Low Impact Development Technology

Larry Coffman, Prince George's County, described tools and techniques to promote a new technology - Low Impact Development (LID). With urban development relentlessly expanding, the need for effective economical stormwater management technology has never been greater. Responding to regulations or recognizing the need to address the adverse environmental impacts of urban runoff, local governments are confronted with developing complex multi-objective stormwater management programs.

Today's comprehensive program not only has to deal with runoff quantity and quality control but also have to address such complicated issues as: ecosystem restoration, combined sewer overflow reduction, fisheries protection, potable surface / ground water source protection, and wetland, riparian buffer and stream protection. Some program managers are beginning to question the efficacy of current stormwater management technology to meet these new water/ natural resource protection objectives.

Many conventional stormwater mitigation approaches such as management ponds exhibit a number of inherent practical, environmental and economic limitations. These include the inability to replicate predevelopment watershed hydrology, elevated water temperatures and costly maintenance burdens. Furthermore, because current mitigation practices only lessen the effects of individual developments on water quality, there is concern regarding the cumulative impacts of the widespread use of conventional mitigation practices that fundamentally alter a watershed's hydrologic regime.

As experience is gained with the current technology, many urbanizing jurisdictions are beginning to question the efficacy of traditional structural approaches to meet complex environmental objectives, and are finding it harder to enforce and fund stormwater programs.

Enter LID Technology

Currently, we design and construct every site with one basic overriding goal - to achieve good drainage (collect, concentrate, convey and treat runoff). As a site is developed its hydrologic functions are first altered on a micro scale. The cumulative impacts of these micro changes result in drastically altered hydrologic regimes which we typically try to mitigate using end-of-pipe management practices. If we can design sites to achieve good drainage, why not design sites with the opposite objective to maintain predevelopment hydrologic functions?

In 1990, Prince George's County, Maryland began exploring alternative stormwater management practices and strategies. The success that was achieved with the pioneering development and use of bioretention (filtering / infiltrating runoff within small depressed landscaped areas) led to the belief that perhaps changing the form and function of the developed landscape could be an important tool in controlling urban runoff. In fact, it was realized that through intelligent site design and micro-scale management, you could not only reduce impacts, you could also begin to restore hydrologic functions.

It was soon recognized that maximizing the efficiency of conventional conservation measures and stormwater management practices could not reasonably be used to maintain or restore watershed functions. A new philosophical approach was needed. LID's basic principles were modeled after and borrowed from nature - managing rainfall at the source using uniform distribution of micro-scale controls. LID seeks to mimic natural functions by uniformly distributing small infiltration, storage, and retention and detention measures throughout the developed landscape.

LID General Principles

LID is achieved by creatively integrating hydrologic functions (volume, frequency, recharge and discharge) into site designs using four basic planning and design management principles.

• First, minimize impacts to the extent practicable by reducing imperviousness, conserving natural resources/ecosystems, maintaining natural drainage courses, reducing use of curbs, gutters and pipes and minimizing clearing and grading.
  
• Second, provide runoff storage measures dispersed uniformly throughout the landscape with the use of a variety of small decentralized detention, retention and runoff use practices.
  
• Third, maintain predevelopment time of concentration by strategically routing flows to maintain travel time and control discharge.
  
• Fourth, implement effective public education programs to encourage property owners to use pollution prevention measures and maintain on lot management practices.

LID Basic Site Planning Strategies

The first step of LID is to minimize or prevent runoff. This step is similar to traditional techniques of maximizing natural resource conservation, limiting disturbance and reducing impervious areas. The major difference between traditional techniques is that with LID you must carefully consider how best to make use of the hydrologic soil groups and site topography to reduce and control runoff. These considerations include:

• maintaining natural drainage patterns, topography and depressions;
  
• preserving as much existing vegetation as possible in pervious soils, hydrologic soil groups A and B;
  
• locating BMP's in pervious soils hydrologic soil groups A and B;
  
• directing impervious areas to less pervious soil groups C and D;
  
• disconnecting impervious surfaces to direct and disburse runoff to soil groups A and B;
  
• flattening slopes within cleared areas to facilitate on-lot storage and infiltration;
  
• re-vegetating cleared and graded areas; and,
  
• maintaining travel time to increase infiltration and evaporation.

Costs
LID case studies and pilot programs show at least a 25 percent to 30 percent reduction in site development, stormwater and maintenance costs for residential development. This is achieved by reducing clearing, grading, pipes, ponds, inlets, curbs and paving. This in turn lowers construction costs allowing builders to add greater value (features) to the property.

One of interesting results of LID's on lot micro-scale approach is that the stormwater management controls become a part of each property owner's landscape (natural areas, rain gardens, open space, open swales, etc). This reduces the public burden to maintain large centralized management facilities and reduces the cost and scale of maintenance to a level the homeowner can easily afford - the cost of routine landscape / yard care and pollution prevention.

Road Blocks to LID
There are a number of roadblocks that must be overcome for the successful implementation of LID. Regulatory agencies, the development community and the public may all have concerns about the use of new technology. In the development of the PRDER LID design manual a multi-agency task force spent over two years to address all the concerns and issues.

Some of the major concerns include:

• lack of a hydrologic analytical methodology to measure LID benefits;
  
• limited road standards which allow for narrow roads, open drainage;
  
• lack of flexibility in review process which promote modification of site;
  
• lack of public education to ensure public maintenance of on-site BMPs;
  
• limited analysis of the approaches cost benefits;
  
• lack of training for regulators, consultants, public officials;
  
• shortage of research to demonstrate the effectiveness of bioretention BMP's; and
  
• lack of field monitoring data to demonstrate the effectiveness of LID in controlling runoff quantity and quality.

Summary
LID is a viable cost effective alternative approach to stormwater management and the protection of natural resources. LID is designed to provide tangible economic incentives to a developer to save more natural areas and reduce stormwater and roadway infrastructure costs. LID can achieve greater natural conservation by using conservation as a stormwater BMP. As more natural areas are saved less runoff is generated and stormwater management costs are reduced.

One extremely fascinating aspect of LID is that when controlling runoff on a micro-scale, there exists a whole new world of possible control practices and strategies. So get out-of-the-box of conventional pipe and pond technology, take up the LID challenge, and try thinking small!

For information on how to obtain Low Impact Development manual and the Bioretention Design manual you can call Larry S. Coffman at 301 883 5834.

Downtown Revitalization Strategies

The Town of Hampstead identified downtown revitalization as one of its key objectives. To address this issue and as a result promote smart growth principles, Team members described techniques and approaches to assist the community in implementing its recently prepared Downtown Revitalization Strategy and build the capacity for long-term preservation and revitalization efforts.

Chestertown - A Case Study Example

Marsha Fritz, a private consultant and one of the architects of the successful Chestertown, Maryland revitalization initiative opened the charrette. Clearly, one of the successful examples of a downtown revitalization effort is that of Chestertown, Maryland. Established in the 18th Century as an official "port of entry", its architecture and institutions (i.e., Washington College) still reflect these early periods of the community's past. Today, the town is similar in population to Hampstead (estimated at 4,000) and is considered the commercial and governmental center of Kent County. Tourism, particularly heritage tourism is a growing industry in the Town and throughout the region.

Some early restoration and protection initiatives occurred that represent the community's long-standing commitment to preserving its assets. For example, in 1911 a private restoration was completed on a circa 1769 home; a national register listing in 1969; and the emergence of Garden Clubs and candlelight tours.

Recognizing the community's interest in preserving the Town's unique historic features and the value in doing so, the government responded by creating a historic district, completing a survey with the Historical Society and the Maryland Historical Trust, and completing several public restoration projects. These projects include restoring the brick sidewalks, renovating the Town Hall, completing a Scott's Point Study, moving and restoring historic buildings to serve as public offices (house and stables converted into a police department); and revitalizing the Chester River Bridge. These initiatives laid the groundwork for the restoration of downtown commercial and residential structures. Furthermore, these projects demonstrated a governmental belief in, and an on-going commitment to, restoring the downtown.

In response to the public commitments, the private sector began to invest in the downtown as well. For instance, the White Swan Tavern, Imperial Hotel, Church Alley and Queen Street were renovated and are now viable businesses and quality neighborhoods.

Partnerships were formed to take advantage of the public - private commitment to the revitalization of the downtown. As a result, there was an increased awareness of the availability of state and federal assistance programs and a growing expertise in grant writing and fundraising. Again, additional events were established including the very popular farmers' market.

To build on this momentum and commitment, a public charrette was organized in 1996 to determine what next steps should be taken to promote redevelopment and revitalization. Over 200 participants selected eight sites in the community on which to focus future revitalization efforts. This charrette helped engage the public, set goals, and establish a vision for the town that reflected its history while looking towards its future.

With all these successes, the Town is still challenged by several things, including suburban sprawl which includes strip shopping centers, lack of recreational opportunities and other issues. However, the tide has been turned and public-private investment in the downtown has resulted in measurable successes.

Home . Who We Are . Funding Sources . Projects & Programs .
Technical Support . Local Governments . Research & Publications .
Table of Contents . Map . Links . Search . Email .

Center for Chesapeake Communities, 229 Hanover St., Suite 101
Annapolis, MD 21401 . (410) 267-8595 . Fax (410) 267-8597

Copyright � 2003-4 Chesapeake Communities. All Rights Reserved

Copyright � 2003-4 Chesapeake Communities. All Rights Reserved