Notes from the Field, June 16, 2011, River Hammers Channelization Works

Sioux City, Iowa.  On Wednesday, June 15, 2011, “Sioux City Journal” photographer Tim Hynds shot an aerial photo of the Port Neal power plant along the Missouri River west of Salix, Iowa.  The image, which appeared in the June 16, 2011, edition of the “Journal,” on page A8 shows the rising Missouri as it flows past the facility.  What’s notable about the picture isn’t its portrayal of the engorged river threatening Port Neal.  Rather, what makes this such a memorable photograph is its depiction of the Army’s pile dikes just upstream from the electrical-generating plant.  Hynds’ photo clearly shows a series of pile dikes in the center of the Missouri River.  The pile dikes are not supposed to be in the center of the river!  Only three weeks ago, the dikes (or wingdams) had been firmly anchored to solid ground on the Nebraska side of the river.  That is where they are supposed to be now.  But in recent days, the river has outflanked the structures.  As a result, the wingdams are no longer attached to any shoreline.  Instead, the former bankline in Nebraska is gone – inundated by the widening Missouri.  The photo indicates that a new channel flows behind the dikes on the landward side.  That channel is shown pouring a thin sheet of water across its former floodplain.  The Army built the dikes to keep the river out of its floodplain.  What is taking place west of Salix is what is referred to in Army parlance as a “loss of alignment.”  In layman’s terms it’s the Missouri “busting out.”  Hynds’ image provides confirmation that the Missouri is dismantling the navigation channel piece by piece, pile dike by pile dike.  If the Missouri is capable of this kind of damage in only one mile of the navigation channel, what is the river doing to the other 752 miles of pile dikes and revetments from Ponca, Nebraska, to the river’s mouth?  Surely the realignment of the channel is extensive.  Another question that is worth considering is this: if the river has already realigned itself after only a couple of weeks of high flows, how much more will it shift its channel during the next two months of flood flows at even higher discharge rates?

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