Investigating the spatio-temporal distribution of bedload dynamics in a gravel-bed river using a combination of field measurements and hydromorphodynamic simulations

Abstract Bedload transport in gravel-bed rivers during floods is highly variable in both space and time due to interactions between flow hydraulics and sediment dynamics at the reach- and micro-scales. Understanding the spatio-temporal distribution of bedload is very useful for river management, but measuring it in the field remains challenging. Our study utilized a novel field measurement approach that combined (1) a cobble-shaped geophone for estimating bedload flux and (2) a cobble-shaped riverbed pressure measurement system (Sphera) for estimating local water depth and bed shear stress. Field data obtained at three observation locations were used to investigate the temporal distribution of bedload changes during a flushing flood, and to calibrate a hydromorphodynamic model. Field survey results indicated that bed shear stress and bedload peaks were concentrated at the rising limb of a flushing flood within straight sections of the channel, while they were concentrated at the falling limb in a meander section. Output from the hydromorphodynamic model was used to determine the spatio-temporal distribution of bedload across the domain, to analyze sediment migration along the channel, and to determine local erosion and deposition, as well as the impact of sediment availability on the bedload distribution. Our findings emphasize the importance of advanced field measurements and a complementary hydromorphodynamic simulation for clarifying complicated sediment transport processes occurring during floods in gravel-bed rivers.