Good question posted.
I do not have the space here to write a real detailed answer but to summarise for you.
Fish can deal with amazing forces of water, they live in it. I have seen salmon negotiate falls that defies the law of physics.
First the surface of the water moves at a speed a great deal faster than at the bed of the river. Fish know how to find current seams that allow them with min expelled energy to stay in a comfort zone. 500 cfs is not that fast, here on the White with all units open it is something like 24,000 cfs. But you can go and catch fish in it. I have fished some rivers that move a great deal faster than that.
Yes, you will find fish around structure that form breaks in the downstream force of water, and they are always good zones to fish.
But your problem is of course being able to control you fly line.
I can give you many answers here so far as fishing techniques that you could use. The bottom line is this. I assume you were nymph fishing.
First you have to able to get the fly down to the fishes zone and that would reguire some addition of weight to your fly or leader or both.
Then you have to consider-- how long can my fly remain in a productive drift zone--that is achieved by allowing sufficient slack line and controlled mends to achive that.
There is a technique called high stick. in extream cases it may be termed as chuck and duck, when a great deal of weight is used. that may be incorporated with one or more flies and the additon of weight to the leader or both.
You are essentially using weight that will allow for the fly to sink real fast, from that point on the rod is held high and you follow the track of the fly for a short distance. You generally do not cast a length of fly line.You use maybe a rod length or less for a short track of the fly in the zone you expect to find fish. It can be very deadly l can tell you.
You can use a indicator or watch the flyline/leader for a hit, I choose not to use a indicator, but l have practised this technique for many years.
It is a perfect method to fish short deep pocket water situations and one when you have problems trying to deal with very fast flow rates. That do not allow for effective long range drifts.
One other tip l will give you is look for zones that have a slower rate of flow and also back water eddy's. many fish can congregate in these places.
With practice you will be able to read water movement and that can tell you a great deal so far as the likely places you will find fish.
Hope this helps you some