Bed Load Transport and Alternation of a Gravel-Bed River Morphology within a Vicinity of Block Ramp: Classical and Numerical Approach

In current river management, we very often use environment-friendly hydraulic structures when it is required for river bed or river bank protection due to erosion of a river channel. Block ramps are one of many methods used to stabilize river beds. They provide a semi-natural solution to certain river engineering problems in mountain streams. When building block ramps, one can use the dissipative behavior of large rock blocks or boulder elements randomly placed on the river bed to enhance fish migration in an upstream direction; thus, they can serve as fish passes. In this paper, we present the results of the numerical modelling of a bed load transport and the morphological changes of a river bed where a block ramp was designed and built. The main aim of the study was to investigate the difference of 2D modelling of a bed load transport along the mountain stream reach with boulder ramps in comparison to the classical methods of Hjulström, Shields, and Russian standard ST-24-2396. The work was carried out on the stream of one of the chosen low-head hydraulic structures, where 25 identical block ramps were constructed for river training reasons. The novel approach of our study is, for the first time in the field, to show a very detailed analysis of block ramp influence on sediment transport and river morphology changes compared to the classical understanding of those phenomena, as well as 2D model results to give hydraulic engineers an inside look into classical and modern approaches of bed load transport calculations. This might be helpful for designing such kinds of hydraulic structures in the future, in all regions where sediment transport calculations are important but do not always require sophisticated modelling.