Estimating Bedload Transport in Braided Gravel-Bed Rivers using Structure–from-Motion Photogrammetry and the Morphological Method

English Abstract:

Monitoring bedload transport in gravel-bed rivers, and braided rivers in particular, has been notoriously difficult due to highly dynamic sedimentary processes that result in considerable geomorphic change, both spatially and temporally. This research aims to characterize fluvial geomorphic change, and subsequently bedload transport, using high-resolution repeat surveys from a Froude-scale physical model of a gravel-bed braided river. The overall goal is to investigate the relationship between morphological dynamics and bedload transport rate and test whether reliable bedload estimates can be based primarily on planimetric morphology and dynamics. Specifically, this research is will examine the role of the morphological active width, defined by the bed area experiencing detectable morphological change, and determining its relationship with bedload transport rate and channel morphology. High-resolution DEMs (±2mm vertically) are created of the physical model surface using Structure-from-Motion photogrammetric techniques. Successive DEMs are used to create a DEM of difference from which the morphological active width and volumes of erosion and deposition are used to calculate bedload transport rate. The use of a physical model is ideal for examining these relationships experimentally over a range of river conditions with both tiltable bed (slopes of 1-2%) and adjustable discharge (0.6-3.2 ls^-1). The bedload transport rate will be independently monitored using a series of sediment traps at the downstream end of the physical model to verify the relationship to the morphological measurements. These preliminary results will contribute to the theory of bedload transport in braided gravel-bed rivers by characterizing the relationship between bedload transport, morphological change and sedimentary processes.