Practical modelling of sand transport and beach profile evolution in the swash zone

A proper prediction of the cross-shore profile evolution in the swash zone at time scales of days to years is important for evaluating beach management scenarios. However, this practical prediction is challenging due to a limited understanding of the complex physical processes in the swash zone. A quantitative evaluation of three existing practical swash-zone sand transport models, i.e. the Larson formula, the Van Rijn distribution model and the Karambas formula, has been conducted in this study. Measured net sand transport rates and beach profiles in seven large-scale flume tests, both low-energy accretive and high-energy erosive wave conditions, are used to assess these three models. Model performance is quantitatively evaluated with the Brier Skill Score (BSS), Root Mean Square Error (RMSE) and erosive/accretive volume. Overall, the Larson model shows the best performance. Nevertheless, the Larson model cannot capture the shoreline change, as it is assumed only valid for the higher part of the swash zone above the still water level (SWL). Additionally, it fails to predict the accretion in the upper swash zone during high-energy erosive conditions. Thus, two improvements are made for the Larson model by (1) extending the application of the Larson model from the still water level towards the run-down limit and by (2) developing shape functions for the equilibrium bed slope in the swash zone. The improved model is validated using six other large-scale wave flume tests. Results demonstrate that the improved Larson model works better than the original Larson model in predicting the profile evolution, shoreline change and total accretion/erosion volume in the swash zone. The improved model shows the potential to be coupled with wave-averaged morphological models for the nearshore zone to predict long-term evolutions of the entire beach profile

Coastal sediment dynamics: recent advances and future research needs

This vision paper discusses the advances made over the last three decades in coastal sand transport and morphodynamics, and the research needs for the coming decades. The prime focus of the paper is on the relationship between the transport of sand particles and fluid motions in the coastal environment based on laboratory and field experiments as well as mathematical modelling. The paper mainly focuses on two main issues: (1) better understanding of sediment transport processes in the coastal zone and (2) the development of improved practical engineering sand transport formulae and morphodynamic models

Suspended and bedload transport in the surfzone : implications for sand transport models

ACKNOWLEDGMENTS The research presented in this paper is conducted within the SINBAD project, funded by STW (12058) and EPSRC (EP/J00507X/1, EP/J005541/1), and received additional funding through the European Community’s FP7 project Hydralab IV (contract no. 261520).Publisher PD

Modeling biogeomorphological interactions in underwater nourishments

To prevent sandy coastlines from further erosion, nourishments are executed in which sand is usually put underwater at the foreshore. Waves and currents transport the sand on the beach and in this way stabilize the coastal profile. Little is known about the interactions of these so-called shoreface nourishments with the benthic populations inhabiting the coastal strip. Benthos is affected by the nourishments, but benthic populations could in turn affect the morphological evolution of the nourished coast. Monitoring has shown that the benthic community will mainly recovery after ca. 1 year. However, the impact of benthos on the sediment dynamics and hydrodynamics is unknown. In this paper we focus on tube building worms, which have a large abundance in the foreshore, live in patches of several square meters in diameter and protrude several centimeters from the sediment in the water column. Tube building worms are included in a numerical modeling tool (Delft3D), by explicitly accounting for the influence of cylindrical structures on drag and turbulence by an extra source term of friction force in the momentum equation and an extra source term of Total Kinetic Energy (TKE) and turbulent energy dissipation in the k-ε equations respectively. The model is validated against field and flume experiments and it shows a significant influence on flow velocities near the bed, bed shear stress and bed-load transport rates. Moreover, model results reveal that tube building worms are able to stabilize nourishments and slow down the migration of the outer breaker bar. Present model explorations indicate that future research should focus on the measurement of the patchy distribution of bio-engineers in the foreshore and their impact on the sediment dynamics and hydrodynamics. Such knowledge will enable process based modeling of the spatial and temporal variation in biological activity on the morphological development of the coastal profile and also it will lead to validation of the proposed model with field measurements.</jats:p