The study examined the effects of drainage networks on floods in Nigeria metropolis, Nigeria. The rapid increase in urbanization without corresponding infrastructures in the city of Nigeria has led to increased incidences of flood as the available drainage channels cannot contend with the volume of storm water. In view of this, the study established gauging stations for the measurement of drainage run off using measuring steel tape. And the volume of flood water was measured using stop watch method (Velocity of flow) and copies of questionnaire were administered to 400 households proportionally to the seven sample units. In view of the study objectives, it determine the relationship between drainage width and depth and floods. In addition, varied descriptive statistics tools were used to give a spot on assessment and understanding of the variables of interest. In view of the response of the gauging and physical measurement, it was established that Nigeria experience heavy rainfall due to poor drainage facilities The result revealed that about 47% of the respondents said flood occur every year in their zone and 41.75% said it occurred most parts of the year. The frequency of flood is compounded with it’s intensity as over 59% of the sampled population agreed that flood of the sampled population agreed that flood intensity is very high in Nigeria. The result further showed that the factors of flood occurrence in the study area is linked to heavy rainfall (26.3%), inadequate drainage channel (22%) poor physical planning (15.5%) among others. On the perceived causes of inadequate drainage channel, the result indicated that abuse of land use plans (28.7%) was a major factor followed by poor monitoring and evaluation of project (21.5%). the study also revealed that the drainage were very narrow and shallows as shown in frequent floods in the city. The incessant flood often leads to water inundating compounds (64.5%), preventing people from going out (11.25%), distortion of the scenic beauty of the environment (6.25%), landslide (4.75%). Based on these findings, the study recommended that since Nigeria is located in a tropical zone characterized by heavy rainfall the government should take proactive measure to mitigate storm water. The present drainage systems should be cleared with shovel by the people on a regular basis to allow for a free flow of storm water. State department of town planning should live up to their bidding by ensuring total compliance to urban ordinance to forestall incessant floods and destruction of properties in the city of Nigeria.
1.1 BACKGROUND TO THE STUDY
Cities the world over are the dominating forces in the organization of human population. As the world most crowded places, cities continue to show increase in urban population. This increase leads to a growing urbanization trend. Duru and Nnaji (2008) defined urbanization as the increase in the population of cities in proportion to the region‟s rural population. Urbanization is the outcome of social, economic and political developments that lead to concentration and growth of large cities, changes in land use and transformation from rural to metropolitan pattern of organization and governance. Rapid growth of towns and cities has been common feature of the developing world (Aderamo, 2008).
Although urbanization is the driving force for modernization, economic growth and development, there is increasing concern about the effects of expanding cities, principally on human health, livelihoods and the environment. The implications of rapid urbanization and demographic trends for employment, food security, water supply, shelter and sanitation, especially the disposal of wastes (solid and liquid) that the cities produce are staggering (United Nations Conference on Environment and Development, 1992). The process of urbanization is believed to be connected with levels of development and some assert that, for a country to develop there is the need for an increased level of industrialization as it is generally accepted that there cannot be urbanization without rapid economic growth (Tettey, 2005). The pattern of urbanization in developing countries, particularly Africa, however, is creating some concern that it may be generating a lot of development problems in the process of its growth.
One of the daunting challenges facing African countries in the wake of unprecedented urbanization during the last few decades is the planning and management of physical infrastructure and the urban environment. As urbanization gathered pace in most developing countries, the problem of inadequacy of infrastructure services and deteriorating urban environment became enormous (Sule, 2009). These problems range from poor housing conditions, inadequate infrastructure, to squatter settlements (Arimah, 2002).
Spurred by the oil boom prosperity of the 1970s and the massive improvements in roads and the availability of vehicles, Nigeria since independence has become an increasingly urbanized and urban-oriented society. During the 1970s, Nigeria had possibly the fastest urbanization growth rate in the world (Sule, 2009). Because of the great influx of people into urban areas, the growth rate of urban population in Nigeria in 1986 was estimated to be close to 6 percent per year, more than twice that of the rural population. Specifically, while only 7% of Nigerians lived in urban centers in the 1930s, and 10% in 1950, by 1970, 1980 and 1990, 20%, 27% and 35% respectively lived in the cities (Okupe, 2002). Over 40% of Nigerians now live in urban centers of varying sizes. Like other developing countries, the rapid growth in urban areas in Nigeria is a „sword of two edges‟ (Sule, 2009). While increasing human capital increased the economic status of the country, the growths of large centers had outpaced government capacity to meet the increasing demand for the provision of basic infrastructural facilities and services. These are manifested in poor investment in roads, housing, water supply, electricity, waste disposal mechanisms, adequate drainage systems etc. (Sule, 2007; Aderamo, 2008; Jimoh, 2008). These problems have continued to persist and made worst due to non-compliance to planning ordinances (Sule, 2010). Appropriate management of drainage systems requires knowledge relating to the system boundary, system resources, interactions between adjacent systems and allowable limits, or thresholds, for each resource. Each of these elements will be unique to the particular system under consideration, and each system must be assessed on its own merits. Flooding has been identified as one of the major factors that prevent Nigeria growing population of city dwellers from escaping poverty and stands in the way of United Nations goal of achieving significant improvement in the lives of urban slum dwellers by 2020 (Action Aid, 2006)
Nigerian coastal cities are daily inundated with flood waters, and millions of properties have been destroyed and lives lost (Eze, 2008). Poor drainage systems are often associated with street flooding, and this has become critical environmental problems in coastal cities of Nigeria such as Lagos, Port Harcourt, Ondo, Warri, Uyo, and Nigeria (Eze, 2008). These towns which are quite close to the Atlantic Ocean experience heavy flooding especially during the rainy season. However, it is not waters from the Ocean that usually floods these cities but the heavy rains, and the low nature of the topography and the poor drainage networks. Aderamo (2008) listed land use problems, increased paved surfaces, river channel encroachments, poor waste disposal techniques, physical development control problems, gaps in basic hydrological data and cultural problems as major causes of street flooding in Nigerian cities.
1.2 STATEMENT OF THE RESEARCH PROBLEM
Worldwide, there has been a rapid growth in the number of people killed or seriously impacted by storms and floods and also in the amount of economic damage caused; a large and growing proportion of these impacts are in urban areas in low- and middle-income nations. For instance, in Nigeria, flooding affected more than three million people in selected urban areas between 1983 and 2009 (Environmental Management Disaster Database). Poor urban infrastructural development and planning is likely to have been a factor in much of this, but even if it was not, it is proof of the vulnerability of urban populations to floods and storms whose frequency and intensity is likely to increase in most places. Henderson (2004) revealed that the level of risk and vulnerability in urban areas of developing countries is attributable to socio-economic stress, aging and inadequate physical infrastructure. Indeed, according to Satterthwaite, Mark, Saleemul, Reid and Romero (2007), hundreds of millions of urban dwellers have no all-weather roads, no piped water supplies, no drains and no electricity supplies; they live in poor quality homes on illegally occupied or sub-divided land, which inhibits any investment in more resilient buildings and often prevents infrastructure and service provision. A high proportion of this are tenants, with very limited capacities to pay for quality housing – and their landlords have no incentive to invest in better-quality buildings. Most low-income urban dwellers face serious constraints in any possibility of moving to less dangerous sites, because of their need to be close to income-earning opportunities and because of the lack of alternative, well-located, safer sites.
Douglas et al (2008) also report that many of the urban poor in Africa face growing problems of severe flooding; they further buttressed the fact that increased storm frequency and intensity related to climate change are exacerbated by such local factors as the growing occupation of flood plains, increased runoff from hard surfaces, inadequate waste management and silted up drainage. Askew (1999) reiterated that floods cause about one third of all deaths, one third of all injuries and one third of all damage from natural disasters globally. Generally, flood events are attributed to global warming, climate change, ocean swell/surge and torrential rains. Although
flood hazards are natural phenomena, damage and lose from floods are mostly the consequences of urbanization without corresponding infrastructural restructuring (Brooks, 2003). Flooding is the most common environmental hazard in Nigeria (Etuonovbe, 2011). Flood disaster is not an ancient phenomenon in the country, and its destructive tendencies are sometimes enormous. Reports have it that serious flood disasters have occurred in Ibadan (1985, 1987 and 1990), Osogbo (1992, 1996, 2002), Yobe (2000) and Akure (1996, 2000, 2002, 2004 and 2006); the coastal cities of Lagos, Port Harcourt, Nigeria, Uyo, Warri among others have severally experienced incidences that have claimed many lives and properties worth millions of dollars (Olajuyigbe, Rotowa and Durojaye, 2012).
The intensity of flood problems over time and space in Nigeria urban centers is closely related to the rapid rate of urban expansion especially where the simultaneous provision of adequate run-off disposal systems are lacking as is the case of most Nigerian cities (Abaje and Giwa, 2008).The implications of recent flooding in Nigerian cities include, among others, loss of life and properties, spread of diseases, deformed livelihoods, assets and infrastructure (Adedeji, Bashir, Bongwa and Oladesu, 2012).
Eze (2008) using both questionnaire and secondary data in the analysis of the history and causes of flood incidence in the city of Nigeria opined that no year passes without flooding in the city claiming lives and properties; on the average four lives were lost yearly to flooding. Eze attributed flood occurrence to expansion of residential areas and the multiplications of paved surfaces including roads and sidewalks. Offiong and Eni (2007) using both conventional questionnaire and secondary data corroborated these claim by observing that the damage to materials is quantified to be well over 115.76 million naira per year. The main factors of flooding in the city of Nigeria in the view of Ofiong and Eni, are increasing demand for concrete surfaces for buildings which has increased surface runoff, and waste waters that have increased the volume of water in rivers, streams and drainage channels. Afangideh, Ekpe and Offiong (2012) examined the implication of changing rainfall pattern on building loss in Nigeria. Rainfall data for the study were collected from the Nigerian Meteorological Agency (NIMET) and Margaret Ekpo International Airport, Nigeria. While data on cost of building loss to flood for the previous 20 years were gotten from the inhabitants of the flood prone areas in Nigeria. The result from their study revealed that annual rainfall intensity with beta coefficient of 0.437 has more implication on cost of building loss to rainfall in Nigeria than annual rainfall duration, with beta coefficient of -0.063. Flooding in urban areas is not just related to heavy rainfall and extreme climatic events; it is also related to changes in the built-up areas themselves. In the case of Nigeria, the problems of street flooding began when some socio economic and anthropogenic activities gained momentum as a means of face lifting the city as State Capital. The influx of people from both rural and adjoining states led to increased demand for housing. Houses were hurriedly built to meet the burgeoning demand for shelter. This alters the aesthetic image of the city as buildings were erected anyhow and anywhere (Sule, 2004), which degenerated into the „ugly face of Canaan city‟ (Iquot, 1982). Today in spite of the fact that Nigeria is acclaimed to be one of the cleanest cities in Nigeria, the menace of flooding has more than double.
However, none of these studies measured the dimensions of drainages and their role in flood events as majority of reviewed studies only mentioned poor drainage system as a factor of flood events in Nigeria. This is the gap the research intends to fill. It is against this background that this research intends to answer the following questions:
- What is the frequency and intensity of floods in Nigeria?
- What is the spatial distribution and intensity of drainage networks in Nigeria metropolis
- What is the effect of drainage width and depth on flood in Nigeria?
- What is the environmental state of drainage network in the metropolitan city of Nigeria?
1.3 AIM AND OBJECTIVES
The aim of the study is to assess the drainage network in relation to flood occurrences in Nigeria. Specifically, the objectives of the study are to:
- examine the intensity and frequency of floods in Nigeria
- evaluate the geometry of selected drainage channels in Nigeria
- determine the relationship between drainage width and depth and floods
- assess the drainage system in Nigeria
1.4 SCOPE AND DELIMITATION
This study was restricted to selected areas of Nigeria Metropolis that are prone to flood occurrence and one area with relatively little or no flooding and it assessed the capability of drainage networks to effectively handle run off volume in the area. The study was conducted in seven purposedly selected locations which include the Cross River University of Technology (CRUTECH) staff quarters, Akim Quo, Ediba, Yellow Duke, MCC Road, Esuk Utan Junctions and satellite town as the control. These locations are selected because they have a history of frequent floods especially during the rainy seasons. In addition, flood prone areas are largely characterized by poor planning as compared to the control. The control (Satellite town) could be said to be an area of both high and medium income earners. In this zone, squatter structures are not common. The study covered duration of six (6) month, that is between March to September, 2014 which falls within the rainy season in Nigeria (Offiong and Eni, 2007).
1.5 JUSTIFICATION OF THE STUDY
Flooding has been identified as one of the major factors that prevents Africa‟s growing population of city dwellers from escaping poverty and stands in the way of United Nations 2020 goal of achieving significant improvement in the lives of urban slum dwellers (Action Aid, 2006). This is because many African cities lack the infrastructures to withstand extreme weather conditions. Poor urban planning together with other urban governance challenges contribute to making African urban slum dwellers most at risk. In Nigeria for instance studies have been conducted to establish the relationship between urbanization and flooding. Many of these studies emphasized the implications of flooding on the environment and socio economic wellbeing of affected cities and the population. Offiong and Eni, (2007) concluded in their study on the effects of urban floods on infrastructure in Nigeria that rainfall duration was the major determinant of runoff volume which leads to drainage infrastructure destruction in the city. Researches of Ahern, Few, Kovats and Matthies (2004); Abaje and Giwa (2007); Ladan (2007); Offiong et.al, (2008); and Eze (2008) summarise that the twin factors of poor urban planning and increased paved surfaces are the main causal factors that increase the frequencies of floods in Nigeria.