My house has a steep pitch, concrete tile roof with many intersecting
interior valleys. During heavy storms, fresh debris (from redwood
trees) collects in the valleys and eventually impedes the water flow
down the flashing. I've done my best to clear out the "debirs dams,"
but every major storm is sure to create a new batch.

Ultimately, I am trying to come up with some method to prevent the
debris from blocking the water flow. One idea is to install an
exterior flashing valley that might also help the small branches slide
down the roof. However, I'm not sure how this can be secured to
concrete tile. A variation of this idea is to install a series of
flashing "steps" on each set of intersecting tiles creating a flashing
waterfall down the valley. And, I have thought of a seasonal solution
that would involve laying some sort of light pipe along the valley to
keep debris from catching in the intersecting tiles. This might not
look very elegant, and I have no idea if it would be effective.

Any suggestions?