ABSTRACT
Numerous approaches describe tidal inlet evolution which results in the interactions between hydrodynamic and bed boundary processes at different spatial and temporal scales. The predictive capacity of these approaches is dependent on the model concept (i.e. data-knowledge, process-knowledge or mixture of both). Data driven models (e.g. semiempirical/empirical) describe long-term evolution (~centuries) while process-based models are generally applied to investigate medium-term evolution (~seasonal). There appears to be a process-knowledge gap from medium-to long-term evolutions. The present analysis attempts to bridge this gap by applying a process-based model at decadal time scales and comparing predicted morphological patterns with measured data and conceptual hypotheses of inlet evolution. Semi-empirical models predict inlet evolution over centuries (Van Goor et al., 2001). Empirical relationships show that equilibrium exists between different morphological parameters: inlet cross-sectional area and basin tidal prism (O’Brien, 1969; Jarret, 1976 and Eysink, 1990), inlet cross-sectional area and discharge (Kraus, 1998) and ebb-tidal delta volume and basin tidal prism (Walton and Adams, 1976). Wang et al (1999) described an equilibrium relation of tidal flats and inlet hydrodynamics based on Speer et al (1991) and Dronkers (1998). A number of conceptual hypotheses have been formulated to explain the morphological changes in the Dutch Wadden Sea inlets (Van Veen, 1936; Sha, 1989; Sha and Van Den Berg, 1993). Process-based approaches to investigate long-term inlet evolutions have been rapidly developed over the past decades. De Vriend et al (1993) and Latteux (1995) described long-term morphodynamics in terms of reduction techniques and selection of representative conditions respectively. More recently Lesser et al (2004) and Roelvink (2006) have introduced the MORFAC technique of morphodynamic upscaling. Marciano et al (2005) used this approach to evaluate the branching channel pattern in the Wadden Sea tidal inlets.
Van der Wegen et al (2006, 2008) and Van der Wegen and Roelvink (2008) discussed long-term morphodynamics of a tidal embayment. A few process-based approaches have attempted to investigate the conceptual hypotheses (Van Leeuwen et al., 2003). However, numerous uncertainties such as the effect of model domain, transport formulations, direction and asymmetry of tidal forcing etc are yet to be investigated. The present analysis investigates these uncertainties employing the process-based model (Delft3D) which incorporates the MORFAC technique of morphodynamic upscaling. Inlet evolution is simulated for several decades based on a schematised approach representing the physical/hydrodynamic characteristics of the Ameland inlet in the Dutch Wadden Sea.
