HomeMy WebLinkAboutCOUNCIL - AGENDA ITEM - 08/14/2012 - 2012 STREETS AND STORMWATER SITE DEVELOPMENT INTIADATE: August 14, 2012
STAFF: Aaron Iverson, Basil
Hamdan, Amy Lewin, Pete Wray
Pre-taped staff presentation: available
at fcgov.com/clerk/agendas.php
WORK SESSION ITEM
FORT COLLINS CITY COUNCIL
SUBJECT FOR DISCUSSION
2012 Streets and Stormwater Site Development Initiatives.
EXECUTIVE SUMMARY
The 2012 Green Initiative (Streets and Stormwater Site Development) addresses several
sustainability elements while encouraging collaboration between the Planning, Development, and
Transportation Service Unit (PDT) and Fort Collins Utilities’ Stormwater Division. The four related
projects are an extension of sustainable practices and concepts recently implemented through the
adoption of the Green Building Code, beyond the building envelope to development sites and City
streets and consist of:
1. Updates to the City streetscape/landscape standards in the Larimer County Urban Area Street
Standards (LCUASS)
2. Development of a new, more flexible City urban street standard
3. Development and implementation of a new Low Impact Development (LID) policy and
associated criteria
4. The design and construction of a demonstration project to incorporate and test elements from
the other projects.
GENERAL DIRECTION SOUGHT AND SPECIFIC QUESTIONS TO BE ANSWERED
Staff is seeking City Council feedback and guidance on each of the four related efforts.
1. Staff is seeking feedback from City Council regarding the new approach to raise the bar for
arterial streetscapes.
2. Staff is seeking feedback from City Council on this update which will provide for more
flexible street standards and create urban street classifications.
3. Does the proposed Low Impact Development Policy and Criteria (which will apply to both
public and private development and infrastructure) correspond with City Council’s desire
to better control stormwater runoff near its source and improve stormwater quality?
a. Should LID be required or incentive-based?
b. Do the proposed criteria provide a practical approach for development and
redevelopment sites?
c. Should LID criteria be limited or targeted based on land use?
August 14, 2012 Page 2
4. In regards to the demonstration project, staff is seeking feedback on the initial concepts,
related costs, and support for moving forward.
BACKGROUND / DISCUSSION
Green Streets is a broad term that includes a number of sustainability elements, such as:
• Alternative street designs that may include narrower street widths and other traffic calming
features to support active modes of travel such as bicycling and walking.
• Integrated system of stormwater management within the right of way that includes volume
reductions (for smaller storm events) and improvement in stormwater quality.
• Aesthetic and functional enhancements which enhance the attractiveness and urban design
of the public realm within the street environment.
The 2012 Green Initiative (Streets and Stormwater Site Development) represents a new opportunity
for collaboration among Planning, Development, and Transportation Service Unit (PDT) and
Utilities on these related projects and schedules and coordination of issues, analysis, staff resources,
public outreach and recommendations, unified under a central theme.
This collaborative effort brings together a number of City departments and includes a joint multi-
department project team, as well as a combined public process, which includes focus group
meetings, public open houses and presentations to the Water Board, Planning and Zoning Board and
the Transportation Board. This memo describes each of the projects, their purpose and goals, and
their role for potentially helping to develop Green Streets in the City of Fort Collins.
1. Larimer County Urban Area Street Standards (LCUASS) Update: Streetscape Design
Standards & Guidelines
The Streetscape Design Standards & Guidelines (SDSG) was adopted in 2001 by the City of Fort
Collins and Larimer County and is Appendix C of the LCUASS, and applies to Fort Collins only.
It provides design guidance for creating visually appealing streets that serve as public spaces and
contribute to Fort Collins’ distinct identity. Its standards and guidelines deal specifically with the
treatment of the parkways (between the curb and sidewalk) and medians. It guides the design and
management of streetscapes in both private development projects and in public sector capital
projects and is used by City staff, developers, and decision makers.
Since the SDSG was first adopted ten years ago, questions and issues have emerged regarding both
the SDSG, and the City’s streetscapes. Research of national best practices has identified new
innovative street design techniques that may be applicable to Fort Collins and can help address these
issues and questions.
This update of the SDSG will identify options for a new approach to arterial streetscapes, including
elements such as landscape plantings, mulches, use of concrete, irrigation systems, and other design
features and amenities. The new standards will be applicable for new streets, and retrofit projects
throughout the City. The level of design will be elevated even further at key gateway intersections.
August 14, 2012 Page 3
These proposed new standards will likely increase cost and potentially impact maintenance and life
cycle. Additionally it will be important to recognize the differences among various arterials with
constrained conditions throughout the City, as well as targeted infill and redevelopment areas.
The new approach is expected to involve a new interdepartmental team to review design and
projects with a program to monitor effectiveness over time and establish a data base to track plant
material conditions and selection, maintenance upkeep, and replacement of landscaping. The need
for a team stems from the multidisciplinary nature of streetscapes, involving engineering, design,
maintenance and water use.
2. Larimer County Urban Area Street Standards (LCUASS) Update: Street
Classifications
Updating the street classifications for the Fort Collins section of the Larimer County Urban Area
Street Standards (LCUASS) is an action item (Near-Term Action for 2011 and 2012, number 11)
in the Transportation Master Plan.
The current street classifications and standards do not allow for much flexibility, which at times
increases the need for time-consuming modifications to standards to develop corridor-specific
exceptions. The purpose of the update is to add more flexibility to the toolbox of street standards
for Fort Collins to support urban environments. The goal is to streamline street development with
context-sensitive design that emphasizes lower vehicle speeds, encourages walking, bicycling, and
transit, and supports stormwater management goals.
Updating the Fort Collins street standards to offer additional urban street design choices is important
to serve the multi modal travel needs of these new and redeveloping areas of our community. The
focus is on a quality multi-modal transportation experience that supports the surrounding land use
and maximizes the use of the existing and future planned streets. (see Attachment 2, pages 18-19
from the Transportation Master Plan).
The project is planned to include the following:
• Review of national best practices
• Coordination with the 2012 Green Streets multi-department team
• Review the implementation of current standards
• Assessment of various cross-sections in Fort Collins and elsewhere
• Proposal of changes, including Low Impact Development-related changes, including capital
costs and operating and maintenance considerations (as described in Section 3 below)
• Assessment of potential changes to the Master Street Plan and Street Oversizing fee policies
• Public outreach with target markets of:
N Developers, Traffic Engineers/Consultants
N Public/Applicants/Neighborhoods
N Landscape Architects.
3. Low Impact Development (LID) Policy
Low Impact Development (LID) is a comprehensive land planning and engineering design approach
to managing stormwater runoff with a goal of replicating natural systems that existed before
August 14, 2012 Page 4
development occurred. LID techniques treat and control stormwater at its source, thereby reducing
the need for large structures or end of pipe treatment systems.
The City’s current LID policy is based on the Urban Drainage and Flood Control (UDFCD) Manual
guidance which Council adopted into the City of Fort Collin’s Stormwater Criteria Manual in
December 2011. The policy states that development and public infrastructure projects are
encouraged (but not required) to use LID practices and technologies in site design based on the “4-
Step Process”. The “4-Step Process” is detailed in Attachment 4 and requires the consideration of
LID technologies early on in the design process. However, the implementation level of LID
technologies is prescribed only in a qualitative manner. There are no objective LID numerical
standards and requirements that have to be met in order to comply with the current policy. The
decision facing Fort Collins is whether to require or incentivize the implementation of LID practices
and technologies or maintain the status quo.
Key components of LID include:
• An overall site planning approach that promotes conservation design at both the watershed
and site levels
• A site design philosophy that emphasizes multiple controls (as opposed to a central treatment
facility)
• The use of swales and open vegetated conveyances (as opposed to curb and gutter systems)
• Volume reduction for smaller storm events as a key objective (as opposed to peak flow
reduction).
Over the last three years, the City has engaged in the design and construction of LID
“Demonstration Projects” at public and private sites. These existing projects are currently being
monitored for structural integrity, cost of maintenance, water quantity reduction and water quality
improvement. Monitoring at these sites will continue beyond the initial implementation of an LID
Policy.
The City LID Policy will affect not only public streets, but also private development. This effort
can be viewed as an extension of the Green Building Code from its original focus toward
implementing sustainable practices outside of the building envelope to the site design and layout.
In order to obtain the widest possible feedback and engage all critical stakeholders for this project
includes an extensive public outreach effort which is incorporated into the project schedule.
In order ensure the City promotes and facilitates the implementation of a sustainable infrastructure
policy, it will be important to conduct an audit of all aspects of the Land Use Code which can have
an impact on this policy. This will affect zoning regulations which impact parking requirements,
street standards, as well as site landscaping requirements.
LID Policy and Criteria Alternatives
Over the last several months, Stormwater staff researched existing LID Policies throughout the
United States and identified key issues and considerations. Staff prepared a number of “Fact Sheets”
that detail the extent of implementation of LID technologies in various peer cities in Colorado and
in other leading stormwater programs around the nation. It should be noted that LID criteria vary
widely from location to location based on geography, climate, hydrology and regulated waterways
August 14, 2012 Page 5
(i.e., the Chesapeake Bay and Puget Sound). Staff developed a draft set of LID criteria and LID
Policy alternatives for review and consideration by the Water Board, other boards and commissions,
City Council and the citizens of Fort Collins. The proposed LID criteria are:
• A minimum of 50% of new impervious surface area must be treated by a LID-type device
or technology (i.e., bio-retention cell, bio-swale); and
• At least 25% of new parking areas must be designed to be pervious; or,
• Implementation of a design alternative that provides equal or better treatment to the previous
requirements.
Stormwater staff prepared the following LID Policy alternatives for consideration:
Required LID Alternative
1. On-site construction of LID to meet the listed criteria. This option would most closely
achieve the micro-scale component of LID strategy but would have limited impact on a
watershed scale.
In cases where on-site construction is not possible or practicable, developers can be given
the option to pay a fee in lieu of construction of LID technologies. The City would pool
funds and construct LID-type stormwater measures as part of its master planning effort
within regional detention facilities. Use of this alternative would dilute the localized/
decentralized component of a LID strategy but could potentially have a wider impact on a
watershed-scale. Since a large portion of Fort Collins is developed, regionally based LID
measures would also provide a retrofit option.
Incentive-Based LID Alternative
2. Adopt a LID strategy on a voluntary but incentive-based system in conjunction with the
current regulations included in the Stormwater Criteria Manual. Examples of incentives
include reduction in stormwater fees through reduced impervious surface area, recognition
through existing City programs such as ClimateWise, or through performance measures
where developers are awarded points based on employing LID strategies onsite that provide
them more flexibility in site development options, such as zoning classifications or floor area
ratios.
Alternative 1 best represents the original LID goal of replicating natural systems and controlling
stormwater runoff near the source. The voluntary nature of Alternative 2 would likely reduce its
impact on a watershed-scale, as similar programs have seen limited implementation levels in other
municipalities.
Water Board and Engineering Committee
On July 11, 2012, Stormwater staff met with the Engineering Committee to discuss the 2012 Green
Initiative and LID Policy Alternatives. Engineering Committee members felt that the incentive-
based option was limited in its appeal and would not lead to significant widespread implementation
of LID strategies. Staff was asked to investigate an option to require the implementation of LID
requirements based on land use, not solely on added impervious surface area.
August 14, 2012 Page 6
At its meeting on July 19, 2012, the Water Board expressed general support for the Stormwater
Utility to develop and implement the proposed LID policy and criteria. Some members requested
illustrations of how the policy would be applied to residential and commercial properties with
concrete examples. Climate was also mentioned as a major factor in LID implementation. Staff was
encouraged to identify solutions that work well regionally such as in the Denver/Boulder area rather
than those based on other regions. At the conclusion of the meeting, support was expressed to
proceed with the policy development and implementation in close cooperation with local experts
such as Dr. Larry Roesner of the Urban Water Center at CSU. Dr. Roesner and his group are
currently under contract to help the Stormwater Utility with the development of a range of
stormwater quality initiatives including the LID Policy development and implementation.
4. Green Street Reshaping Demonstration Project: Location Identification
Implementing a Green Street Reshaping demonstration project is an action item in the
Transportation Master Plan (Near-Term Action for 2011 and 2012, number 15). Specifically, this
project will identify a candidate street(s) for improvements including the potential elements along
with conceptual design and costs. Funding for implementation will be determined through the City's
budgeting process for 2013 - 2014.
Identifying candidate street(s) starts with the development of a set of criteria to identify and evaluate
potential streets for “Reshaping". This evaluation process will address Triple Bottom Line areas,
including economic, environmental, and social factors. Suggestions include:
• Street classification (collector, arterial, local, etc.)
• Traffic volume
• Speed data
• Use by bicycles and pedestrians
• Connectivity of route to key destinations such as schools, parks, commercial/employment
districts, activity centers, transit routes, trails, stormwater conveyance needs, other utilities,
etc.
• Cost – capital and operations/maintenance
• Overlap and/or leverage opportunities:
N Traffic’s Neighborhood Traffic Calming Program
N Transportation Planning’s bicycle route network plan and Pedestrian Plan and Safe
Routes to School
N Street’s pavement maintenance program
N Stormwater Master Plans
N Economic Health/Targeted Infill and Redevelopment Areas
N New development projects
Street projects could range in scope and cost from basic signing/striping projects such as the 2011
LaPorte Avenue Road Diet to a more comprehensive street reconstruction project to include new
elements such as bioswales, medians, curb extensions, parkways, etc. Implementation of any
recommended projects will be dependent upon available resources for construction as well as on-
going operations/maintenance considerations.
August 14, 2012 Page 7
The Rolland Moore West Neighborhood has come forward with a desire for the City to implement
reshaping/green street concepts on Constitution between Drake and Stuart, and Stuart between
Heatheridge and Taft Hill. These two streets are being evaluated as part of this identification
process in 2012. Attachment 7 is a draft of the analysis of these streets, initial concepts and
estimated potential costs for a demonstration project.
Funding for implementation of a demonstration project is being included as a Budgeting for
Outcomes (BFO) request through the 2013-14 budget process.
PUBLIC OUTREACH
The combined public process will include a 2012 Green Initiative (Streets and Stormwater Site
Development) website (fcgov.com/greenstreets), focus group meetings, public open houses, and
presentations to boards and commissions (e.g., Water Board, Planning and Zoning Board and the
Transportation Board), as well as to local community groups, such the Chamber of Commerce and
others. Public Open Houses will target the general public as well as interested and affected
stakeholders such as environmental groups, design professionals and the building industry.
Milestones
August: Public Open House, August 9
Planning and Zoning Board Work Session, August 10
City Council Work Session, August 14
Fort Collins Chamber of Commerce, August 24
September -
November: Water Board
Planning and Zoning Board
Transportation Board
US Green Building Council-Northern Colorado Branch, September 25
Public Open House
December 4: City Council considers adoption of:
• Low Impact Development (LID) Policies
• LCUASS Streetscape Standards Update
2013: Street Classification and Standards Update Completion
Implementation of Demonstration Project
ATTACHMENTS
1. PowerPoint Presentation
2. Excerpt from Transportation Master Plan; pages 18, 19
3. LID Questions and Issues
4. LID Criteria and Policy Fact Sheets
5. LID Discussion Excerpts from Unapproved Water Board Minutes
6. BMP Economics and Sizing 2012
7. Draft Demonstration Project Technical Paper
8/9/2012
1
City Council Work Session
August 14, 2012
2012 Streets and Stormwater
Site Development Initiatives
A collaborative project between:
City of Fort Collins Stormwater Department
City of Fort Collins Transportation Planning Department
City of Fort Collins Long Range Planning
2
2012 Streets and Stormwater Site
Development Initiatives
ATTACHMENT 1
8/9/2012
2
3
Outline
• Overview of Green Streets & Stormwater Site
Development Elements
• Provide details of the four related City projects
• Feedback being requested
• Discuss the next steps for each project
2012 Streets and Stormwater Site
Development Initiatives
4
• Alternative street designs to support active
modes of travel such as bicycling and walking
• Integrated system of stormwater management,
within the street and for private development
• High quality landscaping that looks great and
functions better
What are green streets?
What is green site development?
8/9/2012
3
5
RAIN GARDEN
PERMEABLE PAVEMENT
HIGH QUALITY
SUSTAINABLE LANDSCAPING
BIKE LANE
ON‐STREET PARKING
BULB‐OUT
TRANSIT
ORIENTED
What are green streets?
What is green site development?
6
1. Updating streetscape/landscape standards in the
Larimer County Urban Area Street Standards (LCUASS)
2. Updating LCUASS street classifications to include more
flexible urban standards
3. Update Low Impact Development policies for public and
private development
4. A demonstration project incorporating and testing green
elements
Details of 4 Related City Projects
8/9/2012
4
7
What:
Update landscape standards for arterial street medians
including:
•landscape plantings, mulches, use of concrete,
irrigation systems, and other amenities
Why:
The current standards are about 10 years old and new
innovative streetscape techniques have emerged for
creating beautiful, sustainable streetscapes
Streetscape Design Standards Update
8
Streetscape Design Standards Update
Update Includes:
‐ More color and texture in plantings of annuals,
perennials, and shrubs
‐ Hardscape elements such as railings, pylons,
lighting, planters, walls and paving
‐ For new or reconstructed arterial street medians
Corridors with special designs already in place
8/9/2012
5
9
Streetscape Design Standards Update
10
Streetscape Design Standards Update
Example Streetscapes
Harmony Road & Lemay
8/9/2012
6
11
Streetscape Design Standards Update
Example Streetscapes
12
Streetscape Design Standards Update
Council Input Being Sought
• Feedback from City Council regarding the new
approach to raise the bar for arterial streetscapes
8/9/2012
7
13
Street Classifications Update
What:
Update the City of Fort Collins Street Classifications to
add or update the menu of streets to have more
flexibility within the standards
Why:
Current street classifications and standards are not
flexible leading to:
‐ Challenges in urban or retrofit areas
‐ Time‐consuming variance requests and corridor‐
specific exceptions
14
6‐Lane Arterial Street
4‐Lane Arterial Street
2‐Lane Arterial Street
Major Collector Street
Minor Collector Street
Commercial Local Street
Industrial Local Street
Connector Local Street
Residential Local Street
Narrow Residential Local Street (Alley)
Rural Residential Local Street
Street Classifications Update
What Classifications do we have?
Bigger
To
Smaller
8/9/2012
8
15
Street Classifications Update
6‐Lane Arterial
16
Street Classifications Update
Minor Collector
8/9/2012
9
17
Street Classifications Update
Local Street
18
Widths
•Right of Way
• Roadways
•Medians
•Travel Lanes
•Bike Lanes
•Parking Lanes
• Parkways
•Sidewalks
•Left Turn Lanes
Types of Features
•Left Turn Lanes
• Number of Travel Lanes
• Designated Bike Lanes
Design Details
• Speed Limit
•Setbacks
•Driveway & Street Access
• Continuity
•Curb & Gutter Specifications
Street Classifications Update
What are all the different “standards”?
8/9/2012
10
19
Street Classifications Update
What will this update do?
Evaluate
•Analyze and document
when and where we are
currently not using the
standards
• Understand what is
modified and why
Research
•Review of national best
practices and peer cities
Identify Options
•Propose changes to standards
and identify potential related
costs
20
Street Classifications Update
What will this update do?
Engage the Public
• Developers, Traffic Engineers, Landscape
Architects, Public, Applicants, Neighborhoods
• Assess impacts to the Master Street Plan and
Street Oversizing fee policy
•Work within the City with Engineering, Streets,
Traffic Operations, Stormwater, and others
8/9/2012
11
21
Street Classifications Update
Council Input Being Sought
• Feedback from Council on the need to update the
City’s street classifications and the approach being
presented by staff
22
Proposed
Low Impact Development (LID) Policy
What:
Update the Low Impact Development (LID) Policy to be
applied to private and public site development as well
street projects
Why:
Low Impact Development techniques reduce storm
water pollution and the quantity of storm water run‐off
for smaller storm events
8/9/2012
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23
How is stormwater currently managed?
Current City Practice (Best Management Practices)
Utilizes a set of techniques, processes, activities, or
structural improvements to reduce the pollutant
content of stormwater discharge
Low Impact Development (encouraged)
Manage rainfall at the source for smaller storms with
techniques that infiltrate, filter, store, evaporate, and
detain runoff locally
Proposed
Low Impact Development (LID) Policy
24
Proposed
Low Impact Development (LID) Policy
8/9/2012
13
25
Proposed
Low Impact Development (LID) Policy
26
•A minimum of 50% of new impervious surface area
must be treated by a LID‐type device or technology
(i.e. bio‐retention cell, bio‐swale); and
•At least 25% of new parking areas must be designed
to be pervious; or,
•Implementation of a design alternative that
provides equal or better treatment to the previous
requirements.
Proposed LID criteria:
Proposed
Low Impact Development (LID) Policy
8/9/2012
14
27
Alternative 1. Require LID Improvements
‐ On site construction
‐ Pay a fee in lieu
Alternative 2. Provide Incentives for LID Improvements
‐ Reduced stormwater fees
‐ Recognition through ClimateWise
‐ Performance measures
LID Policy Alternatives
Proposed
Low Impact Development (LID) Policy
28
Council Input Being Sought
Does the proposed Low Impact Development Policy and Criteria
(which will apply to both public and private development and
infrastructure) correspond with City Council’s desire to better
control stormwater runoff near its source and improve
stormwater quality?
Proposed
Low Impact Development (LID) Policy
a. Should LID be required or incentive‐based?
b. Do the proposed criteria provide a practical approach
for development and redevelopment sites?
c. Should LID criteria be limited or targeted based on land
use?
8/9/2012
15
29
What:
Identify a candidate street or streets to “reshape”
utilizing green streets concepts and develop a set of
solutions that range from total re‐construction to simple
re‐striping
Why:
Test green elements such as LID and new landscaping,
understand the cost, and create a process to replicate
throughout the City
Proposed Demonstration Project
30
Targeted Street:
‐ Collector street
‐ Wider than standard
‐ Not pedestrian friendly
‐ Traffic speed concerns
Proposed Demonstration Project
8/9/2012
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31
Potential Green Street Elements
‐Traffic calming –Rain Garden ‐ Paving ‐ Conveyance
Proposed Demonstration Project
32
Narrower Street with 2‐way bike lane
Proposed Demonstration Project‐Example 1
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Proposed Demonstration Project‐Example 1
Item Unit Cost Approx. Cost for
One‐Mile Section
Rain Gardens at Bulbouts $5 per square foot $144,000
Permeable Pavers $10 per square foot $148,000
Landscaping $1.25 per square foot $46,250
Curb & Gutter at Bulbouts $13 per square foot $70,200
Striping (per stripe) $0.25 per linear foot $2,775
Total: $411,225
Narrower Street with 2‐way bike lane
34
Narrower Street with median and
bulbouts at intersections
Proposed Demonstration Project‐Example 2
8/9/2012
18
35
Proposed Demonstration Project‐Example 2
Item Unit Cost Approx. Cost for
One‐Mile Section
Rain Gardens at Bulbouts $5 per square foot $144,000
Median $6 per square foot $133,000
Curb & Gutter for Median $13 per linear foot $96,200
Curb & Gutter at Bulbouts $13 per linear foot $70,200
Striping (per stripe) $0.25 per linear foot $3,700
Total: $447,300
Narrower Street with median and
bulbouts at intersections
36
Council Input Being Sought
•Staff is seeking feedback on the development of a
demonstration project. Funding to construct a
demonstration project is being sought as a 2013/2014
BFO budget offer; other funding sources such as
grants may be pursued as well
Proposed Demonstration Project
8/9/2012
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37
• Public Open Houses targeting general public and key
stakeholders such as environmental groups, design
professionals and the building industry
•Project website (fcgov.com/greenstreets)
•Focus group meetings
• Presentations to boards and commissions (e.g., Water Board,
Planning and Zoning Board and the Transportation Board)
• Presentations to local community groups, such the Chamber
of Commerce and others
2012 Streets and Stormwater Site
Development Initiatives‐Public Input Process
38
August: Public Open House, August 9
City Council Work Session, August 14
Sept‐Nov: Boards and Commissions recommendations
Oct: Public Meeting
Dec: City Council Hearing to consider adoption of:
‐ Streetscape Standards
‐ Low Impact Development Policies
2013: Implementation of Demonstration Project
(as funding is available)
May/June: Street Classification Update
2012 Streets and Stormwater Site
Development Initiatives‐Next Steps
8/9/2012
20
39
More Information
LCUASS Streetscape Update:
Pete Wray, pwray@fcgov.com or 970-221-6754
LCUASS Street Classifications Update:
Amy Lewin, alewin@fcgov.com or 970-416-2040
Low Impact Development:
Basil Hamdan, bhamdan@fcgov.com or 970-224-6035
Demonstration Project:
Aaron Iverson, aiverson@fcgov.com or 970-416-2643
Attachment 2
1
Attachment 3
LID Policy Questions and Issues
1. How did staff generate the current proposed criteria [A minimum of 50% of new impervious
surface area must be treated by a LID-type device or technology (i.e. bio-retention cell, bio-
swale); and at least 25% of new parking areas must be designed to be pervious; or,
implementation of a design alternative that provides equal or better treatment to the previous
requirements.]?
a. Is there a technical reason for selecting the 50% and 25% targets?
The 50 % criterion for LID treatment was born out of our effort to balance the cost and
benefit of LID treatment. There is a point of diminishing returns as demonstrated in
an Urban Drainage Flood Control District (UDFCD) study where fully treating the
entire Water Quality Capture Volume (WQCV) resulted in an over sizing factor of 2.2
when 95% of the storms are being fully captured and treated.
Figure 6. Point of Diminishing Return, the Maximized WQCV. (Urbonas,
et.al., 1990)
Counting Total Runoff and Number of Events Captured
As for the 25% figure for the minimum pervious area, it is based on the LID principle
that the run-on area be no more that twice the runoff area. For practical and ease of
application purposes the 25% level was selected, in order not to impose a large
financial burden on developing and redeveloping property while maintaining that
maximum 2:1 ratio from runoff impervious area to run-on areas pervious area.
2
b. Why select 50% for the LID treatment level?
As mentioned in the study cited above the 50% of the WQCV point was chosen
based on the optimizing the cost of facilities with respect to their impact. According
to the UDFCD study outlier events in the Front Range region tend to drive the design
WQCV beyond the point of diminishing returns.
Please find below the citation from the study:
”Outlier events can skew the sizing upward and are really not an appropriate target
when the goal is to mitigate runoff effects on receiving waters. Often such events
have runoff impact regardless whether the catchment is urbanized or not. A
reasonable suggestion for screening out these outliers is to limit the maximum
WQCV’s basin size to capture of 99.5 percent of volumes or events and to screen out
of the population larger events from analysis. WQ-COSM provides the users such an
option and lets them to decide what this upper screening value is.
This was done in analyzing the five locations, screening our WQCV basins sizes
exceeding 99.5% capture rates. Then, the 95% capture volume-based and event-
based results were compared against each other, which are summarized in Figure 7.
Next, the question was asked what is the additional sizing (and cost) penalty for
capturing 95% of runoff volumes and events versus capturing the volume at the point
of diminishing returns? Table 3 lists the combined effect or sizing for the 95% values
and for volume-based instead of event-based captures. As was expected there was
much variability, ranging from as little as 40% penalty in Seattle to a 220% penalty in
sizing in Denver. Clearly, much research in needed to answer what is the
appropriate cost-effective WQCV basin (i.e., BMP and LID) basin sizing protocol to
effectively mitigate the most serious impacts of urbanization on receiving waters.
Having a simple single, one-size-fits-all standard or regulation is likely to lead to
unnecessary and excessive fiscal and land area expenditures”.
City Combined Ratio of
WQCV Increase
CHICAGO 2.1
DENVER 3.2
NEW YORK 1.5
SEATTLE 1.4
TAMPA 1.75
Table 3. Cumulative ratios of over sizing past the point of diminishing returns and
for volumes instead of events captured for a 60% impervious catchment.
Observations
A clear trend that emerged is that the Net Present Cost of BMPs is a function of their
density in a watershed, the higher the density, the higher the cost per square mile. The
“lot-based” BMPs such as Rain Gardens, Permeable Interlocking Concrete Pavement,
Hydrodynamic Separators and Inlet Inserts exhibited significantly higher NPCs than
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“community-based” BMPs such as Extended Detention Basins, Sand Filter Basins and
Retention Ponds.
As to water quality, some of the “community-based” BMPs, Such as Sand Filter Basins
were as robust in reducing loads as PLDs, while Extended Detention Basins were
almost as robust as Permeable Interlocking Concrete Pavements and Sand Filter Basins
with underdrains.
When communities consider which BMPs to use, it is important to consider not only
initial capital costs, but also the long-term maintenance and administrative costs. While
parties doing land development will naturally favor BMPs with lowest initial costs,
communities also need to look at the long-term maintenance and rehabilitation
commitments under their stormwater discharge permit requirements.
c. Why would we only require that 25% of additional or new parking areas be pervious?
Why not require 25% of all parking areas, regardless of existing or new, to be
pervious?
The reason additional new impervious areas were chosen rather than existing is due
to the fact that a lot of existing development in Fort Collins already has paved areas.
Imposing a condition to retrofit existing development, could potentially make the
regulations costly to implement.
d. Should these percentages be adjusted based on the zoning type, land use, or other
type of criteria? If so, what kind of table/matrix would be appropriate?
LID practices tend to be much more cost effective in "ultra-urban" development areas
as compared to "green field" development. That is because the potential
development gain from less consumption of development land can outweigh the
initial installation costs of LID treatment systems. Using a "life-cycle analysis" for
different LID practices, these initial installation costs can me recouped with a longer
planning horizon.
e. Why does our semi-arid climate (as compared to wetter climates in the Seattle area,
Portland area, etc.) result in different proposed criteria than in other locations?
The combination of climate (rainfall intensities over a short time) soil cover (mostly
low permeability clay soils) and vegetation cover (small amount of tree canopy) that
combine to make LID treatment much more difficult in Fort Collins compared to
Seattle. Combined these three factors have the effect of increasing runoff in a very
short amount of time and reducing the capability of the soil and vegetation to absorb
and reduce the total runoff volume.
2. Compare and contrast why the Puget Sound area and the City of Seattle require infiltration of
100% of storm runoff in Type A soils and we are not proposing a similar criteria?
a. What are Type A soils? How pervious are they compared to other soils?
Hydrologic Soil Groups - Soil groups based on estimates of runoff potential. Soils are
assigned to one of four groups according to the rate of water infiltration when the soils
are not protected by vegetation, are thoroughly wet, and receive precipitation from long-
duration storms.
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• Group A. Soils having a high infiltration rate (low runoff potential) when thoroughly wet.
These consist mainly of deep, well drained to excessively drained sands or
gravelly sands. These soils have a high rate of water transmission.
• Group B. Soils having a moderate infiltration rate when thoroughly wet. These consist
chiefly of moderately deep or deep, moderately well drained or well drained soils
that have moderately fine texture to moderately coarse texture. These soils have a
moderate rate of water transmission.
• Group C. Soils having a slow infiltration rate when thoroughly wet. These consist chiefly
of soils having a layer that impedes the downward movement of water or soils
of moderately fine texture or fine texture. These soils have a slow rate of water
transmission.
• Group D. Soils having a very slow infiltration rate (high runoff potential) when
thoroughly wet. These consist chiefly of clays that have a high shrink-swell potential, soils
that have a high water table, soils that have a claypan or clay layer at or near the surface,
and soils that are shallow over nearly impervious material. These soils have a very slow
rate of water transmission.
• If a soil is assigned to a dual hydrologic group (A/D, B/D, or C/D), the first letter is for
drained areas and the second is for undrained areas. Only the soils that in their
natural condition are in group D are assigned to dual classes.
b. Does each site have to locate the LID feature on Type A soils? What happens if the
Type A soils are not at the low end of the site? How does distributed detention factor
in? How does development have to optimize the site layout?
During initial investigations of a development site, a mapping of the types of soils
present and the topography are overlaid over the proposed development site. In LID
design, it is important to look at the soil distribution in relation to the topography early
on in the process in order to optimize the effectiveness of the LID treatment system.
Since LID in its essence is a distributed type of system it is important to look at the
soil distribution and the potential locations of LID type devices early on in the
process, before the programming on the site is done in order to maximize the
potential impact of the LID devices on the overall site hydrology. Good site
assessment is critical where development is proximate to or may directly impact
sensitive areas. Equally important is creative site design (informed by the site
assessment) that strategically protects native soil, vegetation and hydrology to the
maximum extent possible.
c. What is the predominant soil type in the Fort Collins area? Is the reason we aren’t
proposing this criteria due primarily to our soil types? Other reasons?
Fort Collins soils with the exception of areas around Old Town (in alluvial fan areas)
mostly consist of Type D, poorly drained clay soils.
In Old Town when investigating the installation of the pervious concrete pavement at
the CTL Thompson location our testing indicated undisturbed initial infiltration rates
that exceeded 3 inches per hour which is consistent with a Type A soils. However
following construction activities on the site, due to compaction of soils from
construction traffic, infiltration rates were found to have decreased to the range 1.25
inches per hour. Hence it is paramount that LID sites protect undisturbed highly
pervious areas during construction to preserve their infiltration potential through the
use of construction fencing or other protective measures. These operational criteria
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need to be added to the LID regulations in order for a program to be more
comprehensive.
d. Is the requirement to infiltrate 100% of storm runoff in Type A soils for all events up
to the 100-Year storm?
Rather than using a 100-year design storm event, the Western Washington
Design Manual used in the Puget Sound region requires a continuous simulation of
historic storm events be modeled where the required standards are achieved.
e. What type of storm distribution do they use in the area? Is it flatter and less spiked
than our design storm events? Explain how this impacts the volume and sizing of the
facilities to infiltrate the runoff.
The area receives a considerable amount of moisture which ranges from about 6 in
per month on the average in November to 0.8 inches of rainfall per month in July.
However the 24 hour maximums are much lower than in Fort Collins, our 100-year
event has a maximum of 3.67 in while that of the Seattle region is 1.15 inches in 24
hour period.
Due to the capability of the soils to infiltrate at a regular rate, without reaching
saturation levels, “Type A” soils, prevalent in the Seattle area can take up most of the
high intensity storm with little or no discharge. In addition to the high soil infiltration
rates the area’s vegetation cover allows for a high interception rate; that is, the water
does not even reach the soil since it is held in the vegetation above ground in the
tree canopy and in other low-lying vegetative cover.
According to Puget Sound LID Manual:
"For most storm events, the gentle rainfall intensities are less than the combined
capacity of the interception loss and vegetation and soil storage in native Puget
Sound forests; as a result, overland flow does not occur or is minimal (Booth, Hartley
and Jackson, 2002). Instead, the storm flow moves downslope below the surface at a
much slower rate than overland flow and displaces antecedent, subsurface water in
areas near streams, lakes and wetlands ".
3. Compare and contrast the Puget Sound and City of Seattle area requirement to use LID
techniques to reduce the size of conventional detention facilities (i.e. detention ponds) from
30 – 60% depending on soil and vegetation cover.
Fort Collins has a much lower vegetation cover and infiltration rates compared to the Puget
Sound area. It is much more difficult to achieve the target reduction rates that Seattle has for
detention ponds due to that fact.
a. Would this criteria work for the City of Fort Collins? Why not?
If we were to use the reduction of pond size of 30 to 60 percent that would result in
requiring a large amount of LID facilities and much higher construction costs. Based
on the BMP study performed for the Urban Drainage and Flood Control District
(UDFCD) by CSU, sand filter basins were the most efficient type of facility for
reduction in runoff volumes. That is assuming that the soil underneath the sand filter
can absorb the flow or an underdrain in provided which will reduce the rate and
volume, While all types of LID facilities were effective in removing Total Suspended
Solids (TSS) loading from the runoff effluent.
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EDB – Extended Detention Basin (dry)
RP - Retention Ponds (wet)
SFB-u - Sand Filter Basin w/ Underdrain
SFB-i - Sand Filter Basin w/Infiltration
PLD-u – Porous Landscape Detention w/Underdrain
PLD-i - Porous Landscape Detention w/Infiltration
PICP-u - Porous Interlocking Concrete Paver w/Underdrain
PICP-i – Porous Interlocking Concrete Paver w/Infiltration
HS - Hydrodynamic Device
II - Inlet Insert
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b. If the reason is based on cost, what data do we have to justify that determination?
According to the study prepared for UDFCD regionalized Extended Detention Basins
(EDBs), which are the facilities mostly used in Fort Collins, are the most economical
means of providing stormwater quality treatment using a Net Present Cost
(NPC) basis for comparison.
However directly attributable economic costs may not be the only consideration to
look at when deciding on what type of BMP to use. A community has to balance
costs, environmental impact and social welfare in accordance to our triple bottom line
philosophy. LID design lends itself much better to more clustered development with
large open space areas which will enhance the aesthetic values of the community
and quality of life in general. Here is the relevant information from the UDFCD study:
”Total Net Present Costs of BMP Types
The net present cost (NPC) of a BMP system over its economic life includes all of the
costs discussed earlier, namely, planning, design, construction, construction
observations, review processes, maintenance, rehabilitation and administration of the
program. The costs that are incurred and adjusted for inflation over time are then
converted to the NPC by applying the discount rate (interest rate for municipal
investments), which in this case was estimated at 5%. Figure 3 shows a comparison
for the BMPs in this example and provides the decision makers cost information that
can help in determining which BMPs will serve their community most economically.
However, cost is only one factor, one that has to be balance against the actual
effectiveness of each BMP in removing pollutants and controlling surface runoff
described earlier and illustrated in Figure 1.
Cost Effects of BMP Density
Comparing BMP types to their densities in the watershed reported in Table 2, we
see that there is a direct relationship between BMP density within a watershed and
the system-wide NPCs. Namely, greater densities of BMPs result in higher system-
wide NPCs. This is because constructions, land and maintenance costs are not
directly proportional to BMP size. Also, there are fixed cost for each facility
regardless of size. BMPs with the lowest NPCs fall into a category of “community-
based” or “regionalized” BMPs and included Extended Detention Basins (EDB),
Retention Ponds (RP) and Sand Filter Basins (SFB). The BMP with the highest
NPCs, which we termed as “lot-based”, included the PICP discussed earlier and
Hydrodynamic Separators (HS), Inlet Inserts (II), and Rain Gardens (RGs)”.
Figure 3. Net Present Cost (NPC) of BMP systems for a one-square mile of urban area.
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4. The City of Lacey, WA defines “zero effective impervious surface area” and authorizes
deviations from existing engineering and public works standards to achieve this goal.
a. What types of deviations have been required or accepted in the past?
Currently no developers have implemented enough of the low-impact strategies in the
ordinance to achieve zero effective impervious surfaces. Some developers use only a
few strategies from the ordinance, such as pervious pavements. One project
is completed with a parking lot that is pervious pavement. A second project still in the
design phase will also include pervious pavement in their parking lot.
Designed to be flexible, the ordinance promotes performance standards instead of
specific design standards. For example, the ordinance does not specifically outline
how a developer will achieve near zero impervious surfaces. This is a voluntary
ordinance that offers no additional incentives other than design flexibility.
Currently no benefits exist for the developers to use these practices, so they do not
put in extra effort or time to include these alternate construction methods. The
ordinance will require additional reviewing that can take more time before a developer
can begin building. The new construction methods will deviate from current building
practices that builders are already using.
b. What criteria are used to determine when a deviation from the standards is
appropriate?
Deviations from provisions of Lacey’s Development Guidelines and Public Works
Standards in accordance with the requirements set forth in Chapter.14.31 are based
on the following criteria:
A. The deviations contribute to and are consistent with the zero effective impervious
surface goals of this chapter.
B. The proposed development project offers reasonable assurance that near zero
effect impervious surface will be achieved and maintained.
C. The deviations do not threaten public health or safety.
D. The deviations are consistent with generally accepted engineering and design
criteria, except as necessary to achieve the purposes set forth in Chapter 14.31.
E. The deviations promote one or more of the following:
1. Innovative site or housing design furthering the purposes of the program;
2. Increased on-site stormwater retention using a variety of native vegetation;
3. Retention of at least 60 per cent of natural habitat conditions over the site;
4. Improved on-site water quality beyond that required by current applicable
regulations;
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5. Retention or re-creation of pre-development and/or natural hydrologic
conditions to the maximum extent possible;
6. The reduction of effective impervious surfaces to near zero.
F. The deviations do not allow density greater than what would otherwise be allowed
under city regulations then in effect. The applicant will be required to list and
document the justification for each deviation requested. In order for
such a project to be approved, it must be demonstrated that the project meets all
other requirements of the Lacey Municipal Code except for such specific deviations
and that such project has a reasonable assurance of long term success. There shall
be submitted in conjunction with each such project, covenants, conditions and
restrictions which will be binding upon the property and which require forest retention,
no net increases in impervious surface and such other critical features as the city
may require. (Ord. 1113 §1, 1999).
c. Would a similar criteria work for the City of Fort Collins? Why not?
Achieving a "zero effective impervious area" means infiltrating all post-development
runoff and maintaining a flow regime similar to that of an undeveloped area. Fort
Collins is mostly developed; achieving such standard on a redevelopment site would
be cost prohibitive, due to the nature of our storms which tend to be much more
peaked, the relatively smaller vegetation cover in Fort Collins and the less permeable
soils present. The imposition of such a standard would be physically difficult to
achieve and financially impractical. Even in the Western Washington region
context this policy has not led to any significant implementation and would be even
less practical in Colorado.
5. The City of San Diego requires that LID strategies be used for all Priority Development
Projects. It also recommends LID strategies for Standard Development Projects.
a. What is the difference in the type of projects?
Priority Development projects as defined by the City of San Diego consist of the
following:
Residential Developments of 10 or more units
Commercial Developments greater than one acre.
Heavy Industrial Developments greater than one acre.
Restaurants.
Automotive Repair Shops
Hillside development greater than 5000 sq feet.
Development located within or immediately adjacent to or discharging into water
quality sensitive areas.
Parking Lots with a minimum area of 5,000 sq feet.
Street Road Highway or Freeway.
Retail Gasoline Outlet
Significant Redevelopment-more than 5,000 sq feet of additional or replaced
impervious area.
Other Pollutant Generating Project
All others are Standard Development Projects.
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b. Are the LID strategies tied to specific % requirements or other numerical standards?
According to the City of San Diego LID Manual:
"Treatment control BMPs shall be sized to infiltrate, filter, or treat the water quality
design storm event ".
c. If not, how do they ensure that appropriate LID is applied consistently between
developments?
The City of San Diego does not require a specific type of LID be used. There is a
matrix that helps designers in choosing an appropriate LID technology, based on
land use, impervious amount and watershed area.
d. How do they measure LID performance?
A "Water Quality Capture Volume" (WQCV) is imposed based on the San Diego area
stormwater quality storm. Once that WQCV is provided through the use of any
combination of LID features, the development is deemed to have met the
performance standard.
6. How do the citizens of Fort Collins, the Water Board members and City Council know that
the proposed LID criteria have been fully evaluated, compared and contrasted with
criteria from other communities, and are the best given our unique hydrology, geography,
climate and financial circumstances?
The proposed LID criteria are an effort to balance economic, social and environmental
values. In evaluating alternatives the relative costs were compared to the potential
impact of treating the full Water Quality Capture Volume (WQCV). The City looked at the
potential cost of providing full LID treatment for all sites, the environmental benefits of
using such technologies and the social impact of having greener more pedestrian friendly
streets and developments. In keeping with our triple bottom line approach and looking at
the point of diminishing returns it was decided to use a 50% LID treatment level as a
benchmark. Regulations are not a static entity. It was important to us to have regulations
that will have a potential watershed level impact, do not make Fort Collins regulations too
financially burdensome and maintains or enhance our quality of life. This was the
reasoning behind proposing a 50% treatment level. It was felt that this was a reasonable
starting point based on the studies done to date, based on our unique climate and
geologic conditions, based on the environmental benefit and the economic costs of these
regulations and based on a comparison of these proposed regulations to those of
other leading "green" communities around the United States and the Denver region.
The City has implemented a number of pilot projects that will provide us long term data
regarding the installation, maintenance costs and the effectiveness of different LID
practices. As we learn more from these test sites we will adjust our regulations to match
the community's expectations as well the environmental benefits of such practices.
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7. How can we state that it is more expensive to provide LID treatment? Based on what
technical data?
a. Summarize and provide cost information (per CSU) to address questions that will
arise.
The CSU study establishes that if LID is sized to treat the WQCV the costs of
construction and maintenance would be significantly higher than using a traditional
treatment system BMP such as an Extended Detention Basin (EDB).
However using the WQCV criterion to size an LID treatment system goes beyond the
point of diminishing returns and tends to oversize facilities by nearly 2.2 times in the
Denver region due to our extremely skewed rainfall distribution curve. It is
recommended that capturing 95% of the storm events and screening out high
intensity events be done, in order to keep facilities economical and right-sized.
b. Do we need to do additional financial analysis specifically for Fort Collins? If not,
why?
A Fort Collins specific economic analysis would not be worth the cost since the
Denver region data is considered to be representative of the Fort Collins market
area.
1
Attachment 4
LID Facts Sheets
Common Stormwater Management Terms:
Best Management Practice (BMP): A device, practice, or method for removing, reducing,
retarding, or preventing targeted stormwater runoff constituents, pollutants, and contaminants
from reaching receiving waters. (Some entities use the terms "Stormwater Control Measure,"
"Stormwater Control," or "Management Practice.")
Low Impact Development (LID): LID is a comprehensive land planning and engineering design
approach to managing stormwater runoff with the goal of mimicking the pre-development
hydrologic regime. LID emphasizes conservation of natural features and use of engineered, on-
site, small-scale hydrologic controls that infiltrate, filter, store, evaporate, and detain runoff close
to its source. The terms Green Infrastructure and Better Site Design are sometimes used
interchangeably with LID.
LID Practice: LID practices are the individual techniques implemented as part of overall LID
development or integrated into traditional development, including practices such as bioretention,
green roofs, permeable pavements and other infiltration-oriented practices.
Minimizing Directly Connected Impervious Area (MDCIA): MDCIA includes a variety of
runoff reduction strategies based on reducing impervious areas and routing runoff from
impervious surfaces over grassy areas to slow runoff and promote infiltration. The concept of
MDCIA has been recommended by UDFCD as a key technique for reducing runoff peaks and
volumes following urbanization. MDCIA is a key component of LID.
Maximum Extent Practicable (MEP): MS4 permit holders are required to implement
stormwater programs to reduce pollutant loading to the maximum extent practicable. This
narrative standard does not currently include numeric effluent limits.
Municipal Separate Storm Sewer System (MS4): A conveyance or system of conveyances
(including roads with drainage systems, municipal streets, catch basins, curbs, gutters, ditches,
man-made channels, or storm drains) owned or operated by an MS4 permittee and designed or
used for collecting or conveying stormwater.
Nonpoint Source: Any source of pollution that is not considered a "point source.” This includes
anthropogenic and natural background sources.
Point Source: Any discernible, confined and discrete conveyance from which pollutants are or
may be discharged. Representative sources of pollution subject to regulation under the NPDES
program include wastewater treatment facilities, most municipal stormwater discharges, industrial
2
dischargers, and concentrated animal feeding operations. This term does not include agricultural
stormwater discharges and return flows from irrigated agriculture.
Water Quality Capture Volume (WQCV): This volume represents runoff from frequent storm
events such as the 80th percentile storm. The volume varies depending on local rainfall data.
Within the UDFCD boundary, the WQCV is based on runoff from 0.6 inches of precipitation.
Differences between LID and Conventional Stormwater Quality Management
Low Impact Development (LID) is a comprehensive land planning and engineering design
approach to managing stormwater runoff with a goal of replicating the pre-development
hydrologic regime of urban and developing watersheds. Given the increased regulatory emphasis
on LID, volume reduction and mimicking pre-development hydrology, questions may arise
related to the differences between conventional stormwater management and LID. For example,
Volume 3 has always emphasized MDCIA as the first step in stormwater quality planning and has
provided guidance on LID techniques such as grass swales, grass buffers, permeable pavement
systems, bioretention, and pollution prevention (pollutant source controls). Although these
practices are all key components of LID, LID is not limited to a set of practices targeted at
promoting infiltration.
Key components of LID, in addition to individual BMPs, include practices such as:
An overall site planning approach that promotes conservation design at both the watershed
and site levels. This approach to development seeks to "fit" a proposed development to the site,
integrating the development with natural features and protecting the site's natural resources. This
includes practices such as preservation of natural areas including open space, wetlands, soils with
high infiltration potential, and stream buffers. Minimizing unnecessary site disturbances (e.g.,
grading, compaction) is also emphasized.
A site design philosophy that emphasizes multiple controls distributed throughout a
development, as opposed to a central treatment facility.
The use of swales and open vegetated conveyances, as opposed to curb and gutter systems.
Volume reduction as a key hydrologic objective, as opposed to peak flow reduction being the
primary hydrologic objective. Volume reduction is emphasized not only to reduce pollutant
loading and peak flows, but also to move toward hydrologic regimes with flow durations and
frequencies closer to the natural hydrologic regime.
Even with LID practices in place, most sites will also require centralized flood control facilities.
In some cases, site constraints may limit the extent to which LID techniques can be implemented,
whereas in other cases, developers and engineers may have significant opportunities to integrate
LID techniques that may be overlooked due to the routine nature and familiarity of conventional
approaches. This manual provides design criteria and guidance for both LID and conventional
stormwater quality management, and provides additional facility sizing credits for implementing
Step 1, Volume Reduction, in a more robust manner.
Key LID techniques include:
Conserve Existing Amenities: During the planning phase of development, identify portions
of the site that add value and should be protected or improved. Such areas may include mature
trees, stream corridors, wetlands, and Type A/B soils with higher infiltration rates. In order for
3
this step to provide meaningful benefits over the long-term, natural areas must be protected from
compaction during the construction phase. Consider temporary construction fence for this
purpose. In areas where disturbance cannot practically be avoided, rototilling and soil
amendments should be integrated to restore the infiltration capacity of areas that will be restored
with vegetation.
Minimize Impacts: Consider how the site lends itself to the desired development. In some
cases, creative site layout can reduce the extent of paved areas, thereby saving on initial capital
cost of pavement and then saving on pavement maintenance, repair, and replacement over time.
Minimize imperviousness, including constructing streets, driveways, sidewalks and parking lot
aisles to the minimum widths necessary, while still providing for parking, snow management,
public safety and fire access. When soils vary over the site, concentrate new impervious areas
over Type C and D soils, while preserving Type A and B soils for landscape areas and other
permeable surfaces. Maintaining natural drainage patterns, implementing sheet flow (as opposed
to concentrated flow), and increasing the number and lengths of flow paths will all reduce the
impact of the development.
Minimize Directly Connected Impervious Areas (MDCIA): Impervious areas should drain
to pervious areas. Use non-hardened drainage conveyances where appropriate. Route downspouts
across pervious areas, and incorporate vegetation in areas that generate and convey runoff. Three
key BMPs include: o
Grass Buffers: Sheet flow over a grass buffer slows runoff and encourages infiltration, reducing
effects of the impervious area.
Grass Swales: Like grass buffers, use of grass swales instead of storm sewers slows runoff and
promotes infiltration, also reducing the effects of imperviousness.
Bioretention (rain gardens): The use of distributed on-site vegetated features such as rain
gardens can help maintain natural drainage patterns by allowing more infiltration onsite.
Bioretention can also treat the WQCV, as described in the Four Step Process.
Defining an “LID Project”:
1. Managing stormwater where it falls through small scale engineered drainage facilities
2. Reducing impervious surfaces
3. Maintaining and/or re-establishing native vegetation
4
Regional Practices:
UDFCD Region - Mainly Along the Colorado Front Range
Adopted in part by Fort Collins in December 2011 with local exceptions.
UDFCD has long recommended a Four Step Process for receiving water protection that focuses
on reducing runoff volumes, treating the water quality capture volume (WQCV), stabilizing
drainageways, and implementing long-term source controls. The Four Step Process pertains to
management of smaller, frequently occurring events, as opposed to larger storms for which
drainage and flood control infrastructure are sized. Implementation of these four steps helps to
achieve stormwater permit requirements. Added benefits of implementing the complete process
can include improved site aesthetics through functional landscaping features that also provide
water quality benefits. Additionally, runoff reduction can decrease required storage volumes, thus
increasing developable land.
Developers should anticipate more stringent requirements from local governments to implement
runoff reduction/MDCIA/LID measures (in addition to WQCV capture), given changes in state
and federal stormwater regulations.
The Four Step Process for Stormwater Quality Management
5
CASE STUDIES
City and County of Denver
LID Practices
Required: No Recommended: Yes
LID Criteria
Four Step Process
Implementation Level
Low
Comments: Large scale (watershed level) LID techniques being considered. Technical
team studying options, process ongoing for last 2 years.
City of Loveland
LID Practices
Required: No Recommended: Yes
LID Criteria
Four Step Process
Implementation Level
Low in private development, High in public projects in downtown area.
Comments: LID Implementation mostly on public/capital projects. Substantial Retrofit
Program. Encouraged but not required for private development.
City of Boulder
LID Practices
Required: No Recommended: Yes
LID Criteria
Four Step Process
Implementation Level
Highest in Colorado, still low in general. Strongly encouraged for all new private
development and capital construction program.
6
Puget Sound, Washington
LID Practices
Required: Yes Recommended: Yes
LID Criteria
Developments located in Type A (highly pervious) soils areas must infiltrate 100 percent
of runoff. Other areas must reduce detention pond size by 30 to 60 percent.
Implementation Level
Highest in nation.
Comments: LID projects shall meet the minimum peak and duration flow control
standards per the Department of Ecology Stormwater Management
Manual for Western Washington, current edition.
Through the use of LID integrated management practices identified in
the Puget Sound Action Team’s Low Impact Development Technical
Guidance Manual for Puget Sound, flow control facilities may be
reduced in size as calculated under the Department of Ecology’s 2005
Stormwater Management Manual for Western Washington.
Water quality treatment BMPs shall be provided to treat 91 percent of
the annual runoff volume per the Department of Ecology standards.
All projects shall provide a maintenance plan/program that has been
approved by the City, including source control BMPs.
All projects with Type A (outwash) soils shall infiltrate 100-percent of
Runoff.
LID projects shall reduce the size of conventional detention facilities (e.g., ponds) as
follows:
Calculate the pond volume of a conventional project by using the conventional
modeling assumptions in Table 17.62.020-2: Impervious Surface Maximum
Limits and Modeling Assumptions.
Reduce the conventional volume by the percentage shown in Table 17.62.020-1:
Pond Reduction and Native Vegetation Requirements to find the allowed LID
pond size.
Apply sufficient LID techniques to the project so that when the techniques are
modeled using guidance from Chapter 7 of the LID Technical Guidance Manual
for Puget Sound the conventional pond volume is reduced to the required pond
reduction percentage found in Table 17.62.020-1. LID projects shall preserve
7
native vegetation area according to the percentages shown in Table 17.62.020-1.
If the site has already been disturbed, the site shall be revegetated to meet the
percentages shown in Table 17.62.020-1.
Reduction in pond volumes range from 30 to 60% depending on soil and vegetation
cover.
City of Seattle, Washington
LID Practices
Required: Yes Recommended: Yes
LID Criteria
Type A soils areas must infiltrate 100 percent of runoff. Other areas must reduce
detention pond size by 30 to 60 percent.
Implementation Level
Highest in nation.
Comments: The design and construction of Green Street improvements can be funded by
developers in exchange for increased floor-area-ratio (FAR) or other land use code departures,
as specified in the City of Seattle’s Land Use Code.
Other Examples;
City of Sommamish Washington:
Encourages comprehensive incorporation of LID into project design.
Use of LIDs earns Technique Points toward incentives including density and height
bonuses.
County of Snohomish (Washington)
Incorporate the LID Technical Guidance Manual for Puget Sound by reference
Mandates LID use in certain locations
Authorizes modifications to regulations and construction, drainage, grading, and access
standards for LID project proposals
City of Port Angeles (Washington)
PLID – Planned Low Impact Development Overlay Zone.
City of Lacey (Washington)
Zero Effect Drainage Discharge.
Defines “zero effective impervious surface” and authorizes deviations
from existing engineering and public works standards to achieve this goal.
8
City of Austin, Texas
LID Practices
Required: Yes Recommended: Yes
LID Criteria
Depending on location must infiltrate 100 percent of runoff. Other areas must reduce
detention pond size.
Implementation Level
High on a regional scale.
Comments: The City currently provides a fee-in-lieu-of construction option to land
developers as an alternative to providing onsite stormwater detention or water quality
improvement facilities in certain watersheds if safe downstream runoff conveyance
conditions can be met.
The fees for the alternative to onsite stormwater detention are referred to as Regional
Stormwater Management Program (RSMP) fees and are based on a set of formulas
from Appendix D of the City of Austin Drainage Criteria Manual (COA DCM).
The fees for the alternative to onsite water quality facilities are referred to as Urban
Watersheds Structural Control Fund (UWSCF) fees and are based on a set of formulas
from Appendix T of the Environmental Criteria Manual.
The RSMP fee was adopted in 1985, and the UWSCF fee was adopted in 1991.
RSMP and UWSCF fees are based on added impervious areas.
The fees per acre are high for the first additional acre, of $ 32,000 and decrease to
a minimum of $6,000 per additional acre of impervious area.
9
City of San Diego, California
LID Practices
Required: Yes, with exceptions Recommended: Yes
LID Criteria
All Priority Development Projects must implement LID to treat water quality storm
event.
Implementation Level
High
Comments: Employ Source Control BMPs. Provide Permanent BMP structures. The
applicability of Standard Development Project LID BMP requirements varies depending
on project characteristics such as development density, site location, or other land use
issues.
While certain landscaping LID features may be incorporated into a detached residential
or commercial project, they may not fit into the development footprint of other projects,
such as urban high-rise developments
Priority Development Projects (PDP) are subject to Low-Impact Development (LID)
design standards. PDPs are defined as:
Residential Developments of 10 or more units
Commercial Developments greater than one acre.
Heavy Industrial Developments greater than one acre.
Restaurants.
Automotive Repair Shops
Hillside development greater than 5000 sq feet.
Development located within or immediately adjacent to or discharging into water quality
sensitive areas.
Parking Lots with a minimum area of 5,000 sq feet.
Street Road Highway or Freeway.
Retail Gasoline Outlet
Significant Redevelopment-more than 5,000 sq feet of additional or replaced impervious
area.
Other Pollutant Generating Project
LID strategies for Standard Development Projects include:
1. Optimize the Site Layout
2. Minimize Impervious Footprint
3. Disperse Runoff to Adjacent Landscaping
4. Employ Construction Techniques that Encourage Infiltration
5. Stabilize the site to Prevent Soil Erosion
Structural treatment control BMPs and LIDs may be located on- or off-site, used
singularly or in combination, or shared by multiple new developments.
Treatment control BMPs shall be sized to infiltrate, filter, or treat the water quality design
storm event.
Attachment 5
Excerpt from Unapproved Water Board Minutes, July 19, 2012
Low Impact Development (LID) Update
(Presentation available upon request)
Stormwater and Floodplain Program Manager Ken Sampley reviewed the proposed LID criteria
and introduced Stormwater Quality Engineer Basil Hamdan who shared in presenting this
information. This item goes to Council at the August 14th Work Session.
Highlights:
- The purpose of LID is to treat and control stormwater as close to its source as possible.
- LID is another level of Best Management Practices (BMP).
- The proposed criteria and policy for Fort Collins is quite different than that seen in other
locations for many reasons that include geography, hydrology, climate, soil conditions.
- Criteria:
50 percent of entire lot area for all new development properties should be treated by an
LID-type of device/technology. Staff will discuss the expectations of retrofitting for
redevelopment and grandfathering.
A minimum of 25 percent permeable surface to be required for added parking areas.
Criteria may be adjusted to reflect different land use type and location, such as
adjustments to percentages depending on zoning, type of soil, etc.
- A Triple Bottom Line (TBL) approach is used when applying criteria to consider
environmental, social, and economic impacts. Staff seeks to design programs that balance all
three considerations.
- LID standards are one of four components in the 2012 Green Streets Initiative, along with
streetscape/landscape standards, street classifications, and a green street demonstration project.
- Public open houses take place August 8th. Board recommendations will be sought in October.
- The Water Board’s Engineering Committee provided comments previously.
LID Policy alternatives include LID-required alternatives and incentive-based alternatives.
Mr. Hamdan reviewed the pros and cons of Alternative 1B, “Fee in Lieu of Construction”. These
concepts can be incorporated with BMPs. However, customers may view this as an additional
“stormwater fee”.
Existing City voluntary programs, such as Climate Wise, could be leveraged with Alternative 2,
“Incentive-Based Approach”. However, we would not see the degree of watershed-level impact
as we would with required programs.
Board discussion:
Staff has mentioned the possibility of offering discounts on stormwater fees if citizens install
LIDs on their property. Staff discussed listing it as an incentive, but it is not easy to qualify how
much of an incentive should be offered.
What kind of technical support will the City provide to developers? The exact level of resource
has not been defined yet. Staff wants to provide information and guidance, but it wouldn’t be
staff’s role to design the projects.
A potential customer base might be the homeowners associations (HOA’s). It is an aesthetic,
quality-of-life pitch. Some sites have recreational facilities, and these must be considered on a
case-by-case basis. HOA’s inherit these features from developers, and education is helpful to
them as well as an understanding of who is responsible to maintain them. Water Engineering
and Field Services Manager Jon Haukaas noted the steps that have been taken - outreach and
simple instructions for maintaining Stormwater Control measures to HOA’s, as well as regular
site inspections and identification of a cycle of inspections and maintenance. Our staff is also
considering the future development of a Standard Operating Procedures (SOP) manual. Mr.
Haukaas added there are experienced private engineering firms available to assist HOA’s with
designing the Stormwater Control measures and developing the appropriate corresponding SOP
and maintenance manual.
Discussion took place about promoting LID as an embedded part of streetscaping standards.
The Green Streets concept incorporates many components, including LID, together.
The Utilities participates in monthly coordination meetings with Colorado State University
(CSU). While; the City does not have regulatory control over CSU, CSU is installing BMPs and
LIDs in conjunction with new development or redevelopment of facilities on their campus.
Some Board members questioned whether the semi-arid climate of Fort Collins would present
obstacles to creating viable LID facilities such as those shown in the example Green Street
rendering. Staff noted that climate and hydrology are significant factors to be addressed,
however LID concepts can be implemented to effectively treat and control runoff closer to the
site. The facilities may not look as “lush” as in locations with wetter climates, but they can be
both attractive and effective at improving water quality and reducing runoff volumes for frequent
storm events.
Our community is extremely fortunate to have Dr. Larry Roesener at CSU as one of the leading
expert’s on stormwater quality. Staff acknowledged this valuable technical expert and resource
and noted that Dr. Roesner is involved with Fort Collins in a number of programs and projects
that include stormwater quality monitoring and testing, LID policy development, and stream
restoration identification and prioritization.
The board expressed support for the City of Fort Collins Stormwater Utility to develop and
implement an innovative LID policy and associated criteria.
1
BMP ECONOMICS AND SIZING
Ben Urbonas, P.E., D.WRE 1, Christopher C. Olson2, Ken MacKenzie3 and James C.Y Guo4
ABSTRACT
Communities and agencies responsible for stormwater management (e.g., MS4 permit holders
in United States) face new ever-increasing on-site stormwater runoff control regulations, while
faced with funding limitations. Best Management Practices (BMPs) are employed to meet
these challenges, which come with significant initial costs to install but to maintain in perpetuity.
To examine the real long-term effectiveness and cost a one square mile urban catchment in
the Denver region with mixed land uses was examined with the help of a recently developed
spreadsheet model. Results will be described showing that BMPs capable of capturing runoff
from larger areas are not only more cost-effective, but can compete in effectiveness with
retention control measures.
The other challenge facing stormwater managers is what cost effective sizing of various types
of BMPs are. A new model designed specifically for that purpose is described that has the
potential of saving time and resources in pre-sizing BMP capture volumes for planning and
design purposes.
Introduction
Stormwater water quality management is a mandated practice in USA by the Clean Water Act
of 1972 and is governed by the interpretation of this law by the Environmental Protection
Agency (EPA). In attempting to comply, various states and local governments instituted
programs (jointly referred as “communities”) requiring a plethora of stormwater treatment
and/or disposal facilities, often referred to as best management practices (BMPs) and a subset
of these called low impact development (LID) installations. Often, these requirements are
imposed without considering the long term effectiveness and economics of their decisions.
The latter is crucial for communities to know since by law they are required to insure that the
BMPs they approve for installation will continue to function as designed in perpetuity, or until
replaced by new facilities.
Few analytical tools exist to help communities assess which BMPs are most effective under
their site conditions and what will be long-term budgetary implication of these selections. For
example, the USEPA’s SUSTAIN model (Shoemaker, et.al. 2009) incorporates sophisticated
algorithms for evaluating BMP effectiveness, but its default cost functions are limited only to
construction costs and its use requires a relatively high level of technical expertise. The Water
Environment Research Federation’s (WERF) Performance and Whole Life Costs of BMPs and
SUDS spreadsheet tools (Lampe et al 2005) can be used to estimate the whole life costs of a
1 2 Graduate President, Research Urban Watersheds Assistant, Department Research Institute, of Civil and Denver, Environmental CO, USA Engineering, burbonas@Colorado urbanwatersheds.State
University, org
Fort Collins, CO, USA, colson23@engr.colostate.edu
3 Manager, Master Planning Program, Urban Drainage and Flood Control Dist., Denver, CO, USA, kam@udfcd.org
4 Professor, Department of Civil Engineering, University of Colorado Denver, USA, james.guo@ucdenver.edu
ATTACHMENT 6
2
single BMP at a time, however they lack BMP effectiveness algorithms. Neither of these
explicitly account for inflation of maintenance, operation and administrative costs.
To assist with such decisions, a spreadsheet based computer model titled: “BMP –
Recognizing these shortcoming the Urban Drainage and Flood Control District (UDFCD) in
Denver, Colorado and the Urban Watersheds Research Institute, Inc. partnered to fund the
development by the Colorado State University of the Rational Estimation of Approximate Likely
Costs of Stormwater Treatment (BMP- REALCOST) model (UDFCD, 2010) and is available
from UDFCD at http://udfcd.org/downloads/software/BMP-REALCOST_v1.0.zip along with its
user manual as a download at no cost. The model is Excel-bases, is relatively open source
and is easy to use. It permits the user to assess and adjust, as needed, various program
parameters. The economic analysis accounts for inflation and variations of
construction/maintenance costs by location using the Engineering News Record™
Construction Cost Index (ENR CCI). This paper illustrates how BMP-REALCOST can be used
by communities to compare 10 BMP/LID types when applied to a one-square-mile urban
watershed in Denver, Colorado when selecting what they will accept.
Example BMP-REALCOST Model’s Application
Land Uses within the Example Watershed
The model was used to test a series of BMP applications. Each scenario examined looked at a
single BMP type applied uniformly within the one-square mile watershed. The results then can
be used to illustrate for planners, decision makers and regulators what their choices of the
BMP types means in terms of effectiveness in controlling stormwater runoff and long-term
economic, maintenance and rehabilitation cost, and administrative cost implications. The
example watershed contained a mix of Commercial, Multi-Family Residential and two different
densities of Single Family Residential land uses (see Table 1) along with their assigned
effective imperviousness. This table also lists the per acre cost of land for each of the land
uses in this example.
Table 1. Land Use Distributions, Effective Imperviousness and Land Costs Used.
Catchment
ID Land Use
Area
(ac)
% Effective
Impervious
Land Cost
$/ac
Cross Roads Commercial 50 95% $200,000
Shop & Go Commercial 15 95% $200,000
Apartments Residential - Apartments 100 80% $200,000
Residential 1 Residential 3,000 s.f. Homes 225 51% $130,000
Residential 2 Residential 2,000 s.f. Homes 250 39% $130,000
Input Economic Parameters
Since BMPs are to perform in perpetuity, they will need to be maintained and rehabilitated
when needed. To make comparisons, a long economic life, say 50 years, is appropriate and is
representative of many public works projects. An inflation rate of 4.6% was used, which is the
average published rates over the last 50 years in United States. The interest rate for invested
municipal funds was assumed to be 5.0%, a rate that is little higher than the inflation rate and
one that appears reasonable when looking at the municipal bond rates over the last 20 to 30
years, although returns in 2011 are much lower. A 2009 ENR CCI index of 6570 was applied
to adjust the costs for the Denver region. All default construction and maintenance cost
3
parameters in BMP-REALCOST were input using the 2009 national ENR CCI of 8141, but
some default costs were overwritten by the authors to reflect differences in capital and
maintenance costs between BMPs that require underdrains and ones that do not.
Administrative costs, namely the cost of complying with for the MS4 permit was assumed to be
12% of the annual maintenance costs plus the cost of regular inspections.
The construction costs for each BMP were developed be a consultant to UDFCD (Muller
Engineering 2009). Forty percent were added to these costs to account for contingencies, cost
of planning, engineering, inspection and discharge permit oversight during construction. For
comparison purposes all costs are reduced by the model to a net present cost (NPC) after
accounting for inflation and discount interest rate.
Hydrologic Conditions and Sizing of BMPs
In developing this example, BMPs were sized using protocols recommended for the Denver
region. This includes the complete capture and treatment of the 80th percentile runoff event for
storage BMPs and processing of the 2-year design storm for conveyance BMPs (UDFCD
2004). For this region, the mean annual precipitation is 15.8 inches, the 2-year 1-hour depth is
0.95 inches and the mean storm depth is 0.43 inches (Driscoll et. al 1989).
BMPs Modeled
Table 2 lists the numbers of each BMP, by type, used in this example one-square mile
watershed. It is believed that the densities for site control BMPs that were used in this
example were somewhat low. Also listed are the years between rehabilitations, or periods
needed to rebuild or completely recondition each facility, along with the percentages of the
original capital cost used as the cost of rehabilitation for each BMP.
A total of ten (10) BMP types were analyzed, with some only differing by whether the captured
runoff is infiltrated or discharged to the surface via underdrains. Infiltration is not available in
all cases because of geology, groundwater levels, geotechnical limitations near structures,
potential for flooded basements, polluted groundwater plumes, etc.
Table 2. List of BMP Types and Numbers Used for the Example Catchment.
BMP Type *
No of
BMPs
Years
Rehab
Cycle
% Rehab
Cost of
Capital
EDB - Extended Detention Basin (dry) 27 35 50
RP - Retention Ponds (wet) 18 35 80
SFB-u - Sand Filter Basin w/ Underdrain 27 25 75
SFB-i - Sand Filter Basin w/Infiltration 27 25 80
PLD-u - Porous Landscape Detention w/Underdrain 543 15 30
PLD-i - Porous Landscape Detention w/Infiltration 543 15 30
PICP-u - Porous Interlocking Concrete Paver w/Underdrain 131 25 80
PICP-i - Porous Interlocking Concrete Paver w/Infiltration 131 25 80
HS - Hydrodynamic Device 355 25 100
II - Inlet Insert 709 2 100
4
Model Results for Example Watershed
Reductions in Runoff Volumes and Pollutant Loads
Relative effectiveness of the BMPs in reducing annual surface runoff volumes and Total
Suspended Solids (TSS) loads are compared in Figure 1. Four levels of performance emerge:
1. BMPs with water quality capture volume (WQCV) that infiltrate the runoff into the ground,
namely, SFB-i (90%%), RG-i (86%) and PICP-i (85%) appear to have the best performance
in runoff volume (shown in parenthesis above) and pollutant load reductions.
2. BMPs with WQCV that “filter” the runoff, namely, SFB-u (36%), RG-u (51%) and PICP-u
(35%) with underdrains have the second best performance in runoff volume (shown in
parenthesis above) and pollutant load reductions.
3. BMPs with WQCV that release the captured runoff over extended period of time, namely,
EDB (27%) and RP (6%) capture and detain the runoff for extended periods of time and
have the third best performance in reducing runoff volumes (shown in parenthesis above)
and pollutant loads.
4. The flow-through BMPs without a WQCV, namely, II and HS that provide zero reductions in
runoff volumes and have the lowest levels of pollutant load reductions.
Figure 1. Annual Runoff Volume (left) and TSS Load (right) Reductions
All the estimates in runoff volume and pollutant load reductions are based on the data reported
EPA’s Nationwide Urban Runoff Program (EPA 1983) and the effluent Event Mean
Concentrations (EMCs) reported by the International BMP Database (Wright Water Engineers
and Geosyntec). These data were supplemented by data and experience gathered in the
Denver region by the UDFCD. The pollutant removal percentages in shown in Figure 2 were
calculated by the model using mean influent and effluent concentrations reported in above-
mentioned references.
Effects of Inflation on Net Present Costs (NPCs)
Often BMP selection is done on the basis of initial costs of planning, design, construction and
engineering. However, communities also need to look at the long-term costs over their entire
5
economic life. Inflation then plays a major role in what are the true Net Present Costs (NPCs)
of each BMP installation to the community and its resources. Figure 2 illustrates one of the
figures produced by the BMP-REALCOST and shows the effects of the 50-year average 4.6%
inflation’s rate on maintenance and administrative costs on Rain Gardens (RGs) spread
uniformly across the one-square mile urban watershed.
Figure 2. Effects of inflation on maintenance and administrative costs for a system of
RGs over a one-square mile of urban area in Denver, Colorado.
Total Net Present Costs of BMP Types
The net present cost (NPC) of a BMP system over its economic life includes all of the costs
discussed earlier, namely, planning, design, construction, construction observations, review
processes, maintenance, rehabilitation and administration of the program. The costs that are
incurred and adjusted for inflation over time are then converted to the NPC by applying the
discount rate (interest rate for municipal investments), which in this case was estimated at 5%.
Figure 3 shows a comparison for the BMPs in this example and provides the decision makers
cost information that can help in determining which BMPs will serve their community most
economically. However, cost is only one factor, one that has to be balance against the actual
effectiveness of each BMP in removing pollutants and controlling surface runoff described
earlier and illustrated in Figure 1.
Cost Effects of BMP Density
Examining Figure 3 and comparing BMP types to their densities in the watershed reported in
Table 2, we see that there is a direct relationship between BMP density within a watershed and
the system-wide NPCs. Namely, greater densities of BMPs result in higher system-wide
NPCs. This is because constructions, land and maintenance costs are not directly proportional
to BMP size. Also, there are fixed cost for each facility regardless of size. BMPs with the
lowest NPCs fall into a category of “community-based” or “regionalized” BMPs and included
Extended Detention Basins (EDB), Retention Ponds (RP) and Sand Filter Basins (SFB). The
BMP with the highest NPCs, which we termed as “lot-based”, included the PICP discussed
earlier and Hydrodynamic Separators (HS), Inlet Inserts (II), and Rain Gardens (RGs).
6
Figure 3. Net Present Cost (NPC) of BMP systems for an one-square mile of urban area.
Case of Porous Interlocking Concrete Pavers vs. Conventional Pavement
What emerged was that Porous Interlocking Concrete Pavers (PICPs) had the highest
apparent net present costs (NPC) of all BMPs modeled. As illustrated in Figure 4, that is the
case unless the results are adjusted for the NPC of conventional pavement, which can be done
by subtracting the NPC of equivalent areas of non-permeable pavements. Such adjustments
can result in 50% to 100% reductions in the NPC of PICPs, which levels of adjustment do not
include costs associated with larger drainage systems needed when PICPs are not used.
Figure 4. Annual unit NPC of a pound of TSS removed by PICPs from one square mile of
urban area before (left) and after (right) adjusting for cost of Convectional Pavement.
Finding Water Quality Capture Volume (WQCV)
From above discussion, it is clear that there is a need to find a cost effective size of a WQCV
basin (i.e., size of the vessel) for each type of water capture BMP that is adequate for the task,
but is not oversized. If undersized, the receiving waters will not see the mitigations benefits to
protect their aquatic life and geomorphology. When oversized, waste of valuable land and
fiscal resources is the result. Continuous simulation is probably the most reliable way to size a
7
WQCV basin, using long-term rainfall data to generate runoff and then routing it through the
BMP’s WQCV basin as illustrated in Figure 5. The size of the basin is, in part, a function of its
drain time (i.e., the time it takes to empty a brim-full WQCV basin). This defines the average
discharge flow rate though the basin’s outlet, underdrain or through infiltration into the ground.
Figure 5. Schematic of the routing process through a WQCV basin.
Point of Diminishing Returns
The idea of quantifying the point of diminishing returns for BMP sizing was suggested by
Urbonas, Guo, and Tucker in 1990 (Urbonas, et.al., 1990). This concept was further
developed and tested by Guo and Urbonas using continuous rainfall data at a wide variety of
locations in the United States (Guo and Urbonas, 2002). Since then UWRI, UDFCD and the
University of Colorado Denver jointly developed an easy to use software package Water
Quality Capture Optimization Statistical Model (WQ-COSM) that permit easy and efficient
analysis of the rainfall-runoff volume process using NCDC rainfall data. It is available as a free
download at http://www.urbanwatersheds.org/software/software.html.
WQ-COSM generates an array of WQCVs up to a size that captures 100% of all runoff
volumes and runoff events. It also identifies the point of diminishing returns (i.e., maximized
WQCV) in terms of total volumes captured and number of storms captured. Up to that point,
incremental increases in WQCV basin size result in corresponding favorable returns in terms of
incremental increases in the f volumes of runoff and the storms captured. Beyond that point,
incremental increases in WQCV result in rapidly diminishing returns in the capture volumes
and storms. Figure 6 illustrates this phenomenon, which was found to occur at allocation
throughout the United States examined by the authors.
To find this point of diminishing returns, all incremental WQCV basin sizes are normalized by
the WQCV that fully captures all of the runoff volumes or storm events. Since a few very large
events can skewing the results, the software allows the user to mitigated this by defining the
largest WQCV value that excludes events, say the 99.5 percentile WQCV.
Modeling Surface Runoff
WQ-COSM provided three options for estimating surface runoff volumes, namely, Rational,
Integrated Horton’s and Green-Ampt methods, the latter two use similar algorithms used in
EPA SWMM. National Climatic Data Center (NCDC) continuous 15- and 60-minute
precipitation data is read and checked for errors by the program. The user may exclude
specific seasons, such as snow months, and very small storms form analysis. Rainfall and
runoff volume statistics and, if so desired, information about each storm are provided as output.
8
Figure 6. Point of Diminishing Return, the Maximized WQCV. (Urbonas, et.al., 1990)
Counting Total Runoff and Number of Events Captured
If the cumulative runoff volume being stored within the WQCV vessel during any storm event
does not exceed the basins capacity, the runoff volume for that event is considered to be
entirely captured. If the runoff during a storm causes the basin’s capacity to be exceeded,
some of the runoff overflows or bypasses it. The incremental volume that overflows/bypasses
is added to the cumulative total overflow volume. Two capture ration are defined.
The Runoff Volume Capture Ratio (Rv) is defined as:
(6)
in which, = runoff volume capture ratio.
Ptr = cumulative runoff volume in inches (mm),
Pto = cumulative overflow/bypass volume of runoff in inches (mm),
And the Event Capture Ratio(Rn) is defined as:
(7)
in which, = runoff event capture ratio,
= total number of storm events where runoff exceeded basin’s capacity, and
= total number of storm runoff events.
This bifurcated definition permits the user to decide if the numbers for storms captured is more
important to control than the total runoff volume over the period of simulation. Control of runoff
volumes may have less impact on the receiving water response since the large events in the
series can dominate the WQCV sizing and be targeting the events that produce significant
runoff volumes before urbanization. Sizing for the capture of specific percentage of runoff
events may be more representative for mitigating the effects of urbanization. This topic
probably needs serious basic research in the field and not be based on modeling and opinion
only.
However, there can be a significant difference in size, and cost, when the WQCV basin is sized
to capture a defined percentage of volumes instead of the same percentage of runoff events in
total. Figure 7 show a comparison for five cities in USA, showing the ratio between the basin
sizes of volume-based versus event-based captures at 95% level. Depending on the location
9
and the catchment’s imperviousness, differences can range from zero to as much as 120%
more volumes needed to size for volume-based capture.
Figure 7. Ratios of 95% Volumes/Events Captured for WQCV Basin Sizing Needs
Examples of Application of WQ-COSM
WQ-COSM was used to assess the WQCV basin sizing needs at five locations in United Sates,
namely Chicago, IL, Denver, CO, New York, NY, Seattle, WA and Tampa, FL. It is safe to
conjecture that the receiving waters and their needs for mitigation due to effects of urbanization
vary greatly between all of these locations. As a result a single capture/retention standard will
fail to recognize the variety in their needs.
Also, there probably is a good argument to screen out capture volumes needed to fully capture
large outlier (flood and drainage problem producing) storm events when sizing WQCV basins.
Outlier events can skew the sizing upward and are really not an appropriate target when the
goal is to mitigate runoff effects on receiving waters. Often such events have runoff impact
regardless whether the catchment is urbanized or not. A reasonable suggestion for screening
out these outliers is to limit the maximum WQCV’s basin size to capture of 99.5 percent of
volumes or events and to screen out of the population larger events from analysis. WQ-COSM
provides the users such an option and lets them to decide what this upper screening value is.
This was done in analyzing the five locations, screening our WQCV basins sizes exceeding
99.5% capture rates. Then, the 95% capture volume-based and event-based results were
compared against each other, which are summarized in Figure 7. Next, the question was
asked what is the additional sizing (and cost) penalty for capturing 95% of runoff volumes and
events versus capturing the volume at the point of diminishing returns? Table 3 lists the
combined effect or sizing for the 95% values and for volume-based instead of event-based
captures. As was expected there was much variability, ranging from as little as 40% penalty in
Seattle to a 220% penalty in sizing in Denver. Clearly, much research in needed to answer
what is the appropriate cost-effective WQCV basin (i.e., BMP and LID) basin sizing protocol to
effectively mitigate the most serious impacts of urbanization on receiving waters. Having a
simple single, one-size-fits-all standard or regulation is likely to lead to unnecessary and
excessive fiscal and land area expenditures.
10
Table 3. Cumulative ratios of oversizing past the point of diminishing returns and for
volumes instead of events captured for a 60% impervious catchment.
City Combined Ratio of
WQCV Increase
CHICAGO 2.1
DENVER 3.2
NEW YORK 1.5
SEATTLE 1.4
TAMPA 1.75
Observations
A clear trend that emerged is that the Net Present Cost of BMPs is a function of their density in
a watershed, the higher the density, the higher the cost per square mile. The “lot-based” BMPs
such as Rain Gardens, Permeable Interlocking Concrete Pavement, Hydrodynamic Separators
and Inlet Inserts exhibited significantly higher NPCs than “community-based” BMPs such as
Extended Detention Basins, Sand Filter Basins and Retention Ponds.
As to water quality, some of the “community-based” BMPs, Such as Sand Filter Basins were as
robust in reducing loads as PLDs, while Extended Detention Basins were almost as robust as
Permeable Interlocking Concrete Pavements and Sand Filter Basins with underdrains.
When communities consider which BMPs to use, it is important to consider not only initial
capital costs, but also the long-term maintenance and administrative costs. While parties doing
land development will naturally favor BMPs with lowest initial costs, communities also need to
look at the long-term maintenance and rehabilitation commitments under their stormwater
discharge permit requirements. Figure 2 illustrates the effects of inflation on the escalation of
maintenance costs.
The BMP-REALCOST is a relatively simple desktop model which provides estimates of the
reductions in runoff volumes and in pollutant loads. It also estimates whole-life cycle costs that
consider the costs for planning, design, construction, maintenance, rehabilitation and
administration. All costs can be adjusted for inflation and geographic locations in United States
using the ENR CCI.
A WQCV is an integral part of all BMPs that control runoff volume. When sizing a stormwater
quality control facility system, one needs to balance the needed runoff capture volumes,
effectiveness in protecting receiving waters and life-cycle facility costs. It is imperative that
economic analysis includes costs of planning, engineering, construction and construction
management, permitting, maintenance, eventual rehabilitation and administration, all adjusted
for the effects of inflation.
The continuous simulation software WQ-COSM developed jointly by the Urban Watersheds
Research Institute, Urban Drainage and Flood Control District and University of Colorado
Denver provides easy to use continuous simulation and calculation of water quality capture
volumes as long as NCDC continuous precipitation data are available. The simple
maximization techniques developed by the authors illustrated in Figure 6 can help designers
11
find the a cost-effective sizes for their community of specific client. This software is available at
no cost through the www.urbanwatersheds.org website.
Finally, it is suggested that sizing of most economical facilities look at the number or
percentage of events captured instead of the percentage of runoff volume captured over the
period of analysis. And, that the designer consider screening out the outlier type large storm
events form analysis and they tend to skew upward the WQCV basin size.
References
Driscoll, E.D., Palhegyi, G.E., Strecker, E.W., and Shelley, P.E. (1989). “Analysis of Storm Events
Characteristics for Selected Rainfall Gauges Throughout the United States.” USEPA,
Washington D.C.
EPA (1983). Results of the Nationwide Urban Runoff Program, Final Report. U.S. Environmental
Protection Agency. National Technical Information Service (NTIS) Access No.áPB84-18552.
Washington, D.C.
Guo, James C.Y. and Urbonas, Ben. (2002). Runoff Capture and Delivery Curves for Storm Water
Quality Control Designs, ASCE J. of Water Resources Planning and Management, Vol 128,
Vo. 3, May/June.
Lampe, L., Andrews, H.O., Hollon, M., Jefferies, C., Kellagher, R., Matin, P. 2005. Performance
and Whole-Life Costs of Best Management Practices and Sustainable Urban Drainage
Systems. Water Environment Research Foundation, Alexandria, VA.
Muller Engineering Company Inc. (2009). “Memorandum – Permanent BMP Construction Cost
Estimates.” Prepared for Urban Drainage and Flood Control District., Lakewood, CO.
Olson, C., K. MacKenzie, B. Urbonas (2010). BMP-REALCOST Best Management Practices –
Rational Estimation of Actual Likely Costs of Stormwater - User’s Manual and Documentation,
Urban Drainage and Flood Control District, Part of the BMP-REALCOST Download.
http://udfcd.org/downloads/software/BMP-REALCOST_v1.0.zip.
Shoemaker, L., Riverson, J., Alvi, K., Zhen, J.X., Paul, S., Rafi, T. (2009). SUSTAIN – A
Framework for Placement of Best Management Practices in Urban Watersheds to Protect
Water Quality. National Risk Management Research Laboratory, USEPA, Cincinnati, OH.
Urban Drainage and Flood Control District (UDFCD). (2004). Urban Storm Drainage Criteria
Manual, Volumes 1-3. Denver, CO.
Wright Water Engineers and Geosyntec. International BMP Database. www.bmpdatabase.org
Attachment 7
Green Street
Demonstration Project
City of Fort Collins, Colorado
DRAFT: August 1, 2012
Fort Collins Green Streets Demonstration Project
Atkins Green Streets Demonstration Project | August 1 2012
Table of contents
Sections Page
1. Introduction 3
2. Green Streets 5
2.1. What are Green Streets? 5
2.2. Green Street elements 5
2.3. Best practices: projects, plans, and programs 12
3. Existing conditions and characteristics 14
3.1. Roadway features 14
3.2. Pedestrian facilities 18
3.3. Bicycling facilities 19
3.4. Transit conditions 20
3.5. Accesses 21
3.6. Traffic conditions 22
3.7. Natural areas 23
4. Examples 23
4.1. Rain gardens and bike boulevard 24
4.2. Roundabouts 26
4.3. Median and curb bulbouts 26
4.4. Approximate costs 28
5. Further considerations 29
5.1. Maintenance plans 29
5.2. Private residence improvements and public outreach 29
Figures
Figure 1. Demonstration location 4
Figure 2. San Francisco’s Better Street Plan Website 13
Figure 3. Stuart Street and Constitution Avenue typical sections 14
Figure 4. Neighborhood context map 15
Figure 5. Roadway features 16
Figure 6. Pedestrian access ramps 18
Figure 7. Bike lane on Constitution Avenue 19
Figure 8. Transfort transit routes 20
Figure 9. Accesses along Stuart Street and Constitution Avenue 21
Figure 10. Spring Creek Trail Trailhead at Stuart Street 23
Figure 11. Rain garden and bike boulevard concept 25
Figure 12. Typical proposed cross-section for Stuart Street 25
Figure 13. Roundabout concept 26
Figure 14. Median and curb bulbout concept 27
Figure 15. Typical proposed cross-section for Constitution Avenue 27
Tables
Table 1. Summary of design elements 8
Table 2. Approximate costs for a one-mile section 28
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1. Introduction
In an effort to reshape streets that are presently wider than current standards, as well as improve the natural
environment and community livability, the City of Fort Collins (the City) is seeking to create a “Green Streets
Demonstration Project”. Green Streets are streets that improve the natural and human environment by
implementing attractive streetscapes and urban green spaces. Green Streets generally target the natural
environment, but indirectly improve the user experience. The City has selected Stuart Street from Taft Hill
Road to Shields Street as well as Constitution Avenue from Stuart Street to Drake Avenue as the model
streets for this effort, as shown in Figure 1. The selected location is intended to show the range of
possibilities that Green Streets offer not only to these two streets, but to other locations throughout the city.
As part of the 2010-11 Transportation Master Plan (TMP) update process, one of the key choices or key
areas of update was Reshaping Streets. During the June public outreach, keypad polling results showed that
participants selected Reshaping Streets as the second most desired direction of change for the TMP update.
Based on input from the subteams, boards and commissions, the idea was expanded to include “Green
Street” concepts that would help to achieve more comfortable street environments as well as stormwater
management goals. Reshaping Streets fulfills the triple bottom line goals of economic, human, and
environmental sustainability, and supports the vision for the long-term multimodal transportation system that
will support the Fort Collins community well into the future.
When considered in the triple bottom line context, Green Streets projects provide a variety of benefits.
Economically, they can create more cost-effective opportunities for projects that involve multiple
departments. This could increase the pool of available funding resources for street projects. A potential
increase of operation and maintenance costs could result over existing conditions due to enhanced street
improvements, so it will be important to proactively create maintenance plans for these type of projects.
Socially, Reshaping Streets will create destinations or “great places” that support infill and redevelopment
areas and provide options for connecting to key destinations. Bicycle, pedestrian, and transit facilities will be
enhanced around land uses that are supportive of increased multi-modal activity. The multi-modal
improvements provide positive social benefits, and they also provide environmental benefits due to a
decrease in motor vehicle miles traveled, associated air quality benefits, and keeping the roadway footprint
the same. For more information, see the ‘Reshaping Streets’ section of the Fort Collins TMP.
This technical memorandum expands on the ideas presented in the TMP and specifically demonstrates the
details of how to achieve reshaped streets, or Green Streets. Existing conditions of Stuart Street and
Constitution Avenue are presented, Green Street design elements are explained, and Green Streets best
practices are explored. The results are recommendations on ways in which to implement certain Green
Streets design features, example locations for these elements along Stuart Street and Constitution Avenue,
and the associated costs.
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Figure 1. Demonstration location
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2. Green Streets
2.1. What are Green Streets?
Green Streets are an innovative and effective way to restore the natural health of an environment, calm
traffic, and improve community livability. These types of improvements create attractive streetscapes and
urban green spaces, provide additional natural habitat, and help to better connect neighborhoods and natural
areas. Green Streets have the potential to:
• Clean and cool the air and water
• Increase community and property values
• Enhance pedestrian and bicycle access and safety
• Protect valuable surface and groundwater
• Add urban green space and wildlife habitat
• Help meet regulatory requirements for watershed resource management
• Reduce stormwater upon the sewer system
• Save money on wastewater pumping and treatment costs
A key principle of Plan Fort Collins (City Plan and TMP) is community appearance and design which
discusses: designing the city’s streetscapes with consideration to the visual character and the experience of
users and adjacent properties; integrating public spaces throughout the community and designing them to be
functional, accessible, attractive, safe, and comfortable; and requiring quality and ecologically sound
landscape design practices throughout the community. Green Streets offer many ways to address and
achieve the goals of Plan Fort Collins.
2.2. Green Street elements
Green Street streetscapes are the result of the combination of a variety of design elements. While many
design features target the natural environment, the human environment is also improved. For example, a
rain garden’s primary purpose is to capture roadway runoff and infiltrate the local soils rather than sending
runoff into traditional sewer pipes. However, if located appropriately, a rain garden can be used as a natural
buffer between the travel lane(s) and the sidewalk and/or bike path.
Design features can be divided into the following categories: bioretention elements, paving elements,
conveyance elements, and traffic calming elements. Each category is described in more detail in the
following subsections. The ultimate design for Stuart Street and Constitution Avenue would be some
combination of these elements.
Bioretention elements
Bioretention elements focus on treating stormwater runoff at the source. Examples would include tree pits,
rain gardens and stormwater planters. Bioretention systems collect and filter runoff through layers of mulch,
soil and plant root systems where pollutants such as bacteria, nitrogen, phosphorus, heavy metals, oil and
grease are retained, degraded and absorbed. The treated stormwater is then infiltrated into the ground, or
discharged into a traditional stormwater drainage system. Bioretention elements can:
• Reduce stormwater runoff volume, flow rate and temperature
• Increase ground water infiltration and recharge
• Improve quality of local surface waterways
• Improve aesthetic appeal of streets and neighborhoods
• Provide a shaded, urban green space
• Reduce soil erosion
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Tree pits
Stormwater tree pits consist of an underground structure and above ground plantings which collect and treat
the stormwater runoff. Although underground their structures differ, above ground tree pits closely resemble
traditional street trees. This element is well suited for urban environment where space is limited. Stormwater
tree pits maintenance is generally minimal, but periodically require inspection of the plants and structure.
Periodic testing of the mulch to check for pollutant build up may also be needed. These tree pits have an
average lifespan of 25 years, although the low lying vegetation may need to be replaced more frequently.
Rain gardens
Rain gardens are generally low lying landscaped areas adjacent to paved areas. These gardens can be
planted with a variety of perennials, grasses, shrubs and small trees, and native plant species are typically
recommended. Rain gardens look similar to traditional landscaped areas, but they differ in their design and
function. Rain garden maintenance is generally minimal, but periodically the vegetation and drainage
structures will need to be checked and any sediment or debris will need to be removed. Costs vary
depending on the garden’s size and the amount of vegetation, but generally installation costs $5 to $15 per
square foot.
Stormwater planters
Stormwater planters are generally small, contained areas filled with grassy vegetation. Stormwater planters
are similar to rain gardens in their function, but are generally smaller and more contained. Stormwater
planters add aesthetic appeal, but do not require a large amount of space and are therefore best suited for
city streets, parking lots, and residential properties. Installation and maintenance costs are similar to rain
gardens; however, replacement of the concrete structures surrounding the planter may be an additional
expense.
Paving elements
Permeable pavers and permeable pavement such as porous concrete or porous asphalt are the two main
design features related to Green Street surfaces. Paving elements can:
• Reduce stormwater runoff volume, flow rate and temperature
• Increase ground water infiltration and recharge
• Reduce the need for traditional stormwater infrastructure
• Improve aesthetic appeal of streets, sidewalks and bike lanes
• Decrease surface temperatures
Permeable pavers
Permeable pavers vary in material, shape, size, color, and texture. The pavers are laid across a surface with
space left in between to allow water to percolate into the ground, rather than runoff. The void space in
between the pavers can be filled with sand, gravel, or even vegetation. The pavers are underlain with a
subsurface layer of course gravel which allows the stormwater to be temporarily stored before seeping into
the ground. These types of pavers are best suited for low traffic areas such as parking spaces, or pedestrian
walkways. Depending on the filler, the surface may need to be vacuumed or swept.
Permeable pavement
Permeable pavement can be either asphalt or concrete that is mixed with fewer fine particles to create more
air space which then allows water to permeate through the surface. An underlying layer of fine sediment
filters water and below it, a bed of uniform-grade stones stores water as it infiltrates into the ground.
Permeable pavement is ideal for use in parking lots, walkways and low-traffic streets. Permeable pavement
needs to be vacuumed or swept three to four times a year to prevent pores from becoming clogged and not
allowing infiltration. Permeable pavements generally cost $7 to $12 per square foot, but can eliminate the
need for traditional stormwater infrastructure.
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Conveyance elements
Conveyance elements focus on collecting, filtering and redistributing stormwater runoff. Drainage swales,
channels and runnels are examples of conveyance elements. Conveyance elements can:
• Reduce stormwater runoff volume, flow rate and temperature
• Increase ground water infiltration and recharge
• Reduce the need for traditional stormwater infrastructure
• Improve aesthetic appeal of streets and neighborhoods
• Reduce soil erosion
Swales
Swales are a broad, shallow channel with dense vegetation covering the side slopes and bottom. The plants
in the channel provide filtration, reduce stormwater flow and increase biodiversity.
Channels and runnels
Channels and runnels are concrete or stone lined pathways used to carry rainwater or runoff along the
surface to other features or the sewer system. Runnels are shallow systems usually designed for small
spaces and small to moderate flows, while larger and deeper channels are used to collect and carry
moderate to large flows.
Traffic calming elements
Chicanes, curb bulbouts, roundabouts, and medians are the main design features related to Green Street
projects, as they allow for additional green space along a corridor. Traffic calming elements can:
• Reduce the need for traditional stormwater infrastructure
• Improve aesthetic appeal of streets and neighborhoods
• Create safer conditions for drivers, pedestrians and cyclists
• Slow traffic and provide access control
• Improve air quality
Chicanes
Chicanes are a horizontal diversion of travel lanes that shift a straight roadway to a meandering template.
Shifting a travel lane decreases travel speeds and provides more space for landscaping. Chicanes are
typically used at mid-block sections and can be gentler or more restrictive depending on the design.
Chicanes can improve the pedestrian environment by reducing the width of crosswalks and increasing
pedestrian visibility.
Curb bulbouts
Curb bulbouts are similar to chicanes in that they create a shift in travel lanes, and provide more space for
landscaping. Curb bulbouts, however, are typically found at intersections and are used as a way to narrow
the roadway template and slow traffic. Curb bulbouts can be gentler or more restrictive depending on the
design, and can improve the pedestrian environment by reducing the width of crosswalks.
Roundabouts
Roundabouts provide an opportunity to create a gateway feature along a corridor. Roundabouts vary in size
and shape, but generally the center island can be landscaped. Roundabouts generally improve mobility for
automobiles. The apron that surrounds the center island also provides an opportunity to integrate permeable
pavers into the roadway design, which addresses roadway runoff and helps mitigate drainage issues.
Medians
Medians provide another opportunity for additional green space along a corridor. They vary in size, shape,
and landscaping. Medians, however, can restrict access depending on their location.
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Table 1. Summary of design elements
Cost
Category
Low Impact
Design
Feature
Description Example
Installation Maintenance
Drainage
swales
Swales are broad, shallow channels
with dense vegetation covering the side
slopes and bottom. The plants in the
channel provide filtration, reduce
stormwater flow and increase
biodiversity.
N Willamette and Denver, Portland
Ranges from $5 to
$10 per linear foot
Approximately $200
per year
Conveyance
Channels and
runnels
Channels and runnels are concrete or
stone lined pathways used to carry
rainwater or runoff along the surface to
other features or the sewer system.
Runnels are shallow systems usually
designed for small spaces and small to
moderate flows, while larger and deeper
channels are used to collect and carry
moderate to large flows.
sfbetterstreets.org
Around $75 per
linear foot
Varies
Bioretention
Rain gardens
Bioretention planters or rain gardens
are planted depressions designed to
collect and absorb stormwater runoff
from nearby paved surfaces like streets
and sidewalks. They combine
engineered stormwater control and
treatment with aesthetic landscaping.
NE 23rd and Irving, Portland
Ranges from $5 to
$15 per square foot
depending on
selected vegetation
Ranges from $0.50
to $1 per square
foot depending on
selected vegetation
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Table 1. Summary of design elements
Cost
Category
Low Impact
Design
Feature
Description Example
Installation Maintenance
Stormwater
planters
Stormwater planters are small,
contained vegetated areas designed to
collect and cleanse stormwater. The
treated runoff can either seep into the
ground as groundwater or be
discharged into a drainage system.
They can add functionality as well as
aesthetic appeal.
SW 12th and Montgomery, Portland
$8 to $15 per
square foot
Ranges from $400
to $500 annually
Tree pits
Tree pits are a bioretention system
comprised of an above-ground planting
and an underground structure
consisting of a soil mixture. The
underground soil treats the stormwater
as it drains.
Charles River Watershed Association
Prefabricated
systems range from
$8,000 to $10,000
Ranges from $100
to $500 annually
Paving Permeable
pavers
Permeable pavers may look similar to
traditional pavers but allow air and
water to pass through, providing the
opportunity for temporary storage of
stormwater runoff and/or groundwater
recharge into the soils below.
Westmoreland Permeable Pavement Project, Portland
$8 to $12 per
square foot, which
includes the
underground
infiltration bed
$0.20 per square
foot annually.
Pavers will need to
be completely
replaced roughly
every 25 years
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Table 1. Summary of design elements
Cost
Category
Low Impact
Design
Feature
Description Example
Installation Maintenance
Permeable
pavement
Permeable paving refers to street and
sidewalk paving materials that allow
stormwater to filter through to the soil
below.
George Mason University
$7 to $12 per
square foot, which
includes
underground
infiltration bed
$400 to $500 per
half acre annually
for street sweeping
Curb bulbouts
Curb bulbouts extend the sidewalk into
the parking lane to narrow the roadway
and provide additional pedestrian
space. They can be used at corners
and at mid-block. Curb extensions
enhance pedestrian safety by
increasing pedestrian visibility,
shortening crossing distances, slowing
turning vehicles, and visually narrowing
the roadway.
SE 42nd and Belmont, Portland
Ranges from
$10,000 to $35,000
per corner,
depending on size
(consists of curb &
gutter, as well as
bioswales, rain
gardens, or tree
pits)
$0.50 to $1 per
square foot annually
to maintain
landscaping
Traffic Calming
Chicanes
A horizontal diversion of travel lanes
that can be gentler or more restrictive
depending on the design. Shifting a
travel lane decreases travel speeds and
provides more space for landscaping.
They can be used at corners and at
mid-block.
SE 12th and Clay, Portland
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Table 1. Summary of design elements
Cost
Category
Low Impact
Design
Feature
Description Example
Installation Maintenance
Medians
A separation of travel lanes designed to
limit access and narrow the roadway.
Medians can be level with the road,
depressed, or raised. The center can be
used as landscaping space.
Charlotte Complete Streets
$6 per square foot
(excludes curb &
gutter)
Varies
Roundabouts
An intersection with one-way circulation
around a center island. Roundabouts
are safer than traditional signalized
intersections and help slow through
traffic.
Mathis Ferry Rd., Mt. Pleasant, SC
$50,000 to
$250,000, depends
on island features
Varies
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2.3. Best practices: projects, plans, and programs
This section highlights the following projects, plans, and programs from around the country that set the
standard for Green Streets improvements:
• Portland Green Streets Program and SW 12th Avenue; Portland, Oregon
• San Francisco’s Better Street Plan; San Francisco, California
• Tenth Street Project, Concept Master Plan; City of Lake Oswego, Oregon
Portland Green Streets Program, SW 12th Avenue; Portland, Oregon
The City of Portland’s streets and ROWs collect a majority of the stormwater discharge, which can carry
pollutants into the city waterways. The Green Streets program strives to mitigate the impacts of runoff
through transportation-related development, using vegetated facilities that manage stormwater on-site. The
program calls for Green Street improvements to be incorporated in all city-funded projects as required by the
Stormwater Management Manual. Qualifying green street projects are funded partially by the “1% for Green”
fund. To receive this funding, the proposed development must treat stormwater in the public right of way, but
only exceeding the requirements of Portland’s Stormwater Management Manual. Any city-funded project that
does not trigger the Stormwater Manual but occurs in the right of way must pay into the “1% for Green” fund
an amount equal to one percent of the construction costs.
Portland’s Green Streets Program strives to involve and educate the community. For some projects, a small
sign is erected on-site with a description of how the system functions and where to find more information on
sustainable stormwater solutions. Additionally, volunteers can become Green Street Stewards and help
maintain the facilities by weeding, watering, and picking up trash and debris. For more information on
Portland’s program, visit: http://www.portlandonline.com/bes/index.cfm?c=44407
The SW 12th Avenue Green Street Project is just one example of Portland’s efforts. The paramount design
challenge for retrofitting SW 12th Avenue Green Street was finding sufficient space to locate the stormwater
planters while minimizing conflict with other streetscape elements. The project was awarded the General
Design Award of Honor from the American Society of Landscape Architects (ASLA) is 2006. For more
information on the project, visit: http://asla.org/awards/2006/06winners/341.html
San Francisco’s Better Streets Plan; San Francisco, California
San Francisco’s Better Streets Plan, which was adopted in 2010, states that, “Better Streets are designed
and built to strike a balance between all users regardless of physical abilities or mode of travel. A Better
Street attends to the needs of people first, considering pedestrians, bicyclists, transit, street trees,
stormwater management, utilities, and livability as well as vehicular circulation and parking”. The Better
Streets Plan provides comprehensive guidance for a variety of street types including greening and
stormwater management. For more information, visit: http://www.sfbetterstreets.org/
Tenth Street Project, Concept Master Plan; City of Lake Oswego, Oregon
The City of Lake Oswego in Oregon receives an average of 41 inches of rain a year. In an effort to explore
sustainable methods for handling such runoff, the City chose Tenth Street between Evergreen Road and E
Avenue as their model site. Although the project’s main objective was to provide a more sustainable
approach to surface water management, the City took the opportunity to also address some broader
community goals and ambitions relating to creating a gateway and a distinctive place. The project’s primary
goals included:
• Design a Green Street that slows and treats stormwater within the ROW, rather than pipes it directly
to our rivers and streams.
• Provide a consistent and attractive streetscape that beautifies the neighborhood and enhances its
livability.
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• Create a pathway that provides children with a safe route to school and the community with an
attractive walking experience.
• Develop a unique gateway that defines Tenth Streets’ edges, welcomes its residents and visitors,
and is a true asset to the community.
For more information, or to download the plan, visit: http://www.ci.oswego.or.us/publicworks
Figure 2. San Francisco’s Better Street Plan Website
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3. Existing conditions and characteristics
Stuart Street and Constitution Avenue are located just southwest of Old Town and Colorado State
University’s campus. Stuart Street is an east-west corridor, approximately 1 mile long and Constitution
Avenue is a north-south corridor approximately 0.75 mile long. The two streets serve a range of travel
including automobiles, pedestrians, and bicycles. The streets are generally surrounded by residential
neighborhoods, with some residential properties having direct driveway access to the streets. The
surrounding area characteristics are shown in Figure 4.
3.1. Roadway features
Both streets are two-lane, residential collectors with a posted speed limit of 25 miles per hour (MPH). The
existing right-of-way (ROW) as measured from the back of the sidewalk is approximately 60 feet throughout,
with some areas extending to over 70 feet. Stuart Street and Constitution Avenue both include five-foot wide
dedicated bike lanes as well as eight-foot wide on-street parking. The existing typical section is shown in
Figure 3.
Figure 3. Stuart Street and Constitution Avenue typical sections
Only two intersections within the study area are signalized: Constitution Avenue at Drake Road and Stuart
Street at Shields Street. Additionally, one intersection is four-way stop controlled: Stuart Street at
Heatheridge Road.
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Figure 4. Neighborhood context map
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Stuart Street and Constitution Avenue have multiple marked crosswalks including the Taft Hill Road, Shields
Street and Drake Street intersections. Stuart Street has seven speed bumps and Constitution Avenue has
two large crosspans that, although used for drainage purposes, typically decrease vehicular speeds.
Roadway features are displayed in Figure 5.
Figure 5. Roadway features
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3.2. Pedestrian facilities
Sidewalks are present on both sides of Stuart Street and Constitution Avenue. Generally, sidewalks are
attached to the street and are 4 feet wide; however, in a few areas, the sidewalks narrow to 3 feet.
Additionally, there is a section approximately 300 feet in length on the northern side of Stuart Street that is
missing sidewalk. The portion of the street without a sidewalk is located between Constitution Avenue and
Heatheridge Road, as shown in Figure 6.
Figure 6. Pedestrian access ramps
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Currently, 10 out of the 34 intersections lack the proper number of access ramps. According to the Larimer
County Urban Area Street Standards, access ramps must be installed at all intersections for all
reconstruction of curb and sidewalk. The standards state that four-way intersections require access ramps at
all intersection corners and “T”-Intersections require at least three ramp accesses.
The ramp requirements also state that a driveway may be used as an access ramp if it is designed to meet
ramp standards and is directly across from another ramp. Of the 34 intersections, six are using driveways as
access ramps, but it cannot be determined if these driveways meet ramp design requirements. Additionally,
Larimer County requires truncated dome warning detection panels and specific slopes on every access
ramp. None of the ramps in the project area have warning detection panels, and it is unknown if the ramps
make use of the necessary slopes. For access ramp details, refer to Construction Drawings 1603, 1604,
1605, 1606, and 1607 in the Larimer County Urban Street Standards.
3.3. Bicycling facilities
Stuart Street and Constitution Avenue include approximately 5-foot wide dedicated bike lanes in both
directions. The Spring Creek Trail network runs parallel to Constitution Avenue through Rolland Moore Park,
and has a trailhead located on Stuart Street, just west of Shields Street. The trail can also be accessed from
Winfield Drive and Scarborough Drive off Constitution Avenue. It is recommended that the bike lanes remain
a part of every Green Street alternative. Figure 7 shows a bike lane on Constitution Avenue.
Figure 7. Bike lane on Constitution Avenue
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3.4. Transit conditions
Although there are no transit routes directly on Stuart Street or Constitution Avenue, multiple routes are
located in the vicinity. Transfort route 2 goes westbound on Prospect Road; route 3 goes eastbound on
Prospect Road; route 6 goes northbound and southbound on Taft Hill Road; route 7 runs northbound and
southbound for a brief time on Shields Street; and route 19 goes northbound and southbound on Shields
Street. The routes, and their directions, are identified in Figure 8.
Figure 8. Transfort transit routes
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3.5. Accesses
Both streets are lined with accesses to neighborhoods and private residences. Fourteen residential street
connections are located along Stuart Street and thirteen residential street connections are located along
Constitution Avenue. Additionally, approximately 30 residential properties have direct access to Stuart
Street, and approximately 55 residential properties have direct access to Constitution Avenue. Accesses are
identified in Figure 9.
Figure 9. Accesses along Stuart Street and Constitution Avenue
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3.6. Traffic conditions
Traffic volume data was provided by the City for Stuart Street and Constitution Avenue. Traffic counts and
speed studies were conducted on Stuart Street between Taft Hill Road and Shields Street as well as on
Constitution Street just north of Scarborough Drive. The existing average daily traffic (ADT) is 1,400 on
Stuart Street and 1,600 on Constitution Avenue. These ADTs fall within an acceptance range for two-lane
collector streets.
The speed studies concluded that an average of 58 percent of vehicles were traveling above the speed limit
of 25 MPH. The 85th percentile speed on Stuart Street is 30 MPH and the 85th percentile speed on
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Constitution Avenue is 29 MPH. The 85th percentile speed is the speed at or below which 85 percent of
drivers travel on a given road. This speed indicates the speed that most drivers on the road consider safe
and reasonable under ideal conditions. It is often used as a guideline by traffic engineers for setting an
appropriate speed limit on a roadway.
3.7. Natural areas
Stuart Street and Constitution Avenue provide access to multiple natural areas including: Red Fox Meadows
Natural Area, Fischer Natural Area, and Ross Natural Area. The Spring Creek Trail network runs parallel to
Constitution Avenue through Rolland Moore Park, and has a trailhead located on Stuart Street, just west of
Shields Street, as shown in Figure 10. The trailhead, which is located approximately 150 feet south off the
street, leaves a great buffer space for Green Streets gateway features.
Figure 10. Spring Creek Trail Trailhead at Stuart Street
In addition to the natural areas, the Mullaney Wetlands and Detention Basin Outdoor Classroom are located
just north of Stuart Street. Although there are multiple natural features surrounding the two streets, minimal
landscaping is provided immediately along Stuart Street and Constitution Avenue and other aesthetic
features are not present. With multiple surrounding natural areas and parks, Stuart Street and Constitution
Avenue are appropriate locations to consider updating with Green Street features.
4. Examples
To further demonstrate how Green Street elements can be combined to create attractive streetscapes, the
following concept alternatives were developed: rain gardens combined with a bicycle boulevard on Stuart
Street, a roundabout including space for a green gateway feature at Stuart Street and Constitution Avenue
and finally, curb bulbouts combined with a median on Constitution Avenue. The three concept alternatives
are further developed in sections 4.1, 4.2, and 4.3.
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4.1. Rain gardens and bike boulevard
The first concept alternative addresses the wide paved area along Stuart Street. This concept includes rain
gardens planted in curb extensions. The rain gardens are eight feet wide and help collect and treat the
stormwater runoff. They allow for 12-foot travel lanes, making the road feel narrower, which tends to cause
drivers to slow down. In this concept, the rain gardens replace the seldom-used existing parking lane. They
can be used between accesses but can be sparse enough that some of the parking is kept. Rain gardens
serve many practical purposes in cleansing runoff and slowing traffic, but also provide a more attractive
streetscape. Drainage patterns need to be analyzed in order to effectively place the rain gardens in areas
where they will be most beneficial.
Also included in this concept is a two-way bike boulevard. This enhanced bike lane features two 5-foot bike
lanes, one in each direction, and a 4-foot strip of pavers, level with the road, separating it from the travel
lanes. Permeable pavers could be used to increase infiltration and reduce the amount of runoff to the
existing stormwater infrastructure. A dedicated bike boulevard allows users to travel mostly uninterrupted
down the length of the road while keeping them safely away from traffic. In this concept, the bike boulevard
is located on the south side of Stuart Street and completely removes the existing parking lane. As shown in
Figure 9, there are only five driveway access points along the south side of Stuart Street, making the bike
boulevard a more feasible option. Bike boulevards can be used in places with significant bike traffic and
limited access points. Too many accesses can put the bicyclists in more danger than a traditional bike lane.
Also, the bike boulevard should be separated from vehicle traffic by pavement markings, a raised curb,
pavers, or a wall where possible. Figure 11 shows an example of how the layout would be carried through a
four-way intersection at Stuart Street and Ridgewood Road, and Figure 12 shows the typical cross-section of
the concept.
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Figure 11. Rain garden and bike boulevard concept
Figure 12. Typical proposed cross-section for Stuart Street
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4.2. Roundabouts
The second concept alternative involves a roundabout at the intersection of Stuart Street and Constitution
Avenue. Smaller roundabouts are ideal for wide roads in neighborhoods. They slow traffic through the
intersections but also provide safe and efficient intersection control. If a roundabout is implemented at the
entrance to a town or neighborhood, the center island can be used to include gateway features like signs
and landscaping. The necessary curb extensions are opportunities for extra landscaping or even rain
gardens where drainage would allow. Roundabouts require a significant amount of ROW, but increase
safety, efficiency, and aesthetic appeal to intersections. Figure 13 shows how the roundabout would be
incorporated into the intersection of Stuart Street and Constitution Avenue.
Figure 13. Roundabout concept
4.3. Median and curb bulbouts
The third concept alternative addresses the wide paved area along Constitution Avenue. This concept was
considered separately from Stuart Street because of the many accesses along the road. Included in the
concept are a 6-foot median, two 6-foot bike lanes, and curb bulbouts at the intersections. Medians narrow
the road and serve as a traffic calming device. The center of the median can be planted or landscaped to
add aesthetic appeal to the corridor. Xeriscaping or low-water landscaping with drought tolerant plants could
be used in the median to minimize maintenance and potentially eliminate the need for irrigation. Medians
also limit access, which can be a positive or negative effect. Limiting access can improve traffic flow, but
restrict access to driveways, especially in a neighborhood. However, in this concept the median would break
at each intersection, so the longest median would be no more than 500 feet long. Medians can be
implemented on any road with enough width to provide a more attractive streetscape, to slow traffic, or to
limit access.
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Curb bulbouts are another traffic calming device that also improves pedestrian safety. Installing bulbouts on
the corners slows approaching vehicles and shortens the crossing distance for pedestrians. They also
provide ideal space for additional landscaping, which could include anything from grass to a dedicated rain
garden. Rain gardens could be implemented at corners of the intersection where low points exist. At corners
where high points exist, other types of landscaping or xeriscaping could be used in the bulbout area.
Bulbouts are helpful along corridors with high pedestrian volumes and wide roadways. They can be used at
every intersection or only intersections where pedestrian crossings are needed. Figure 14 shows how this
concept would look through the four-way intersection of Constitution Avenue and Scarborough Drive.
Figure 15 shows the typical cross-section for the concept.
Figure 14. Median and curb bulbout concept
Figure 15. Typical proposed cross-section for Constitution Avenue
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4.4. Approximate costs
To get approximate costs for adding various Green Street items, assumptions were made on the number of
intersections per mile, as well as widths and lengths of various proposed improvements. For a typical
residential street, the assumption of 15 intersections per mile was used, with the majority (80 percent) of
these intersections being three-way intersections.
Each rain garden was assumed to take up approximately 800 square feet at each intersection corner (50 feet
long, 8 feet wide, along each leg). Thus, at a typical three-way intersection with rain gardens on two corners,
approximately 1,600 square feet of rain gardens would be needed. At a typical four-way intersection,
approximately 3,200 square feet of rain gardens would be needed.
For a typical mile, with the assumption of 15 intersections per mile, approximately 30 percent of the mile
would be taken up by intersections, leaving 70 percent of the mile (approximately 3,700 linear feet) for
medians, landscape areas, pavers and bike lane striping.
These approximate costs do not include removals, new pavement, new sidewalk, new perimeter curb and
gutter, or utility relocations.
Table 2. Approximate costs for a one-mile section
Item Quantity Approximate Unit Cost Approximate Cost
Drainage swales
(bioswales)
3,700 linear feet $5 per linear foot $18,500
Runnels and channels 3,700 linear feet $75 per linear foot $277,500
Rain gardens at bulbouts
28,800 square feet (12
intersections with 1,600
square feet each; 3
intersections with 3,200
square feet each)
$5 per square foot $144,000
Stormwater planters
360 square feet (12
intersections with 20 square
feet each; 3 intersections with
40 square feet each; assume
10 square feet per planter)
$10 per square foot $3,600
Tree pits
36 (12 intersections with 2
each; 3 intersections with 4
each)
$8,000 each $288,000
Permeable pavers
14,800 square feet (3,700
linear feet, 4 feet wide) $10 per square foot $148,000
Permeable pavement
(asphalt) for parking
29,600 square feet (3,700
linear feet, 8 feet wide) $7 per square foot $207,200
Permeable pavement
(concrete) for sidewalks
44,400 square feet (3,700
linear feet, 6 feet wide, one
on each side of the street)
$12 per square foot $532,800
Landscape (sod and
irrigation)
37,000 square feet (3,700
linear feet, 10 feet wide) $1.25 per square foot $46,250
Curb and gutter at
bulbouts
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Item Quantity Approximate Unit Cost Approximate Cost
Median
22,200 square feet (3,700
linear feet, 6 feet wide)
$6 per square foot $133,200
Curb and gutter for median
7,400 linear feet (3,700 linear
feet on each side of median)
$13 per linear foot $96,200
Striping
3,700 linear feet for each
stripe (number of stripes
varies per street cross
section)
$0.25 per linear foot
$925
(per stripe)
5. Further considerations
There are various other considerations for the City to be aware of when proceeding with the development of
Green Streets projects. Some things to consider include maintenance plans, private residence improvement
plans, and public outreach programs. These items are described in further detail below.
5.1. Maintenance plans
As Table 1 shows, there are certain maintenance costs associated with the various design elements. When
developing the design plans, it is important to concurrently develop a maintenance plan in order to outline
the goals and objectives, the future costs, and other items or tasks associated with maintenance.
Management plans and protection mechanisms could be integrated into the maintenance plan, to ensure the
improvements continue to provide their maximum benefit over time.
Developing a maintenance plan could also help identify funding sources across multiple departments within
the City, as well as possibly within other levels such as the county or State.
5.2. Private residence improvements and public outreach
Part of the maintenance plan could also include a section on property owner education. A volunteer
maintenance program could also be developed to have local residents assist with various maintenance
activities. The City could provide materials and items needed for the maintenance, and have training
programs and incentives for the property owners. Property owners could also add improvements to their own
property to complement the public improvements.
A public outreach program would need to be implemented to provide information to the property owners
regarding the improvements and the associated maintenance practices. The benefits and function of the
improvements could be presented in these outreach materials to inform property owners of what to expect.
By keeping the property owners informed and involved in the process, the community could help influence
the final design and construction of the improvements.
5,400 linear feet (150 linear
feet at each bulbout corner;
12 intersections with two
bulbouts and 3 intersections
with 4 bulbouts)
$13 per linear foot $70,200
Ranges from $6,000
to $10,000
$0.50 to $1 per
square foot annually
to maintain
landscaping