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 Tri (Tri) posted on Wednesday, July 04, 2007 - 04:45 pm
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Dear All,
In "Lateral erosion" tab, if "Lateral Method 2" is chosen, the user must identify the value of "Cross stream gradient factor". The default value is 2. However, I wonder if I want to use the model for a big river system, what value should I use?
Apart from lateral method, at the bottom of this tab (i.e. "Lateral erosion" tab), there is a parameter called "Pit depth" and the default value is 20. I wonder what does it mean? and why is it 20?
Best regards,
Tri Van |
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Hi Tri,
OK, lateral erosion is still experimental at the moment (5.7r) and I think - that this value is no longer used - but the box is still in the form, so I would ignore it for now.
Pit depth is an interesting variable.
THe lateral scheme creates a cross stream 'gradient' according to which some of the sediment is routed (I am writing this part up at present). Pit depth stops the model eroding pits that are too deep - it may create pools that are unfeasibly large. THe max pit depth can be DX/pit depth value. So for a 10m grid cell, its 10/20 = 0.5 deep |
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Copy of message from Nico:
at the moment i´m trying to integrate the lateral erosion.
i just have the problem that at low flow the river is eroding to much and at high flow not enough.
do you know how i can do that?
i´m tryng to keep the TAU velocity threshold as high as possible, so that the lateral erosion gets more sensitive to the flow velocity, and in the mean time lateral erosion low. Problem is that by doing this i got to much incision in the channel.
is there a kind of spin-up for the lateral erosion as well?
you have any suggestion?
Thanks in advance,
Nico |
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Hi Nico
You've identified a big issue here - one that I hope I've fixed. But maybe you can check it for me!
The problem is that lateral erosion (in that version) is a constant mukltiplied by the tau. Bed erosion is semi threshold and the function of Tau^x... so you can find that the banks erode but are not then moved by the bed erosion leading to fat wide shallow channels. AND like you noted it does not really increase with increased flows. In the version I am playing with at the moment I use the SAME sedimennt transport rules for lateral eerosion as for bed, except the lateral is also multiplied by the radius of curvature and a constant.
I'll post a link to a trial version at the end of this post. I'd like it if you can try it for me - I'm testing it quite heavily at the moment. It may well behave differently in other ways too (as I'ev changed quite a few other things). You'll probably need a much higher lateral constant (try 1 - 10 to start with) and let me know how it works (or not!)
Tom
http://dl.dropbox.com/u/2948013/CAESAR%206.1%20test.exe |
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| Nico Batz (Nico) posted on Monday, February 15, 2010 - 10:07 am
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thanks for the test version,
i started to play a bit around with this version.
it seams to be faster,
and it is less prone to incision if TAU is calculated with the flow-velocity.
i need results within the next 2 weeks, so that i stay in my thesis schedule.
i will try to check as much as i can.
can you give me some info on what you changed in this version?
so that i don´t need to check all the parameters again.
Thanks
Nico |
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| With the lateral erosion the main changes are in using the same sediment transport law as used for incision (so it cannot erode laterally faster than it can vertically). The constant has to be set quite a bit higher as a result. Try 0.5 > 2 in a braided channel - less in slower moving |
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