On Oct 22 there will be a procession conducted from the Thewet area down to Wat Arun. Government release here. To be noted: Also there will be practices sporadically before then, with dress rehearsals on Oct 13 and Oct 18. See here.
I saw a video of a previous procession while visiting the Royal Barge museum back in March. I wish I could make it to Bangkok for the event.
Please be aware that during the days of rehearsal mentioned above the express boat and all river traffic will sieze operations from 11:00 AM until 6:30 PM