GULLY EROSION MENACE IN UYO: CAUSES, EFFECTS AND CONTROL …

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,


&

ANANA, UNYIME ABASI E.

Department of Food Science and Technology,


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



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



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.



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.



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).



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).



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



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



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



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.



(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.



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



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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