Cedar Rapids Gazette: Predicting River Crests More Than About Rainfall

Friday, July 4, 2014

Predicting river crests about more than rainfall

Government agencies share data to get most accurate predictions

By Erin Jordan, The Gazette
Published: July 3 2014 | 9:59 am - Updated: 3 July 2014 | 12:27 pm in Flood 2014, News, Public Safety Rotator,
 90  18  0


Workers from Streb Construction Co and the City of Iowa City erect HESCO flood barriers along the shore of the Iowa River by Cole's Mobile Home Court in Iowa City on Wednesday, July 02, 2014. (Adam Wesley/The Gazette-KCRG)

Predicting floods is a complicated business involving not just rainfall, but also geometry of river channels, character of hill slopes and mathematical formulas.

Boiled down, the data can help Iowans know when to start sandbagging or evacuate before high water.

“For the general public, what really matters is just how high the river can get,” said Witold Krajewski, director of the Iowa Flood Center at the University of Iowa.

The Army Corps of Engineers predicted Wednesday morning the Coralville Lake would top the spillway next week, but later in the day scaled back the numbers slightly. Small revisions like this are constant because rain upstream can affect the whole system.

The predictions start with knowing the landscape in and around waterways.

Digital topographic maps from the U.S. Geological Survey show elevation points for every 100 yards across the country, Krajewski said. Scientists in Iowa also have access to LiDAR, or Light Detection and Ranging technology, that involves laser readings from planes that fly over the landscape.

Elevation maps allow scientists to figure out the locations of river channels and basin boundaries.

Also important to flood predictions is the character of the hill slopes that run into waterways, Krajewski said. A grassy field will absorb more water than a paved parking lot.

These base numbers go into computer models that help scientists understand how different rainfall amounts will affect the region.

The Iowa Flood Center uses weather radar to create rainfall maps. They then can calculate how rainfall will accumulate over hill slopes, into streams and on to major rivers in Iowa.

A network of river gauges and sensors attached to bridges across the state also feed real-time information on water level via satellite to agencies such as the flood center and the National Weather Service.

Iowa had more than 350 river gauges and sensors in June 2013, which was nearly double the number of gauges used during the historic floods of 2008. More gauges result in more accurate crest predictions.

At USGS gauge sites, biologists regularly measure the flow of the water, which is critical for the weather service to develop forecasts.

The National Weather Service provides inflow reports used by the Corps to predict crests at man-made reservoirs, such as Coralville Lake, said Jim Stiman, chief of the Corps’ Water-Control Section. The reports show the previous 24 hours of rainfall and rain predictions for the next two weeks, he said.

In turn, the Corps provides the weather service with information about how much water is being released from the reservoir, which helps predictions for downstream communities.

“It’s a collaborative effort, for sure,” Stiman said.

The public can see real-time reports from Iowa’s network of river gauges at several websites, including: www.rivergages.com, http://ia.water.usgs.gov or http://water.weather.gov/ahps/region.php?state=ia.

The Iowa Flood Center uses its data for research, but also makes it available to the public online through the Iowa Flood Information System. The interactive database allows users to see maps of how different flood levels will affect their towns.

- See more at: http://thegazette.com/subject/news/predicting-river-crests-about-more-th...

Predicting river crests about more than rainfall

Government agencies share data to get most accurate predictions

By Erin Jordan, The Gazette
Published: July 3 2014 | 9:59 am - Updated: 3 July 2014 | 12:27 pm in Flood 2014, News, Public Safety Rotator,
 90  18  0


Workers from Streb Construction Co and the City of Iowa City erect HESCO flood barriers along the shore of the Iowa River by Cole's Mobile Home Court in Iowa City on Wednesday, July 02, 2014. (Adam Wesley/The Gazette-KCRG)

Predicting floods is a complicated business involving not just rainfall, but also geometry of river channels, character of hill slopes and mathematical formulas.

Boiled down, the data can help Iowans know when to start sandbagging or evacuate before high water.

“For the general public, what really matters is just how high the river can get,” said Witold Krajewski, director of the Iowa Flood Center at the University of Iowa.

The Army Corps of Engineers predicted Wednesday morning the Coralville Lake would top the spillway next week, but later in the day scaled back the numbers slightly. Small revisions like this are constant because rain upstream can affect the whole system.

The predictions start with knowing the landscape in and around waterways.

Digital topographic maps from the U.S. Geological Survey show elevation points for every 100 yards across the country, Krajewski said. Scientists in Iowa also have access to LiDAR, or Light Detection and Ranging technology, that involves laser readings from planes that fly over the landscape.

Elevation maps allow scientists to figure out the locations of river channels and basin boundaries.

Also important to flood predictions is the character of the hill slopes that run into waterways, Krajewski said. A grassy field will absorb more water than a paved parking lot.

These base numbers go into computer models that help scientists understand how different rainfall amounts will affect the region.

The Iowa Flood Center uses weather radar to create rainfall maps. They then can calculate how rainfall will accumulate over hill slopes, into streams and on to major rivers in Iowa.

A network of river gauges and sensors attached to bridges across the state also feed real-time information on water level via satellite to agencies such as the flood center and the National Weather Service.

Iowa had more than 350 river gauges and sensors in June 2013, which was nearly double the number of gauges used during the historic floods of 2008. More gauges result in more accurate crest predictions.

At USGS gauge sites, biologists regularly measure the flow of the water, which is critical for the weather service to develop forecasts.

The National Weather Service provides inflow reports used by the Corps to predict crests at man-made reservoirs, such as Coralville Lake, said Jim Stiman, chief of the Corps’ Water-Control Section. The reports show the previous 24 hours of rainfall and rain predictions for the next two weeks, he said.

In turn, the Corps provides the weather service with information about how much water is being released from the reservoir, which helps predictions for downstream communities.

“It’s a collaborative effort, for sure,” Stiman said.

The public can see real-time reports from Iowa’s network of river gauges at several websites, including: www.rivergages.com, http://ia.water.usgs.gov or http://water.weather.gov/ahps/region.php?state=ia.

The Iowa Flood Center uses its data for research, but also makes it available to the public online through the Iowa Flood Information System. The interactive database allows users to see maps of how different flood levels will affect their towns.

- See more at: http://thegazette.com/subject/news/predicting-river-crests-about-more-th...

By Erin Jordan, The Gazette

Predicting floods is a complicated business involving not just rainfall, but also geometry of river channels, character of hill slopes and mathematical formulas.

Boiled down, the data can help Iowans know when to start sandbagging or evacuate before high water.

“For the general public, what really matters is just how high the river can get,” said Witold Krajewski, director of the Iowa Flood Center at the University of Iowa.

The Army Corps of Engineers predicted Wednesday morning the Coralville Lake would top the spillway next week, but later in the day scaled back the numbers slightly. Small revisions like this are constant because rain upstream can affect the whole system.

The predictions start with knowing the landscape in and around waterways.

Digital topographic maps from the U.S. Geological Survey show elevation points for every 100 yards across the country, Krajewski said. Scientists in Iowa also have access to LiDAR, or Light Detection and Ranging technology, that involves laser readings from planes that fly over the landscape.

Elevation maps allow scientists to figure out the locations of river channels and basin boundaries.

Also important to flood predictions is the character of the hill slopes that run into waterways, Krajewski said. A grassy field will absorb more water than a paved parking lot.

These base numbers go into computer models that help scientists understand how different rainfall amounts will affect the region.

The Iowa Flood Center uses weather radar to create rainfall maps. They then can calculate how rainfall will accumulate over hill slopes, into streams and on to major rivers in Iowa.

A network of river gauges and sensors attached to bridges across the state also feed real-time information on water level via satellite to agencies such as the flood center and the National Weather Service.

Iowa had more than 350 river gauges and sensors in June 2013, which was nearly double the number of gauges used during the historic floods of 2008. More gauges result in more accurate crest predictions.

At USGS gauge sites, biologists regularly measure the flow of the water, which is critical for the weather service to develop forecasts.

The National Weather Service provides inflow reports used by the Corps to predict crests at man-made reservoirs, such as Coralville Lake, said Jim Stiman, chief of the Corps’ Water-Control Section. The reports show the previous 24 hours of rainfall and rain predictions for the next two weeks, he said.

In turn, the Corps provides the weather service with information about how much water is being released from the reservoir, which helps predictions for downstream communities.

“It’s a collaborative effort, for sure,” Stiman said.

The public can see real-time reports from Iowa’s network of river gauges at several websites, including: www.rivergages.com, http://ia.water.usgs.gov or http://water.weather.gov/ahps/region.php?state=ia.

The Iowa Flood Center uses its data for research, but also makes it available to the public online through the Iowa Flood Information System. The interactive database allows users to see maps of how different flood levels will affect their towns.