Fighting the Floods
USGS Response to Louisiana Floods Part of Larger Flood Science Mission
From August 12-14, extreme rainfall from a tropical depression fell on southern Louisiana resulting in historic flooding. More than a dozen people died and tens of thousands have been displaced.
Although not a first-responder agency, USGS played an important role during these floods, as it does for flooding throughout the United States. Data and science from the USGS is used during and immediately after floods, as well as throughout the long-term recovery.
During the Flood
USGS science plays a significant role during floods. Data from streamgages and other measurement stations are provided to the National Weather Service, the U.S. Army Corps of Engineers, and other state and local first responders. In addition, many of the streamgages provide real-time data, so responders can keep an eye on local water levels with up-to-the-minute information.
In addition to the first responders, the National Weather Service uses data from the streamgages to help forecast flooding. With many streamgages having records going back more than 30 years, forecasters can model what varying levels of precipitation might have on whether a river will flood.
To ensure the data provided by streamgages is accurate, USGS crews make every effort to do manual discharge measurements. By doing these measurements in person, USGS crews can verify the accuracy of the data the streamgages provide. These manual discharge measurements are done regularly during maintenance visits, but are also done specifically during flooding events to make sure streamgages are functioning properly under extreme weather conditions.
During the Louisiana floods, USGS streamgages provided this real time data from 33 streamgages, 12 of which registered peaks of record. As soon as the roads were passable, USGS crews set out to do the manual discharge measurements that ensured the accuracy of the streamgages, completing 24 so far.
The Immediate Aftermath
As the floodwaters recede, one of the first things USGS crews focus on is repairing damaged equipment. Since streamgages are located on rivers and creeks, they run the risk of damage or destruction from floodwaters. Because streamgages form the backbone of the USGS flood response, repairing them is a high priority.
The next step is to fill in the blanks left by the downed streamgage. To do this, USGS scientists will perform an indirect measurement, where high water marks will be taken and integrated into knowledge of the stream’s hydrology and other information to deliver an estimated streamflow during the period the streamgage was down.
In addition, USGS will often partner with other agencies, particularly the Federal Emergency Management Agency, to do high water mark measurements in urban areas affected by flooding. High water marks are thin lines of debris floodwaters will leave behind on buildings, trees and other stationary objects. These delicate lines will indicate to scientists the highest point the flood reached, however, they are easily destroyed – both by people cleaning up and by natural weathering – so collecting them is a time-sensitive effort.
During the Louisiana Floods, 15 streamgages were damaged or destroyed and to date, 14 have been repaired. The last is expected to come back online in the next few days. In addition, seven indirect discharge measurements have been scheduled.
Science for the Long Term Recovery
USGS science doesn’t just provide important information during the disaster; it also helps underpin future planning to mitigate a potential disaster’s damage. One particular use is the modeling efforts that are informed by the streamgages and high water marks. These help create flood inundation maps, as well as inform FEMA’s Flood Insurance Rate Map.
In addition, during the manual discharge measurements, USGS scientists will often collect water samples that can be used to study water quality and sediment. Floods can inadvertently mobilize chemicals and other contaminants from people’s homes, businesses, or other manmade sources, as well as naturally occurring ones like heavy metals. USGS water quality work can help identify where those chemicals end up and what effects they may have on the environmental health.
For the Louisiana Floods, USGS and other federal partners are still assessing the damage, so it will take time before the long-term recovery needs are fully known. However, the data collected so far will be brought to bear for those needs as well as other floods throughout the United States.
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