The data were analyzed to eliminate all sites where the laser hit a house or other structure, and researchers were left with an accurate map of how high the ground stood.
The margin of error was about half a foot, officials said -- very accurate compared with the topographical maps familiar to hikers, which mark only every 20 feet, officials said.
This home was razed after flooding from Hurricane Isabel. In Shady Side, a study found that rising waters could make the area even more prone to flooding, potentially causing tens of millions of dollars in damage.
(Courtesy Of Anne Arundel County)
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The researchers then compared the elevation map to an overhead view of the neighborhood and noted the elevations of houses, businesses and other lots. Then began the difficult task of determining which areas would flood, when they might flood, and whether the water would recede or stay for good.
On the Eastern Shore, the study found that the Hooper Islands were in serious danger of permanent flooding, which scientists call "inundation." The study found that if waters were to rise three feet over the next century, 153 properties could be inundated there -- more than at either of the other two sites.
Regarding the St. Mary's County communities, the study found that some roads might be inundated, along with 63 properties, if the sea level rose by three feet.
In Shady Side, by contrast, very little of the neighborhood sits below three feet of elevation. Instead of inundation, officials said, the main danger would come from flooding -- which would essentially be given a head start by a permanent rise in the water level.
"If Isabel comes again in 30 years, it will be this much worse," said Jeffrey A. Michael, a Towson University economics professor who worked on the study.
How much worse? Michael's study estimated that Shady Side would incur about $44 million more in flood damage during storms over the next century if the sea level rose two feet, and up to $60 million more in damage if it rose three feet. He said the estimates were made using flood insurance rates set by the Federal Emergency Management Agency that are based on an area's estimated potential for flood damage.
Sections of Anne Arundel suffered serious damage during Isabel last year, when floodwaters as high as six feet swept over bayside communities on the county's northern and southern ends.
"We learned that there's a lot of properties in this county that are still below basic flood elevation," said Bill Bryant, the county's administrator of inspection services.
In Shady Side, some people are still living in trailers or other temporary housing because of flood damage.
Trying to prepare for another such storm, state officials say they are eager to have laser-assisted elevation maps made of all of the state's low-lying areas. Maps are being prepared for all of Howard, Anne Arundel, St. Mary's and Charles counties, and they have been completed for many counties on the lower Eastern Shore.
Authorities said the maps will be used to create emergency management plans so police and fire departments will know which areas to focus on during floods. Talbot County, on the Eastern Shore, has given maps to residents and firefighters that show how much flooding could be expected from hurricanes of various sizes.
In many places, including Anne Arundel County, regulations require houses to be built at least one foot above estimated flood levels. But Kehoe of the DNR said that "we can't necessarily just build our way out of the problem."
The reason: Even if houses stay dry, the neighborhoods can't survive if roads, lawns, wells and septic systems are underwater.
For areas such as Shady Side, the data are making state officials wonder how much more development should go in.
"Do you want to keep putting people in there," asked Miller of the DNR, "when we know it floods when it rains hard?
