PHYSICAL SETTING

Posted by on 2/12/2003 10:27:08 AM
Post Comment PHYSICAL SETTING Nigeria

Geology: The FCT is almost predominantly underlain by high grade metamorphic and igneous rocks of precambrian age.

National Assembly Complex
National Assembly Complex

Generally trending NNESSW, these rocks consist of gneiss, migmatites and granites. A schist belt outcrops along the eastern margin of the area. The belt broadens southwards and attains a maximum development to the southeastern sector of the area where the topography is rugged and the relief is high. In general, the rocks are highly sheared (Kogbe, 1978). The rocks of the area can be divided into five major groups, as follows:

Metamorphosed Supracrustal (Exogenetic) Rocks: Mica Schist (sh), Marble (m), Amphibolite and Amphibole Schist (a), FineMedium Grained Gnesis.

Migmatitic Complex: Migmatite (mi), Migmatitic Gneiss (mg), Granite Gneiss (gg), Porphyroblastic GraniteGneiss (pg), Leucocratic GraniteGneiss (lg) . Intrusive GraniteCoarse Grained Granite (eg) .

Minor Intrusions: Rhyolites (ry), QuartzFeldspar Porphyry (py), Daca titea and Anddesites (an), Dolerites and Basalts (b) .

Other Formations: Quartzite (qz), Pegmatite (p), Quartz vein (q)

Relief: The lowest elevation in the Federal Capital territory is found in the extreme southwest where the flood plain of the river

Abuja City Gate
Abuja City Gate

Guraja is at an ele vation of about 70m above sea level. From there, the land rises irregularly eastwards, northwards and northwestwards. The highest part of the territory is in the northeast where there are many peaks over 760m above sea level. Hills occur either as clusters or form long ranges.

The most prominent of these include the Gawa range in the northeast, the Gurfata range southwest of Suleja, the BwariAso range in the northeast, the Idon Kasa range north west of Kuje and the Wuna range north of Gwagwalada. Elsewhere in the territory, there are many rather roundish isolated hills usually called inselbergs. Inbetween the major hills are exten sive plains, the most important of which are the Gwagwa plains, the lkuGurara plains, the Robo plains and the Rubochi plains. Indeed, about fifty two per cent of the Federal Capital Territory con sists of plains. Out of these plains, the Gwagwa plain was selected for the building of the Federal Capital city (FCC).

Climate: The FCT has two main seasons, rainy (April to October) and dry (November to March). The high altitude and undulating terrain of the territory act to provide a regulating influence on its weather. During the dry season, the typical month being March, the temperature varies between 30C in the northeast to about 37C in the southwest.

NNPC Headquarters Building
NNPC Headquarters Building

This period is characterised by high diurnal ranges when drops of as high as 17C may be recorded between the highest and lowest temperatures in a day. During the rainy season, temperatures drop considerably due to dense cloud cover. The annual range also drop to around 7C, especially between July and August. The Federal Capital Territory records relative humidity, in the dry season, of some 20 per cent in the afternoon at higher elevations and at more northern locations but about 30 percent in the extreme south.

This rather low relative humidity, coupled with the high afternoon temperatures, account for the desiccating effect of the dry season which is also marked by the presence of the har mattan haze. During the rainy season, the after noon relative humidity rises everywhere to above fifty percent. In terms of physiological comfort, the high relative humidity in the extreme south of the Territory gives the area a heat trap effect which makes it uncomfortably hot.

For maximum human comfort, northern locations are better, especially locations to the northeast where the FCC is being built. Rainfall in the FCT starts from about March in the southernmost part of the territory, to about April at the northern limits. The rainfall of the territory depicts very high seasonal fluctuation (sometimes as high as seventynine percent). The annual range is in the order of 1,100mm to 1,600mm.

Abuja International Conference Center
Abuja International Conference Center

The end of the rains is around October in the northern parts of the territory and about November in the extreme south. The FCT is located on the wind ward side of the Jos Plateau and this creates conditions favourable for the higher rainfall total as one moves from the south to the north, and this is rather strange in a country where the rainfall decreases from the south to north. This gives the FCT more rain than areas on the same or even more southerly latitudes.

This can be deduced from the fact that Lokoja and Makurdi, just south of the FCT have 1,146mm and 1132mm total annual rain fall respectively, compared with Suleja and Jos, just north of the FCT, which have the higher annual rain fall of 1,632mm and 1,403mm, respectively (Abumere, 1993). One noteworthy phenomenon of weather in the Territory is the frequent occurrence of disturbance or line squalls.

This is a weather condition heralded by the occurrence of dense, dark, cumulonimbus clouds with thunder and light ning, followed by strong winds and rainfall of very high intensity. Such rainfall may last for up to half an hour and is then followed by drizzle of several hours duration. This weather condition is then replaced by a few days of bright, clear skies. The phenomenon is associated with high connective activity aided by relief effects. It is thought to originate from the Jos Plateau region and to travel from East to West across the territory.

It is most common in the late afternoons at the beginning and end of his to buildings, ripping of their roofs, where these are ien indifferently tacked down. Another weather phenomenon noticeable within the FCT is associated lay. with the presence of isolated hills (inselbergs). These exert an influence on local weather out of Age proportion of their size. These inselbergs trigger off onvectional activity and give rise to intense relief rain in their immediate surroundings.

Soils and Vegetation: The soils of the territory the are generally shallow and sandy in nature, especially on the major plains such as lkuGurara, Roboes, and Rubochi. The high sand content particularly son makes the soils to be highly erodible. The shallow depths is a reflection of the presence of stony lower horizons. Those on the famous Gwagwa plains are however deep and clayey, perhaps reflecting the the influence of parent materials like gabbro and fine the tomedium textured biotite granite.

Thus, the soils rich of the Gwagwa plains are the most fertile and pro ian ductive. In addition, their being more or less from ally exposed interfluve summits, makes them ideal for urban development. The FCT falls within the guinea savannah vegetation zone of Nigeria.

Patches of rain forest, constituting about 7.4 per cent of the total mass of vegetation, however, occur in the Gwagwa plains, esespecially in the gullied terrain to the south and rugged southeastern parts of the territory. Patches Che of the rain forest contain trees such as Antirisern africana, Anthocleista noblis, Ceiba pentandra, Cola the gigantea, Celtis spp., Chtorophora excels, Khaya grand'ifo nd lia, terminalia superb, Piptadenianum africanum, Lophira on alata, Temlinalia ivorensis, Triplochiton scleroxylon and Dracaena arborea. The dominant vegetation of the is territory is classified into three savannah types, as fall follows:

Park or Grassy Savannah: This occupies about fiftythree percent of the total the area of the FCT. It is annual in nature ain and only a few trees are found among the just grasses, namely, Albiza, Zygia, ain Butrospermum paradoxum, Daniellia olively and parkia clapperfoniana.

Savannah Woodland: This covers (her about 12.85 percent of the total area and occurs mostly in the rugged and less accessible parts of the territory, especially in the Gurara, Robo and Rubochi half plains and surrounding hills. The commonest tree species found include Afzela hen africana, Anogeissus leicarpus, The Buttyroscarpus paradoxum, Daniellia tive oliveri, Kyaya senegalensis, Prosophis rigi africana, Uapaca tonoensis, Albiza spp., rom Vitex doniania, Bombax costatum and non Pterocarpus erinaceus.

Shrub Savannah: Occurs extensively in rough terrain close to hills and ridges in all parts of the territory, and cover about 12.9 per cent of the total area. Specie composition varies extensively.

Ecological Problems: Movement of people into the territory has continuously been on the increase. A very significant aspect of this increase in the FCT population is its concentration in a few areas; i.e. the city and the satellite towns of Nyanya, Karu, ldu, Gwagwa, Gwagwalada, Kubwa, Kuje, Abaji and Kwali. Beside overstretching of social amenities, such a concentration naturally increases the intensity of several human activities, with enormous consequences on the environment. The major ecological problems that are thus inflict ed on the FCT include:

Soil Erosion and Gullying: Human activities like urban growth, vegetation clearance and cultivation have pushed land use activities towards highly fragile areas, and increased the fragility of the less fragile ones. Today, there are several areas of heavily eroded badlands' sur faces and numerous gullies of varying dimensions, some of which cover up to about 0.1 sq. km in areal extent (Table 37.2).

Soil Degradation: Another dimension to the effect of population increase on the FCT environment is the increased pressure being exerted on land for food production. Under such situation, more nutrients are being exported out of the soil than are being replaced through conven tional soil fertility maintenance practices. A major implication of such removal is occurrence of soil degradation.

Though no comprehensive studies have so far been conducted to examine the extent of this problem, it is nevertheless reason able to assume that under the present farming systems, soils of the FCT are undergoing some forms of degradation. At any rate, processes like erosion and vegetation removal are themselves important agents of soil degradation.

Devegetation: To prepare lands for both cultivation and urban development, some forms of vegetation clearance have to take place irrespective of the inherent role the vegetation is playing in sustain ing the ecosystem of the area where the clearance is being made. On the other hand, game chasers sometimes freely set vegetation on fire in order to enable them have access to wild animals.

In the FCT. the oroblem has assumed a serious dimension, because, while there are some guidelines for urban growth for instance, none exists for ensuring that the development becomes environment friendly. However, there are attempts, many of them private, being made to afforest areas around settlements to particularly provide shade and for aesthetics.

Urban Waste Management: Though regulations for urban growth do exist on the territory, their strict enforcement has become extremely difficult, especially in the satellite towns of the territory. Consequently, for instance, sites designated in the master plans as refuse disposal sites are in many cases converted into builtup areas and consequently refuse disposals are made sometimes on areas designated as green areas and parking spaces. Without effective monitoring and disposal arrangements, several parts of the FCT are now turning into eyesores. Chup (1998) has cited studies on the FCT that quantified solid wastes being generated in some parts of the city as ranging between 56mm3 to over 2,020mm3 per site (NIBC, 1998).




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UMUNNAsays...

who is the author of this work, the name will be needed for citation