gully erosion menace in uyo: causes, effects and control …
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Sapientia Foundation Journal of Education, Sciences and Gender Studies (SFJESGS), Vol.3 No.3 September, 2021; pg. 31 – 45 ISSN: 2734-2522 (Print); ISSN: 2734-2514 (Online)
GULLY EROSION MENACE IN UYO: CAUSES, EFFECTS AND CONTROL MEASURES 31
GULLY EROSION MENACE IN UYO: CAUSES, EFFECTS AND CONTROL MEASURES
UDOUMOH UNWANA I.
Department of Agricultural and Food Engineering,
University of Uyo, Uyo, Nigeria
AHUCHAOGU ISRAEL
Department of Agricultural and Food Engineering,
University of Uyo, Uyo, Nigeria
EHIOMOGUE PRECIOUS O.
Department of Agricultural and Bio-Resources Engineering,
Michael Okpara University of Agriculture, Umudike, Nigeria
SAM EDIKAN M.
Department of Agricultural and Bio-Resources Engineering,
Michael Okpara University of Agriculture, Umudike, Nigeria
&
ANANA, UNYIME ABASI E.
Department of Food Science and Technology,
Michael Okpara University of Agriculture, Umudike, Nigeria
Email: [email protected]
ABSTRACT
The formation and expansion of gullies have become one of the greatest environmental
problems facing many towns and villages in south-south and south-eastern Nigeria.
From field studies, new gully sites are formed during each rainy season due to
torrential rainfall, nature of underlying geology, high soil erodibility, and undulating
topography that characterize the region as well as removal of vegetal cover due to
urbanization and other anthropogenic factors. The massive soil loss in Uyo caused by
gully formation results in severe ecological damages, soil fertility depletion,
considerable loss of soil structure, loss of lives, reduction of soil biodiversity, reduction
in agricultural productivity, food insecurity, disruption of socio-economic activities in
the study area, leading to untold hardship, pollution/contamination of surface
water(receiving water bodies) in the catchment area. This paper reviews the causes,
consequences and possible solutions to the ravaging effects of this environmental
hazard in the study area. This work will serve as a benchmark study for other erosion-
prone regions of South-South and South-Eastern Nigeria if the scientific, engineering,
sociological approaches which are discussed herein are adopted.
Keywords: Gully erosion, Causes, Consequences, Erosion control, South-South Nigeria.
1. Introduction
Soil erosion by water is a serious problem in many parts of the world. It is categorized as the
most serious environmental problems because it threatens agriculture and the natural
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GULLY EROSION MENACE IN UYO: CAUSES, EFFECTS AND CONTROL MEASURES 32
environment (Hudson, 1981). Erosion degrades soil by removing topsoil, decreasing plant
nutrients, rooting depths and water reserve. Augmentation of population, overgrazing,
agricultural activities on steep slopes with marginal soils in combination with heavy and
sporadic rainfall, make huge areas extremely sensitive to erosion. The degradation of soil by
erosion is of particular concern because soil formation is extremely slow (Hudson, 1981).
Among the consequences of soil erosion is the reduced ability of cultivating possibilities on
eroded hill slides and sedimentation of water reservoirs, which reduces irrigation possibilities
and leads to decreased agricultural production. The potential erosion risks are higher under
intensive arable land use than under forestry or pasture land uses.Soil water erosion is very
dynamic and spatial phenomenon that depends on relief geometry and surface properties
influencing overland flow (Jaroslav et al., 1996). Soil erosion is a common disaster that can be
caused by nature because of the soil properties and also by man as a result of improper
environmental Management (Ejaz et al., 2010). Erosion is a serious threat to humans and
infrastructures because of the devastation it can cause to homes, farmland, roads, water
supply, communication, and migrations (Idah et al., 2008).
Soil erosion occurs when soil particles are carried off by water or wind from a location and
deposited in another location (Pimentel and Kounang, 1998; Toy et al., 2002). Erosion begins
when rain or irrigation water detaches soil particles and move across it to other place (Trout
and Neibling, 1993). Soil erosion is identified as one of the key challenges that impact on
diverse sectors of our human existence ranging from the depletion of top nutrient rich soils,
lowering agricultural productivity and volume storage depletion of reservoirs through
sedimentation (Gupta 2010, Coulombo, 2010; Wang et al, 2013).
Gully erosion is an advanced stage of rill erosion. Rills are localizedwashes or channels created
when water concentrates into small rivulets in the field. The little streams or rills carry more
soil as they pick up speed or grow in size. The abrasive particles they carry scour the sides
and bottoms of the channels. Rills are relatively small and can be obliterated by conventional
tillage equipment. However, total soil loss, even in a single storm can be great because rill and
sheet erosion occur simultaneously. Rills when neglected develop in size and become gullies.
Rills can be up to 0.3m deep. If they become any deeper than 0.3m they are referred to as gully
erosion. Thus, rill erosion is often described as the intermediate stage between sheet and gully
erosion. Sheet erosion is the planar removal of surface soil by the action of either raindrop
splash, shallow flows of surface of water, or even by wind. Another name for rill erosion is
inter-rill erosion (Suresh, 2006; Rahab, 2008).
Gully could also be caused by runoff concentrating at a point on agricultural lands. In this
case, water concentrates in depressions caused by localized weakening of the vegetation cover
by grazing or bush burning and enlarges until several depressions coalesce and an incipient
channel is formed. Erosion is concentrated at the heads of the depressions where near-vertical
scarps develop over which supercritical flow occurs. Some soil properties are detached from
the scarp which results in deepening of the channel and undermining of the headwall, leading
to collapse and retreat of the scarp up slope (Suresh, 2006).
According to Essien and Essien, 2012,Udosen(2018; Udoumoh (2018), soils in Uyo have
high sand and low clay content with sandy-loam mixture, thus the soil particles have less
aggregate stability. Also, due to torrential rainfall in the area, during rainy season, the area
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GULLY EROSION MENACE IN UYO: CAUSES, EFFECTS AND CONTROL MEASURES 33
experiences rise in groundwater table, leading to an increase in hydraulic head, high
subterranean flow rate, all geared towards the enhancement of gully formation and
expansion.
The rate of gully erosion depends primarily on the runoff-producing characteristics of the
watershed; the drainage area; soil characteristics; the alignment, size, and shape of the gully;
and the slope in the channel. A gully develops by processes that may take place either
simultaneously or during different periods of its growth. These processes are (1) waterfall
erosion or head-cutting at the gully head, (2) erosion caused by water flowing through the
gully or by raindrop splash on exposed gully sides, (3) alternate freezing and thawing of the
exposed soil banks, and (4) slides or mass movement of soil into the gully (Schwab et al., 1983).
This paper gives a comprehensive review of the causes, devastating effects, and control
measures of gully erosion in Uyo.
2. Causes of Soil Erosion
Soil erosion generally is caused by several factors working simultaneously or individually to
detach, transport and deposit soil particles in a different place other than where they were
formed. The resultant effects of this phenomenon are deep cuttings and ravine which dissects
the entire land surface. Some of the identified natural causes of soil erosion include tectonism
and uplift, climatic factors, geotechnical properties of soil, among others. Anthropogenic
causes include farming and uncontrolled grazing practices, deforestation, and mining
activities (Abdulfatai et al., 2014; Nuga et al., 2006; Uwanuruochi and Nwachukwu, 2012).
2.1 The Role of Topography
Hudson (1981) observed that in simplest terms, steep land is more vulnerable to water erosion
than flat land for reasons that erosive forces, splash, scour and transport, all have greater effect
on steep slopes. Soil erosion generally is a function of slope attributes. The slope length and
the amount of soil erosion have always been proportional to the steepness of the slope. Also
the slope geometry of hill sides (i.e. whether convex or concave) often contribute significantly
to soil loss and gully development. When anyerosion site is directly on top of a hill, itsintensity
will differ from relatively plainsurface. Similarly, a site initiated by roadconstruction will also
have a differentintensity from that located in a farm. In all,location determines how the
denudingagent(s) will loosen and carry away theweathered materials (Nnodu et al., 2008).
In southern Nigeria, Ofomata (1985), found that there is a positive relationship between relief
and soil erosion while in south-western Nigeria, Lal (1976a) observed an increased severity of
soil erosion as the slope changed from 5 to 15%. On a 15% slope he recorded a total soil loss
of 230 t/ha/yr from bare plots as against soil loss of 11.2 t/ha/yr on 1% slope. The topography
of southern Nigeria according to Ofomata (1975) can be classified into three relief units. These
units are the plains and lowlands including all the river valleys, the landscapes and the
highlands. It is observed that the uplands which are made up of highly friable sandstones
yield easily to erosion and induce gullying even on slopes of about 5%. The highlands with
somewhat stable lithology resist gullying but provide aggressive runoff which moves down
to devastate the lowland areas especially at the toe slopes and river head-waters as shown in
Figure 2.1.
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GULLY EROSION MENACE IN UYO: CAUSES, EFFECTS AND CONTROL MEASURES 34
2.2 Influence of Climate
The rainfall of Uyo, Akwa Ibom State, generally is heavy and aggressive. The state lies North
of the equator and within the humid tropics and has a mean annual temperature between 26–
270C and two distinct seasons: the wet season (April to October) and the dry season
(November to March). In the south and central parts of the state, the rainy season lasts for
about 7 or 8 months but, towards the far north of the state, it reduces to about 6 months. The
rains are of high intensity and of bimodal pattern with two peaks in July and September, and
a period of 2-3 weeks of little or no rain (called August Break) in between (Essien and Essien,
2012).
The dry season gives rise to the post-season characteristics of a maximum rainfall regime in
which the months with the heaviest rainfall are usually June and July for the first rainfall
maximum and September for the second maximum. The annual rainfall ranges from 2,000mm
on the northern fringe to over 3,000mm along the coast (Essien and Essien, 2012).
The nature of the rainfall regime contributes significantly to the erosivity of rainfall. Rainfall
erosivity is the potential ability of rain to cause erosion. It is also a function of the physical
characteristics of rainfall (Onwualu et al., 2006). Obi and Salako (1995) reported that the
raindrop sizes obtained generally in the Guinea savannah ecological zone of West Africa
ranged from 0.6 to 3.4 mm. The mean drop sizes (D50) of 28 rainfall events ranged from 1.1 to
2.9 mm. There are experimental evidences to suggest that intensity and energy are likely to be
closely linked with erosivity.
2.3 The Influence of Vegetation
The dominant forest types in Akwa Ibom State include the saline water swamp, fresh water
swamp forest and the rainforest. The native vegetation of Uyo has been completely replaced
by secondary forest of predominantly oil palms, woody shrubs such as grasses. The forest is
noticeable around hamlets, watercourses, tree crop plantations and forest reserves (Essien and
Essien, 2012). The constant deforestation of the former rainforest due to population explosion
and increased agricultural activities in the region expose the bare soils to the vagaries of
weather thus escalating the soil erosion problems. The implication is that the soils are
frequently subject to different degrees of erosion including accelerated erosion.
Vegetation and land use are one of the most important factors in soil erosion process in south-
east and South-South Nigeria, Uyo inclusive. Suresh (2006) noted that vegetation acts in a
variety of ways by intercepting raindrops through encouraging greater infiltration of water
and through increasing surface soil organic matter and thereby reducing soil erodibility. Thus,
choosing an appropriate land use can drastically curtail soil erosion.
In southern Nigeria soil erosion especially gullies are most intensive on soil on which the
former growth has been disturbed, that is mostly on agricultural soils stripped of growth for
reasons of infrastructural developments such as road and housing construction. Ofomata
(1985) showed that in the region soil erosion is connected mainly with agricultural activities
and other related land use activities such as mining, road building, urbanization,
industrialization and general infrastructural development. These land use activities deprive
the soil surface of its vegetation and also contribute directly to sliding, slumping, interrill and
rill erosion including gullying.
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GULLY EROSION MENACE IN UYO: CAUSES, EFFECTS AND CONTROL MEASURES 35
2.4 The Influence of Geology
The geological formation in Uyo is the Coastal Plain Sands, which occupies more than
75% of Akwa Ibom State soils [(Essien and Essien, 2012). The soils are derived from the parent
materials and are highly weathered and dominated by low activity clays; the dominant soils
in Akwa Ibom State are of inter-fluvial slope with a pattern of increase in clay content down
the profile and are generally of low organic matter content (OMC), low water storage capacity,
low Cation Exchange Capacity (CEC) and highly susceptible to erosion (SLUK-AK,1989).
The general influence of lithology on soil erosion processes is manifest directly by the
resistance of the denuded bed rocks exposed to the flow of water and affected by the character
of parent materials whose properties are given by the bed rock. The direct effect of bedrock is
also manifest in the properties of the soil forming parent materials which conditions the
principal properties. Some geological materials are vulnerable than others to aggressive
energy of the rainfall and runoff. High erosion risks match with units of weak unconsolidated
geological formations. This is more pronounced when such geological units coincide with
medium to long and even very long slopes with marked gradients. The geology therefore
plays direct and indirect influence on the gully formation. The indirect effect is on the soil
formation and the nature of soil which contribute significantly to erosion processes.
2.5 The Influence of Soil Factor (Erodibility)
The erodibility of the soil is defined as the vulnerability or susceptibility of the soil to
erosion (Igwe, 2012). It is a measure of a soil’s susceptibility to particle detachment and
transport by agents of erosion. Igwe (2003) remarked that a number of factors such as the
physical and the chemical properties of the soil influence erodibility. Generally, soils that are
high in silt, low in organic matter are the most erodible (Bhattacharyga et al., 2015). A soil type
becomes less erodible with decrease in silt fraction, regardless of the corresponding increase
in the sand fraction (Ugwu, 2016; De Vente and Poesen, 2005; Lane et al., 1998; Soufi and Isale,
2001).
Soil erodibility is a measure of soil susceptibility to detachment and transport by water, which
is in turn determined by different soil properties as well as the rainfall characteristics.
Aggregates stability, organic matter, clay mineralogy, and other chemical and physical soil
properties are important factors, which affect soil erodibility as well as rainfall. Soil aggregate
stability and erodibility indices are two main crucial factors, which contribute to soil erosion
and runoff (Hammadet al., 2006; Pimentel, 2000).
Factors affecting the erodibility of a soil includes: particle size of soil, land slope, vegetation,
presence of salt and colloidal matter in the soil, moisture content of soil, soil compaction,
human activities, and rainfall characteristics (Suresh, 2006). The soil factor, referred to as soil
erodibility in the Universal Soil Loss Equation (USLE) is defined as the ease with which soil
is detached by splash during rainfall or by surface flow or both (Renard et al., 1997). Soil
erodibility is related to the integrated effect of rainfall, runoff, and infiltration on soil loss and
is commonly called soil-erodibility factor (K). Soil texture, structure, organic matter, bulk
density or compactness, as well as chemical or biological characteristics of the soil influence
soil-erodibility (Babalola, 1978; Goldman et al., 1986).
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GULLY EROSION MENACE IN UYO: CAUSES, EFFECTS AND CONTROL MEASURES 36
The Universal Soil Loss Equation is as shown in Equation 1.1 (Wischmeir and Smith, 1965):
A = RKLSCP Equation 1.1
where A = Soil Loss; R = Rainfall erosivity; K = Soil erodibility; L = Slope Length factor; S =
Slope steepness factor; C = Crop management factor; P = Conservation factor.
2.6 Anthropogenic Influence
An important factor which contributes significantly to soil erosion problem in Uyo, is
anthropogenic influence arising from misuse of land. The formerevergreen forest belt in Akwa
Ibom hasbeen deforested through excessivefarming, urban development, buildinghouses,
markets, churches, schools, roads,NITEL and NEPA lines etc. Theseunplanned developments
in recent yearsexpose the weak, acidic and sandy soil toerosion (Effiong, 2011). Poor farming
systems have contributed to collapse of soil structure and thus encouraging accelerated runoff
and soil loss due to erosion. The process of uncontrollable grazing caused by the nomads has
resulted in deforestation of the landscape while indiscriminate foot paths created on the
landscape has helped the incipient channels on the landscape to form. These channels
eventually metamorphose to gullies especially when they are not checked at inception. Road
constructions including uncontrolled infrastructural developments have contributed
significantly in gully developments. Some road networks under construction have been
abandoned in the region due to gully formation (Udosen, 2013).
3. Description of the Study Area
The study was conducted in three gully erosion sites located at Anua Uyo, University of Uyo
(Uniuyo) permanent site, and Dump site along old stadium road (also known as Uyo old
village road) situated between Latitudes 50 11 and 50 31 N and Longitudes 70551 and 80 051 E,
within the tropical rainforest belt with evergreen vegetation (see more details on Figures 1.1
and 1.2).
Figure 1.1: Map of Akwa Ibom State showing the study area.
Source: Department of Geography, University of Uyo, (2017).
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GULLY EROSION MENACE IN UYO: CAUSES, EFFECTS AND CONTROL MEASURES 37
Figure 1.2: GIS Map of Uyo Urban showing gully sites (sample locations).
Source: Computed by the researcher, (2017).
The selection of the sites was done based on a study tour. All three gullies were active gullies.
These gullies typically range from 0.5m to as much as 25 to 30m in depth. During this active
gully stage, erosion is intense and the associated morphological characteristics (e.g., width,
depth, slope, etc) are variable.
Uyo is the capital city of Akwa Ibom State and presently occupies a total land mass of 1,250,000
km2 of which a substantial percentage is used for agriculture. About 50,000 ha of its area are
affected by gully erosion, with gully sites and ravine wide spread over the area (SLUK-AK,
1989).
The geological formation in Uyo is the Coastal Plain Sands, which occupies more than 75% of
Akwa Ibom State soils (SLUK-AK, 1989). The soils are derived from the parent materials and
are highly weathered and dominated by low activity clays; the dominant soils in Uyo are of
inter-fluvial slope with a pattern of increase in clay content down the profile and are generally
of low organic matter content (OMC), low water storage capacity, low CEC and highly
susceptible to erosion. The dominant forest types in Uyo include the saline water swamp,
fresh water swamp forest and the rainforest.
The native vegetation has been completely replaced by secondary forest of predominantly oil
palms and woody shrubs such as grasses. The forest is noticeable around hamlets,
watercourses, tree crop plantations and forest reserves. The state lies North of the equator and
within the humid tropics and has a mean annual temperature between 26-270C and two
Sapientia Foundation Journal of Education, Sciences and Gender Studies (SFJESGS), Vol.3 No.3 September, 2021; pg. 31 – 45 ISSN: 2734-2522 (Print); ISSN: 2734-2514 (Online)
GULLY EROSION MENACE IN UYO: CAUSES, EFFECTS AND CONTROL MEASURES 38
distinct seasons: the wet season (April to October) and the dry season (November to March).
In the south and central parts of the state, the rainy season lasts for about 7 or 8 months but,
towards the far north of the state, it reduces to about 6 months.
The rains are of high intensity and of bimodal pattern with two peaks in July and September,
and a period of 2-3 weeks of little or no rain (called August Break) in between. The dry season
gives rise to the post-season characteristics of a maximum rainfall regime in which the months
with the heaviest rainfall are usually June and July for the first rainfall maximum and
September for the second maximum. The annual rainfall ranges from 2,000mm on the
northern fringe to over 3,000mm along the coast (Essien and Essien, 2012).
Figure 1.3: ActiveGully Erosion site in Uyo(at the University of Uyo permanent campus)
Fig. 2: Gully erosion at
Fig.1.4: Gully initiation at Afaha Oku, Uyo
4. Devastating Effects of Gully Erosion in the Study Area
According to findings from Abdulfatai et al., (2014), Udosen (2013), SLUK-AK (1989), Effiong
(2011), Igwe(2004), Pimentel(2000), Igwe (2012), Okorafor et al., (2017), Ofomata (1985), and
Udoumoh et al., (2018), the effects of soil erosion in a gully-affected area is summarized as
follows:
i. Lost or destruction of farmlands, buildings, roads, homes, and sometimes lives.
ii. Development of bad land topography
iii. Loss of natural vegetation and economic trees
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GULLY EROSION MENACE IN UYO: CAUSES, EFFECTS AND CONTROL MEASURES 39
iv. Loss of nutrient-riched top soils thus reducing agricultural productivity/ output
v. Pollution/ contamination of surface, subsurface, and groundwater resources in the
catchment area.
vi. Leads to eutrophication of streams and rivers
vii. Reduction in reservoir capacity and useful life of receiving water bodies in the
catchment area due to siltation and sedimentation, ie sediment loads carried by surface
flows to the receiving streams/rivers.
viii. Destruction of aquatic lives in receiving water bodies due to eutrophication
ix. Isolation of adjacent villages and towns which is sometimes caused by continuous
gully expansion
x. Distortion of movement due to breakage of major road networks. Example of this is
the untold hardship accentuated by the gully expansion at the NtakInyang region of
the Ikpa watershed, hindering people in that region from accessing Uyo from the
Afaha Oku area.
5. Methods of Erosion Control
Measures adopted to control soil erosion in general are classified as; (1) biological measures,
and (2) engineering measures. The biological measures of erosion control are basically
adopted when the land slopes are small ie less than 2% in general and erosion problems are
not severe. When the land slopes are more than 2%, engineering measures may be necessary
(Murty and Jha, 2011).
Sometimes, biological measures are also adopted in conjunction with engineering measures.
For instance, waterways that are located in seepy draws or below seeps, springs, or pipe
outlets may be wet for long periods. The wet condition will inhibit the development and
maintenance of a good vegetal cover and will cause the soil to be in a weak, erosive condition.
In such situation, subsurface drainage or diversion of such flow is essential to the success of
the waterway. Thus, the vegetated waterway is a biological measure of erosion control and
the subsurface drains require engineering measures of erosion control. Usually a small
concrete or asphalt channel of about 0.2m2cross-section is placed in the bottom of the
waterway to carry the prolonged low flows. Also, seepage along the sides or upper end of the
waterway may be intercepted by subsurface drains. Drains are placed on one side of the center
of the waterway to prevent erosion leading to exposure of the drain in case of failure of the
waterway.
The engineering measures of controlling water erosion includes the installation of control
structures suchas drop spillways, chutes, formless flumes, pipeless spillways, etc. whereas
large gullies may be controlled by reduction of the surface inflow, by shaping and intensive
natural or artificial revegetation, or by the installation of control structures such as drop
spillways, chutes, formless flumes, pipe spillways, waterways construction can be used to
stabilize small gullies.
Terracing is an engineering soil conservation practice, used to control the soil erosion in highly
sloped areas. Terracing involves the construction of embankment or ridge and steps-like
structure across the land slope to check the flow of surface runoff and to reduce the soil loss.
In this system, the effective length of land slope is reduced to a large extent. From
experimental evidence it has been found that the soil loss is directly proportional to the slope
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GULLY EROSION MENACE IN UYO: CAUSES, EFFECTS AND CONTROL MEASURES 40
length of power 0.5. According to this statement, if the length of slope is increased as twice,
the soil erosion increases in proportion of 1.4 times. In addition, terraces also play an
additional role in trapping the splashed soil particles and depositing them over the benches
(Suresh, 2006).
The four broad methods that could be used to control gully erosion in the study area are (i)
diversion of runoff, (ii) vegetative methods, (iii) construction of temporary structures, and (iv)
construction of permanent structures.
(i)Diversion of runoff: the surface runoff, as it flows down the land slopes, gains in kinetic
energy. At the point when the kinetic energy is enough to dislodge the soil particles, the
flowing water starts eroding the land surface. The rate of gully erosion depends on the amount
of runoff concentrated at a particular point, the longitudinal slope and soil characteristics.
Excess runoff can be channeled to streams/ rivers by the construction of drainage. Diversion
of runoff is usually achieved by constructing diversion drains. The diversion drain is a shallow
channel put across the slope above the gully. The purpose of this drain is to intercept the
runoff coming from the area above the gully. The intercepted runoff is let off at a point in the
gully well protected so that no further erosion at that point occurs. The design of the diversion
drains consists in determining the area of cross section for the given catchment area and
slope.The first step in planning the gully control program is to plan to control the runoff from
the catchment area. This may be done by using good land and crop management practices,
such as contouring, strip cropping and terracing (Murty andJha, 2011).
Contouring is the practice of performing field operations, such as plowing, planting,
cultivating, and harvesting, approximately on the contour. This practice helps to reduce
surface runoff by impounding water in small depressions, and decreases the development of
rills. Contouring on steep slopes (rolling lands) or under conditions of high rainfall intensity
and soil erodibility will increase gullying because row breaks may release the stored water.
Breakovers cause cumulative damage as the volume of water increases with each succeeding
row. Many studies, including the findings of Harrold (1947) revealed that contour cultivation
together with good sod waterways reduced watershed runoff by 75 to 80 percent at the
beginning of the season. The reduction dropped to as low as 20 percent at the end of the year,
leaving an annual average reduction in runoff resulting from contouring of 66 percent.
Strip cropping is the practice of growing alternate strips of different crops in the same field.
The strips are placed on the contour in order to control water erosion. The three types of strip
cropping are contour, field, and buffer strip cropping. In contour strip cropping, layout and
tillage are held closely to the contour and the crops follow a definite rotational sequence. In
field strip cropping, strips of uniform width are placed across the general slope. In buffer strip
cropping, strips of a grass or legume crop are placed between contour strips of crops in the
regular rotations. Buffers may be even or irregular in width or placed on critical slope areas
of the field. This is done to ensure protection from erosion or allow for areas of
deposition(Schwab et al., 1983). In any given case, the type of strip cropping used is a function
of the cropping system, topography of the area as well as the types of erosion hazards
observed in the area.
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GULLY EROSION MENACE IN UYO: CAUSES, EFFECTS AND CONTROL MEASURES 41
(ii)Vegetative methods (cultural method) of gully control: these comprise the natural
vegetation and artificial vegetation of the gully. Natural vegetation occurs automatically
whenever the runoff that is causing the gully is diverted and grazing is controlled from the
eroded area. Thus, grasses, shrubs and trees native to the area starts to grow in the gully thus
the vegetal cover helps to stabilize the gully and hinder further expansion. Artificial
vegetation involves the planting of grasses such as Eulaliopsis binate (Babiyo),
SaccarumPontaneum, Thysanolaena maxima, Themeda species, Axonopuscompressus, etc,
along the gully beds and banks in order to stabilize the gully. The grasses should be such that
suit the local soil and climatic conditions. They should be established both on the bed and
the sides either by seeding or by sodding. It is always recommended that enough width be
provided so that the flow velocities do not cause damage to the grassed surfaces.
(iii)Temporary structures for gully erosion control are designed to retard the flow of water
and reduce the channel erosion. In addition, they retain some quantities of sediment and
moisture which helps in establishment of vegetation (Murty and Jha, 2011). The designs
developed for temporary structures of gully control involves: brushwood dams, loose dams,
rock-filled dams, woven wire dams, etc. Brushwood check dams are locally available
vegetation cuttings in their construction. Two types of constructions that are generally
applied are single post row brushwood check dams and double post row brushwood check
dams. The single post row brushwood check dam is used when the expected runoff is small
in quantities whereas the double post row dam is used when the expected runoff is in large
quantities. In the woven wire dam, a wire mesh is used to hold the stones in place. All the
check dams involving stones are to be adopted in areas where stones are available. The rock
fill dams and the woven wire dams are more lasting than the loose rock dams (Murty and
Jha, 2011). There are no standard principles for the design of these temporary structures.
They are to be designed in situ the needs and availability of materials in a given situation.
Other temporary structures include earth, sod, rocks, logs, etc.
(iv)Permanent structures of gully erosion control; these are designed to protect the gullies
from further expansion and at the same time help in storage of water. Three types of
structures commonly used are (1) chute spillway, (2) drop spillway, and (3) drop-inlet or pipe
spillway. Chute spillways are used at the head to convey the water safely to the gully head.
The drop spillways are used along the gully bed to act as control points so that the gully bed
is not eroded below the crest level of the structure. The drop inlet spillways are used at
appropriate locations in the gully for storage of water. The permanentstructures for gully
control consist of three main components. These are inlet, conduit and the outlet. Water
enters the structure through the inlet and is conveyed through the conduit. The water leaves
the structure through the outlet. The outlet is mainly responsible for dissipating the energy
of the water so that the water flowing through the structure does not cause erosion
downstream of the structure (Murty and Jha, 2011; Schwab et al., 1993). Design of permanent
gully control structures is given in Schwab et al., (1993). The advantages of temporary
structures of gully control over permanent structures are: (1) they make use of less expensive,
locally available materials, and require little or no technical know-how for their construction.
On the other hand, the advantages of permanent structures for gully control over temporary
structures are; they last longer since they are constructed with permanent materials.
Secondly, they serve dual capacity of stabilizing the gully as well as for storing water. Also,
they have adequate capacity to handle the runoff.
Sapientia Foundation Journal of Education, Sciences and Gender Studies (SFJESGS), Vol.3 No.3 September, 2021; pg. 31 – 45 ISSN: 2734-2522 (Print); ISSN: 2734-2514 (Online)
GULLY EROSION MENACE IN UYO: CAUSES, EFFECTS AND CONTROL MEASURES 42
6. Recommendations
It is an established fact that soil erosion is a continuous natural phenomenon/ hazard which
cannot be stopped completely but can be managed and minimized to ensure soil and water
conservation. This study recommends the following steps toward the reduction of soil loss/
arable lands due to gully formation: It is an established fact that soil erosion is a continuous
natural phenomenon/ hazard which cannot be stopped completely but can be managed and
minimized to ensure soil and water conservation. This study recommends the following steps
toward the reduction of soil loss/ arable lands due to gully formation:
Cultural method (also known as vegetative tecnique by Simpson, 2010) of erosion
control has been found to be a a cvheap and effective method. Plantiing of plantain
and banana on the floodplains can also be an effective measure of erosion controll.
Governmnet at all levels should take it as a matter of importance and urgency to
respond to gully issues at its developmental stage.
Since the causes of gully erosion include both natural and anthropogemnic sources,
and bearing it in mind that we have little or no control over the natural causes of gully
erosion, stakeholders(local, state, and federal ministries of environment, agriculture,
etc ) should discourage all practices that are capable of initiating gully erosion. In
otherwors, governement should enact laws against such activities that favour gully
growth and initialization.
Research findings and suggested solutions should be implemented by the local, state,
and Federal Governement.
Levelling by bulldozing to level out small and incipient sheet erosion sites as soon as
they are noticed, as well as proper channelling of run-offs and then applying the
preventive measures, could be the most important and effective method of control of
gully erosion in Uyo.
Considering the poor soil quality attributes, soil conservation and management
practices must place premium on improving the soil organic matter content with its
potential to improving soil structural stability, and thus reduce soil erosion and
gullying in the study area. This is because the high bulk density and low porosity
values were also accentuated by the fact that the sand particles tend to lie in close
contact because of lack of bridging materials like organic matter; the soil being
characterized by low organic matter content.
If all the above raised suggestions are adhered to, it is believed that the havoc done by
gully erosion in Uyo, South-South Nigeria, would be eliminated or better still,
prevented in order to ensure the security of our Natural resource as well as achieve
optimum agricultural productivity from it.
7. Conclusion
Erosion is a serious problem worldwide. Guly erosion, which is an advanced stage of erosion
has developed into ravines in uyo, the capital of Akwa Ibom State, South-South Nigeria. Gully
erosion control is very essential to maintain the crop productivity of the soil as well as to
control sedimentation and pollution in streams and rivers. The absence of systematic and
periodic review of operations and practices relating to environmental protection is
responsible for the continuous degradation of our ecosystem, leading to the formation/
expansion of gullies in Uyo, South- South Nigeria. This study has proffered solutions to the
problems of gully erosion in the study area. Oblivious of the fact that soil erosion is a
continuous natural process which cannot be stopped out rightly but can be managed and
Sapientia Foundation Journal of Education, Sciences and Gender Studies (SFJESGS), Vol.3 No.3 September, 2021; pg. 31 – 45 ISSN: 2734-2522 (Print); ISSN: 2734-2514 (Online)
GULLY EROSION MENACE IN UYO: CAUSES, EFFECTS AND CONTROL MEASURES 43
minimized, it is the believe of the researcher that if all the suggested solutions here are
carefully adopted, the menace of soil erosion in the study area may soon be controlled, halted,
or reduced to a minimal level.
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