MORPHOLOGY OF THE HOLOCENE MISSOURI RIVER IN NORTHWESTERN MISSOURI

The goal of this project, funded through the USGS-EDMAP program, is to map paleochannels of the Missouri River. We examined the reach of the river in Holt County, Missouri north of US 159 covering three quadrangles (Big Lake, Craig and Corning). Combining this project with similar projects along the river completed in previous years will determine the cause of the Missouri’s transition from meandering to braided.

Initial mapping was conducted using aerial photographs to locate paleochannels of the Missouri River. Aerial mapping was field checked and mapping was completed at a scale of 1:24,000. Mapping was augmented by drill logs obtained by drilling holes using a hand auger to drill to depths between six and eight meters. A total of sixty-six holes were drilled in the three quadrangles. Four of the drilled samples were taken for Optically Stimulated Luminescence (OSL) tests to obtain dates for several landforms.

The reach of the mapped river follows a similar pattern seen upstream and we recognize a sharp transition from a meandering to a braided channel. However, in contrast to other upstream reaches that transition quickly, the mapped reach contains intermediate forms – meander bends which contain more, smaller channels than a meandering system but fewer, larger channels than a braided system – which are not preserved farther upstream. Downstream transitional forms indicate a gradual transition between meandering and braided. In the mapped reach, the transitional forms are found intermingled with braided forms, which could indicate that the preservation of these intermediate forms in the mapped reach merely indicate a quirk in an established braided system. The mapped area also shows the distinctive braid morphologies found in the downstream reaches. The mapped area, which is transitional geographically, also appears to be transitional morphologically in that it contains elements otherwise distinct to either upstream or downstream reaches.