The highly-urbanized Town Line Brook watershed contains parts of four coastal towns that were long ago developed on a former salt marsh and that continually flood during storm events. Causes of flooding in the area were believed to include tidal and stream flow restrictions and lack of adequate drainage due to the highly urbanized conditions. Impacts of flooding include water quality problems, sedimentation, damage to homes and businesses, sewer backup conditions, and increased runoff.
The Massachusetts Environmental Trust (MET) provided grant funding to study the exact causes of the flooding in the Town Line Brook area, and to propose a variety of management and engineering options to correct the problem. Previously, large amounts of study dollars had been spent that produced any number of hard engineering solutions that would cost tens of millions of dollars in infrastructure improvements. MET was hoping to find an effective solution that would not drain the public coffers.
Geosyntec's Scope of Services
MET retained Geosyntec to provide an alternatives analysis, stormwater and water quality modeling, and stormwater best management practice design for the Town Line Brook watershed. Geosyntec's first task was to develop a bibliography of all of the previous studies that had been done in order to bring all of the new members of the Town Line Brook Oversight Committee up to speed.
Geosyntec then used a Geographic Information System (GIS) and the Storm Water Management Model (SWMM) to develop a model of storm flows through the extensive urban stormwater collection system. The outcome of this was a digital representation of overflow conditions for varying water levels under different conditions. As part of our public outreach efforts, Geosyntec, along with MET and a local watershed council, hosted a public forum and a strategy session for public officials and citizens to address flooding, water quality and public access issues in the Town Line Brook watershed.
Geosyntec provided a variety of management options to MET. These included additional tide gate installations to better manage the flushing of tidal marshes, monitoring an existing tide gate to determine if its elevation settings were correct, restoration of some former saltwater marsh habitat for off-line storage during storm events, and an evaluation of whether to reconnect the nearby Linden Brook tributary to its original outlet location outside of the Town Line Brook watershed to reduce flooding. Geosyntec also produced a compressed, easy-to-understand, 10-page Action Plan that was geared towards the general public and municipal decision makers to better help them understand the benefits and drawbacks of the various options.
Geosyntec provided MET with a wide range of hard and soft engineering approach options. The MET selected the offline storage option of diverting stormwater flows over a certain level into a restored salt marsh wetland area. Geosyntec is now in the process of designing and installing this system which will greatly reduce the amount of flooding in the Town Line Brook area due to storms, minimizing the negative effects of such events on the local citizens and their property. In addition, Geosyntec was selected for a follow-on project to design and construct a wetland combined with public access features to create a multi-use wetland treatment park.
Due to our successful efforts and innovative design solutions for the flooding problem in the Town Line Brook watershed, Geosyntec was also awarded a two-year follow-up contract for community education to disseminate results of the hydraulic and hydrologic study and promote awareness of water quality and flooding issues in the watershed.