WILLIAMSBURG — On Aug. 30, the Healey-Driscoll administration announced the town was awarded a Municipal Vulnerability Planning grant of $682,085 to study the Mill River watershed. The award was the largest among $31.5 million in grants for this round of the program.

According to Gaby Immerman, chair of the Mill River Greenway Committee, a stakeholder, the study will include some very cool modeling.

“Engineers will perform something called a hydraulic and hydrologic study,” Immerman said. “It measures the shape of the banks and the volume of water that the riverbanks can hold, and the conditions of the bottom of the streambank. It measures that volume and builds a model of the river system, so that then you can ask the model to show you what would happen if there was a five inch rain storm.”

Cataclysmic rainstorms are becoming more common, but road maintenance on Route 9 may also have prompted the award. The state road is in line for planned maintenance. Immerman said that every 20 to 30 years the Massachusetts Department of Transportation grinds off the pavement and refurbishes the drainage system of numbered state roads. Gaby’s committee sought to incorporate the 10-foot wide greenway path, the primary goal of the committee, into the work to be done.

Immerman was an original member of the Greenway Committee, which was established in 2009. Back then, committee members joked they might be able to get MassDOT to build the path by 2025. The planned maintenance of Route 9 probably won’t take place until 2025 or 2026, though that has not been finalized, Immerman said. At that time the path may also be laid out and built.

The weather cooperated last month when the severity of flooding after a storm caused enough damage to draw Gov. Maura Healey out to Williamsburg to survey the devastation. Many influential circumstances aligned to bring the planning grant to Williamsburg, according to Town Administrator Nick Caccamo. Some of the groundwork was laid when the goals of the watershed modeling and survey were identified in a report released in 2020.

“The long range will be understanding what the watershed really is, given the growing impacts of the climate crisis, and how substantially they will affect Williamsburg,” Caccamo said. “Are we building for a 100 year flood, a 1,000 year flood, things like that. It poses some potentially critical planning efforts as MassDOT is engaging with significant construction projects around the Mill River … including the Bridge Street project, the presumed reconstruction of Route 9 and the Mill River Greenway.”

The grant funding will be distributed over two years, roughly half each year, with fiscal year 2024 being year one. The research and planning will also be parsed around two focal efforts. The first will be to understand the Mill River and its drainage rates. The second focus will be to understand the forests and lands in the higher reaches of the watershed and how they can reduce cataclysmic flooding.

How can forests retain more water? Immerman said the town’s vulnerability to flood damage can be reduced in two basic ways. The first is to make the downtown corridor, bisected by the Mill River, more resilient in the face of fast rising waters. The second is to increase the watershed’s ability to hold water, to slow drainage into the downtown corridor.

Two actions of forests, capturing carbon and retarding runoff, both work to stabilize the watershed.

“One is carbon sequestration, they are a sink for carbon, taking carbon out of the atmosphere. And the second is, they serve as sponges that catch and hold and filter stormwater, so that it goes into river systems more slowly,” Immerman said. “It slows down the movement of water.”

Williamsburg is the lead town on the planning grant because it fits snugly into the watershed. While the boundaries of the watershed exceed the town lines with Ashfield, Goshen, Chesterfield and Westhampton, the vast majority of the Mill River watershed drains out of Williamsburg.

Several well known area firms will handle the design, research and planning financed by the grant. Vanasse Hangen Brustlin will perform engineering services while Dodson and Flinker complete conceptual designs for infrastructure projects. Hilltown Land Trust is scheduled to draw up conceptual designs for landscape conservation projects.

Immerman, also on staff at the Smith College botanical garden, has been with the effort to build a mixed use path connecting the two village centers in Williamsburg for about 14 years. Now, a start date may well be in sight.

“We got that conversation started with [MassDOT] long enough ago that we have successfully incorporated this vision for the Mill River Greenway into the DOT’s planned rebuild of Route 9,” Immerman said. “We started this committee in 2009. We’re a pretty scrappy bunch, that’s for sure.”