Land is the basis for every form of physical development and constitutes the primary medium for food production, for the provision of shelter and utilities, for the manufacture of goods and the establishments of institutions to support the basic needs of modern communities (Lasun and Olufemi, 2006). Hence, it’s the farmer’s most important asset and plays essential role in increasing as well as sustaining the agricultural production (Idoma and Muhammad, 2014). Ukaejiofo (2009) noted that land lies at the heart of social, political and economic life of most African countries. He stressed further, that, it is the key factors for economic growth and development of every nation and the foundation for shelter in the urban areas as well as the source of livelihood in the rural areas. Therefore, it is an indisputable source of employment and wealth.
In Nigeria, land has been subjected to miscellaneous uses such as recreation, wildlife, industries, communication, building, agricultural and other uses. The percentage of agricultural land area in Nigeria according to World Bank Report, published in 2010, was 81.80 in 2009. Hence agricultural activities constitutes the largest user of land and to facilitate rural development, high priority has to agricultural sector (Idoma and Muhammad). But over the years, land resources has been misused and hampered by human interference and natural forces. These human activities (mostly farming practices) and natural forces (such as flooding and erosion) could be responsible for the degradation of the natural environment (Ukaejifor, 2009). Flooding as described by Efe and Mogborukor (2013) may be as a result of heavy rainfall or streams overflowing their bank. If flooding persists for days farmlands may be damaged and water table may rise thereby increasing the stream channel size (Mogborukor, 2012). This has been the situation in Edo State especially in Ikpoba riverine community where there was been a negative effect of farm practices on stream channel size along Ikpoba River. This has also in no small measure hampered effective land management in the state. Most of the lands in some of the local government in the state and other parts of Nigeria are cultivated by small-scale farmers.
A substantial amount of agricultural production takes place under the traditional system characterized by primitive production technology, shifting cultivation rotational bush fallow, wide spread illiteracy among the peasant farmers, and minimal application of improved inputs such as fertilizer, agro-chemical and farm machinery (Adaji, 2010; Idoma and Muhammad, 2014). Shifting cultivation as pointed out by Odemerho (1988) is the major system of traditional agricultural is southwest Nigeria. It incorporates long following and inter-cropping of several crops a single plot so that most of the inter locking crowns and the plant matter protect the soil from direct raindrop impact.
Historically, shifting cultivation operates efficiently under a low population density and an abundant supply of arable land. Under these conditions, excessive soil erosion, runoff generation, and long-term decreases in soil fertility were largely minimized. Today, with increasing rural population, acute land shortages, shortened fallows, single cropping, and the need to grow cash crops, the shifting farming system modified to meet these conditions no longer protects the soi (Odemerho, 1998). The soils become more vulnerable to the high rainfall erosivity of the area. With the continuous use of shifting cultivation under inefficient management practices, potential increases in the sediment practices, potential increases in the sediment and runoff supplies to river systems become more probable (Odemerho, 1988).
Stream channel enlargement occurs in response to change in stream flow regime accompanying the conversion of the natural rainforest cover to different land uses in small head water basins in southwestern and southern Nigeria. Stream basins draining areas subjected to traditional agricultural activities tend to develop relatively larger stream channel bank full cross-sectional areas than those draining areas under fallows of various lengths or forest cover (Odemerho, 1988). He added that stream hydraulic geometry is also significantly altered by agricultural activities. The individual relationship of stream channel width, depth, and velocity of changing discharges, as expressed in the hydraulic exponent values, is shown to change as basin surface passes from one traditional agricultural land use phase to another (Miller et al, 2011).
Stream channels develop morphological characteristics and dydraulic geometry which approximate a form of stability that is adjusted to these prevailing hydrologic and sedimentologic conditions. If the increases in the sediment and run off from plots reaching the river system are \large enough, the streams cannot make international adjustments to maintain their previous equilibrium stable (Miller et al, 2011). They further opined that instead, these additional discharges introduce imbalances into the stream channel system sufficient to initiate significant adjustments in both the channel capacity and hydraulic geometry until new equilibrium state is re-established.
The conversion of the natural rainforest cover to different traditional agricultural land uses is causing the stream channel to adjust to the additional run off and sediment produced such that over the years stream channel size are enlarged and hydraulic relations altered. This ongoing process results in an unstable environment and is affecting the soil resources (Odemerho, 1992).
Surface run off is a major character of streams. Rain falling on exposed soils titled for agriculture or cleared for construction purposes accelerate erosion and transport soil particles and pollutants to stream channels. Before the practice of agricultural especially on a larger scale stream typically ran clearly year round because natural vegetation prevented soil loss. As a result, stream water was not turbid. Clearing away the original forest for agriculture and logging have resulted in both erosion and more run-off into the stream land to aggravate flooding problems in the basin (Odemerho, 1992; Omiunu, 1988).
In the past decade, a variety of studies demonstrated how urbanization (especially farming practices) of a drainage basin could significantly affect its hydrology by increasing flood magnitudes and increasing lag-times (Cater, 2011; Harmer, 2012, Anderson, 2010). Recent studies have shown that the changing hydrologic conditions imposed by farming practices have found effects on stream morphology and dynamics (Blackie, 2012; Douglas, 2010; Lai, 2016; Hudson, 2009; Dunne, 2007; 2008; Knight, 2009). Leopold (2013) has shown that progressive farming practices through urbanization of a drainage basin can result in changes of river channel size and form with time. A survey of the fluvial literature sees such changes to be tending towards two directions that are quite distinct. The first direction of change is represented by Park (2007) who observed that high sediment supply to stream during construction phase eventually decreases channel size due to enhanced deposit. The second position is represented by Astratas (2010) who noted that increased flood to stream during post construction phase increases channel size.
Fox (2016) and Knox (2007) have demonstrated that significant differences exist in the response of urban and rural stream reaches to large floods. Enlargement and reduction ration which express the difference between predicted and observed values related such changes in the literature (Harmer, 2012, 2013). However, the operation of negative feedback mechanism in the fluvial system act as both repeller and environmental boundary to the realization of this downstream propagation of disturbance always (Odemerho, 1992).
Despite the importance of these results from the studies cited, there still remain a great shortage of quantitative data on the effects of farms practices on stream channel size previous studies of the influence of farm practices on floods, sediment yield and stream dynamics are insufficient (Nishimura et al, 2007)
The predominant occupation of the Bini’s rural population is agriculture, broadly defined to include crop farming, livestock and lumbering. Over many parts of Edo State (especially in the Ikpoba River Basin), between 75 to 90 percent of the rural population farm the land. Like most developing African Countries, the population of Edo state is rapid with its attendant pressure on agricultural lands.
In the Ikpoba River Basin, the land resources have been and are still, inefficiently managed through the indiscriminate removal of natural vegetal cover by increased cycles of burning and cropping (Avwunudiogba, 2008). The effect on stream basin hydrology of vegetal removal or modification of land due to land utilization for agriculture under inefficient management practices can be categorized as: Increase in total surface runoff, increase in peak flow rate, decrease in base flow, decrease in water quality and increase in sediment load especially during land preparation for seeding (Odemerho, 1988).
To develop and manage a river basin and fluvial system effectively, it is necessary to identify and minimize the adverse effects of existing structures and activities in the river basin. It is equally important to predict and take into account the potential adverse effects of proposed schemes. This requires data on the factors that control the mechanics of fluvial system. The data should cover the basin characteristics in relations with geomorphology and river mechanics, erodibility of drainage basin and temporal effects. This is because unstable rivers may destroy structures, result in loss of property, lead to boundary disputes, enhance aquatic habitats and aesthetic quality, affect surface and subsurface drainage lands. It is against this background that this study is carried out to critically examine the effects of farm practices on stream channel size along Ikpoba River.
1.2 Statement of the Problem
In the Ikopba River Basin, the natural balance between vegetative cover and climate has been disrupted. This disequilibrium between vegetation and climate is not examined here in the light of climate change. Instead, it is seen as a phenomenon produced in response to the activities of man which is purely agricultural practices.
Apart from the fact that agricultural land use accounted for a much greater proportion of the total land area in the basin, cultivation has become more clearly concentrated in the vicinity of the river and its tributaries.
Again, practically the whole bank of the river is now actively farmed. Settlement is mostly located adjacent to the cultivated land, and thus relatively close to the river. These activities have greatly increased erosion in the basin causing the river channel to alter its hydraulic variables so that it can accommodate the additional runoff and sediment produced by erosion in the fields bordering onto the river. Changes in the fluvial characteristics are often imposed on a framework of short term fluvial variability or shifting environmental conditions for the purpose of identifying and interpreting responses mechanisms. Therefore, the identification, analysis and prediction of human induced fluvial adjustment is a challenging task.
In the Ikpoba River Basin, agricultural land use has resulted into de-vegetation in the Basin. Population pressure on land has also led to conversion of steeper slopes and marginal lands into agricultural land use (Odemerho, 1992). This has led to much modification of the landscape. Consequently, the soils become more vulnerable to the high rainfall erosivity of the area. With continued agriculture under inefficient land management practices, potential increases in the sediment and run off supplies to river systems become more probable. As a result, stream channels tend to develop morphological characteristics and hydraulic geometry which approximate a form of stability and change to these prevailing hydrologic and sedimentoogic conditions. If the increase in the runoff and sediment from plots are large enough, the stream cannot make internal adjustment to maintain their previous equilibrium state instead, these additional discharges system sufficient to initiate significant change in both the channel capacity and hydraulic geometry until new equilibrium state is re-established (Oyegun, 1994). This study therefore seek to address the aforementioned problems and profer appropriate recommendation.
1.3 Aim and Objectives of the Study
The main focus of this study is to look intensively at the effects of farm practices on stream channel size along Ikpoba River, Edo State. The study is also aimed at identifying the various types of farming practices along the river bank. In order to achieve the desired were designed to guide the study.
1.4 Research Questions
The researcher asked the following questions to guide the research work. These questions will be answered in due course.
The researcher tested the following null hypotheses.
1.6 Significance of the Study
The relevance of this research is on the overall quest to preserve the stream channel size and to checkmate the growing pace of urbanization (agricultural farm practices). The following are some of the benefits of this research;
1.7 Justification for this Study
Various forms of human-induced variability are significant challenges to management strategies and control technologies. Among these are hydrological sedimentological, flooding, channel and system wide control. The Ikpoba River Basin has suffered serious disturbance and modification. Agricultural practices accounts for about 60 percent while construction accounts for 25percent and natural forest 15percent. At the moment, no relevant works have been done that specifically address farm practices and stream channel size in the basin.
Again, this basin is a humid tropical one, and it was not prudent to transplant untested foreign concepts, paradigm and theories developed under different conditions fairly satisfactory. At the same, there was need to cover significant gaps and weakness in the field of fluvial geomorphology as they currently exist in the humid tropics. There was also a need for equations and model development/improvement based on the results of this study. This is necessary because while all branches of geomorphology use models and equations, the fluvial geomorphologists use them most because fluvial geomorphology is one of the most complex and less understood of all branches of geomorphology (Idoma and Muhammad, 2014).
While each or a combination of these issues related to the Ikpoba river basin become more strident and challenging in the coming year; it is hoped that this study will provide a background to the issues as they emerge. Besides, it is hoped that this study will strengthen the appreciation of a geographer’s approach to the river basin management and bring nearer home so many theories, models and methodologies developed at enormous expense and published in learned journals but which remains unused because they have never been tested in the field. This is a very serious matter to my mind because one major reason for carrying out a research is to make result available to the practitioner. But when a researchers loses touch with the user (the practitioner of the profession), then his work becomes academic in the derogative sense of the word.
1.8 STUDY AREA
This study area is located in Edo State, Nigeria. It is one of the most prominent river which serve as a source of livelihood to the inhabitants.
1.8.1 Location and Size
The study area lies between latitudes 060 011N and 060 071N of the equator and longitudes 050 041E and 060 011E of the Greenwich Meridian. The Ikpoba river drains approximately 730.2km2 (Odemerho, 1992). The river has a maximum stage discharge of 320cm and a minimum of 191cm (Owena River Basin Authority 1996). All or parts of the following communities are within the drainage basin: Iruhe, Urukosa, Uzuolla, Obazagbon, Oloh, Ugbessan, Morgan Camp, and Ijaw Camp 1 and 2. These communities from part of the Benin City Metropolis area and are primarily suburban residential. Because of their proximity to Benin City Metropolitan and the presence of remaining developable land, they have been under increasing pressure to continue development (Mogborukor, 2009).
The Ikpoba river basin is underlain by deeply weathered sedimentary rock that is often referred to as the Benin formation which is of the Miocene-Pleistocene age. This Benin formation consists of yellow and white sands sometimes containing cross-bedding. Iron stained gritty beds and sandy clay lenses may occur in the formation. The Benin formation has over 90% sandstone with shale interactions (Murat, 1970). The sandstone are poorly exposed along the river bank although their monopoly is conspicuous as the form gently sloping red sandy soils. The formation is coarse grained, gravelly, locally fine grained, poorly sorted, sub-angular to well rounded and bears lignite streaks and wood fragments (Azeez, 1989). It is a continental depositional environment. Very little hydrocarbon has been associated with the formation.
Another geologic formation that is readily disenable at the river banks resemble the Imo shale group. The shales are dark, fissile and increases in thickness to the base. They alternate with beds of fine to medium grained iron-stained sandstones. A portion of river channel, as one examines the long profile further consists of mudstone that resembles the Nsukka-formation age, lithology and environment of deposition. Some part of the river channel and flood plains contains alluvia sands. This only covers a small portion of the studied area. The alluvial deposits consist of very fine sands and clays. They are rich in nutrient due to deposition. The alluvial soils are derived from mass wasting of the sedimentary rocks. The sediments are carried in suspension and are deposited at the river banks (Mogborukor, 2009).
1.8.3 Relief and Drainage
The topography of the basin is mainly an undulating plain with a relative relief metres (Odemerho, 1992). Slopes range between 1.50 and 30. Relief in the basin is as a result of fluvial processes that has led to the dissection of the flat-lying sedimentary units. Therefore, the drainage divides are the points of maximum relief. Generally speaking, the basin is a flat and monotonous a gradational plain without any marked topographical features. The basin geographically speaking, borders the southwest of Esan Plateau. The generalized contours, based on the interpolation of one (1) kilometer topographical sheets reveals that on the whole, the basin slope is from north to south as well as slightly from northwest to east. Their smoothness get disturbed when they lie athwart a river course (Mogborukor, 2013). There is thus little lithological complexities. So imperceptible and unrecognizable is the belief that is eaves little impression about any topographic variation in the mind of the observer. The noticeable expression of relief are the sandy wastes and little mounds created by shifting river courses, marshy (Shallow depressions filled by water during rains), luxuriant shrubs and river bluffs.
The Ikpoba River takes its source from Esan Plateau (Fuggle, 2011). Rivers Osiomo and Ohunwan constitute major tributaries to the river. However, they flow across a small section of the study area. The entire stream course is bordered by floodplains extending from approximately 15metres to 185metres on either bank, except in headwater reaches where the floodplain is observed on only one bank (Odemerho, 1992). The river exhibit dendritic drainage pattern. The occurrence of this drainage system indicates homogenous, uniform soil and rock materials and is typified by the landform of soft sedimentary rocks, and old dissected coastal of the Ikpoba river can be seen in its correct perspective when swollen by the annual rains, when the river overflows its banks. However, in the dry season, the waters are confined to its channels, some are so shallow that it can be wadded through. Over the years, the Ikpoba river has consistently moved east wards in the Benin city urban reaches. This has led to leaving behind abandoned dry channels. The river stretches over a distance of 52kiometres.
1.8.4 Soil Characteristics
The soils have been classified as ferrallitic, being highly leached and having high proportion of kaolinite and free iron oxides, but general without a lateritic iron pan layer (Areola, 1990). According to the Nigerian soil map, prepared by the Federal Survey (1967), the soil type can be categorized as feral soils on loose sandy sediments. Vine (1970) grouped the soils of the area into Alagba series. The soils were also classified as ferrallitic soils in which the weather able minerals have undergone complete decalcification with resulting materials consisting mainly of sequioxides.
The soils of the study area are generally referred to as structure less, because they are devoid of cementing agents (Ogidiolu, 2006). This soils have also been referred to as low activity clay soils. Consequently, the nitrogen content of the soils is very low on account of low organic matter content. The acidic condition of the soil is reflected by a pH value of 5-6 in top soils but decreases with depth (Udo and Sobulo, 2011).
The studied area is located in the humid tropics under the Aw climate of Koppen’s 1918 classification. The basin proper experienced the tropical moist climate (Odemerho, 1992). The annual rainfall in the areas exceeds 2000mm (Ogidiou, 2006), with a bimodal distribution. The first peak occurs in July with monthly precipitation of 344.7mm. the second peak monthly precipitation of 457.2mm occurs in September. Most of the storm are convective outbursts and they have high short term intensities (Ogidiou, 2006). Two distinct seasons are experienced in the basin (Mogborukor, 2013), which are the dry and wet season. These seasons are controlled by the position of the Inter-Tropical Discontinuities (I.T.D) whose movements are reflected in the corresponding shifts rain belts. The wet season begins in March and reaches its first maximum in July and the second in September. Both maximum are separated by a brief spell referred to as the “August Break”. The dry season is short and may last from November to February. In any case, rainfall is experience in al the months of the year with January and December being the driest. Temperature is also fairly uniform in the basin. While the highest mean monthly temperature of 29.10c is recorded in March, the lowest (24.40c) is recorded in June.
The study area exhibit the moist tropical rainforest as natural vegetation (Keay, 2002). The high forest has been removed and destroyed in most parts by human activities which are mainly farming and lumbering (Ogidiolu, 2006). The study area occupies an area previously covered by climax tropical rainforest with a character by climax tropical rainforest with a characteristic vertical layered canopy, extensively described in the literature (Keay, 2002). Fresh water swamp forests mainly in the form of riparian vegetation fringe the river channel. But today, the rainforest is nothing more than a gallery of riparian forest bordering stream channels and valleys. The rest of the catchment areas remain a mosaic of farm lands, fallow bushes at various stages of maturity, and urban uses.
Today the primary forest is completely replaced by secondary forest resulting from prolonged agricultural activities. The remaining landscape in the basin is excessively denuded by fire and cultivation under high population density. Some of the predominant tree species are vertex doniana, Terminalia glaucosens, Terminal macroptera, and Afzelia African. Tall grases and herbs are also found and the dominant species include pennisetun purpureum, monocybium ceresiforeme and chromoaena Odoratum.
On a mesoscae, the study area presents uniform physical environment of geology, relief, soil, climate, and vegetation, reducing the inherent variability attributable to these factors. On a microscale however, these factors produce a geomorphology that, while dynamic, has enough large-scale regularity to allow fluvial variables to be examined, explained and linked with channel modifications within the context of catchment disturbance by human activities.
The population of Ikpoba River Basin has been increasing steadily since 1952. For example, the cumulated figure for the studied basin was 364,000 in 1952, and by 1963 it rose to 652,000 (Onokeraye, 1980). In 1991, the figure was put at 922,804 (Census News, 2007). Currently it is estimated that the population is placed at 3.1million people (Federal bureau of statistics, 2015 estimate. And because population increase is intimately tied to resource use, this rapid population has had its effects on the fluvio-geomorphic characteristics in the basin through agricultural practices. The type of interruptions in the geomorphic equilibrium caused by agricultural land use consequent upon population pressure on the land are best discussed under human impact on the vegetation. Continued population growth in the basin, despite the local existence of Malthusian- type and medical checks, is likely to result in further denudation of the plant cover. In general terms, the extent of man’s disturbance of the vegetation depends on population numbers, duration of settlements and levels of technology[whitlow, 2007].
1.8.8 socio-economic activities.
The main socio-economic activities of the people in this area is farming. Farming as an occupation is partly responsible for the anthropogenic landscape. The people of Ikpaba in Edo State engage mainly in cassava farming, they also engage in cash crop farming, such as rubber tapping and palm nut collection for palm oil production and lumbering. Along the banks of Ikpoba river banks, there exist various mining sites for stones, sharp and plastering sand. The sand stones and plastering sand are manually dredged along the bank of Ikpoba river. This mining activity is one of the major occupations of the inhabitants of Ikpoba river and its environs.
Agriculture which involves the production of a wide variety of livestock, as well as storage, transportation and marketing of agricultural products remains the oldest and the most rife industry of man in the world. Till today, globally man needs agricultural products for foods, shelter, for earning case income and for operating, the industry especially the agro- industries.
The hydromorphic soil along the banks of Ikpoba river are alluvial soils that is good for cultivation of maize, okro and water yam. These crops are mostly planted at the bank of Ikpoba river in the month of December to January and harvested before the commencement of heavy rain in May/June.
Traditionally, Ikpoba river was an agro- settlement whose inhabitants were virtually subsistence farmers. With the establishment of schools, churches, small scale trades the post office and heath institutions, Ikpoba river began to have a population that consist of a large proportion of farmers and farming assistants and a small proportion of a non-farm population.
1.9 scope and limitation of the study.
The scope of this research tries to cover Ikpoba river and its environs especially the rural and riverine areas which have natual forest vegetation and fertile land for farm practices and agricultural activities. Emphasis is placed on the conservation of water and vegetation resources in the urban area in order to conserve the area’s biodiversity.
The scope of the study was initially designed to cover all the quarters and villages along Ikpoba river. However, because of time and financial constraints, the scope was scaled down. In this regard only selected quarters were covered in this study. The time was also short to carry out the research work coupled with academic work. Inability of the researcher to access some remote areas as well as language and communication barrier were some of the challenges encountered during the course of this research work.
These limitations notwithstanding, the data generated from this study and research finding will be of invaluable assistance to the forest guards, water resource personnel, River Basin Authority, fishermen, water guards, Ministry of Environment and water resources and conservation Management authorities to reduce the growth of urbanization (cutting down of trees along Ikpoba river bank for mining and construction activities) which have degraded the natural vegetation and water resources of the natural environment.