Raising / lowering cross sections from the inversion elevation

[Zoran]

Dear modellers,

I have a cross profile of my river every 100 m as well as the invert elevation every 10 m. I would like to use this information to raise / lower my cross profiles that I have interpolated every 10 m. Any idea if that’s possible ?

Regards,
Zoran

[cameron]

You can use the Channel Design/Modification tool

[Zoran]

Dear Cameron,

I looked for an answer to my problem using the channel design / modification tool and the vertical datum adjustement tool.

Regarding the channel design modification tool, I can’t find a way to modify only the channel invert without applying an arbitrary template (which would completely modify my profiles)? It seems to me that the column Fixed Elev. is used to wedge the invert elevation of the template but does not allow to modify only the invert value.

Regarding the vertical datum adjustment, it allows me either to shift all the points in my profile(s) by a certain value, or apply the modification on the channel or overbank. I have not found how to shift only the invert channel.

Regards,
Zoran

[cameron]

I am a little confused to what you want. You don’t want to raise/lower the entire cross-section. You don’t want to raise/lower a section of the channel. Both of these would modify your invert.

The invert of your cross-sections are based on the the lowest point between bank stations. Are you saying you only want to adjust that single point? If you were to only adjust that single point, it may not be the invert anymore if it was raised above another point in the channel.

The channel modification tool can use a generic template or an actual cross-section as the template. You can specify a slope or elevation for it to develop the invert profile you want at the spacing you wanted. You can also control how much of a cross-section changes, either all of it or only what is in the channel.

[Zoran]

Dear Cameron,

I realize that my question was not clear.

I am trying to modify my cross profiles interpolated in a gradual and natural way from the invert elevation.

Here is a schema that summarizes what I want to do:

Left figure: the shape of a cross-section when only the invert point is modified -> this risks causing discontinuities in the profile

Right figure: the look of a profile that has been gradually modified from the bank station to the invert station. The correction (delta) is maximum at the lowest point and zero at the banks. If L is the distance between the bank station and the invert station and x is the distance between an arbitrary station and the bank station, the correction of the elevation at each station is given by the following relation: dY = x / L * DY.

Hoping to have been clearer.
Zoran

[cameron]

You would need to write a script to modify the cross-section to do what you would like.

[Zoran]

Dear Cameron,

This is also what I thought.
I plan to write a python script for QGIS which can do this. If it works well I’ll share it with the community.

Regards,
Zoran

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