I-29 damaged by Mo. River flood (updated 4:54-p.m.)

News

August 12th, 2011 by Ric Hanson

The Missouri River has yet to recede across Interstate 29 in southwest Iowa, and the full extent of the damage is uncertain, but one thing is known: the road is in worse shape than officials had hoped. Bob Younie, head of maintenance for the Iowa Department of Transportation said in a briefing Thursday, that an 11-foot deep hole has been scoured beneath I-29 where it goes up an embankment to an overpass, near Hamburg. The hole, he says, is getting bigger. Younie called the situation a “Setback…in the recovery from the flooding.”

That section of interstate he described was closed in June because of the Missouri River flooding. There are four Interstate bridges in that area. Younie said the worst case scenario would be for all four bridges to get washed out by flooding, but so far that, hasn’t happened. He said the best case scenario, which is no longer possible, would have been if the bridges and their approaches would escape without major damage.

Younies says so far, one bridge approach has seen significant scouring, and a parallel bridge is threatened by scouring. The only way to know for sure how much damage the bridges and roadway have sustained, is after the water recedes, and an assessment gets underway. The water may linger in the area for at least another month, but even that’s not a given.

Here’s the DOT Press Release issued today (Friday), at 3:41-pm

AMES, Iowa – Aug. 12, 2011 - The Iowa Department of Transportation (DOT) is
reporting that the Missouri River flooding has undermined the south bridge
approaches of dual Interstate 29 bridges at mile post 1.4 in Fremont County and is
threatening the bridges. The seriousness of the damage will undoubtedly prolong
flood recovery efforts aimed at eventual reopening of the interstate when the waters
recede. 

The dual set of bridges were constructed in 1972, are 40 feet wide and 179 feet
long, and located in the northbound and southbound lanes of I-29. The bridges take
I-29 traffic over Drainage Ditch Number 6.

The full extent of the damage to the bridges, roadway approaches and embankment are
not known at this time due to the high-velocity flood waters that are still rushing
under the bridge. But there is damage readily apparent at the site, including
collapsing of the pavement, loss of material and scouring at least 11 feet deep. 

Mitigation efforts are underway to attempt to reduce further loss of the soil under
the bridge approach pavement. But the efforts have had little success as the rushing
flood waters continue to wash away the large rock placed at the site. 

It is too soon to determine what corrective actions will be necessary, but stability
and safety of the structure is threatened primarily due to the extent of the scour.
The piling that support the bridge are 35 feet long and have been partially exposed
(no longer embedded in the river bottom) due to the scouring action of the flood
water.

Due to an earlier levee breach, flood waters from the Missouri River are flowing
inland, affecting I-29 and area tributaries and streams. 

The Iowa DOT will continue to provide the public with regular updates on the damages
caused by the flooding, as well as recovery efforts when the waters begin to recede
later this month. 

This is an unsafe area for the public to enter due to the possibility of undermined
pavement.

Due to these types of safety hazards, never enter a closed roadway, even after the
flood waters recede.