Hi A, while I did study fluvial geomorphology back at uni, somehow I ended up in IP video surveillance!
One of the studies we did was of a river that had a major flood event some decades ago. There were various mechanical devices set up to record data about water levels and flow rates. However in a catastrophic flood, the only measurements that could be made were when each of these devices stopped reporting data because they were washed down the river! That's how it was possible to work out how high the flood reached at certain times. The logs lying high up in the crowns of trees made it clear that ordinary water-measuring devices were never going to be able to survive such a flood.
Having glanced at the web link you provided, it would appear that radar has some merit if the unit is placed high enough above the river so that it could never be wiped out by a catastrophic flood. Otherwise it might just be washed away too. I'm not sure why they picture a unit right down next to the river. It might well provide early warning which would be very helpful but then might be washed away, when the flood continued to rise, which seems like a waste.
I noticed the unit relies upon a 3G cellular connection which would be a bottleneck for high resolution video but may be OK for sending pictures fairly frequently.
I'd suggest asking if the unit can be placed a long way above the water level or if it has to be down close where it might be washed away in a flood event.