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August 18, 2016

Six streamgages Set peaks of record and 50 stations were overtopped by floodwaters.

USGS recorded historic flooding in South Louisiana on its streamgage network, with 30 registering above flood stage over the course of several days. At least six streamgages set a peak of record, four of which have been in operation for more than 30 years. In addition, two streamgages showed a rise of 30 feet in two to three days.

In addition to the realtime streamgages recording above flood stage for several days, several streamgages were damaged during the flooding. Many of these gages were overcome by flood waters, while some were destroyed by debris carried by the fast moving water.

In the graphs created by the streamgage data, the timeline of the flooding becomes clear. Here are several hydrographs derived from data collected at three USGS streamgages in south Louisiana:

Image shows a hydrograph of the Comite River at Comite, LA.
The hydrograph for the USGS streamgage on the Comite River at Comite, LA. Graph taken on August 18, 2016.

Comite River near Comite, LA

This streamgage is located on the Comite River, one of the major drainage rivers for North Baton Rouge and its surrounding suburbs, including Baker and Zachary. The hydrograph illustrates  increasing gage height (water depth) beginning the night of Wednesday, August 10, tapering off a bit Thursday, August 11, before trending sharply upward until it crested early Sunday, August 14.

Because the Comite is a major drainage river, the flood waters have been slow to recede because of the many flooded tributaries that drain into it. In addition, the Comite empties into the Amite River, which has also been in a record flood stage. This compounding flooding has resulted in the backwater flooding which has forced water into so many neighborhoods.

Image shows a hydrograph illustrating the flooding on the Amite River at Denham Springs
The hydrograph for the USGS streamgage on the Amite River at Denham Springs, LA. Graph taken on August 18, 2016.

Amite River near Denham Springs, LA

The Amite River is the primary drainage river for Baton Rouge and its surrounding area. It makes its way from near the Mississippi state border through Denham Springs and the Interstate 12 corridor before emptying into Lake Maurepas.

Because of its status as the primary drainage river, once it began to flood, it caused backwater flooding all throughout the Baton Rouge area. The graph illustrates a slower rate of increasing gage height, as compared to the Comite River, because it is a deeper river system and accustomed to larger volumes of water flowing through it. As Denham Springs is about halfway down the Amite, this streamgage has shown significant dropoff in the water level as the floods have moved downstream.

Image shows a hydrograph that illustrates the flooding on the Amite River at French Settlement
The hydrograph for the USGS streamgage on the Amite River at French Settlement, LA. Graph taken on August 18, 2016.

Amite River near French Settlement, LA

This streamgage is located on the Amite River near its emptying point into Lake Maurepas. As its graph illustrates, the water levels here did not begin to rise until August 13, when it passed flood stage. In addition, its water levels have been slower to drop, because all of the floodwaters that have drained upstream on the Amite, Comite, and other tributaries is still making its way downstream.

Next Steps

USGS crews are out servicing all of the affected streamgages, and they will continue to report streamflow and river height information here. In addition, USGS scientist will survey high-water marks and make indirect measurements to determine streamflow where streamgages suffered damage or at locations where previously measured streamflow have exceeded peak of record.

USGS monitors water conditions in Louisiana at 261 sites using streamgages and other measuring instruments. This information provides important data for agencies like the National Weather Service for flood forecasting, infrastructure information for the U.S. Army Corps of Engineers and state agencies, and water alerts for the general public. Sign up for water alerts here!

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