Pine Brook Flood Fix: Bigger Culvert, Wider Channel, $12M?

by Judy Silberstein

(February 14, 2008) Engineering consultants were at the Monday, February 11 Larchmont Village Board meeting with updates on four separate projects to reduce the volume of water rushing through the Pine Brook Drive area during storms of varying intensities.

The consultants, Ken Pritchard and Jason Tonne from Dvirka and Bartilucci, had been tasked with providing further details for four flood mitigation projects, two upstream in New Rochelle and two in Larchmont. In addition, they had studied some aspects of flooding downstream along the Premium River and met with residents from those neighborhoods.

Keeping Water to Manageable Levels

Mr. Tonne explained that the lowest-lying section of Pine Brook Drive is approximately 8 feet above sea level. In a storm, keeping the “hydraulic water gradient” below 8 feet means the water remains at grade – above that, it starts to flood the streets. The consultants found that storms likely to occur at least every two years now produce water levels of 9.6 feet – significantly above grade.

Improvements at Beechmont Lake in New Rochelle (dredging, new walls, etc.) were not expected to help retain significant amounts of water – levels would still rise to 9 feet in a 2-year storm, and close to 19 feet in a 10-year event.

By itself, diverting water from around the Chatsworth Avenue area through a new culvert at Mayhew Avenue would only lower peak flows at Pine Brook to 8.7 feet for the 2-year storm and 18 feet for the 10-year.

Installing huge retention tanks under the ball fields on Fifth Avenue in New Rochelle would bring levels at Pine Brook down to 8 feet in a 2-year storm, but they would be at 14.5 in a 10-year event.

The most effective option would be to install a new, wider culvert near the end of Pine Brook Drive. It would run approximately 1000 feet, passing under the Boston Post Road and discharging in the narrow channel that flows to the Premium River. This solution keeps water at 6.3 feet in a 2-year storm and at 10.2 in a 10-year event.

However, to keep from exacerbating flooding on the other side of the road, the consultants recommended doubling the width of the channel – and that would require purchasing all or a portion of the adjacent property, Tony’s Nurseries.

“What we do with the Tony’s Nursery property is critical,” said Mayor Liz Feld. It’s on the market, she said, but the owners are unlikely to sell just the slice needed to widen the channel. Trustee Jim Millstein noted that the 3.5 acre property could be put to other purposes. (Ball fields and parks are among uses recently discussed.)

Engineering consultant Jason Tonne, from Dvirka and Bartilucci, shows how water from New Rochelle, Town of Mamaroneck and Larchmont flows through the Pine Brook Drive culvert and into the Premium River basin on the way to Long Island Sound.

Despite reassurances from Mr. Pritchard, some residents near the Premium River were unconvinced that widening the channel would be sufficient to prevent the new culvert from making things worse for them – either from more water or more sedimentation. Mamaroneck Town Councilwoman Phyllis Wittner, who lives near the Premium Marsh, cautioned the Larchmont board to consider “the impact of that amount of water on tidal wetlands.”

“Anyone of these solutions – by itself – may create another problem,” noted Ms. Kolbert. The board is looking to find the correct combination, she said.

Finding the Funds

And of course, any option depends on a great deal of external funding to implement. The culvert/channel option alone could cost as much as $12 million, $5 million for the culvert, around $700K for widening the channel, and the rest to acquire the land.

“It’s a lot of dough for a little village,” said Mr. Millstein.

Mayor Liz Feld announced she had just heard that Congresswoman Nita Lowey had succeeded in getting Larchmont $125K from the Department of Homeland Security that could be applied to flood mitigation. Larchmont has made an additional request for $8 million (See: Pine Brook Flooding: $14M in Potential Fixes) NY Assemblyman George Latimer is working to secure as much as $30 million in state funds for the Westchester area; and Westchester County has already committed $10 million per year for flood mitigation.

Of course there will be a lot of competition for those funds from other communities. Nevertheless, Mr. Millstein said Larchmont was “way ahead of the curve” with a “very serious study” that should help in applying for these and other funds.

Getting "the dough" will require "working together" and a lot of lobbying, suggested a number of board members. That was something Jay Fisher, a Pine Brook Drive resident, was willing to begin right away. "We will make our voices heard in an organized way," he promised, "that work should start tomorrow."