Extending Surveyed Cross Sections

[Simon Roberts]

Hi everyone,

I’m working on a river reach, where we’ve had the river surveyed with cross sections being at approx 20-30m spacing.

Obvioulsy the surveyor hasn’t surveyed the floodplain and I’m hoping to extend the sections, with the elevations being picked up from the LiDAR data or terrain.

Is there a way to do this within HEC RAS where I can ‘dogleg’ the sections so that they don’t intersect? I’ve used the ‘Extend Cut Lines and Sta/Elev’ option, but this looks like it only extends them straight out and I can’t seem to adjust the cut lines while maintaining the station/elevation data from the survey.

Any help would be appreciated.

Thank you
Simon

[Luis Partida]

When I have had to do this, it always ends up being a tedious Excel and RAS exercise. So here is what i do, i take the Original Cross-section data and paste it into Excel. In the same geometry within RAS select edit >move Points> and extend the cross section to where you want it at. Then within the cross-section editor select the button that cuts the cross section from the underlying terrain. Take the new station elevation data and paste that next to the original cross-section data in excel. From here you need to perform a routine of matching station data and cutting out data from the terrain where there is survey and merge the 2. From here you can re-paste this into the cross-section data editor and have a geo referenced survey/LiDAR cut cross section.

[Scott Miller]

An approach to extend 1D cross-sections within Mapper would be to use the survey to interpolate a channel, then export it as a surface. Bring that surface into a new terrain with lidar below it. Copy the surveyed cross-sections to a new geometry associated with the hybrid terrain, extend them, and use the terrain to cut new elevations.

You could, alternatively, generate a survey surface in CADD. Check with survey or CADD staff.

[Scott Miller]

Point of clarification: What format is the survey? Easting/northing/elevation or distance off baseline station?

[Simon Roberts]

Hi Scott,

The survey is in easting/northing/elevation

Thank you

[Luis Partida]

Definitely use Scott’s method, that is WAY easier, and I will be using that from now on too so, Thanks Scott!

[Simon Roberts]

Hi both, thank you for your replies.

When you say extend the sections in RAS Mapper, do you mean to just edit the Cross Sections layer and then move the points to where you want them extended to?

[Simon Roberts]

I’m just having trouble, as whenever I try and edit the cross sections and move the points, the stations and bank markers are all over the place!

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