Floating Treatment Wetlands – Open Water Installations Call for Alternate Approach

According to the Environmental Protection Agency, pollution affects approximately 40 percent of our nation’s waterways, and as such is one of the country’s top environmental challenges.

Floating Wetland PlantingThe Maryland Port Administration (MPA) is committed to the stewardship of the Chesapeake Bay, including the wildlife that depends on aquatic and shoreline habitat, and is working to reduce the impact of stormwater runoff from its facilities. With limited opportunities for conventional stormwater management at their cargo terminals, they are aggressively and actively looking at emerging technologies. In particular, MPA is pursuing approaches that capitalize on their unique access to waterfront shoreline, including the installation of floating treatment wetlands (FTWs). Although this best management practice is not currently recognized by many regulatory organizations, these pilot installations are being investigated by the Chesapeake Bay Program to potentially receive treatment credit.

Port facilities and other waterfront properties that install FTWs can capitalize on opportunities not only to treat water quality, but also to improve aesthetics and increase public awareness. However, not all applications can follow the same approach. MPA has piloted installation of FTWs in two locations: a wet pond at the Masonville terminal and an open water location in Colgate Creek between the Dundalk and Seagirt terminals. Although small FTW systems are often used to enhance water quality treatment in stormwater ponds, open water installations are less common. Permitting is more complex, and setting them so they remain in place can present a challenge.

Typically, smaller FTW islands in shallow waters can be set in place with a mooring line attached to a weight allowing them to swing with the wind, similar to a buoy or boat mooring. Conversely, MPA’s long, narrow open water islands needed a different approach. While there was a potential to use attachments to shore points or bridge abutments, this was considered less aesthetically pleasing. Instead our team decided to anchor the island to keep it in place, with enough scope to allow it to shift with wind direction and rise and fall with tides and storm surges. After investigating concrete blocks for anchors, we decided to use Danforth anchors.

Floating Wetland Installation Anchors and Boat

This decision was based on several factors including their long history of use for mooring installations, their abundant availability through marine supply houses, and their significant holding power. Danforth anchors are also much simpler to set from a small boat compared to 50 pound blocks. The number of anchors used was determined based on projected wind load on the island assuming full-growth vegetation. At present, the island has withstood 40 mph wind gusts and remained in place as Colgate Creek froze over.

We’re looking forward to the results of the Bay Program’s Expert Panel report as this approach continues to gain attention. If recognized by the regulatory organizations, this highly efficient and cost-effective treatment could be a key factor in helping to improve the quality of open water systems. For more information about these open water opportunities, check out the article in our Innovator magazine.