You can lock a channel by using the command below:
r.lock #channelnamehere/id
This will stop anyone messaging in the channel until you feel it's ready to be reopened.
You can reopen a channel by using the command below:
r.unlock #channelnamehere/id
If you need to lock/unlock multiple channels at once, it's the same procedure as locking a single channel, except you can add as many channels as you need to lock.