CHAD, a lake of northern Central Africa lying between 12° 50' and 14° 1o' N. and 13° and 15° E. It lies about 85oft. above the sea in the borderland between the Sudan and the Sahara. The lake has greatly shrunken since it was first seen by Europeans ; this is attributed to the progressive desiccation of the region. Thus a town which in 185o was on the southern margin of the lake was in 1905 over tom. from it. But as the west shore is perfectly flat, a slight rise in the water causes the inundation of a considerable area, a fact to be remembered in considering the estimates made as to the size of the lake. In any case the Chad is but the rem nant of what in recent geological times was a very much larger sheet of water spreading south, north east and east of its present limits. A considerable area lying to the north-east is below the level of the lake. Around the north-west and north shores is a con tinuous chain of gently sloping sand-hills covered with bush. In the east, the country of Kanem, the desiccation has been most marked. Along this coast is a continuous chain of islands run ning from north-west to south-east. They are generally low, being composed of sand and clay, and lie from 5 to tom. from the shore, which throughout its eastern side nowhere faces open water. Two principal groups of islands are distinguished, the Kuri archipelago in the south, and the Buduma in the north. The in habitants of Buduma were noted pirates until reduced to order by the French. The coastline is, in general, undefined and marshy, and broken into numerous bays and peninsulas. It is also, especially on the east, lined by lagoons which communicate with the lake by intricate channels, while across the middle of the lake are numerous mud-banks, marshes, islands and dense growths of aqueous plants. Another stretch of marsh usually cuts off the northernmost part of the lake from the central sections. The open water varies in depth from 3 f t. in the north-west to over 20 in the south. Fed by the Shari and other rivers, the lake has no outlet. The flood water brought down by the Shari in December and January causes the lake to rise to a maximum of 24ft., the water spreading over low-lying ground, left dry again in May or June. But after several seasons of heavy rainfall the waters have remained for years beyond their low-water level. Nevertheless the loss by evaporation (estimated in the dry season to be loin. a month) and percolation is believed to exceed the amount of water received.
The southern basin of Chad is described under the Shari, which empties its waters into the lake about the middle of the southern shore, forming a delta of considerable extent. Beyond the south east corner of the lake is a channel or depression known as the Soro or Bahr-el-Ghazal (not to be confounded with the Bahr-el Ghazal affluent of the Nile). This channel goes north-north-east and some 2 50m. from the lake reaches its lowest point, 500f t. below Chad, in what is known as the Kiri lake (now dry). The remarkable levels led to the supposition of a connection between the basins of the Chad and the Nile. The French explorer, Jean Tilho, in his 1912-17 expedition showed that this was not the case and that the Chad is a closed basin. The Soro depression contin ues north-east some distance beyond Kiri. Then in the valleys between the Tibesti and Ennedi mountains the ground gradually rises and forms the watershed between Nile and Chad. In this direction, however, Chad at one time extended to the foothills of Tibesti and Borku. Besides the Shari, the Yedseram and Ulge enter the Chad on the south. The only other important affluent of the Chad is the Waube or Yo (otherwise the Komadugu Yobe), which rises near Kano, and flowing eastward enters the lake on its western side 4om. N. of Kuka.
Lake Chad is supposed to have been known by report to Ptol emy, and is identified by some writers with the Kura lake of the middle ages. It was first seen by white men in 1823 when it was reached by way of Tripoli by Walter Oudney, Hugh Clapperton and Dixon Denham. By them the lake was named Waterloo. In 185o James Richardson, accompanied by Heinrich Barth and Adolf Overweg, reached the lake, also via Tripoli, and Overweg was the first European to navigate its waters (1851). The lake was visited by Eduard Vogel (1855) and by Gustav Nachtigal (187o), the last-named investigating its hydrography in some de tail. Owing to an exaggerated belief in its economic importance there was during the partition of Africa a "race" for Lake Chad; in 1890-93 its shores were divided by treaty between Great Britain, France and Germany. The first of these nations to make good its footing in the region was France. A small steamer, brought from the Congo by Emile Gentil, was in 1897 launched on the Shari, and, reaching the Chad, navigated the southern part of the lake. A British force under Col. T. L. N. Morland visited the western or Bornu side of the lake at the beginning of 1902, and in May of the same year the Germans reached Chad from the Cameroons. In 1902-03 French officers under Col. Destenave made detailed surveys of the south-eastern and eastern shores and the adjacent islands. In 19o5 Boyd Alexander, a British officer, found that the lake then contained few stretches of open water. Later travellers found a good deal of open water; the extent of the water varying from year to year. One of the ancient trade routes across the Sahara from Tripoli to Kuka in Bornu strikes the lake at its north-west corner, but this has lost much of its former importance. As one of the results of the World War, that part of the lake region which was German passed (1919) under French mandate.
See the works of Denham, Clapperton, Barth and Nachtigal cited in the biographical notices: Jean Tilho in La Geographie (March, 1906) ; and the Geog. Journal, vol. lvi. (1920) ; Boyd Alexander, From the Niger to the Nile, vol. i. (1907) ; A. Chevalier, Mission Chari-Lac Tchad 1902-1904 (1908) ; E. Lenfant, La Grande Route du Tchad (1905) ; H. Freydenberg, Etude sur le Tchad et le bassin du Chari (1908) ; P. H. Lamb, "Notes on a visit to Lake Chad" in Geog.
Journal (Dec. 1921) .