Water table on some parts of LI at record levels

Measurements taken last week at more than 40 wells in flood-prone parts of Long Island show the water table at those sites has risen up to 2 1/2 feet in the last year.

Scientists from the U.S. Geological Survey checked monitoring wells in Riverhead, Central Suffolk and Southwestern and Central Nassau and found levels in some wells are the highest on record.

The water table had risen between 1 1/2 to 2 1/2 feet over the past year - a spike that likely worsened flooding in some areas after last week's downpour.

The problem is likely to linger for some residents though the Survey's scientists emphasized the reasons for flooding differ from site to site, depending on local soil and the depth to groundwater.

In parts of Smithtown and Central Islip, water levels appear to have risen from .23 feet to 2.46 feet just in the past month - bad news for homes built in old stream channels or other low-lying areas. On top of that, a layer of clay in the soil beneath much of Smithtown prevents water from draining quickly to lower aquifers.

"Those basements that are flooding are actually in contact with the water table," said Ronald Busciolano, a hydrologist with the agency's New York Water Science Center in Coram. "Since the groundwater system drains relatively slow, you can have elevated levels causing flooding for months and even years."

Busciolano said he expected to see a similar rise in groundwater levels across the region when the agency conducts a full groundwater survey later this month. Last month's storm capped the wettest March on record here.

"This is quite a wet period we're going through, so it really jumped," Busciolano said. "Usually, depending on the year, you see half a foot to a foot."

In other places, the sheer rush of water and impermeable soil seem to have played a bigger role in the flooding.

While some wells in Riverhead hit record highs last week, the well north of flooded Horton Avenue was actually lower than it was two years ago - when no catastrophic flooding was reported. Researchers think flooding there last week was due to saturated clay soils, not because of rising groundwater.

In Nassau, the team found groundwater was rising to levels not seen since the 1960s, when the installation of sewers caused a rapid drop in the water table. Still, Busciolano said flooding in Old Westbury was likely due to impermeable clay soil and heavy runoff.