Fluvial evolution of the central Platte River sand body near Grand Island, Nebraska

This dissertation presents new data sets unavailable in previous studies of the central Platte River to better characterize and quantify the processes involved in the creation and evolution of a braided stream system. In the first study, sediment cores, wireline logs, borehole cuttings, and optically-stimulated luminescence (OSL) data were used to characterize the dimensions and chronology of a new model of the Platte River entrenched valley fill. Periods of entrenchment and aggradation within the different valley elements were associated with regional climate changes. In the second study, data compiled from aerial photography, general Land Office maps (GLOs), and discharge data of the Platte River braided channel were used to provide new insight toward the understanding and quantification of channel evolution and partial abandonment of the central Platte River. Analysis of aerial photographs and GLOs in ArcMap™ show that channel areas and widths decreased from 1858 to 2006. Stabilization through vegetation of bars and channel banks is cited as the major contributing factor to the development of anabranching system within the boundaries of the 1858 channel. The Wood River, a tributary to the Platte River, has also experienced channel evolution in the form of an increase in sinuosity, after occupying an abandoned channel of the Platte River at the beginning of the 20th century. Platte River channel evolution is explained using a channel abandonment model that accounts for the gradual abandonment of the Platte River and its evolution from a braided to an anabranching system. In the third study, wireline logs, sediment cores, aerial photography, and ground penetrating radar (GPR) data from the central and lower Platte River channel were used to reformulate the vertical sequence alluvial facies and bar initiation models of the Platte River. GPR profiles of the active central and lower Platte Rivers exhibit a general lack of large downstream-directed planar cross-beds, indicative of downstream-accreting macroform bars that dominate previous alluvial facies and bar inception models. Therefore, three new vertical facies models are introduced to account for stratigraphic features prevalent in the central and lower Platte not accounted for in previous models