Gambiajoki, joki Länsi-Afrikassa, 700 mailia (1120 km) pitkä, nousee Guinean tasavallassa ja virtaa länteen Gambian läpi Atlantin valtamereen. Sen tärkeimmät sivujokit ovat Sandougou ja Sofianiama. Gambia on yksi Afrikan hienoimmista vesiteistä ja ainoa Länsi-Afrikan joki, johon pääsee helposti merellä kulkevalla meriliikenteellä. Se muodostaa yhdistävän tekijän Gambian itsenäiselle valtiolle, joka koostuu kapeasta maajousta joen molemmilla rannoilla. Gambian ja Senegalin välinen poliittinen erottelu on kuitenkin jo pitkään estänyt joen ja sen vesistöalueen luonnonvarojen kehittämistä, vaikka molemmat maat perustivat vuonna 1978 Gambian joenkehitysjärjestön (Guinea liittyi vuonna 1980).
Tietokilpailu
Kohde Afrikka: tosiasia vai fiktio?
Afrikan suurin maa on Algeria.
Lähteestään Fouta Djallonin ylängöllä Gambia seuraa käämitysreittiä suulleen, joka on ria tai hukkunut suisto. Jokikanavien jakaminen ja yhdistäminen - punomiseksi kutsuttu ilmiö - on luonut joen keskivälille useita saaria, joista kaksi suurinta ovat Elephant Island ja MacCarthy Island. Jokea yhdistää lukuisia puroja, nimeltään bolons, joista suurin on Bintang Bolon, joka virtaa siihen etelästä. Joen laakson leveys vaihtelee huomattavasti sen kulkua pitkin. Jokilaakso on leikattu hiekkakivelle, joka on peräisin Paleogene- ja Neogene-ajoista (ts. Noin 65–2,6 miljoonaa vuotta sitten).
Dense mangrove swamps fringe the lower river for 60 miles (97 km) inland, after which freshwater swamps and salt flats on low-lying stretches alternate with dense clumps of small trees and shrubs that line the cliffs. On the higher slopes of the riverbank, swamps and shrubs give place to parkland and tall grass. The wild oil palm grows along the valley bottom.
The vegetation of the river and of its creeks provides a favourable habitat for insects, animals, and birds. The swamps provide a breeding place for mosquitoes and tsetse flies. The river abounds in fish and river creatures, including the hippopotamus and the crocodile. Among the 400 bird species that have been recorded are the kingfisher, the cuckoo, the swallow, the heron, the sunbird, the hawk, and the grass warbler.
The swampy region closest to the river, with its dense masses of mangrove trees often growing more than 100 feet (30 m) high, abounds in wildlife but has been of little use for either agriculture or human settlement. The grass-covered river flats (known locally as banto faros) of the lower river are rendered useless for cultivation by the salt water that periodically inundates them, and settlements on them are few. The flats of the middle and upper river are of some agricultural value, however. Much of the grassland is regularly cleared, and the light soils are easily cultivable. The annual flooding of the fertile alluvial loams of the middle flats makes them especially suitable for intensive rice cultivation. On the light sandy and well-drained soils of the higher slopes, peanuts (groundnuts) grow particularly well. Cultivation and settlement have therefore taken place in the middle flats and on the higher slopes, with many villages being located on the borderline between the flats and the plateau, thus avoiding both the flooding of the lower slopes and the increasing aridity of the higher terrain.
The Gambia is one of the most navigable of African rivers; its chief value, therefore, has been its transportation function. As the main artery of the state of The Gambia, it is the principal means of transporting passengers, freight, and mail in the territory. North-south river crossings are provided by ferries such as those plying between Barra and Banjul, Banni and Kerewan, Farafenni and Yelitenda, and Kau-ur and Jessadi.
