Yesterday, Huntley Meadows Park manager Kevin Munroe, along with staffer Elena Ryan, gave a recap of plans for restoration of the park’s central wetland. Much has changed and much has stayed the same since plans were discussed in public meetings in 2007. Since then, the commonwealth has okayed the dam design as meeting “special low hazard” criteria, reflecting projections that the impact downstream of a failed dam during a 100-year storm would be no worse than if the dam weren’t there at all. However, the county’s Department of Public Works and Environmental Services insists on a 600-foot wide spillway to the north of the dam, to mitigate the potential of the earthen structure being overtopped. Such a spillway would stretch most of the way from the observation tower to the hike-bike trail.
So Kevin and his team are (somewhat reluctantly) considering a concrete structure instead, which would provide its own spillway. They’re looking at designs and facings that would temper the aesthetic intrusion of an obviously man-made structure. Kevin showed one slide of a dam at the Patuxent reserve that looks not unattractive, to my eye.
Plans to remove and replant have also been shelved, along with dredging and construction pools. As Kevin put it, the intention is to use water levels to manage the plant life.
Elena Ryan has been looking at the relationship between rainfall and water levels in the wetland. She’s got two years of observations from a water level gauge positioned off the boardwalk on the near side of the tower. Her regression analysis tells her that for every inch of rainfall, water levels in the wetland rise 3.25 inches over the course of three days.
Kevin recapped the purpose of the restoration project with the following elevator speech (paraphrased by me): Beaver marshes move through stages of succession; one of these, the hemi-marsh, shows the highest level of biodiversity; because both biodiversity and marshlands are in decline, the Park Authority and Huntley Meadows community are working to manage the wetland to hemi-marsh conditions.
This summary introduces a term of wetland ecology new to me: the hemi-marsh. A hemi-marsh (also known as low-water marsh) is characterized as a 50-50 mix of open water and emergent vegetation. However, it’s a relatively unstable condition. Since mid-century or so, the park’s wetland has been oscillating between wetter lake marsh/high-water marsh conditions (at the extreme, a eutrophic lake), and drier wet meadow/dry marsh conditions.
Hemi-marsh conditions favor certain bird species of concern in our region, among them Least Bittern (Ixobrychus exilis), Common Moorhen (Gallinula chloropus), Pied-billed Grebe (Podilymbus podiceps), and King Rail (Rallus elegans), considered an indicator species for hemi-marsh.
After talks, we took a brief walk with Kevin in the park as late afternoon came on. Ice has begun to skim the water edges. My fingers and toes haven’t developed their winter anti-freeze yet. Northern Shovelers (Anas clypeata) and Green-winged Teal (A. crecca) have moved in for the season; most of the male shovelers are out of their eclipse plumage and are dressed for breeding already. An American Beaver (Castor canadensis) seemed more interested in his crepuscular meal than in our small party.