Laboratory Modeling of the Morphological Development and Flood Event Response of Skewed Meandering Rivers

Abstract:

Meandering river channels are commonly found all over the world and beyond. The planform geometry of these meandering rivers have important implications for the in-stream hydraulic conditions and sediment transport patterns, which ultimately impact their morphological development processes. Understanding the relationships between these processes can yield insights for improved stream restoration efforts and hazard mitigation, both in understanding the dynamic sediment transport and redistribution processes and in preventing the migration of rivers into property or infrastructure.

Despite extensive research conducted on river systems, limited studies have examined the morphological behaviour of irregular planform geometries, such as skewed meandering river channels. In a skewed channel planform, the apex of the meander bend becomes shifted in either the up-valley or down-valley direction to form an asymmetrical meander shape. Compared to regular (symmetrical) meandering planform geometry, past research has shown that this skewness produces different flow conditions and morphological development processes depending on the orientation of skew. However, few studies have investigated skewed meandering rivers in a laboratory setting, especially with unconfined bed and bank conditions.

In this work, a series of experiments were conducted in a sand-filled laboratory flume under fully unconfined bed and bank conditions. Two different skewness orientations were tested under the same hydraulic conditions to determine the effect of increased skewness on morphological changes. In addition, the experimental channels were subject to a period of higher flow to assess their morphological response to a flood event. Comparisons of morphological development over time were made with digital elevation models captured using photogrammetric techniques. Results showed different patterns of bank migration, bar formation, and adjustments in channel geometry for the different skewness orientations. These morphological differences could also be extended to differing flow conditions within the channel. The obtained results can assist in stream restoration and river engineering projects to determine the optimal meandering planform geometry for stream stability and flood resiliency purposes.