Advances in management tools for modeling artificial nourishments in mixed beaches

- Beach profile and coastline evolution of a nourished mixed beach are addressed.
- Test of longshore sediment transport equations and the one-line model with field data
- Limited benefit of nourishment partly due to coastline morphology and sediments used
- Van Rijn equation provided the best fits to the measured beach profiles and coastlines.
- Management tool to predict the morphodynamic response of mixed sand-gravel coasts

This paper addresses the evolution of a mixed beach (Playa Granada, southern Spain) forced by an artificial nourishment project through the analysis of field observations and the modeling of hydro- and morphodynamics. The beach profile and coastline were periodically surveyed over a six-month period; a wave propagation model was calibrated by means of hydrodynamic measurements; four longshore sediment transport (LST) equations were tested through comparisons with bathymetric data; and the one-line model was applied between topographic surveys. The results indicate that severe coastline retreat (dry beach area loss > 208 m2/day) occurred during the 45 days following the intervention. This is mainly attributable to the morphology of the nourished coastline, the different characteristics of the sediment used for replenishment compared to natural sizes, and the occurrence of an intense westerly storm. The dry beach extension increased afterwards influenced by the westward LST due to the dominance of easterly waves. The Van Rijn formulation was found to provide the best fits to the observed volumetric changes, obtaining modeled/measured ratios of 93.1% and 77.4% for the two study beach profiles. The outputs of the one-line model based on the Van Rijn approach were also the best, with root-mean-square errors decreasing during the study period and lower than 4.6 m over the last 3 months. These results show that the joint application of a calibrated wave propagation model, the LST equation proposed by Van Rijn and the one-line model constitutes a management tool for predicting the evolution of these complex coastal settings.