Flood FAQ

A flood is an event where water runoff or rain temporarily covers two or more acres or affects two or more properties.

The Big Sioux River and Skunk Creek are the two primary flooding sources affecting the City of Sioux Falls. The Big Sioux River upstream of Sioux Falls has a drainage area of 5,718 square miles. Skunk Creek, its upstream tributary, has a drainage basin of 570 square miles.

Since 1881, the City of Sioux Falls has experienced flooding from the Big Sioux River 19 times and from Skunk Creek 8 times. Updated August 2023.

Most flooding events occur during March and April and are caused by snow melt. Flooding caused by rainfall has historically occurred during June. 

While any area can flood, the most common are floodplains. Those areas are shown on FEMA’s Flood Insurance Rate Maps (FIRM) and City of Sioux Falls maps online. Flood Insurance Rate Maps (FIRM) are available for downloading here. 

FEMA identifies flood hazard areas throughout the U.S. and it's territories by producing maps (such as the Flood Insurance Rate Maps – FIRM’s). Areas of flood hazards are identified on these maps. The floodplain is considered a high-risk area having a 1 percent chance of occurring in any given year and is commonly referred to as the Special Flood Hazard Area (SFHA). 

A floodplain development permit is required to be submitted.Development is considered with any change to the property. Some examples are, but not limited to, new buildings, remodels, demolition, lot grading, underground work, paving, placement of signs, etc.

It’s how high water expected to rise during a flood. More specifically, it’s the water surface elevation of the 1-percent annual chance flood.

Elevation certificates are required for properties within the floodplain and for residential properties built within 100 feet of the floodplain. 

No, with FEMA’s Risk Rating 2.0 program elevation certificates are no longer required. About the National Flood Insurance Program. Frequently Asked Questions. Federal Emergency Management Agency. Floodsmart.gov