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

Abstract

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.

Journal of Water and Land Development

“…For 2D models, we are not always sure if we have an appropriate mesh size or a long enough time for calculations. It is very often not a fault of the model but rather a limitation of computer power since we cannot wait for the results for days or even, in the case of 3D modelling, for weeks [PLESIŃSKI et al 2018b;2022]. Thus, the main point of our research presented here is that for engineering activities such as designing simple hydraulic structures and/or predicting some river bed changes, it is worth using classical approaches.…”

“…If one has time and has to follow such requirements, in our opinion that it is appropriate to start from a 1D model and then continue with 2D or 3D; this is mostly dependent on time and the skills of the designer because one has to bear in mind that learning 2D or 3D models often takes a considerable amount of time [SZYMKIEWICZ 2000;2012]. Thus, for river managers and people who design lowhead hydraulic structures or deal with riverbank erosion, we would definitely recommend simple solutions, which in fact, are not so simple what they seem to look like, because they need experience and knowledge of rivers, especially in the regional context [KAŁUŻA et al 2018;PLESIŃSKI et al 2018b;2022;RADECKI-PAWLIK et al 2015;WYŻGA et al 2016;.…”

“…The similarity between a river and its model can only be partially verified. In this sense, only some modelling results might be used for design recommendations [PLESIŃSKI et al 2015;2018b;2022]. Ultimately, the engineer who decides if the model works correctly and if the results are reliable.…”