Environmental Effects of Gully Erosion in Nigeria Case Study of Nanka Community, Orumba North, L.G.A of Anambra State

Soil is the most vital natural resources on earth. This is because it hosts both animate and inanimate beings and over three quarters of the world’s man-made developments are being carried out on land. Nanka is an Igbo speaking community covering five (5) settlements in Orumba North Local Government Area of Anambra State, South Eastern Nigeria. The studyis aimed at evaluating the effects of gully erosion in Nanka Community of Anambra State and with a view to recommend sustainable mitigation measures for environmental improvement. The use of questionnaires, maps, pictures, literature review, soil sample collection and laboratory analysis were part of the research methodology. The study revealed that both the natural and anthropogenic such as road construction without drainage, deforestation, solid waste disposal in water ways, rainfall intensity and nature of soil among others are the causal factors of gully erosion in Nanka Community. The respondents agreed that rainfall intensity and nature of soil are the major cause with about 36.02% and 30.11% respectively. At 0.05 level of significance, the critical table value of‘ t test’ is 2.78 while the calculated value of R2 is 0.31(31%) for the test of hypothesis. However, it was also observed that the effects of gully erosion in Nanka Community encompass destruction of residential homes, psychological trauma and loss of lives and farmlands among others. The mitigation measures to tackle the problem are land reclamation, aforestation, construction of roads with drainages, removal solid waste materials in water channels, public sensitization / awareness campaign and construction of embankments through public and private participation programme.


Figure 2.2: Niger Delta Region of Nigeria showing some States affected by Gully Erosion with Anambra State
having the highest points of Gully Erosion. Source: Egboka, B.C. E (1993) "The Raging War"

Materials and Method
To undertake this study, the following were applied: Reconnaissance Survey, Research design, data Needs and Sources, Data Collection, Research Population, Sampling Method, Sample size Data Collection Instrument and Method of Data analysis.

Reconnaissance Survey
A reconnaissance survey was carried out to ascertain the nature of the erosion taking place in the area as well as knowing the types of vegetation cover in the area. This was made possible using the map of the study area.

Research Design
The study is non-experimental in design, because it will portray the current impact of gully erosion on the affected people of Nanka, South-eastern Nigeria. The study is descriptive survey research as opinion will be sampled with the use of questionnaires and measurement by the researcher. The respondents were given opportunity to express their opinions in the questionnaire.

Sources of Data Primary Source
Primary source of data are direct observation from field work, oral interview and the use of questionnaire.

Secondary Source
Secondary sources of data include topographic maps, to be used to ascertain the study location and produce a geologic sedimentological map of the area. More so, library materials such as journals, published and unpublished B.Sc. M.Sc. and Ph.D thesis, text books and conference papers were used particularly during literature review.

2.2.4Field Measurement of Areas Affected by Gully Erosion
Measuring instruments such as ranging poles, compass, pegs and tape were used to measure the identified gully erosion site in the study area. With the help of the aforementioned measuring instruments, the length, depth, width, slope and angle of each identified erosion site were determined in meter and were used for analysis to determine the volume of eroded soil in each of the gully site.

Collection of Soil Samples from selected gullies
With the aid of soil auger, soil samples were collected in each identified gully site in the study area. The samples were collected at depth of 50-100cm for particle size analysis.

Laboratory Analysis of Soil
To determine the particle size of the collected soil samples, Hydrometer method was used to carry out the analysis of the soil samples. This method quantitatively determines the physical proportions of three sizes of primary soil particles as determined by their settling rates in an aqueous solution using a hydrometer. Proportions are represented by stated class sizes: sand ranging from 2000 -50 um; silt ranging from 50 -2.0 um and clay < 2.0 um (USDA Soil Survey).

Determination of Erodibility Factor and Predicted Soil Loss
K(%) = (%Sand + %Silt) x 100 (%Clay) The predicted soil losses for the various areas will be done using revised universal soil loss (RUSLE) equation. A = 2.24RK Where -A = soil loss converted to ton/ha/yr by multiplying by 2.24 R = Rainfall factor and given as 0.5H H = Mean annual rainfall K = Erodibility factor 2.2.8Questionnaires Administration Questionnaire is the major instrument for data sourcing. Sets of structured questionnaire were designed to gather information on the causes, effects and control measures of gully erosion in the area. A total number of 400 questionnaires were administered to the respondents within 14 days interval. The number of questionnaires returned is 372 while 28 were lost (see table 3.1). The questionnaires were designed to elicit information on the following: a. Causes of soil erosion in the study area. b. The effects of the gully in the study area. c. The mitigation measures employed by the community in curbing or curtailing the spread of the gully in the study area. A trial study was carried out with the questionnaire administered to five (5) respondents to each of the study area and proved that most of the respondents are uneducated and needed explanation to the questions. The questions were divided into sections A and B. Section A is the general questions, section B is the questions on the effects.

Sampling Method and Sample Size
Simple random sampling was adopted in the course of this research for the purpose of selecting households and respondents affected by gully erosion living at the gully proximate areas. 400 Respondents were selected from heterogeneous populations that make up gully affected migrants and other unaffected living populations of Nanka area. Respondents comprise only of men and women from Isiakpuenu-Nanka, Ududo-Nanka, Enugwu-Nanka, Ubahu-Nanka and Amako-Nanka communities of the area. This section involves the use of statistical techniques in analyzing and interpreting the data/information from the responses provided by the questionnaire.
Techniques that were adopted in data analysis are those that enhanced organization, examination and presentation of treated data. Frequency tables and corresponding percentages of the frequencies were used where appropriate. The use of tables and simple percentages assisted in clear representation of existing problem conditions.
Descriptive statistical analysis was applied to deal with the methods and techniques of summarizing and describing information (data). Percentages, proportion and mean were applied to get other parameter. Test of significance was used to test the validity of the first hypothesis. Pearson's Product Moment Correlation Coefficient was also used to analyse the relationship between the length and the depth of the gully in the area as it relates to soil loss volume. While multiple linear regression equations were used to test the validity of the second hypothesis.

Causes of Gully Erosion in the study area.
Numerous factors collectively distort, erode and modify the soil surface. In the study area, both natural and anthropogenic causal factors are perceived to cause gully erosion as you can see from the tables (4.1&4.2) below. Table 3

.1: Natural causes of Soil erosion in the study area CAUSES
Isiakpuenu -Nanka

Ubahu -Nanka
Total %  (134) of the respondents agreed that rainfall intensity is the main natural causes of soil erosion in the study area. It can also be deduced that 30.11% of the respondents agreed that the nature of soil is one of the natural causes of soil erosion in the area. From the table also, the nature of vegetation cover and nature of topography accounted for 21.50% and 12.37% respectively.

Table 3.2 Anthropogenic causes of gully erosion in Nanka CAUSES
Isiakpuenu -Nanka

Ubahu -Nanka
Total % 74 the clearing of land mainly for construction and building purposes contributed to the gully formation.
Furthermore, sand excavation as perceived by 19.89% of the respondents causes gully erosion in the area while 11.83%, 10.48% and 12.10% of the respondents opined that poor agricultural practices of the farmers, overgrazing by the animals and dumping of refuse at the water channels respectively contributed to the causes of gully erosion in the study area From the responses derived from the causes of gully erosion in the study area, it could be inferred that the main natural and anthropogenic causes of gully erosion arerainfall intensity and deforestation respectively. From table 3.3 above, it can be deduced that the main effect of gully erosion in the study area as perceived from the responses of the indigenes is frightful scenic environment created by the gully and this accounted for 23.66% of the total responses. This is followed by the pollution of the water bodies which accounted to 17.48% of the responses. 17.20% of the respondents agreed that infrastructures are constantly being lost as a result of the gully.
More so, 13.44% of the respondents agreed that ancestral homes are being destroyed on daily basis especially during the rainy season when the impact of the gully is most spelt out, thereby threatening the inhabitants to either pack out of their ancestral homes or stand the chance of being brutally displaced. Respondents who constituted about 10.22% of the responses agreed that loss of farmland is one of the consequences faced by the community while 9.40% and 8.60% of the respondents believed that trauma and loss of relatives respectively are the consequences/effects suffered by the community as a result of the gully.

Control Measures of the gully erosion in the study area
Different erosion control measures have been employed by the inhabitants of the study area to check and control the problem of soil erosion menace. These measures were explained in the table below. Table 3.4 Control measures adopted in curtailing gully erosion in Nanka community CONTROL MEASURES

Ubahu -Nanka
Total %  Table 3.4 above, presents information on the measures adopted in curtailing gully erosion in the study area. From the table, 24.19% (90) of the respondents, agreed that the main control measure adopted by the people of the community in combating the gully is aforestation while 19.89% of the respondents agreed that the construction of run-off pits as well as clearing of the water channels are the control measure adopted in the fight to control the spread of the gully. However, 20.17% of the respondents are of the opinion that construction of a good drainage network contributed to the control measure employed by the community in the fight against the gully. Again, 15.86 % of the respondents believed that sand filling is one of the control measures adopted by the community in Journal of Environment and Earth Science www.iiste.org ISSN 2224-3216 (Paper) ISSN 2225-0948 (Online) Vol.9, No.10, 2019 the control of the gully. From the study, it could be inferred that aforestation is the major practice that has been imbibed by the community in their bid to combat the gully erosion.

Measurement of gully
Gullies of different dimensions were found and measured by a researcher in the study area. The measurement was divided into three dimensions of length, depth and width. This measurement was taken in order to determine the volume of soil loss in the gully erosion site. Table 3  From the table above, it could be deduced that the severity and magnitude of the gullies in the study area are certainly not the same. For example, Gully in Ududo-Nanka seemed to be more severe than other gullies. This is because, it has the longest, deepest and widest gully among other gullies within the region with the length of 58m, depth of 60m and width of 28m. This is followed by IsiakpuenuNanka which has the length of 32.5m, depth of 52.5m and width of 22.5m. Other locations have varying lengths, depths and widths as the case may be.The slope gradients of the study gully site ranged from 25 0 -65 0 , ordinarily under vegetal cover, these slope gradients would not enhance erosion processes as such but due to exposure to direct raindrop impact and human activities couples with poor civil engineering work to control the runoff, gully has become pronounced virtually in every catchment.   Table 3.6presents information on the results on the physical and biological characteristics of soil in the study area and the findings revealed that the soil in the study area is predominantly loamy sand with mean % value of sand being 71.3% while clay, loam and silt are 7.5%, 19.5% and 13% respectively. The high proportion of sand and the low proportion of clay could be attributed to the high friability and detachability nature of the soil which makes it vulnerable to agents of erosion especially under a high rainfall intensity. The organic matter content in each gully site is low and this could be attributed to the subsurface wash caused by heavy run-off water and this in consequence would not support plant growth.
The table also presents information on bulk density in the study area and it shows that the value of bulk density obtained from the gully sites ranged between 1.73-1.74g/cm 3 . As against the range of 2.0-4g/cm 3 considered for well aggregated grassland (Okogbu, 2015). This low values obtained from the sites is an indication that the soil is of highly porous nature and could not retain water, hence the erosive effect of heavy runoff will be more in the area than in other places with high bulk density.

Volume of eroded soils in the study gully sites
Determination of erodibility factor and predicted soil loss: K(%) = (% sand + %silt) x 100 % Clay The predicted soil losses for the various areas were done using revised universal soil loss (RUSLE) equation. A = 2.24 RK Where A = soil loss converted to ton/ha/yr by multiplying by 2.24 R = Rainfall factor and given as 0.5H H = Mean annual rainfall K = Erodibility factor Journal of Environment and Earth Science www.iiste.org ISSN 2224-3216 (Paper) ISSN 2225-0948 (Online) Vol.9, No.10, 2019 Table 3.7presents information on the volume of soil loss in each of the identified gully site in the study area. The results revealed that Ududo Nanka recorded the highest volume of soil loss in the area with a soil loss of 3,120 metric tones and this accounts for 24.06% of the total soil loss in the region. This is followed by Amako Nanka which has 2,912 metric tones of soil loss and accounts for 22.46% of the total soil loss in the gully region. Enugwu Nanka, and Ubahu Nanka accounts for 19.10% and 17.71% of the total soil loss in the region respectively. The least soil loss is recorded in Isiakpuenu Nanka with a percentage loss of 16.67%. From the table, it could be depicted that the total volume of the soil loss in the study area is 12,966 metric tonnes just in one year. The implication is that if no effective and immediate measures are put in place, soon there will not be any arable land left for farming and this will result in serious famine in the area. Again, all other aspect of life such as social, religious, commercial activities etc would be hampered by the loss of land.

CHAPTER FIVE 4.0 CONCLUSION AND RECOMMENDATION 4.1 Conclusion
As stated, this research study was concerned with the investigation of the causes, effect as well as the control measures of soil erosion in Nanka. It is doubtless that from time immemorial, man has been in contention with nature especially in environmental degradation. Soil erosion is seen as a natural disaster affecting land owners, business holders and the entire inhabitant of Nanka Community.
In the course of the investigation, we discovered that the heavy rainfall throughout the year, poor soil composition, topography, loss of vegetative cover etc. culminated in forming gully erosion in the study area. Gully erosion has caused untold hardship and environmental damage to the residents of the community where several buildings and infrastructures have been destroyed.

Plate 3.3: Residential Buildings under threat by gully at Amako, Nanka
Plate 3.4: Residential Buildings under threat by gully at Amako, Nanka As regards to preventive measures, the government and the inhabitant have devoted much time, resources and energy in mitigating the problems associated with the gully incidence in the study area. Gutters are constructed across different areas especially where there are road networks. Afforestation programmes were employed in curbing the menace, sand filling of gullies, construction of run-off pits in homes and at strategic places in the community, clearing of water channels and public sensitization / awareness campaign as part of the mitigation measures for sustainability and to prevent or reduce future occurrence.

Recommendations
From the study, it is evident that gully erosion as observed has been a continuous, severe and destructive environmental hazard plaguing the inhabitants of the study area. It has defiled all possible solutions employed by the inhabitants of the area. Since environmental hazard as soil erosion do not have local or international boundaries, it is necessary to employ measures that will bring a continuous checking of the increasing problem in the area. An extensive geology of the area should be done to understand the hydrological map of the area in order to design protective and preventive measures in line with the water courses.
Firstly, the measure already employed in combating soil erosion in the area such as construction of embankment, gutters, drainage networks and sand filling should be upgraded and should be done at the right time.
Secondly, the various levels of government should embark on public enlightenment campaigns through their environmental agent (FEPA) so that the people can be educated on consequences and adverse effects of some activities like deforestation, sand excavations, dumping of refuse in water channels etc.
Thirdly, cover crops trees and flowers should be planted in compounds and along major streets to reduce the rain drop impact on the landscape.
Lastly, individuals should be discouraged from building houses across areas that are prone to soil erosion. This will help to reduce the incidence of exposure of building foundations. Government can achieve this through formulation of bye laws and policies that will act as a guide to the use and misuse of land uses.