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Introduction to Local Stormwater Bylaws and Low Impact Development

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A local stormwater bylaw is a good way for communities to promote Low Impact Development (LID) techniques. Numerous communities in the Commonwealth have recently developed stormwater bylaws that incorporate LID, and the Executive Office of Environmental Affairs has included a model stormwater/LID bylaw in the Massachusetts Smart Growth Toolkit. This primer describes the key elements of a stormwater bylaw, recognizing that any such bylaw should be tailored to local conditions.

View model stormwater bylaws and regulations in the Stormwater Bylaws Toolkit

Why a local stormwater bylaw?

Stormwater is currently regulated under the Federal Clean Water Act (National Pollution Discharge Elimination System) which applies to municipal stormwater systems and construction areas over an acre; and under the Massachusetts Wetlands Protection Act (MA Stormwater Policy), enforced by local conservation commissions in and near jurisdictional wetlands.

In many communities, a patchwork of local codes (zoning, subdivision rules and regulations, board of health regulations) may provide overlapping and sometimes conflicting regulation of stormwater discharges.

A municipal stormwater bylaw can replace this patchwork with a single set of standards, resulting in environmentally sensitive development throughout the community. The bylaw will also provide developers with more predictability, efficiency, and rapid review due to the consistency of site design standards in all permitting processes. These standards should be reflected in all applicable local regulations such as subdivision regulations, wetland regulations, site plan regulations, etc.

How does a stormwater bylaw work?

A stormwater bylaw establishes a Stormwater Authority—which may be the Planning Board, Conservation Commission, Building Inspector, or another municipal entity—and requires that all projects over certain thresholds obtain a stormwater permit from the Stormwater Authority.

The bylaw and/or accompanying regulations should also specify permit procedures and performance standards, which must meet or exceed the standards of the Massachusetts Stormwater Policy, in order to prevent conflicting standards near wetland areas.

Performance standards should include recharge volumes, peak discharge rates, and water quality volumes, as well as special requirements that apply near environmentally sensitive areas or at stormwater ‘hotspots’ (such as gas stations.) The bylaw and regulations can also specify the engineering methodologies that should be used to model stormwater runoff.

How does a bylaw promote Low Impact Development?

Any stormwater bylaw should be structured so that it promotes the use of Low Impact Development techniques, including:

  • low impact site design
  • innovative stormwater techniques (such as bioretention)
  • nonstructural practices for stormwater management

This can be done through a system of stormwater credits that become part of the sites engineering calculations. By accounting for the treatment provided by low-cost, low-impact techniques, stormwater credits provide an incentive for engineers and developers to use more low impact techniques and to reduce their reliance on conventional stormwater structures

Credits may be given for “environmentally sensitive development” with preserved open space, limited impervious coverage, stream buffers, and open section roadways; such a development might be assumed to meet certain water quality and recharge standards.

Other credits might be associated with “disconnection” of rooftops or impervious surfaces, whereby the runoff from roof drains and impervious surfaces is directed to vegetated areas where it will infiltrate; the ‘disconnected’ area is deducted from the impervious surface area used to calculate water quality treatment volumes, and the infiltration of this runoff can help to satisfy recharge requirements.

The use of grass channels or vegetated stream buffers might also qualify for credits that acknowledge the water quality and recharge benefits of these techniques.

The stormwater bylaw should allow the stormwater authority to permit the use of innovative structural practices (such as bioretention) not included in the Massachusetts Stormwater Manual, provided proper documentation of effectiveness has been provided.

Implementation and Expert Review

The stormwater bylaw can assign any existing board or department as the official Stormwater Authority, depending on local conditions, existing regulations, and current permitting processes. Often, stormwater bylaws assign the Planning Board or Conservation Commission as the Stormwater Authority; planning boards already have a community-wide authority, while conservation commissions already have some experience with stormwater permitting through the Wetlands Protection Act.

In some communities, the department of public works may be the most appropriate entity due to their experience with stormwater. In any case, the review process should provide a mechanism for other boards with a demonstrated interest in drainage issues (such as the Board of Health) to review stormwater plans and provide comments to the Stormwater Authority.

Regardless of what entity is designated as the Stormwater Authority, the bylaw should outline a mechanism for expert review where necessary. This is usually done through an engineering and consultant review fee assessed to the proponent, a mechanism commonly used for wetland applications and subdivision reviews.

Developers may be concerned about the cost and time involved in consultant review, but as with wetland and subdivision reviews, a thorough, well-prepared application that includes all the necessary information (including all calculations) will generally result in a rapid and favorable review. A unified stormwater review process will also be more efficient for developers than the current patchwork of regulations.

Exemptions

The stormwater bylaw should provide for exemptions, so that minor projects with limited stormwater consequences will not require a stormwater permit. Commonly, exemptions are granted for small projects (e.g., less than 5,000 square feet); agricultural activities; maintenance and landscaping; fences; and gas, water, electric, or telecommunication utilities. Single family homeowners should be exempt for most activities such as roof replacement, patio construction, outbuilding construction, home additions, driveway resurfacing, etc. The stormwater authority should also be able to grant waivers for certain projects and for certain standards where they are not pertinent.

The bylaw must include standards for redevelopment projects; the Massachusetts Stormwater Policy currently requires such projects to meet standards to the maximum extent practicable, and any local bylaw should be compatible with this requirement.

Maintenance

It is critical for a stormwater bylaw to require all applicants to submit an operations and maintenance plan. The O & M plan should specify the parties responsible for the system, a map of the system, and a schedule for maintenance tasks. Particular attention should be given to the inspection and cleaning of pre-treatment devices, including removal of trash and sediment. The plan should also grant the Stormwater Authority all necessary easements for inspection and maintenance, if necessary. Where stormwater management structures are located on private property, the developer may need to create deed restrictions that require property owners to maintain stormwater structures in functional condition in perpetuity. Some communities also require a permanent surety bond from developers to cover any unforeseen contingencies.

How does it relate to other local codes?

A stormwater bylaw is intended to replace the current patchwork of stormwater standards that exists in most communities. In order for this to work, other local bylaws and regulations of must be reviewed and modified where necessary to ensure consistency with the new stormwater bylaw. In particular, boards should delete any clauses that require applicants to obtain a drainage permit from anyone other than the new Stormwater Authority, and they should eliminate local performance standards that differ from those of the stormwater bylaw, in order to avoid confusion. (Because Conservation Commissions are required to enforce the Massachusetts Stormwater Standards for projects subject to the Wetlands Protection Act, it is ideal if the local stormwater bylaw is stricter than the state standards.) Many zoning, wetland, and board of health codes also establish design guidelines (different from performance standards) for stormwater structures—these guidelines should be consolidated and standardized in a stormwater guidance document that can accompany the regulations.

While consistency and streamlining of regulations is necessary, the Stormwater Bylaw must recognize that boards other than the Stormwater Authority still have a fundamental interest drainage issues. A Stormwater Bylaw should always provide opportunities for other boards (such as the Board of Health) to review Stormwater Plans so that that their concerns are addressed within the unified stormwater process.

A review of local bylaws and regulations for consistency with the Stormwater bylaw may also identify opportunities for modifications that will help promote lower impact development and decentralized stormwater management. A local codes checklist is available to help communities review local policies and modify them where necessary to promote narrower roadways, natural drainage systems, conservation of natural areas, and other fundamentals of Low Impact Development.

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Parking Strategies by Topic Area

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Variations and alternatives to a minimum parking requirement

Establish flexible parking requirements based on:

  • Alternative mode access (especially proximity of transit, but also pedestrian and bicycle facilities)
  • Expected demographics of residential developments (age, income, other auto-ownership factors)
  • Parking studies providing data to support requests to reduce or increase parking
  • Implementation of programs to reduce the need for parking spaces, such as parking cash out, un-bundled parking, shared parking, priority parking for carpools, or car sharing (see parking and transportation demand management)
  • Count on-street parking towards minimum parking requirements (see flexible minimum requirements).
  • Reduce or eliminate minimum parking requirements for some or all uses downtown.
  • Allow or require developers to pay into a fund to be used for building public parking rather than providing parking spaces (see fees-in-lieu).
  • Establish maximum allowances for how much parking may be built by use and/or by neighborhood (see parking maximums).
  • Allow or require developers to pave only a portion of the required parking initially, while retaining land sufficient to meet the rest of the requirement as a landscaped reserve, which may be used as a park, playground, garden, etc. until the parking is needed, if ever (see landscaped parking reserves).
  • Encourage shared parking between uses with parking demands peaking at different times of the day, week, or year (see shared parking).

Design strategies to mitigate negative consequences of parking

Hide the parking

Lot design (see mitigating environmental impacts) – encourage or require:

  • Provision of compact car spaces in large parking lot
  • Use of alternatives to paved surfaces for low-traffic parking areas
  • Stormwater management with Low Impact Development techniques in parking areas
  • Shade trees in parking lots to mitigate heat and air quality impacts

Managing the Parking Supply Efficiently

  • Price parking where demand exceeds supply
  • Set the price of parking to recover costs and mitigate parking demand
  • Use revenue from parking meters to pay for costs associated with parking, while ensuring high levels of street and sidewalk maintenance in metered districts (see parking benefit districts)
  • Make payment easy at meters or paid daily/hourly spaces with advanced payment technology
  • Set limits on parking hours or duration to encourage shoppers rather than employees/commuters or vice versa
  • Improve information for motorists on where parking is available to maximize efficiency of existing parking
  • Encourage shared parking between uses with parking demands peaking at different times of the day, week, or year
  • Develop an employee permit parking program to encourage downtown employees to park at the periphery and leave the prime spaces for customers
  • Enforce parking regulations in a way that doesn’t alienate drivers

Address Overflow and Spillover Parking

  • Require or encourage the development of overflow parking plans for special events and peak periods, especially in cases where minimum parking requirements have been lowered
  • Encourage or develop off-site parking for overflow – park and ride lots may serve as off-site lots to access downtowns if shuttle service is provided
  • Develop a residential permit parking program to address potential spillover effects
  • Develop an employee permit parking program to ensure that employees of downtown businesses can park for a full day if they need to drive to work
  • Allow non-residents to buy permits or pay for parking in permit districts, and use the revenue to benefit the district through additional maintenance, etc. (see parking benefit districts)

Strategies to reduce demand for parking

Plan for and prioritize alternative modes through implementation of a Parking and Transportation Demand Management program, including measures such as:

  • Parking cash out programs
  • Providing free or discounted transit passes
  • Priority parking for carpools or vanpools
  • Provision of bike parking and amenities such as lockers and showers
  • Car sharing programs (e.g. Zipcar)
  • Shuttle services from nearby transit stations or satellite parking lots
  • Ride-matching services that help people identify potential carpool or vanpool partners
  • Guaranteed ride home services that allow employees who don’t bring a car to work to get a free ride home (usually via taxi) if they need to stay late, or if they need to leave unexpectedly in the middle of the day
  • Charge for on-street parking in downtown or other busy areas, or increase the cost of parking to reflect the demand for parking (see charging for parking).
  • Charge for student parking at high schools, especially if there is a fee for riding the bus.

Conducting a Parking Study

Paying for Public Parking

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Sustainable Transportation: Parking Toolkit

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Courtesy of Diana Angstadt

This toolkit is designed to help local officials, developers, citizen board members, and advocates understand the sources of parking issues in their communities and identify potential solutions. The strategies outlined in the toolkit address a variety of situations and concerns in ways that save money, protect the environment, support local businesses, and encourage alternatives to driving.

The toolkit includes information on how to do a parking study, regulatory tools to tailor parking supply, strategies to reduce parking demand, parking management tools to make more efficient use of existing parking, information on financing parking, and many local examples. There are several ways to access the information in the toolkit:

Parking: A balancing act

Determining the right amount of parking is always a delicate balancing act, between the need for access in an auto-oriented world and the desire to minimize traffic and the sometimes harmful impacts autos bring. Many communities are concerned about the negative impacts of having too little parking – neighbors complain, cars are parked illegally, shop owners worry about discouraging patrons, lenders and developers worry about the desirability of their properties, drivers waste time hunting for parking spaces, etc. Recently,  some communities have begun to realize that too much parking can be as detrimental to the community as too little, and have taken steps to reduce parking requirements and improve the efficiency of existing parking.

Parking Costs

Constructing and maintaining parking is expensive. Construction costs per space can range from roughly $1,500-2,000 per space for surface parking in suburban areas to over $20,000 for underground parking in urban areas, not counting land costs, which can be substantial, especially in urban areas. Annual operation and maintenance costs can run from $100-500 per space. All told, the annual costs per parking space can run from roughly $400 a year for suburban surface parking, over $1,200 a year for a 2-level suburban structure, to over $2,000 for an urban parking structure. [1] In addition to the direct costs of building and maintaining the spaces, parking takes up space that could otherwise be used for additional commercial space or housing; incurs environmental costs including increased stormwater runoff and pollution and heat island impacts; and costs to the transportation system from its impact on the relative appeal of driving versus alternative modes. These costs should be recognized and balanced against the benefits parking provides in driver convenience and access.

Parking Needs

There is no simple, correct answer on how much parking is needed. The answer for your community will depend on:

  • Area of interest (town and neighborhood centers will have different needs than stand alone developments)
  • Access available to that area (less parking is needed for locations with good walk and transit access)
  • Type of development existing or planned (residential parking needs are greatest overnight, office during the day, and some retail uses will need the most parking on weekends).

Where there is a mix of uses parking can be shared. But the answer to parking needs is also a local policy choice – to invest in auto-oriented versus transit and pedestrian transportation options, to concentrate development or to spread out, and how best to maximize local tax revenues.

The best way to understand the parking needs in your community is to start with a survey of the existing parking situation. Whether your concern is parking in the town center or how much parking to require of a new development, you need to know how much of what types of parking is currently available and how is it used. In most cases, the survey should include both public and private parking, on-street as well as off-street spaces. Many simple counts can be accomplished by local volunteers, and traffic consultants are usually available for the more complicated process of estimating future demand. Basic guidance on how to do a parking study and examples of some recent local studies are available in this toolkit

Besides providing counts of existing use, surveys are also helpful in determining community priorities. Many communities have used surveys of local businesses to help determine parking needs. Convening a community parking or transportation committee is another common approach, allowing many different voices to be heard and to work together for a solution.

Sources

1. Todd Litman, Victoria Transport Policy Institute, “Parking Evaluation: Evaluating Parking Problems, Solutions, Costs, and Benefits”, Online TDM Encyclopedia, https://www.vtpi.org/tdm/tdm73.htm#_Toc18599156.

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Stormwater Bylaws Toolkit

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This toolkit displays model bylaws and regulations that MAPC has created in partnership with six communities in the region.

The links provided below are to both drafts and final versions of bylaws and regulations. In many cases, MAPC provided drafts up to a point, and the municipalities did the final edits during the adoption/approval process. Please contact each community for the latest version of the bylaws and regulations.

MAPC also conducted codes reviews of existing bylaws and regulations to assess their consistency with Low Impact Development (LID) principles.

Hopkinton

MAPC helped the town of Hopkinton draft the regulations and appendices and reviewed their codes to assess consistency with LID principles.

Ipswich

MAPC helped the town draft the bylaw and regulations and regulations for the issuance of stormwater management and connection and discharge permits.

Lexington

MAPC helped the town draft the bylaw and regulations.

Sudbury

MAPC helped the town draft the bylaw and regulations and appendices and reviewed their codes to assess consistency with LID principles.

Topsfield

MAPC helped the town draft the bylaw and regulations and reviewed its zoning bylaw for consistency with the new stormwater bylaw and regulations.

Wakefield

MAPC helped the town draft the bylaw and regulations.

Wilmington

MAPC helped the town draft the bylaw and regulations and appendices and reviewed their codes to assess consistency with LID principles.

Resources

Please stay tuned for more resources.

Questions?

Contact Martin Pillsbury, Environmental Division Manager.

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Foreclosure Resource Guide for Municipalities

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As a municipal leader, you see the impact of foreclosures firsthand and know the ripple effects this crisis has on your community. The Commonwealth of Massachusetts, state agencies, nonprofit organizations, and some municipalities are providing assistance to address the causes and effects of foreclosures on our local communities.

Local governments can be an important resource for residents by providing information to consumers. They can also be leaders in developing programs, policies, and ordinances to protect their community’s quality of life. Local governments can help educate residents about where and how to access financial and foreclosure counseling.

In 2008, MAPC began working with the Metro Mayors Coalition to help address foreclosures in the Coalition’s 13 urban communities. Recognizing the regional implications of foreclosures, this Foreclosure Resource Guide is intended to assist communities throughout the MAPC region.

This Foreclosure Resource Guide contains resources and tools to help governments protect communities and residents from the effects of the national foreclosure problem.

MAPC’s Presentation to the Metro Mayors Coalition

  • Addressing Foreclosures in the Metro Mayors Communities
  • PowerPoint Presentation to the Mayors
  • Foreclosure and Loan Resets Map
  • Metro Mayors Communities Foreclosure Maps
  • Metro Boston Data Common

You can also access subprime lending data and municipal-level data about the number of foreclosure auctions in FY2008 on the MetroBoston DataCommon DataMap Tool.

Resources for Municipal Leaders

In this Guide:

External Resources:

State-Approved Foreclosure Counseling Agencies

When a homeowner needs help, timing is critical. A delayed reaction to lender notices will make it more difficult for the owner to keep their home. Not every homeowner will turn to their bank as a first resource. Even if an owner contacts their lender, not every homeowner will be able to receive a “loan workout”. Counseling and support can help owners keep their homes. As a municipal employee, you may receive calls from homeowners looking for help. You should direct these owners to a local counseling agency or hotline.

MAPC Events Related to Foreclosures

Visit the Metro Mayors Coalition page to review materials from a foreclosures briefing for the coalition.

How can MAPC help?

If you would like technical assistance in dealing with issues related to foreclosures in your community, please contact Chief Housing Planner Karina Milchman.

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Locate Parking Strategically

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Where to Put Parking in Walkable Districts

Businesses often want parking to be as readily visible and easily accessible as possible so that potential patrons arriving by car will know that they will be able park nearby quickly and easily. Building parking in front of buildings where it is most visible from the street, however, seriously detracts from the pedestrian environment and makes the area less comfortable to spend time in. When buildings front directly on the street, they create a lively and inviting environment where people can feel comfortable walking from store to store, rather than getting back in the car to drive a block or two to their next destination. To balance these concerns, one solution is to require that new buildings in a downtown or any area that is intended to be pedestrian friendly locate their parking behind the building, away from the street, but ensure that there is adequate signage directing drivers to available parking. In more auto-oriented areas, a few “teaser” spaces can be provided along the side of the building on the driveway that takes drivers to the lot in back (see graphic below).

Teaser parking image

Source: Van Meter Williams Pollack and Urbsworks, Inc. “Parking Design Issues”, Report for the City of Palo Alto, CA, March 2004, p. 2.

In more urban areas where structured parking is more common, the quality of the urban environment can be preserved by wrapping parking garages in other uses, such as retail.

Local examples:
  • The Metropolitan Area Planning Council worked with the towns of Millis, Stoughton, and Bedford to develop and secure adoption of bylaws defining mixed use overlay districts that include language encouraging strategic location of parking: “To maintain a pedestrian-friendly environment, motor vehicle parking spaces shall be located behind or beside buildings to the maximum extent possible. Motor vehicle parking shall not be located directly between the building and the street alignment.”
  • The City of Cambridge zoning code states that “No on grade open parking space shall be located within a required front yard setback.” (Section 6.44.1(b))
  • The City of Beverly prohibits accessory off-street parking within the front yard of any district (except for one- and two-family dwellings) and employee parking within the front yard in the restricted industrial, research and office district (see regulation).
  • The Town of Acton prohibits parking between the front of a building and the street in its four village districts (see regulation).
National example:
  • The City of Palo Alto’s Comprehensive Plan includes a policy to “Minimize the negative physical impacts of parking lots. Locate parking behind buildings or underground where possible (Policy L-75).” [1, p. 1]

Additional resources:

  1. Van Meter Williams Pollack and Urbsworks, Inc. “Parking Design Issues”, Report for the City of Palo Alto, CA, March 2004.
  2. Maryland Governor’s Office of Smart Growth, Driving Urban Environments: Smart Growth Parking Best Practices, March 2006; p. 19-20. Available as a download.
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Fees-in-Lieu of Parking Spaces

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When Private Off-Street Parking Isn’t the Best Solution

In areas of more intense activity or where the community wants to promote density, requiring each use to provide separate parking facilities can degrade the pedestrian environment, limit density, and encourage drivers to drive from one site to the next rather than parking once and walking between nearby destinations. One solution to this is to allow developers to pay fees into a municipal parking or traffic mitigation fund in lieu of providing the required parking on site. The fees can then be used to provide centralized public parking. In some cases, the community may wish to establish the fund in such a way that it can also be used for for transit, bicycle, and pedestrian improvements that can reduce parking demand. By consolidating parking in centralized public lots or structures and allowing developers an alternative to providing parking on-site, a fee-in-lieu system can encourage in-fill development and redevelopment in existing downtowns or historic buildings. It can also improve the overall efficiency of parking provision by addressing the needs of the area as a whole, rather than the needs of each individual site.

In lieu fees can be established as a flat rate per parking space not provided or per square foot of floor area, or through a case-by-case determination for the development as a whole. Uniform fees are much easier for the community to administer and developers to use. Fees may be imposed as a property tax surcharge or charged when a development is permitted [1]. In order to make paying a fee more attractive to developers than providing parking on site, it must save them money. On the other hand, the fee must be high enough to allow for development of centralized parking facilities or to make enough transit or non-motorized mode improvements to put a dent in parking demand. In-lieu fees of any kind should be linked to an index of construction costs, or should be reviewed and updated regularly, so that inflation and changing conditions will not distort them. If they are allowed in a large geographic area, it may be wise to set graduated fees that are higher in areas where land values are greater or to reflect where a public surface lot would be built rather than a garage.

If the fee is assessed per space, it may make sense to factor in differences between the number of parking spaces that would be required if they were built for the sole use of the development and provided free to users and the number required in a shared public facility where there is some cost to park. Factoring in reductions in the number of spaces that the developer must pay for, in essence, can mean that the fees are both cheaper than what it would cost for the developer to provide parking on site and sufficient to cover the full cost of the parking that will need to be built. The reductions from the minimum parking requirements should ideally be standardized rather than determined case-by-case, but could be calculated based on the extent to which the anticipated peak parking hours of the new use overlap with the current peak parking hours for municipal lots in the area. For example, predominately weekend and evening uses such as movie theaters would be given a greater reduction in places where weekday demand is highest and little or no shared parking reduction if evening and weekend hours are already busy. Another consideration might be the anticipated duration of parking for the use, e.g. less reduction for employee (all-day) parking than for shopper (short-term) parking. The community may grant an additional reduction in the number of spaces the developer must pay for if motorists will have to pay to park, as this may reduce parking demand somewhat by encouraging carpooling or use of alternative modes.

Developers may be concerned that the lack of on-site parking will make their development less attractive, especially if there is not much public parking available, or it is not convenient to the site. If developers are allowed to choose between providing parking on-site and paying the fee, those who most value on-site parking will build it, and those who don’t will not be forced to. Another concern is that the parking may not be built where or when the developer would like it. Fees-in-lieu are more effective when there is sufficient concurrent development in a defined area to generate the funding to develop municipal parking structures or when there is sufficient excess parking capacity in public lots already to absorb the demand from new developments until additional spaces can be built or non-auto improvements made. The community may also allow developers to defer payment until the parking spaces are built.

Local examples:
  • New uses or changed uses on constrained sites in the Town of Braintree Village Zoning District that are unable to meet their minimum off-street parking requirements may be required as part of a Special Permit to pay an annual fee per space (to be set by the Planning Board at a public hearing) to allow the Town to provide the off-street parking (see regulation).
  • The City of Northampton makes special provisions for the Central Business District for meeting off-street parking requirements: payment of a fee in lieu of providing required off-street parking is allowed by right. The one-time fee of $2,000 per space is used to add parking spaces, improve the utilization of existing spaces, or reduce the need for new parking in the CBD (see regulation).
  • The Town of Oak Bluffs allows uses proposed for the B-1 business District that are unable to meet the off-street parking requirements to make a payment in lieu of providing the spaces. The payments are annual per space and depend on the number of required spaces, but range from $50 to $100 per space each year (see regulation).
  • In the Town of Ashburnham’s Village Center District, the Zoning Board may allow non-residential uses to pay a fee in lieu of providing required parking spaces. The fee is based on the fair market value of the parking spaces waived plus the cost of building that number of spaces, as estimated by the Planning Board with the advice of the Highway Superintendent (see regulation).
National examples:
  • Developers in the Coconut Grove neighborhood in Miami can satisfy minimum parking requirements by providing off-street parking, contracting spaces elsewhere, or paying in-lieu fees. The city uses the fees to provide structured public parking, to improve transit service, and to maintain sidewalks and pedestrian facilities, helping to maintain the district’s walkable character [1].
  • The City of Orlando, Florida, requires developers to pay fees in lieu of the first required space per 1,000 square feet of floor area, and allows them to choose whether to pay fees or supply the parking for the rest [2, p. 236].
  • Vancouver, British Columbia, calculates its in-lieu fee as the expected cost per space to construct a public parking structure, minus the expected revenue from the parking charges for each space. The fee represents the portion of the structure’s cost that is not covered by the parkers [2, p. 236].
  • Santa Monica, California allows developers in the Third Street Promenade commercial district to pay an in-lieu fee of $1.50 a year per square foot of floor area, regardless of use. The money is used to build public garages behind the stores. This favors uses with high parking requirements, and has resulted in many movie theaters and restaurants locating in the area, creating a dense, pedestrian-friendly district. [2, p. 235]

Additional Resources:

  • U.S. Environmental Protection Agency, Parking Spaces / Community Places: Finding the Balance Through Smart Growth Solutions, January 2006; p. 20-21. Available as a free download at https://www.epa.gov/smartgrowth/parking.htm, or download the full PDF below
  • Donald Shoup, The High Cost of Free Parking (2005), Planners Press, American Planning Association; Chapter 9. Available for purchase from https://www.planning.org/APAStore/Search/Default.aspx?p=1814.
  • Donald Shoup, “In Lieu of Required Parking”, Journal of Planning Education and Research (1999) 18: 307-320. Available as a free download from https://shoup.bol.ucla.edu/.
  • Maryland Governor’s Office of Smart Growth, Driving Urban Environments: Smart Growth Parking Best Practices, March 2006; p. 4-5. Available as a free download.
  • Fitzgerald & Halliday, Inc., Northwest Connecticut Parking Study – Phase II: Model Zoning Regulations for Parking for Northwestern Connecticut, Northwestern Connecticut Council of Governments and Litchfield Hills Council of Elected Officials, September 2003; p. 20. Available as a free download from https://www.fhiplan.com/PDF/NW%20Parking%20Study/NW%20Connecticut%20Parki… or by clicking here.
  • Christopher V. Forinash, et al., “Smart Growth Alternatives to Minimum Parking Requirements“, Proceedings from the 2nd Urban Street Symposium, July 28-30, 2003. Available as a free download from https://www.urbanstreet.info/ or click here for the PDF.
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Fact Sheet: Infiltration Trenches and Dry Wells

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Infiltration trenches and dry wells are standard stormwater management structures that can play an important role in Low Impact Development site design. Dispersed around the site, these infiltration structures can recharge groundwater and help to maintain or restore the site’s natural hydrology. This approach contrasts with conventional stormwater management strategies, which employ infiltration as a secondary strategy that occurs in large basins at the end of a pipe.

The parking lot runoff directed to this infiltration basin is pretreated by a vegetated filter strip. Note concrete level spreader (at right) to facilitate sheetflow across filter strip. Photo: California Stormwater Quality Association

Management Objectives

  • Increase groundwater recharge through infiltration.
  • Reduce peak discharge rates.
  • Reduce total runoff volume.

Dry wells and infiltration trenches store water in the void space between crushed stone or gravel; the water slowly percolates downward into the subsoil. An overflow outlet is needed for runoff from large storms that cannot be fully infiltrated by the trench or dry well. Bioretention, another important infiltration technique, is discussed in another fact sheet. Infiltration trenches do not have the aesthetic or water quality benefits of bioretention areas, but they may be useful techniques where bioretention cells are not feasible.

Applications and Design Principles

Infiltration structures are ideal for infiltrating runoff from small drainage areas (<5 acres), but they need to be applied very carefully. Particular concerns include potential groundwater contamination, soil infiltration capacity, clogging, and maintenance. Pretreatment is always necessary, except for uncontaminated roof runoff. Trenches and dry wells are often used for stormwater retrofits, since they do not require large amounts of land; directing roof runoff to drywells is a particularly cost-effective and beneficial practice. Whether for retrofits or new construction, multiple infiltration structures will be needed to treat large sites; they are often used in the upland areas of large sites to reduce the overall amount of runoff that must be treated downstream.

Trenches and dry wells are tough to site in dense urban settings, due to the required separation from foundations, and because urban soils often have poor infiltration capacity due to many years of compaction. Infiltration trenches and dry wells should not receive runoff from stormwater hotspots (such as gas stations) unless the stormwater has already been fully treated by another stormwater treatment practice to avoid potential groundwater contamination.

Perforated Pipe for Runoff

A perforated pipe delivers rooftop runoff to the full length of this infiltration trench, under construction. After completion the area will be covered with sod and the trench will be invisible. Photo: Cahill Associates, Inc. 2004

Infiltration structures must be constructed with adequate vertical separation from the groundwater table, generally 2’ or more between the bottom of the trench or pit and the seasonally high groundwater table. Soils must be sufficiently permeable (at least 0.3”/hour) to ensure that trenches can infiltrate quickly.

Infiltration trenches and dry wells operate on similar principles, though trenches are linear troughs and dry wells are round or square in plan view. In both cases, the excavated hole or trench, 3’-12’ deep, is lined with filter fabric and backfilled with washed, crushed stone 1.5”-3” in diameter. The bottom of infiltration trenches is often filled with a 6”-12” filter layer of washed, compacted sand. A 4”-6” perforated PVC observation well will permit monitoring of the structure and observation of drainage time.

Trenches and dry wells should be designed to store the design volume and infiltrate it into the ground through the bottom of the trench or well within 72 hours. Because of their limited size, infiltration structures are best used to infiltrate the first inch/half inch of runoff from frequent small storms; they are not effective for infiltrating the runoff from large storms. Overflow from trenches and dry wells should be directed to a swale or other conveyance, sized to prevent erosion.

Because dry wells and infiltration trenches can be prone to clogging, pretreatment of stormwater runoff is a necessity. Where dry wells accept roof runoff through a system of gutters and downspouts, screens at the top of downspouts should suffice. For runoff from paved surfaces, designers should use grass swales, filter strips, settling basins, sediment forebays, or a combination of two or more strategies to pretreat stormwater before it is discharged to an infiltration trench or dry well. In groundwater protection areas (Zone II and Interim Wellhead Protection Areas) infiltration may only be used for uncontaminated rooftop runoff.

Benefits and Effectiveness:

  • Dry wells and infiltration trenches reduce stormwater runoff volume, including most of the runoff from small frequent storms. Consequently, downstream pipes and basins are smaller, and the local hydrology benefits from increased base flow.
  • Dry wells and infiltration trenches also reduce peak discharge rates by retaining the first flush of stormwater runoff and creating longer flow paths for runoff.
  • Infiltration structures are moderately expensive to construct and can help to reduce the size of downstream stormwater management structures.
  • These techniques have an unobtrusive presence; they do not enhance the landscape (like bioretention areas do), but they have a lower profile than large infiltration basins.

Limitations:

  • Infiltration trenches and dry wells cannot receive untreated stormwater runoff, except rooftop runoff. Pretreatment is necessary to prevent premature failure that results from clogging with fine sediment, and to prevent potential groundwater contamination due to nutrients, salts, and hydrocarbons.
  • Infiltration structures cannot be used to treat runoff from portions of the site that are not stabilized.
  • Rehabilitation of failed infiltration trenches and dry wells requires complete reconstruction.
  • Infiltration structures are difficult to apply in slowly permeable soils or in fill areas.
  • Where possible, the design should maintain a minimum separation from paved areas (generally 10’, depending on site conditions) to prevent frost heave.
  • Unlike bioretention areas, infiltration trenches and dry wells do not help meet site landscaping requirements.

Maintenance:

  • After construction, inspect after every major storm for the first few months to ensure stabilization and proper function.
  • On a monthly basis, remove sediment and oil/grease from pretreatment devices, overflow structures, and the surface of infiltration trenches.
  • Semi-annually, check observation wells 3 days after a major storm. Failure to percolate within this time period indicates clogging
  • Semi-annually, inspect pretreatment devices and diversion structures for sediment build-up and structural damage.
  • If ponding occurs on the surface of an infiltration trench, remove and replace the topsoil or first layer of stone and the top layer of filter fabric.
  • Upon failure, perform total rehabilitation of the trench or dry well to maintain storage capacity within 2/3 of the design treatment volume and 72-hour exfiltration rate.

Cost:

Infiltration trenches and dry wells are moderately expensive to construct. Because trenches and dry wells can infiltrate stormwater closer to the source, conveyance structures such as swales and pipes can be downsized. It is important that developers and property owners provide a budget for maintenance activities, since lack of maintenance is the primary cause for premature failure of infiltration structures.

Design Details:

  • Determine infiltration rate of underlying soil through field investigations; use a minimum of one boring at each dry well, two borings at each infiltration trench, with at least one additional boring every 50 feet for trenches over 100 feet. Base trench/drywell sizing on the slowest rate obtained from soil infiltration tests. Determine the infiltrative capacity of the soil through an infiltration test using a double-ring infiltrometer. Do not use a standard septic system percolation test to determine soil permeability.
  • Do not use trenches or dry wells where soils are >30% clay or >40% silt clay.
  • Use of vertical piping for distribution or infiltration enhancement may cause the trench or drywell to be classified as an injection well which needs to be registered with the state.
  • Trim tree roots flush with the trench sides in order to prevent puncturing or tearing the filter fabric. Since tree roots may regrow, it may be necessary to remove all trees within 10 feet of the infiltration structure and replace them with shallow-rooted shrubs and grasses.
  • If used, distribution pipes should have ½” perforations and should be capped at least 1 foot short of the wall of the trench or well.
  • For infiltration trenches receiving runoff via surface flow, a horizontal layer of filter fabric just below the surface of the trench, covered with 2”-6” of gravel or crushed stone, will help to retain sediment near the surface; this will prevent clogging and allow for rehabilitation of the trench without complete reconstruction.
  • Required set backs for surface water supply (Zone 1 and Zone A): 400 feet setback from a source and 100 feet from tributaries. Required setback from private wells: 100 feet
  • Required setback from septic systems: 100 feet. Required setback from building foundations: 10 feet for drywells and 20 feet for infiltration trenches.
  • Because of clogging problems, infiltration trenches and drywells should never be used to infiltrate runoff from drainage areas that are not completely stabilized. For best performance, contractors, should avoid compaction of soils around trenches and dry wells during construction.

Additional information:

The Massachusetts Stormwater Technical Handbook (Volume 2), found on the MA Department of Environmental Protection stormwater publications page, includes design details for infiltration trenches and dry wells.

Download a print-ready PDF version of this document below. To request hard copies of this document, please e-mail [email protected].

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Fact Sheet: Low Impact Site Design

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Conventional development strategies treat stormwater as a secondary component of site design, usually managed with “pipe-and-pond” systems that collect rainwater and discharge it off site. In contrast, Low Impact Development embraces hydrology as an integrating framework for site design, not a secondary consideration. Existing conditions influence the location of roadways, buildings, and parking areas, as well as the nature of the stormwater management system.

LID site design is a multi-step process that involves identifying important natural features, placing buildings and roadways in areas less sensitive to disturbance, and designing a stormwater management system that creates a relationship between development and natural hydrology. The attention to natural hydrology, stormwater “micromanagement,” nonstructural approaches, and landscaping results in a more attractive, multifunctional landscape with development and maintenance costs comparable to or less than conventional strategies that rely on a pipe-and-pond approach.

Sensitive site landscaping is an important component of Low Impact Development. Ecological landscaping strategies seek to minimize the amount of lawn area and enhance the property with native, drought-resistant species; as a result, property owners use less water, pesticides, and fertilizers. The maintenance of vegetated buffers along waterways can also enhance the site and help protect water quality.

A clustered subdivision with smaller setbacks and preserved natural areas (left) contrasts with a conventional subdivision where all the trees have been removed.

Design Objectives

  • Develop a site plan that reflects natural hydrology.
  • Minimize impervious surfaces.
  • Treat stormwater in numerous small, decentralized structures.
  • Use natural topopgraphy for drainageways and storage areas.
  • Preserve portions of the site in undisturbed, natural conditions.
  • Lengthen travel paths to increase time of concentration and attenuate peak rates.
  • Use “end of pipe” treatment structures only for quantity/rate controls of large storms.

Applications and Design Principles

LID site planning is similar to Conservation Subdivision Design (CSD) process, though LID site planning can be applied to both residential and nonresidential development as well as redevelopment projects. The four step process of CSD (identify conservation areas; locate home sites; align streets and trails; draw in lot lines) provides a serviceable framework for the LID site design process, which involves designing a stormwater management system in conjunction with the second and third steps of the CSD process.

Site Analysis

An LID site planning strategy will begin with an assessment of environmental and hydrologic conditions on a site and identification of important natural features such as streams and drainageways, floodplains, wetlands, recharge groundwater protection areas, high-permeability soils, steep slopes and erosion-prone soils, woodland conservation areas, farmland, and meadows. This investigation will help to determine what “conservation areas” should be protected from development and construction impacts, and what site features (such as natural swales) might be incorporated into the LID stormwater system.

The site analysis will also identify a “development envelope” where development can occur with minimal impact to hydrology and other ecologic, scenic, or historic features. In general, this will include upland areas, ridge lines and gently sloping hillsides, and slowly permeable soils outside of wetlands. The remainder of the site should be left in a natural undisturbed condition. It is important to protect mature trees and to limit clearing and grading to the minimum amount needed for buildings, access, and fire protection; lawn areas increase runoff that must be managed, whereas preservation of wooded areas reduces the volume of stormwater that must be treated. Construction activity, including stockpiles and storage areas, should be confined to those areas that will be permanently altered, and the construction fingerprint should be clearly delineated.

Locate Development and Roadways

Based on the development envelope from the site analysis, developers and their consultants should prepare potential site development layouts. These layouts should minimize total impervious area; reflect the existing topography; and utilize existing drainageways, swales, depressions, and storage areas in their natural state. The goal is to minimize the amount of runoff that must be treated in a stormwater management system.

In order to reduce site coverage but not square footage, site development layouts may include buildings clustered together, parking structures (instead of lots), or taller buildings with a smaller footprint relative to floor area. However, these strategies may conflict with local land use regulations that address density, height, frontages, and lot coverage, so consultation with local officials is critical to help them understand the rationale for the proposed development plan. Other strategies for minimizing impervious surfaces include reduced road widths, smaller parking areas, permeable paving, and green roofs, all of which are described in greater detail in other LID fact sheets.

Once approximate building locations are known, general roads alignments can be identified. Roads should not cross steep slopes, where cutting and filling will unnecessarily disturb drainage patterns; instead, roadways should follow existing grades and run along existing ridge lines or high points. As a rule of thumb, roadways should run parallel to contours on gentle slopes, and perpendicular to the contours on steeper slopes. On sites where a large amount of parking is required, it should be broken up into multiple smaller parking lots; this can also help to reduce grading on hilly sites, since separate parking areas can be placed at different elevations.

Conventional development strategies concentrate stormwater runoff in storm sewers and deliver it to a few large ponds for treatment at the end of the pipe. Low Impact Development seeks to create multiple small “sub-watersheds” on a site and treats runoff close to the source in smaller structures.

Create a Decentralized Stormwater System

The actual location of buildings and the alignment of roadways should be determined in conjunction with the design of the stormwater management system. The goal of this process is to minimize “directly connected impervious area”—those impervious areas that drain directly into a pipe-and-pond stormwater system. Designers should seek to maintain or create small sub-watersheds on the site and “micromanage” the runoff from these sub-watersheds in small decentralized structures, such as swales, bioretention areas, infiltration structures, and filter strips. Paved surfaces should be graded and crowned so that they form multiple “mini-watersheds;” the runoff from each small drainage area should to a different bioretention area, swale, or filter strip. Roof runoff should be sent to rain barrels, cisterns, dry wells, and vegetated areas via level spreaders.

LID site design should also seek to maximize the travel time for stormwater runoff. Conventional pipe systems increase the speed of stormwater runoff, resulting in bigger peak discharge rates (and therefore bigger ponds) at the end of the pipe. In contrast, LID seeks to increase the time of concentration (the average travel time for rainfall) through a variety of techniques: retain stormwater in small structures close to the source (described above), provide as much overland or sheet flow as possible, use open drainage systems, provide long travel paths, and use vegetation to increase surface roughness.

Wherever possible, site design should use multifunctional open drainage systems such as vegetated swales or filter strips which also help to fulfill landscaping or green space requirements. Swales and conveyances can be designed to increase travel length (and time of concentration) with long flow paths that loop around parking lots or other features, rather than more direct routes. The result is increased infiltration and more attenuated peak discharge at the downstream end of the site—the peak comes later and is smaller.

LID stormwater structures (such as bioretention areas and infiltration trenches) should be sized to treat the stormwater from frequent, low intensity storms for water quality and infiltrate it into the ground or slowly release it; they should not be expected to completely manage the peak discharge rate or volume from large storms. Volume and rate controls at the downstream end of the site may still be necessary, but much smaller as a result of LID site design, decentralized stormwater management, and long travel paths.

Benefits and Effectiveness:

  • A comprehensive approach to site design is the most effective, cost-efficient means of minimizing stormwater runoff. A small investment in design at the outset of the project can reduce the expense associated with conventional stormwater systems.
  • An LID site design approach based on natural hydrology will integrate the built space into the natural environment, giving the development integrity and an aesthetically pleasing relationship with the natural features of the site. Many LID stormwater management structures also serve as site landscaping.
  • Developers who take a careful, comprehensive approach to site design—one that accommodates local development goals and protects important resources—run into less resistance from neighbors and local boards concerned about the aesthetic and environmental impacts of development.
  • Site designs that involve a minimal amount of clearing, grading, and road/parking lot construction have lower overall site development costs.
  • Small, distributed stormwater “micromanagement” techniques offer an advantage over centralized systems because one or more of the individual structures can fail without compromising the overall integrity of the stormwater management strategy for the site.
  • Smaller decentralized facilities feature shallow basing depths and gentle side slopes, which reduce safety concerns as compared to deep ponds that must be fenced off.

Limitations

  • The comprehensive LID site analysis and design process can rarely be conducted “in house” by developers; it requires the assistance of knowledgeable and qualified engineers and landscape architects.
  • Some LID site designs that seek to cluster development and reduce lot coverage may conflict with local land use regulations or public perceptions about what type of development is desirable (a compact multistory building may be more visible than a single story building with a larger footprint.) Consequently, some public education may be necessary as well as cooperation among developers, advocates, and regulators who recognize the values of the LID site design approach.

Maintenance

* There are no particular maintenance requirements associated with an LID site design, but b y reducing the amount of stormwater runoff and associated stormwater management structures, LID can reduce the amount of maintenance required on a site.

Cost

The cost of an LID site design will vary depending on the site. The expertise necessary to create a comprehensive site plan may cost more than a simple engineering plan that ignores natural conditions and treats stormwater using a “pipe and pond” system; however, the resulting plans are commonly less expensive to construct and maintain, and the additional landscaping and aesthetic value of an LID development will add a premium to the sales price.

Additional References:

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Parking Wrapped in Active Uses

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Parking Structures for a Pedestrian-Friendly Environment

In downtowns and other areas where the pedestrian environment is important, parking structures can disrupt and degrade the urban fabric, creating blank concrete walls amid more engaging storefronts. Parking structures should not be located on busy pedestrian streets, major commercial streets, or on valuable intersections (read more about locating parking strategically). Parking structures that must be located in places where they will impact the pedestrian environment should be designed with retail or other commercial uses along the street. This keeps the area active at street level and maintains visual interest. It also benefits the developer by providing an additional source of revenue through the lease or sale of the commercial space. This wrapping of active uses around a parking structure can mean anything from integrating small newsstands, coffee shops, or corner stores on the main street face to creating parking structures that are surrounded by mixed uses, including government offices, police or public safety substations, larger scale retail, and/or private office space, on 3 or more sides and all levels.

Local examples:
  • In 2001, as part of a broader rezoning effort, the City of Cambridge revised its zoning code to exempt underground parking facilities from Gross Floor Area calculations. The new regulations state that the roof of an underground parking facility must not be more than 4 feet above the ground, and that it must be below either a non-parking structure or an open space amenity or pedestrian circulation area. This offers an incentive to create underground parking and to have active first-floor uses. For additional information, see Section 5.25 of the Cambridge Zoning Ordinance
National examples:
  • Washingtonian Center in Gaithersburg, Maryland includes a parking structure with retail and commercial uses on the first floor. [1, p.24]
  • The 15th & Pearl Mixed-Use Parking Structure in Boulder, Colorado is a 700-car parking structure with five levels above grade and two below. Three sides of the structure are wrapped with a total of 7,500 square feet of ground floor retail space and 7,500 square feet of upper level office space in separately-constructed buildings attached to the parking structure. The City of Boulder’s parking authority occupies the office space, while the retail space is leased to individual stores. The parking is not visible from Pearl Street, a primary pedestrian and shopping corridor, but the parking entrances are clearly marked and emphasized on the side streets. Architecturally, the buildings’ brick and steel facades reflect the historic architecture of the surrounding area, and each of the exterior buildings has its own character. The development of the structure, which was completed in 1999, spurred redevelopment along the East End of the Pearl Street Mall. The cost of the facility was $11.5 million (1999 dollars). The retail space is fully leased and parking spaces generate revenue for the City through long-term, daily, and hourly fees. [2]

Additional Resources:

  1. Maryland Governor’s Office of Smart Growth, Driving Urban Environments: Smart Growth Parking Best Practices, March 2006. Available as a download.
  2. Patric Dawe, “New Urbanist Parking Concepts: Solution to Sprawl through Parking Innovation“, Parking, National Parking Association, March 2004; pp. 38-44.
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