Flooding forecast for South Platte River scaled back - Omaha.com
Published Tuesday, September 17, 2013 at 12:00 am / Updated at 6:32 pm
Flooding forecast for South Platte River scaled back
Advice for residents in water's path
The Nebraska Emergency Management Agency is sending six employees and a mobile operations center to Ogallala to work with local emergency officials and to coordinate the state's response to potential flooding. Residents are urged:

» To cancel recreational activities along the South Platte River.

» To stay out of floodwaters. The velocity of the water will be faster than usual and unsafe.

» To keep informed by watching TV, listening to the radio or going online for information and instructions.

» To secure homes. If you have time, bring in outdoor furniture. Move essential items to an upper floor.

» If instructed to do so, to turn off utilities at the main switches or valves.

» To disconnect electrical appliances. Don't touch electrical equipment if you are standing in water.

» Not to walk through moving water. Six inches of moving water can cause you to fall. If you have to walk in water, walk where the water is not moving. Use a stick to check the firmness of the ground in front of you.

» Not to drive into flooded areas. If floodwaters rise around your car, abandon the vehicle and move to higher ground if you can do so safely.

» To avoid floodwaters, even if they look safe. Water can contain sewage, debris and bacteria.

Photo slideshow: Flood preparation along the South Platte River

* * *

Update: The National Weather Service's latest forecast for the South Platte River in southwest Nebraska indicates the crest could be lower than originally expected. That forecast is based on the assumption that debris in the river doesn't jam together and cause a sudden worsening of localized flooding.

Today's forecast:

• Roscoe (east of Ogallala): The river was at its normal low level this morning but was expected to begin rising through the day. It was expected to be three-fourths bankful at Roscoe by midday Wednesday, quickly rising out of its banks and causing minor flooding the rest of the day. It was projected to reach moderate flood stage by about midnight Wednesday. By Thursday evening, it was expected to peak at 12.5 feet, which would be a little more than a foot over the record set in 1995. It is expected to cause moderate flooding, by inundating homes along the river. The forecast indicates it isn't likely to flood the Interstate 80 interchange at Roscoe, the key improvement over earlier forecasts.

• North Platte: The river is expected to begin rising early Thursday morning and reach three-quarters bankful Thursday night. During the day Friday, it is expected to leave its banks and cause minor flooding, cresting at 13.5 feet early Saturday morning. This would be a half-foot below of the record set in 1935, but still at minor flood stage. This crest stage is still uncertain, according to the weather service.

• Brady: The river is expected to begin rising on Friday, reach three-fourths bankful during the day, then spill out of its banks and cause minor flooding Friday evening. The crest at Brady is still uncertain but could be 9.6 feet early Sunday morning, which would match the record set in 1973.

Nebraskans are collecting sandbags, building levees and plugging culverts as they prepare for floodwaters pushing down the South Platte River from Colorado.

Uncertainty surrounds the flood threat because of a lack of accurate information and the unpredictable consequences of floodwaters in a drought-depleted but debris-choked river.

“The magnitude of flooding could be unprecedented,” Earl Imler of the Nebraska Emergency Management Agency said in a statement released Monday.

Factors creating the uncertainty:

» Lack of accurate information. The power and volume of the flooding in Colorado has broken or exceeded the capacity of flood gauges, so officials don't know how much water is headed east.

The first useful assessment of South Platte River levels occurred Sunday in Fort Morgan, Colo., said Bob Swanson of the U.S. Geological Survey in Nebraska. But even that reading was inadequate because the river had already dropped at least 2 feet, he said.

Fresh readings Monday night at Julesburg, Colo., were expected to better assess the threat to Nebraska.

» Drought. Severe and extended drought has left the South Platte River virtually devoid of water, so there is plenty of room to accommodate floodwaters. In some areas of Nebraska, the river isn't expected to overflow its banks, the National Weather Service said.

» Debris. This is the big wild card. As drought depleted the river, trees and shrubs grew, and debris piled up. As the surge of water moves through, it will probably dislodge the vegetation and debris, piling it against choke points in the channel, such as bridges. If that happens, the choke points could send water spilling across the valley.

“When that water hits bridges along the South Platte, it will be difficult for it to stay in the channels,” said Brian Dunnigan, director of the Nebraska Department of Natural Resources. “Debris in the water is going to be the biggest issue and could contribute to additional flooding.”

Here's one thing officials do know: At Fort Morgan on Saturday evening, the river rose about 9 feet in two hours as the bulk of a roughly 15-foot surge came through.

“We're kind of in uncharted territory,” said Kenny Roberg, meteorologist at the National Weather Service office in North Platte.

Some flooding is likely at various points along the length of the South Platte and along the Platte River, even if it is only minor, Roberg said.

“We want people to know that ... this is likely to meet or exceed Nebraska's historic floods on the South Platte River,” he said.

The flood forecast is likely to change, but as of Monday evening, these were the predictions:

» Roscoe: Water began rising overnight, and the river was expected to peak at major flood stage Thursday night at more than 11 feet higher than it was Monday.

» North Platte: Water will begin rising Wednesday and will peak Friday night within two-tenths of an inch of the record. Moderate flooding was expected as a result.

» Brady: Water will begin rising Thursday morning and peak Saturday morning, with moderate flooding expected.

Eastern Nebraska: It was too soon to tell. Floodwaters were expected to reach Kearney on Sunday and Louisville on Sept. 30, according to the weather service.

Southwest Nebraska emergency officials are alerting owners of property along the river of the risk, said Ron Leal, region 21 emergency manager.

At Big Springs in Duel County, workers are plugging a culvert beneath the rail line so water can't flow into town, Leal said. A temporary dike is being built for the local grain elevator.

Most officials said they expected Interstate 80, U.S. Highway 30 and railroad tracks near the Platte to remain open.

Tom Sands, operations manager for the Nebraska Department of Roads, said crews have inspected bridge crossings and positioned equipment to be ready for whatever comes. Travelers can monitor the department's 511 phone line and website for information on road closings.

County bridges and county roads are probably at the most risk, said Al Berndt, assistant director of the Nebraska Emergency Management Agency.

NEMA is working with state agencies to prepare for flooding, Berndt said, and will open a mobile command center at Ogallala.

Some agency preparations:

» The Nebraska Department of Natural Resources, National Weather Service and Nebraska Information Analysis Center are developing models to assess how communities could be affected.

» Nebraska State Patrol planes are flying over the river to photograph the channel and determine which areas are most vulnerable to backups or damage.

» The Nebraska Department of Environmental Quality has provided NEMA with information on what chemicals are stored near the river.

Part of the problem, said Roberg of the weather service, is that the Platte River valley has changed dramatically in the decades since the last big flood. Development and other changes since record flooding in 1935 are likely to send water along unexpected paths, he said.

Roberg said that once the river crests, it is likely to plateau and then slowly drop. People should expect to see significant water in the Platte through at least the end of the month, he said.

There is the potential for good news from this flood, said Swanson of the U.S. Geological Survey. It will help refill reservoirs and recharge the alluvial aquifer along the Platte, he said. And it should scour vegetation from the river channel and create new habitat for wildlife.

The Central Nebraska Public Power and Irrigation District plans to divert as much water as possible from the Platte River to refill its reservoirs.

The water level in Jeffrey, Midway and Johnson Lakes will rise. Johnson Lake could see a 5-foot rise; Jeffrey Lake needs only about 1.5 feet to fill up.

Contact the writer: Nancy Gaarder

nancy.gaarder@owh.com    |   402-444-1102    |  

Nancy writes about weather, including a blog, Nancy's Almanac. She enjoys explaining the science behind weather and making weather stories relevant in daily life.

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