PHYSICAL SETTINGPost Comment PHYSICAL SETTING Nigeria
Geology: The geology of Kebbi State is dominated by two formations preCambrian Basement Complex in the south and south east and young sedimentary rocks in the north. The Basement Complex region is composed of very old volcanic and metamorphic
Aliero Onion Market, Birnin-Kebbi
rocks such as granites, schists, gneisses, quartzites and migmatites. In addition, there are metasediments such as phyllites and metaconglomerates.
The sedimentary region consists of rocks of the Gwandu, Illo and Rima groups whose ages range from the Cretaceous to the Eocene. The Gwandu group consists of massive clay grits interbedded with sandstone while the Illo and Rima groups consist of pebbly grits, sand stones and clays, mudstones and siltstones respectively. Minerals that can be found in the state include quartz, kaolin, piotolitic bauxite, clay, potta sium, silica sand and salt.
Relief: Kebbi State can be divided into three relief regions, namely the high plains in the south and south east, the plain landscape in the north and the riverine lowland of the Niger and lower Rima valleys. The high plains are characterized by dissected crystalline rocks with hill ranges and domical rises (inselbergs).
It is approximately 700m above sea level. The plain landscape forms part of the vast Sokoto plains which is an end tertiary plantation surface (Davis, 1982). It is a monotonous lowland, sedimentary in origin, with average height of about 300m above sea level. The plain surface is interrupted by isolated flattopped lateritecapped hills and ridges.
The riverine lowlands are mainly the flood plains of the major rivers which are very wide, up to 8km in many areas. They are characterized by levees, backswamos and terraces.on the natural vegetation (Silviconsult, 1992).
Kanta Museum, Argungu
Soils: In the northern part of the State, two groups of soils can be identified, the upland and fadama soils. These two soil groups are generally characteristic of the entire SokotoRima Basin. While the upland soils are sandy and well drained, the fadama soils are generally clayey and hydro morphic, especially in the backswamps.
In the south and southeastern parts, the weathering of the Basement Complex rocks has given rise to three types of soils. These are the ferruginous tropical soils, black cotton soils and lithosols. These soils are subject to stripping by erosion as a result of topographic characteristics typical of the area.
Vegetation: The natural vegetation of the State consists of a Northern Guinea Savannah in the south and southeast. They are characterised by mediumsized trees such as Parkia Clappertoniana (locust bean tree) and Bytyrosfperrrium (Shea butter tree) and Combretum species. In the north, the Sudan Savannah consists of open woodland with scattered trees such as acacia aibi da (gawo), Parkia Clappertoniana, Porassus and dum palms.
Argungu Lake (site of the famous Argungu Fishing Festival )
The natural vegetation has however been altered in many areas by intensive cultivation, grazing, fuelwood harvesting and bush burning, giving rise to a form of parkland dominated by trees like Piliostigma, Ziziphus, Mangifera Indica and Tamarindus, especially in the south. The practice of silvipastoralism by herdsmen in addition to browsing and bush fires in the dry season have done damages to Young trees, thereby takina a heavy toll
Drainage: The drainage system in Kebbi State is dominated by River Rima system with major tributaries like Gawon, Zarnfara and Gubin Ka. These tributaries rise in the Basement Complex region of Sokoto State and flow westward to join the Rima. However, in the southern part of the state, there are other less important rivers such as Danzaki, Soda and Kasanu, all of which flow to join the River Niger to the south of the state.
Most of these rivers first flow through deep and narrow valleys with steep gradients on the Basement Complex rocks, and then through broad shallow valleys when they flow through the sedimentary formations. The Rima itself flows in a broad sweeping valley through the sedimentary area and then into the River Niger in the south west, creating extensive flood plains that have no semblance to present discharges.
The Restaurant of Argungu Grand Fishing Hostel (the home of the great Argungu Fishing Festival)
Thus indicating that it is a product of a more humid Quaternary period in the past. In terms of flow regimes, most of the rivers are storm channels maintaining bankfull discharges after individual rainstorm events only to dry out with the cessation of rainfall. This characteristic is also reflected in seasonal flow situations.
Climate: Kebbi State enjoys a Tropical Continental type of climate. This is largely con trolled by two air masses, namely Tropical Maritime and Tropical Continental, blowing from the Atlantic and the Sahara Desert respectively. These air masses determine the two dominant seasons wet and dry.
The wet season lasts from April to October in the south and May to September in the north; while the dry season lasts for the remaining period of the year. Mean annual rainfall is about 800mm in the north and 1000mm in the south. Temperature is generally high with mean annu al temperature of about 26°C in all locations. However, during the harmattan season (December to February) the temperature can go down to about 21 °C and up to 40°C during the months of April to June.
Night temperatures are generally lower (Kowal and Knabe, 1972). Relative humidity is generally low (40 per cent) for most of the year except during the wet season when it reaches an average of eighty percent. This explains the hot dry environment which is in sharp contrast to a hot humid environment in the southern parts of Nigeria.
Ecological Problems: One of the major problems associated with the physical environment Kebbi State is that of desertification (SEP, 1992) This phenomenon is a serious constraint to development in the northern part of the state. The areas mostly affected are Gwandu, Argungu, Birnin Kebbi Jega, Maiyama, Arewa and Dandi local government areas.
In these areas, desertification manifests itself through incidence of wind erosion, dune accumulation and exposure of lateritic ironstone on the landscape. However, significant achievements have been made by the state towards finding solution to the problem. These efforts consist of estab lishment of shelter belts, woodlots, roadside plantations and forest reserves. Desertification is the product of a number of factors, both natural and manmade.
Some of these factors include, limited rainfall, indigenous methods of cultivation, excessive sourcing for fuel wood and indigenous grazing techniques. All these have com bined to deprive the environment of its natural vegetation, thus accelerating the incidence of soil erosion. Related to the problem of desertification is that of drought occasioned by the belowaverage annu al rainfall and uneven distribution. Furthermore, there are no edicts to curtail bush burning and wood cuttings.
Other ecological problems afflicting the state include those of flooding, pest infestation and gullies. The problem of flooding is restricted more to the Rima valley, and it is caused by uncontrolled release of water from the Goronyo and Bakolori reservoirs iinstream in Soknto and Zamfara States respectively.
Flooding has become an annual event since 1988. It occurs when excess water is released from the Bakolori and Goronyo dams upstream. Flooding has caused devastation of croplands within the flood plains, of settlements bordering them and loss of lives (Iliya and Mamman, 1996). The problem of pests, especially grasshoppers, caterpillars and quella birds, has been well documented in the literature on famine in Hausaland (Apeldorn, 1981).
Pest problems tend to be more pronounced during periods of long cessation of rains during the wet season. More recent ones are the 1986 and 1994 grasshopper invasions that destroyed many crop lands. Since the creation of the state and the need to develop the state capital, the search for laterite for building and road construction had resulted in a number of deep trenches and gullies. These have consequently increased the rate of erosion.
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