ASSESSING BEDFORM DYNAMICS AND BEDLOAD SEDIMENT FLUX IN SANDY BRAIDED RIVERS USING AIRBORNE AND SATELLITE IMAGERY: A COMPARISON OF AERIAL, DRONE AND CUBESAT APPROACHES (Invited Presentation)

Quantifying the flux of bedload sediment remains difficult, if not impossible, in many rivers – both small and large – around the world. Yet such data are essential in assessing the impact of human infrastructure, understanding the geomorphology and sedimentology of channel change and assessing ecological status. The use of bedform tracking has been utilized for many years to quantify bedload flux both across and down channel. However, such tracking relies on acquisition of accurate bathymetry that can be logistically difficult, time-consuming and expensive.

This paper details the use of aerial imagery from three sources – airplane, drone and satellite – to quantify bar migration and bedload sediment flux in the sand-bed South Saskatchewan River, Canada. Images from manned airplane sorties (MAV), repeat unmanned aerial vehicle (UAVs) surveys, and Planet CubeSat satellite imagery are used to quantify dune and bar kinematics. Structure-from-Motion (SfM) techniques and application of a depth-brightness model are used to produce a series of Digital Surface Models (DSMs) at low and near-bankfull flows. Analysis suggests a depth-brightness model approach can represent the different scales of bedforms present in sandy braided rivers with clear and shallow (< 2 m deep) water.

The aerial imagery is used to quantify the spatial distribution of unit bar and dune migration rate in several reaches. Sediment transport rates for dunes and unit bars, obtained by integrating migration rates (from UAV) with the volume of sediment moved (from DSMs using MAV imagery) show near-equivalence in sediment flux. Hence, reach-based sediment transport rate estimates can be derived from unit bar data alone. Moreover, our results demonstrate that reasonable estimates of sediment transport rate can be made using just unit bar migration rates as measured from 2D imagery, including satellite images, so long as informed assumptions are made regarding average bar shape and height. With recent availability of frequent, repeat satellite imagery, and the ease of undertaking repeat MAV and UAV surveys, for the first time, it may be possible to provide global estimates of bedload sediment flux for large or inaccessible clear-water rivers that currently have sparse information on bedload sediment transport rates.