Notes from the Field, July 6, 2011, Tumbling Trees

Sioux City, Iowa.  The persistent high water of the Missouri is beginning to take a toll on the trees lining the stream’s banks.  The saturated soil around the roots of the trees no longer provides a strong base of support.  Thus, when high winds or strong river currents strike the vulnerable trees, they easily tumble over into the floodwater.  Dozens of large and small trees are lying on their sides in the engorged Missouri just a mile downstream from its juncture with the Big Sioux River at Sioux City, Iowa.  The number of downed trees is going to increase exponentially as the summer moves toward fall and the Army keeps the discharge rate out of Gavin’s Point Dam at 160,000 cubic feet per second.  The loss of bankline timber will increase runoff into the Missouri for years to come.  Healthy timber tracts halt or slow runoff by storing water in root systems, trunks, and leaves.  Once the trees are dead and gone, rain will hit the valley floor and more quickly drain into the Missouri.  River edge trees also act as a natural means of bank stabilization.  Trees slow down erosive currents, deflect water from the bankline, and keep valley soils from rapidly washing away.  The absence of trees along the river will lead to intensified bank erosion.  Additionally, the loss of timber strips adjacent to the river means that agricultural chemicals, feedlot fecal matter, and urban storm water (which contains automobile lubricants) will readily find its way to the Missouri.  The destruction of river side timber will have serious negative repercussions for the health of the Missouri River ecosystem.

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