August 5, 2021


Big Sioux River Flooding


River Flood Warnings continue to run up and down the Big Sioux River in eastern, South Dakota today.  Flooding along the river has shutdown may rural roads and caused flooding on farm lands.  The flooding conditions along and near the river is expected to continue this week with a few locations starting to see improvements.

Below we broke down the National Weather Service's forecast for locations along the river starting up river and working our way south.

Photo Credit: NWS

Starting with the Big Sioux River near Watertown, Flood Warnings are in effect for the area.  The river level at 10:15am CDT was at 9.66 feet which is 1.66 feet over flood stage.  The forecast is calling for the river to increase to about 10.6 feet at around 1:00am CDT Thursday morning.  After the crest, the Big Sioux River is forecast to decrease and hopefully be out of moderate flood stage by Friday afternoon.

Down river in Castlewood, a flood warning remains in effect for the area as river levels are at moderate flood stage with a reading of 11.99 feet at 10:45am CDT.  Increase to the river's level are expected to increase through Thursday morning and forecast to peak at about 12.6 feet.  Forecast calls for the river levels to drop into minor flood levels Sunday morning and continue to decrease in levels.

Photo Credit: NWS
Photo Credit: NWS

The Big Sioux River south of Brookings has a different story then the stations up north.  The river level is at major flood stage sitting at 13.0 feet at 11:45am CDT.  The forecast calls for the river to increase to 13.1 feet around Thursday afternoon and hold until Sunday.  By later in the day on Monday, the river is expected to be at moderate flood stage and minor flood stage by Wednesday afternoon.

Sitting at 15.46 feet at 11:30am CDT, flood warnings are in effect for the Dell Rapids area.  The river level this morning was at major flood stage and forecast to remain there until Tuesday afternoon.  The forecast calls for a slight increase with a peak level at around Friday night into Saturday morning.  By next Wednesday's, the river's level looks to be into the minor flood stage category which is under 14.0 feet.

Photo Credit: NWS
Photo Credit: NWS

Sioux Falls is observing moderate flooding stage with a reading of 21.78 feet at 10:16am CDT this morning near North Cliff Avenue.  Forecast continues to drop river levels in town and be into the minor flood stage category by Monday afternoon.  Flood warnings remain in effect for the river area.

Please keep in mind that gauge readings may be affected by ice.  The river forecast graphs are credited to the National Weather Service and for the latest readings and forecast, please visit their website at