Introduction
This page explains the workflow for deriving default settings for a new version of XBeach. Default settings are important for users with limited experience with XBeach. For these users the number of exposed settings should be limited, preferably to case related input, like waterlevels, bathymetry and wave conditions, only. The occasion of setting up this workflow is the preparation of XBeach as assessment model for the Dutch coast. In line with the current WTI project leading this preparation, this workflow is limited to application for the Dutch coast and 1D. Different default settings for different applications may be derived by using this workflow.
Overview
The workflow consists of the following steps:
- Create long list of XBeach settings
- Conduct marginal sensitivity analysis on erosion volume above SSL on long list
- Submit long list including sensitivity results to expert panel
- Create short list of XBeach settings based on feedback expert panel
- Compute variation matrix of relevant ranges for settings on short list on relevant cases
- Pick the combination of settings with smallest RMS error with respect to erosion volume above SSL
Long list
The long list is constructed based on parsing the params.F90 file for settings and removing any parameters that are either case-dependent input (e.g. Hm0) or irrelevant (ships, groundwater flow, etc.).
Marginal sensitivity analysis
The marginal sensitivity analysis is performed using a default dune profile and representative settings for the Dutch coast (normative conditions). Using this model, a single parameter is varied over the applicable range of values. The default values are always included. The sensitivity is subsequently determined by looking at the variation in erosion volume depending on that parameter setting.
Expert panel
- Dano Roelvink
- Ad Reniers
- Jaap van Thiel de Vries
- Robert McCall
- Ap van Dongeren
Short list
Variation matrix
Resolution vs. dimensions
We can choose either to vary a large number of parameters (dimensions) using a limited resolution or vary a small number of parameters using a high resolution.
Cases
- Deltaflume ?
- Deltaflume 2006
- Boers ?
- 1953 storm surge
Result
Discussion
Several topics within this workflow are still being discussed. These discussions are briefly mentioned below.
Performance indicators
XBeach allows a variety of performance indicators to be used to compare the performance of one set of settings against another. For example, a profile comparison with measured data may be used by computing a BSS score. The BSS score itself, however, is subject to discussion for this purpose. Moreover, comparison data is often obtained from flume experiments on scale. These experiments use scaling rules that are derived by comparing erosion profiles rather than profile shape. The profile shape for these tests can thus not be used. For now, we use the erosion volume above SSL as performance indicator. Another advantage of this indicator is that it relates well to other calibration studies for dune assessment models in the Netherlands.
Scaling
Comparison with data is often done using data obtained from flume experiments. These experiments are performed on scale. XBeach allows us to simulate the experiment at the scale of the experiment rather than on a 1:1 scale. As for now, this is not done for two reasons. First, the scaling within XBeach is still subject to discussion. Second, other calibration studies for dune assessment models also first scaled the experiment results and then performed the calibration.
