The Tisbury select board voted unanimously Wednesday in favor of a town-funded project to reduce flooding at the infamous Five Corners intersection.

The town, in partnership with the University of New Hampshire Stormwater Center, will create a larger underground basin to allow better water flow out to the sea. Work could start later this year. 

Tisbury has been trying to fix Five Corners for years, and this new effort is seen as a first step towards making the crossroads — one of the most traveled around the Island — easier to traverse during storms.

Town administrator John (Jay) Grande told the board he expects the work to cost no more than $400,000, with no borrowing required.

“We do have the funding in place to carry out the project,” Mr. Grande said.

The University of New Hampshire Stormwater Center developed the plan after studying the intersection’s drainage woes, Tisbury department of public works director Kirk Metell said.

“Anything that exceeds 1.5 inches of rainfall overwhelms our basins and our outfall pipe, which causes flooding down at Five Corners,” Mr. Metell said.

Even 1.3 inches of rainfall can produce significant flooding, said UNH engineering professor James Houle, director of the stormwater center.

“That significant flooding translates into a health and human safety factor, not just from the pollutants that are accumulating right there and the traffic moving in and out, but [as] the entrance and egress point for the Island,” Mr. Houle said.

The nearest outfall pipe, which emerges at the beach near Tisbury Wharf, also clogs with every incoming tide as the water sweeps material from the harbor bottom into the pipe’s mouth, Mr. Metell said.

“That requires the DPW to go down and remove those spoils before every rain,” he said. 

Even without rainfall, the pipe can contribute to flooding at Five Corners, the lowest part of Tisbury at just a few feet above sea level.

“The outfall pipe does not have a check valve or a similar valve that stops water from flowing back from the sea to our roadways, so every time there is high winds or waves, the water travels back … and also adds to that flooding,” Mr. Metell said.

Mr. Houle said the plan is to reduce Five Corners flooding by combining three existing catch basins into a single underground structure at the beach.

The concrete chamber will release water from all three pipes into the harbor through a large main outlet at the shoreline, with a secondary stormwater outlet for emergencies.

“Instead of three one-foot outlets, we’ll have one three-foot-diameter outlet …and then we’ll have a four-foot-by-two-foot cutout on the very top that will allow excess drainage to spill,” Mr. Houle said.

“We’re not going to say it’s going to alleviate all of the flooding, but it’ll alleviate some of the flooding by providing that relief point,” he said.

To keep water from flowing back into the drainage system, Mr. Houle plans to use a proprietary product called a Tideflex check valve.

Self-sealing Tideflex valves were originally developed for the federal Environmental Protection Agency, which tested the technology for two years, according to the valve manufacturer’s website.

“It’s a neoprene fitting that goes on the outlet pipe that allows water to flow out of the pipe, but not back in,” Mr. Houle said.

Wednesday’s decision signals the end of Tisbury’s patience with the Massachusetts Department of Transportation, which has been studying potential solutions for Five Corners.

“We’ve waited four years for this other planning process to unfold,” Mr. Grande said.

Because the UNH plan does not expand the footprint of the area’s drainage system, Mr. Houle said it shouldn’t trigger the need for additional permits.

The limited scope of the work will also keep down costs, said Mr. Grande, who called $400,000 a high-end estimate.

“It’s a footprint repair, with these enhancements, within our right-of-way,” he said.

Mr. Metell said he expects work to begin this fall.

In other business Wednesday, the select board accepted a $136,000 pledge from Vineyard Power for a grant to add solar energy with battery storage to the Tisbury Senior Center, and accepted a town meeting warrant article for tree planting from former select board member Tristan Israel.

The board also created a capital planning advisory committee, appointing as members Alex Meleney, Abbe Burt and Holly Mackenzie.