Flood depth map

A new map shows just how high the waters rose during last summer's flood.

East Baton Rouge authorities unveiled a map Thursday that details which streets and neighborhoods took on a few feet of water and which got much more.

Among other things, the map shows all of the neighborhoods along the Comite River where the flood reached heights over ten feet. Similar areas exist along the Amite River, Jones Creek and other bodies of water.

The new data is based on high water mark surveys taken by the U.S. Geological Survey and the Amite River Basin Commission. City-parish senior geographic information system analyst Brandon Jumonville then combined those findings with existing elevation and watershed maps to determine the maximum water depth during the flood, GIS manager Warren Kron said.

"Lots of people have asked us, 'It's great to know where it flooded, but how deep did the water get?'" he said.

The city-parish can also use the new model to help apply for federal aid.

When roads are submerged, the soil underneath becomes saturated and loses its shock absorption qualities, said Tom Stephens, the city-parish's chief design and construction engineer. That means that when pressure is applied — say, from evacuees' cars and debris trucks — the road takes a pounding.

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A few feet of water over a road for a week is enough to cause damage, though there are a number of variables that come into play.

Stephens said the city-parish is working with an engineering firm that helped New Orleans apply for federal aid after Hurricane Katrina to fix flood-damaged roads. The flood depth model will show engineers where to look for roads and other infrastructure like pumping stations that have been prematurely aged by the flood.

The new map also compared the scientific model to the rough and ready version produced days after the storm by looking at aerial photos, 911 calls and Facebook posts from residents pointing out flooded areas. There are some disparities between the two, but overall Kron said the new map validates the earlier effort.

The newest map is the final entry on the city-parish's flood story data set at http://ebrgis.maps.arcgis.com/apps/MapSeries/index.html?appid=1c4ac9fca97846d2a1780a90fc68c6eb.

The full, technical version with all the layers and metadata is available at http://ebrgis.maps.arcgis.com/home/webmap/viewer.html?webmap=c67e95809261466595dcbf5860d6a29a.

Follow Steve Hardy on Twitter, @SteveRHardy.