BROOK. A small stream. One of “the sweet words of Scripture,” because the Bible was written in lands near the desert, and by men who therefore appreciated water. Many brooks are named in the Bible—e.g., Besor (1Sam.30.9), Cherith (1Kgs.17.3-1Kgs.17.7), and Kidron (2Sam.15.23). The word rendered “brooks” in the KJV in Isa.19.6-Isa.19.8 seems to refer to the Nile or its irrigating streams; in Ps.42.1 it may refer to “channels” (niv “streams”). The word nahal, translated “brook” over forty times in the KJV, often means “a wadi”—i.e., a torrent in winter and spring that dries up in summer.
Today some of these brooks are called wadis in Arab. The Arnon is Wadi Mojib, Cherith may be Wadi Yabis, Besor is Wadi Ghazzeh, and the “river” of Egypt is perhaps the Wadi el-’Arish although some think it is the Nile. The word wadi is more accurate since some brooks are nothing more than dry washes except during flood season. This is illustrated well in 2 Kings 3:16f. The Spanish arroyo describes the same thing in the SW United States. The fact that the valley between Jerusalem and the Mt. of Olives is called the Brook Kidron is ample evidence that it may refer to a gully in which water rarely or never runs. Even though water is only occasionally present in some brooks, the dry bed is often the best place to dig for water or to plant. Only one other word in Heb. is rendered “brook” in the RSV and that is the hapax legomenon of 2 Samuel 17:20 (מִיכַ֣ל).
International Standard Bible Encyclopedia (1915)
In Palestine there are few large streams. Of the smaller ones many flow only during the winter, or after a heavy rain. The commonest Hebrew word for brook is nachal, which is also used for river and for valley, and it is not always clear whether the valley or the stream in the valley is meant (Nu 13:23; De 2:13; 2Sa 15:23). The Arabic wady, which is sometimes referred to in this connection, is not an exact parallel, for while it may be used of a dry valley or of a valley containing a stream, it means the valley and not the stream. ’Aphiq and ye’or are translated both "brook" and "river," ye’or being generally used of the Nile (Ex 1:22, etc.), though in Da 12:5-7, of the Tigris. Cheirnarrhos, "winter-flowing," is applied in Joh 18:1 to the Kidron. Many of the streams of Palestine which are commonly called rivers would in other countries be called brooks, but in such a dry country any perennial stream assumes a peculiar importance.