Water Level Sensors Provide Better Picture of Potential Floods
In June 2008, floodwaters swamped eastern Iowa. The water in Cedar Rapids rose to within about 18 inches of the level that the U.S. Army Corps of Engineers had previously calculated would be reached only in the worst-case scenario for the Cedar River. This flood caused more than $1.5 billion in damage in Iowa alone, according to the National Oceanic and Atmospheric Administration’s National Climatic Data Center.
To better prepare for floods, the state established the Iowa Flood Center on the University of Iowa campus in 2009 to study and research the causes of floods. Currently, the state’s largest rivers and streams are monitored by a data collection network built by U.S. Geological Survey (USGS). This hydrologic data helps emergency managers and planners estimate how high flood waters will go. To strengthen and supplement this network, the center’s researchers designed and built inexpensive stream gauges to track conditions on smaller waterways that were not being monitored. The Iowa Department of Natural Resources (IA DNR) supported the purchase and distribution of 50 of these gauges, starting in the fall of 2010.
With water level information coming in from a wider and more comprehensive sensor array, emergency managers can better determine if a flood is imminent well before it happens and decide whether to evacuate an area, place sandbags along the waterway, or take other action to prepare. “We’re really hoping to get better information into the hands of emergency management personnel so they can make better decisions while it is still raining,” said Chuck Corell, chief of the Water Quality Bureau for IA DNR.
The sensors provide basic information about the water level of a stream, according to Witold F. Krajewski, director of the Iowa Flood Center and professor of civil and environmental engineering at the University of Iowa. Installed on structures like bridges, each sensor sends sound waves toward the water. By measuring the time it takes for the sound wave to bounce back to the sensor, the equipment can calculate the distance to the water. This information is compared against the depth of the bottom of the waterway, which researchers measure when sensors are installed. Through this comparison, emergency managers can determine when a river or stream reaches flood stage. The sensors are powered by a solar panel, and they transmit data to the Iowa Flood Center’s computer server database via an inbuilt cell phone modem. Each sensor transmits a timed reading to meet the user’s needs.
The USGS stream gauges collect many different types of data, and as a result, cost thousands of dollars each to install and operate. This limits their numbers in Iowa to 150, though Iowa has enough waterways to require about 25,000 bridges. The Iowa Flood Center is focusing on using simpler, less expensive sensors to collect basic water level data from the many smaller streams that feed into the larger waterways the USGS already monitors. The Iowa Flood Center gauge network will provide additional advance notice to emergency managers when a major waterway is approaching flood stage, according to Krajewski. “If you have observations at smaller streams, that gives you a better ability to make predictions for larger rivers that affect larger populations,” he said.
The City of Palo in eastern Iowa volunteered to be among the test watersheds for the stream gauge project. Floods covered 98 percent of the city in June 2008, and the community wanted to be more prepared for future flooding, according to Dave Schoettmer, a member of the Palo Storm Water Management Committee. “With the sensors, the effects of any rainfall can be known and allow for warnings to areas that will be affected,” said Schoettmer. As part of their participation, Palo and other communities will pay the bills for the cell phone modems that allow the gauges to transmit data back to the Iowa Flood Center.
In addition to providing information about water levels, the gauges could help researchers refine flood prediction models, according to Krajewski. The data collected by the gauge network will help researchers track how rainfall affects the water levels of various streams. Eventually, the Iowa Flood Center would like to provide detailed local flood forecasts to supplement the information the National Weather Service provides for population centers and regions. The gauges could also improve understanding about the velocity of flood waves, according to Krajewski. Such knowledge will help water quality experts in predicting how water pollution spreads in waterways, he explained. The Iowa Flood Center provides data on the readings to the public on its Website, www.iowafloodcenter.org through the Iowa Flood Information System (IFIS).
The stream gauge project could supply the foundation for a broader flood observation and warning network in the future, according to Corell. “I would like to see emergency managers put these [gauges] throughout the counties so everyone could see when there might be a problem upstream from where they are,” he said.
For more information, visit www.iowafloodcenter.org.