4.1 sand Filters & Storm Drain Inlet Protections 17
Section 5—Street Trees 19
5.1 Street Trees 19
Section 6—Definitions 20
Section 7—References 20
City of Rancho Palos Verdes Table of Contents April 2015
Resolution No.2015-24
Exhibit A
Page 4 of 23
Green Streets Manual
SECTION 1 - INTRODUCTION
1.1 WHAT ARE GREEN STREETS?
Roads present many opportunities for green infrastructure application. One principle of green
infrastructure involves reducing and treating stormwater close to its source. Urban transportation right-
of-ways integrated with green techniques are often called "green streets." Green streets provide source
controls for stormwater runoff and pollutant loads. In addition, green infrastructure approaches
complement street facility upgrades, street aesthetic improvements, and urban tree canopy efforts that
also make use of the right-of-way and allow it to achieve multiple goals and benefits. Using the right-of-
way for treatment of stormwater runoff links green with grey infrastructure by making use of the
engineered conveyance of roads and providing connections to conveyance systems when needed.
Green streets are beneficial for new road construction and retrofits. They can provide substantial
economic benefits when used in transportation applications. Coordinating green infrastructure
installation with broader transportation improvements can reduce the cost of stormwater management
by including it within larger infrastructure improvements. A large municipal concern regarding green
infrastructure use is maintenance access; using roads and right-of-ways as locations for green
infrastructure not only addresses a significant pollutant source, but also alleviates access and
maintenance concerns by using public space. Also, right-of-way installations allow for easy public
maintenance.
Green streets can incorporate a wide variety of design elements including street trees, permeable
pavements, bioretention, and swales. Although the design and appearance of green streets will vary,the
functional goals are the same; provide source control of stormwater, limit its transport and pollutant
conveyance to the collection system, restore pre-development hydrology to the maximum extent
practicable, and provide environmentally enhanced roads. Successful application of green techniques
will encourage soil and vegetation contact and infiltration and retention of stormwater.
1.2 WHY ARE GREEN STREETS BEING REQUIRED?
This Green Streets Manual provides guidance to comply with the Municipal Separate Storm Sewer
System (MS4) Permit (Order Number R4-2012-0175), and any subsequent permit, which requires that
jurisdictions in Los Angeles County reduce contaminants in runoff to improve water quality in
waterways.These requirements stem from the National Pollutant Discharge Elimination System (NPDES)
requirements of the Clean Water Act (CWA).
The MS4 Permit requires Green Streets strategies to be implemented for transportation corridors.
Transportation corridors represent a large percentage of the impervious area within Los Angeles and
therefore generate a substantial amount of runoff from storm events. The altered flow regime from
traditional roadways, increased runoff volume, and high runoff peak flows, are damaging to the
environment and a risk to property downstream.
Traditionally, street design has focused on removing water from the street as quickly as possible and
transferring it to storm drains, channels, and water bodies. Stormwater runoff can contain bacteria and
other pollutants, and is thereby regulated at the state and local level (refer to Table 1 for a list of
pollutants typical of roads). Green Streets will help to transform the design of streets from the
conventional method of moving water off-site as quickly as possible to a method of storing and treating
water on-site for a cleaner discharge into the waters of the U.S.
City of Rancho Palos Verdes Page 1 April 2015
Resolution No.2015-24
Exhibit A
Page 5 of 23
Green Streets Manual
Street and road construction applies to major arterials, state routes, highways, or rail lines used for the
movement of people or goods by means of bus services, trucks, and vehicles, and transportation
corridors within larger projects. Projects which are required to follow this Green Streets Guidance
Manual include the following:
1. Street and road construction of 10,000 square feet or more of impervious surface area.
2. Street and road redevelopment resulting in the creation or addition or replacement of 5,000
square feet or more of impervious surface area on an already developed site. Redevelopment
does not include routine maintenance activities that are conducted to maintain original line and
grade, hydraulic capacity, original purpose of facility or emergency redevelopment activity
required to protect public health and safety. Impervious surface replacement, such as the
reconstruction of parking lots and roadways which does not disturb additional area and
maintains the original grade and alignment, is considered a routine maintenance activity.
Redevelopment does not include the repaving of existing roads to ma Britain original line and
grade.
Table 1: Examples of Stormwater Pollutants Typical of Roads (Managing Wet Weather with Green Infrastructure Municipal
Handbook:Green Streets,2008).
Pollutant Source Effects
Trash Littering Physical damage to aquatic animals and fish,
release of poisonous substances
Increased turbidity,increased transport of soil
Sediment/solids Construction,unpaved areas bound pollutants,negative effects on aquatic
organisms reproduction and function
Vehicle brake pads,vehicle tires,motor oil,vehicle
Metals(Copper,Zinc, Lead, Toxic to aquatic organisms and can accumulate in
emissions and engines,vehicle emissions,brake
Arsenic) sediments and fish tissues
linings,automotive fluids
Organics associated with Vehicle emissions,automotive fluids,gas stations Toxic to aquatic organisms
petroleum(e.g., PAHs)
Vehicle emissions,atmospheric deposition, Promotes eutrophication and depleted dissolved
Nutrients fertilizers,leaf shed oxygen concentrations
B Creates a harmful environment for humans and
i acteria Animal traffic
'aquatic life
City of Rancho Palos Verdes Page 2 April 2015
Resolution No.2015-24
Exhibit A
Page 6 of 23
Green Streets Manual
1.3 PLANNING AND DEVELOPMENT
Ideally, a site would be designed to capture and use or infiltrate the entire runoff volume of a storm,
however site and design constraints make it difficult to achieve that goal. This Green Streets Manual is
designed to provide guidance with BMP selection based on site constraints typical to street design.
Streetscape geometry, topography, and climate determine the types of controls that can be
implemented. The initial step in selecting a stormwater tool is determining the available open space and
constraints. Stormwater controls should be selected using the hierarchy represented in Figure 1, the site
guidelines represented in Table 2, and the location opportunities listed in Table 3.
1.3.1 Site Considerations
Specific elements which should be given special consideration in the site assessment process for
applicable Green Streets include:
• Ownership of land adjacent to right of ways.The opportunity to provide stormwater treatment
may depend on the ownership of land adjacent to the right-of-way. Acquisition of additional
right-of-way and/or access easements may be more feasible if land bordering the project is
owned by relatively few land owners.
• Location of existing utilities. The location of existing storm drainage utilities can influence the
opportunities for Green Streets infrastructure. For example, stormwater planters can be
designed to overflow along the curb-line to an existing storm drain inlet, thereby avoiding the
infrastructure costs associated with an additional inlet. The location of other utilities may limit
the allowable placement of BMPs to only those areas where a clear pathway to the storm drain
exists.
• Grade differential between road surface and storm drain system. Some BMPs require more
head from inlet to outlet than others; therefore, allowable head drop may be an important
consideration in BMP selection. Storm drain elevations may be constrained by a variety of
factors in a roadway project (utility crossings, outfall elevations, etc.) that cannot be overcome
and may override stormwater management considerations.
• Longitudinal slope. The suite of BMPs which may be installed on steeper road sections is more
limited. Specifically, permeable pavement and swales are more suitable for gentle grades. Other
BMPs may be more readily terraced to be used on steeper slopes. Infiltration should not be
considered for slopes greater than 10%.
• Soil suitability. Infiltration BMPs require specific types of soil. The site assessment should
determine the type of soils on the site and the infiltration rate of the soils if infiltration BMPs are
proposed.
• Land subsidence potential. If infiltration is proposed, the increased potential for land
subsidence must be considered and addressed in a geotechnical investigation.
• Potential access opportunities. A significant concern with installation of BMPs in major right of
ways is the ability to safely access the BMPs for maintenance considering traffic hazards. Vehicle
travel lanes and specific areas potentially hazardous for maintenance crews should be identified
during the site assessment. The Green Streets WQ.MP should provide subsequent steps to avoid
placing BMPs in the identified hazardous areas.
City of Rancho Palos Verdes Page 3 April 2015
Resolution No.2015-24
Exhibit A
Page 7 of 23
Green Streets Manual
1.3.2 Design Considerations
The drainage patterns of the project should be developed so that drainage can be routed to areas with
BMP opportunities before entering storm drains. For example, if a median strip is present, a reverse
crown should be considered, where allowed, so that stormwater can drain to a median swale. Likewise,
standard peak-flow curb inlets should be located downstream of areas with potential for stormwater
planters so that water can first flow into the planter, and then overflow to the downstream inlet if
capacity of the planter is exceeded. It is more difficult to apply green infrastructure after water has
entered the storm drain.
Green Streets projects are not required to treat off-site runoff; however treatment of comingled off-site
runoff may be used to off-set the inability to treat areas within the project for which significant
constraints prevent the ability to provide treatment.
Applicable Green Streets projects should apply the following site design measures to the maximum
extent practicable and as specified in the local permitting agency's codes:
• Minimize street width where feasible while maintaining traffic flow and public safety.
• Add tree canopy by planting or preserving trees/shrubs.
• Use porous pavement or pavers for low traffic roadways, on-street parking, shoulders or
sidewalks.
• Integrate traffic calming measures in the form of bioretention curb extensions.
1.3.3 BMP Sizing for Applicable Green Streets Projects
An 85th percentile standard design storm should be used to determine the appropriate size, slope, and
materials of each facility. After identifying the appropriate stormwater facilities for a site, an integrated
approach using several BMPs is encouraged. To increase water quality and functional hydrologic
benefits, several stormwater management BMPs can be used in succession. This is called a treatment
train approach. The control measures should be designed using available topography to take advantage
of gravity for conveyance to and through each facility. All Green Streets designs must be based off of a
published design standard.
The following steps should be used to size BMPs for applicable Green Streets projects:
1. Delineate drainage areas tributary to BMP locations and compute imperviousness.
2. Look up the recommended sizing method for the BMP selected in each drainage area and
calculate target sizing criteria.
3. Design BMPs per a published design standard.
4. Attempt to provide the calculated sizing criteria for the selected BMPs.
5. If sizing criteria cannot be achieved, document the constraints that override the application of
BMPs and provide the largest portion of the sizing criteria that can be reasonably provided given
constraints. If BMPs cannot be sized to provide the calculated volume for the tributary area, it is
still essential to design the BMP inlet, energy dissipation, and overflow capacity for the full
tributary area to ensure that flooding and scour is avoided. It is strongly recommended that
BMPs which are designed to less than their target design volume be designed to bypass peak
flows.
City of Rancho Palos Verdes Page 4 April 2015
Resolution No.2015-24
Exhibit A
Page 8 of 23
Green Streets Manual
1.3.4 Alternative Compliance Options for Applicable Green Streets Projects
Alternative compliance programs should be considered for applicable Green Streets projects if on-site
green infrastructure approaches cannot practicably treat the design volume. The primary alternative
compliance option for applicable Green Streets projects is the completion of off-site mitigation projects.
The proponent would implement a project to reduce stormwater pollution for other portions of
roadway or similar land uses when being reconstructed to the project in the same hydrologic unit,
ideally as close to the project as possible and discharging to the same outfall.
1.3.5 Infiltration Considerations
Appropriate soils, infiltration media, and infiltration rates should be used for infiltration BMPs. If
infiltration is proposed, a complete geotechnical or soils report should be undertaken to determine
infiltration rates, groundwater depth, soil toxicity and stability, and other factors that will affect the
ability and the desirability of infiltration.
Infiltration infeasibility may result from conditions including the following:
1. The infiltration capacity of the underlying soils is less than 0.3 inch per hour.
2. Locations where seasonal high groundwater is within ten feet of the bottom of the infiltration
facility;
3. Locations susceptible to land subsidence;
4. Locations within 100 feet of a groundwater well used for drinking water;
5. Brownfield development sites or other locations where pollutant mobilization is a documented
concern;
6. Locations with potential geotechnical hazards;
7. Smart growth and infill or redevelopment locations where the density and/ or nature of the
project would create significant difficulty for compliance with the onsite volume retention
requirement.
City of Rancho Palos Verdes Page 5 April 2015
Resolution No.2015-24
Exhibit A
Page 9 of 23
Green Streets Manual
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EXEMPT PROJECTS
. Redevelopment does not include routine maintenance activities that are conducted to maintain original line and grade,hydraulic capacity, 5
original purpose of facility or emergency redevelopment activity required to protect public health and safety.Impervious surface
replacement,such as the reconstruction of parking lots and roadways which does not disturb additional area and maintains the original
grade and alignment,1 considered a routine maintenance activity.Redevelopment does not include the repavirg of existing roads to
maintain original line and grade. ;R
GREEN STREETS CATEGORIES
Lt Street and road construction applies to major arterials,state routes,highways,or rail lines used for the movement of people or goods 4,
by means of bus services,trucks,and vehicles,and transportation corridors within larger projects.Projects which are required to follow •
the Rancho Palos Verdes Green Streets Guidance Manual include the following:
fi 1. New street and road construction of 10,000 square feet or more of impervious surface area. i.
f
2. Street and road redevelopment resulting in the creation or addition or replacement of 5,000 square feet or more of impervious 1
surface area on an already developed site.
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,. GREEN STREETS BMP SELECTION
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Figure 1:BMP Selection Flow Chart.
City of Rancho Palos Verdes Page 6 April 2015
Green Streets Manual
Table 2:BMP Selection by Street Context(Model for Living Streets Design Manual,2011).
v
BIORETENTION DETENTION PAVING INLET PROTECTIONS
STREET Vegetated i Infiltration Trenches Permeable Storm Drain i Storm Drain i Pipe Filter
CONTEXT Swales Planters Buffer Strips Rain Gardens &Dry Wells Pavement Inlet Screens i Filter Inserts I Inserts
.
Downtown ✓ V. V. V. • V. V.
Commercial •
•T
Commercial Commercial V. V. V. V. V. V. ✓
Throughway
Neighborhood ✓ • V. V. V. V. V.
Commercial •
Downtown V. V. V. V. V. V. V. V.
Residential
Residential
Residential V. V. ✓ V. V. V. V.
Throughway
Neighborhood V. V. V. V. V. V. V. V
Residential
Industrial Industrial V. I V. V. V. V. V. V. V.
And Mixed-Use ✓ V. V. • V. V. V. V. V.
Mixed-Use
Sidewalk V. C V. V. V. V. V. V. ../Furniture Zone
I Park Edge V. i V. V. V. V. V. • V. V.
Special ✓ V. V. V. V. V. V. V.
Boulevard
Ceremonial •
(Civic) •
Alley ✓ ✓ V. V. V. V.
Shared Public
Small V. V. V. V. •
• V. V.
Way
Walk Street V. V. V. V. V. V. V.
X
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City of Rancho Palos Verdes Page 7 April 2015
Resolution No.2015-24
Exhibit A
Page 11 of 23
Green Streets Manual
Table 3:BMP Location Opportunity Summary.
BMP Location Opportunity Summary
Bioretention • Adjacent to traveled way and in frontage or furniture sidewalk zones
• Can be located in curb extensions,medians,traffic circles,roundabouts,and any other landscaped area
• Suitable for constrained locations
Infiltration Trench/Dry Well • Can be located under sidewalks and in sidewalk planting strips,curb extensions,roundabouts,and medians
Rain Gardens • Can be integrated medians,islands,circles,street ends,chicanes,and curb extensions
• Can be located at the terminus of swales in the landscape
Permeable Pavement • Suitable for parking or emergency access lanes
• Can be located in furniture zones of sidewalks especially adjacent to tree wells
• Cannot be placed in areas with large traffic volume or heavy load lanes
• Avoid steep streets
• Cannot be placed within 20 feet of sub-sidewalk basements
• Cannot be within 50 feet of domestic water wells
Flow-Through Planters • Above-grade planters should be structurally separate from adjacent sidewalks
• At-grade planter systems can be installed adjacent to curbs within the frontage and/or furniture zones
Vegetated Swales • Can be located adjacent to roadways,sidewalks,or parking areas
• Can be integrated into traffic calming devices such as chicanes and curb e>tensions
• Can be placed in medians where the street drains to the median
• Can be placed alongside streets and pathways
• Should be designed to work in conjunction with the street slope
Vegetated Buffer Strips • Can be located in multi-way boulevards,park edge streets,or sidewalk furniture zones
• Can serve as pre-treatment
Treatment BMPs • Can be located in a catch basin,manhole,or vault
• Can be installed on an existing outlet pipe or at the bottom of an existing catch basin with an overflow
• Can be placed on existing curbside catch basins and flush grate openings
• Can be installed on the existing wall of a catch basin and on the curb side wall of a catch basin
• Minimum set-backs from foundations and slopes should be observed if the BMP is not lined
Street Trees • Can be placed on sidewalks,in furniture zones,and on medians
• Adequate spacing must be provided between trees and street lights,pedestrian lights,accessible parking
spaces,bus shelters,awnings,canopies,balconies,and signs
City of Rancho Palos Verdes Page 8 April 2015
Resolution No.2015-24
Exhibit A
Page 12 of 23
Green Streets Manual
SECTION 2 - INFILTRATION
Infiltration systems utilize rock, gravel, and other highly permeable materials for on-site infiltration. In
these systems, stormwater runoff is directed to the system and allowed to infiltrate into the soils for on-
site retention and groundwater recharge. During small storm events, infiltration systems can result in
significant or even complete volume reduction of stormwater runoff.
Infiltration should be used to the maximum extent practicable. Biotreatment BMPs should be
considered if infiltration is found to be infeasible due to low infiltration rates, soil instability, high
groundwater, or soil contamination.
Infiltration BMPs may become damaged by stormwater carrying high levels of sediment, therefore pre-
treatment features should be designed to treat street runoff prior to discharging to infiltration features.
Media filters, filter inserts, vortex type units, bioretention devices, sumps, and sedimentation basins are
several pre-treatment tools effective at removing sediment.
2.1 INFILTRATION TRENCHES AND DRY WELLS
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Figure 3:Infiltration Trench(Model for Living Streets Design Manual,2011).
Description
Infiltration trenches are linear, rock-filled features that promote infiltration by providing a high ratio of
sub-surface void space in permeable soils. They provide on-site stormwater retention and may
contribute to groundwater recharge. Infiltration trenches may accept stormwater from sheet flow,
concentrated flow from a swale or other surface feature, or piped flow from a catch basin. Because they
are not flow-through BMPs, infiltration trenches do not have outlets but may have overflow outlets for
large storm events.
Dry wells are typically distinguished from infiltration trenches by being deeper than they are wide. They
are usually circular, resembling a well, and are backfilled with the same materials as infiltration
trenches. Dry wells typically accept concentrated flow from surface features or from pipes and do not
have outlets.
Infiltration trenches and dry wells are typically designed to infiltrate all flow they receive. In large storm
events, partial infiltration of runoff can be achieved by providing an overflow outlet. In these systems,
significant or even complete volume reduction is possible in smaller storm events. During large storm
events,these systems may function as detention facilities and provide a limited amount of retention and
infiltration.
City of Rancho Palos Verdes Page 9 April 2015
Resolution No.2015-24
Exhibit A
Page 13 of 23
Green Streets Manual
Location and placement guidelines
Infiltration trenches and dry wells typically have small surface footprints so they are potentially some of
the most flexible elements of landscape design. However, because they involve sub-surface excavation,
these features may interfere with surrounding structures. Care needs to be taken to ensure that
surrounding building foundations, pavement bases, and utilities are not damaged by infiltration
features. Once structural soundness is ensured, infiltration features may be located under sidewalks and
in sidewalk planting strips, curb extensions, roundabouts, and medians. When located in medians, they
are most effective when the street is graded to drain to the median. Dry wells require less surface area
than trenches and may be more feasible in densely developed areas.
Infiltration features should be sited on uncompacted soils with acceptable infiltration capacity. They are
best used where soil and topography allow for moderate to good infiltration rates (0.3 inches per hour
or better) and the depth to groundwater is at least 1.0 feet. Prior to design of any retention or infiltration
system, proper soil investigation and percolation testing shall be conducted to determine appropriate
infiltration design rates, depth to groundwater, and if soil will exhibit instability as a result of infiltration.
Any site with potential for previous underground contamination shall be investigated. Infiltration
trenches and dry wells can be designed as stand-alone systems when water quality is not a concern or
may be combined in series with other stormwater tools.
Perforated pipes and piped inlets and outlets may be included in the design of infiltration trenches.
Cleanouts should be installed at both ends of any piping and at regular intervals in long sections of
piping, to allow access to the system. Access ports are recommended for both trenches and wells and
can be combined with clean-outs. If included, the overflow inlet from the infiltration trench should be
properly designed for anticipated flows.
2.2 RAIN GARDENS
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Figure 4:Rain garden(Model for Living Streets Design Manual,2011).
Description
Rain gardens are vegetated depressions in the landscape. They have flat bottoms and gently sloping
sides. Rain gardens can be similar in appearance to swales, but their footprints may be any shape. Rain
gardens hold water on the surface, like a pond, and have overflow outlets. The detained water is
infiltrated through the topsoil and subsurface drain rock unless the volume of water is so large that
City of Rancho Palos Verdes Page 10 April 2015
Resolution No.2015-24
Exhibit A
Page 14 of 23
Green Streets Manual
some must overflow. Rain gardens can reduce or eliminate off-site stormwater discharge while
increasing on-site recharge.
Location and Placement Guidelines
Rain gardens may be placed where there is sufficient area in the landscape and where soils are suitable
for infiltration. Rain gardens can be integrated with traffic calming measures installed along streets, such
as medians, islands, circles, street ends, chicanes, and curb extensions. Rain gardens are often used at
the terminus of swales in the landscape.
2.3 PERMEABLE PAVEMENT
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Figure 5: Permeable pavement during a storm event (Model
for Living Streets Design Manual,2011).
Description
Permeable pavement is a system with the primary purpose of slowing or eliminating direct runoff by
absorbing rainfall and allowing it to infiltrate into the soil. Permeable pavement also filters and cleans
pollutants such as petroleum deposits on streets, reduces water volumes for existing overtaxed pipe
systems, and decreases the cost of offsite or.onsite downstream infrastructure. This BMP is impaired by
sediment-laden run-on which diminishes its porosity. Care should be taken to avoid flows from
landscaped areas reaching permeable pavement. Permeable pavement is, in certain situations, an
alternative to standard pavement. Conventional pavement is designed to move stormwater off-site
quickly. Permeable pavement, alternatively, accepts the water where it falls, minimizing the need for
management facilities downstream.
Location and Placement Guidelines
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Figure 6:Possible pervious pavement design layout(Model for Living Streets Design Manual,2011).
City of Rancho Palos Verdes Page 11 April 2015
Resolution No.2015-24
Exhibit A
Page 15 of 23
Green Streets Manual
Conditions where permeable pavement should be encouraged include:
• Sites where there is limited space in the right-of-way for other BMPs;
• Parking or emergency access lanes; and
• Furniture zones of sidewalks especially adjacent to tree wells
Conditions where permeable pavement should be avoided include:
• Large traffic volume or heavy load lanes;
• Where runoff is already being harvested from an impervious surface for direct use, such as
irrigation of bioretention landscape areas;
• Steep streets;
• Gas stations, car washes, auto repair, and other sites/sources of possible chemical
contamination;
• Areas with shallow groundwater;
• Within 20 feet of sub-sidewalk basements; and
• Within 50 feet of domestic water wells.
Material and Design Guidelines
A soil or geotechnical report should be conducted to provide information about the permeability rate of
the soil, load-bearing capacity of the soil, the depth to groundwater (10 feet or more required), and if
soil will exhibit instability as a result of implementation. Infiltration rate and load capacity are key
factors in the functionality of this BMP. Permeable pavement generally does not have the same load-
bearing capacity as conventional pavement, so this BMP may have limited applications depending on
the underlying soil strength and pavement use. Permeable pavement should not be used in general
traffic lanes due to the possible variety of vehicles weights and heavy volumes of traffic.
When used as a road paving, permeable pavement that carries light traffic loads typically has a thick
drain rock base material. Pavers should be concrete as opposed to brick or other light-duty materials.
Other possible permeable paving materials include porous concrete and porous asphalt. These surfaces
also have specific base materials that detain infiltrated water and provide structure for the road surface.
Base material depths should be specified based on design load and the soils report.
Plazas, emergency roads, and other areas of limited vehicular access can also be paved with permeable
pavement. Paving materials for these areas may include open cell paver blocks filled with stones or grass
and plastic cell systems. Base material specifications may vary depending on the product used, design
load, and underlying soils.
When used for pedestrian paths, sidewalks, and shared-use paths, appropriate materials include those
listed above as well as rubber pavers and decomposed granite or something similar (washed or pore-
clogging fine material). Pedestrian paths may also use broken concrete payers as long as ADA
requirements are met. Paths should drain into adjoining landscapes and should be higher than adjoining
landscapes to prevent run-on. Pavement used for sidewalks and pedestrian paths should be ADA
compliant, especially smooth, and not exceed a 2 percent slope or have gaps wider than 0.25 inches. In
general,tripping hazards should be avoided.
City of Rancho Palos Verdes Page 12 April 2015
Green Streets Manual Resolution No.2015-24
Exhibit A
Page 16 of 23
Design considerations for permeable pavement include:
• The location, slope and load-bearing capacity of the street,and the infiltration rate of the soil;
• The amount of storage capacity of the base course;
• The traffic volume and load from heavy vehicles;
• The design storm volume calculations and the quality of water; and
• Drain rock,filter fabrics, and other subsurface materials.
Maintenance Guidelines
Maintenance of permeable pavement systems is essential to their continued functionality. Regular
vacuuming and street sweeping should beperformed to remove sediment from the pavement surface.
The bedding and base material should be selected for long life and sufficient infiltration rates.
SECTION 3 - BIOTREATMENT
Biotreatment BMPs are landscaped, shallow depressions that capture and filter stormwater runoff.
These types of BMPs are an increasingly common type of stormwater treatment device that are installed
at curb level and filled with a bioretention type soil. They are designed as soil and plant-based filtration
devices that remove pollutants through a variety of physical, biological, and chemical treatment
processes. They typically consist of a ponding area, mulch layer, planting soils, and plants. Stormwater is
directed to the system and pollutants are treated as the stormwater drains through the planting soil and
either infiltrated or collected by an underdrain and directed to a collection system.
Biotreatment should only be used in cases where infiltration has been proven infeasible due to low
infiltration rates,soil instability, high groundwater, or soil contamination.
.1 IORETENTION
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Figure 7:Bioretention system(Model for Living Streets Design Manual,2011).
City of Rancho Palos Verdes Page 13 April 2015
Resolution No.2015-24
Exhibit A
Page 17 of 23
Green Streets Manual
Description
Bioretention is a stormwater management process that cleans stormwater by mimicking natural soil
filtration processes as water flows through a bioretention BMP. It incorporates mulch, soil pores,
microbes, and vegetation to reduce and remove sediment and pollutants from stormwater. Bioretention
is designed to slow, spread, and, to some extent, infiltrate water. Each component of the bioretention
BMP is designed to assist in retaining water, evapotranspiration, and adsorption of pollutants into the
soil matrix. As runoff passes through the vegetation and soil, the combined effects of filtration,
absorption, adsorption, and biological uptake of plants remove pollutants.
For areas with low permeability or other soil constraints, bioretention can be designed as a flow-through
system with a barrier protecting stormwater from native soils. Bioretention areas can be designed with
an underdrain system that directs the treated runoff to infiltration areas, cisterns, or the storm drain
system, or may treat the water exclusively through surface flow. Examples of bioretention BMPs include
swales, planters, and vegetated buffer strips.
Location and Placement Guidelines
Bioretention facilities can be included in the design of all street components; adjacent to the traveled
way and in the frontage or furniture sidewalk zones. They can be designed into curb extensions,
medians, traffic circles, roundabouts, and any other landscaped area. Depending on the feature,
maintenance and access should always be considered in locating the device. Bioretention systems are
also appropriate in constrained locations where other stormwater facilities reqr.i ring more extensive
subsurface materials are not feasible.
If bioretention devices are designed to include infiltration, native soil should have a minimum
permeability rate of 0.3 inches per hour and at least 10 feet to the groundwater table. Sites that have
more than a 5 percent slope may require other stormwater management approaches or special
engineering.
3.2 FLOW-THROUGH PLANTERS
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Figure 8:Flow-through planter(Model for Living Streets Design Manual,2011).
City of Rancho Palos Verdes Page 14 April 2015
Resolution No.2015-24
Exhibit A
Page 18 of 23
Green Streets Manual
Description
Flow-through planters are typically above-grade or at-grade with solid walls and aflow-through bottom.
They are contained within an .—pereable liner and use an underdrain to direct treated runoff back to
the collection system. Where space permits, buildings can direct roof drains first to building-adjacent
planters. Both underdrains and surface overflow drains are typically installed with building-adjacent
planters.
At-grade street-adjacent planter boxes are systems designed to take street runoff and/or sidewalk
runoff and incorporate bioretention processes to treat stormwater. These systems may or may not
include underdrains.
Location and Placement Guidelines
Above-grade planters should be structurally separate from adjacent sidewalks to allow for future
maintenance and structural stability per local department of public works' standards. At-grade planter
systems can be installed adjacent to curbs within the frontage and/or furniture zones.
All planters should be designed to pond water for less than 48 hours after each storm. Flow-through
planters designed to detain roof runoff can be integrated into a building's foundation walls, and may be
either raised or at grade.
For at-grade planters, small localized depressions may be included in the curb opening to encourage
flow into the planter. Following the inlet, a sump (depression) to capture sediment and debris may be
integrated into the design to reduce sediment loadings.
3.3 VEGETATED SWALES
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Figure 9:Vegetated swale(Signal Hill,CA).
Description
Swales are linear, vegetated depressions that capture rainfall and runoff from adjacent surfaces. The
Swale bottom should have a gradual slope to convey water along its length. Swales can reduce off-site
stormwater discharge and remove pollutants along the way. In a swale, water is slowed by traveling
through vegetation on a relatively flat grade. This gives particulates time to settle out of the water while
contaminants are removed by the vegetation.
City of Rancho Palos Verdes Page 15 April 2015
Resolution No.2015-24
Exhibit A
Page 19 of 23
Green Streets Manual
Location and Placement Guidelines
Swales can easily be located adjacent to roadways, sidewalks, or parking areas. Roadway runoff can be
directed into swales via flush curbs or small evenly-spaced curb cuts into a raised curb. Swale systems
can be integrated into traffic calming devices such as curb extensions.
Swales can be placed in medians where the street drains to the median. Placed alongside streets and
pathways, vegetated swales can be landscaped with native plants which filter sediment and pollutants
and provide habitat for wildlife. Swales should be designed to work in conjunction with the street slope
to maximize filtration and slowing of stormwater.
Swales are designed to allow water to slowly flow through the system. Depending on the landscape and
design storm, an overflow or bypass for larger storm events may be needed. Curb openings should be
designed to direct flow into the swale. Following the inlet, a sump may be built to capture sediment and
debris.
3.4 VEGETATED BUFFER STRIPS
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Figure 10:Vegetated buffer strip detail(Model for Living Streets Design Manual,2011).
Description
Vegetated buffer strips are sloping planted areas designed to treat and absorb sheet flow from adjacent
impervious surfaces. These strips are not intended to detain or retain water, only to treat it as a flow-
through feature. They should not receive concentrated flow from swales or other surface features, or
concentrated flow from pipes.
Location and Placement Guidelines
Vegetated buffer strips are well-suited to treating runoff from roads and highways, small parking lots,
and pervious surfaces. They may be commonly used on multi-way boulevards, park edge streets, or
sidewalk furniture zones with sufficient space. When selecting potential placement the need for
supplemental irrigation should be considered. Vegetated buffers can also be situated so they serve as
pre-treatment for another stormwater management feature, such as an infiltration BMP.
City of Rancho Palos Verdes Page 16 April 2015
Resolution No.2015-24
Exhibit A
Page 20 of 23
Green Streets Manual
SECTION 4 - TREATMENT BMPS
4.1 SAND FILTERS&STORM DRAIN INLET PROTECTIONS
As described in Section 1 of this Green Streets Manual, it may be infeasible for specific projects to apply
infiltration or biotreatment BMPs. In these cases, sand filters or filter inserts as treatment BMPs can be
considered as an alternative. Sand filters and filter inserts can be designed to prevent particulates,
debris, metals, and petroleum-based materials conveyed by stormwater from entering the storm drain
system. All treatment BMP units should have an overflow system that allows the storm drain to remain
functional if the filtration system becomes clogged during rainstorms. All storm drain inlet protections
must be of a style and configuration approved by the agency with ownership of the inlet.
Typical maintenance of catch basins includes scheduled trash removal if a screen or other debris
capturing device is used. Street sweeping should be performed by vacuum sweepers with occasional
weed and large debris removal. Maintenance should include keeping a log of the amount of sediment
collected and the data of removal.
The following are examples of acceptable treatment BMPs:
• Sand Filters:Sand filters are designed to filter stormwater through a constructed media bed and
to an underdrain system. As stormwater flows through the media pollutants are filtered out of
the water. The filtered water is conveyed through the underdrain to a collection system.
Pretreatment is necessary to eliminate significant sediment load or other large particles which
would clog the system. Minimum set-backs from foundations and slopes should be observed if
the facility is not lined. Filters should be designed and maintained such that ponded water
should not persist for longer than 48 hours following a storm event.
• Cartridge Media Filters: Cartridge media filters contain multiple modular filters which contain
engineered media. The filters can be located in a catch basin, manhole, or vault. The manhole or
vault may be divided into multiple chambers so that the first chamber may act as a pre-settling
basin for removal of coarse sediment while the next chamber may act as the filter chamber.
Cartridge media filters are recommended for drainage areas with limited available surface area
or where surface BMPs would restrict uses. Depending on the number of cartridges,
maintenance events can have long durations. Locations should be chosen so that maintenance
events will not significantly disrupt businesses or traffic. Inlet inserts should be sized to capture
all debris and should therefore be selected to match the specific size and shape of each catch
basin and inlet. Filter media should be selected to target pollutants of concern. A combination of
media may be used to remove a variety of pollutants. Systems with lower maintenance
requirements are preferred.
• Storm Drain Inlet Screens: Inlet screens are designed to prevent large litter and trash from
entering the storm drain system while allowing smaller particles to pass through. The screens
function as the first preventive measure in removing pollutants from the storm water system.
The city's street sweeping department should be consulted to ensure compliance with local
specifications and to schedule regular maintenance. Annual inspection of the screen is
recommended to ensure functionality. Note that most LA River drainage areas are already
protected using connector pipe screens through collective systems.
City of Rancho Palos Verdes Page 17 April 2015
Resolution No.2015-24
Exhibit A
Page 21 of 23
Green Streets Manual
• Storm Drain Pipe Filter Insert:The storm drain outlet pipe filter is designed to be installed on an
existing outlet pipe or at the bottom of an existing catch basin with i,in overflow. This filter
removes debris, particulates, and other pollutants from stormwater as it leaves the storm drain
system. This BMP is less desirable than a protection system that prevents debris from entering
the storm drain system because the system may become clogged with debris. Outlet pipe filters
can be placed on existing curbside catch basins and flush grate openings. Regular maintenance is
required and inspection should be performed rigorously. Because this filter is located at the
outlet of a storm drain system, clogging with debris is not as apparent as with filters at street
level.This BMP may be used as a supplemental filter with an inlet screen or inlet insert unit.
City of Rancho Palos Verdes Page 18 April 2015
Resolution No.2015-24
Exhibit A
Page 22 of 23
Green Streets Manual
SECTION 5 — STREET TREES
5.1 STREET TREES
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Figure 11:Street trees(Signal Hill,CA).
Description
Healthy urban trees are powerful stormwater management tools. Leaves and branches catch and slow
rain as it falls, helping it tosoak into the ground. The plants themselves take up and store large
quantities of water that would otherwise contribute to surface runoff. Part of this moisture is then
returned to the air through evaporation to further cool the city. As an important element along
sidewalks, street trees must be provided with conditions that allow them to thrive, including adequate
uncompacted soil,water,and air.
The goal of adding street trees is to increase the canopy cover of the street, the percentage of its
surface either covered by or shaded by vegetation. The selection, placement, and management of all
elements in the street should enhance the longevity of a city's street trees and healthy, mature
plantings should be retained and protected whenever possible.
Benefits to adding street trees include:
• Creation of shade to lower temperatures in a city, reduces energy use, and makes the street a
more pleasant place in which to walk and spend time
• Slowing and capture of rainwater, helping it soak into the ground to restore local hydrologic
functions and aquifers
• Improving air quality by cooling air, producing oxygen, and absorbing and storing carbon in
woody plant tissues
April
City of Rancho Pains Verdes Page 192015
Resolution No.2015-24
Exhibit A
Page 23 of 23
Green Streets Manual
SECTION 6 - DEFINITIONS
Best Management Practice(BMP)—Operating methods and/or structural devices used to reduce
stormwater volume, peak flows, and/or pollutant concentrations of stormwater runoff through
evapotranspiration, infiltration, detention,filtration, and/or biological and chemical treatment.
Bioretention—Soil and plant-based retention practice that captures and biologically degrades pollutants
as water infiltrates through sub-surface layers containing microbes that treat pollutants.Treated runoff
is then slowly infiltrated and recharges the groundwater.
Conveyance—The process of water moving from one place to another.
Design Storm—A storm whose magnitude, rate, and intensity do not exceed the design load for a storm
drainage system or flood protection project.
Detention—Storrnwater runoff that is collected at one rate and then released at a controlled rate. The
volume difference is held in temporary storage.
Filtration—A treatment process that allows for removal of solid (particulate) matter from water by
means of porous media such as sand, soil, vegetation, or a man-made filter. Filtration is used to remove
contaminants.
Furniture Zone—The furniture zone is the area which lies between the curb and pecestrian zones and is
intended to house utilities and pedestrian amenities.
Hardscape—Impermeable surfaces, such as concrete or stone, used in the landscape environment along
sidewalks or in other areas used as public space.
Infiltration—The process by which water penetrates into soil from the ground surface.
Permeability/Impermeability—The quality of a soil or material that enables water to move through it,
determining its suitability for infiltration.
Retention—The reduction in total runoff that results when stormwater is diverted and allowed to
infiltrate into the ground through existing or engineered soil systems.
Runoff—Water from rainfall that flows over the land surface that is not absorbed into the ground.
Sedimentation—The deposition and/or settling of particles suspended in water as a result of the
slowing of the water.
Stormwater—Water runoff from rain or snow resulting from a storm.
Transportation Corridor—A major arterial,state route, highway, or rail line used for:he movement of
people or goods by means of bus services, trucks, and vehicles.
SECTION 7 - REFERENCES
1. Los Angeles County. Model for Living Streets Design Manual. 2011.
2. U.S. Environmental Protection Agency (EPA). Managing Wet Weather With Green Infrastructure
Municipal Handbook: Green Streets. December 2008.
3. Orange County. Technical Guidance Document. May 2011.
City of Rancho Palos Verdes Page 20 April 2015