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The Effect Of Flood On Roads Durability In Nigeria
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CHAPTER ONE
INTRODUCTION
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.
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