Analysis of Morphological Evolution of an Incipient Chute Cutoff using UAS and LIDAR

Meandering rivers constantly alter their form, eroding sediment along their outer banks and depositing it along their inner banks. Outer bank erosion outpaces inner bank deposition, so river sinuosity increases until the channel erodes into itself (neck cutoff) or forms a new channel between two points (chute cutoff) and sinuosity is reduced. Chute cutoff must be partly controlled by channel-forming processes on the floodplain, which introduces additional complexity compared to neck cutoffs. Yet despite the importance of chute cutoff on controlling meandering river form, their formational processes are not well understood. This presentation documents the evolution of an incipient chute cutoff in a farm field along the East Fork White River, Indiana, USA, using high temporal and spatial resolution LIDAR topography. Aerial photography obtained in 2013 reveals the formation of a large scour pit in the center of the incipient chute channel. The pit is roughly the same width and length as the chute channel width, and has banks as high as the main channel banks. In Spring of 2018, data obtained from LIDAR integrated with an unmanned aerial system shows the presence of a series of smaller pits within the chute, each with a depth less than half the depth of the large pit. A second LIDAR scan, obtained after a flow with mean velocities over one m/s through the chute, shows morphological changes to the channel and erosion of the pits associated with overbank flooding. A third LIDAR scan after heavy rain, but without overbank flooding, shows infilling of the pits due to sediment flux associated with overland flow into the chute from the surrounding floodplain. The formation and morphological evolution of pits within a chute channel have not been document in the field, but could be important mechanisms for chute channel evolution.