Flooding is a perennial problem caused by severe and torrential rainfall or rivers and oceans overflowing its banks as a result of high tides, thereby submerging land areas. In other words, floods could arise from a very large amount of water that has overflowed due to heavy downpour of rainfall or from a source such as river or a broken pipe onto a previously dry area. These are very common occurrences in coastal towns and other areas of the world like the Niger Delta part of Nigeria.

Rivers State, for instance, experiences flooding regularly and is prone to perennial flooding either when there is severe rainfall or high sea tide occasioned by increase in volume of rivers or the ocean.

Flooding takes place when lakes, ponds, river beds, soil and vegetation can not absorb all the water; water then runs off the land in volumes that can not be carried within stream channels or retained in lakes, natural ponds and man-made reservoirs. About thirty per cent of all precipitation becomes run off and that amount might be increased by water from melting glaciers.

Flood that rises rapidly with little or no advance warning is called a flash flood. Flash flood normally results from extensive rainfall over a relatively small area or if the area was already saturated from previous precipitation.

Flooding can be exacerbated by increased amount of impervious surface or by other natural hazards, wild fires or deforestation which reduce the supply of vegetation that can absorb rainfall. Moreover, flooding may occur due to severe winds over water, unusual high tides, tsunamis or failure of dams, retention ponds or other structures that retain water.

Flood also occurs in rivers when flow exceeds the capacity of the river or the sea channel particularly at bends or meanders. It often causes damage to homes, communication and electrical installations, businesses etc if they are located in natural flood plains of seas or rivers.

From time past, people have lived and worked by the water to seek sustenance and capitalise on the gains of cheap and easy travel and commerce by being close to the water. The fact that humans continue to inhabit areas threatened by flood damage is an evidence that the perceived value of living close to the water supersedes the cost of repeated periodioc flooding.

Meanwhile, the area geographically regarded and known as the Niger Delta with its estuary that empties into the Atlantic ocean is very prone or susceptible to flooding and its effect. This area is bordered by the coastline with its coastal shoreline that is characterised by flood plains which give rise to flooding just like other deltaic regions of the world. For instance, the Nile delta in Egypt that empties into the meditaranean sea, the Mississippi delta area of the United States that empties its water into the ocean and most of the areas or towns around these coastal regions experience various forms of flooding at different times of the year.

Coastal towns and cities in Nigeria, like Eket, Uyo, Port Harcourt, Bonny, Warri, Yenegoa etc. have suffered considerable losses from the effects of flooding. Flood has so many negative impacts. It destroys property and endangers the lives of humans and other living things including plants – vegetation; causes soil erosion and resultant sediment deposition elsewhere such as further downstream or down the coast. The breeding ground for fish and other marine life and wild life habitats become polluted or completely destroyed.

Prolonged high flood causes traffic obstruction and delays in areas that lack good drainage system or elevated roadways such as Rumuomasi/Market junction in Port Harcourt – Aba road, and Oroworukwo near St. John’s Bus stop on the same expressway. Flood does interfere with drainage and economic uses of lands, such as interfering with crop and animal farming. Structural damage could arise from bridge collapse, sewer lines, bank lines and other structures within floodways. Waterway navigation and hydro electric power are often impaired, including aviation navigation as flood could lead to delay or cancellation of flights or even cause crashes etc.

Only recently, the United Nations Envrionment Programme (UNEP) predicted that climate change will increase the risk of flooding in Europe and other parts of the world. According to United Nations (UN) report, in 1998, 23 million people were affected as a result of flooding in Xian, China including three thousand people dead. About one million people lost their homes. While in 1996, the monsoon flood in India affected more than five million people in the northern and eastern parts of the country. Severe floods have also killed over two hundred people in India and Bangladesh and left millions homeless.

Here in Lagos, Nigeria , in 2011, many lives were lost and valuable property worth millions of naira were lost to flood not to talk of the damage done to bridges, roads, communication lines etc. Similar thing is repeating itself this year.

It is pertinent to note that, flooding usually brings with it health hazards; it brings infectious diseases like malaria fever, pneumonic plague, dermatopethia, dysentery, common cold etc. And for areas which have no electric supply as a result of flooding, food poisoning may occur as food may not be properly frozen.

Therefore, for the world to be able to contain flooding which comes with its attendant dangers and tragedies, a wise society should build towns and cities in ways that can accommodate flooding and not trying to avoid it. Attempting to go against nature is most certainly risky. Man from time immemorial, has put in place measures to help check the menace of flooding. These measures include planting of vegetation to retain excess water, terracing hillsides to slow water flow downhill and the construction of floodways such as man-made channels or drainages to divert flood water.

A good example is the floodway channel being constructed by the Rivers State Government from Okporo road at Second Artillery all the way, to be diverted into the Ekere creek canal to help check flooding experienced in that area.

Other techniques that can be devised with increased development and advancement in technology  to check flooding include the construction of dams, levees, dikes, reservoirs or retention ponds to hold extra water during times of flooding. Damming of rivers or seas and their associated reservoirs are designed completely or partially to assist in flood protection and control. Most large dams have flood control reservations in which the level of the reservoir must be kept below a certain elevation before the onset of the rainy season so as to allow a certain amount of space in which flood water can fill.

In many towns and cities, government could build river defences, since rivers are prone to floods if not properly managed. These defences include bunds reservoirs and levees. They are used to prevent rivers from bursting their banks. In the event of these defences failing, emergency measures such as sand bags or portable inflatable tubes are used. The issue of coastal flooding has been effectively addressed in Europe and Amercia with coastal defences such as sea walls, beach nourishment. In Lagos, the state government has adopted this approach in shoring up Bar Beach in Victoria Island, thereby proecting it from ocean surge as well as barrier islands.

Another measure that can help stem flooding is tide gates. This is used in conjunction with dikes and culverts. These gates can be placed at the mouth of streams or small rivers where an estuary begins or where tributary streams or drainage ditches connect to wet lands. Tide gates close during incoming tides to prevent tidal waters from moving upland and open during outgoing tides to allow water to drain out via the culvert and into the estuary side of the dike. The opening and closing of the gates is driven by the difference in water level on either side of the gate. These are good examples all the vulnerable states in Nigeria can implement especially in the coastal states to help check perennial flooding.

One of the most elaborate and largest flood control measures is found in the Netherlands, where they are referred to as delta works with the Osterschelde dam as its crowning achievement. The construction was made in response to the North sea flood of 1953 in the south-western part of the country. This is one giant measure taken by the Netherlands government to help control and mitigate the effects of flood year after year, as it is one of the most flood prone areas in the world. Nigeria stands to gain a lot if it can borrow a leaf from all these examples.

Ayooso is a Port Harcourt-based public affairs analyst

Samson Ayooso