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PHYSICAL SETTING


Location and Geology:


Borno, the most north-easterly state in Nigeria, with an area of 69,435 sq.
km has a physical setting which arises from an amalgam of factors relating to
location, geology, climate as well as the intensity of resources exploitation
in the area. Since the state lies between latitude 10N and 13N and longitude
12 and 15, because of the broad geographical extent, its physical setting
is bound to be varied.


 









Shehu's Palace Roundabout,Makurdi

Shehu's
Palace Roundabout,Makurdi


A greater part of the state lies on the Chad Formation. This is an area that
was subjected to prolonged continental and lake sedimentation as a result of
the downwarp of the Chad Basin in the Pleistocene Period. The Chad Formation
is separated by Cretaceous Bima and Kerri sandstones. The volcanic areas of
the Biu Plateau and the Basement Complex areas of the Mandra Mountains are found
in the south and southeast, respectively.


Relief:Physiographically, Borno State could be divided into two broad
relief regions, namely, the hilly/mountainous area of generally over 600m above
sea-level; and the plains of less than 600 metres above sea-level. The highlands
dominate the south and southeastern parts of the state, covering about one-third
of the total land area of Bomo. The remaining two-thirds of the land area is
dominated by plains of generally less than 600m above sea-level.


The Highlands:Southern and southeastern Bomo is predominantly hilly,
geologically underlain by the Basement complex. The areas classified under this
category comprise rugged features like mountains, plateaux, ranges of hills,
ridges, escarpments, volcanic cones, inselbergs and other related features.
Within this relief region are other prominent landscapes such as the Biu Plateau
which lies to the south and the Gwoza and Mandara highlands to the southeast.


The Biu Plateau is a structural and topographic divide between the Upper Benue
Basin to the south and the Chad Basin to the north. The plateau is a rugged
terrain overlain by volcanic rocks, whose extent covers over 500 sq. km. A number
of wellpreserved volcanic hills, made up of basaltic agglomerates, ash, lavas
and tuff create miniature escarpments and also form permanent relief features
in the northern parts of the plateau. A mean altitude of about 650m above sea-level
lies in the southeastern corner of this region.









Maiduguri City Gate

Maiduguri
City Gate


The altitude reaches 775m above sea-level at Wade Hill and is well over 800m
on the Wiga Hill within the plateau. The elevation of the plateau descends gradually
to I the north and to the west, where the highlands of t the plateau pass into
the plains underlain by basaltic rock north of Buratai and east of Miringa.
The Miringa volcanic zone has a number of well preserved volcanic cones, which
stand above the plateau, along a north-northwest to south-southeast axis. These
cones are characterised by well f defined craters with breached rims and steep
conical sides.


The Mandara Mountain complex is situated at the southeastern part of the region.
The rocks on the Mandara Mountain belong predominantly to the granite suite,
the most widespread of which is a coarse granite composed of quartz and feldspar
with little biotite. The area records the highest altitude in the Bomo region,
attaining heights of between 900-1200m above sea-level in the extreme south
(Udo, 1970). The Gwoza and 1 Kirawa hills are the most prominent hills that
form part of the Mandara Mountains.


The Plains: The bulk of the state, from the central to the northern
parts, lie on a vast open plain which is flat or gently undulating. The landscape
is developed on the young sedimentary rocks of the Chad Formation. This extensive
plain contains no prominent hills and attains an average elevation of 300m above
sea-level, sloping towards the Lake Chad level. The open nature of this landscape,
especially its uniformity, is striking during the rainy season when vast areas
in the Yedzeram Valley and the immediate neighbourhood of the Lake Chad are
flooded.


The area features a variety of fluvial and aeolian landforms like fossil sand
dunes, beach ridges and interdunes and ridge depressions. These features are
said to be a combined effect of endogenic and exogenic processes, traceable
to the Pleistocene and the Holocene climatic periods respectively. The area
is made up of mainly clays, with some sand horizons and gravels. The Chad Formation
is overlain by sandy drifts which may be up to 90m thick in central Bomo and
under which ironstones were formed around Kukawa.


The Bama Beach Ridge, made up of layered lacustrine sands and gravels, marked
the limit of an expanded Lake Chad which existed during the wet climatic phase
in the Sahara about 6,350 years ago (Thiemeyer, 1992). This wide and somehow
featureless plain is interrupted in the extreme north by sand dunes, such as
the Gudumbali dune field, whose origin date back to a drier era, perhaps preceding
the formation of the Lake Chad itself. Some of these dunes are dead and inactive
and have since been colonised by vegetation.


Drainage:The Bomo region is drained by two groups of rivers, one is
bound towards the south draining to the Benue system, while the other is towards
Lake Chad. The region is generally drained by seasonally flowing rivers, whose
peak flows are recorded during the rainy season in the months of July and August.
The Biu Plateau to the south is largely drained by the Hawul River, which flows
southwards and discharges its waters into the Gongola River.


 









Sahel Savannah with Irrigated Fields

Sahel
Savannah with Irrigated Fields


The River Yedzeram, which drains the southeastern and eastern parts of the
region, takes its source from the Mandara Mountain and flows northeastward through
the pediments and the relatively flat plains towards Lake Chad. However, the
volume of water reaching Lake Chad has been drastically affected in recent years
by drought and abstractions upstream.


Inter-basin water transfer in 1994 has resulted in some of the flows of theYedzeram
River being diverted to the Ngadda system to supply water to Lake Alau tor the
domestic water requirements of Maiduguri. Owing to the nature of the terrain
in central Bomo, which appears to have very low gradient down to the lake, and
the character of the heavy dark clay soils {firki) which extend many kilometres
around the southern and


southwestern margins of the lake, few of the rivers flowing towards Lake Chad
actually reach the Lake. Most of the water is lost through the combined effects
of percolation and evaporation from the firki swamps and marshes dominating
the entire basin. The Ngadda River originates from the same source with the
Yedzeram system. Rivers Ngadda and Gombole are often perceived as one by many
authors, even before the inter-basin transfer, because of the confused flow
pattern at the Gombole and Sambisa forest marshlands.


The northern part of Borno is drained by River Yobe which is highly seasonal,
recording high flows during the rainy season and reducing to virtually small
pools during the dry season. Lake Chad itself is a vast expanse of shallow water
with only a quarter of its shores lying within Nigerian territory. The huge
inland drainage basin of about 2.2 million sq. km was believed to have been
formed during the Pleistocene, with a large Pleistocene Lake about 50,000 years
ago.


The Mega-Chad (or the enlarged ancient Lake Chad) was at the centre, with the
Bama Ridge as its terminal end around 25,OOOBP. It is the largest inland drainage
basin in Africa and among the largest in the world. It is shared by four countries,
viz, Cameroun, Chad, Niger and Nigeria. The size of Lake Chad in 1962 was about
25,000 sq. km.


Its shallow depth of between one to six metres, makes it the shallowest lake
of its size in the world. The Sahelian drought of 1972-74 reduced the area of
the lake to 9,000 sq. km. Further drought reduced the lake to just around 3,000
sq. km in 1986, thereby exposing large areas as dry lands (Kolawole 1988).


Soils:


The soils of Borno State vary in colour, texture, structure, physico-chemical
and other essential characteristics from the hilly south to the northern dune
landscape.


Vertisols dominate the flat plains close to Lake Chad; and also in the depressions.
These are 'heavy dark clay soils (Firki) which develop wide cracks during the
dry season. On the dunes are regosols which are shallow with weakly developed
profiles. The volcanic and Basement Complex areas have fertile clayey loamy
soils in the valley bottoms, but skeletal soils and rock outcrops occur along
the gentle and steep slopes.


Climate and Vegetation:









Gwoza Hills,Gwoza

Gwoza
Hills,Gwoza


Three seasons have been identified: the cool dry (harmattan) season (October-March),
hot dry season (April-June) and rainy season (July-September). Temperatures
are high all the year round, with hot season temperatures ranging between 39C
and 40C under the shade. In the southern part of the state, the weather is
relatively mild.


The rainy season lasts for less than eighty days in the extreme north, but
is as high as 140days in the extreme south. The mean annual rainfall is over
800mm on the Biu Plateau but less than 500mm the extreme north around Lake Chad.
Rainfall variability is over 100 per cent.


Droughts are endemic and rainfall tends to have been in decline since the 1960s
(Department of Meteorological Services, 1992). Relative humidity is generally
low throughout the state, ranging from as low as 13 per cent in the driest months
of February and March to the highest values of seventy to eighty per cent in
the rainy season months of July and August.


Two vegetation zones are identified in the state: Sudan savannah and southern
Sahel. The semiarid nature of the Sahel and northern Sudan savannah makes the
vegetation consist mainly of open acacia tree savannah.


In the wetter south scrub vegetation is interspersed with tall trees and woodland.
Vegetation has been greatly modified in most places as a result of over-cultivation
and over-grazing. Land degradation and desertification have been on the increase,
causing the desert to advance southwards.


Ecological Problems: The major ecological problems evident in Borno
State can be broadly categorised into two: those associated with geographical
location in the Sudano-Sahelian region; and those associated with the shrinkage
or recession of Lake Chad. The major location-associated problems include drought,
desertification and wind erosion, while those associated with the recession
of Lake Chad are problems of large-scale agricultural development projects,
and the decline in fishing. specifically, the problems are as follows:


Drought: This is a recurring hazard and one of the major ecological
problems in Borno State. The intensity of the problem









Pulka Rocks,Gwoza

Pulka
Rocks,Gwoza


when it occurs, however, increases northward towards the Sahara. Drought manifests
in the wilting of crops due to insufficient precipitation resulting in wide-spread
crop failure, drying up of rivers, lakes, ponds, falling groundwater table and
the general lack of water for most activities.


Others are the loss of livestock, diseases, famine, rural-urban migration,
and other hardships. During the drought years of 1972/73 and 1983/84 some stations
in Borno, like Monguno, Kukawa, Damasak and Mallam Fatori, recorded less than
250mm of rainfall and this was a cause for concern to agriculturists, meteorologists,
hydrologists and environmental scientists.


Desertification: The level of desertification in Borno ranges from
moderate to severe as one moves northward. The symptoms of desertification can
be seen in the decline in productivity, as well as the progressive reduction
in vegetation cover such that the land becomes incapable of supporting any population.


Scarcity of fuelwood, decrease in surface and groundwater resources, excessive
evaporation, accumulation of toxic salts in the soil, malnutrition and southward
migration of man and geomorphological responses such as the shifting of sand
dunes. All the local government areas in northern Bomo State have discernible
symptoms of desertification.


Soil Erosion:Both water and wind erosion are ie evident in Bomo State.
But by far, wind erosion is most severe in Bomo by virtue of the nature of the
climate in the area. Wind erosion, as experienced in the area, is most active
during the dry season and in the early parts of the rainy season when the vegetation
cover on the surface is less and the soil n is loose. During such periods, the
entire area experiences dust storms.


Water Resource Loss: The recession of Lake Chad is associated with
the persistent drought in the entire Sudan-Sahelian region. Other than al droughts,
the abstraction of the flows of rivers Logone and Shari, Yobe and Yedzeram have,
to a great extent, affected the lake level. The loss of id water in the lake
has bearings on agriculture, fishof ing and other socio-economic activities.


Since the barea is fragile and highly susceptible to drought, other recession
of the lake therefore has seriously of affected the livestock sector. Herds
often follow the al lake water as it recedes, or emigrate from the state. g.
The net result of water loss, is the abandonment of some settlements, the loss
of time and energy in search of water for both man and livestock over of long
distances, and the loss of vegetation cover.


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