You can cut shallow canals with a piece of track, and "Smooth Spline" tool. (set at 17m)
You can also cut the river channel with track, and "Smooth Spline" tool. (Set at 10m)
You can run a track down that "Jaggie" midsection (set at @ 14.5m) and it will raise the jaggies under he terrain.
With the topography tab st at minimum radius, you can tug up and down on all 4 corners of one 10 x 10 grid (one corner at a time) (very meticulous).
There are various "Walls", that have a horizintal grass plane included, that can hide imperfections in the canal terrain.
Math and Trainz go hand in hand ... I have laid track, and walls, within 0.01m tolerances (all very time consuming).
The metric system is easy, as Trainz is measured in meters.
Thre are various Metric to English conversion web pages for cyphering things out.