Help! After a massive rainstorm deep rivulets have formed under my deck undercutting a support. What is my best course of action?

I've tried to take a couple of pictures to illustrate what I mean: http://ift.tt/1PTnraC. I believe I've traced the source of the water back to a downspout which I've now tried to direct away from this area. Any suggestions on what to do to fix this? Should I just refill in with dirt and rock? Should I have a structural expert look at it? The deck is very large and multi tiered. This is the only effected support. Thanks for any suggestions.

Submitted May 30, 2015 at 03:39AM by brassface http://ift.tt/1FkBV97