AVALON – October is the likely start point for an ambitious $10-million project to ease recurring flooding in Avalon’s north end.
Borough Engineer Thomas Thornton explained that the pre-construction survey, design, permit and bidding tasks alone would carry the project into 2020.
“This is a big and complex project,” Thornton said. Actual construction will probably not begin until the fall of 2020.
The north end of Avalon is sometimes referred to as "the bowl" because its contours make it difficult for standing water after a severe rainstorm to find a natural drainage point.
The stormwater pump and drainage system in the area are no longer up to the task of dealing with the effects of major rain events, and those events are occurring with greater frequency.
The project calls for pump stations at 11th and 22nd streets with larger, more powerful pumps than those currently in place.
The pipe system that drains and collects the water will also be replaced. With the water drained from the streets faster, the pumps will direct the water through larger 30-inch outfall pipes that dispose of the water in both the ocean and the bay.
The system for carrying the water for disposal into the ocean or bay will require new penetration of the dunes and the back bay sea wall built by the Army Corps of Engineers.
Thornton said the project might require as many as four to five federal and state permits, a process that adds time to the pre-construction schedule.
The proposal from Mott MacDonald for the pre-construction engineering services comes in at $646,000.
Thornton’s estimate of construction costs is $9.5 million, although the still-to-be-completed design process may find ways to alleviate some of that projected expense.
Basing the design around a major rain event adds complexity in other ways as well. Regulating the system, especially the larger pumps, for smaller storms requires a way to use the capacity appropriately.
The goal is to have the pumps respond in a variable way and not go on and off repeatedly when dealing with smaller storms.
Each of the two pump stations will have larger footprints than they now require and greater elevation for the structure and the gas-powered generators. The elevation could be “Six to seven feet up from existing grades,” Thornton said. He noted that the stations would be shielded with a “tasteful structure.”
The design phase of the project will result in all the construction drawings and plans. By the time bidding is expected in 2020, the borough will have to decide on how it wants to phase the construction itself.
The outfall pipes present their own difficulties. The large outfall pipe from the 11th Street pump station may need to penetrate the Army Corp wall west of 8th Street. Thornton said that the design phase would seek alternatives possibly along the borough’s jetty in the area.
From 22nd Street the pumps will direct water through outfall pipes that go through the dunes and extend out to the ocean. Replacing the current 21-inch pipe with a 30-inch pipe presents issues of weight, size, elevation, the impact of wave actions and the dangers presented by erosion at the beach.
At its first meeting in October, the council is expected to approve approximately $120,000 for the initial work over the remaining months of 2018.
With that an ambitious and expensive project to mitigate the impact of rain event induced flooding will begin.
To contact Vince Conti, email email@example.com.