Hello,
I am trying to make a simulation with HEC-RAS in 1D/2D. I only have the topographic and bathymetric sections for some of the river reaches. There is a scientific method for estimating the geometry of river sections for the reaches without the geometry based on river section of other reaches of the river?
In my case there is a area that is a estuary, however I don't have also the bathymetric/topographic data for this area. There is any method for estimating this based on SRTM data for example or other information?
More than a "scientific method" I would say "practical method". For natural streams you could try to stablish so called "hydraulic geometry relations". Below is a link to the founding work on these subject. But a quick search in google may provide you with several papers on these issue discussing the pros and cons of these approach.
https://pubs.usgs.gov/pp/0252/report.pdf
But just remember that these relations, being empirical in nature, have to be developed for specific regions.
Regarding topography you may for sure use SRTM (with its different variants) or any other remotely sensed data: there is also ASTER and ALOS World 3d available for free and then a couple of more that you can buy. In any case, these only provide information for areas free of water at the time the imagery was taken at the best (some data sets may mask the areas under water using the extent of water bodies at a time other than the one when the images were taken, but this is not such a big issue).
Bathimetry is actualy more complicated. In principle you need field data, but you might be able to make some approximations using time series of aerial or satellite images. The top width of the channel cross section is of course the easiest to determine. Depth and lower width, well, they are almost impossible to determine since they remain "hidden" to the naked eye. You may use some indicators like the slope of the river banks but in any case you will not reach a very precise result.
Finally, for reaches between crosssection I would recomend doing a simple interpolation (you may use HEC-RAS for that), and not to try some approximation.
Please learn in this links:
1 - https://pubs.usgs.gov/pp/0252/report.pdf
2 - https://bepl.ent.sirsi.net/client/en_US/default/search/detailnonmodal/ent:$002f$002fSD_ILS$002f0$002fSD_ILS:1143754/ada
3 - http://citeseer.ist.psu.edu/showciting?cid=2246334
Good luck
You can take a look to the following study from Journal of Hydrology:
Comparison of new generation low-complexity flood inundation mapping tools with a hydrodynamic model
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