Physical Setting

Posted by on 1/14/2003 7:34:51 PM
Post Comment Physical Setting Nigeria

Geology: The whole of Akwa lbom State is underlain by sedimentary formations of Late Tertiary and Holocene ages. Deposits of recent alluvium and beach ridge sands occur along the coast and the estuaries of the Imo and Qua lboe Rivers, and also along the flood-plains of creeks. Inland, a greater part of the state consists of coastal plain sands, now weathered into lateritic layers, especially in Ini, Ikono, Etinan, Ikot Ekpene, Ibiono and ltu LGAs. A belt of shales associated with sandstones and limestones, north of Nkari and Obotme, extends down to ltu. The latter lithologies include the late Cretaceous Nsukka Formation at the base followed by the early Tertiary Imo Shale and the phosphatic Ameke Formation. Upwards, the geologic succession passes imperceptibly into thick sequences of clays, sands and gravel. Gravel beds and pebbly sands are commonly exposed on hillsides, road-cuts and stream channels in the north-eastern parts of the State . Generally, the sands in Akwa lbom State are mature, coarse and moderately sorted. Quartz is the sole framework element, and monocrystalline quartz constitutes about two-thirds of the quartz varieties.

Relief: Akwa lbom State lies entirely on the coastal plain of south-eastern Nigeria, where no part constitutes an area of appreciably high relief. Apart from the northern extreme corner of Obotme and Nkari and the north-eastern parts around ltu, Itam, Ibiono and Ini where the land is intensely dissected into a broken "valley and ridge" terrain, the landscape of Akwa lbom State comprises a generally low-lying plain and riverine areas with no portion exceeding 175m above sea-level. The land rises steadily northward from the sea-level at Eket in the south to 150m at Obotme in the north. The physiography of the State may be further sub-divided into five contrasting land form regions (from south to north):

(1) Beach ridge complex;

(2) Mangrove swamps;

(3) Gently undulating sandy plains;

(4) Sandstone hills and ridges with steep sided valleys; and

(5) Obotme steep-sided and isolated hills.

From the shoreline with a wide sandy surf beach, to about IOkm inland, is a strip of recently deposited marine sand characterised by a succession of sub parallel sand ridges. The beach ridges cover most of Eket, Ikot Abasi and a part of Mbo. East of Upenekang, the sand ridges with an average width of 200m are remarkably straight. The Okoroete area is also characterised by straight ridges. Intervening swales are reflected in a strong lineation of vegetation of dense raffia palm thickets, and differ markedly from the sparse scrub on the sand ridges. The mean altitude of the sand ridges is 30m, rising to 50m at its northern boundary. Farming is very restricted on the sand ridges but an oil palm plantation sited between Ibeno and Eket is thriving.

Mangrove swamps are extensively developed in the coastal and estuarine areas in the State. As in other parts of the Nigerian coast, the mangrove ecosystem is extending into the estuaries and flood plains of the Imo River at Ikot Abasi, the Kwa River at Eket and the Cross River at Mbo and Oron. But large tracts of riverine swamp and flood plain environments with wetland characteristics, flank the Qua lboe River valley through Etinan and Abak LGAs. Mangrove swamps also occupy the tidal mudflats laced with tidal channels, and the winding waterways, some about 20m wide. Small creeks that meander strongly develop as branches of the main channels. Such a system of intricately connected creeks can be seen east of the Imo River estuary at Uta Ewa and Ikot Abasi, where a complex network of drainage channels has broken the coastal area into a jigsaw of irregularly shaped tidal flats. Mangrove development can also be found at Jamestown, Ebughu, Oron and Nwaniba. The mangrove swamps are succeeded landward by upland alluvial depositional terraces which extend into the valleys of the Imo, Kwa, lkpa and Enyong rivers, where low natural levees descend into heav ily forested back swamps.

More than 75 per cent of Akwa lbom State con sists of level-to-gently undulating sandy plains where rivers are few and far between. Shallow depressions contain seasonal lakes that serve as sources of rural water supply in many areas. Itak clan in Ikono LGA contains four such seasonal lakes. Much of ltu, Ibiono, Ini and Ikono LGAs consist of very rough, intensely dissected terrain, with a landscape comprising steep-sided hills, valleys and narrow-crested sandstone ridges. Settlements in these areas are restricted to a few isolated sites. Agriculture and the road network are also adversely affected. Soil erosion has intensified considerably especially where gullying takes place.

The topography at Obotme is rugged, consisting of hills and ridges with steep-sided valleys which occupy much of Ini, Ikono, ltu and Ibiono LGAs. The hills and ridges of this region, which are separated by flood-prone lowlands, are remnants of the west-east extension of the Enugu-Okigwe escarpment which terminates at Arochukwu. The slopes are greatly ravaged by erosion and landslides, especially during the rainy season.

The drainage network in the upland part of Akwa lbom State is not dense, as rivers are few and distant apart with wide interfluves. Only one major river, the Qua lboe River, traverses the entire State from north to south. A major tributary of the Cross River, the Enyong Creek, drains the highly dissected terrain in Ikono, Ibiono and ltu.

Climate:
Because of the effects of the Maritime and the Continental Tropical air masses, the climate of Akwa lbom State is characterised by two seasons, namely, the wet or rainy season and the dry season. In the south and central parts of the State, the wet or rainy season lasts for about eight months but towards the far north, it is slightly less. The rainy season begins about March-April and lasts until mid-November. Akwa lbom State receives relatively higher rainfall totals than other parts of southern Nigeria. The total annual rainfall varies from 4000mm along the coast to 2000mm inland.

The dry season begins in mid-November and ends in March. During this brief period, the whole Continental Tropical air mass and its accompanying north-easterly winds and their associated dry and dusty harmattan haze. However, as a result of the proximity of the state to the ocean, the harmattan dust haze, (locally known as "ekarika") is not usually too severe as in the Sahelian zone of northern Nigeria. Sometimes it lasts for only a few weeks between December and January. The harmattan period is usually advantageous to the farmers because it is congenial for harvesting and the storage of food crop. Temperature values are relatively high in Akwa lbom State throughout the year, with the mean annual temperatures varying between about 26°C to 36°C. Akwa lbom State has relative humidities which vary between about 75 per cent to 95 per cent, with the highest and lowest values in July and January respectively. In January, areas which lie within 30 to 40 km from the coast experience mean relative humidities of more than 80 per cent, while values in areas further north vary between about 70 per cent a to 80 per cent.

Vegetation And Fauna. The existing climatic factors in Akwa lbom State would have favoured luxuriant tropical rainforests with teeming populations of fauna and extremely high terrestrial and aquatic biomass. However, both the vegetation and the fauna of the State are largely depaupurate because of strong human population pressure. The native vegetation has been almost completely replaced by secondary forests of predominantly wild oil palms, woody shrubs and various grass undergrowths. Akwa lbom State is reputed to hold the highest oil palms per capita in Nigeria. Mangroves cover extensive parts of the coastal Local Government Areas of Ikot Abasi, Eket, Mbo, Oron, ltu, Uquo-lbeno, Uruan and Okobo. Farmland mixed with oil palm and degraded forests predominate in the rest of the state.

Ecological Problems: Erosion menace in the form of gullying in the upland areas, and beach erosion along the coastal areas have attained a high degree of severity and destructiveness in Akwa lbom State. Gullies are now destroying agricultural land and even forest reserves in the northern parts, notably Ini, Ikono, ltu and Ibiono LGAs. At Obotme, farmlands have been so badly eroded that it has become necessary to discontinue the cultivation of what used to be good farmlands only a few years ago. Year after year at Obotme, farmlands are abandoned as old gullies devour more land and new gullies are opened. But gullying is not just a rural phenomenon as in Imo, Abia and Anambra states.

In fact, gullying has come to town. In the urban centres of Uyo, Ikot Ekpene and Oron, gullies are extending through streets, undermining buildings and eventually destroying them. The notorious Uyo Ravine, for example, has encroached on urban land and houses at Eka Street, threatens the University of Uyo Town Campus, and is defiantly creeping towards the doorstep of the Governor's office and residence. Factors that combine to cause severe gully erosion are poor land use prac tices, especially the development of sunken footpaths along valley and hill slopes.

Many other associated ecological problems are directly traceable to gullying. The soil removed from cultivated lands on the upper valleys set up a chain of damaging reactions down-valley, which are far reaching in their effects. The resulting accumulations of sediments on the lower levels and bottomlands impair drainage, thus creating serious shortage of water in the rural areas with gullied terrain. In Akwa lbom State, the struggle by man to conserve land by arresting and preventing large scale gullying and soil removal has been going on for some time. The State and Federal Governments have been reclaiming erosion sites.

The severest cases of coastal erosion occur in Uquo Ibeno LGA especially at Ibeno where the Oua lboe Oil Terminal is located. Next in severity is Ikot Abasi LGA where the village of Uta Ewa had lost almost half of its land mass before the Federal Government intervened to reclaim a portion of the eroded shoreline. Oron LGA also has its problems of shore erosion. At Jamestown, a relatively new protection measure is being undertaken but the old protection at Oron would definitely need maintenance in some places.

In Akwa lbom State, oil exploration and exploitation are major threats to the environment of the coastal areas. Environmental pollution of air, water, soil, crops and recreational facilities are the concomitant effects of petroleum exploitation which have adversely affected the riverine ecosystem. The coastal fisheries have been extensively depleted through oil spillage. Gas flaring from Mobil and Shell flow stations and oil wells has also been another environmental hazard which cause much damage to houses, vegetation and animal life, but flaring is about to be totally eliminated. Impacted sites are, however, yet to be fully restored to their natural state.




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