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Hannahp

19/07/2017 08:52:35

Hi all, I have recently downloaded the Environment Agency's Product 7 data- original EA model of fluvial flood height and flow in order to run them myself for a  small watercourse that hasn't had the flow data extracted for it yet due to its size. I have measured the network of nodes to be 520 but only 250 are permitted for my version of Flood Modeller Free. Any way to easily remove unwanted data to bring the network down to the required size? Also any other helpful hints/tips/experience would be greatly apreciated, Many thanks HP 

david.hughes

19/07/2017 10:32:48

Best answer

Hi Hannahp,

Unfortunately, if you're trying to run FMP linked with TUFLOW, you'll need the Flood Modeller Pro licence. You're quite right that the Free version of FMP will allow the user to build, edit, saev and run 1D simulations with up to 250 1D nodes, but the Pro licences is required to go over 250 1D nodes OR link to TUFLOW.

Each of the 1D nodes was placed in the model for a reason so the only easy way to trim the network down to below 250 nodes would be to select sensible trim locations (i.e. only model 2km of the watercours instead of 5km for example). But whilst doing this could bring your node count below 250, you'd still need the pro licence to run it linked with TUFLOW.

Dave

kv

Flood Modeller Support

21/07/2017 18:13:57

Hi, Hannah,

Thank you for this forum post.

Following on from the information provided by David, I can add that Flood Modeller Free (from v 4.3) now allows one to link with TUFLOW (via 10 1D-TUFLOW links only), therefore trimming the model down to 250 nodes to work with Flood Modeller Free may now be possible even for linked models, but is likely to turn into a very tedious job (and may not be possible due to teh complexity of the original model).

Indeed, there must have been a reason for including these many nodes into the model, but there can be a few suggestions that can potentially help one in such a situation. However, please bear in mind that any reduction to the number of nodes will lead to the changes of resulting water levels and flows, which will need to be checked if they still fit the purpose of the study.

- there are several “soft” rules for cross section spacing following the source as specified here: Samuels, P.G. (1990): Cross-section Locations in 1-D Models – International Conference on River Flood Hydraulics, White WR (ed), John Wiley.

These rules are summarized below:

• There are no hard rules about cross-section spacing
• Cross-sections should be no more than 20B apart, where B is the top width of the channel
• Cross-sections should generally not be more than 1/(2s) apart, where s is the mean slope of the river (as a decimal)
• Cross-sections should generally not be more than 0.2D/s apart, where D is the typical depth of flow (or bankfull depth for a flood model
• In areas where the mean flow velocity exceeds 1m/s, the wetted cross-section area should not change by more than about 35% between sections

Therefore you can check your model if the cross section spacing fits more or less the rules as listed above. If it does, then most likely there is not much you can do (apart from following the suggestions below). If it does not, then you can try to decrease the cross section spacing so that it fits the rules as per above. And then check your results.

- check if the model has interpolate units - these are usually inserted for stability. So if these are removed, you may need to see if you can improve stability using other means such as via decreasing a time step or modifying the advanced parameters. Again, check the results after this.

- break your model into several smaller models. Here specifically (but also for other suggestions as listed above) you have to bear in mind that it is only 10 1D-TUFLOW links can be included for Flood Modeller Free to work. You can then take the flows from the downstream point of one model and manually insert it as an inflow to the other model. With linked model it may be more involved or impossible, depending on the flows in the 2D domain, but I thought I will mention this option any way. Another item to watch out here is the backwater effect. Such an effect won’t be represented at all at the points upstream of your disjoint locations. Again even if you manage to split your model into smaller ones and fitting into the limits of Flood Modeller Free (especially the limitation on the links), then you will need to check your results anyway (as per the previous options)

Another piece of information that may be useful to you is the fact that there are other ways of getting Flood Modeller such a renting software.

I hope this is of help.

Please let us know how you are getting on.

Kind regards
Kostya

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