Do check the title deed carefully, as you may possibly be in a situation where you have two different grades of land title on the same plot. I have seen land before where the land further back from the river was classed as NS4 chanote land, but the land closer to the river was of a much lesser title.
This was because the land closest to the river was formed by alluvion, which would make you the riparian owner. As such you normally have the right to plant and harvest on alluvion land, but not necessarily to construct a building. I note from your plan above that you want to situate a house closest to the river, so it would be good to check.
Make very certain that the land has the correct concrete surveying pegs in place and that there is no (or minimal) land formed by alluvion in the plot.