USGS Science Helps Disaster-Struck Communities Understand Flash Flooding

June 15, 2010 - The Little Missouri River in Southwest Arkansas experienced a flash flood Friday, with waters that rose over 20 feet in just 5 hours, killing 20 people. In response to this severe and unusual flooding the USGS deployed a team of scientists to document and study the flow and height of the floodwater as it coursed down the Little Missouri River and its tributaries.

“Flash flooding is one of the biggest causes of natural hazard-related deaths in the United States and we are here collecting data to understand what happened from a hydrologic standpoint, in order to help the emergency management community and National Weather Service better protect and educate the public,” said Dr. Robert Holmes, USGS National Flood Specialist. “For those camping in one of these beautiful spots near flowing water, it is important to know how high and how fast the water can rise in the case of flash floods."

Flash flooding happens when intense thunderstorms dump large quantities of rain into steep or urban watersheds in a short period of time. Flash floods are hard to predict, but data collected by the USGS is crucial to formulating better predictive models. These models are needed by forecasters and emergency responders to warn the public and improve planning, in order to minimize the impacts of future floods.

The team of USGS scientists in Arkansas is using hydrologic forensics to reconstruct the discharge, elevation, and velocities of the flood. These scientists are surveying the high water marks and geometry of the river for input into hydraulic models. The models estimate the peak flow rate of the flood as the water rushes down the streams.

Information from these models is compared to long-term records collected by the USGS on nearby rivers to determine how often such floods are likely to occur. Knowing how often a flood is likely to occur helps area communities decide whether to require higher construction elevations, warning systems, or flood-control works.

“In addition to collecting data for long-term uses, the USGS collects real-time data to aid those making daily decisions about water-related activities, whether for resource management, business operations, flood response or recreation,” said Robert Mason, a USGS hydrologist. “This recent flash flood illustrates the importance of constantly monitoring the flow of our Nation’s waters and quickly disseminating the information to those who need it.”

The USGS recently released a new service, called WaterAlert, that allows users to receive text or email updates about specific river flows, groundwater levels, water temperatures, rainfall and water quality at any of the sites where USGS collects real-time water information. WaterAlert helps inform emergency responders, recreationalists, campers and others about current water conditions, such as flooding, so that they can take appropriate action. The service is located at http://water.usgs.gov/wateralert/.

The USGS operates approximately 7,500 streamgages as part of the National Streamflow Information Program, which provides emergency responders and the public with long term, accurate and unbiased information on streamflow in real-time.

The recent flooding occurred early Friday morning, June 11, 2010. According to Mason, this area in Arkansas is a known flood “hot spot” because of the relatively steep terrain and proximity to the Gulf of Mexico. The Gulf supplies vast quantities of humid air, and as this air flows over the mountains and hills, it rises and cools, resulting in intense rains.