p19 0f the River of Cradles book, where it mentions the river is tidal to below the cataracts south of 3 kilometre island. Of interest is the mention that the tides rise 6m with the Blue moon, with flood tides reaching ten metres. Sounds like North Western Australia/Northern Territory.
So I think the river folk time their cargo trips to Pavis to coincide with the tides once every 6 or so days.