Flood — Pottawattamie, Iowa

2011-07-01 to 2011-07-31 · near Grable, Pottawattamie, Iowa

Event narrative

Flooding along the Missouri River gradually worsened over Pottawattamie county during June and persisted into July as record releases from Gavins Point Dam brought widespread flooding along the River. The river near Omaha climbed to a little under 36 feet by the end of June before falling slightly early in July before reaching a second peak around 36 feet in late July before falling slightly by early August. The flooding in Pottawattamie county closed 16 miles of Interstate 29 north of Council Bluffs and also closed I680 from the Mormon Bridge to its junction with I29 near Crescent. Several parks and recreation areas were also flooded along with the parking lots and parts of the parking garage of 2 riverboat casinos. Other county roads and farm land near the river were also flooded. At least 100 homes in Council Bluffs were evacuated and about 10 businesses were closed. Tens of thousands of sandbags were filled and deployed to help shore up weak spots in the federal levee in the Council Bluffs area. Some homes near the river experienced seepage into basements from high ground water levels. The flooding continued into August. As of early July the city of Council Bluffs had spent or committed over 5.5 million dollars for flood relief/prevention.

Wider weather episode

A record rain event in May in eastern Montana combined with other storms in April and May plus early spring snow melt and brought record high water to the Missouri River chain of reservoirs. Heavy rain events and late season snow melt contributed to record runoffs above Sioux City in June of 13.8 million acre feet, and in July of 10 million acre feet. These all contributed to record releases from the Missouri River Reservoirs. Releases from Gavins Point Dam, which is the last in the chain, increased to around 160,000 cfs by the middle of June and remained that high through July. The previous record release was 70,000 cfs. The high releases and periodic rains produced flooding which gradually worsened from May into June and then continued through July and into August. The river near Nebraska City, which is normally a little over 1,000 feet wide, widened to a channel of more than 2.6 miles with some holes over 60 feet deep. The flooding closed around 40 miles of Interstate 29 in western Iowa and also several other highways and highway bridges along the river.

View location on OpenStreetMap → (41.4911, -96.0342)

Source: NOAA Storm Events Database, event_id 309609. Narrative written by the NWS forecast office that issued the report.