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Literature Summary and Benefits
Associated with Alternative Development Approaches

Green Development Alternatives

(Literature Summary)

Introduction

Urban development has proven to greatly alter the quantity and quality of receiving water resulting in cumulative impacts on the physical, chemical, and biological integrity of ecosystems (Galli, 1992). The impacts on water resources is especially significant when we realize that more than half of the world's population lives within 60 km of the shoreline (as cited in Cheema, 1994). Urbanization has been associated with significant degradation of aquatic, riparian, and terrestrial habitat, and impacts to coastal ecosystems; loss of wildlife corridors; increases in the intensity, frequency, duration, and transport capacity of the hydrologic regime; and increases in pollutant buildup. In many cases innovative zoning and site planning requirements reduce impacts by preserving sensitive areas such as wetlands and floodplains. However, developed areas continue to exhibit significant disturbances due to massive grading.

The Impacts of Uncontrolled Development

Development and land use impacts are cumulative and synergistic in nature, causing an array of hydrologic, water quality, and natural resource impacts. The changes that occur during land development are often unnecessarily dramatic and can cause catastrophic impacts on a watershed ecosystem. Hydrologic, water quality, and natural resource impacts occur due to mass grading and changes in existing site topography; reduction and elimination of natural vegetated cover; isolation and reduction in size of valuable habitat; and reduced ability of a site to perform the natural water quality treatment functions of infiltration, evapotranspiration, physical settling and attachment, and biological decay. Poor site planning can result in excess stormwater runoff, soil erosion and sedimentation, streambank instability, and unnecessary loss of valuable natural resources and wildlife habitat. In addition, the way development is planned on a large community or watershed scale can exaggerate development impacts. Traditional patterns of development or growth, referred to as "urban sprawl", result in low-density, suburban growth that expand suburban areas, fill in vacant land between neighborhoods, and rely heavily on automotive transportation. The impacts of this "sprawl development" have been cited throughout the literature in terms of lost agricultural land, impacts to environmentally sensitive areas, decentralized urban job centers, economic impacts to older existing communities and increased costs of infrastructure needed to serve these areas (Fulton, 1978; Moe, 1995). Environmental impacts of traditional development patterns and uncontrolled site specific modifications can be grouped into hydrologic alterations, water quality impacts, and natural resources impacts.

Hydrologic Alterations

The natural hydrological regime can be significantly altered by landscape changes that result from urban development. These alterations reflect the response of the site to the cumulative impacts of changes in the topography and flow pathways (resulting from grading and man-made stormwater conveyance systems) and changes in infiltration, interception, and evapotranspiration capacities (resulting from reduced vegetative cover and increased impervious surfaces).

Hydrologic responses to development can be characterized by a significant increase in the surface component of storm runoff volume; a rapid concentration of overland flow during storm events, resulting in higher in-stream flow velocities and peakflows; an increase in the runoff erosive and pollutant- carrying capacities, and limited subsurface recharge, resulting in an apparent low interevent baseflow. Development-related hydrologic impacts can adversely change channel morphology, baseflow, currents, pools and riffles, streambed substrate, bank stability, and in-stream and riparian vegetation. These single storm event response alterations result in long-term changes of the hydrologic regime that can be described in terms of changes in the frequency and duration of high flows; increases in overland flow concentration; loss of interception, infiltration, and depression storage; peak discharge increase; peak time reduction; increases in the frequency of discharges; and flow velocity increases. These cumulative changes can result in secondary impacts including: increased flooding, accelerated erosion/sedimentation rates, flashy stream flows, increased frequency of discharges, increased water temperature, and reduced stream baseflow. Simmons and Reynolds (1982) noted a 20 to 85 percent decrease in dry-weather flows in several urban New York watersheds after development. Similar findings were discovered during the Belle Hall study where the storm water runoff from a "sprawl" development was compared to that of a traditional town development. The computer model analysis showed the difference in total volume of runoff between the two sites could be as much as 43 percent (USEPA, 1996).

Changes in these physical parameters may preclude the attainment of designated water body uses. When values for these parameters fall outside the range of natural variability, they can be considered physical stressors that might impair aquatic ecosystems through loss of habitat and impacts on aquatic life. The biological integrity of streams can best be protected if development effectively reproduces the predevelopment hydrologic regime (surface and subsurface) and maintains water quality levels, thereby minimizing riparian, aquatic, and terrestrial habitat degradation and destruction.

Water Quality Impacts

Good water quality in streams is important to restoring and ensuring the survival of riparian areas and in-stream systems, important for the food, water, and protective cover they offer wildlife. During the development of a single-family residential community, surface water and groundwater quality is typically impacted through increases in erosion and sedimentation processes; residential lawn care and car care practices; pollutants from the deterioration of materials used in cars, roads, and buildings; and atmospheric deposition. Through water quality modeling, Dr. Elizabeth Blood, of the Jones Ecological Research Center, Georgia, found through the Belle Hall study that urban sprawl type development patterns could result in three fold increases of sediment yields, and higher nitrogen and phosphorus loadings, and chemical oxygen demand (EPA, 1996). A large percentage of the stream systems in urbanized watersheds exhibit medium to extremely severe channel erosion and deposition due to uncontrolled or inadequately controlled stormwater runoff. This not only leads to seriously unstable and unsafe conditions, but also results in loss of valuable instream habitat; adds to the sedimentation problem in downstream systems; can lead to reduced sunlight and dissolved oxygen conditions, killing fish and other biota; can contribute to toxicity problems from heavy metal and hydrocarbon contamination; and, most importantly, leads to further erosion and sedimentation downstream by causing a chain reaction through increasing bedload and thus further erosion.

Urbanization and changes in land activities can lead to a number of stressors affecting a watershed ecosystem. The impacts of these stressors affect both the human and wildlife inhabitants, as well as the aquatic and terrestrial resources. The combined effect of stressors on a watershed ultimately leads to ecosystem degradation.

Natural Resources Impacts

Urbanization has been associated with significant degradation of natural resources through loss of ecosystem quality and connectivity, and loss of wildlife corridors. In spite of site planning requirements to reduce impacts by preserving sensitive areas such as wetlands and floodplains, developed areas continue to exhibit significant disturbances due to massive grading.

Ecosystem degradation can occur due to a number of natural and man-made changes within a watershed. Ecosystem stability is primarily governed by five processes: habitat structure, energy or food sources, biological interactions such as prey-predator relationships, water quality, and hydrology. Despite extensive efforts during the past 20 years in environmental resource protection and management, the overall condition of natural ecosystems generally continues to decline. The number of old- growth forested acres has decreased, and the number of acres of wetlandsvaluable ecosystems themselves and important transition and edge zones for upland ecosystem specieshas dramatically declined. The number of listed threatened, rare, and endangered species continues to increase, and in-stream aquatic ecosystem habitat continues to decline due to severe stream degradation.

Reductions in natural ecosystem stability and changes in ecosystem diversity will ultimately have negative impacts on the quality of life for citizens through threats to human health and safety, aesthetics, regional growth and infrastructure, population size, and the economy. This is because humans are an integral part of an ecosystem. Most people and environmental programs depict an "outside" role for humans in ecosystem processes. However, this approach has left us with a continuing and widening ecosystem diversity crisis that threatens our ability to sustain natural resources.

Green Development Alternatives

Green Development presents new challenges in implementing environmental protection and water quality in an effort to promote economic prosperity and a clean and safe environment in which to live and work. Green development approaches focus on flexible zoning, preventive planning, intelligent management of natural resources and water quality, and implementation of treatment/control technologies at multiple scales from development sites to watershed planning.

Green development goes by many names: "new urbanism", neo- traditional, village, and cluster to name a few. It's an alternative approach that moves away from urban sprawl-type suburbs to more traditional towns that combine planned open space with mixed-use neighborhoods that provide housing, shopping, employment, and recreation, all within walking distance. Figures 1 and 2 (Adapted from Living the American Dream: Density and Home Ownership, SCCCL Land Development Bulletin, 1993) offer a visual comparison between low- and high- density development.

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Figure 1. Low-density, traditional development.

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Figure 2. High-density, green development.

After World War II, suburbs were, and still are, designed "as if families were large and had only one breadwinner, as if jobs were all downtown, as if land and energy were endless, as if another lane on the freeway would end traffic congestion" (Bookout, 1992). Green development signifies a return to pre- World War II design conventions townhomes that create a street wall effect, apartments above retail stores, outbuildings, alleys, and gridded street patterns (Hamblen, 1988).

Green Development balances urban development impacts and site design features while enhancing lot yields, reducing development costs, and encouraging development and economic growth. The overall goal is to achieve a balance between economic growth, quality of life, and environmental protection. Green Development achieves these objectives through:

• flexible zoning and subdivision requirements
  
• management of growth through agriculture and natural resources preservation
  
• comprehensive and integrated site planning
  
• reduction in site imperviousness
  
• restoration of the site hydrologic regime to mimic the natural or predevelopment condition
  
• maintenance of surface water and groundwater quality and minimization of the generation and off-site transport of pollutants
  
• minimization of disturbance of riparian habitat functions
  
• preservation of terrestrial habitat ecological functions and maximizing conservation of woodland and vegetative cover
  
• use of compact, pedestrian-friendly development practices.
  

Throughout the literature references to Green Development components that help to facilitate these goals exist.

Flexible Zoning and Subdivision Requirements

Green Development employs alternative zoning options such as overlay districts, performance zoning, incentive zoning, imperviousness overlay zoning, planned unit development zoning and watershed-based zoning to allow for innovative site layout options such as cluster development. For example, performance zoning is used to allow flexibility in where or how development is designed, as long as the impact of the development is kept within specified acceptable limits. Performance based zoning, in various degrees, is practiced in the towns of Sanibel Island, Florida; Pine Barrens, New Jersey; Breckenridge and Fort Collins, Colorado; and Medford, New Jersey (Einsweiler and Miness, no date).

Seaside, Florida, is a well documented example of incorporation of flexible zoning regulations to allow alternative building designs. Although the primary objective was not increased environmental protection, the incorporation of flexible zoning alternatives sets the stage for further site layout and site design flexibility that may result in increased environmental protection (Steuteville, 1996). Davidson, Huntersville, and Cornelius Counties in North Carolina, have implemented flexible zoning ordinances that allow the developers to choose between old and new zoning options (Steuteville, 1996). In another example, Maryland's Chesapeake Bay Critical Area Act incorporates a flexible zoning approach using a "floating zone". The floating zone is a specialized use district that permits certain land uses in accordance with an overall development plan without requiring legislative action (Kenney, 1985).

Alternative zoning options have been used to provide protection of critical drinking water resources as well. Hebron, Connecticut, for example, developed new zoning regulations in the form of an aquifer protection overlay zone to protect a future water supply site (Murphy, 1990).

Management of Growth Through Agriculture and Natural Resources Preservation

Growth management systems and techniques can be used to minimize the impacts of suburban sprawl, while preserving sensitive natural resources, agricultural lands, and maintaining a sense of community within the development. Alternatives to growth management are numerous, and can take the form of location controls, such as traditional zoning, performance based approaches to regulating growth, and mitigation type approaches such as purchasing of development rights, conservation easements and the use of special districts such as farm districts. Green Development can incorporate any or all of these options to managing growth. The option, or growth management tool selected depends on the purpose of the growth management program, and the resources available to enforce such a program.

One example is illustrated in the Ahwahnee Principles, currently implemented by Cathedral City, Ontario, where development is implemented based on specific plans designating where new growth, infill or redevelopment will be allowed to occur (Corbett and Velasquez, 1994). According to Meeks (1990), nine states and another seven are incorporating growth management and comprehensive planning acts to change the nature of land use planning and the decision making processes to provide economic development, farm and forest land preservation, natural resource conservation, affordable housing, coordinated infrastructure and transportation development. These states include Florida, Georgia, Hawaii, Maine, New Jersey, Rhode Island, Oregon, Vermont, Washington, California, Maryland, New York, Pennsylvania, Virginia, and West Virginia.

Comprehensive and Integrated Site Planning

Site planning involves the determination of the specific uses for land areas and their layout and design within a developable parcel. Green Development approaches to site planning require a comprehensive review and understanding of a land parcel's existing featurestopography, water resources, forest resources, soils, climate, wildlife habitat, and existing land useswhich will play a major role in determining the feasibility of the site design. Green Development incorporates the following site planning principles: reduce hydrologic impacts; protect water quality; protect natural resources; minimize grading; and design a mulitfunctional site layout of roads, lots and utilities. Green Development site planning approaches set goals based on the needs of existing natural resources to measure the performance of site planning methods.

Green Development approaches to site grading reduce excessive mass grading to minimize land disturbance through: site fingerprinting, minimal disturbance, cluster development, fitting the site design into the landscape and providing development incentives through credits for preservation and minimization.

• Minimal Disturbance: The Northridge development, in Prince George's County, Maryland, incorporated Green Development grading techniques by reducing side slopes along roadways to minimize disturbance and save existing trees (MOP, 1995; Salant, 1996). The Village of Woodsong, Shallote, North Carolina, uses alleys as a means of staging house construction to minimize disturbance (Milliken, 1996).
  
• Clustering: The USEPA has identified clustering development as a method to concentrate development and construction activity on a limited portion of a site, leaving the remaining portion undisturbed (USEPA, 1993). Clustering is cited as one option to minimize environmental impacts of development by the Maryland Office of Planning (MOP, 1994). Haymount, Virginia, is one development example of the use of clustering to minimize site impacts. In Haymount, the developer will disturb only 32 percent of the land, setting aside the remaining area as agricultural preservation. By comparison, in typical, large lot developments 80 percent of the site could be disturbed to grade lots and by the infrastructure needed to serve them (Mayer, 1996).
  
• Fitting the Site Design Into the Landscape: Reduced grading approaches incorporated by Green Development can also help reduce the costs of development. For example, the Urban Land Institute has found that development costs rise dramatically when slopes are greater than 10 percent (ULI, 1980) due to extensive requirements for cut and fill.
  
• Natural Resource Preservation: Preserving a site's natural amenities such as trees, terrain, and views may significantly reduce land development costs by using the natural landscape features rather than requiring the construction of new, constructed features. These principles are incorporated into the Ahwahnee Principles setting aside natural features in parkland (Corbett & Velasquez, 1994). San Diego, California protects the natural terrain of its hillsides through hillside protection zoning districts. Likewise, McHenry County, Illinois, regulates unstable soils and steep slopes using a steep soils overlay district (Mantell et al., 1990).

Reduction in Site Imperviousness

Site imperviousness refers to the ratio of area on a developed parcel that prevents infiltration. Impervious surfaces generally take the form of paved roads, parking lots, roof tops, sidewalks, and driveways. As development occurs, existing land areas are converted to less impervious surfaces, either through paving, compaction or replacement with buildings. Urbanization often results in changing the use of land from forested, open space or agricultural uses to residential, commercial or industrial uses. Thus, a reduction in pervious surfaces is generated, almost directly proportional to this change in land use. Studies have shown that property values may increase 5 to 32 percent with reduced impervious cover (Land Ethics, 1994). This may be due to overall improved site aesthetics or lower housing costs.

Green Development approaches attempt to reduce site imperviousness through reductions in rooftop density, sidewalk and driveway design, and road layout. Narrow street right-of- ways, continuous street frontages, and comfortable street scapes, often used by neo-traditional designs to allow for pedestrian, bicycle and automobile co-existence, can provide added benefits in reducing overall site imperviousness.

• Rooftop Density: Development plans that reduce the number of rooftops per acre of disturbed area may reduce hydrologic impacts of development. For example, cluster options that provide for flexibility in lot layouts can reduce road length by 50 to 70 percent (Land Ethics, 1994). Disconnecting the rooftop runoff through infiltration practices may also reduce the impacts of rooftop densities. The Village of Woodsong incorporated rooftop cisterns as a means of capturing stormwater runoff for reuse, thereby hydrologically disconnecting this impervious surface (Milliken, 1996).
  
• Lot Layout: Lot layout options determine the total road length required to serve each dwelling unit through lot setback restrictions, thereby influencing road imperviousness. Lot setback restrictions such as lot area, and front, side and back yard setbacks, lead to requirements for driveway and sidewalk design. Flexibility in zoning and subdivision regulations to alter lot layout options can therefore reduce overall site imperviousness. Green Development options might include such lot layouts as "zero-lot-line" development. This approach was incorporated by the Northridge Villas Project, to reduce house footprints and side yard requirements (Salant, 1996). Separations between outbuildings and primary dwellings in the Village of Windsong development helped to create less impervious surface (Milliken, 1996). The same development placed houses closer to the street, reducing required disturbance area and driveway lengths.
  
• Road Layout, Sidewalks, and Driveways: Providing on-street parking on one side of the street can decrease overall site imperviousness by 25-30 percent per dwelling unit served (Sykes, 1989). Reductions in impervious surface can reduce overall development costs. One-half of the cost of residential construction can be attributed to roads, sidewalks, driveways, and parking spaces (Schueler, 1995). "Neo-traditional" developments incorporating cluster type site layouts, reduce the length of roads required to serve a community, and therefore the site imperviousness. Duany and Plater-Zyberk have suggested that this may lead to a 75 percent reduction in overall infrastructure costs (Forgey, 1995). Varieties of road designs can reduce overall site imperviousness. The Village of Woodsong, in Shallotte, North Carolina, incorporated narrower street designs, reducing imperviousness and thus less stormwater runoff. Additional benefits from this street design included reduced traffic speeds (Milliken, 1996). In addition, the use of common driveways is encouraged to minimize development impacts.
  

Natural Resources Protection

Natural resources protection is part of many urban design and planning programs. Site development can result in natural resources impacts or, if done properly and comprehensively, can contribute to natural resources protection goals while still providing for economic growth. Green Development approaches incorporate the following planning considerations to lessen the impacts of development on watershed natural resources functions:

• Comprehensive planning and careful site design to avoid changes in landscape form or topography, changes in hydrology, changes in vegetative cover, and reduction in connectivity.
  
• Maintenance of watershed natural resources density and protection of contiguous natural resources areas.
  
• Protection of existing natural resources areas through use of buffers around disturbed areas designed in a manner that provides a habitat edge that enhances their aesthetic, wildlife, and potential economic value, and reduces maintenance requirements such as mowing.
  
• Minimization of grading and disturbance impacts from road design and layout requirements.
  
• Location of buildings and building restriction lines at the edge of woodland or natural resources to maximize the amount of contiguous natural resources area left undisturbed.
  

Successful examples of achieving these planning considerations, cited throughout the literature, have incorporated cluster development, minimum disturbance, site fingerprinting, greenbelts, greenways, and trails, woodland conservation, transition zones, wildlife corridors, stream buffers, and streambank stabilization techniques. Many existing state and local regulations promote Green Development natural resources protection components. For example, the State of Maryland Economic Growth, Resource Protection and Planning Act, Section 3.05(a)(1)(vi) of Article 66B of COMAR, promotes environmental elements that protect sensitive areas from the adverse effects of development. These areas include streams and their buffers, 100-year floodplains, habitats of threatened and endangered species, and steep slopes (State of Maryland, 1983). Conservation planning to minimize natural resources impacts is a goal of the Chesapeake Bay Critical Area Overlay Zone program. In this Overlay Zone, cutting or clearing of trees is generally prohibited without an approved conservation plan. Replacement and reforestation is required for all clearing.

Wildlife habitat protection, transition zones and wildlife corridors are components of Green Development plans to maximize natural resources and habitat protection. Protection of these areas not only is a vital part of natural ecosystem management, it has also been found that these areas can provide hazard mitigation for flooding, slope instability and fire damage (National Park Service, 1992). And, as stated in the Ahwahnee Principles, wildlife corridors can help establish visual community boundaries (Corbett & Velasquez, 1994). The Town of Falmouth, Massachusetts, has enacted a wildlife corridor regulation that protects permanent and contiguous corridors and special areas for the feeding, breeding, and normal home range movement of wildlife (Mantell et al.,1990). Some jurisdictions, such as Kent County, Maryland, have used incentive zoning options, such as density bonuses, to promote the use of clustering (MOP, 1994). Calvert County, Maryland, uses overlay zoning to designate areas required for cluster development. The original zoning density limits act as a baseline for computing lot densities on allowed developed areas, after special protection areas or natural resources are defined and "set aside" (MOP, 1994).

Greenways and greenbelts, often incorporated for recreation and aesthetic purposes into development planning, can provide an open space buffer protecting sensitive natural areas. One popular alternative development approach, known as a greenway, is a corridor of open space that is managed for conservation and/or recreation (Florida Greenways Commission, 1995). Greenways provide habitat protection and serve as filters for air, noise, and water pollution. They also promote walking, jogging, bicycling, canoeing, and cross-country skiing.

Green Development designs incorporate greenbelts to protect such resources as rivers and streams, wildlife refuges and endangered wildlife habitat, floodplains, farms, wildlife corridors, and scenic roads. Examples of such greenbelts include the Bay Circuit Program in Boston Massachusettes, Nantucket Island, Massachusetts, and the San Francisco Bay Area, California (Mantell et al.,1990). The Woodlands, a development in Houston Texas, successfully incorporated open space into a network of greenways, preserving natural drainage as flood control, as well as wildlife habitat, recreation, and a natural wood setting (Smith, 1993; Sykes, 1989).

Alternative Site Layout Options

Green development alternative site layout options incorporate changes in lot frontage, lot setbacks, and reduced lot sizes in return for increased environmental protection. Lot frontage is the required length of a lot that follows along a road. Lot setbacks are the distances required for the rear and side yards providing buffers from adjacent yards. Reduced yard setbacks can impact overall site imperviousness, road requirements and development costs. For example, Sykes (1989) cites a situation where a front yard setback of 20 feet, as compared to a conventional 30 foot requirement, is more than sufficient to allow a car to be parked in the driveway without encroaching into the public right-of-way. This scenario reduces the driveway and walk pavement by 30 percent or more.

Clustering development is one option incorporated by many Green Development examples to implement alternative site layout options. Clustering development can reduce lot setback requirements and lot width frontage requirements. Zero-lot-line development practices also incorporate Green Development lot layout goals through reductions in side yard restrictions and increases in overall unit-lot densities. Northridge Villas Project, in Prince George's County, Maryland, have incorporate the zero-lot-line site layout to save existing woodland area as common area for use by the community (Salant, 1996). Other Green Development options include flag lot developments, currently incorporated in the Fairfax County, Virginia Site Planning Manual (Fairfax County, 1995), lot imperviousness ratios, shared driveways, reduction of on-street parking, alternative use of slopes, and flexible road right-of-ways and road widths.

Many of these options impact development costs, resulting in substantial savings to developers. For example, at an estimated cost of $500.00 per driveway apron, implementing shared driveways can lead to substantial reductions in development costs (Schueler, 1995). Alternative road layout options using road plans that designate length of cul-de-sacs and the number of branches of side streets off collector roads can reduce road pavement length, and associated cost, by as much as 25 percent (ULI, 1980).

Green Development Stormwater Management

Green Development plans incorporate mulitfunctional site design elements into a stormwater management plan. Such alternative stormwater management practices as on lot micro-storage, functional landscaping, open drainage swales, reduced imperviousness, flatter grades, increased runoff travel time, and depression storage can be used to reduce hydrologic impacts of most developments. In the development of Somerset, Prince George's County, Maryland, stormwater impacts are addressed by maximizing the opportunities for treating runoff through infiltration or filtration and using active public participation in pollution prevention practices. For this development, water quality and quantity control measures are integrated into every aspect of the development's landscape site design using on lot bioretention facilities (Coffman et al., 1996).

Presented to the U.S. Environmental Protection Agency, Office of Wetlands, Oceans, and Watersheds; Rod Frederick, Work Assignment Manager; in conjunction with Oceans and Coastal Protection Division; Margherita Pryor, Jessica Cogan; September 30, 1996; Prepared by--Tetra Tech, Inc., 10306 Eaton Place, Suite 340, Fairfax, VA 22030; Under EPA Contract #68-C3-0303; Work Assignment #3-112

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