Flood warnings have been issued for portions of the Cheyenne and White rivers in western South Dakota because of ice jams.
The National Weather Service office in Rapid City issued the warnings Monday morning.
Melissa Smith, an NWS hydrologist, urged people to be careful around floodwater and said motorists should heed the slogan “turn around, don’t drown.”
“You never know what the pavement is like or what the road base is like underneath the water,” Smith said. “It doesn’t take a lot of water to wash away a vehicle.”
The weather service issued a flood warning until 9:15 a.m. Friday for central Oglala Lakota County, west-central Jackson County and southeastern Pennington County. Specific areas expected to experience flooding include the White River around Interior, Rockyford and Slim Buttes.
The weather service said ice-jam flooding is occurring along the White River from the Badlands to the Nebraska line.
“River levels along the White River will continue to fluctuate all week, as ice jams form and release,” the weather service said. “The flooding will continue until all the ice is out of the river and the majority of the snow has melted.”
Flood warnings are also in effect until further notice for the White River near Oacoma and the Cheyenne River near Wasta.
Monday morning, the White River near Oacoma was at 22.2 feet, where it was expected to stay with some fluctuations. The flood stage is 15 feet.
The Cheyenne River near Wasta was at 13.2 feet, where it was also expected to stay with some fluctuations. The flood stage is 13 feet.
Smith said the flooding is being exacerbated by frozen ground, which is not absorbing water. She said the frost depth at the weather service office in Rapid City is 2-3 feet.
“Having that frozen ground, it acts a lot like asphalt would,” Smith said. “It doesn’t allow that water to penetrate. It’s all just starting to run off.”
A winter storm dumped up to 2 feet of snow on parts of western South Dakota last week and created massive drifts with winds reaching 70 mph.
Smith said the forecast for this week does not include any significant precipitation. Temperatures are expected to warm up gradually and reach highs in the 50s by Wednesday, with overnight lows in the 20s and 30s.