Small Town News

Scientist says sea level rise is hard to predict, changes coastline

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Models that predict the effect of sea-level rise on coastal communities are not reliable, one local scientist says.

Tony Pratt, director of shoreline management with the Department of Natural Resources and Environmental Control, said the earth has built-in cooling and warming mechanisms that scientists do not well understand. Over long periods of time, cooling and warming trends, including the movement of graders, have shaped the coasts that we inhabit, he said.

Pratt spoke last month at a meeting of the Science and Technical Advisory Committee of the Center for the Inland Bays.

Scientists say sea levels have always fluctuated, changing the shape of coastlines. Sea-level rise is dynamic, said Pratt. It affects coastal erosion, land loss and wetlands. It also has the potential to affect coastal species and could influence coastal water supplies, he said.

Attempts to simplify sea-level rise have merit, but are erroneous, said Pratt. "Land inundation maps do not represent reality. They take current topography and add 2 feet of water. It assumes land forms are static - they are not," he said.

The land responds to change, and so do people, said Pratt. Beach replenishment projects are one way people respond to changes in their environment, he said.

Pratt said at current rates of sediment deposition, some wetlands seem to be keeping up with sea-level rise.

Seventy-five million years ago, today's coastline was underwater, said Pratt. The Cape Region has been submerged under the Atlantic; the ocean once touched the Appalachian Mountains.

As evidence, Pratt cited whale skeletons found far inland. Chunks of bog material and tree stumps deposited on beaches after storms also offer evidence of where wetlands used to be, he said.

Two thousand years ago, Delaware would have felt like Maine today, before the present coastline was formed, said Pratt.

"We've had these forces at work for a long time. It's a question of how well we understand diem and how well we adapt to them," he said..

There are two kinds of sea-level change, said Pratt.

Eustatic refers to a change in the volume of the entire ocean. Relative sea-level change addresses the changes at a particular location.

Causes include tectonic lift or subsidence, a problem Pratt says is occurring in Texas, where oil and gas are being extracted from the earth. The change in sea level at one location is often greater than the global change,-said Pratt.

Such fluctuations are important to coastal communities and to management plans, he said.

He also points to Sitka, Alaska, which is rising out of die water.

"It's not all the same everywhere. We have to think relatively," he said.

Trying to model complicated global thermal activity that is not well understood is difficult, he said. Current models are not working well, he noted.

Shorelines are in a constant state of flux, he said, concluding that people will soon have to find a balance between a growing population and economic growth and protecting wildlife and the habitat that protects shorelines.





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