Management of Environmental Problems and Hazards in Nigeria

Smart N. Uchegbu, Harold Chike, C.A. Udeh

• Publisher: Routledge
• Year: 2017
• Print ISBN:
  9780815390381
• eBook ISBN:
  9781351153386
• Topic: Business
• Subtopic: Business General
• Index: Business

This unique collection of essays examines the environmental problems facing contemporary Nigeria. The relationship between environmental degradation and such social issues as poverty and pollution growth has been impressively analyzed. There is also a well-researched discussion on how government and citizens can work towards achieving sustainable development with long-term solutions to ecological disorders. This book provides a valuable resource for academics and professionals in the general area of environmental management as well as those searching for long-term solutions to Nigeria's particular ecological disorders.

Part I
Effective Survival Measures for Environmental and Ecological Hazards in Nigeria

1 Erosion Phenomenon and Development Dynamics in South-Eastern Nigeria

M.A. IJIOMA AND U.O. AGBAEZE

Introduction

South-eastern Nigeria is characterized by high rainfall, highly erodile soils, high population density and great pressure on land resource. Under these environmental conditions, the amount of rainfall, its intensity and frequency of occurrence, particularly during the long wet season (March-November), result in raindrop impact, runoff, floods and erosion. These have serious consequences on the environment, thus demonstrating the sensitivity of the region as well as its social and economic development to climatic events. This is particularly true of the Awka-Orlu uplands and the Enugu-Awgu-Okigwe escarpment where gully erosion episodes considerably reduce the limited land resources. These lead to series of development and population problems not only in the affected areas, but also in other parts of South-eastern Nigeria.

The erosion phenomena, the studies of which involve the studies of the hydrological parameters such as rainfall intensity, infiltration rate, runoff and sediment yield, have indicated the vulnerability of South-eastern Nigeria to climatic events. The climatic events in turn affect the removal of nutrients from the soils and, hence, the growth and climatic adaptability of plants, as well as the reduction of soil depth which deprives plants of stability and anchorage in the soil, and the ultimate soil erosion which could manifest in form of landslide, sheet, rill, gully, stream bank or coastal erosion.

In the south-east as in many other parts of Nigeria, for instance, rainfall intensity, raindrop impact, and infiltration rate act in different proportions as either assets or constraints to influence the quality of land resources. During certain periods, rainfall of low intensity encourages soil moisture infiltration which determines the effectiveness of moisture for plant growth and production, while during some other periods when rainfall intensity is high, raindrops compact the soil and discourage infiltration. This condition leads to high runoff which removes nutrients in sheet wash erosion or, in more concentrated form, leads to gully development.

It is therefore not surprising that rainfall characteristics are generally regarded as the most important as far as the impact of climate on landuse and gully development are concerned. As noted in (Krynen, 1988), for instance, "Erosion by water is the result of energy developed by the water as it flows over the surface of the land". In the erosion process, therefore, soil particles are detached from the soil mass and transported to another location. Since the whole of South-eastern Nigeria is characterized by highly erodible soils and high rainfall, as already noted, there are large areas where life is greatly imperilled or can only barely be sustained on a very modest scale due to soil erosion.

In this chapter, rainfall characteristics and other hydrological parameters are discussed in relation to the concepts of erosion in Southeastern Nigeria. Also, the extent to which these parameters can be used to predict erosion in the region is indicated. In particular, the effects of erosion hazards on development and their economic and social consequences are examined.

Rainfall in South-eastern Nigeria

The South-eastern region of Nigeria lies between latitudes 50N and 70N approximately. Basically, the distribution of rainfall in the region and indeed in Nigeria is controlled by the seasonal migration and pulsation of the Inter-tropical Discontinuity (ITD) accompanied by two air masses. These air masses include: firstly or the tropical continental air (cT) originating from the Sahara desert and which is both characteristically dry and dusty, and secondly, the tropical maritime (mT) air originating from the Atlantic Ocean and which is warm and humid. The mT air mass influences the south-eastern region and the other areas in Nigeria within the same latitude throughout the year resulting in rainfall for about 8-12 months of the year.

In contrast to the mT air mass, the cT air mass influences the region for a shorter part of the year, and lasts for approximately 4 months or less. Because of the influence of latitude, more rainfall is experienced in stations located on relatively higher latitudes than the surrounding areas. In areas such as the eastern uplands, relatively higher rainfall occurs, thus illustrating the significance of relief in the pattern of rainfall distribution. Other important factors of rainfall in the south-east are the various synoptic disturbance lines. When these occur, their effects are such that some areas experience showery weather while some other areas experience heavy rainfall. For example, the occurrence of line squalls is associated with intense instability accompanied by torrential rains characterized by thunderstorm and lightning often with strong winds.

The combined effects of these various factors result in a pattern of distribution of rainfall which generally decreases from the coast to the inland, in Nigeria. The coastal areas of the south-east have the highest annual amounts of rainfall which are generally more than 2000mm. For example, the Forcados-Brass axis and the Eastern uplands receive more than 4000mm of rainfall per year. In general, the greater part of the southeast has annual rainfall between 2000mm and 3000mm. For instance, the mean annual rainfall levels for Calabar, Port Harcourt, and Umudike, during the 1941-85 period, were 2900mm, 2400mm and 2100mm respectively.

The general pattern of rainfall distribution, the examples of which are described above, shows mean conditions which can be changed by synoptic disturbances and produce variations in relatively small areas. Rainfall variations often occur in intensities and amounts, particularly at the beginning and ending of the rainy season, and these can result in floods and erosion. In recent years, for instance, many flood disasters which caused considerable damage to lives and property have been reported in the Southeastern States. In November 1979, for instance, flood rendered 100 families homeless at Ughele and Umuma-Ishiaku. The flood disasters which occur with every rainy season at Ndieogoro in Aba have affected over nine hundred and forty residential houses. In addition, floods have given the area a slum appearance characterized by the existence of human wastes, and other types of soil wastes. In fact, the area has become a haven for scavenging animals and disease-borne insects. Also, the coastal areas of the south-east experience flood disasters occasionally.

Erosion

Erosion is the major environmental hazard in the South-east, of which Greenland (1975) identified rainfall characteristics as the major environmental cause. According to many writers (see for example, Aneke, 1988; Ofomata, 1981, 1988; Igbozurike, 1977), erosion definitions can be objectively divided into two groups, namely, the geologic erosion and the accelerated erosion. Geologic erosion can be defined as a natural soil-forming process which goes on continuously and cannot be controlled. Accelerated erosion, on the other hand, is related to man's activities which degrade the protective vegetal cover of the earth's surface. In this case, the massive destruction of the thick tropical rain forest of the south-eastern Nigeria, due to the increasing pressure of the population on the land initiates and accelerates erosion. As described by Grove (1951), accelerated erosion occurs in definite stages. First, the beginning of shifting cultivation in the primary forest; secondly, the incision of part of the surface 'red earth' by gullies following the establishment of villages in the forest; thirdly, further increase in the number of gullies as a result of the concentration of water flow along the numerous footpaths leading especially to streams on which the villages depend for domestic water consumption; and finally the development of a whole complex of gullies following a rapid increase in population, as well as greater intensity of cultivation and a shortening of the period of fallow (Grove, 1951; Ofomata, 1988).

Within the last two decades, south-eastern states have experienced serious erosion problems (geologic and accelerated) at various places. These erosion problems, particularly the accelerated type giving rise to gullies in many parts of the region, have become an annual phenomenon, broadening in proportion with every passing year. The erosion episode is usually related to rainfall erosivity, and therefore has given rise to a growing appreciation of the vulnerability of the environment to rainfall intensity. This has also led to strong reactions to erosion problems by the governments and people of the states within the region as well as the Federal Government and some international organizations. Moreso, it has led to several symposia and conferences, an example of which was the International Symposium on Erosion in South-eastern Nigeria, held at the Federal University of Technology, Owerri in April, 1988. In this symposium, attempts were made to answer some questions on erosion problems in south-eastern Nigeria. The questions usually raised in such symposia and conferences include:

• a) What factors are responsible for high rate of erosion in the region?
• b) Why is it that erosion problems are very acute in the South-eastern areas when compared to other areas with similar physical conditions in the south of Nigeria?
• c) How can the problems resulting from high rainfall amount and intensities be solved and the disastrous consequences of erosion events minimized?

Despite the fact that the understanding of erosion processes and the underlying sciences are important in answering the above questions, not much scientific study has been done in these directions in the South-eastern States.

Relationship Between Hydrological Parameters and Erosion in South-eastern Nigeria

Few attempts have been made to analyze and determine the hydrological processes of erosion in South-eastern Nigeria (see for example; Niger-Techno., 1979; Aneke, 1988; Krynen, 1988). Krynen (1988) studied rainfall amounts and rainfall intensities (quantity of rainfall in a given time) in Imo State using an automatic rain recorder. He further compared estimates of rainfall intensities based on measurements of runoff from test plots using the threshold rainfall intensities of 25mm/hr estimated to cause erosion in Africa.

From this and other related studies mentioned above, the following conclusions were drawn:

• a) that tropical rainfall is of high intensity during short periods resulting in infiltration rate of 50mm/hr;
• b) that in the study area, the main activity of erosion can be expected in July, August and September because the convective rainfall during this period is usually of high intensity and limited to small areas;
• c) that the infiltration rate for farmland on slope of 10% equals approximately 80mm/hr while that for farmland in flat area equals approximately 400mm/hr.

In addition to the above findings, the examination of the relationships between rainfall/infiltration and runoff/sediment yield concluded as follows:

• a) that there is hardly any contribution to runoff/sediment yield from rainfall in flat farmland area;
• b) that on farmland on slopes of 9% the runoff to be expected from rainfall has a mean intensity of approximately 200mm/hour during a period of lOmins resulting in 36mm of water that has to be stored temporarily;
• c) for constructed areas, the maximum contribution of rainfall to runoff will be with an intensity of 294mm/hour during lOmins. period, resulting in an 49mm of water that eventually has to be stored.

Based on the relationships discussed above, it becomes clear that;

• a) the problem of erosion occurs a couple of times per year during short periods;
• b) that runoff on farmland will concentrate according to the topography of the area;
• c) that runoff on constructed areas is bound to those areas, and has no relation to the topography; and
• d) that runoff will flow into a natural course and carry sediments as well, partly, as transport agent from detached soil particles of sheet erosion and partly, because of its own capacity to carry a sediment load eroded by the tracing force along the bottom.

Also, studies have been carried out on the runoff and sediment yield as well as soil loss in some parts of South-eastern Nigeria. For instance, Krynen (1988) studied the Imo River basin with a size of approximately 460km2 and a sub-basin of 30km2. Although the result is still preliminary, he found a soil loss of 1.2 t/ha/year for the sub basin and a soil lo...

Table of contents

• Cover
• Half Title
• Title
• Copyright
• Contents
• List of Figures
• List of Tables
• List of Contributors
• Foreword
• Preface
• PART I: EFFECTIVE SURVIVAL MEASURES FOR ENVIRONMENTAL AND ECOLOGICAL HAZARDS IN NIGERIA
• PART II: POVERTY AND ENVIRONMENTAL DEGRADATION
• PART III: THE ROLE OF GOVERNMENT AND CITIZENS IN ENVIRONMENTAL MANAGEMENT
• PART IV: PROBLEMS AND PROSPECTS OF SUSTAINABLE DEVELOPMENT OF THE NIGERIAN ENVIRONMENT