Flood — Pottawattamie, Iowa

2011-08-01 to 2011-08-31 · near Grable, Pottawattamie, Iowa

Event narrative

Flooding along the Missouri River gradually worsened over western Pottawattamie county during June and July and persisted into August 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, flood stage is 29 feet, before falling slightly in July and a little more by early August. By the end of the month decreased releases from Gavins Point Dam had allowed the river to fall to around 31 feet. The flooding in Pottawattamie county closed roads along the river including 16 miles of Interstate 29 north of Council Bluffs and Interstate 680 east of north Omaha. Several parks and recreation areas were flooded along with parking lots and parts of the parking garages of 2 riverboat casinos. 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 which came close to failing in July. Some homes near the river experienced seepage into basements from high ground water levels. Although river levels had dropped by the end of August, minor flooding persisted into September. The U.S. Army Corps of Engineers stated that a little over $6 million was spent on levee repair/work in Pottawattamie county. As the river fell by the end of August it became apparent that Interstate 680 had been undercut by the current completely destroying the pavement from the river to its junction with I29 near Crescent. The Iowa Farm Bureau Federation estimated that the flood event caused total crop and economic losses of $ 31.2 million in Pottawattamie county.

Wider weather episode

A record rain event in May in eastern Montana combined with high water from storms in April and May, plus snow melt from a much above normal snow pack, all contributed to bring record high water to the Missouri River chain of reservoirs by late Spring. Then residual snow melt and additional rains produced record 13.8 million and 10.0 million acre feet of runoff above Sioux City in June and July respectively. This helped contribute and sustain record releases from the Missouri River Reservoirs from mid June into early August. Releases from Gavins Point Dam, which is the last in the chain, reached around 160,000 cfs by the middle of June and remained that high into early August before dropping to around 90,000 cfs by the end of the month which help alleviate some of the flooding. The flooding continued into September but moderated greatly. By the end of September the Omaha district of the U.S. Army Corps of Engineers estimated it spent $56 million directly and indirectly in battling the river throughout its share of the basin. In western Iowa 46 miles of Interstate 29 were closed due to flooding and around 250,000 acres of farmland were inundated. The Iowa Farm Bureau Federation estimated that the flood event caused total crop and economic losses of $207 million in southwest Iowa.

View location on OpenStreetMap → (41.5112, -96.0288)

Source: NOAA Storm Events Database, event_id 322997. Narrative written by the NWS forecast office that issued the report.