New Hampshire

Rising groundwater on N.H. seacoast could pose road hazard

Several roads in Portsmouth, N.H., are among the most vulnerable, the researchers say.
Keith Bedford/Globe Staff/File 2016
Several roads in Portsmouth, N.H., are among the most vulnerable, the researchers say.

You’ve heard of rising sea levels. But what about rising groundwater?

As sea levels go up, groundwater is expected to rise, and researchers from the University of New Hampshire have found that certain roads on the New Hampshire seacoast — some as far as 2 miles from the shore — could suffer as a result of this unseen hazard.

The press release from UNH states that Route 286 in Seabrook and Gosling Road in Portsmouth are among the most vulnerable, and that without “drastic improvements,” motorists can expect stretches of these roads to deteriorate more quickly, require more maintenance, and be closed for longer periods of time.

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Jayne Knott, a civil engineering doctoral candidate in UNH’s College of Engineering and Physical Sciences, was the lead author of the study, which was recently published in Transportation Research Record.

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“Previous road vulnerability studies have looked at road surface flooding, but groundwater has not been addressed,” Knott said in a press release. “We found that the effects of surface water flooding on roads occur within a mile of the coast, and groundwater rise effects can occur more than twice that, sometimes all the way to Pease Tradeport,” an industrial park that includes the Portsmouth International Airport.

“The worst enemy of pavement is water,” Jo Daniel, professor of civil and environmental engineering and a coauthor on the study, said in the press release. “If the soil and substrate under the pavement get wet, then the strength that we had counted on to carry the traffic isn’t there anymore. So the pavement develops ruts and cracks, allowing more water to get into the underlying layers which makes the situation worse and closing roads for long periods of time to dry out impacting both commuters and tourists.”

Emily Sweeney can be reached at esweeney@globe.com. Follow her on Twitter @emilysweeney.