Flood — Monona, Iowa

2011-08-01 to 2011-08-31 · near Albaton, Monona, Iowa

Event narrative

Flooding along the Missouri River gradually worsened over Monona county during June and July as record releases from Gavins Point Dam brought widespread flooding along the river. Conditions improved markedly during August as releases were reduced and the river level at Decatur dropped below flood stage late in the month. Flooding in Monona county was mainly confined to agricultural lowlands, recreation areas and roads near the river. However, Blencoe started sandbag operations in June as did other businesses from Blencoe to Onawa. The flooding forced the post office in Blencoe to move operations to a nearby town. Late in June the Highway 175 bridge over the Missouri between Decatur and Onawa was closed due to erosion of the abutment on the Iowa side of the bridge and the bridge and highway remained closed through August. The Iowa Farm Bureau Federation estimated that the flood event caused total crop and economic losses of $32.3 million in Monona 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 → (42.2185, -96.3817)

Source: NOAA Storm Events Database, event_id 322988. Narrative written by the NWS forecast office that issued the report.