In 1999, work began on securing the required environmental permits and approvals for the Phase II bioengineering projects. The Massachusetts Natural Heritage and Endangered Species Program (NHESP), one of the regulatory agencies involved in the permitting process, had documented one of the Phase II sites as potential habitat for the Cobra Clubtail dragonfly (Gomphus vastus), a Species of Special Concern in Massachusetts. Pursuant to the Massachusetts Wetlands Protection Act regulations, any work done within the estimated habitat for rare wetlands wildlife is to have "no short- or long-term adverse impacts" on the habitat. NHESP's concern was that the bank stabilization projects could potentially impact the Cobra Clubtail dragonflies if the shoreline habitat where the nymphs transform into adults was altered. NHESP recommended that pre- and post- construction surveys be conducted to evaluate the impact of bank stabilization on the habitat of Cobra Clubtail. The local Conservation Commissions have incorporated this NHESP recommendation, as well as others related to rare dragonfly species, into the Orders of Conditions issued for construction at the Phase II sites.
The consulting firm A Natural Focus
, was hired to conduct the pre- and post- construction surveys.
In 2001, a pre-construction survey was conducted at the first Phase II site to document the number and species of dragonflies emerging at the site. In subsequent years, pre-construction surveys were conducted at 5 more Phase II sites. Following construction of each site, surveys were conducted on an annual basis to document the number and species of dragonflies emerging at the site, to observe the patterns and behavior of the emerging nymphs, and to assess the effects of bank stabilization on the insects. This ongoing study also includes several reference sites within the Turners Falls Power Pool. A total of 18 dragonfly species have been documented in this reach of the Connecticut River, including 8 that are listed by the state of Massachusetts as either Species of Special Concern, Threatened, or Endangered.
Five species of dragonfly, including 2 listed as Endangered Species and 1 listed as Threatened, emerge from the water as nymphs and shed their pupal skins at or very close to the first vertical surface they encounter. Dragonflies are soft for the first half-hour after emerging from their skins and are at risk of being injured or killed by waves from passing boats and rapidly fluctuating water levels. Until their bodies harden and their wings dry, they cannot move further up the bank. At the bioengineering sites, the first vertical surface the dragonflies encounter is almost always a piece of angular rip-rap. Dragonflies that emerge at or very close to the waterline are at significantly higher risk of injury or death on a rip-rapped bank than on a natural bank.
Based on the number of injured and dead dragonflies observed in 2002 and 2003, the consultant recommended the following:
Cover the rip-rap with a layer of sand and gravel. Where this happened naturally along a short stretch of rip-rap, the nymphs of the five vulnerable species of dragonflies tended to climb farther up the bank instead of shedding their skins close to the water line.
Use rock of multiple sizes, with enough large stones to secure the bank and with sufficient small rocks to create a gradual slope that would allow the nymphs to crawl beyond the 18-inch "splash" zone created by boat wakes.
Changes to Bioengineering Designs
A smaller size of rip-rap (1- to 3-inch diameter) was used on a shallow slope at the Durkee Point site. The survey data indicated that the 5 vulnerable species of dragonflies crawled farther up the slope, beyond the "splash" zone, before shedding their skins. However, using smaller rip-rap does not always protect these species. At another Phase II site where smaller stone was used (2- to 4-inch in diameter), the consultant found that during low water levels, a sandy beach was exposed below the rip-rap. The emerging nymphs had to crawl several feet to reach the rip-rap. Most of them shed their skins at the base of the rip-rap and were vulnerable to injury or death from boat wakes and rising water levels. In future years, additional survey data from this ongoing study may provide more insight as to how the bioengineering designs can be refined for this reach of the Connecticut River.