The 1998 Flood

Atlantic

Cass County is no stranger to flooding.  2019 was a rough spring for much of Iowa, especially southwest Iowa.  In late May Emergency Management Director for Cass County, Mike Kennon, was informing residents again that there was heavy flooding on the West Nishnabotna River.  Many roads were closed in the southeastern part of the county due to water on the roadways.  Kennon asked residents not to drive through water on roadways, always a more dangerous situation than it, at first, might seem. 

Many Cass County residents will remember the flood of 1998 on the East Nishnabotna River.  As a result of severe thunderstorms, “more than 8 inches of rain fell over a large part of Cass County.  The rain gage at Atlantic, Iowa, recorded a 24-hour total rainfall of 13.18 inches.”  At the time of the 1999 US Geological Survey report on the flood, this was a statewide record for the greatest amount of rainfall in a 24-hour period.

“The peak discharge was 41,400 cubic feet per second in the east Nishnabotna River near Atlantic.”  This extraordinary amount of water was topped by the cubic feet per second volume downstream: “60,500 cubic feet per second in the East Nishnabotna River at Red Oak and 65,100 cubic feet per second in the Nishnabotna River above Hamburg.”

This peak discharge at Atlantic exceeded the theoretical 200-year flood.  The peak discharge at Red Oak and Hamburg both exceeded the theoretical 500-year flood.  

Sources: on-line: “Roads Closed in Cass County Due to Flooding,” KSOM, May 24, 2019; Edward W. Fischer, “Flood of June 15-17, 1998, Nishnabotna and East Nishnabotna Rivers, Southwest Iowa,” US Department of Interior and US Geological Survey, USGPO, 1999.