Experimental research on channel closure in braided rivers

Abstract

The dynamic nature of braided rivers can lead to river bank erosion, bankline shifts and navigational hindrance. River training measures can be implemented in order to mitigate these problems. An alternative to conventional river training works is the closure of a channel within the braided network. Until recent there has been no systematic research on channel closure and guidelines or recommendations were absent. Recent simulations with numerical models on sand-bed braided rivers investigated both the effects of channel closure around the island and on the braided network. The results of these studies have their limitations and validation with physical models or pilot tests are necessary. Therefore, the objective of this thesis is to obtain a better understanding of the local morphodynamic effects of interventions aiming at channel closure in braided rivers.

This has been done by conducting flume experiments with a simplified section of a braided river with gravel-bed similarity. At first the laboratory experiment was designed such that a stable and reproducible planform developed. A section, consisting of an upstream fixed Y-shaped confluence followed by an alluvial island surrounded by two channels and fixed outer banks, was used to systematically study the local effects of channel closure. The obtained results were analyzed and compared with the numerical studies of Ostanek Jurina (2017) and Schuurman et al. (2016).