As Len has noted, there is no rule of thumb. Sediment does certainly deposit on the very inside of turns except when it doesn't. Learning to read the water is really the only last resort to take a shot at where the channel runs. Where commercial, every day traffic transits waterways, the dredging from their wheels forms the channel. In many places the ONLY way channels are kept open is by boats working in the area. That's why, all else failing, following one of them in is probably a good idea, especially when it comes to shifting inlets.
Alberg 35: With a philosophical flourish Cato throws himself upon his sword; I quietly take to the ship.