On May 19, stakeholders and researchers came together for a final meeting to discuss climate changes that will impact Mattapoisett Neck Road in the coming decades, as well as the more immediate need to make decisions on how best to move forward with culvert repairs. Their discussion also included conceptual designs for elevating the nearly sea-level roadway.
Presenting data and its impact on the roadway was Adam Finkle of the Woods Hole Group, who responded to a question from Select Board member Jordan Collyer asking if elevating the roadway would have a negative impact on the hydrology of neighboring parcels and if it might also create an earthen dam effect.
Finkle said that the next stage of the project is to study hydrological impacts by modeling several concepts. He said that erosion may represent a problem and that the study would also model unintended consequences related to building up the roadway slopes to achieve the desired elevation, a number yet to be determined. Finkle did state that projections indicate the roadway would experience daily flooding if not elevated by the year 2050. He said that any roadway modifications would be a balancing act between improvements and coastal areas. Finkle cautioned that there is evidence now that there are no viable plants under shrub and tree canopies, a condition that will eventually erode the existing slopes allowing more flooding occurrences.
In describing one roadway concept, Finkle said that at 7.5 feet of elevation, water would not overtop the roadway by the year 2070. He also said, however that whenever roads are built up, they also must build out, and agreements with all regulatory agencies would be needed to approve the work.
On the question of whether or not a larger culvert would benefit Molly’s Cove, Dean Audet of Fuss and O’Neil said, “There is no science in place that tells if increased culvert size would help either the cove or flooding.” He said that a larger culvert might flood areas not previously subject to flooding. “We want to make sure we don’t create erosion.”
Andrea Judge of Fuss and O’Neil offered two culvert solutions. One would include precast walls surrounding a pipe. The second would create a larger opening embedded deeper into the mud, a design that she said would benefit natural stream systems and help the wildlife. Other improvements such as drainage systems and utilities should be timed in concert with roadway work, she suggested.
Earlier in the meeting, Judge and Eileen Gunn of Fuss and O’Neil described elevation concepts. First, they said the current elevation is a mere 2.3 feet and, if left unchanged, would experience daily flooding by 2050-2070. They said the maximum height the team members had considered is 7.5 feet, a height that would provide the greatest resiliency, but again, would impact the slopes.
If nothing is done to the elevation, the teams still offered some hope. The removal of invasive plants and the addition of salt tolerant vegetation could help, they said. While sunny day flooding at high tides remain an issue, storm flooding might be somewhat mitigated.
The town has received a Coast Zone Management grant in the sum of $74,981 to complete the study and roadways concepts.
Mattapoisett Neck Road Climate Resiliency Project
By Marilou Newell