Hastings' Dictionary of the Bible (1898)
RIVER OF EGYPT. This phrase is found five times in the English Bible, and is the translation of two Hebrew terms. Nahar Mizraim, rendered "river" in Gen 15:18, and usually denoting a perennial stream; hence it perhaps refers to the Nile, and to the Pelusiac branch of the Nile, as the eastern limit of the territory promised to Abraham, but which his posterity never occupied, possibly because of its desert character. Nahal Mizraim. Num 34:5; Josh
15:3-4, Josh 15:47; 1 Kgs 8:65; 2 Kgs 24:7. This phrase does not denote a perennial stream, but usually a torrent bed, either partially or totally dry in summer, and having a running stream only in the rainy season. Nahal, therefore, exactly corresponds with the Arabic word wady, for which we have no English equivalent. Hence "Nahal Mizraim," or "torrent of Egypt," is generally used in Scripture to designate the old boundary between Palestine and
Egypt, and is identified with the modern Wady el-Arish, which drains the great central basin of the desert, between the passes of Jebel et-Tik and Sinai. The various wadies of this region unite in one, but without forming a perennial stream, and the torrent-bed reaches the Mediterranean about 40 miles south-west of Gaza, and nearly midway between the Red Sea and the eastern branch of the Nile.