Coarse sediment particle motion under highly asymmetrical waves with implications for swash zone sediment transport

Hydrodynamics and sediment transport in the swash zone are unique and very complex phenomena. Acquiring a robust model for predicting sediment motion in the swash zone requires in-depth insight about the behavior of sediment particles in highly asymmetric and turbulent waves that continuingly uprush the beach face and retrieve in backwashes. In order to consider a physical system of the coarse particle motion in the swash zone with a reduced number of external parameters and capture some of the realism of the situation, the experiments are conducted in rather simple conditions to provide some information about the particle responses in terms of jump length against asymmetric waves to be implicated for the swash zone. The results show that despite reduction of many external parameters, jump length is still a highly skewed stochastic parameter. The probability distribution of jump length is quite wide (large variance) and skewed, different from that of saltation length in steady unidirectional flow, in which the distribution is close to normal. Considering integral of excess energy of an arbitrary single wave over its duration as a rational and meaningful representative of flow condition, the average jump length JL¯ incremental trends reduces in the higher energy condition, resulting in a linear trend in logarithmic scale. The JL¯s due to higher turbulent kinetic energy follow similar trend of less turbulent flow conditions.

► A piece of laboratory data is provided to address the behavior of sediment particles in highly asymmetric waves. ► The probability distribution of particle jump length (JL) due to asymmetric waves is quite wide and skewed. ► Integral of excess energy of an arbitrary single wave over its duration is considered as representative of flow condition. ► The average jump length (JL¯) incremental trends reduces in the higher energy condition, resulting in a linear trend in logarithmic scale. ► The JL¯s due to higher turbulent kinetic energy, follow similar trend of less turbulent flow conditions.