This is a project based on Dune's River preset available from NWDA. I made some slight adjustments to a few of the supplied features and I reseeded the PFs to my liking. I must say I highly recommend this pack, it's very well organized, there is a lot to learn from and you get not only the desired terrain and water features, but lots of cool surfacing and the road as a bonus. I am mesmerized by the river itself, I tried to do something similar on my own and miserably failed...
I have also added objects from my Black Friday acquisitions from the HQ Pine and HQ Spruce Tree packs. There are some bushes from the NWDA dry bush bundle interspersed and one model of Dune's grass, which is I think looks excellent.
The geese are from Walli.
I wanted to add more populations, but when rendering the final version I got a low memory warning, so I called it good

Rendered in TG 3.4