On the Relationship between Experimental and Numerical Modelling of Gravel-Bed Channel Aggradation

Abstract

This communication explores the use of numerical modelling to simulate the hydro-morphologic response of a laboratory flume subject to sediment overloading. The numerical model calibration was performed by introducing a multiplicative factor in the Meyer–Peter and Müller transport formula, in order to achieve a correspondence with the bed and water profiles recorded during a test carried out under a subcritical flow regime. The model was validated using a second subcritical test, and then run to simulate an experiment during which morphological changes made the water regime switch from subcritical to supercritical. The “relationship” between physical and numerical modelling was explored in terms of how the boundary conditions for the two approaches had to be set. Results showed that, even though the first two experiments were reproduced well, the third one could not be modeled adequately. This was explained considering that, after the switch of the flow regime, some of the boundary conditions posed into the numerical model turned out to be misplaced, while others were lacking. The numerical modelling of hydro-morphologic processes where the flow regime is trans-critical in time requires particular care in the position of the boundary conditions, accounting for the instant at which the water regime changes.

On how defining and measuring a channel bed elevation impacts key quantities in sediment overloading with supercritical flow

“…The critical Shields parameter, c * , is the other important parameter in the Meyer-Peter and Müller formula (1948) The numerical solver used to solve the system (5) is embedded in the BASEMENT software provided by ETH Zürich / Laboratory of Hydraulics, Glaciology, and Hydrology (VAW). This solver was already used to represent experiments carried on in the present channel by Zanchi et al (2019). .…”

“…The present manuscript is a follow-up of an earlier experimental campaign carried out at the Politecnico di Milano (Radice and Zanchi 2018;Zanchi et al 2019;Zanchi and Radice 2021) where sediment aggradation was studied in subcritical flow, providing simple predictors for the celerity of propagation and the height of an aggrading front and numerically reproducing some benchmark experimental results. Furthermore, in the prior campaign, ad hoc image-based measurement methods were devised for measuring the relevant parameters.…”