A vocabulary of landscape — a landscape of words
1367 entries
slackwater
Slackwater is the pause between the ebb and the flood when the tidal stream stops running, before it turns and goes the other way. It is not the same as high or low water: in many places the current keeps running for an hour or more after the level has stopped rising or falling, so slack and high water can be well apart. It is the working window for crossing a race, an overfall, or a narrows.
Etymology
The word uses slack in its ordinary English sense of loose or without tension, which is a different word from the Norse slack meaning a hollow, on this site. The nautical vocabulary of tide is unusually precise for a set of words this old: flood, ebb, slack, spring, neap, set, and drift each name one thing.
Notes
How long slack lasts varies enormously. In an open estuary it can be half an hour of gentle water; at a serious tidal gate it can be a few minutes between one direction running hard and the other. Working out when it will occur at a given place is the basic skill of tidal passage-making, and the answer usually comes from a tidal stream atlas rather than from the height tables.