Development of bed forms due to waves blocked by a counter current

TL;DR

This study investigates how wave-blocking by a counter current influences the formation and segmentation of bed forms in a sediment bed, revealing distinct zones with different ripple and bar structures.

Contribution

It uniquely identifies wave-blocking effects on bed form development and characterizes the resulting spatial segmentation of sediment bed morphology.

Findings

Wave-blocking occurs at a critical wave frequency.

Distinct bed form zones with asymmetric and symmetric ripples are observed.

Flow deviations and turbulence characteristics are affected by wave-blocking.

Abstract

Experiments are conducted in a laboratory flume on the propagation of a surface wave against unidirectional flow with a sediment bed. This paper presents the spatial variation of bed forms induced by the wave-blocking phenomenon by a suitably tuned uniform fluid flow and a counter-propagating wave. The occurrence of wave-blocking is confirmed by finding a critical wave frequency in a particular flow discharge in which the waves are effectively blocked and is established using the linear dispersion relation. The novelty of this work is to identify the wave-blocking and its influence on the development of bed forms over the sediment bed. Interesting bed form signatures are observed at a transition of bed forms in three zones, with asymmetric ripples having a steeper slope downstream face induced by the incoming current, followed by flat sand bars beneath the wave-blocking zone and more symmetric ripples below the wave-dominated region at the downstream. This phenomenon suggests that the sediment bed is segmented into three different regions of bed geometry along the flow. The deviations of mean flows, Reynolds stresses, turbulent kinetic energy, and power spectral density due to the wave-blocking phenomenon are presented along the non-uniform flow over sediment bed. The bottom shear stress, bed roughness and stochastic nature of the bed form features are also discussed. The results are of relevance to engineers and geoscientists concerned with contemporary process as well as those interested in the interpretation of palaeoenvironmental conditions from fossil bed forms.