March 30, 2006

3 advances show the future of site development

SvR Design Co.


Amid recent advances in sustainable design and construction, one issue many are facing is how to make these new approaches and materials common practice.

Three key advances in site development include rainwater harvesting, soil amending and permeable pavements.

The success of these advances in design and permitting is exciting. However, implementation needs to be improved or the industry could see roadblocks as it seeks to move sustainable site design to standard practice. As with many advances, acceptance comes down to evidence that these techniques will prove effective and result in lifecycle cost benefits.

Rainwater harvesting

Photo courtesy of SvR
Porous pavement is gaining wider acceptance in Washington. Seattle's High Point neighborhood is home to the city's first residential porous-pavement street, at 32nd Avenue Southwest.

More public-sector agencies are harvesting rainwater, incorporating cisterns into their building designs to gather and reuse water for toilet flushing and on-site irrigation during the spring and summer. With the appropriate rainwater-storage system, a building's water consumption rate can drop by up to 80 percent.

Rainwater harvesting should gain traction if Washington state's House Bill 1735 passes in 2007.

The bill would remove permit requirements for capturing less than 1,000 gallons of rainwater, and will set the processes to govern collections of more than 1,000 gallons. If the bill passes, pilot projects will be required, and the state Department of Ecology will have a say in its case-by-case implementation.

Soil amendments

Amending the soil, which is widely used in landscaping and erosion control, could have a net-beneficial impact in helping attenuate water runoff for urban developments.

This practice involves adding organic material into compacted soils to improve the ground's ability to absorb rainwater. As jurisdictions such as Seattle and Portland prove the benefits of this practice through monitoring, amending soils will likely move from an "add on" to a legitimate technique to manage stormwater runoff, and owners will receive credits for its use.

To enhance the effectiveness of attenuating water through the technique of soil amending, the designer and contractor should discuss the sequence of the amending and construction techniques to avoid unneeded compacting, which could defeat the purpose of soil amending.

Porous pavement

Porous cement concrete pavements, which have been used mostly in the Southeast, are gaining acceptance in Washington. These pavements provide water-quality treatment and stormwater management within otherwise hard-surface areas.

While this pavement is used more frequently in private applications, the city of Seattle recently completed the first public residential street in the state. Several recent trends are contributing to its rise in use.

First, the National Ready Mix Association has recently developed a pervious concrete contractor certification program to improve quality control for design and installations.

Second, standardized methods for post-construction testing, specifically for porous cement concrete pavement, are being developed by the American Concrete Institute. This testing will help the public sector accept the material as appropriate for the long lifecycle requirements of public infrastructure and provide an indication of desired infiltration performance.

Third, jurisdictions throughout our region are beginning to revise their drainage codes to provide stormwater flow control and treatment credits for developers that use porous cement concrete or other permeable pavement applications. In addition, some jurisdictions are revising their monthly drainage fees to include credits for sites that have replaced impervious pavements with porous or permeable pavements.

The quality of the installations will improve as industry standards are developed and jurisdictions articulate and implement the credits to be received. The result will be a visible improvement in stormwater management and health in Northwest waterways.

Improving communication

The heavy construction industry is progressing but has a ways to go toward understanding the intent behind key aspects of sustainable site design. Meanwhile, the designers have a ways to go toward effectively communicating the intent behind their designs.

For example, a bioretention area usually gets cut during the first phases of construction. Often, sediment-laden rainwater is directed to these areas. This limits the effectiveness of the bioretention areas as stormwater filtration and attenuation devices.

Ideally, these bioretention areas are covered and kept in pristine condition. As designers, we need to better communicate our intent to the contractors so the installations will meet the goal.

Standard site construction practices do not work effectively with sustainable site construction. Contractors and designers should work together to address sequencing, soils, vegetation and installation of permeable surfaces. Controlling flow and erosion at its source is a new method and philosophy — it is not simply an issue of achieving compliance.

Peg Staehel is a principal of Seattle-based SvR Design Co., a civil engineering, landscape architecture and restoration firm that specializes traditional and sustainable planning, design and construction administration.

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