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26/02/2017 05:51:03

We're trying to represent a reach which contains some informal woody dams - build ups of branches and woody debris which impede flow but may get dislodged by higher flows. Is there any guidance on modelling these?


28/02/2017 09:30:25

I gave a presentation on modelling debris dams using FMP back at the 2015 user conference. I've provided a link to a stripped back version of the presentation slides below. As far as I'm aware, there is no guidance on how these should be modelled and there is no dedicated debris dam unit either. You'll need to get creative with combinations of units to represent the various key flowpaths and do sensitivity testing on any assumptions.


Hope that helps!


28/02/2017 09:49:08


In my case, we dont have any data to calibrate the model. The other option would seem to be to represent the overall effect of the dams by increasing roughness, similar to the approach taken in the Pickering  Slowoing the Flow study (http://www.forestry.gov.uk/pdf/Pickering_crim_report_April_2010.pdf/$FILE/Pickering_crim_report_April_2010.pdf)



06/03/2017 10:58:42

Another option to consider, would be the use of the blockage unit as you can vary the percentage of blockage with time, that would allow you to model the dislodging of the woody debris - the limitation to this would be the that the blockage unit assumes a vertical blockage in the channel so the portion of blockage would need to take this into account.

Along a similar theme, you could also use a breach unit attached to a spill unit (or series of spill units) to simulate the dislodging of the woody debris.


20/11/2019 13:43:21

Coming back to answer my own question,

More generic guidance on this subject is available in this recently published paper



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