Dear XBeach expert,
Deltares is reconsidering the default settings of XBeach for the use of XBeach as advanced assessment model for the Dutch coast. As scientific developer or advanced XBeach user we would like your opinion on this subject.
XBeach provides about 250 parameters to be set by the user. Many of those are related to case-specific input or are related to processes and functionalities that are not relevant for the application as assessment model for the Dutch coast, like vegetation, ship waves, groundwater flow, etc. Still a list of over 80 parameters will be available to the user discarding all above.
An assessment model is supposed to be suitable for application by non-advanced users. Therefore we would like to minimise the fraction of these 80+ parameters exposed to the average user, preferable by a 100% so that only case-specific data is to be supplied by the user. In order to do so, we need to offer a default set of parameter settings that are applicable for dune assessment computations along the Dutch coast.
In order to arrive at such default set, we intend to systematically vary the parameter settings for a selected set of validation cases that are representative for the Dutch coast. Ultimately we will pick the set of parameters that resembles the validation measurements best.
However, a set of 80+ parameters is way to large for systematic variation. Only if we would pick 2 values per parameter and a single validation case it would take a zillion years to compute. Therefore the first step is to eliminate these 80+ parameters to less than 10 parameters based on expert judgement. This is where your help is appreciated.
We listed all relevant XBeach parameters below. We would like you to assign 25 points to the parameters that should, according to you, be considered in the systematic variation. We will divide about 10.000 XBeach simulations over the parameters that received the most points. The number of parameters is not set beforehand. We will consider including more parameters over the number of variations per parameter.
We attached two plots that provide some insight in the (marginal) sensitivity of XBeach for the 80+ parameters considered. The marginal sensitivity is determined by running a 1D XBeach simulation using a schematised profile representative for the Dutch coast and normative storm conditions representative for the location Hoek van Holland. During each simulation only a single parameter is varied within it's applicable range. Some parameters depend on others. In these cases both parameters are set, but only the parameter of interest is varied within it's range (hwci, jetfac, waveform, facsd, z0, betad, BRfac, bed).
The first plot shows the sensitivity of the erosion volume above SSL for each parameter over it's valid range of values. The black dot depicts the default value. The red line is a linear fit excluding outliers. The second plot shows the range of erosion volumes found when varying each parameter. The second plot is ordered based on the variation of erosion volumes found.
Please use these plots as guidance, not as the whole truth. The plots are generated using a single model set-up only and not representative for all cases that should be taken into consideration. Also some parameters with large influence are not good candidates for systematic variation. For example, the parameter "sus" has a large influence, but it is probably not a good idea to calibrate the model turning suspended sediment transport on or off. On the other hand, it might not be so useful to include a parameter to the short list that has no influence at all.
A few remarks on the continuation of this calibration effort might be important as well:
* We only look at 1D cases (transects)
* We only look at erosion volumes above SSL as performance indicator (we will look at profiles separately)
* We will scale the validation cases to prototype scale and run XBeach at that scale (we will look into scaling issues separately)
* We do not include the depthscale parameter in this study, it is always 1, but we will include the parameters set by the depthscale parameter (we will look into scaling issues seperately)
* We exclude the following processes / functionalities from calibration:
** vegetation
** wind
** ships
** non-hydrostatic
** drifters
** mpi
** morfac
** discharge
** groundwater flow
** beach wizard
** sediment fractions
** stationary wave solver
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