June 28, 2007

Study your options when banking or reserving wetlands

  • The city of Bothell is looking at restoring or enhancing 12 acres of wetlands in Thrasher’s Corner to offset development on other wetlands.

    Images courtesy of Arcadis
    The city of Bothell is studying the bank approach, top image, and the reserve approach for a wetland restoration at Thrasher’s Corner.

    When the state of Washington was planning the design and construction of the collocated University of Washington/Cascadia Community College campus in Bothell, it became apparent that even the best building and facility layout would negatively impact about six acres of wetlands. While federal, state and city regulations required that these impacts be mitigated, the state went beyond the letter of the law and restored the structure and functioning of the entire North Creek riparian ecosystem on the site.

    Five years later and approximately a mile upstream, the city of Bothell is targeting the Thrasher’s Corner area for a restoration of its own. The city recently hired Arcadis and Steve Winter at ESA Adolfson to develop a conceptual restoration plan.

    A changing site

    Thrasher’s Corner in Bothell is a place to live, work and play. The property targeted for restoration is home to chinook and coho salmon, and a foraging ground for bald eagles and other raptors.

    Thrasher’s Corner looks and functions very differently today than it did before Bothell’s population boomed. Increased urbanization has changed the flow patterns in North and Filbert creeks, and will likely continue to change the flow patterns as development continues. On the property itself, years of use as a dairy farm have altered the ecosystem, allowed nonnative plants to encroach, and reduced habitat quality for local wildlife.

    The challenge

    In a region where land is increasingly scarce, habitat restoration can be vitally important to growth and development. The Thrasher’s Corner habitat restoration work is an example of this. To keep up with the influx of people and the demand for services, the city has planned a number of capital improvement projects, some of which are likely to result in unavoidable impacts to waters or wetlands. Federal, state and city regulations require that these impacts be mitigated in order to move forward with the city’s proposed projects.

    To ensure that wetlands-related issues don’t hamper the completion of these important improvement projects, scientists and city leaders are investigating approaches at Thrasher’s Corner that will address current mitigation needs. This will allow near-term projects to proceed while the city works to meet future growth and development mitigation demands.

    Improving wetlands

    In the past, mitigation work often focused on developing new wetlands to replace those that were impacted by projects. But with increasing demands on available land, the city is looking to restore area and function to the existing degraded wetlands at Thrasher’s Corner.

    Previous examination of the property indicates that approximately 12 acres out of about 30 total acres of on-site wetlands could be restored or enhanced. To determine how to get the most functional improvement from these 12 acres, scientists will apply the hydrogeomorphic (HGM) approach on the property.

    The HGM approach is a federally supported, reference-based functional assessment model that provides a rapid and efficient means of quantitatively evaluating changes in ecosystem functions. Changes are calculated based on existing site conditions as well as projected post-restoration conditions. This approach offers an objective mechanism to demonstrate functional changes that may result from various design alternatives.

    Scientists are conducting a survey of the Thrasher’s Corner property and will follow with a comprehensive restoration design report. This report will identify what actions can be performed to improve ecosystem function and will examine whether these actions, given current state and federal regulations, will be sufficient to meet the city’s short- and long-term mitigation needs.

    To bank or to reserve?

    Applying good science is only part of what will eventually decide the success of the Thrasher’s Corner habitat restoration project.

    In concert with their on-the-ground work — or in-the-water work, as the case may be — researchers are also working to identify the administrative, cost and regulatory implications of how to best manage the mitigation offset potential of the project.

    The question is should the city create a mitigation bank or a mitigation reserve.

    The bank approach typically involves conducting a large-scale habitat restoration/improvement project. The benefits of such a project would be calculated using the HGM approach and then “banked.” These banked benefits, or credits, could then be spent by the city as necessary to mitigate the effects of capital improvement projects on waters or wetlands.

    The reserve approach, on the other hand, involves conducting smaller-scale restoration/improvement projects over time as necessary to meet the mitigation demands of the city’s capital improvement projects. These smaller-scale projects would be detailed in a comprehensive long-term restoration plan that balances the city’s projected mitigation demands with the mitigation potential of the Thrasher’s Corner property.

    Arcadis’ habitat restoration projects are not always stand-alone activities like those at Thrasher’s Corner. Often, habitat restoration specialists work side-by-side with engineers and researchers in the development of integrated projects.

    Engineers and scientists, for example, can combine disciplines to integrate aquatic habitat restoration into complex sediment management projects for ports and other waterfront facilities.

    Patrick Keaney is the business unit leader for the Arcadis BBL Specialty Services Business Unit. He is a senior vice president at Arcadis and sits on the firm’s Priority Board and Bellevue Foundation in the Netherlands.

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