And placing rip rap along an outside bend channelizes that section causes further erosion downstream and, flattens out the pool so much so that the pool disapears. It also deflects the flow from under the bank that would otherwise flow through the substrate of the bank so rip rap also warms the water, or more correctly since water flow through the bank cools the water, rip rap doesn't allow the cooling.
As for stoning a pool if one must throw stones to "wake up a pool" perhaps one should learn to fish, not all trout are caught on dry flies, that would make things too easy. But stoning a pool, give me a break.