The project will focus on three main components:
A six-week field experiment will be conducted on Loe Bar, a 1km long gravel barrier on the southwest coast of England. The field experiment will involve collection of a high-quality field data set on swash hydrodynamics (runup, swash depths and flow velocities), beach groundwater dynamics, sediment transport and beach morphological response for a range of conditions, including storm waves.
Analysis of the field data will focus on quantification of wave run-up characteristics, swash flow velocities, net sediment transport over individual swash events, swash/groundwater interactions and morphological change across the intertidal zone over tidal cycles. Argus video systems will be set up to cover the entire beach allowing the alongshore variability in swash hydrodynamics and beach response to be considered.
The field data will be used for two purposes:
- Increase our understanding of swash morphodynamics on gravel beaches under calm and energetic wave conditions.
- Provide data with which to improve the parameterisation of the swash morphodynamics in the numerical model XBeach.
Monitoring gravel beach storm response on nine gravel barrier sites
Although the data collected during the fieldwork at Loe Bar are necessary to customise XBeach for gravel beaches, the data set is necessarily limited to a single beach and to a single storm. To apply and test the improved XBeach model to a variety of gravel barrier settings and wave forcing conditions, a larger data set is required. This will be achieved using additional data from a further ten beaches have been selected to collectively represent most of the gravel beach environments and management approaches found in the UK. Each site is part of the CCO or the University of Plymouth monitoring programme.
None of the data sets at the selected sites are likely to include overwashing and breaching events, and these extreme storm responses will be investigated at a number of additional gravel sites, including Porlock, Dunwich and Pevensy. Laboratory scale data from the large-scale Deltaflume BARDEX data set, which includes significant overwashing will also be used for XBeach model calibration.
Analysis of the storm response data will focus on the quantification of cross-shore and longshore transport rates, and the associated morphological response. Additionally, we will attempt to identify critical thresholds separating the different types of beach response. The storm response data set will be used for two purposes:
- Increase our understanding of the morphological response of gravel beaches to storms.
- Help improve the capability of XBeach to predict storm impacts.
Numerical model development
XBeach is a vertically-averaged, cross-shore and longshore model for waves, tides, currents and morphology of the nearshore area, beaches, dunes and backbarrier during storms. It is a public-domain model that has been developed by a consortium of UNESCO-IHE, Deltares, Delft University of Technology and the University of Miami.
XBeach has been developed for sandy beaches and cannot be applied to gravel beaches without significant modifications. The approach in this project will be to use data from Loe Bar to develop, implement and validate the XBeach model for gravel environments. This work will result in a new version of XBeach that will have the ability to simulate accurately the morphodynamic response of gravel beaches to changing wave and water-level conditions and to high energy storms.
The calibrated and validated version of XBeach suitable for predicting gravel barrier response to storms will be developed and be made freely available on the XBeach web site. However, setting up the model for practical applications is not trivial, and requires considerable modelling expertise and time investment. The NUPSIG project therefore plans to develop a user-friendly and interactive Graphical User Interface (GUI) to use XBeach. The GUI will enable easy uploading of barrier geometry and forcing conditions (waves and water level), and will provide clear graphical and numerical output of the simulated barrier response.
The product is aimed at practical beach management and coastal engineering applications and will enable evaluation of:
- the effect of coastal engineering structures
- beach recharge schemes
- barrier reshaping.
Example of an XBeach simulation of storm flooding