Laboratory determination of aggradation wave celerity due to sediment overloading in supercritical flow

The manuscript presents an experiment-based formula to estimate the celerity of propagation of an aggradation wave along a river channel overloaded with sediment. The celerity parameter is important from an engineering point of view, since changes in river morphology can largely contribute to hydraulic hazard; managing the latter may require a reliable prediction of how long it would take for an aggradation wave to propagate from sediment source areas to a critical spot. In the present study, the determination of the aggradation wave celerity was approached experimentally, realizing laboratory runs with sediment overloading and detailed temporal measurement of the resulting bed profiles. Supercritical flow conditions were considered, as most representative of upland environments. In these conditions the aggradation process is dispersive, requiring particular care in quantifying a representative celerity for the wave; exploiting a synergy with a literature analytical depiction of the aggradation process, the local and instantaneous celerity of propagation of the bed elevation was suitably averaged to estimate a bulk celerity value for each experiment of the campaign. A formula is provided allowing to predict the experimental values of this bulk celerity within ±25 % accuracy; the only control parameter in the formula is the load ratio that represents the degree of sediment overloading.