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State Monitors Sea Level Rise for Future Risks

DOVER - Decades had passed since a storm sent saltwater and fish into corn and bean fields west of Prime Hook National Wildlife Refuge.

Then, a late-season storm in May caused flooding along the Delaware Bay and pushed fish way beyond their normal, bay, river and creek habitats.

Some state environmental officials wonder if what happened in May could be a glimpse at Delaware's future.

They are developing a sea-level adaptation plan for the state -- a project that will use high-tech mapping and modeling to predict what rising sea levels could mean for a state with 25 miles of ocean coast and even more land along the Delaware Bay and River, the Nanticoke River and dozens of tributaries in the bigger river systems.

"It's not just Sussex County we're worried about. It's everywhere," said David Carter, an environmental program manager with the state coastal management program.

By some estimates, every one-foot rise in sea level translates to a one-foot rise in flood levels.

At Lewes, relative sea level is rising at a rate of about 3.16 millimeters a year -- equal to the height of three stacked pennies. Lewes may be a little off the pace for the state, where the average in the past 100 years is about 3.3 millimeters a year -- equivalent to 192 stacked pennies. That equals a little more than a foot of rise in a century.

Rising waters and erosion have affected iconic structures such as the Cape Henlopen Lighthouse, which tumbled into the sea in 1926, and the two World War II towers at Gordons Pond in Cape Henlopen State Park, once far from the ocean's edge, now surrounded by water in storms and extremely high tides.

Some of the rise comes from global factors such as thermal expansion of the ocean water and melting polar ice. Some of the impact is local, from loss of land from erosion or settling.

Some is man-made -- for instance, from the creation of stabilized inlets, or structures that block the natural flow of sediments to coastal marshes.

And at Cape Henlopen, there is the steady, natural movement of sand along the shoreline to the point of the cape -- a geological feature that has seen dramatic changes over time.

The International Panel on Climate Change has estimated that sea level will rise from as little as 7.2 inches to as much as 23.6 inches by 2100. Planning with photography

That uncertainty makes sea-level rise a challenge for coastal and environmental planners, Carter said.

His group, working with other state and federal agencies, will use LiDAR digital photography to map vulnerable areas.

LiDAR uses light detection ranging to use a radar-like pulse of light to map the land, allowing it to "see" the bottom of clear, shallow waters.

LiDAR is used by everyone from state planners -- most recently for new, highly detailed maps that show how land is being used in Delaware -- to emergency planners, who can use it to better design evacuation routes.

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