A Cross-Shore Beach Profile Evolution Model

Abstract

Developing an accurate and reliable time-averaged beach profile evolution model under normal and storm conditions is a challenging task. Over the last few decades, a number of beach deformation models have been developed under limited experimental conditions and uncertainties, and sometimes they required a long computation time. It is quite evident that a large amount of wave, current, sediment and beach profile data is available today. The present study leads to the development of a simple two-dimensional beach profile evolution model with on-offshore sand bar formation under non-storm and storm conditions based on the time-averaged suspended sediment concentration models of Jayaratne & Shibayama [2007] and Jayaratne et al. [2011]. These models were formulated for computing sediment concentration in and outside the surf zone under three different mechanisms: 1) suspension due to turbulent motion over sand ripples, 2) suspension from sheet flow layer and, 3) suspension due to turbulent motion under breaking waves. The suspended load is calculated by the product of time-averaged sediment concentration and undertow velocity from edge of the wave boundary layer to wave trough, and mass transport velocity from wave trough to crest (bore-like wave region). Sediment transport in wave boundary layer is computed from the modified Watanabe [1982] model. Rattanapitikon and Shibayama [1998] wave model is used to calculate the average rate of energy dissipation due to wave breaking. The beach deformation is calculated from the conservation of sediment mass while the avalanching concept of Larson and Kraus [1989] is used to re-distribute the sediment mass in neighbouring grids for a steady solution. Published field-scale experimental and natural beach profiles from 5 high-quality data sources from 1983-2009 [Kajima et al., 1983Kraus and Larson, 1988; Port and Airport Research Institute, Japan, 2005, 2009;Hasan & Takewaka, 2007, 2009Ruessink et al., 2007] are used to verify the performance of the proposed numerical model. The key feature in this process-based model is that it takes about a couple of minutes to simulate beach profiles of a 2-3 days storm qualitatively at a fairly satisfactory level using a standard personal computer. It is found that the present numerical predictions are not better than the null hypothesis as the model is in a stage of ongoing development. Therefore, it is believed that the final model is often more value to a practical coastal engineer than a very detailed study of hydrodynamics and sediment transport study, however an incorporation of swash dynamics, more precise evaluation of offshore sand bar formation and continuation to a longer time scale with precise beach deformation is recommended as the next stage of the model.Key words: Two-dimensional beach profile evolution model; time-averaged suspended sediment concentration; on-offshore sand bar formation; average rate of energy dissipation; conservation of sediment mass; avalanching concept; field-scale experimental and natural bea...

Modeling Bed Evolution Using Weakly Coupled Phase-Resolving Wave Model and Wave-Averaged Sediment Transport Model

“…The terms related to the line integral on the left-hand side of Eq. (20) are calculated starting from the depth integration of the product of the wave-averaged horizontal velocity vertical distribution and wave-averaged suspended sediment concentration vertical distribution (similarly to Jayaratne et al [2014]), in order to take into account the sediment transport related to the undertow and the effects produced on the concentration by the eddy viscosity vertical distribution.…”

Effects of sedimentation on soil physical and chemical properties and vegetation characteristics in sand dunes at the Southern Dongting Lake region, China

“…With increasing elevation, the sedimentation rate will gradually decrease, and as a result, the growth capacity of sand dune plants and their positive feedback effects on soil structure and soil fertility may gradually increase. Although considerable studies have focused on exploring the developmental processes of lake beaches1920, the underlying mechanisms, especially those related to the effects of sedimentation on beach soil and plants, have not been satisfactory explained2122.…”

Modeling of Berm Formation and Erosion at the Southern Coast of the Caspian Sea

“…Therefore, most morphodynamic models cannot reproduce the results correctly under various wave conditions in different coastal regions. Nevertheless, researchers (e.g., Larson and Kraus 1989;Southgate and Nairn 1993;Roelvink et al 2010;Kobayashi et al 2008;Jayaratne et al 2014;Tabasi et al 2017) have continued their efforts to propose morphodynamic models to obtain reasonable results by improving hydrodynamic and morphodynamic calculations. The hydrodynamic and morphodynamic equations of these models include free parameters that should be calibrated for each specific site to achieve reasonable results.…”