The Oxbow Road neighborhood is a residential area in Lexington, MA made up of Oxbow Road, Constitution Road, and Freemont Street, and is bordered by Route 128/95. This major highway system contributes substantial stormwater runoff into the municipal drainage system with a discharge to Kiln Brook. The neighborhood has a history of severe periodic flooding during rain events, specifically along Oxbow Road and Constitution Road.
An intense summer thunderstorm in 2017 produced 2.5 inches of rain in merely forty minutes and resulted in significant street flooding and drainage surcharging throughout the neighborhood. This incident was a catalyst in leading the Town to hire Environmental Partners in 2017 to evaluate the existing drainage system through modeling with the goal of creating a long-term solution to this damaging problem.
Drainage Study & Modeling
Field investigations were carried out with the critical objective of providing data to develop a detailed stormwater model. The work delineated the boundary of the watershed that contributes stormwater to the Kiln Brook outfall and identified drainage connectivity and maintenance issues. While EP determined the depths and condition of critical manholes throughout the drainage system, a subconsultant conducted pipeline inspections using closed circuit television methods.
Using results from field investigations, EP updated the Town’s drainage system GIS data and incorporated this information into a drainage system hydrologic/hydraulic model. Additionally, advanced GIS-based stormwater modeling software, PCSWMM, was used for this study to allow for a more detailed watershed and drainage analysis.
After the 2018 completion of the Oxbow Road Drainage Study, EP recommended a series of drainage improvements to address the problematic flooding conditions along Constitution Road, Oxbow Road, and Freemont Street. Additional recommendations suggested that the work be divided into multiple phases due to the invasive extent of construction and associated costs including:
Phase 1 – Kiln Brook Outfall & Stream Restoration
Phase 1 would allow for the later upstream enhancements of Phase 2 to increase hydraulic capacity of the existing drainage system and mitigate flooding of the roadways and residential areas.
The design of Phase 1 improvements included daylighting approximately 175 linear feet of existing drainage pipe, wetland restoration, and increasing the size of upstream drainage structures within Constitution Road. EP supported the Town in procurement of the box culvert and custom drainage structures to allow for 2021 construction. Phase 1 was bid in June of 2021 and construction has reached substantial completion. Final completion will conclude in Spring 2024 with final wetland plantings and site restoration.
Phase 2 – Oxbow Road Relief Drain
The goal of Phase 2 is to mitigate the flooding associated with existing hydraulic limitations along the Oxbow Road/Constitution Road drainage network. The improvements include installation of a 36-inch relief drain to improve hydraulic capacity of the drainage system and improvements to the inlet drainage piping and headwall. Permitting and Final design was completed in Summer 2023 with construction beginning Spring 2024. Upon completion of Phase 1 and 2, residents of the Oxbow Road neighborhood will face reduced occurrence of nuisance flooding events.