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siripen_ace

Difference in water level at the ISIS/TUFLOW boundary

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Hi,

 

I have built a 1d/2d model with extended sections in ISIS model and link to TUFLOW but found that there is a 'jump' in water level between between the two ISIS nodes going from ISIS to TUFLOW. I have tried to applied an 's' flag on the hx lines along the floodplain but it doesn't seem to make any difference. 

 

The attached long profile shows that the water level 'jumps' from node CHE0_029(ISIS only extended section) to CHE0_030(ISIS/TUFLOW). 

 

I use the normal method of linking using hx line. (HX line in pink, CN line in green, CD polygon in blue, ISIS node in red)

 

Any suggestions to improve the transition at the boundary between extended section in ISIS to floodplain in TUFLOW, please?

 

post-44149-0-34212600-1400255562_thumb.j

post-44149-0-48454500-1400255761_thumb.j

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Hi Siripen,

 

Your schematisation is very nearly as I would have it! The only thing is that the 'wings' on your HX lines (where they go accross the floodplains at right-angles to the channel) should be connected to the fully extended ISIS section at CHE0_029, as it is that section that contains the water on the floodplain upstream of your 2D area.

Indeed, I would actually normally spot my extended reach of ISIS open channel at a junction and start the truncated reach on the other side of that junction, so the transition is instantaneous. The HX 'wings' are then soley connected to the channel upstream of the junction (noting you can't actyally link a boundary to only the last node of an open channel reach, so use the F flag in the CN lines to assign 0.99 and 0.01 weightings to link to the downstream-most and penultiamte nodes respectively) and then useing separate HX lines link the sides of the truncated open channel, downstream of the junction, in the normal way.

 

To summarise, in lieu of drawing a picture, you have:

 - Normal HX lines along the banks of the truncated sections, to pass water from the channel to the adjacent 2D floodplains.

 - HX 'wings' which serve to pass water down the floodplain from the extended ISIS sections into the 2D domain.

 

I hope that makse sense! If anybody wants some diagrams, say so and I'll try and generate some.

 

Others may do differently of course... :)

 

PHA.

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Hi PHA,

 

We build some 1d/2d models with extended sections in ISIS model and link to TUFLOW. We have never used "HX" wings but it seems helpful. Could you please generate a diagram of your schematisation ? We are very interested in it.

 

Thanks in advance,

 

Mathieu

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Hi PHA,

 

Thank you for your advice. Your schematisation seems to work well and the transition is smoother. 

 

Mathieu, I've got a screenshot of the new schematisation here but I'm not sure why I can't seem to find a button to upload images...

 

Regards,

Siripen

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I found this topic very interesting but unfortunately I do not get what PHA means with "HX wings" as I only have used wings in the 1D cross sections when there are instabilities and the grid size is fairly small (like 2m or so). Could anyone upload an schematisation please?

The way I would do it is extending the HX to be snapped to the CD polygon as the best representation comes from having the same/approximately width in 1D and 2D but also the same or similar elevation at the end of the CN line (to account for the top of bank). I generally use a zln_TOB (top of bank) layer to impose the elevations I have in surveyed cross sections but I also get elevations from my LiDAR in between and for interpolates.

I will be looking forward to know if the applied schematisation is the same as the one I would use. I am always eager to learn and improve :)

Regards to all,

Monica

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