Summary: In this article, we highlight the causes of flooding as well as its effects and suggest measures for addressing the problem of flooding in Nigeria. In other words, the aim of the article is to identify the factors causing flooding in Nigeria, examine the effects of flooding in Nigeria and suggest measures for controlling flooding in the country. This review is important because understanding the causes of flooding, the effects o flooding, and measures for control of flooding provide necessary knowledge for the effective management of flooding in Nigeria.
Flooding is one of the major environmental crises of the 21st century, especially in coastal areas. This is because of the general rise in sea level globally, due to global warming.
In Nigeria, the saturated nature of the wetlands in the Niger Delta makes the region most vulnerable to flood events.
Periodic floods occur on many rivers, forming a surrounding region known as flood plain. Rivers overflow for reasons like excess rainfall.
Generally floods occur when ponds, lakes, riverbeds, soil and vegetation are unable to absorb all the rain water. Rain water then runs off the land in quantities that cannot be carried within stream channels or retained in natural ponds, lakes and man-made reservoirs. Consequently much of the rainfall (sometimes as high as 30 percent) becomes runoff.
It is important to note that natural floods can be quite beneficial to nature. The thing that makes natural floods a disaster is when flood waters occur in areas populated by humans and in areas of significant human development. Otherwise, when left in its natural state, the benefits of floods outweigh the adverse effects.
In the next section, we take a look at the causes of flooding in Nigeria.
There are two primary causes of flooding in Nigeria. These are climate change, and building on floodplains.
Climate change has brought about an increased severity and intensity of rainfall most especially in the coastal areas across the Nigeria. Furthermore, new developments (physical structures) on floodplains increase the risk of flooding downstream.
Climate change impact has resulted in increased rainfall severity and intensity in coastal regions across Nigeria. High intensity rainfall for a short period of time. Furthermore, climate change has brought about global warming with attendant melting of ice caps and global rise in sea level.
Urban Encroachment of Flood-prone Areas: The development of physical structures on flood plains has reduced infiltration surfaces through preponderance of concretization. This increase in the level of concretization and asphalting of the land-surface has resulted in enhanced runoff from rainfall while diminishing the infiltration rate of the soil. The implication is that more water from rainfall is available on the surface of the earth to run as surface flow which we call flood. At the same time, the infiltration capacity of the soil is reduced due to the preponderance of urban infrastructure such as buildings, asphalted roads, concrete car parks and other paved surfaces.
Collapse of dam and/or other reservoirs has also been responsible for some cases of flooding in Nigeria.
Another cause of flooding in Nigeria is blockage of rivers and other drainage channels. Moreover, absence of drainage channels also constitute another cause of flooding especially in urban settlements.
The topography of the area also contributes to the incidence of flooding in Nigeria. Perhaps, this explains why low-lying regions of the Niger Delta (and Lagos) are more vulnerable to flooding when compared to other regions of the country.
Flooding has resulted in contamination of water supplies. Sometimes this affects the only source of drinking water for the community. Consequently, clean drinking water becomes scarce. Unhygienic conditions and Spread of water-borne diseases becomes inevitable. Therefore, the contamination of potable water supplies during a flood has had immediate health effects upon affected people and animals.
In extreme cases flooding may cause a loss of life.
Torrential rains pushed rivers over their banks, collapsed mud houses and washed away livestock. Damage bridges and caused a dam to overflow, submerging buildings, displacement from homes, the loss of personal valuables and the ongoing fear and insecurity caused by the experience.
Urban flooding of residential areas damage buildings and destroys lives and properties and causes the obstruction of traffic. It has also caused loss of man-hours, loss of revenue, water-logging of playing fields and recreational parks, pollution and contamination of urban water sources, and general environmental degradation.
The economy can also be severely affected by flooding. Businesses may lose stock, patronage, data and productivity and disruption to utilities and transport infrastructure can have knock-on effects to a wider area. Tourism, farming and livestock can equally be affected. Vital infrastructure may also be damaged or disrupted. Electricity and gas supplies can be interrupted to individual properties but also to wider communities if sub stations and transformers themselves are flooded. Road links, railways, canals etc., may be blocked causing disruption to the wider transport network and accessibility severely disrupted for local inhabitants, especially amongst those considered most vulnerable and loss of communications networks.
A significant effect of flooding in Nigeria is its impact on agriculture. Flooding has damaged farmlands, which often translates to crop failures, food shortages, price hike of food items, hunger, malnutrition, starvation, dislocation, displacement, broken families, increased crime wave and societal restiveness.
1. There are some strategies that can be employed to lessen or eliminate the impacts of flooding on society and environment. In this section, we examine some of these strategies.
2. Construction of artificial levees along river banks which are vulnerable to flooding.
3. De-silting of urban drainage conduits (gutters)
4. Tree planting and cover-cropping of unstable slopes to reduce run-off coefficient, which in turn reduces slope wash, flooding and gully erosion
5. Enforcement of Town Planning Laws to avoid building of structures on natural/artificial drainage channels
6. Periodic dredging of silted rivers
7. Rain water harvesting
8. Building of flood control dams and reservoirs
10. Provision of adequate and sizeable drainage network for effective evacuation of runoff after heavy rainfalls
11. Increase in urban open spaces (lawns and parks) to encourage infiltration
Contemporary flood problems are largely the product of climate change which in itself is the consequence of human mismanagement of earth’s resources. Therefore, in order to address the current flood problems in Nigeria, there is the need to mitigate and possibly reverse climate change mainly by reducing greenhouse gas emissions and re-appraising our use of earth’s resources. Furthermore, there is the need to re-appraise the drainage network in most Nigerian cities in order to keep pace with recent urban expansion.
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