CHANNEL, CHANNELS OF THE SEA (אָפִיק, H692, to hold, to contain, to be strong, a stream, to grow up, to grow, to flow). The word may refer to the channels of rivers and irrigation systems as well as of the sea. Metaphorically Job 40:18 describes the bones of Behemoth as “tubes of bronze,” but in Job 6:15 the expression alludes to treacherously fickle Palestinian streams (and men). In Psalm 69:2, 15 it is the threatening rush of floodwater which is envisaged, but Psalm 126:4 alludes to the fertilizing effect of flashfloods on crops in the Negev. In Isaiah 8:7 warning is given that in refusing the gentle waters of Shiloah (the Davidic kingdom) Israel lies exposed to devastating flood as the Euphrates (Assyria) bursts its channels.
In two identical passages (2 Sam 22:16; Ps 18:15) the channels of the sea and the foundations of the world are depicted as laid bare by the breath of God. Some see allusion to the ancient misconception of a world-encircling ocean stream guided by hidden channels, while others claim reference to the sea floor corrugations detected by oceanographers. But the passage reads more naturally as a poetic allusion to the Red Sea floor laid bare for Israel’s crossing.
International Standard Bible Encyclopedia (1915)
The fact that many streams of Palestine flow only during the rainy season seems to be referred to in Job 6:15; and perhaps also in Ps 126:4.