It is hardly necessary to state that these words signify a hollow sweep of ground between two more or less parallel ridges of high land. The structure of the greater part of the holy land does not lend itself to the formation of valleys in our sense of the word. The abrupt transitions of its crowded rocky hills preclude the existence of any extended sweep of valley. Valley is employed in the Authorized Version to render five distinct Hebrew words.
'Emek. This appears to approach more nearly to the general sense of the English word than any other. It is connected with several places.
Gai or ge. of this there is fortunately one example which can be identified with certainty--the deep hollow which compasses the southwest and south of Jerusalem. This identification establishes the ge as a deep and abrupt ravine, with steep sides and narrow bottom.
Nachal. This word answers to the Arabic wady, and expresses, as no single English word can, the bed of a stream (often wide and shelving, and like a "valley" in character, which in the rainy season may be nearly filled by a foaming torrent, though for the greater part of the year dry).
Bik'ah. This term appears to mean rather a plain than a valley, though so far resembling it as to be enclosed by mountains. It is rendered by "valley" in (34:3; Joshua 11:8,17; 12:7; 2 Chronicles 35:22; Zechariah 12:11)
has-Shefelah. The district to which the name has-Shefelah is applied in the Bible has no resemblance whatever to a valley, but is a broad, swelling tract of many hundred miles in area, which sweeps gently down from the mountains Judah to the Mediterranean. It is rendered "the vale" in (1:7; Joshua 10:40; 1 Kings 10:27; 2 Chronicles 1:15; Jeremiah 33:13) and "the valley" or "the valleys" in (Joshua 9:1; 11:2,16; 12:8; 15:33; Judges 1:9; Jeremiah 32:44)
Main reference: Smith's Bible Dictionary (1860s)
Bible Gallery and Bible Illustrations (thousands of images)