ORINOCO, a river in the north of South America, falling north-east into the Atlantic between 60° 20′ and 62° 30′ W. It is approximately 1500 m. long, but it is several hundred miles longer if measured by its Guaviare branch. Lying south and east of the main stream is a vast, densely forested region called Venezuelan Guiana, diversified by ranges of low mountains, irregular broken ridges and granitic masses, which define the courses of many une.xplored tributaries of the Orinoco.
In 1498, Columbus, when exploring the Gulf of Paria, which receives a large part of the outflow of the Orinoco, noted the freshness of its waters, but made no examination of their origin. The caravels of Ojeda which, in 1499, followed almost the same track as that of Columbus, probably passed in sight of one or more of the mouths of the Orinoco. The first to explore any portion of the mighty river was the reckless and daring adventurer Ordaz. In his expedition (1531–1532) he entered its principal outlet, the Boca de Navios, and, at the cost of many lives, ascended to the junction of the Meta with the parent stream. From Ordaz up to recent times the Orinoco has been the scene of many voyages of discovery, including those in quest of El Dorado, and seme scientific surveys have been made, especially among its upper waters, by Jose Solano and Diaz de la Fuente of the Spanish boundary line commission of Yturriaga and Solano (1757–1763), Humboldt (1800) and Michelena y Rojas (1855–1857). The last ascended to the Mawaca, a point about 170 m. above the northern entrance to the Casiquiare canal, and then a few miles up the Mawaca. A little knowledge about its sources above these points was given by the savages to de la Fuente in 1759 and to Mendoza in 1764, and we are also indebted to Humboldt for some vague data.
At the date of the discovery, the Orinoco, like the Amazon, bore different names, according to those of the tribes occupying its margins. The conquistador Ordaz found that, at its mouth, it was called the Uriaparia, this being the name of the cacique of the tribe there. The Caribs, holding a certain section of the river, named it the Ibirinoco, corrupted by the Spaniards into Orinoco. It was known to other tribes as the Barraguan and to others as the Maraguaca. The Cabres called it the I'aragua, because it flooded such a vast area of country.
The principal affluent of the Orinoco from the Guiana district is the Ventuari, thu head waters of which are also unknown. It is an important stream, which, running south-west, joins the Orinoco about 90 m. aljove its Guaviare branch. Two other large triljularies of the Orinoco flow north from the interior of this mysterious Guiana region, the Caura and the Caroni. The former has recently been explored by Andre, who found it greatly obstructed by falls and rapids; the latter is about 800 m. long, 400 of which are more or less navigable.
South of the Guaviare, as far as the divortium aquarum, between it and the Rio Negro branch of the Amazon, the country is dry and only partially swept by moisture-laden winds, so that few streams of moment are found in its southern drainage area; but north of it, as far as 6° 30′ N., the north-east trade winds, which have escaped condensation in the hot lower valley of the Orinoco, beat against the cold eastern slopes of the lofty Colombian Andes, and ceaselessly pour down such vast volumes of water that the almost countless streams which flow across the plains of Colombia and western Venezuela are taxed beyond their capacity to carry it to the Orinoco, and for several months of the year they flood tens of thousands of square miles of the districts they traverse. Among these the Apure, Arauca, Meta and Guaviare hold the first rank.
The Apure is formed by two great rivers, the Uribante and Sarare. The former, which rises in the Sierra de Merida, which overlooks the Lake of Maracaibo, has 16 large affluents; the latter has its sources near the Colombian city of Pamplona, and they are only separated from the basin of the river Magdalena by the “Oriental” Andean range. From the Uribante-Sarare junction to the Orinoco the length of the Apure is 645 m., of which Codazzi makes the doubtful claim that 564 are navigable, for there are some troublesome rapids 114 m. above its mouth, where the Apure is 3 m. wide. The numerous affluents which enter it from the north water the beautiful eastern and southern slopes of the Merida, Caraboso and Caracas mountain ranges. A few of them are navigable for a short distance; among these the most important is the many-armed Portugueza, on the main route south from the Caribbean coast to the llanos. A few large streams enter the lower Apure from the south, but they are frequently entangled in lateral canals, due to the slight elevation of the plains above sea-level, the waters of the Apure, especially during flood tirne, having opened a great number of caños before reaching the Orinoco.
The “Oriental” Andes of Colombia give birth to another great affluent of the Orinoco, the Arauca, which soon reaches the plain and parallels the Apure on the south. Perez says that the Sarare branch of the Apure has formed a gigantic dam across its own course by prodigious quantities of trees, brush, vines and roots, and thus, impounding its own waters, has cut a new channel to the southward across the lowlands and joined the Arauca, from which the Sarare may be reached in small craft and ascended to the vicinity of Pamplona. The Arauca is navigable for large boats and barges up to the Andes, and by sail to its middle course. In floods, unable to carry the additional water contributed by the Sarare, it overflows its banks, and by several caños gives its surplus to the Capanaparo, which, about 18 m. farther south, joins the Orinoco.
The Meta is known as such from the union of two Andean streams, the Negro and Humadea, which rise near Bogota. At their junction, 700 ft. above sea-level, it is 1000 ft. wide and 7 ft. deep in the dry season, but in flood the Meta rises 30 ft. It is navigable up to the old “Apostadero,” about 150 m. above its mouth, but launches may ascend it, in the wet season, about 500 m., to the junction of the Negro with the Humadea. In the dry season, however, it is obstructed by reefs, sandbanks, shallows, snags, trees and floating timber from the “Apostadero” up, so that even canoes find its ascent difficult, while savage hordes along its banks add to the dangers to be encountered.
The Guaviare is the next great western tributary of the Orinoco. Eugenio Alvarado, a Spanish commissioner for the boundary delimitation of Colombia with Brazil in 1759, informed the viceroy at Bogota that the rivers Arivari and Guayabero rise between Neiva and Popayan, and unite to take the composite name of Guaviare. In those times they called it Guaibari, or Guayuare. The Guaviare is about 500 m. long, of which 300 are called navigable, although not free from obstructions. Its upper portion has many rapids and falls. The banks are forested throughout, and the river is infested by numerous alligators, so ferocious that they attack canoes. Two-thirds of the way up, it receives its Ariari tributar> from the north-west, which is navigable for large boats. Near its mouth the Guaviare is joined by its great south-western affluent, the Ynirida. Above its rapid of Mariapiri, 180 m. up. this stream runs swiftly through a rough country, but for a long distance is a succession of lakes and shallow, overflowed areas. Its head-waters do not reach the Andes.
Between the Guaviare and the Meta the Orinoco is obstructed by the famous Maipures cataract, where, in several channels, it breaks through a granite spur of the Guiana highlands for a length of about 4 m., with a total fall of about 40 ft., and then, after passing two minor reefs, reaches the Atures rapids, where it plunges through a succession of gorges for a distance of about 6 m., winding among confused masses of granite boulders, and falling about 30 ft. At the mouth of the Meta it is about 1 m. wide, but as it flows northwards it increases its width until, at the point where it receives its Apure affluent, it is over 2 m. wide in the dry season and about 7 m. in floods. It rises 32 ft. at Cariben, but at the Angostura, or narrows, where the river is but 800 ft. wide, the difference between high and low river is 50 ft., and was even 60 in 1892.
The Orinoco finds its way to the ocean through a delta of about 700 sq. m. area, so little above sea level that much of it is periodically flooded. The river is navigable for large steamers up to the raudal or rapid of Cariben, 700 m. from the sea, and to within 6 m. of the mouth of the Meta. Maintaining its eastern course from the Apure, the main stream finds its way along the southern side of the delta, where it is called the Corosimi river, and enters the sea at the Boca Grande; but in front of the Tortola island, at the beginning of the Corosimi and 100 m. from the sea, it throws northwards to the Gulf of Paria another great arm which, about 100 m. long, and known as the Rio Vagre, bounds the western side of the delta. En route to the gulf the Vagre sends across the delta, east and north, two caños or canals of considerable volume, called the Macareo and Cuscuino. The delta is also cut into many irregular divisions by other canals which derive their flow from its great boundary rivers, the Corosimi and Vagre, and its numerous islands and vast swamps are covered with a dense vegetation. The Boca Grande outlet is the deepest, and is the main navigable entrance to the Orinoco at all seasons, the muddy bar usually maintaining a depth of 16 ft.
The Spanish conquistador and his descendants have not been a blessing to the basin of the Orinoco. All they can boast of is the destruction of its population and products, so that the number of inhabitants of one of the richest valleys in the world is less to-day than it was four centuries ago. The entire river trade centres upon Ciudad Bolivar, on the right bank of the Orinoco, 373 m. above its mouth. The only other river port of any importance is San Fernando, on the Apure. It is a stopping-point for the incipient steamer traffic of the valley, which is principally confined to the Apure and lower Orinoco. It occupies, however, but a few small steam craft. There is steam connexion between Ciudad Bolivar and the island of Trinidad. Cattle are carried by vessels from the valley to the neighbouring foreign colonies, and a few local steamers do a coasting trade between the river and the Caribbean ports of Venezuela. A transit trade with Colombia, via the Meta river, has been carried on by two small steamers, but subject to interruptions from political causes. (G. E. C.)