THE EFFECT OF FLOOD ON ROADS DURABILITY IN NIGERIA
Background to the study
Globally, disasters are said to have devastating effect on economic development, livelihoods, agriculture, and health, social and human life (Wood, 2005). They are sudden, accidental events that may cause deaths or injuries. Abam (2006) defined flood as a large volume of water which arrives at and occupy the stream channel and its flood plain in a time too short to prevent damage to economic activities including homes. It is a natural hazard like drought and desertification which occurs as an extreme hydrological (run off) event (Nwafor, 2006). It could also be seen as the inundation of an area not normally covered with water, through a temporary rise in level of stream, river, lake or sea (Emodi, 2012).Prolonged rainfall events are the most common causes of flooding worldwide. Floods are generally regarded as extreme hydrological events, where there is excess of water which may have devastating effects. According to Ayoade (1988), flooding in the tropics is regarded as partly or wholly climatological in nature as they result from torrential rainfall.
Flood disaster is not a recent phenomenon in Nigeria and its destructive tendencies are sometimes enormous. According to the United Nations Environment Program (UNEP, 2006), flooding is one of the major environmental crises ravaging the universe within the century and the millennium. This is especially the case in most wetlands of the world. The reason is attributed to the general rise in sea level globally, due to the global warming as well as the saturated nature of the wetlands in Nigeria. Periodic floods occur on many rivers, forming a surrounding region known as flood plain. Within the cities, human activities such as rapid industrialization and urbanization, population growth, exploitation of natural resources and location of infrastructures (dams, piers and lands) exacerbates the occurrence of floods. Askew (1999) reiterated that floods cause about one third of all deaths, one third of all injuries and one third of all damages from natural disaster.
Floods occur in Nigeria in three main forms; coastal flooding, river flooding and urban flooding. Coastal flooding occurs in the low lying belt of mangrove and fresh water swamp along the coast (Folorunsho and Awosika 2001; Ologunorisa, 2004). It is typically a function of storm surge, waves (driven by wind) and heavy rainfall. River flood is a function of rainfall and run off volumes within the river valley. It occurs in the flood plain of larger rivers where sudden short-lived flash floods are associated with rivers in the land areas where sudden heavy rains can change them into destructive torments within a short period (Folorunsho and Awosika 2001; Ologunorisa, 2004). Urban flooding on the other hand occurs in towns, on flat or low lying terrains especially where little or no provision has been made for surface drainage or where existing drainage has been blocked with municipal waste, refuses and eroded soil sediments (Ali, 2005).
Oderrerho (2004) and Nwafor (2006) identified twelve (12) causes of urban flooding. They include; Surcharges in water level due to natural or man-made construction of flood paths, sudden dam failures, inappropriate land use, deforestation of catchment basins, reclamation, construction sites and solid waste, inadequate drainage capacity to cope with urbanization and excess encroachment in flood ways. Urban flood problem is a global experience but the management practices differ according to prevailing technologies and aptness in planning concern.
Nott (2006), points out that flood events may not be considered a natural hazard unless there is a threat to human life and property. The most vulnerable landscape for floods are low lying coast and deltas, and small basins subject to flash floods. Empirical researches (Okereke, 2007; Kolawole et al., 2011) have highlighted the basic consequences of flooding as; loss of human lives, submerging of residence and streets, inflow of sewage, municipal pollution and health hazards, traffic obstruction, aesthetic discoloring, cleanup cost and disruption of services, infrastructural damage, and economic loss.
In flood events, socio-economic life and livelihood of the affected people may be distorted, in most cases farmlands and livestock are submerged which are the major source of people’s livelihood. Flood losses are devastating as many never get recovered after the flood recedes. Vulnerable communities suffer great losses in events of flood, especially when the flood is unprecedented. Hunger, famine, disease and epidemic outbreak are usually resultant impacts of flood (Mmom and Aifesehi, 2003). Malaria and typhoid outbreaks after floods in tropical countries are common. It has been estimated that in India and Bangladesh 300 million people live in areas that are affected by floods (Nott, 2006).
It is well known that the rate of road deterioration increases if the water content of the granular material increases. In rigid pavements (i.e., concrete), temperature gradients across the concrete slab can cause structural defects.Diefenderfer, et al. (2002). Diefenderfer, et al. (2002) presents no less than six adverse effects related to excess water: reduction of shear strength of unbound materials, differential swelling on expansive sub grade soils, movement of unbound fines in flexible pavement base and sub base layers, pumping of fines and durability cracking in rigid pavements, frost-heave and thaw weakening, and stripping of asphalt in flexible pavements. On the positive side, ensuring proper (optimal) water content greatly improves packing of the road during construction, and may also increase its resilience when trafficked, even though this effect is often neglected. It is generally desired to keep the road as close to or less than optimum water content as possible over time as water and road construction do not make for a harmonious couple.Dawson, A.R. (2009).
According to McRobert, J. et al. (2000), Drainage is often described as the central and most important aspect of design, construction and maintenance of any road, including unsealed roads. Drainage of unsealed roads can be of even greater importance because lower quality design and construction standards and marginal materials are generally used, which are more permeable to water. Poor drainage will reduce the life of the pavement and have serious environmental impacts if left unchecked. There are many approaches to reducing erosion of exposed surfaces associated with unsealed roads, such as side drains, cut-off contour banks and batter slopes. Any road will readily concentrate runoff, so there is a need to design and construct roads to allow for frequent and safe discharge.
During the rains, part of the rain water flows on surface and part of it percolates through the soil mass as gravitational water until it reaches the ground water. Some water is retained in the pores of the soil mass and on the surface of soil particles which cannot be drained by normal gravitational methods and this retained water is termed Held water. It is required that the surface water from the carriageway and shoulder should effectively be drained off without allowing it percolate the sub grade. The surface water from adjoining land should also be prevented from entering the roadway. The side drains should have sufficient capacity and longitudinal slopes to carry away all the surface water collected. This improper drainage system causes the failure of road pavements due to many reasons such as increase in moisture content, decrease in strength, mud pumping, formation of waves and corrugations, stripping of bitumen, cutting of edges of pavement and frost action.
1.2 Statement of Problem
Incidents of flood are not a recent phenomenon to people of Makurdi as they have been living in flood prone areas for centuries. Like most urban areas of the third world, Makurdi has experienced accelerated population growth which has led to changes in the land use activities. Land use changes in particular, have a direct impact on the magnitude and behavior of floods (Civco et al 2002). Flash floods are common features in Nigeria during the rainy season(May-October) but the country’s flood event of the year 2012 have been described as the most devastating in over 40 years.
Two major events took place between the months of September and October 2012 in Nigeria, namely the Ladgo Dam flood in Adamawa State, and the River Benue and Niger adjoining States floods (Niger and Benue States). The event pushed most of the country’s rivers over their banks and submerged hundreds of kilometers of urban and rural land. This resulted in widespread devastating flood disaster that hit the country cutting across major cities in about 14 states that borders the Niger-Benue River. The flood submerged houses and several transportation routes throughout the affected areas nationwide. Overall, an estimated 1.3 million people were displaced and about 431 people lost their lives with several hectares of farmland destroyed (MISNA, 2012). Though the unusually large flood was predicted by the Nigeria Metrological Agency NIMET, government at all tiers failed to act on time, resulting in the worst humanitarian crises in Nigeria since the civil war in 1967-1970.
Despite the expected increase in frequency and magnitude of flood in the Nigeria and invariably Makurdi, few impact assessment studies on the socio-economic livelihood of the people have been undertaken to establish the underlying causes of their vulnerability. In the absence of comprehensive data and information, the measures to cope with flood have remained ad hoc.
Objective of the study
The main objective of this study is to examine the effect of flood on roads durability in Nigeria. Specifically, the study aims to:
Ascertain the causes of flood in Nigeria
Examine the socio-economic effect of flood in Nigeria
Examine the effect of poor drainage on flood incidents in Nigeria
To ascertain if flood affects road durability in Nigeria
What are the causes of flood in Nigeria ?
What is the socio-economic consequences of flood in Nigeria?
Does poor drainage system the reason for flood incident in Nigeria?
Does flood affect road durability in Nigeria?
significance of the study
The importance of this research cannot be overemphasized because of its immense significance to different groups of people who are in need of information that it will provide. Its significance includes the following:
The study will enable the management of flooding and provide an in-depth understanding and knowledge of the flood prevention strategies available so that they can adopt them adequately.
The study will also serve as a source of secondary data for students and scholars who intend to carry out similar studies in the future.
Scope/Limitation of the scope
The scope of this study in terms of its content is restricted to the flood effects on road durability with special attention to Makurdi the state capital of Benue state.