By Tom McDermott
On May 17, Ramboll Americas Engineering Solutions presented its Blind Brook Flood Resiliency Report to the City Council in what was deemed a “Work Session”. It was the Council’s opportunity to talk to the experts and ask questions. Earlier, Ramboll had held sessions for “stakeholders” to gather input for their report; residents will have future opportunities to ask their own questions of the Council and the consultant. Ramboll has focused on the Blind Brook Watershed flooding issues only.
The presentation, which is available on the City’s website, was comprehensive and complicated, reflecting the nature of Rye’s flooding problem. Flood mitigation involves several jurisdictions both upstream and downstream and various neighborhoods and districts within Rye’s own borders, state and federal bureaucracies and funding, and much permitting. Not to mention a potential two billion gallons or so of water hurtling downstream from the impervious Westchester County Airport, and beyond.
Mayor Josh Cohn may have had good reason to say, in his opening remarks, that these were “first steps and early days.”
Two of Ramboll’s stated goals were to review the project’s objectives during the initial “screening” phase and discuss Blind Brook’s characteristics. Main objectives are to identify projects that would be most meaningful to the community and to prioritize projects with the most potential to be funded and constructed. The two-pronged approach involves hydrologic measures to reduce flow and local measures which focus on infrastructure and resiliency.
Ramboll expects the next “refinement” phase of the project to be completed in July.
The consultant is using revised rainfall estimates, including 9.03 inches for a 100-year event (Hurricane Ida was 8.7 inches), 6.41 inches for a 25-year event. The 100-year rainfall would result in an estimated 925,000,000 gallons of runoff at Cayuga Street in Indian Village.
The nature-based focus of the project includes County Airport ponds, and possible berms (raised beds) at SUNY Purchase and the former Doral Arrowwood property. Local flood mitigation projects include the grading of the Highland Road parking lot where many vehicles were trapped and a number of rescues were required during Ida, and I-95 and Metro-North culvert improvements, among many others.
Ramboll tried to make made an important point several times: when searching for the most meaningful projects and the best outcome for investment, it depends on where you are along Blind Brook. If you divert water with a Metro-North culvert at Theodore Fremd away from a vulnerable area near Elm Place, it flows back into a raging Brook before Locust Avenue. This particular example prompted a number of negative comments from Councilmembers, as did the grading of the Highland Road lot which they thought could negatively impact Indian Village or downtown.
Compounding various projects makes impact difficult to project according to both Ramboll and Rye City Planner Christian Miller, “two plus two may not make five; two plus two may make three”.
Concerning the cost of some of these projects, even if they could get funded and various jurisdictions could agree on which ones to implement, Ramboll took what they termed a conservative approach. They label low cost at $2 million or less, medium at $2 to $5 million, high at $5 to $ 10 million, and very high at over $10 million. Work upstream on ponds and berms that was estimated to cost $6 million would now cost, according to Ramboll, close to $30 million due to the enormous cost today of disposing of soil.
Rye sits in what Ramboll calls a “very flushy” watershed. Water’s advantage is that it does not need to recognize boundaries and jurisdictions. It finds its way. The presentation suggests that the entire Blind Brook ecosystem – upstream and downstream, towns and villages, districts and neighborhoods may have to learn how to get “flushy” themselves to find, fund, and finish enough projects to make a difference.