Conservation Design Principles and Practices
The following definitions and principles are provided by the Conservation Design Resource Manual, 2003.
Conservation design is a design system that takes into account the natural landscape and ecology of a development site and facilitates development while maintaining the most valuable natural features and functions of the site. Conservation design includes a collection of site design principles and practices that can be combined to create environmentally sound development.
The main principles for conservation design are:
- flexibility in site design and lot size
- thoughtful protection and management of natural areas
- reduction of impervious surface areas
- sustainable stormwater management
A similar term, conservation development, is used to describe a development that is designed and constructed using the principles of conservation design. Conservation design is one of many tools available to communities committed to implementing sustainable development practices. Sustainable development is development that meets the needs of the present without compromising the ability of future generations to meet their own needs.
The following 4 sections provide insight into these guiding principles. The fifth section, Green Infrastructure: Connectivity of Green Space, touches on the need to connect these green spaces both within and outside of conservation developments, in order to maximize the potential benefits of this strategy.
Principle 1 -- Site Design and Lot Size
Lot design standards, especially zoning and subdivision regulations pertaining to residential subdivisions, often limit site design options. This often leads to developments in which all land is divided up into building lots and streets, with natural areas and open space limited to undevelopable land and wetlands. In particular, minimum lot size requirements—often mandated to insure homeowners maximum private front, back, and side yards—tend to minimize the ability to conserve, enhance, or even recover natural areas within a site (NIPC, 2003).
By allowing flexible lot design standards that are density neutral, such as implementing standards for the overall density on a site without minimum lot size requirements, it is possible to meet the concerns of developers while conserving natural areas and systems. Through this strategy, an equivalent number of residences can be clustered, yielding an added benefit to developers by reducing the development costs of the site's infrastructure (roads, sewer, streetlights, water, etc.), as well as the long-term infrastructure maintenance costs carried by the public sector (NIPC, 2003). Site and lot design in more urban environments can be less flexible in order to incorporate existing infrastructure.
The diagrams below show the contrast between conventional and conservation design. Clustering and smaller lot sizes found in conservation design allow a site to maximize open space while maintaining the same number of lots.
|Click image for larger version.|
Credit: Copyright Conservation Design Forum, Elmhurst, IL. www.cdfinc.com
But perhaps the key benefit of flexible lot design standards is its facilitation of designs that are sensitive to the unique natural features and systems of each development site. Randall Arendt, a national expert in conservation design, outlines the following four step process for arranging the development site
- Identify all potential conservation areas, taking into consideration all inherently unbuildable areas floodplains, wetlands, steep slopes), along with buildable areas that are environmentally sensitive (stream and wetland buffer areas, woodlands) or historically and culturally significant.
- Locate the house (or other building) sites, taking care to maximize views and access to natural areas and other amenities (typically the developers will ensure that this is done, in order to maximize the value of each residence).
- Design the street and trail systems, maximizing the efficiency of the street system and ensuring easy access to walkways and trail systems within the development.
- Draw in the lot lines.
Principle 2 -- Protection and Management of Natural Areas
Conservation design encourages the dedication of open space that will protect and restore natural areas and resources, as well as provide for passive recreation where appropriate (NIPC, 2003). Planning for open space and natural resource protection through conservation design must include short- and long-term management. There are four approaches to managing natural areas: (1) The natural area may be dedicated to the municipality or county, or another public agency such as a park district, forest preserve, or conservation district; (2) A homeowners association may take possession of the natural area; (3) A conservation easement can be granted to the government (local, state or federal) or to a non-profit organization (i.e. a conservation land trust like the Nature Conservancy) whose primary purpose is in assisting with conservation development and design; or (4) The natural area may remain in the private ownership of the developer or another entity (NIPC, 2003).
One strategy of this principle is the incorporation of plants native to this region often referred to as native or natural landscaping. "Native landscaping" refers to the use of prairie, woodland, wetland, and floodplain plants that flourished in northeastern Illinois prior to European settlement. However, for our purposes, we shall use the term "natural landscaping." Natural landscaping uses native plants but also broadly implies giving the "look" of the landscape prior to the mid-1800s and the beginning of sustained intense settlement and development. Additionally, natural landscaping implies an attempt at restoration or reconstruction of the landscape to look and function as it did in the time that Native Americans inhabited the land (NIPC, 2004). Natural landscaping is also essential for residential or commercial areas that utilize conservation features such as green roofs, bioswales, rain gardens, filter strips, and stormwater detention basins. As a part or a whole native landscaping is a versatile tool for conservation design.
Natural landscaping serves as a wise alternative to more conventional methods of landscaping. The predominant landscaping material of northeastern Illinois is "weed-free" turf grass lawn, brought to the United States by European settlers. This grass is short-cropped and short-rooted, which does not fare well in the harsher climates of northeastern Illinois. Turf grass lawns' roots grow to only a few inches, while natural landscaping uses native plants that have deep roots (from 5 to 10 feet in most cases, up to 15 feet). These deep roots are necessary to hold the soil together and prevent erosion. Even more, natural landscaping serves as a way to save money while still being aesthetically pleasing and environmentally friendly. Based on estimated costs in 2003 (assuming regular installation and maintenance practices for both natural landscaping and conventional turf grass) the total annual cost per acre of installing and maintaining natural landscaping, such as prairie grasses and forbs, was 63% less than the cost of installing and maintaining conventional turf grass with an irrigation system. Estimated cost savings continued to increase due to implementation on a large site, as demonstrated that over a ten-year period, and based on a 25-acre site, natural landscaping costs 66% less than conventional turf grass (Conservation Design Forum, from NIPC, 2004).
Root Systems of Prairie Plants
©1995 Conservation Research Institute, Heidi Natura
(Click image for larger version.)
Additionally, there are many other benefits to using natural landscaping in lieu of turf grass. Natural landscaping improves water quality by increasing soil permeability, reducing runoff volumes while increasing the landscape's ability to retain nutrients, which in turn reduces the need for various forms of chemical fertilization. Natural landscaping increases aesthetic values and helps to create a distinct community image, adding to the desirability of an area's real estate and open space. Natural landscaping enhances native biodiversity, providing a habitat for birds, butterflies, and other wildlife, in addition to increasing educational and recreational opportunities throughout northeastern Illinois (NIPC, 2004)(The Nature Conservancy and Chicago Wilderness).
Principle 3 -- Reduction of Impervious Surface
The reduction of impervious surfaces is a principle of conservation design that yields multiple benefits when implemented. Better Site Design defines impervious surface as "any surface in the urban landscape that cannot effectively absorb or infiltrate rainfall (NIPC, 2003)." The progression of new development typically results in the conversion of natural land to impervious surface cover. Common impervious surfaces include sidewalks, parking lots, building footprints, roads, swimming pools, roof tops, garages, and patios. All of these surfaces can be designed or retrofitted to redirect stormwater runoff away from the sewers opting for absorption directly into the ground or into a holding mechanism-natural or man-made. By keeping excessive stormwater runoff out of the sewer system and closer to the point of origin, water quality is increased because the stormwater accumulates fewer pollutants on its shortened path. Additional benefits include recharged soils, reduced flooding and reduced sewer overuse and related maintenance costs (NIPC, 2003).
Reducing impervious surface areas also has a substantial impact on the natural landscape. Increased impervious cover and the subsequent increased stormwater runoff can negatively impact stream functions, cause stream bank erosion, degrade stream habitats, increase pollutant loads in streams, deplete the surrounding wetlands and prairies, and lower the diversity of native fish species, insects, and fresh water organisms (Ibid).
The design of new development and its amenities should consider the reduction of impervious cover in the early stages of project conception. For example, interior roads within suburban developments can be narrowed and curbs reduced. Setbacks can also be reduced, and houses clustered, shortening roads and driveways, decreasing the amount of concrete poured and the cost to the developer for supplies and construction time. This also decreases the amount of water infrastructure needed to carry the stormwater runoff to the sewers. Based on 1997 costs, the Northeastern Illinois Planning Commission's Reducing the Impacts of Urban Runoff calculated an average savings of $910 per residence for reducing street, sidewalk, and driveway width in a new residential development. A particularly effective—and far-reaching—means of reducing impervious surfaces is for municipalities to design flexible ordinances that allow for the opportunity to utilize these conservation design techniques.
Green roofs, landscaped parking lots, and permeable pavement/pavers are a few practices that can also help reduce impervious cover and runoff. These are strategies especially beneficial to urban environments, where impervious surface is denser and less green space is available. It should be noted that these practices should take into consideration the accessibility (ex: sidewalks) and topography of a site and maybe not be appropriate for all situations.
Reducing impervious surfaces can also decrease the heat island effect found in many urban areas (The Nature Conservancy and Chicago Wilderness). According to the Environmental Protection Agency (EPA), the heat island effect can cause the air and surface temperatures to be 2-10 degrees warmer than surrounding rural areas, which can add to the effects caused by global warming.
The city of Warrenville isusing permeable pavers to rebuild a one-mile stretch of Warrenville Rd. The $4.7 million dollar project is expected to be completed this fall. Mayor David Brummel states that "While the road is more expensive than a traditional surface, it reduces the possibility of flooding and prevents the "freeze-thaw cycle" that causes potholes." For more information click here.
Imagine that….in 2040, every roof top is a green roof….
New technology is being used to help monitor the degree of imperviousness on an individual site and even at the city level. This can be seen in the following e xample:
Innovation in Mapping: Impervious Surface Mapping Using Satellite Remote Sensing
The Metropolitan Council of Minnesota is working with the University of Minnesota's Remote Sensing and Geospatial Analysis Laboratory to use satellite imagery to generate Imperious Surface Area maps. By integrating aerial photography and spectral-radiometric responses of Landsat TM imagery satellite data, the Metropolitan Council of Minnesota can calculate the imperious surface area percentage of a location as well as the degree of imperviousness ranging from 0%-100%. An example map of the Twin Cities is posted at http://rsl.gis.umn.edu/impervious.html
Principle 4 -- Sustainable Stormwater Management Techniques
Seeing as so much of conservation design is focused on improving the way water relates to a site, implementing sustainable stormwater management techniques is the next logical principle to be applied in conservation design. The benefits include decreased flooding, improved water quality, decreased erosion and sedimentation, and improved groundwater recharge. These techniques seek to turn a source once seen strictly in need of disposal into a resource that nourishes.
Sustainable stormwater management techniques can be implemented in a variety of ways, depending on the characteristics of land as well as its surrounding environment and current ordinances. Best Management Practices (BMPs) defined as "structural, vegetative, or managerial approaches designed to reduce stormwater runoff volume, maximize natural groundwater recharge, and treat, prevent, or reduce degradation of water quality due to stormwater runoff," are often used to return water directly to the ground thus bypassing the sewer system. Biofilteration, filter strips, swales, infiltration trenches, green roofs, rain gardens, natural landscaping, naturalized detention basins, and permeable pavement/pavers are among the most common BMPs (NIPC, 2003).
(See also Stormwater Best Management Practices.)