The sophistication of land development is a far cry from the primitive methods of the past. In green building, terms sometimes get muddied. For example, in this article we’ll discuss both sustainable development and Low Impact Development. First let’s clarify the definition of LID.
LID focuses specifically on how water enters, is stored on-site and leaves a site. LID practices, which continue to evolve, apply several methods to reduce resource waste, runoff and potential pollution. These include minimizing impervious surface, protecting and enhancing native vegetation and soils and managing stormwater at its source—not treating it as someone else’s problem.
Low impact development has benefits for every party involved, including the silent parties (wildlife). The more we learn about wetlands, the more critical their role in the entire ecosystem. Protecting and even restoring them with LID helps to preserve wildlife habitat and decreases stormwater runoff and erosion that can cripple or destroy aquatic systems. Using less water, energy and natural resources, and avoiding toxic chemicals prevents pollution, reduces waste and decreases the strain that we place on the environment
Development that incorporates LID minimizes impervious surfaces, protects and enhances native vegetation and soils and manages stormwater at its source. These practices have evolved in the past two decades, to include carefully siting buildings, minimizing impervious surfaces and infiltrating runoff. And that evolution didn’t happen by accident.
Mistakes of the Past
Low Impact Development requires smarter decisions during planning, design, permitting and construction, and these sometimes involve upfront investments. If they’re not already doing so, it’s likely that municipal and county planning officials in your region will require the use LID or environmental site design (ESD), in part because of mistakes of the past. In the late 1980s and booming 1990s, especially, poor handling of storm runoff caused ever more damage to wetlands, channels and natural assets such as rivers. On a national scale, runoff-related events such as the “dead zone” in the Gulf of Mexico have given localized storm water control more urgency.
Previously, developers would control stormwater by building a pond or a detention type system as a sort of “purgatory” to hold the estimated difference between pre-development runoff and post-development runoff. Then the developer (or whoever ended up in charge after construction was done), would release that stormwater over a longer period of time, to match the pre-development peak rate.
This may sound rational, but that’s not how nature works. In the natural environment, there would be a momentary peak rate in the stream channel, not a sustained one. So, by releasing the retaining pond water at peak level over many more hours or even days, soils and natural barriers can’t handle the stress. That erosive energy creates excessively wide stormwater channels and disrupts the natural flood plain.
But those outward erosion signs only hinted at the deeper ecological damage. Aquatic habitats and sensitive wetlands were severely compromised. In part, this is because erosion often has a cascading effect. One problem leads to others. For example, stream erosion often causes formerly buried sewer pipes to be exposed, resulting in pipe breaks that sends sewers overflowing into the stream.
Also, because of stream bank erosion, trees fall at the top of the bank into the channel during a flood event. As they hurtle downstream, they bang into exposed pipes and manholes, causing more breaks. This process not only causes raw sewage overflows--it also upsets the wastewater treatment process downstream and robs the sewage collection system of capacity.
How Does Nature Do It?
As the description above suggests, changes had to be made in how development handles stormwater. So LID changed the discussion, beginning with the premise that water management has to closely replicate natural hydrologic systems.
For example, in an undeveloped site, plants, soil features, topography and solar energy combine to address flood events. Water is purified, redirected, and evaporated, not simply trapped in pipes and underground detention basins. It also has a chance to replenish aquifers this way.
With LID, for example, instead of one large pond which discharges stormwater, the plan includes multiple micro-facilities on the landscape and multiple points of entry for runoff. These include porous pavement, pavers that allow infiltration below them for both walkways and roadways. Green roofs are another option, still fairly uncommon in the U.S., they’re rapidly gaining acceptance in Asia and parts of Europe. Arguably of even more importance is the growing science of bio-retention--using plants and natural landscape features to slow, filter, absorb and otherwise manage storm events.
One key to successful bioretention is that the developer and affected homeowners adjust their pre-conceived ideas about their local landscape. Too often, lawns and other managed (i.e. fertilized, mowed and watered) landscape features are used in places where a wetland or natural system of wild grasses and swales might be more appropriate for water management. This is especially true in planned communities and rental properties, where landlords tend to terraform the landscape for lawnmowers, not people or gardens. But a less conventional hillside with swales, or natural wetland with 4-ft. tall grasses, frogs and dragonflies can do a lot more to mitigate runoff damage.
Pollutants in stormwater runoff have been regulated under the Clean Water Act since the 1970s, but it took until the 1990s for a permit program to be developed by the EPA. Typically, water quality can be compromised by numerous point-source pollutants. Consider the typical water treatment utility, trying to control municipal and industrial wastewater treatment plants, outdated, leaking septic systems, fertilizer runoff from farms, and urban stormwater laced with heavy metals and petroleum byproducts. It’s clear that that planning must be done more regionally, balancing all sources of pollution likely to enter the nearest watershed.
For example, a watershed based approach has been required in the 64,000-sq.-mile Chesapeake Bay watershed since December 2010, when the EPA developed a Total Maximum Daily Load (TMDL) for nutrients and sediment in the Bay.
The TMDL is basically a pollution “diet” for the Bay-literally measuring the pounds of nitrogen and phosphorus--and tons of sediment--that can be discharged from all sources per day. The upper threshold is “fishable, swimmable” water quality requirements of the Clean Water Act.
It’s important to note that the TDML didn’t come about by accident. The EPA’s action followed a suit by the State, along with sport fishing associations and Bay advocacy groups. They had become concerned by the growing anoxic zone (deep water areas without dissolved oxygen) in the Chesapeake Bay. As described above, this dead zone condition exists in many water bodies across the nation, including the Gulf of Mexico the Great Lakes, San Francisco Bay and the Puget Sound. These areas will surely be next to prepare Watershed Implementation Plans (WIPs), which serve as a blue print for how states and local jurisdictions will reduce nutrients and sediment from all sources, including stormwater, in order to achieve the TMDL.
It’s not enough to simply adopt LID principles for future developments. There’s a lot of old damage to undo. Clearly, no developer is going to revisit a built out subdivision and redo the landscape plan without a potential profit incentive.
One such incentive might be changes an area’s allowed density. Many municipalities, which realized too late the ongoing, hidden costs of suburban sprawl—maintenance, school bus service, road maintenance, etc.), might be happy to revisiting such neighborhoods and reconsider restrictions on neighborhoods or planned communities with existing infrastructure--roads, transit systems, water and sewer, and--to some extent--storm water management.
As an added benefit, redevelopment allows urban planners to look at how connected and pedestrian-friendly the existing developed areas of an area are. They may be able to improve transit modes and reduce pollution on that front as well. It’s also a chance to measure the environmental impact of existing buildings, and adjust the landscape for stormwater management. As density is added to a community, residents are likely to see the value of retrofitting their existing homes to improve energy efficiency and reduce water waste.
A Water Conscious Future
The days of the sprawling greenfield development appear to be waning. New development will occur on a smaller footprint, using the landscape for open space that has multiple functions--urban tree canopies, storm water management, native habitats and walking trails.
Is it going to be complicated? Yes.
But jurisdictions are now looking to modify their ordinances and building codes to eliminate the barriers to implementing LID. At the same time, more building codes are adopting the international green standards and allowing tax incentives and priority expedited review for projects that are pursuing green building certification.
And regulators have begun to add new layers to this already complicated process. For example regulations have begun to specify how much sediment can enter waterways.
Sediment from construction sites has been regulated under the Clean Water Act since the 1990s, but implementation and enforcement has been uneven across the country. The recent development of an effluent limitation guideline (ELG), including an effluent sampling requirement and a turbidity limitation (currently stayed) are indications that construction site sediment controls are on the way. These may require ongoing monitoring and maintenance.
You can find pdf files of some good guide books on LID online, most of them published by the EPA. Although they tend to be a few years old, they provide a good basic primer on the most common LID techniques. We’ve included links below.
Eco-sensitive landscape design isn’t just a fad. Increasingly, it’s becoming the norm. And applying the widely tested and simple techniques of LID are one way to stay ahead of regulators, at the same time protecting local rivers, aquifers and ponds.
To view this article as it appears in our March 2012 issue, with sidebars and resource information, please visit our Magazine Archive.