A study commissioned to assess drainage in four Sag Harbor neighborhoods—Spring and Garden Streets, the Rogers Street recharge basin, Hempstead Street near Havens Beach and Redwood Road—calls for over $1 million in improvements to allay flooding during heavy rain events.
The Sag Harbor Village Board of Trustees will host a work session on Thursday, February 6, at 1 p.m. to discuss the study. D&B Engineers & Architects, P.C.—the firm that drafted the recommendations at the request of the village board—will make a presentation during the session.
According to Sag Harbor Mayor Brian Gilbride, while the work session is public it is being hosted to give board members the ability to quiz D&B officials about the study.
“Otherwise I would view this as a work in progress,” said Mayor Gilbride. “Does it show we have a system in place that takes care of some of the rain? Yes. Is there more we can do? Yes.”
The village board commissioned the study after residents engulfed the Municipal Building with complaints about flooding during Super Storm Sandy in 2012. Addressing drainage and flooding issues in Sag Harbor was a campaign promise made by virtually every candidate seeking office in the last village election, which saw the re-election of Mayor Gilbride as well as the election of former mayor and trustee Ed Deyermond and La Superica owner Ken O’Donnell.
In September, Sag Harbor was hit with rainstorm that brought approximately 6.25 inches of rain in just a few hours. Homes in all flood-prone neighborhoods in the village were inundated with water. The Tripp family who live on Hempstead Street, next to the Havens Beach drainage ditch—a ditch that had just recently been a part of a remediation project when that storm hit—reported six feet of water in their basement.
According to the New York State Stormwater Design Manual six inches of rain in a 24-hour period is considered a 25-year storm. A hundred year storm is defined as 7.5 inches of rain in a 24-hour period. The 6.25-inch rainfall in September occurred over just five and a half hours.
The D&B study had two objectives. The first was to provide a hydrologic and hydraulic analysis of each flood prone neighborhood and the existing stormwater management systems in place. The second goal was to prepare a preliminary evaluation of alternatives to mitigate flooding conditions in each neighborhood.
The Rogers Street recharge basin has a tributary area of approximately 26.5 acres, according to the D&B report. Runoff from that acreage flows overland to the low-lying areas into an inlet structure, which runs through a 36-inch diameter pipe and into a recharge basin. That basin, according to D&B, has storage capacity for 28,000 cubic feet of runoff. A two-year storm bringing 3.5 inches of rain in a 24-hour period would create almost twice that amount of runoff at 47,436 cubic feet.
“Based on these results, the Rogers Street basin lacks the storage capacity to contain the two-year event,” reads the D&B report.
In order to increase the storage capacity of the neighborhood, D&B recommends four alternatives. The first involves adding drywells throughout the 26.5-acre tributary area. To cover the volume of storage needed for a 10-year storm, the engineers recommend 111, 10-foot diameter, 12-foot deep drywells installed within the village roadway right-of-ways. The estimated cost of this project is $1 million.
Another alternate would be to increase the size of the basin, although D&B engineers note that the only way to do that would be to obtain 0.75 acres of land adjacent to the basin and excavate to increase the storage capacity. The cost to excavate and enlarge the basin is estimated at $500,000 and does not include property acquisition.
The last alternative for this area is the construction a pump station and outfall to Sag Harbor Bay with the capacity to handle a 10-year storm. A disadvantage, notes the report, is that a continuous power supply is needed for this to be effective and storms often disrupt power. A discharge pipe to the bay would have to be constructed under Division Street. The total construction cost, before easements, would be $850,000.
Another recommendation would be to build a pump station that would feed to a new recharge basin at the intersection of Division and Marsden Street, although the village would need to purchase that property to make it a reality.
The Havens Beach watershed collects approximately 138 acres of runoff in any storm event—runoff that eventually makes its way to Hempstead Street and through an 18-inch storm sewer that leads to the newly remediated drainage ditch. That ditch flows into Sag Harbor Bay.
According to D&B’s report, during any 100-year storm similar to what occurred last September, the flood plain surrounding the drainage ditch would be totally submerged at its current elevation, reaching surrounding areas and some adjacent properties. D&B recommends adding an additional catch basin on Hempstead Street and replacing an existing 18-inch storm drain with a 30-inch storm drain to the drainage ditch to increase the ability for water to flow through the ditch. The firm also recommends an emergency overflow pipe to Sag Harbor Bay for flood protection during large storm events. Implementing those recommendations would cost $80,000.
At Redwood and Notre Dame roads, Princeton Road and South Redwood Road in Redwood, D&B recommends adding an addition catch basin and drywell to offset flooding at a cost of $15,000.
In the draft plan available as of press time, plans to address flooding at Spring and Garden streets were not included, but according to Mayor Gilbride they would be presented on Thursday.
He added the village has already reached out to grant writer Jen Mesiano to see what funding would be available to the village for drainage and flooding improvements.