By Carol P. Bartold, Senior Reporter
Nov. 29, 2017: The recently completed Phase I of the Federal Emergency Management Agency (FEMA) Midland Valley Drainage Project passed its first “live event” test in late October when the remnants of Tropical Storm Philippe dropped up to 3.5 inches of rain in the region.
“We know that the system functioned as it was supposed to,” said Village Administrator Jim Palmer.
Phase I of the flood mitigation system includes two stormwater mains, a 72-inch force main pipe, which runs parallel to Midland Avenue, and a 36-inch force main line, which runs underneath Hayes Field on The Bronxville School campus. Wet wells and subterranean storage chambers were also installed in the Hayes Field area to catch excess stormwater runoff to hold that runoff.
Palmer reported that, at approximately 8:00 pm, after a full day and evening of steady rain, he observed stormwater flowing into the wet wells and the storage chambers at the school, as the system was designed. He noted that stormwater runoff began to flow into the wet wells when the 36-inch force main became overwhelmed. Water flow in the 72-inch line did not reach a volume that caused it to flow into the storage chambers.
“We could see the water flowing into the system,” Palmer said, “and not out of the catch basin in the elementary school parking lot as it has in the past.”
When the wet wells filled up significantly, Palmer noted, one of the two pumps, installed aboveground and adjacent to Hayes Field, near Midland Avenue, activated.
The pumps installed at the pumping station are designed to send excess stormwater through pipes extending underneath the elementary school parking lot, across Midland Avenue, and under a corner of the Bronxville Public Library property. Pipes then cross beneath Pondfield Road and continue under part of village hall and then follow Palumbo Place to a discharge point at Laurel Brook, near the intersection of Gramatan Avenue and Palumbo Place.
“I quickly drove over to the new water discharge point at Laurel Brook and observed the water coming out of the discharge valve,” Palmer said.
He also walked to Scout Field to observe the discharge point of the existing gravity stormwater system. He saw that system’s 36-inch line entirely under water. “When that line becomes overwhelmed,” he explained, “water can’t exit at the Bronx River.” That condition, he said, caused water to overflow from the school catch basin and flood the elementary school parking lot during past storms. That overflow is now caught by the new system and pumped into Laurel Brook.
Palmer also reported that he did not observe any water flowing out of the Garden Avenue and Meadow Avenue catch basins, both tied to the 36-inch force main.
“The test was a real positive,” Palmer said.
Originally slated to cost $6.9 million, the FEMA funded $5.2 million, or 75 percent of the flood mitigation project. The Village of Bronxville and the Bronxville Free Union School District each agreed to provide $861,238, the remaining 25 percent of the funding needed. When bids exceeded the project’s original cost, village and school officials decided to split the project into two phases in the interest of proceeding with construction while pursuing sources of funding needed to complete the work.
As part of the flood mitigation project’s Phase II, The Bronxville Free Union School District’s proposed capital project includes plans to install the remaining three pumps called for in the flood mitigation system’s design.
When all five pumps are in place, a brick-walled enclosure will be built.
Pictured here: Pumps that are part of the FEMA flood mitigation project at The Bronxville School.
Photo by N. Bower