Abstract

The sedimentological analysis of the bedload sediment in River Nun (Amassoma, Ebeni and Ogobiri) was carried out to determine the variation in the size distribution pattern, sediment maturity and mode of transportation. In an attempt to achieve the above result, some analysis was carried out on sample collection at 7 locations in Amassoma, 8 each from Ebeni and Ogobiri along River Nun where histograms and cumulative curves were plotted.The average mean size of 1.52Φ, 1.31Φ and 1.23Φ in River Nun (Amassoma, Ebeni and Ogobiri) indicates that sediments are medium sand. This implies that sediment is deposited in low energy environment. The average sorting value of 1.18Φ, 1.05Φ and 1.07Φ in River Nun (Amassoma, Ebeni and Ogobiri) indicates poorly sorted means they are not effectively deposited. The average Skewness value of -0.56Φ, -0.38Φ and -0.24Φ in River Nun (Amassoma, Ebeni and Ogobiri) indicates very negatively skewed means not smoothed. The average kurtosis value of 1.28Φ, 1.32Φ and 1.37Φ in River Nun (Amassoma, Ebeni and Ogobiri) implies Leptokurtic means predominantly consist of finer fraction. The mode of transportation of the Bulk sample analyzed in River Nun around Amassoma, Ebeni and Ogobiri indicates suspension saltation.

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CHAPTER ONE

INTRODUCTION

1.1   Background to the Study

The River Nun (Amassoma, Ebeni and Ogobiri) are distributary of the River Niger which is 4,100km, long arises from the Guinea Highland (Allen 1970). These river mentions above are the case study points and are used for the sedimentological characteristics analysis of bedload sentiments in the Niger Delta.

Geographically the study points River Nun (Amassoma) is located in Southern Ijaw Local Government Area Bayelsa State Ebeni, Ogobiri is located in Sagbama Local Government Area Bayelsa State. These rivers arise from the central Niger Delta down the coasts of the Niger Delta and lies between the lat 4O to 5ON and longitude 6O5” to 7OE. The Amassoma, Ebeni and Ogobiri rivers are among the major rivers that supply sediments to Bayelsa State. The River Nun empties into the Atlantic Ocean. During high tide, the ocean in return sends sand driven waves and others within decreases with increase in distance from the mouth of the river to its source.

This means that River Niger, the environment of deposition in these three rivers is continental to marine environment.
The three rivers are seriously tidally affected but increase in volume during the flood season and decreases in volume and current during dry season. The sediments characteristics in these rivers also gives a clue about the principles of uniformitarianism which states that the present is the key to the past (James Hutton, 1975) and (Charles Lyell, 1830). Many geologists prefer actualism in place of uniformitarianism.

The term actualism comes closer to conveying Hutton’s principle that the same processes and natural laws that operated in the past are those we can actually observed or infer from observation as operating at present.

Characteristically, the Amassoma, Ebeni and Ogobiri rivers consist primarily of coarse, sand and fragments of silt which grade from fine-medium, grain as you progress downstream. The River Niger flows across a lot of formations and at its Southern part gives rise to the River Nun, forcados. Accord1ing to Potter (1978), the most suitable locations to collect samples from big rivers are near the mouths, at the end of the Delta because sampling here minimizes petrographicvariations between and among the different stream sediment within a river system.

Following the above illustrations, samples were collected from the bottom of the rivers in different locations. A total of 23 samples were collected from the rivers, 7 from Amassoma, 8 each from Ebeni and OgobiriRiver. According to Petti John (1975), there should be a sufficient information and analysis on the size, shape and arrangement of sediment for competence and efficiency of the transporting processes. For the above mention, good studies of sedimentologically characteristics analysis of the rivers were carried out to know the grain sizes distribution and sediments characteristics as well. The study carried out in the Amassoma, Ebeni and Ogobiri rivers shows that they are among the major rivers that supplies large quantity of sand to the Niger Delta and Nigeria as a whole for construction processes and also form source rock of the Niger Delta.

1.2   Aims and Objectives

The main aims and objectives of the study area are:

  1. The mode of transportation of the sediment and their environment of deposition.
  2. The downstream variation of the bed load sediments of the river.
  3. The occurrence of major and minor source areas for sediments.
  4. The sedimentologically characteristics of various locations.
  5. To make further recommendations.

1.3   Literature review

The study of the texture and composition of sediments in is for the purpose of providing models for interpreting several aspect of ancient fluvial sand, grain size distribution, mineralogy and paleogeographic setting of ancient rivers as studied by Friedman 1967, 1969, (Mark 1981), Suttner etal 1981, Dickinson and Suczek, 1979 etc. In Nigeria, much work has not been carried out on the coastal Niger Delta in particular, the River Nun. The only published work available of the Niger Delta is that of the Allen (1964, 1965) and other unpublished report of Nedeco (1959). Also sediments have been studied for the Imo and western Andoni Rivers (A major 1989, Amajor and Ngerebara 1990) that are part of the eastern Niger Delta. All these studies were bases on sedimentological characteristics to characterized fluvial sediments in and around some major rivers in the Niger Delta.

The River Nun shows that sediments are ranging from coarse to medium grains and average composition in terms of textural maturity is due to the distance of transportation undergone by the sediments. As analyzed by Reineck and Singh (1973). The coarser sediments are deposited by high velocity or energy environment and medium or fine grain sediments are deposited by low energy environment, all within a fluvial environment. The fluvial environments consist mainly of saltation loads with some infiltrated suspensionloads, they are positivelyskewed and leptokurtic (Folk, 1973). River sediments are affected by the creeks supplying sediments to it’s as demonstrated by Waigh (1995), Inman (1979). In his study of grain size characteristics shown that the sorting coefficient is strongly dependent upon the mean grain size. the study of sediments characteristics in River Nun are very significant because it provides information on the knowledge of the Niger Delta, particularly the sediment distribution pattern and its relevance to the principles of uniformiterianism, or actualism, creating major facts in designing and maintaining any coastal engineering structures (Palmer, 1976, Inman and Bush, 1975).

1.4  Location of the Study Area

The Nun River (Amassoma, Ebeni and Ogobiri) are located at the coastal part of the Niger Delta, in other words theylayswithin the southern part of the NigerDelta and link into the Atlantic Ocean. The NunRiver is directly linked to the
River Niger through Southern Ijaw and Sagbama in Bayelsa State. 7 samples were collected at different locations in Amassoma and 8 each from Ebeni and Ogobiri River making total of 23 samples.

1.5   Climate and Vegetation

The study area lies under the tropical savannah where the whole area is covered with thick giant grasses and trees. In general, Amassoma, Ebeni and Ogobiri are composed of dense and very tall trees, Raffia palm, Bamboos and with grasses. There are also ferns found in the study area specifically on the flood plains.

The vegetation of these different areas is characterized by two distinct seasons (rainy and dry). During rainy season there is an increase in growth of vegetation as during dry season there is a decrease in vegetation. There are certain condition that effect thick vegetation area particularly the river channels fallen raffia palm, palm trees and grasses result to inadequate directional flow of water, thereby causing suspension, saltation and traction sediment load to deposit by the rivers forming sandbars and various shapes.

1.6    Climate Condition

The climate condition also falls within the tropical climate zone of the Niger Delta. That is the Southern Nigeria where there is a constant change in rainy and dry seasons respectively. The two distinct seasons valid are:

The rainy (Wet season) commences only April and last October with maximum rainfall in July and September. A break of about two weeks occurs in August.

The dry season (Harmattan period). This started from November to late March and experience harmattan winds. I.e. the North east trade wind which decrease the temperature of the area causing the environment to be chilly between December and January.
The rainy season is caused by the south west trade wind from the Atlantic Ocean while the dry season (harmattan) is caused by the North east trade winds from the Sahara desert. There is a continuous increase in the rivers volume and it over-flows its bank during rainy season. While during the dry season the volume of water in the rivers decreases back to its original level. The hottest periods are February and March when the mean annual temperature is about 32Oc.

1.7   Relief and Drainage

In terms of relief the study area is characterized by coastal flats plains with a gentle slope. The Nun (Amassoma, Ebeni and Ogobiri) rivers consist of its main channel and few distributaries. These rivers respectively and all drains into the Atlantic Ocean.
The intake and discharge are the basic characteristicsof these rivers. These rivers are intake by infiltration, direct precipitation and surface turn off water. While discharge of the rivers by human consumption, agricultural activities such as irrigation, building and road construction. The intake process is the source of sediment supply to the rivers bringing different types of sediment eroded. The intake processes increases during the rainy season and decreases during the dry season along the course. Example the recent flood occur in October 2012 in some part of Nigeria is an intake system.

1.8   The Stratigraphy of the Study Area

The stratigraphy of the quarnternary and tertiary Niger Delta has been study and recognized by short and Stauble (1967) from boreholes and oil wells. During their study, sediments shows Holocenegeomorphologic stratum which underlain by the Benin, Agbada and Akata formations.

Benin formation: The Benin formation extends from the west across the whole Niger Delta area and southward beyond the present coastline. It consist about 90% sandstone with shale intercalations. It is of Oligocene to recent having a thickness of 6000ft. Very little hydrocarbon accumulation has been associated with the formation.

Agbada formation: Agbada formation is a sequence of sandstones and shale. It consists of an upper predominantly sandy unit with minor shale intercalations and a lower shale unit which is thicker than the upper sandy unit. It is over 10,000ft thick, ranges from Eocene to recent in the Delta surface. It is the major area hydrocarbon reserves of the Niger Delta.

Akata formation: This formation is uniformshale consisting of dark grey sandy, silty shale with plant remains such as forams (Asseez in Kogbe 1976) with the overlying Agbada formation. Planktonic foraminifera may account for over 50% of rich microfauna and the benthonic assemblage indicating the shallow marine shelf depositional environment. It is over 4000ft thick from Eocene to recent.

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1.9   Geologic Setting

The tertiary Cenozoic or the modernNiger Delta occupies the southernmost part of Nigeria. The eastern boundary corresponds to the Calabar flank and cut across Onitsha through Ituk High. The Western boundary also corresponds to the chain oceanic transform fault also known as the Benin hinge line. The Niger Delta advances from the Benue Trough down to the end of the Trough which is the Atlantic Ocean. The recent Niger Delta was formed during the third and final phase of deposition cycle of the southern Nigerian basin which started in the Paleocene. The water found in the Amassoma, Ebeni and Ogobiri Rivers drain the quaternary deposit is of the Niger Delta, and at the middle and the lower course of the rivers flows the Oligocene to recent Benin formation. The sediments in the Niger Delta arebrought in by two drainage processes. The Niger Benin River system and the less important or subordinate cross-River-Imo River system.

The Recent Niger Delta can be subdivided into four major intergradational geomorphologic units as explained by Wigwe (1975), from the land to the sea (North to the South). These are;

  1. Dry deltaic plain with rare fresh water swamps.
  2. Extension fresh water swamps and meander belts.
  3. Saltwater mangrove swamps, estuaries, creek and lagoon.
  4. Abandoned and active coastal Island and beaches the Bight of Biafra.

The Amassoma, Ebeni and Ogobiri Rivers fall into the second subdivision where freshwater and meander belts dominate the area.

 

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