The Charles River watershed is experiencing climate change impacts, such as heavy precipitation and flooding, which can create significant damage. Weston & Sampson, along with the Charles River Watershed Association, was selected to develop the Charles River Flood Model (CRFM) to forecast expected flooding scenarios and test watershed scale adaptation strategies for 14 communities in the 270-square-mile portion of the Charles River watershed that drains to the Watertown Dam. Weston & Sampson modeled 10 different 24-hour duration rainstorms in the watershed:
- 3 present day storms: 2-year or 50% chance of occurring annually, 10-year or 10% chance of occurring annually, and 100-year or 1% chance of occurring annually
- 6 corresponding future storm scenarios: 2-, 10-, and 100-year design storm events projected for mid-century (2030/2050), and 2-, 10-, and 100-year design storm events projected by late in the century (2070/2090)
- 1 extreme rain event of 11.7 inches in 24 hours, which was used in a similar modeling effort in the neighboring Mystic River Watershed
The team also assessed the impact of six different flood mitigation strategies employing green, nature-based solutions. These include adaptation measures such as onsite storage, raingardens, bioretention basins, reduction in impervious surfaces, and others that focus on the protection, restoration, and/or management of ecological systems to safeguard public health, provide clean air and water, increase natural hazard resilience, and sequester carbon. Weston & Sampson, in association with Communities Responding to Extreme Weather (CREW), also sought extensive public input to inform the modeling scenarios and develop solutions that would work best for each community.
The CRFM represents the impacts of flooding across the watershed from various types and sizes of rainstorms under both present and future climate scenarios and can be used to test the efficacy of various flood mitigation measures. It is augmented by the online Flood Model Results Viewer, an interactive web-based GIS application to view present and future flood risks in the watershed that allows the user to see the flood mitigation benefits from an array of green infrastructure strategies.
CHARLES RIVER WATERSHED FLOOD MODEL
Weston & Sampson worked with the Charles River Watershed Association, who, using grant funding from the Massachusetts MVP program, has developed and released the first ever comprehensive stormwater flood model for the Upper and Middle Charles River watershed. The model will aid in planning for mitigation of flooding caused by increased precipitation.
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