Stormwater Quality and Quantity
The most obvious benefit of conservation design is the positive impact on stormwater quality and quantity. All the principles of conservation design contribute to improving this indicator. Site design that "clusters" lots together, leaving larger continuous open space, allows for natural drainage and cleansing of stormwater before it is introduced to conventional infrastructure. By design, more environmentally sensitive areas can be left undeveloped, as open space. This can include isolated streams, wetlands, high quality woodlands and prairies. Cluster design is most often seen in suburban or rural settings (The Nature Conservancy and Chicago Wilderness).
Natural landscaping can improve stormwater quality and quantity because of its deeper root system. Deep root systems stabilize the surrounding dirt which helps minimize erosion and sedimentation into waterways increasing water quality while also increasing the permeability of compacted soils. Healthy soil can hold more stormwater runoff, thus diverting it from the sewer systems while recharging the aquifer (NIPC, 2004). In addition deeper root systems require less water to maintain a healthy growth. Natural landscaping also uses less pesticides and fertilizers (NIPC, 2003). The U.S. EPA estimates that nearly 70 million pounds of active pesticides ingredients are applied to urban lawns each year with an average acre of lawn receiving 5-7 pounds of pesticides annually (The Stormwater Manager's Resource Center). These pesticides often find their way into waterways potentially through urban runoff or groundwater infiltration (NIPC, 2004). For more information visit: http://www.epa.gov/pesticides/
Reducing impervious surface areas also improves stormwater quality and quantity. When precipitation falls on parking lots, rooftops, streets and sidewalks instead of soaking into the ground at the point of impact, the water is diverted into a sewer system. En route to the sewer system, the runoff or discarded precipitation picks up pollutants, including car oil and gas as well as debris in the path of the runoff, compromising water quality (NIPC, 2003).
Incorrectly designed impervious surfaces can cause flooding and stream channel erosion. In bigger storm events, the quantity of stormwater can also be a problem. Large amounts of water rush into the sewer and natural water systems overwhelming their capacity. If there is less impervious surface, there is less runoff to be managed and a reduced quantity of water to be diverted into these systems. Reduced runoff into the sewer systems saves energy due to decreased pumping and treatment (NIPC, 2004). Conservation design helps alleviate these issues by promoting narrower streets, reduced driveway length, green roofs, and alternative walkway and parking lot design, and promotes the use of permeable pavement and pavers that allow water to pass into the ground onsite (NIPC, 2004).
Lastly, implementing sustainable stormwater management techniques will have a positive effect on stormwater quality and quantity. These techniques are similar to those used to reduce impervious surface and include green roofs, bioswales, rain gardens, native landscaping and naturalized detention basins (The Nature Conservancy and Chicago Wilderness). On a larger scale, developments can tie all these techniques together in what is called an urban runoff mitigation plan. An urban runoff mitigation plan is a permanent structural solution to managing the maximum amount of stormwater onsite (NIPC, 2004). All of these techniques address water quality and quantity in some form.
(See also Stormwater Best Management Practices.)
Implementing the principles of conservation design can potentially increase biodiversity and thus have a positive effect. Conservation design promotes the creation, retention, and management of open space. This open space creates a habitat for many different ecosystems with wide varieties of animal and plant species. By preserving open space, biodiversity is also preserved (NIPC, 2003).
A simple definition of "biodiversity" is "biological diversity" (Chicago Region Biodiversity Council, 1999b). More so, "biodiversity" is the entire array of genes, species and ecosystems in a region. Biodiversity can be measured numerically, but it can also be measured by the variety of natural communities that exist side by side in any given area (i.e. the number of wetlands, meadows, and savannas in close proximity to each other) (Chicago Region Biodiversity Council, 1999a).
There are six principles to remember when using conservation design to create more biodiversity. First, open space that has already been preserved or marked for conservation has to be managed so that biodiversity is protected or restored. Second, preserving larger parcels of open space increases the potential for larger, more varied habitats. Third, water resource management policies should be developed and implemented, as proper water resource management promotes the sustaining of natural communities, therefore promoting biodiversity. Fourth, more research is necessary if we are to fully understand the effects of development and/or ecological restoration on biodiversity. Fifth, citizens should be better educated on biodiversity and its importance in our lives. Finally, local and regional development policies should place higher priority on the preservation of open space, natural areas, and biodiversity (Chicago Region Biodiversity Council, 1999b).
The northeastern Illinois region, like other regions nationally and globally, contains diverse animal and plant species (Daily, 1997). Increased biodiversity is important, beyond its aesthetic appeal and recreational opportunities, because society is dependent on healthy and productive ecosystems.
Air Quality and Greenhouse Gas Emissions
Conservation design improves air quality and reduces greenhouse gas emissions, which are shown to be a cause of climate change. Although reducing greenhouse gas emissions is a very complex problem that needs thoughtful and wide-reaching answers, we can start by addressing the design of our buildings and communities. Construction and modern lifestyle trends are very energy reliant and therefore very fossil fuel reliant. One way conservation design seeks to relieve a portion of this energy use by opting for implementation of natural landscaping that reduces maintenance and naturally cleans the air.
Replacing conventional landscaping (turf grass) with natural landscaping reduces greenhouses gases by requiring 90% less maintenance (Illinois Green Government Coordinating Council). Landscaping maintenance equipment (mowers, weed edgers, leaf blowers, etc.) are powered by gasoline, electricity or battery, all which have either direct or indirect green house gas emissions including carbon monoxide (CO), carbon dioxide (CO2), nitrous oxides (NOx), sulfur dioxide (SO2), VOCs (volatile organic compounds) and air toxins such as benzene. Gasoline lawn and garden equipment account for up to 5% of ozone-forming VOCs in areas with smog problems (USEPA, Green acres).
"Each weekend, about 54 million Americans mow their lawns, using 800 million gallons of gas per year and producing tons of air pollutants." On an annual basis one gas mower emits 87 lbs. of CO2 and 54 lbs. of other pollutants into the air and over its life produces as much air pollution as 43 new cars, each being driven 12,000 miles (People Powered Machines).
Even the often accidental spillage of fuel while performing lawn maintenance has also become part of the problem. "The EPA estimates that 17 million gallons of fuel, mostly gasoline, are spilled each year while refueling lawn equipment. That's more than all the oil in spilled by the Exxon Valdez, in the Gulf of Alaska (People Powered Machines)."
In addition to cutting back landscaping maintenance, conservation design's use of natural landscaping provides an additional service as well. "Native plants help to reduce the amount of CO2 in the atmosphere by taking in CO2 and storing the carbon in the body of the plants, roots and soil. Native plants work much better than traditional mowed grass as a carbon sink due to their extensive root systems and increased ability to retain and store water (USEPA, Green acres)."
The effects on energy consumption by implementing conservation design are somewhat unclear. Conservation design strategies such as maximizing natural areas and minimizing paved areas can lead to a reduction in the overall ambient temperature, lowering cooling costs in the summer (Wade, 2000) (Stone, 2001). In addition conservation design often results in the preservation of trees which, in addition to lowering temperatures in the summer, can act as windbreaks that reduce heating costs in winter (McHenry County, 2008). Local sources state that the use of sustainable stormwater techniques reduces stormwater amounts that enter the sewer system which saves energy used for pumping and treating the additional water.
More directly, conservation design tends to encourage the clustering of dwellings, which has a number of energy benefits. For one, necessary infrastructure is reduced, indirectly reducing the energy consumed in the production of the materials used in that infrastructure, as well as the fuel expended in its construction. With clustering, fewer street lamps are required, and the energy necessary to light the community should be reduced. Energy normally lost traversing longer lengths of electrical wire, or fuel wasted driving longer distances within a subdivision, can be saved by clustering dwellings together, shortening distances and increasing efficiency (NIPC, 2003).
But a lingering reality of conservation designed subdivisions is that they tend to be built in greenfield areas that already possess the most attractive natural lands, have the greatest potential for the reintroduction of natural areas and systems, or where land is simply the least expensive (NIPC, 2003). Not surprisingly, this tends to encourage conservation designed developments that are farther from traditional centers and public Transportation, contributing to greenfield development and greater dependence on the automobile, increasing VMT (Vehicle Miles Traveled)—and therefore increasing energy consumption.
With this in mind, Prairie Crossing was created next to a commuter rail station that is heavily used by the majority of the community's residents who work in downtown Chicago. But this tendency for conservation design to be located in or beyond the exurbs is problematic and underscores the need for the creation of conservation developments in pre-existing urban and infill areas, near traditional commercial and civic centers, and public Transportation.
But perhaps the greatest reductions in energy consumption are gained by the fact that those who build and want to live in conservation design developments tend to be adherents to green design and methods of construction. Often beginning with materials created with less energy than conventional materials, wise green design can yield significant reductions in personal and community energy consumption over the long term. For example, homes at Prairie Crossing are models of energy efficiency, resulting in approximately 50 percent less energy use for heating and cooling than conventional homes (NIPC, 2004) (Town of Cary, 2000).