Behind all the sandbagging, road closures, and evacuations instituted in preparation for this month’s flood is data — hard numbers — from river gauges and sensors operated and interpreted by the U.S. Geological Survey.
Some of the gauges spouting off water levels and discharge readings up the Cedar River didn’t exist during the historic 2008 flood, which rushed into Cedar Rapids at unprecedented and unanticipated levels. That experience prompted the USGS to install gauges in Vinton and Palo, allowing more precise river-level forecasts in the future — which is now, said Clint Van Schepen, hydrologic technician based in the U.S. Geological Services Iowa Water Science Center in Iowa City.
“They are helping Cedar Rapids be more accurate,” he said.
Van Schepen and hydrologic technician Sophie Pierce this month have been traveling down the flooded Cedar River to inspect its gauges — including stations at Palo, Vinton, Waterloo, Cedar Falls and tributaries like New Hartford, Hudson, and Shell Rock.
“The stages and discharges that come from all those gauges help make as accurate prediction as possible,” Van Schepen said.
In addition to checking stationed gauges and sensors, Van Schepen and Pierce use a sort-of boat fitted with an acoustic Doppler and a GPS unit to confirm readings are accurate.
“It pings off particles in the water, and it can tell what velocity the water is moving at,” Pierce said. “It profiles all the way down to the bottom so we get better accuracy.”
The device, called an “Acoustic Doppler Current Profiler,” stays on the water surface and can take 15 to 30 minutes to do its job. The technicians then analyze the readings and communicate with their office, which passes the information on to the National Weather Service and the Army Corps of Engineers.
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“They can update their models as we give them information,” Van Schepen said, adding the information is updated on the USGS website within hours. “Our sites are open to everybody.”
Part of the USGS profile of river-monitoring tools are contact and non-contact sensors. Contact sensors are installed in the water and measure amounts flowing above. Non-contact sensors are stationed on bridges, and use radar technology to measure the distance to the water flowing below.
The variety of tools and technology help technicians confirm and reaffirm readings in an effort to validate projections and improve the accuracy of forecasts.
“There is a lot of redundancy,” Van Schepen said. “We measure how much is coming through and then we validate so we’re kicking out the most accurate data we can.”
The USGS on Saturday added a new non-contact sensor on the 12th Avenue Bridge in Cedar Rapids in anticipation of this week’s flood. The bridge’s height, keeping the sensor dry in most circumstances, has the agency considering making it the “permanent sensor site.”
Right now, the permanent sensor site is on the Eighth Avenue Bridge. The new 12th Avenue Bridge sensor just before noon Monday reported the river was at 20.16 feet — matching projections.
Van Schepen said that as he and Pierce have traveled down the Cedar River tracking this month’s flood event, readings from their varying tools have aligned and forecast levels have played out as projected.
“Our gauges have been operating really well,” he said.
This flood is different, however, due to its “drawn out peaks” — meaning crests are longer, according to Van Schepen. The Iowa Flood Center shows the Cedar River reaching 23 feet about 1 a.m. Tuesday and staying there until dropped just below that 12 hours later.
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Van Schepen said this flood also is different in that today’s technology allowed for more planning and preparation.
“That’s why we put out so many people and dispersed them to these gauges,” he said. “We want to collect as much data as possible while this event is happening so we get a good sense of what the magnitude is, how it compares to previous floods, and how it’s going to impact infrastructure for cities, counties, and state departments.”
But, Van Schepen said, they could go even further, and technology is heading there.
“In our science, time is so critical. More data is always better. We’re always wanting to collect more and more data,” he said. “The more information we have on all these floods, the better it will assist us down the road.”