1)I verified the vertex of my centerline, and it looks ok.
you can make 100% sure they snap by using the snapping options in the editor menu
2)I just run the XS process, and it runs well, without error message, but indeed the distance between cross sections seems wrong.
That is unfortunate. You basically need to start over at this point because we have spent a lot of time trying to figure out what goes wrong in these instances and never figure anything out.
3)I saw that I can change manually the to-from nodes and the arclength, but will it really work in the following? Will it consider my changes? And also, if I set it manually, the arc length value will be quiet imprecise ! I mean, the point of using Hec-GEO-Ras was to have that computed automatically! Because I don't have those measurement, I would have to make rough estimates.
In the attribute table you can right click on a field and there is an option to calculate geometry. This will calculate the length(or area if using a polygon) in just about any unit you would ever want.
4)So I guess I'll have to try your solution. But I didn't get exactly what I'm suppose to do.
You said I should extract the cross sections and stream centerline files, and put them in a new mxd file, but that you have one mxd file for each stream reach.
You should export the data so you dont have to 100% start over. You do not want to get your old georas data in the same mxd as your new so by exporting it to a regular shapefile you avoid that. During our dealings with this issue we have restarted a number of projects and had them still fail while adding in the old data so it can be directly copy&pasted. It shouldnt make a difference, but it does.
5) So should I create one mxd file for each reach of each river (so for me 5 mxd files) or just for each river (so 3 mxd files, considering the main river as one reach).
And then in each mxd file I put the same complete TIN file and the exported cross sections and river shape files, that I edit to keep only the portion I'm interested?
For simplicity sake, i would just go with the 3. This issue only shows up when you have multiple stream centerlines so having a single element for your main stream is not an issue.
6)And when you export it into Hec-Ras to make the simulation, can you make one simulation for the entire river with geometry from different files? It will understand how to connect the different reaches?
When you import all 3 georas setups into HEC-RAS they will all come in just fine, but will not be connected together. To connect them, open the main geometric data window in HEC-RAS, zoom to the confluence, then in the edit menu at the top, select "Move Object." Select the last vertex of your tributart and move it so that it intersects with your main stream. This will automatically break the main stream and add the junction.
Sorry for all those questions, but I never run Hec-Ras with Hec-GEO-Ras yet, so I don't know how it works exactly.
Its not normally this much of a pain. Georas is definitely the fastest and most reliable way of getting your data into RAS, but it has its quirks.