A tideline refers to where two
currents in the
ocean converge. Driftwood, floating seaweed, foam, and other floating debris may accumulate, forming sinuous lines called tidelines (although they generally have nothing to do with the
tide).
There are four mechanisms that can cause tidelines to form:
Where one body of water is sinking beneath or riding over top of the surface layer of another body of water (somewhat similar in mechanics to subduction and/or uprisal of the earth plates at continental margins). These types of tidelines are often found where rivers enter the ocean.
Thomson, R.E. 1981.
Oceanography of the British Columbia Coast. Department of Fisheries and Oceans. Canadian Special Publication of Fisheries and Aquatic Sciences 56. Ottawa. 291.