Graduation of Anne Floor de Beer

26 October 2017 15:00 - Location: Room 0.96, Faculty of Civil Engineering and Geosciences - By: Webmaster Hydraulic Engineering

"The influence of incident waves on runup: a comparison between a phase-averaged and a phase-resolving Xbeach model "| Professor of Graduation: Prof. dr. ir. A.J.H.M. Reniers, supervisors: dr. ir. M.F.S. Tissier (TU Delft), dr. ir. M.A. de Schipper (TU Delft), dr. ir. R. T. McCall (Deltares), dr. ir. J. W. Long (USGS)

As a result of breaking waves a thin wedge of water runs up the beach face, of which the height it reaches is called runup, which is responsible for beach and dune erosion especially under storm conditions. It is therefore important to predict runup accurately. Empirical parameterizations with the goal of simply predicting runup and its components, the time-mean component setup and the time-varying component swash, were developed, but they can not be validated for extreme conditions as runup measurements are hardly available then. Instead they can be validated with runup data simulated by numerical models, such as the process-based Xbeach model. However, under mild to intermediate
energetic conditions at the intermediate-reflective beach of Duck, North Carolina, the incident and infragravity frequency parts of swash are underpredicted by the phase-averaged Xbeach Surfbeat model, but performance can be improved by using the phase-resolving Xbeach Non-hydrostatic model: this model resolves all wave and swash components. A  validation of both Xbeach models for the runup data of the SandyDuck’97 experiment was done, followed by identification of the differences in hydrodynamics responsible for runup prediction differences and their origin in the cross shore.

On an intermediate-reflective beach such as Duck Xbeach Non-hydrostatic is a better predictor of runup,
significantly improving performance for incident and infragravity swash while predictive capability for setup is similar: the difference in incident swash is due to the resolving of incident wave and swash components while the difference in infragravity swash is mainly driven by a difference in infragravity wave height prediction between the two Xbeach models. The latter partly originates at the offshore model boundary and is the results of interaction between wave boundary conditions in the start of the domain. Also infragravity wave transformation differs between the Xbeach models
but no explanation for this was found. In order to find an explanation for wave heights at the start of the domain should be identical. Finally hydrodynamic differences relevant for the infragravity swash prediction develop within the swash zone. With the final goal of validating empirical parameterizations for simply predicting runup in mind, the performance of Xbeach Non-hydrostatic must not only be tested under low to intermediate energetic conditions but also under storm conditions. Also other type of beaches must be included, to be able to give an indication of which Xbeach model should be used in which situation.