We did not scout either of these rapids, so my recollections of them come from one quick ride through.
Alder Creek - Large pour over rock on right, wave train with fun waves. Class IIish.
Black Creek - Big pile of rocks in river center. Most folks run the left side. Well defined tongue leading into big waves and a fairly solid drop. I ran down the tongue and got a big bounce. Others in my group ran towards the right side of the tongue and didn't get as big of a bounce. Long fun wave train. Class IIIish.
Salmon Falls - Sadly one of my favorite rapids is now covered.
There are lots of videos of Black Creek on You Tube. A few of Alder Creek.