Couple of recent trips down the Kiachnish have reported issues with trees with one in particular causing problems and a pretty definite portage - quotes and information below:
17th September - "There are lots of trees down in the Kiachnish, most can be avoided / are passable but should still be treated with extra caution, there is one however blocking the S bend rapid about half way through the gorge. Eddy out in the pool above in plenty of time otherwise grab the last sketch boil / eddy on river right and get out of there before an epic happens. There is a fun seal launch off a ledge above the rapid on river left launching you into the bottom of it for some fun downtime".
6th October - "Managed to clear most of the smaller branches from this fallen tree on Saturday (the 4th) so if anyone does miss the eddy they should wash under the tree... still, the main trunk remains firmly stuck and is not really something you want to try to paddle under".
So for the meantime, sounds like you want to give this a wide berth....