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interface with SWASH wave model (Zijlema et at)?

MM
Marco Miani, modified 5 Years ago.

interface with SWASH wave model (Zijlema et at)?

Wind Posts: 40 Join Date: 4/1/14 Recent Posts
Hello developers.

In the attempt of pursuing my research interest I am keenly interested in investigating the breaching process for sand dunes at a very high resolution, both spatial and temporal.

I am currently using SWASH wave model (Zijlema et al). Ideally, I would be interested in both: deterministic wave filed and, at the same time, (wave driven) bed evolution to include the positive-feedback mechanism in simulations.

Currently, I still have to study the manual carefully to understand what Xbeach can (or will possibly be able to) do, but I see that a non hydrostatic aspect is included already.

However, for my specific needs, the ideal setup would be, the combination of a phase resolving wave model driving the slumping and breaching on sand dunes.

Any inputs are highly appreciated.
Thank you.

Kind regards.
Marco
Arnold van Rooijen, modified 5 Years ago.

RE: interface with SWASH wave model (Zijlema et at)?

Swell Posts: 239 Join Date: 11/7/11 Recent Posts
Hi Marco,

You are right that in principal XBeach and SWASH are quite similar in a way. I think the most important difference is that SWASH can be used in 3D mode while XBeach is depth-averaged. On the other hand XBeach contains formulations for sediment transport and morphology.

The standard version of XBeach resolves low frequency waves while the short waves are resolved using a wave action balance (see manual and Roelvink et al 2009 for more details). But if I understand your message correctly, you want to also resolve the short waves.

Within the XBeach code an early version of SWASH was implemented a few years ago, which we now refer to as the non-hydrostatic module of XBeach (see http://oss.deltares.nl/web/xbeach/documentation/non-hydrostatic_report_draft.pdf). This version of XBeach is phase-resolving and should be pretty much identical to SWASH, except for that it can only be used in depth averaged mode.

The process of breaching is currently being studied by a few MSc students at Deltares and some more researchers using XBeach, so we expect to have a better idea on the performance of the model for those processes in the near future. Some preliminary results that I have seen are very promising. For example, you can find a nice recent presentation (JOSNMOD conference) about XBeach and breaching here: (presentation of Heloise Muller): https://publicwiki.deltares.nl/display/JONSMOD/Presentations+2014.

I think at this point everyone is using the standard version of XBeach for breaching, I don't think anyone is using the non-hydrostatic version of XBeach for breaching yet

Hope this helps.

Cheers,
Arnold
MM
Marco Miani, modified 5 Years ago.

RE: interface with SWASH wave model (Zijlema et at)?

Wind Posts: 40 Join Date: 4/1/14 Recent Posts
Hi Arnold and Robert.

Thank you very much for responding to the question I raised as well as for the links you've posted.

Yep, XBEACH cannot include layers (unlike SWASH), so it has to be run in depth averaged mode. Since depth averaged approach cannot reproduce breaking correctly, wave run up on sand dunes is frequently under-estimated, sometimes severely.

I am now in the process of setting up XB in nonhydrostatic mode and see what happens.The scale I am interested in, is small. Say meters (approx 50-80 meters along shore and 150-200 cross shore, starting from dune crest). In this setting, I am interested in recreating the "head cut" example, proposed by Dano (see video available on XB home page), but driven (and triggered!) by up-running waves.

This approach might have some limitations, but still I want to give it a try. Set up a sample run, something quick and dirty, and see what happens.

The ideal outcome, would be a successful embedding of XB into SWASH, so that latter would feed former.
The dominant variable describing both phenomena (i.e. velocity, well resolved by SWASH, even vertically), could be passed between wave model AND erosion model. But this might be something too ambitious for my PhD... As for now I'll (try to) keep my feet on the ground and carry out my current plan.



Will let you know how this turns out.
M
Robert McCall, modified 5 Years ago.

RE: interface with SWASH wave model (Zijlema et at)?

Wind Posts: 83 Join Date: 3/24/11 Recent Posts
Hi Marco,

I think I'd like to add to Arnold's post. Is there a particular reason you think you need to resolve the incident band (wind/swell wave) motions? If the beach you are looking at is dissipative during storms, then using XBeach to solve the infragravity wave motions, along with the wave-action balance for the short waves (so, solving wave energy, but not the phase of the short waves) should be fine to drive dune slumping. In fact the dune slumping algorithm in XBeach has been designed with this combination in mind.

If the beach you are looking at is reflective, rather than dissipative, then you may have to move to the short wave-resolving version of XBeach.

Another couple of references on modelling overwash and breaching using XBeach:

Roelvink et al 2009: http://dx.doi.org/10.1016/j.coastaleng.2009.08.006 (look for the ZWIN case)
McCall et al 2010: http://dx.doi.org/10.1016/j.coastaleng.2010.02.006
Lindemer et al 2010: http://dx.doi.org/10.1016/j.coastaleng.2010.06.004

Robert