USGS notes flood's quirks

COUNCIL BLUFFS — This flood is different.

Joe Gorman can smell and see the difference in the Missouri River.

“It's reservoir water,” he said.

Not floodwater from a thunderstorm deluge, the kind of storm that erodes Corn Belt cropland and fills rivers with muddy waves that carry the faint smell of fertilizer and pesticides.

“This flood is clear, clean and wide,” Gorman said.

Gorman knows rivers and floods. He is one of about a dozen U.S. Geological Survey hydrologic technicians who launch boats daily on the flooding Missouri to take the swollen stream's vital statistics along its 385-mile path at Nebraska's eastern edge.

The crews — who have special permission from the U.S. Coast Guard to boat the off-limits river — gather precise information about how much water is flowing past specific points and how fast it's moving. They measure the depth of the channel and the width of the flooded waterway.

Once ashore, they relay this and other information to the National Weather Service and the Army Corps of Engineers, where the data is fed into computers to help forecast flood heights and adjust reservoir releases.

One morning last week, Gorman and Matt Noon — a combined 54 years of river surveying experience — launched a flat-bottomed boat into the Missouri from the levee on the Council Bluffs side of the Bob Kerrey Pedestrian Bridge.

Gorman steered the 20-foot aluminum vessel. Noon hunched over a laptop computer showing readings from a sonar device lowered into the water off the bow. A spare tire on the floor of the boat was Noon's desk.

They made four round-trip crossings from the flooded future site of the Great Lawn park on the Iowa side to the nearly submerged railing at Omaha's Lewis & Clark Landing.

The water was about 12 feet deep at Council Bluff's future park. It was nearly 10 feet deep off the railing in Omaha.

“If the river would be a little higher, we could float right over the top of that guardrail,” Gorman said.

During each crossing, an Acoustic Doppler Current Profiler — the gizmo on the bow — sends electronic pulses into the water three times a second. The echo of the sound waves off water particles and the river bed produces a profile of the river's depth and width and the velocity and direction of the current.

Noon's computer dissects the data and provides instant readings on the average volume of water flowing downriver.

The USGS routinely operates five stream gauges on the Missouri in Nebraska. Four more were added after Army engineers increased releases from the Missouri's rain- and snowmelt-bloated reservoirs in the Dakotas and Montana.

Crews from Iowa, Nebraska and South Dakota now conduct river surveys at least weekly at gauging stations below Gavins Point Dam near Yankton, S.D., downstream at Sioux City, Iowa, and in Nebraska at Decatur, Blair, Omaha, Plattsmouth, Nebraska City, Brownville and Rulo.

Gorman said regular surveys are necessary because the river shifts so much. When silt riverbanks scour and sand streambeds shift, it changes the area of the stream and the volume of water flowing past a point.

Gorman and Noon recently installed portable stream gauges on Indian and Mosquito Creeks in Council Bluffs, on Willow Creek at Missouri Valley, Iowa, and near Hamburg, Iowa.

Not all their tools are high-tech.

To determine how much sediment is suspended in the Muddy Mo, they gather water in glass quart jars that are launched to the river bottom in a torpedo-shaped device on a cable.

“Normally, we get a lot of sand in the Missouri River,” Gorman said. “We're not getting a lot.”

During one of the crossings, Noon noted that the sonar device wasn't producing a clean reading. It needed to be adjusted to drop a few more inches into the water, a job safely done only on land.

Gorman steered the boat upstream and revved the throttle powering the two 40-horsepower outboard motors. His target was Lewis & Clark Landing's empty marina, about 50 yards upstream, but the boat barely moved against the current.

Gorman throttled down, turned the boat east and cut instead across the channel to the still Iowa side, where he and Noon made the adjustment.

The Missouri usually flows at about 4 mph. Technicians measured velocities up to 11.6 mph during the early days of the flood, before the river spilled out of its banks.

“That's swift,” Gorman said. “It can be kind of exciting when you come out of a dead backwater. You've got to be ready. It wants to take the boat from you.”

During their recent Omaha-Council Bluffs survey, Noon said the river's velocity averaged nearly 5 mph. One reading near the surface hit more than 11 mph. The river was 1,490 feet wide and carried about 195,200 cubic feet of water per second.

After finishing the Omaha survey, Gorman and Noon surveyed the Missouri at Nebraska City, where flooding has widened the normal 1,100-foot channel to more than 2.6 miles.

The normal depth of the channel there ranges from 12 to 16 feet, sometimes reaching 25 to 30. Gorman and Noon found a hole 66 feet deep.

The river carried 220,000 cubic feet of water per second past Nebraska City. About 179,000 cubic feet per second was in the channel. Nearly 41,000 cubic feet per second flowed over Iowa Highway 2 on the river's east bank.

“I've been doing this since 1972, and I've measured a lot of high water, but just to see the amount of land inundated where the river broke out of the channel is amazing,” Gorman said.

Gorman said the water was so high at Rock Port, Mo., that he could have driven his boat to the back flaps of a fireworks tent at the Interstate 29 interchange and bought firecrackers.

Forecasts call for continued flooding at least into August.

“The river's going to be up for a long time,” he said. “That's the thing about this one. Most other floods hit a peak and drop slowly. This is just going to be up.”

Contact the writer: 402-444-1127, david.hendee@owh.com

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