The surveyors who've helped map Hurricane Katrina's storm surge continue to refine their data, but one thing seems certain. Every suspicion that the storm was as bad as any we've ever seen is being confirmed.

On Scenic Drive in Pass Christian, there's a water mark inside a house that's been measured at roughly 28 feet. Two others in the neighborhood confirm it.

At Interstate 10's Jourdan River bridge in Hancock County, there's a debris line on the east end that's about 28 feet. Another mark at the Turkey Creek bridge in Gulfport shows the same surge.

At the Beach Mini Mart near the east end of the U.S. 90 bridge over Biloxi Bay, an inside mark measures 20 feet.

Along Interstate 10's Pascagoula River bridge, it's about 13 feet.

"The flood elevations are extraordinarily high," FEMA's Todd Davison said. "Anybody who has studied storm surge, these are well in excess of 100-year flood numbers."

FEMA spearheads compiling the surveying data and hopes to release the first round of tabular data this week. A high-resolution online map should be available in mid-November.

The agency has already released suggestions to city officials on how to rebuild, making a first-cut prediction at what the ultimate goal of this project is, an updated 100-year flood zone map.

Working backward

The efforts to measure Katrina's storm surge are an effort in forensic meteorology. Think "CSI: Gulf Coast" with surveyors taking the place of coroners and investigators, plumb bobs, GPS units and spray paint instead of DNA kits, rubber gloves and toe tags.

Soon after the storm, teams from three government agencies hit the ground in South Mississippi. Most of the information that's been released has come from the U.S. Geological Survey team's work along the I-10 corridor.

The Army Corps of Engineers' Mobile office hit east Jackson County, where it was easier to access with the I-10 bridge damage. FEMA contracted URS Corporation, a huge international engineering firm that's also involved in preparations to rebuild the U.S. 90 bridges, to go in and fill in the rest of the map.

A preliminary compilation of data shows 100 locations that have been measured, although less than a third have rough elevation numbers calculated.

Survey crews look at a variety of indicators to measure storm surge. Typically, they look inside buildings because waves don't blur the true height of the surge.

"If it was inside somebody's home, they didn't want to go in there and spray paint the walls," said Mickey Plunkett of the Jackson USGS office, "so they'd get a surveying instrument inside and tie it to a fire hydrant or wheel curb outside."

Katrina has caused extra difficulties because many benchmarks used in surveying were washed away or damaged. The USGS crews, for example, used the surface of the I-10 bridges, which are known heights from the state transportation department, to measure from.

Computer simulations help

Trying to figure out exactly what happens during a storm is difficult. It's up to computer modeling to take a look at what happened.

"The reason we run the computer simulations is the observations break down," said Pat Fitzpatrick, Mississippi State University's GeoResources Institute hurricane expert. "The tide gauges are all destroyed by the storm."

The GRI has run models for Katrina showing the storm's impact in motion. It and LSU are the only schools that run the Advanced Circulation Model, according to Fitzpatrick. He says it's better than the National Weather Services model, using parallel computing power to examine small chunks of water that can model bayous, canals and coastal contours better.

The two models use the same equations, inputting wind data from the National Hurricane Center, hurricane eye size, the breadth of hurricane- and tropical storm-force winds and speed of movement.

The most accurate simulation takes into account the tides, but takes several weeks to run. The simulations done for Katrina were done without, creating a 2- to 3-foot error in an area that doesn't feature a wide range of tides. In the Mississippi simulation, Waveland starts taking on water on Aug. 29 at 5 a.m., with water moving up the Jourdan River. Three hours later, water is 12 to 15 feet high in Waveland and areas around Biloxi are starting to flood.

At 11 a.m., there are dramatic differences. Water is five miles inland west of Bay St. Louis, at 27 to 33 feet. The rest of the Mississippi Coast has major inundation with surge heights of 18 to 24 feet. Fitzpatrick's team also ran simulations on Louisiana, which yielded interesting results. He doesn't think Lake Pontchartrain got high enough to overflow its levees into New Orleans.

Instead, the computer results imply that there was a structural failure in those levees.

What happens now?

Mapping all the real-world data continues, and it will do so for quite some time. FEMA will release a series of maps like it did after Ivan hit Alabama and the Florida Panhandle (www. fema.gov/ivanmaps). They will start with the mid-November maps. Eventually, there will be very interactive products online, with links to photos of actual locations where the measurements were taken.

But the ultimate goal of the effort is a revision of the 100-year, or one-percent flood maps used by the insurance and financial industry to set rates and determine where money should be loaned to rebuild.

The advisory information that went out is the first step in that.

"If you're a good driver, you get better rates. If you're not a smoker, you get better rates," he said. "Floods are the same. People who use the advisory information will get better rates."

Katrina's massive storm surge will change the way South Mississippi thinks about storms. It'll do so beyond the psychological impact she's brought to the area, in more concrete ways like this flood map.

Davison said that it won't strictly reflect Katrina. Experts think it's beyond the pale of a 100-year event.

Instead, it will take into account the 25 years or so since the last revision that have changed the historical basis for the maps, storms like Elena, Opal, Ivan and Dennis.

"It's fair to say the 100-year is going to go up," Davison said, "but they won't go to the Katrina levels."