Redd scour is when the velocity of the flow gets high enough to move the rocks that cover the redd. The higher the flow the higher the velocity, in general. But there are lots of "but"s.

If the stream can spread out into a floodplain, wide channel then the velocity decreases. Confine the channel and velocity increases.

When fish spawn, they turn over the gravel. Rocks settle by weight which means the rocks get heavier as you go deeper into the streambed. Mass spawning turns over the whole bed. This has been shown to then require a higher flow to mobilize the gravel. The result? A particular flow might scour out redds at low spawner density and totally undisturbed them at a high spawning density.

Anything that increases peak flows, whether logging, clearing for development, installation of impervious surface (roof) will increase the probability and frequency of scour.

You probably won't see an actual scoured redd as the stream will naturally smooth the spawning beds. Finding a lot of dead eggs, like Rvrguy said, is a sure sigh though.