The Gambia is situated in the Sahelian
zone on the
West Coast of Africa. It is one of the smallest countries
in Africa (the smallest being Seychelles archipelago)
and has a total area of 11,300 square km, of which about 20
percent is described as wetland. The river runs from east
to west, dividing the country in two strips of land 25 to
50 km wide and about 300 km long.
The country has a total boundary length of 820 km (510 mi),
of which 80 km (50 mi) is coastline.
The River Gambia, the
country's major waterway, rises in Guinea and follows a twisting
path for about 1,600 km (1,000 mi) to the sea.
A flat plateau of tertiary sandstone, capped with an infertile
ironstone crust, gently rises from 10- 15 m at the coast to
100 m at 400 km inland. The rest of the catchments consists
of older worn Paleozoic and Pre-Cambrian rock with a maximum
height of about 1500 m in the Fouta Djallon. Pleistocene and
Holocene (Nouakchottian transgression) exist along the coast,
along the estuaries and in river valleys.
The landscape two major geomorphologic units can be distinguished
between the uplands and the lowlands:
On the upland plateaus, weathered tropical soils are found.
These soils have low intrinsic fertility and low water
retention capacity, but their drainage conditions are good.
The plateau is intersected by watercourses flowing downwards
on the lowlands. These streams have formed narrow fluvio colluvial
The lowlands include the floodplain of the River
Gambia in the Upper Valley, and tidal plains (Banta Faros)
in the Central Valley and Lower Valley. The soils of the lowlands
are flat, fine textured and poorly drained. In the LV potentially
acid sulphate soils occur, which can become acidic soils unless
water logging is prevented by drainage.
Outside salinity risk areas (Scott Wilson Kirkpatrick, 1993),
freshwater can be found throughout The Gambia, at depths ranging
from 4 to 30 mbgl (metres below ground level). In general,
depths increase with proximity to the border with Senegal.
Groundwater recharge depends on the quantity and spatial and
temporal distribution of rainfall, surface geology, and land
use (Howard Humphreys and Sons, 1974; Chow, 1964). Good quality
surface water within the country
is only found in the eastern third of the River
Gambia. From June to December, freshwater availability
is boosted by flows from the middle and upper Gambia River
Basin areas. Low flows from January to May are mostly sustained
by local rainfall (Njie, 2002).
main feature of the land is predominantly Guinea
woodland savannah and Sahelian scrub with with mangroves
concentrated near the estuary of the River
Gambia and along its banks and Bolongs.
The vegetation is comprised of the Savannah type with shrub and
grass understoreys. Mangroves are found in the western half of the
country in the floodplains of the river region. The cultivable land
area is roughly 430,000 hectares, which is 38 percent of the
total area. Back in 2002 available arable land was 250,000 hectares, while 5,000 hectares were
under permanent crops.