WESTFIELD — The project to raise the height of the “high hazard” Powdermill Dam is one step closer to being started after the City Council approved allocating $245,094 for its design and permitting on Monday night.
“It’s undersized now and needs to be raised,” said City Engineer Allison McMordie about the dam located about 700 feet south of the city’s transfer station on Twiss Street.
The $245,094 is being combined with $950,000 of America Rescue Plan Act money already appropriated to get the city closer to meeting the 35% match — $2.135 million — needed to fund the $7.7 million federal project, she said.
McMordie said the city has yet to identify where the remaining $940,000 needed for the match will come from, but said it has a couple of years before the balance is needed.
The city, like every city and town across the nation, was facing a deadline of Dec. 31 to encumber the ARPA funds — they must also be spent before the end of 2026, which was why the council approved the allocation this week.
The Powdermill and Arm Brook dams, located about 2,200 feet apart, are a significant large part of the city’s protection from flood waters and both have been designed as a “high hazard potential” by the U.S. Department of Agriculture’s Natural Resources Conservation Service for over a decade with the potential of “catastrophic” damage if one or both failed.
The Powdermill Dam meets the high hazard criteria because it protects 363 residences, 82 apartments, 45 non-residential properties, two public properties and 19 major roads, including Interstate 90, one railroad, six bridges or culvert crossings and multiple utility lines, McMordie said.
There is also the potential for loss of life, she said.
The NRCS “conservatively” estimated that once the dam is rehabilitated it will protect at least 1,352 people living/working/driving downstream.
Over the last several years, people have been using the dam and surrounding property “as something of a recreation area … an ATV track,” McMordie said.
She said the city has been trying to limit the ATV use by placing boulders along trail lines, but the prohibited activities have continued.
In fact, the ATV track lines can be seen in Google Earth satellite images of the dam.
According to the rehab project design prepared by the NRCS, the crest of the dam will be raised about 2 feet to an elevation of 205 feet above sea level, or 49 feet above eye level. The current auxiliary spillway, which will be built within about 100 feet of the Pioneer Valley railroad spur, will be hardened with concrete and a labyrinth weir will be installed, and a concrete basin with an outlet will be installed.
The existing pond drain will be removed, which will allow Powdermill Brook to naturally re-establish through the flood pool, according to the design plan.
Once the project is finished, the flood protection will ensure that the downstream flooding level remains consistent for both a “100-year flood” (a flood with a 1% chance of occurring in any given year) and a “500-year flood” (a flood with a 0.2% chance of occurring in any given year), providing protection against significant flood events for the next 75 years, according to the design plan.
With the deadline to spend the ARPA funds by Dec. 31, 2026, McMordie said the project should start a year or two later.
The Powdermill Brook Flood Control Project, was part of a larger federal flood control project, started in 1961 and completed in 1964, according to a report published in 2021 by the city’s Flood Control Commission.
It was designed to handle a 100-year flood level storm and controls 2,894 acres of runoff, and contains 100,000 cubic yards of earthen fill, and is 47 feet above the Powdermill Brook basin.
