Improving Baltimore Harbor’s Water Quality with Nature-Based Solutions

Media Coverage

Source: Civil + Structural Engineering Magazine
April 1, 2021
Improving Baltimore Harbor’s Water Quality with Nature-Based Solutions

Floating wetlands remove nitrogen from the water through the beneficial bacteria (biofilms) growing on its plastic base material and the new growth of native tidal marsh plants within that base. With roots taking up nutrients directly from the water, the intent is to use these plants to remove the excess nitrogen before it can fuel an algal or bacterial bloom.

To test the stability and resiliency of a future large-scale project, McLaren Engineering Group worked with architectural design firm Ayers Saint Gross to develop a 15-foot by 20-foot prototype living shoreline ecosystem that is currently exceeding expectations at the National Aquarium’s campus in the Inner Harbor. Experts from both the Aquarium and Biohabitats guided the development of the man-made structure by applying the sciences of marine biology, conservation planning, and ecological restoration into the design.

A major challenge with sustaining small-scale floating wetlands in the past is failure due to their long-term maintenance and short service lives. The more thriving the wetland, the heavier and more unbalanced the structure would become, causing it to tip or sink. McLaren and their project team took into consideration the lessons learned from these previous structures to design a floating wetland with inert plastic materials and an adjustable buoyancy system to counteract the accumulation of ongoing marine growth. This design solution blurs the boundaries between natural and structured urban environments, showing they can coexist and flourish together. 

The most prudent and cost-effective solution for creating stability in the low freeboard required by the plantings (highest marsh levels only extend 6 inches above water) was adding a controllable ballast system, counteracting the effects of added marine growth weight. By calculating the sinking rates from the prototype, the design team arrived at an estimated fouling load of 1.5 pounds per square foot per year, which will gradually taper off to near zero before year 10.