Is RAS Mapper saying my cross sections are backward?

[LorenAmelang]

I’m a landowner in a small private community which owns a dam in California, so is facing the new requirement for inundation mapping. I’ve done GIS work in the past, so I thought I’d try to make a map… I had no idea how deep this goes…

I’m using QGIS and RiverGIS, and just loaded my third try at a model into HEC-RAS. The previous model went unstable immediately, but it used 10 meter DEM data which I guess is not good enough. So this one used 1 meter data.

The export file loaded, and I fixed a few things in the Geometric Data Editor. The big blue arrows know the flow directions, and the station numbers decrease along each reach. But then I peeked at the RAS Mapper. The stationing along each cross section and the bank station positions seem to make sense only if you are looking upstream instead of downstream!

Row 1 in the table is just below the ‘y’ at the top of the map. Like 9.92 to 358.77. More bank on the right… Row 2 is just below it – more bank on the left. (Those banks are FEMA’s “100 year” flood limits – I will probably need to narrow them significantly once I can see them properly.) Geometric Data Editor shows the same positioning, but the bank stations are almost invisible there. Individual cross profiles agree.

Problem is the flow is from top to bottom of that map section, so left-right seems reversed! Yet all the widths make sense with the centerlines and bank lines… I have not tried running any analysis of this model yet…

Here’s that Row 2 line in the export file:

CROSS-SECTION:
STREAM ID:FORSYTHE CREEK
REACH ID:3
STATION:19380.179686727
…
CUT LINE:
6191960.81181022, 2239868.32521887 <-- "Left Bank" end 6192336.17856862, 2240006.52723293 <-- "Right Bank" end SURFACE LINE: 6191960.81181022, 2239868.32521887, 364.29 ... 6192336.17856862, 2240006.52723293, 363.75 END: Looks like HEC-RAS is showing what RiverGIS sent it... And here's the same line in the original SAGA cross section layer: MultiLineString ((6191960.81181022431701422 2239868.32521887170150876, 6192336.17856862302869558 2240006.52723292959854007)) 31 2 0 364.32315061 ... 363.73513569 Looks like RiverGIS passed on the lines SAGA created... The file it worked from already had proper StreamCenterline stationing and downstream direction. Guess it doesn't know the HEC-RAS left to right rule. Is this a problem? Is there a HEC-RAS way to flip left and right without flipping upstream and downstream? Will the cross sections flip around the river flowpath, or around one end or the other? And most importantly, will the DEM data then be flipped from reality? If I have to start over, is there a way to tell SAGA:CrossProfiles to draw left to right downstream? (Not in the QGIS toolbox interface...) Is doing this with free, open-source tools just hopeless?

[LorenAmelang]

Thank you gerar200 for pointing me to the right menu!

I started with this – QGIS on the left, Geometric Data Editor on the right, showing cutline 19380 extending well beyond the bank line to the (screen left) west on the “right” side of my stream looking downstream. HEC-RAS shows all cutlines L-R reversed:
Cross 19380 original QGIS, with HEC xyz plot.JPG

I used this on 19380 (in HEC-RAS 5.0.4):
HEC_RAS -> Edit -> Geometric Data Editor -> GIS Tools -> GIS Cut Lines -> Reverse Cut Lines -> (select river and reach – “all” shows no items! But see below…)

–> Check the “Node Types …” button before selecting lots of items! Sometimes it has all node types selected, even though you triggered it from a Cross Section specific menu item.

And while it reversed the XS left right arrow as expected, it also reversed the geometry, moving the whole channel westward and reversing the shape of it, leaving the wide bank area on the (screen right) east, “left” side of the stream:
Cross 19380 original QGIS, with Reverse Cut Lines.JPG

So I reversed that back and tried the other option:
HEC_RAS -> Edit -> Geometric Data Editor -> GIS Tools -> GIS Cut Lines -> Reverse XS Stationing and Cut Line Data
(For a single XS line, in Geometric Data Editor, left click the line, select “Reverse XS Stationing and Cut Line”, which does the same thing.)

These options reverse the HEC-RAS idea of left and right, _without_ moving the stream channel or spoiling the elevation profile.
Cross 19380 original QGIS, with Reverse XS Stationing and Cut Line Data.JPG

If you’re flipping your entire reach, you can click “All RS” to have the right arrow select all of the stations (you won’t see any action until you click the right arrow…) If you’re flipping your entire project, you can click “All Rivers” when the dialog first opens to have the right arrow select everything.

To see handy XS direction arrows in Geometric Data Editor, View -> View Options … -> Cross Section Properties -> XS Direction Arrows

To see map coordinates in Geometric Data Editor, hold Ctrl key, click a point.

P. 6-187 “Reverse Cut Lines” in the HEC-RAS “User’s Manual” Version 5.0 February 2016 sort-of describes the first function. I guess P. 6-166 “Reverse Stationing Data” must be trying to describe the other option, but it doesn’t match my HEC-RAS 5.0.4 at all, and isn’t very helpful.

Does anyone have a PDF manual that allows copying text? I can hardly believe it, but all the ones I’ve found are “protected”.

So I think my left-right issue is solved! I wonder what I get to learn next…

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