Sediment Transport Modelling and Morphological Trends at a Tidal Inlet

Abstract

Currently it is of great concern the morphological changes observed at distinct coastal systems. Frequently, drastic episodes of coastal erosion, threatening the houses built near the shore, and land loss are reported. At coastal lagoons and estuaries, increasing accretion can interfere with the water renewal and therefore with the local ecosystems. At inland harbors, the accretion of inlet and channels can restrict the navigation and consequently the harbor conditions and its management. The sediment transport, identified by patterns of erosion or accretion, can be evaluated by single formulae that compute the bedload and suspended load or by sediment transport models. In the literature are published formulae for bed-load transport of sediments in conditions characteristic of coastal waters, covering current alone, current plus symmetrical waves, current plus asymmetrical waves alone and integrated longshore transport. Due to the fact that sand transport models are often based on semi-empirical equilibrium transport formulae that relate sediment fluxes to physical properties, such as velocity, depth and grain size, it is crucial to perform sensitivity analysis of the formulae used. Pinto et al. (2006) compared four sediment transport formulations considering only the tidal current only: Ackers and White (1973); Engelund and Hansen (1967); van Rijn (1984a,b,c) and Karim and Kennedy (1990). The authors concluded that the van Rijn formula is the most sensitive to basic physical properties. Hence, it should only be used when physical properties are known with precision. The sediment transport modules, coupled with hydrodynamic and wave modules compose the morphodynamic models, resulting in very complex systems emergent in the last years. In the past 30 years, morphodynamic models have been developed (Nicholson et al., 1997). Among them the MIKE21, developed by the Danish Hydraulic Institute DHI (Warren and Bach, 1992) and DELFT3D, by WL|Delft Hydraulics DH (Roelvink and Banning, 1994), are the most popular. Most of the morphodynamic studies are generally related on engineering methods and techniques for coastal defense. The DELFT3D model was applied by several authors, such as Grunnet et al. (2004), Xie et al. (2009) and Tung et al. (2009), between others. Grunnet et al. (2004) applied DELF3D to