jake these spillway problems have been known for over twelve years, and still the authorities that be in california and to an extent in DC , continued to divert billions in state funds to soft projects rather than face up to projects that didn’t meet their agenda priorities. the net effect of building a back up spillway is to prevent dam failure and thats exactly what happened. soil erosion as bad as it is is much prefer to catastrophic dam failure. you need to take your sand castle theory to the stream in a rain storm and watch it go from clear to very muddy as debris blocks and water eats around it in any number of ways with the net effect of reshaped earth on a stream level basis. environmental activist as wonderful as they are sometimes are there own worst enemy when they are always the no party and stand in the way of progress that can protect. ya’ll need water , dams have provided that before recorded history, put your environmental concerns on a back burner and fix the dams by diverting soft projects money back to hard money projects. by the way whats with all those concrete rivers rushing needed water back out to sea in southern california? isn’t all that concrete robbing poor old bacillus prognosticator of his just deserves of good old dirt?