As rivers and streams approach their confluence with the Mississippi , their canyons grow progressively steeper and deeper , particularly in the last in their journey to their mouths . The change in elevation above sea level from ridgetops lining a stream to its confluence with the Big River can reach well past in only a few miles . The Waukon Municipal Airport is reliably established as being above sea level . The Army Corps of Engineers maintains a river level in Pool 9 of about above sea level , which covers Lansing . Maps and signs issued by the Iowa Department of Transportation indicate Waukon and Lansing are apart on Iowa Highway 9 . This is a drop of more than in less than ( and this along a very minor tributary of the Mississippi ) . " The role of isostatic rebound on the process of stream incision in the area is not clearly understood . " There are many small towns in the Driftless Area , especially in river valleys , at or upstream from the Mississippi . Small towns in a deep steep valley going down to the Mississippi are at risk every 50 to 100 years or so of a major flood , as with the wreck of Gays Mills , Wisconsin , in August 2007 , or the holding of the levee in Houston , Minnesota , ( on the South Fork Root River ) at the same time . Metropolitan areas have flood walls ( '' See '' 2007 Midwest flooding ) . In August 2018 , the region yet again experienced record-breaking flooding in valley towns such as Coon Valley , Wisconsin , La Farge , Wisconsin and Viola , Wisconsin . The Kickapoo River flood stage is 13 feet but was recorded as high as 23 feet during the 2018 flood which was declared a statewide emergency . Many community members were rescued by boat from the Wisconsin Department of Natural Resources . Days later when two dams in Ontario , Wisconsin broke it created flood water downstream in Readstown , Wisconsin , Soldiers Grove , Wisconsin and Gays Mills , Wisconsin
2007 Midwest flooding
2007 Midwest flooding
Driftless Area