ABSTRACT
Gully erosion is an environmental hazard that is ravaging the landscape of Ungogo area. This study was carried out to investigate the geological and geotechnical control of gully erosion in the study area. Geological field mapping was carried out to assess the causes and extent of erosion. Soil samples were collected from four (4) gully sites at depth between 0 – 5m, 0.5 – 1m and 1 – 1.5m for geotechnical analyses. Four (4) index properties of soil were determined: Specific gravity, sieve analysis, Atterberg test and compaction test both in accordance with British standard code: BS-1377-2, 1990. Specific gravity values were used to determine the probable risk of erosion. The grading index recorded from the sieve analysis showed that coefficient of uniformity ranged between 17.2 – 1.13 and coefficient of curvature ranged between 6.01 – 0.85. The coefficient of permeability falls between coarse sand and silt. The plasticity index of the soil samples were found to be 4%, 5%, 9%, 2%, 7%, 6% 2%, 20%, 9%, 11%, 3%, and 3% and all the soil samples from gully sites have their plot clustered within clay of low plasticity and silt of low plasticity indicating cohessionles properties thus the potential for the control of gully erosion formation in the area. The optimum moisture content and the maximum dry density of the soil indicated that soils are majorly loose sand and this could pave way for erosion susceptibility. Mitigation measures such as Landfilling, construction of check dam, geo-textile, fencing and stabilization are recommended for the control of gully erosion in the area.
CHAPTER ONE
1.0 INTRODUCTION
1.1 Background to the Study
Erosion is the gradual or quick geomorphologic process whereby surface layer of weathered rocks or sediment are removed, transported and deposited elsewhere by an agent of denudation thus leaving an exposure of lower soil horizon (Egboka, 2000). It is a worldwide phenomenon which ravages large areas of land particularly in high rainfall locations (Amangabara, 2012). Soil erosion has been documented from the earliest of times as severe environmental hazard (Poesen et al., 1998; Tebebu et al., 2010).
Gully erosion is a form of erosion that threatens roads, bridges, building, soil productivity and fence (Bruce, 2006). It occurs from region to region based on the mineral compositions of the soil. Soil erosion is mostly an accelerated process under which soil is bodily removed/displaced and transported away faster than it was formed. Soil erosion commences with rain droplets which displace soil particles, removing them and eventually depositing them at a new location entirely different from their original site of displacement. It occurs not constantly all over the year though, the formation of gully always begins by an increase in discharge at some point in the beginning of rainy season, while gullies tend to stabilize and fill up during the transition towards dry season where the discharge is drastically reduced.
The factors that contribute to control of gully erosion includes: geology, geomorphology, soil texture, biological diversity, vegetation cover and climate (Ofomata, 1988). It can be caused by other factors including climatic factors (precipitation, wind and storm), geological factor (porosity permeability and sediment types), physiography, hydrogeology, and geotechnical properties of the soil materials (John et al., 2015).
1.2 Statement of the Research Problem
Gully erosion is an epidemic environmental hazard in Nigeria and the area under study is no exception. The end result of the threat leads to destruction of farm lands, loss of natural habitat, loss of plant and animal diversity, deterioration of soil water quality, destruction of socio-infrastructural facilities, and displacement of people (Okoro et al. 2011). It causes destruction of soil quality farmland, collapse of buildings, roads and bridges (Bruce, 2006).
Erosion formation is a global problem causing threat to life and properties and it result is now serious problem in Ungogo area putting the residents in danger. The root causes of the problem have not been identified and studied despite the seriousness of gully erosion problems prevalent in the study area. No systematic work on the geological and geotechnical control of gully erosion is documented.
1.3 Justification for the Research
Investigation of the geological and geotechnical properties of soil has the potential to determine the factors and the causes of gully erosion formation. There is no systematic study of the geological and geotechnical control on erosion available in the study area, therefore, Knowledge of the geological and geotechnical conditions of the area under study is essential to provide basic information of the geologic condition and will help policy makers make informed decisions on possible mitigation measures and control.
1.4 The study Area
1.4.1 Location and Accessibility
The study area lies between Latitudes (12˚7’30”N, 12˚4’45”N) and Longitudes (8˚28’30”E, 8˚30’55”E). The map was enlarged to a scale of 1:12,500. Ungogo Arewa, Bakin Kasuwa, Daurawa and Tudun Murtala are the major settlements in the study area. The area is accessible by major road that runs through Ungogo Arewa to Nadara Doka (Figure 1.1). There is a minor road that linked from Bakin Kasuwa to Laying Maigari to Ungogo Arewa.
Figure 1.1: Location of study area
1.4.2 Climate
The climate of the study area is typical of tropics which is divided into two main seasons; the dry and wet seasons. The wet season lasts for about five to six months (May- September), while the dry season lasts from October to April. The average rainfall falls between May (63.3 – 48.2mm) to August (133.4 – 59mm) the wettest month. The temperature of Kano State usually ranges between 33-15.80C, although sometimes during
the Hamattan, the temperature may drop as low as 100C (NIMET, 2015).
1.4.3 Vegetation
The vegetation of the area is typically of semi-arid savannah. The Sudan savannah is sandwiched by the Sahel savannah in the north and the Guinea Savannah in the south. The canopies of the trees are very wide and most of them are less than 20m tall. The following are the common trees widely scattered within the study area: baobab Adanosi adigitata (Hausa: kuka), Sclerocary abirrea (Hausa: danya), Anogeissus leiocarpus (Hausa: marke), Vitex doniana (Hausa: dinya), desert date Balanties aegyptica (Hausa aduwa), ebony Diospyro smespiliformis (Hausa: kanya), locust bean Parkia clappertoniana (Hausa: dorawa), Acacia albida (Hausa: gawo), Neemazadirachta indica (Hausa: dogonyaro), Ziziphus spinachristi (Hausa: kurna). These trees are very resistant to drought. Domesticated crops include groundnuts, sorghum, and, cowpeas, millet, beans, and rice.
1.4.4 Relief and Drainage
The study area forms part of the plains of the Hausa land with elevation not greater than 500m above mean sea level. The general relief of the study area is between 450m and 480m
(Figure 1.2). Kansuwa River is an ephemeral river which flows northeastward and linked to channels around the area.
1.4.5 Settlement and Land Use
Farming is the commonest land use in the study area. Farming is practiced by traditional methods, which involved the use of hand tools such as hoes, cutlasses, shovel and diggers. The common crops grown are maize (Zea mays), guinea corn (Sorghum spp.), beans (Vigna unguculata) and groundnuts (Arachis hypogea).
1.5. Aim and Objectives
This work is aimed at investigating the geological and geotechnical control of gully erosion development in Ungogo area.
The objectives are:
i. To produce a geological map of the study area on a scale of 1:12,500.
ii. To determine the dimension of the gully sites of the study area.
iii. To determine the particle size distribution of the soil of the study area.
iv. To determine the plasticity of the soil of the study area.
v. To find out the optimum moisture content and maximum dry density of the soil.
1.6 Scope of the Research
This work covers the study of the geology of the area and investigating the contribution of geotechnical properties of soil to the formation and expansion of gully erosion in Ungogo of Kano, North Western Nigeria.
1.7 Organization of Study
This consists of five chapters. Chapter one is the introduction which presents the background of the study, statement of the problem, justification, climate and vegetation, relief and drainages, aim and objectives and scope of the research. Chapter two discuses the literature which includes the geology of Nigeria, gully erosion formation, causes of gully erosion formation, influence of geology, influence of soil factor and geotechnical index properties of the soil. Chapter three is the methodology adopted for the study. It includes field mapping, sample collection, sample preparation, and laboratory analyses. Chapter four presents the results and discussions. Chapter five is the conclusion and recommendations.
This material content is developed to serve as a GUIDE for students to conduct academic research
GEOLOGICAL AND GEOTECH NICAL CONTROL OF GULLY EROSION, UNGOGO, KANO, NORTH WESTERN NIGERIA
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