Stopping the ocean – or not

South Shore residents have returned to their normal lives in the months since Hurricane Sandy, but many people’s thoughts are starting to turn to the potential for another big storm. Is it possible to stop the floodwaters that inundated coastal neighborhoods? they wonder.

The answer, sadly, is no. There are ways to mitigate flooding –– to slow it down and hold it back for a time. But a foolproof way to stop the Atlantic Ocean, when it lashes out in its full fury, does not exist.

“There is not a fail-safe engineering solution” to stopping the ocean, said Brian Schneider, the assistant deputy commissioner of the Nassau County Department of Public Works, who is a hydrogeologist.

During Hurricane Sandy, floodwaters were forced through storm drains that let out into the bays, so, logically, many are wondering whether it is possible to install flapper valves on the storm drains’ outlet pipes that would keep water from the bays from flooding into the drains and onto local streets.

Such flapper valves exist, said Schneider, whose south Merrick home was flooded during Sandy. (He did not return to his water-soaked house for three months after the storm.) If there had been flapper valves on the more than 3,700 drain outlets across Nassau, they may have stopped backflow in the drainpipes. The trouble, however, was that floodwaters not only came through the drains, but also over land.

Flapper valves installed on the outlet pipes, Schneider said, might have impeded the flow of water from the streets into the bays. That, he said, might have caused even deeper street-level flooding.

“The water is going to go where it’s going to go,” he noted.

Schneider spoke of his hometown. In south Merrick, a 10-foot tidal surge raced over the finger-like canals that line the coast and pummeled the community during Sandy. Early in the morning of Oct. 29, before the storm unleashed its full fury, floodwaters had already breached the bulkhead at Cammans Pond, which connects to a canal, and floodwaters spilled into the street. That water needed somewhere to go, and after the high tide subsided, it filtered into the storm drains and back out into the bays, only to return later that evening.

Schneider pointed out that Nassau does not own most of the storm drains throughout the county. It owns the larger “trunk” lines, while the towns and cities, which have varying budgets and debt levels, own the rest. Installing drain flaps, Schneider said, would cost millions of dollars –– funding that would be hard to come by in these times of fiscal restraint.

Finally, Schneider said, Nassau’s storm drains are not sewer lines, which are separate –– unlike New York City, where storm drains and sewer lines feed into the same system.

Sewer lines connect to one of two sewage-treatment plants –– Bay Park and Cedar Creek. In western Nassau, Bay Park was overrun by floodwaters and experienced a catastrophic failure, causing sewer lines to back up into people’s homes and onto streets.

In eastern Nassau, however, Cedar Creek held up in the storm, and sewage did not back up. That is not to say, though, that no residents in eastern Nassau had sewage backups in their homes. If a home had a toilet on a flooded first floor or basement, the floodwaters may have opened up an already inundated sewer line into the house, causing a backup.

In the end, Schneider said, any home that is in a federally designated flood zone –– that is, any home below seven feet above sea level –– could be flooded during a major storm.

“If you’re below elevation seven,” he said, “you’re going to be at risk.”

All that a homeowner can do, it appears, is to prepare as thoroughly as possible –– sandbagging around entryways to the home and boarding up windows –– and hope for the best.

Herald staffers have written hundreds of stories focusing on Hurricane Sandy and its continuing aftermath. To see more of them, visit www.liherald.com/sandy or scan the box at right with your smartphone.