Bedform distribution, dynamics, and ecological potential during a flood event in a large channelized river

We present a classification framework for bedform distribution and dynamics, applied to ecological potential in a large, sand-bedded, channelized river. Our objective was to understand how ecological processes would be affected by varying bedforms and velocity fields during a flood event. We mapped a 3.6-kilometer reach of the Lower Missouri River eight times over the course of a large flood event in the spring and summer of 2019, using a multibeam echosounder for bathymetry and an acoustic Doppler current profiler to characterize velocity fields. Discharges ranged from 3,680-7,360 cubic meters per second (m³*s^-1) and the reach was sampled weekly over a flood event with a peak flow of 8,200 m³*s^-1. Bedforms ranged in size from less than a meter (m) in wavelength and amplitude to dunes greater than 4 m high and 150 m long. Small dunes were located in lower velocity regions on the inside bend and behind wing-dikes as well as superimposed on larger dunes. Larger dunes were generally located in the channel thalweg and associated with higher flow velocities, but dunes did not necessarily scale with discharge over the course of the flood, potentially due to sediment supply limitations and hysteresis effects. Changes in bedform size over the course of the flood event were most pronounced in the thalweg; less change in bedform size occurred behind wing dikes on the inside bend of the channel. Although information about distributions of fish and invertebrates are limited due to the difficulties in sampling these dynamic environments, contextual ecological information allows some inference about the ecological relevance of bedform dynamics, especially with respect to habitat quality, habitat disturbance (and refugia), and flow vectors that affect advection and retention of food items and larval fish.