It has to be something that is a bit more durable, something nice right at the rivers edge will get damaged in high water years and completely destroyed in a flood.
What Calgary needs is some sort of a public beach. I've kayaked through Harvie Passage on a hot day and it's completely full of people, and that area is definitely NOT meant as a beach. People are remarkably dumb on it too, last time I went through people are diving off rocks right in front of you and getting mad that you almost run them over. That happened about 5x then I saw a lady on a cheap inflatable raft getting carried through the rapids with people chasing after on the banks. No paddle and likely unable to swim. I feel like the same thing will happen with the river surf park, too many people looking to swim will disrupt the river surfing aspect. There is definitely demand for something, but given the variability of the water level and intensity on the rivers, it needs to be some sort of artificial lake or pond. Sikome is a good start, but it's too small and that water is gross. The private lakes in the south work well, but they are exclusive.