Abstract
The recovery of beaches after a storm can be influenced significantly by ridge-runnel migration. Ridges are made up of large volumes of sand which is important for the coastal sediment budget. The experiment described in this paper gives an insight into the complex hydrodynamics and sediment transport mechanisms related to onshore ridge-runnel migration. Detailed water free surface elevation, fluid velocity and sediment transport rate measurements were taken in a mobile bed wave flume with a focus on the effect of water ponding and runnel drainage on the profile evolution. The measured results have been used to calibrate the time-averaged numerical cross-shore model CSHORE. The model has the capability to deal with the effect of a pronounced profile depression (water-filled runnel) forming on the intermittently wet and dry zone of the beach. Results of the experiment compared with the corresponding numerical model computations show that the rapid onshore migration of a ridge-runnel system under fairly energetic wave conditions can be computed with CSHORE but further improvements of the model are necessary.
Highlights
This paper deals with coastal ridge-runnel migration which can play a significant role in beach recovery after storms
Ridge-runnel systems are dynamic coastal morphology features with important implications for beach recovery after storms and for the coastal sediment budget in general due to their large volumes of sand being set in motion by wave action
The offshore return of water and sediment can occur over the ridge crest or through rip channels intersecting the ridge at specific locations
Summary
Background This paper deals with coastal ridge-runnel migration which can play a significant role in beach recovery after storms. Robin et al (2009) measured morphological changes, hydrodynamics and sediment tracer movement for one intertidal bar located in an ebb delta inlet system They carried out four short experiments (one tide cycle each) under different wave and tide conditions. The cited work shows that ridge-runnel systems are an important morphological feature because they affect the sediment transport patterns in the intermittently wet and dry zone significantly Scope of this Study We conducted a ridge-runnel physical model experiment in a movable-bed wave flume to investigate the migration of these morphological features in a controlled laboratory setting. Measurements of high-resolution profile changes, overwash transport rates, shallow water flow velocities and free surface elevation along the flume and in the intermittently wet and dry zone allowed for the creation of a unique ridge-runnel migration data set and formed the basis for numerical comparison. This paper is intended to supplement that information by giving further detail about the experiment setup, the data analysis and the numerical model extension for ridge-runnel migration
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