ecological problems of soil erosion

7/30/2019 Ecological Problems of Soil Erosion

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Chapter 15

THE ECOLOGICAL PROBLEMS OF SOIL EROSION INNIGERIA

Isah H. Jimoh, Department of Geography,

University of Hariri, Ilonn.

Introduction

Quite a number of geomorphic events provoke ecological problems, and such geomorphic events cover a broad spectrum including flooding, fire disasters, typhoon and hurricane winds, soil erosion, etc. Anyof these events is capable of negatively remodifying the human landscape. Essentially, the issue of interest in this chapter is that soil erosion has assumed diverse destructive dimensions and hastherefore, attracted attention from a number of scholars. Most of such scholars have argued that thisgeomorphic event operates mainly on the human landscape and has been defined as the removal of soilresource by water or wind at a rate faster than that at which new ones form (Morgan, 1980). Erosionhas equally been defined as the removal of soil resource from one location, which is depositedelsewhere (Jimoh, 1994). Implicit in the list of definitions is the fact that it connotes reduction in thenutrient status of soil in locations relative to points of deposits.

The ecological problems of soil erosion can assume a number of dimensions. For example, inthe opinion of Cooke & Doornkamp (1974), erosion may be in the form of geologic or acceleratedtype. Geologic type of erosion refers to erosion incident taking place outside the undue interferencefrom man. That is, the removal of soil materials from one place to another under natural conditions.Accelerated erosion on the other hand, occurs due to the activities of man. Alternatively, erosion canequally be viewed in terms of its nature such as rill, sheet and gully. Rill erosion is the development of series of narrow grooves of not more than tens of centimeters, which are capable of being erasedthrough ploughing. Sheet erosion refers to the uniform removal of soil resources from a given earthsurface. While gully erosion as defined by The Dictionary of Geological Terms refers any erosionalchannel so deep and wide that wheeled vehicles cannot cross it. Any of these and classifications

portrays erosion as a dangerous event whenever and wherever it occurs.. thus, to fully understand the


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mechanics of erosion requires a clear understanding of the initiating factors.

Factors of Soil Erosion

Research efforts in the tropics show that the most important factor that is of direct relevance to erosionstudies in rainfall, while other factors include topography, soil, geology and land managementtechniques (Young, 1972; Olson, 1982; FAO, 1987; Jeje & Agu, 1990).

Several attribute of rainfall bear direct relevance to the incidence of erosion in the humanlandscape. Such attributes include: rainfall intensity, drop size, duration of fall, annual total amount,frequency of fall, kinetic energy and terminal velocity, among others (Ologe, 1972; Oyegun, 1980).These rainfall characteristics have been observed by Elwell & Stocking (1974) to have the ability toloosen up soil structures and consequently remove earth materials from different surfaces. As a matter of fact, the obvious significance of rainfall attributes has been aptly pointed out by Ofomata (1965)thus:

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It is not the total but rather the nature and intensity of rainfall which are important Whilerain may fall continuously for two, three or four hours, one notices that most of it comes duringthe first 40 minutes of the period of fall. They are the type of rainfall which causes so muchdamage in a relatively short time

Giving more credence to rainfall factor is the development of surface run-off which results from poor soil infiltration capacity due to soil compaction, in most cases, is a product of human activitiesand the nature of rainfall (Morgan, 1969; Fullen, 1985; Jeje & Agu, 1990). This is because thedevelopments of surface run-off assist tremendously in the detachment of earth materials and their transportation too.

In addition, the factor to topography largely explains the rate of erosion occurrence in any givenarea. For instance, presence of scarp and vale topography encourages rapid ground lowering (Zingy,1940; Hudson, 1983; Walling, 1983). This is because steep gradients supply a force of accelerationwhich enhances the speed of surface run-off. Thus, earth materials are easily moved to new locations

by the surface run-off (Coleman, 1981; Meyer, 1986).

Further, the geological compositions in an area determine its vulnerability to the rate of erosion.For instance, in an area where the local geological composition is poorly consolidated, the activity of denudation over it is usually significant. This situation is well represented over the poorly cementedsandstones of the former South Eastern parts of Nigeria (Jeje, 1982). This scenario can further beaccentuated due to the nature, type and characteristics of soil in an area. The physical characteristics of soil comprise sand, loam, bulk density, clay, saturated hydraulic conductivity, among others, whichvary widely in disposition in soils. Thus, these parameters largely determine the degree of coherence of soil and therefore, greatly explain the rate of the vulnerable response of soil to erosion. For instance, adeep soil with uniform contents of sand and clay materials is not susceptible to much erosion becausethe aggregates may be so well packed as to be difficult to detach. Conversely, soil that is entirely clay isnot permeable and

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therefore, permits the development of surface run-off, which in turn erodes the soil (Jeje, 1982). Also,soil with high sand contents is prone to erosion because, once surface run-off is generated; the sandaggregates are easily removed. This scenario therefore, explains the preponderance of sand materials insediments (Garland, 1987). But, other attributes of soil that can explain its rate of vulnerability to soilerosion include the size and shape of soil particles, binding effects of plant roots on soils, litter on soilsurfaces and soil infiltration capacity (OKeefe, 1975; Oyegun, 1980).

Finally, the land management techniques adopted in an effort to interact with ground surface isyet another critical erosion factor. For instance, the activities of man have been regarded as theimmediate cause of soil erosion (Eckholm, 1976; Bradford, 1977; Gougie, 1981). This implies that manis a geomorphological agent (Howard & Remson, 1978; Toy, 1982). Essentially, mans activitiescomprise overgrazing, over-cultivation, monocultivation, construction and developments, settlementexpansions, increased exploitation of natural resources, building of roads, construction of dams,construction of irrigation projects, large-scale open cast mining, the burrowing and digging activitiesof both man and animals, dragging of logs of wood along ground surface, and careless engineering

work (Wolman, 1977; Hudson, 1983). As a matter of fact, man has the ability to put his environmentinto various uses (Whyte, 1961), which in turn encourage the emergence of surface run-off andconsequently the removal of earth materials (Coleman, 1981; and Lal, 1981).

Generally, the rate of erosion within the human landscape is vested in the joint operationaleffects of external input (rainfall) and the internal conditions of the system (landscape factors).However, understanding the systems components in this way will assist in explaining and predictingthe systems output (earth materials) and consequently reaching decisions that can positively amelioratethe deteriorated environmental conditions.

Ecology of Soil Erosion Problems

The problem of widespread erosion in Nigeria has been known

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since 1910 (Floyd, 1965). Essentially, soil erosion occurs in many parts of Nigeria under differentgeologic, climatic and soil conditions. But, the severity of the erosion incidence varies considerablyfrom one part of the country to another. Also, several reports on this geomorphic event from various

parts of Nigeria have been written (Stamp, 1938; Low, 1956, Chalk, 1963; Townsend, 1965). Areasmostly affected by erosion are thought to be the Agulu and Nanka districts of the eastern part of

Nigeria, and the Shendam and western Pankshin areas of Plateau State, Nigeria (Udo, 1970; Okigbo,1977). In addition, the Imo State government in Nigeria has estimated that about 120,000 km 2 of landhas been devastated by gully, 8 villages destroyed and 30,000 people have had to be resettled as a resultof gully erosion in the district. Recently, the erosion damage in the Imo and Anambra States of Nigeria,has been estimated as causing loss of over 20 tons of fertile soil per annum, which amounted to a costof over 300 million naira per annum, with gullies extending to depths of over 120m to 2km wide insome places (Adeleke & Leong, 1980). In 1994, about 5,000 people were rendered homeless due toerosion in Katsina State, Nigeria, while properties worth over 400million naira and many lives werelost. Other areas affected by erosion include Auchi in Edo State, Efon Alaye in Ondo State, Ankpa andOkene in Kogi State, Gombe in Bauchi State, among others. In addition, erosion incidence indicates


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physical loss of available land for cultivation. For example, an expanse of land of about 1,000 hectaresof cultivable land has been lost to erosion at the Agulu-Nanka area of Nigeria. Further, loss of homes,farm crops, disruption of communication routes, financial losses and attendant hydrological problemsare equally parts of erosion problems.

Generally, erosion can be gainfully said to have been taking its tolls on most parts of Nigeriaand this has left untold suffering in the various sectors of the economy (fig 1).

Studying Erosion Problems

Soil erosion is increasingly being recognized as a hazard throughout the globe. However, efforts ateffectively

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1lulum

S(3lmn1orj Rock!tPollCombrlonlPrt-Cambf Ion t^ntoui andMilomorphle Reek elth 8l*fn*At Cftmpl** LLL.


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...Zorla aria

(2)... Jei/Sltindom/Ponluhlfiorta

0 ISO 320Km.1 I II I

Figure 1: Geology of Nigeria and soil erosion disaster areas. Source: Oyegun (1986).

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controlling the incident whenever and wherever it occurs have always failed. Thus,understanding the erosion mechanics and perhaps the methods available to its study canconsiderably assist the conservation strategies with a view to achieving a high level of success inerosion control. Thus, according to Jimoh (20030, the understanding of erosion mechanics andthe conduct of researches on erosion include a number of stages as follows:

(a) Identification of the data required for the study

This requires a clear understanding of the philosophy of the research. Thus, data sets can then besourced to meet objectives of the study appropriately. However, data may be classified intoclimatic variables (rainfall features), landscape variables (soil factor, plant cover and slopedegrees) and the socio-economic factors.

(b) Available methods in erosion studies

These include the application of erosion pins, sediment traps, Morgan splash pan and

questionnaire administration (Jimoh, 2003). However, it is instructive to note that theadministration of questionnaire is employed to complement the data generated either through theapplications of erosion pins, sediment traps or the Morgan splash pan. Again, the adequacy of theerosion study method depends on the scope of the work and the philosophy, too.

(c) Application of the appropriate analytical framework

Certainly, data sets cannot speak for themselves. Analyzing them with appropriate analyticaltool(s) will largely assist in understanding the research question(s) and the ability to takemeaningful decisions, too. In essence, analytical methods such as descriptive statistics, bivariate


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and multivariate statistical methods of analyses are desirable.

Given this scenario, especially in the understanding of the mechanics of soil erosion andthe available approaches to studying the geomorphic event, it then becomes easy to handle the

problems as they arise in any part of human landscape.

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This indeed constitutes the focus of the next section of this work.

Managing Erosion Problems

Approaches to conserving erosion problems are multidimensional. For instance, on the one hand,Eze-Uzomaka (1979) groups the erosion measures into three, namely:

(a) Agricultural measures (crop rotation, mulching, cover cropping, contour farming,massive afforestation of gully heads, slopes and floors, barring farming activities, shiftingcultivation, and no tillage;

(b) Engineering measures which are designed for gullied areas and may be grouped into (i)catchment measures such as terracing and interceptor drains, (ii) slope measuresinvolving slope reduction and wicker works, and (iii) invert measures such as check dams. These measures focus on velocity of flow and hence the carrying capacity of run-off water and allow for the safe disposal of the excess water (Lal, 1980);

(c) Public enlightenment measures on the effect of bush burning, inadequate drains aroundhouses, land disputes resulting into land fragmentation for a number of erosion proneuses, religious and sociological hindrances, among others.

Recent studies have, however, unveiled that once the percentage surface cover required to protect a land use type from erosion incidence can be appropriately determined, the menace of erosion can possibly be checked or kept at minimal levels (see Oyegun, 1980; Jimoh, 1997;

2003).Importantly, management measures highlighted are site specific. That is, in some areas,

the measures often fail. Therefore, understanding the soil mechanics and ensuring appropriatelinkages in the application of the measures will largely assist in ameliorating the deterioratingenvironmental conditions.


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Conclusion

Erosion problems are basic issues at a global scale. This is possibly due to their limitlessimprints, which are frequently hazardous in their operations. Such erosional problems affect manand his environment. However, most governments have expended colossal amounts of money ina bid to check the erosional problems; yet, the problems still persist. This chapter has identified

the factors of their occurrence, methods of study with a view to understanding their mechanics of operations and the management techniques.

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References

Adeleke, B.O. & Leong, G.L. (1980), Certificate Physical and Human Geography, Oxford:Oxford University Press Ltd, pp.42-43.

Adeleke, J.R. (1993), The study of flood hazards in Nigeria. An unpublished seminar paper,Department of Geography, University of Ilorin, pp.8-9

Bradford, G.M. & Kent, A.W. (1977), Human Geography: Theories and Their Applications,Oxford: OUP Ltd, pp.7-8.

Coleman, R. (1981), Footpath Erosion in the English Lake District, Applied Geography 1 (2):121-125.

Cooke, R.U. and Doornkamp, J.C. (1974), Geomorphology in Environmental Management: AnIntroduction, Oxford: OUP, pp.22-44.

Chalk, A.I. (1963), Soil Conservation in Northern Nigeria and a Suggested Programme,Consultant Reports, No. 34, United State Agency for International Development.

Eckholm, E.P. (1976), Losing Ground, New York: W.W. Norton and Co., pp.233.Elwell, A.H. & Stocking, A.M.(1974), Rainfall Erosivity Over Rhodesia, Institute of British

Geographer, 1 (2): 231-232.Eze-Uzomaka, J. (1979), Soil Erosion and its Control in Eastern States of Nigeria, NISER

3:51-82.FAO (1987), Soil and Water Conservation in Semi-arid Areas, Soil Bulletin 57:21-98.Floyd, B. (1965), Soil Erosion and Deterioration in Eastern Nigeria, Nigerian Geographical

Journal, 1 (8):33-44.Fullen, M.A. (1985), Erosion of Arable Soils in Britain, Journal of Environmental Studies,

20:55-69.Garland, G.G. (1987), Rates of Soil Loss from Mountain Footpaths: An Experimental Study in

the Drakensberg Mountain, South Africa, Applied Geography , 7:41-54.

319


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Goudie, A (1981), Geomorphological Techniques , London: George Allen Urwin Ltd, pp.156-180.

Howard, A.D. & Remson, I. (1978), Geology in Environmental Planning, USA McGraw-HillInc., pp.142-143.

Hudson, N.W. (1983), The Erosion Risk of Compaction , Journal of Soil and Water , 11 (3):29.Jeje, L.K. & Agu, A.N. (1990), Run-off from Bounded Plots in Alakowe in South Western Nigeria, Applied Geography, 10:63-74.

Jeje, L.K. (1982), Soil Erosion and Changes in Some Physiochemical Properties of Soils inEjiba Area, Kwara State, Silver Jubilee Conference of Nigerian Geographical

Association, pp.7-8.Jimoh, H.I. (1994), Response of land use Surfaces to Erosion during Intense Rainfall in Okun

Drainage Basin of Ilorin City, Nigeria, Occasional Publication Series 1 of the FBSS,Unilorin, pp.79-82.

Jimoh, H.I. Individual Rainfall Events and Sediment Generation on Different Surfaces in Ilorin, Nigeria, A ph.D. Thesis submitted to the Department of Geography, University of Ilorin,

Ilorin, pp. 220.Jimoh, H.I. (2003), The Techniques in Erosion Studies, in Jimoh, H.I. (ed.), Techniques in Environmental Studies, Ilorin: Haytee Press & Publishing Co. Ltd, pp. 96-107.

Lal, R. (1980), Soil Conservation: Preventive and Control Measures, in Moss, R.P.C (ed.), Soil Conservations, Problems and Prospects. , pp. 175-181.

Lal, R. (1981), Management of the Soils for Continuous Production: Controlling Erosion andMaintaining Physical Condition, in Greenland, D.J. (ed.), Characteristics of Soils,Oxford: OUP, pp.137-189.

Low, K.A. (1956), Soil Conservation Report (Unpublished), Northern Nigeria Ministry of Agriculture, Regional Research Station, Savannah.

320


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Meyer, L.D. (1986), Erosion Processes and Sediment Properties for Agricultural Cropland, inAbraham, D. (ed.), Hillslope Processes, Winchester: Allen 8 Urwin Inc., pp. 55-76.

Morgan, M.A. (1969), Overland Flow and Man Chorley, in R.J. (ed.), Water, Earth and Man: A Synthesis of Hydrology, Geomorphology and Socio-economic Geography, Methuen &

Co. Ltd, pp.239-240.Morgan, R.P.C. (1980), Field Studies of Sediment transport by Overland Flow, Journal of Earth Surface Processes and Landforms, 5 (4): 307-316.

Ofomata, G.E.K. (1965), Factors of Soil Erosion in Enugu Area of Nigeria, NigerianGeographical Journal, 8:45-59

OKeefe, P. (1975), The Process of Soil Erosion, in Pauls (ed.), African Environment, Problems and Prospect, London: International African Institute, pp. 63-65.

Okigbo, D. (1977), Farming Systems and Soil Erosion in West Africa, in Greenland, J & Lal,R. (eds), Soil and Water Conservation and Management in the Humid Tropics, U.K: JohnWiley & Sons.

Ologe, K.O. (1972), Gullies in the Zaria Area. A Preliminary Study of Headscarp recessions,

Journal of the Environment and Social Sciences, A.B.U., Zaria, (1): 55-60.Olson, G.W. (1982), Opportunities for Improving Land Uses through Soil SurveyInterpretations Perspectives, in Prinya, N. (ed.), First International Symposium on Soils,

geology and land Forms/Impact on Land Use Planning in Developing Countries,Bangkok, Thailand.

Oyegun, R.O. (1980), The Effects of Tropical rainfall on Sediment Yield from different land usesurfaces in Sub-urban Ibdan. A Ph.D. Thesis submitted to the Department of Geography,University of Ibadan, pp. 21-151.

Stamp, L.D. (1938), land Utilisation and Soil Erosion in Nigeria, Geographical Review, 28:32-45.

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Townsend, S. (1965), Report on Short-time Assessment of Sardauna Province as SoilConservation Specialist, Consultants Report, pp. 6-57, United States Agency for International Development.

Toy, T.J. (1982), Accelerated Erosion: Process, Problems and Prognosis, Journal of Geology,

10:524-529.Udo, R.K.(1970), Geographical regions of Nigeria, London: Heinemann.Walling, D.E. (1983), The Sediment Delivery problems, Journal of Hydrology, 65: 209-237.Whyte, R. (1961), Evolution of Land use in South-Western Asia, in Stamp, D.L. (ed.), A

History of Land Use and Regions, Paris: UNESCO.Wolman, M.G. (1977), Changing Needs and Opportunities in the Sediment Field, Journal of

Water Resources Research, 13 (1): 50-54.Young, A. (1972), Slopes, Geomorphology Text 3, Edinburgh: Oliver & Boyd, pp. 25-72.Zingy, A.W. (1940), Degree and Length of Scope as it affects Soil Loss in Run-Off, Journal of

Agricultural Engineering, 21 (2): 59-64.

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