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The Gambia - Geography

The Gambia is the smallest country on mainland Africa, with an extent of about 330 km east to west, and less than 50 km north to south. It is a former British colony, forming an enclave within Senegal, a former French colony. The Gambia is one of the most densely populated countries in West Africa. The highest concentration of people is around the increasingly urbanized landscape spreading outward from The Gambia’s capital, Banjul. The city is built on a small peninsula tucked between mangrove-lined estuaries and the broad mouth of the Gambia River, which rises out of the Fouta Djallon Highlands of Guinea. With its natural port, Banjul is an important trading post between West Africa and the world.

The Gambia lies entirely within the drainage basin of the Gambia River, a basin that extends well into Senegal and Guinea. The river’s channel only descends 10 m as it flows from The Gambia’s eastern border to its mouth at Banjul. The river’s flow is very seasonal, and sea water intrudes some 200 km upriver during the dry season. The land is also flat, especially in the western half. In the eastern part of The Gambia, the river carves a meandering path through laterite-capped plateaus; terraces and shallow valleys characterize the terrain. The highest point is Red Rock, at only 53 m above sea level.

After flowing east of the Futa-Jallon highlands for 120 miles northwards, the Gambia sweeps round to the west, forcing its way through a series of gorges down to the plains. At Sillakunda, above the last gorge, the channel, averaging 1,000 feet in width, still stands at an elevation of 560 feet. Even after reaching the plains its extremely tortuous course is interrupted by some boulders and ledges, such as the sill of Barra-Kunda, over 270 miles above the estuary. This point is accessible to light craft during the dry season, the most favorable for navigation, the current being then weakest.

But usually deep-sea vessels stop much lower down, opposite MacCarthy Island, 170 miles from the mouth, where the tide is still felt in the dry period. The mean discharge has not been accurately measured, but it is known greatly to exceed that of the Senegal, regard being had to the much smaller extent of its basin. But here the rainfall is heavier and more frequent, the period, especially from July to September, being very wet. On August 9, 1861, there occurred a downpour of 9 inches in twenty-four hours, and in the same year two others of over 3 inches each.

But despite the large volume of fresh water rolled down from the upper reaches, the Lower Gambia is an estuary rather than a river, an inlet of brackish or salt water. Above the mouth its banks are over 6 miles apart, although the mouth itself is only 24 miles wide, with a mean depth of 65 feet. Here the largest vessels can easily ride at anchor, for the bar, which has still 30 feet at low water, lies some 12 miles off the coast. Several winding branches penetrate far inland, one of which, Oyster Creek, shows by its very name that it is not a fluvial but a marine channel. Other tortuous creeks penetrate through the wooded alluvial tracts northwards to the Salúm estuary.

The Gambia’s five ecoregions are all transboundary areas that have their counterparts in Senegal. The Gambia River forms a natural boundary between the northern ecoregions and the one in the south — the South Bank Zone (SB). Over a century ago, most of the country was blanketed by Sudanian woodlands, wooded savannas, and gallery forests. Today, most of the more wooded landscapes are found on the south side of the river, where the South Bank Zone extends seamlessly into Senegal’s Casamance (CAS) ecoregion. The woodlands nearer the coast are denser and have much higher biodiversity than those in the east.

Major systems of mangroves and mudflats are found along the coast near the mouth of the river, extending nearly half way up the length of the country. These constitute the Estuary Zone (EZ), an ecoregion that extends well into the Saloum River complex in Senegal. North of the Gambia River, three ecoregions reflect the varying degrees of human transformation of natural landscapes into agricultural ones. The North Bank Agricultural Zone (NBA) is almost entirely devoted to groundnut, millet, and maize cultivation on sandy soils. The Agricultural Expansion Zone (AEZ) is a mix of broad cultivated valleys among laterite plateaus with shrub and tree savannas. In the east, the Eastern Transition Zone (ETZ) is more sparsely populated, and the predominance of lateritic plateaus has spared the region from the more intensive human pressures of the western regions.

Until the middle of the 20th century, The Gambia’s landscapes were extensively wooded, as part of the broad Sudanian wooded savannas that sweep across this latitude of West Africa. Today, vegetation density and diversity increases from east to west, as well as from the relatively drier north to the moister south. The Gambia’s land cover has changed dramatically. The first change is the expansion of agriculture as the savannas are cleared for farming. The second is the rapid urban sprawl of Greater Banjul and beyond.

Among The Gambia’s semi-natural landscapes, savanna — which ranges from open shrub and tree savanna to dense wooded savanna — is still the predominant class by area. However, the maps show that it is giving way to agriculture. In 1975, savanna occupied 51.3 percent of the total land area, whereas in 2013 it occupied 43.4 percent. In the eastern and southern regions of the country, the savanna land cover is also becoming more fragmented as village lands devoted to agriculture coalesce.

The Gambia’s forests offer a more mixed picture of change. Majestic gallery forests (and fringing riparian forests along humid bottomlands) once lined most of the streams and drainage ways. They often occur on deeper soils with shallow water tables. These areas are also favored for rice cultivation and other uses. As a result, gallery forests are being seriously depleted by clearing, or degraded by selective logging of large trees for high value wood. In 1975, 324 sq km of gallery forest were mapped. By 2013, only 185 sq km remained, a loss of over 42 percent. In contrast, The Gambia’s mangrove forests have been fairly stable, with a slight increase in area from 602 sq km in 1975 to 654 sq km in 2013.

With the French introduction of groundnuts as a cash crop in Senegal in the 1800s, the production of groundnuts gradually spread across the border into western The Gambia. The northern half of The Gambia was the first to embrace large-scale groundnut cultivation because of its proximity to the major groundnut producing region of Senegal. By the 1930s, this area had become The Gambia’s main agricultural region. Patches of savanna used for grazing and forest resources were still present, as seen in the 1975 map. By 2013, The Gambia’s western portion, north of the river, had become almost continuously cultivated, and the traditional system of bush fallow largely abandoned. Agricultural expansion continues in all regions. In the east, where it was once found mainly on deeper soils in valleys, rainfed cultivation has now expanded into the terraces and plateaus. At the national level, agriculture in 1975 was found on 21 percent of The Gambia’s land area. The area increased to 23.9 percent in 2000, and 28.1 percent in 2013.