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Application Of Geoinformatics Techniques In Controlling Flooding In Vulnerable Roads And Buildings In Nigeria
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1.6.3 Geology/ Soil
Port
Harcourt lies on the recent coastal plain of the eastern Niger Delta.
Its surface geology consists of fluvial sediments. This includes the
recent sediments transported by Niger River distributaries and other
rivers, such as Andoni, Bonny and New Calabar. These materials deposited
as regolith overburden of 30m thickness are clays, peat, silts, sands
and gravels. The depositional sequence exhibits massive continental sand
stones overlying an alternation of sandstones and clays of marginally
marine origin, but eventually grading downwards into marine clays.
Sands, by far, form the largest group of rock types in Rivers State,
while mud constitutes all the polluted brackish waters of the riverine
areas. However, peat constitutes the various vegetal and animal remains
that lie in bogs and shallow pits. The gravel and pebbles form the last
unit of the subsurface rock type, and are usually found at the base of
the river channels. There are three major soil groups in Rivers State,
namely: the marine and fluvial marine sediments; the mangrove swamp
alluvial soils; and freshwater brown loams and sandy loams. The marine
and fluvial marine sediments are found in the wet coastal region. The
soils are organic in nature and essentially sandy in texture. Some
consist of mud mixed with decayed organic matter. The mangrove swamp
alluvial soils are found in the northern part of the coastal sediments
zone. They are brownish on the surface, sometimes with an unpleasant and
offensive odour. The soils of the swamps are rich in organic matter in
the top layer, but contain too much salt especially in the dry season.
The third soil group, the brown loams and sandy loams are found in the
fresh water zone of the delta. The levees which form the common land
forms of this zone are made up of rich loams at their crests, changing
to more acidic and more clayed soils along their slopes.
1.6.4 Vegetation
The
"upland" area was originally occupied by rainforest which has been
drastically modified by human activities. In most places, economic
trees, particularly oil palm, have been preserved and thus the sobriquet
for this vegetation as "oil palm bush." The riverine area is divisible
into three main hydro-vegetation zones namely, the beach ridge zone, the
saltwater zone and the freshwater zone. The beach ridge zone is
vegetated mainly by fresh water swamp trees, palms and shrubs on the
sandy ridges and mangroves in the intervening valleys or tidal flats.
The saltwater zone is the tidal flat or swamps vegetated by the red
stilts rooted mangrove (Flhizophora racemosa) and two other species of
mangrove. The outliers of raised alluvial ground or coastal plain
terrace within the swamps are vegetated by tall forest tree species and
oil palm. The freshwater zone is mainly the Upper and Lower Delta
floodplains of the Niger, having fresh water forest trees which are the
edaphic variants of the rainforest. The Abura tree, oil palm, raffia
palm, shrubs, lianas, ferns and floating grasses and reeds are the
typical vegetation.
1.6.5 Hydrology
Rainfall in Port Harcourt
is seasonal, variable, and heavy. Port Harcourt is a city of physical
difficulties, such as low lying terrain riddled with an intricate system
of natural water channels; too much surface water and a high rainfall;
uninhabitable mangrove swamps and some parts of the state suffer from
inaccessibility due to seasonal flooding.
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