The boat channel

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TIGHAR has sometimes used the term "boat channel" to refer to channel blasted through the reef, oriented perpendicular to the shore, that allowed small boats to cross the reef and land close to the sand line. Oceanologists use the term boat channel in a different sense.

The so-called boat channel runs south out of Tatiman Passage, parallel to the shoreline. There is a similar channel running north out of the passage along the Nutiran shore.

The channels are the result of a "longshore current" scouring a two- to four-foot depression in the underlying coral close to the sand line of the beaches. When waves strike a shoreline at an angle, they tend to produce a current that runs parallel to the shoreline. The effect of prevailing winds, the longshore current, and gravity causes "longshore drift" of beaches.

The path of water to escape the reef runs along the shore until such a point where it can find its way off the reef in a natural channel 90 degrees to the beach.

Howard Alldred (RIP), "Location and Geology of Nikumaroro":
Either in association with the beachrock outcrops, or as a result of its absence, a “boat channel ” runs along the inboard edge of the reef flat. ...
On Nikumaroro, where it is actually present, it is a non-navigable series of discontinuous channels, troughs and pools, not usually more than 1-metre deep. They form temporary sediment traps.