Uzokwe's Searchlight

Sunday, August 6, 2017

Alfred Obiora Uzokwe, P.E



he frequent rains and consequent flooding events that overtook Nigerian cities for a period of time, especially in July, was a huge source of concern. Everywhere one turned, there was flooding of mammoth proportions! Lekki, Victoria Island, Port Harcourt, Awka, Asaba, even Abuja, were seriously affected. The pictures of flooded buildings, cars filled with water and people trying to go from one end of a street to the other in kayaks was very disheartening. Obviously, property worth billions of naira were destroyed. People in Lekki and Victoria Island posted pictures of flooded homes and I felt very sorry for them.

In Lagos state, officials attributed the Lekki flood to high tide in the lagoon that constricted flow of storm water into it. They also complained that thrash dumped by residents into drainage channels were restricting movement of storm water. One reason that was adduced for the flooding that I found absurd was that some buildings were erected on floodplains. To that I ask: who approved the building permits for construction of these “illegal” structures?

But back to the reasons posited for the flooding, some of them make sense but something was missing. Very few people officially reflected on the fact that climate change may be the chief reason for the frequent and more intense rains with consequent flooding. As is often said, if you do not know what caused your misfortune, you have very minimal chance(s) of solving it.

For years now, scientists have been saying, with sound scientific evidence, that the earth is experiencing climate change at a rate never seen before. They aver that the saturation of the earth’s atmosphere with greenhouse gases, like carbon dioxide, is creating an anomaly that is causing it to warm. Warmer air retains more moisture and when cold air comes in contact with the warm air, the moisture condenses and falls as rain. The more the moisture in the atmosphere, the more severe the rain events. This is part of what Nigeria and other nations around the globe are currently experiencing. When one adds the issue of rising sea levels into the mix, the problem becomes particularly hydra-headed.

The unfortunate thing is that while most other nations agree with the science of global warming and are putting processes and infrastructure in place to tackle the problem, Nigeria, which is already disadvantaged because of non-existent or poor drainage infrastructures, is doing nothing significant to confront the problem head on. In statements to the public while the flooding issue lasted, Lagos State officials asked residents in the affected areas to move upland to ride out the storm which they said would soon recede. The question is: if the flooding occurs as frequently as climate scientists predict, what would be their message to residents every time? “Just move upland, wait for a few days and then return”? That is not good enough.

As a matter of urgency, Nigeria must begin to develop and implement a robust response plan to warming climate and the resultant flooding problems. The plan must include Mitigation, Adaptation and Resilience building.

Mitigation is the effort to minimize activities that result in the generation and release of greenhouse gases into the atmosphere. Adaptation means modifying existing infrastructure or designing new ones to adapt to the new reality of frequent flooding. Infrastructure includes buildings, drainage systems, bridges, flood walls and levees. Resilience building is designing infrastructure to withstand the effects of climate change like flooding.

Granted, mitigation should be the natural first step in combating climate change and its concomitant effects. However, climate change is already here and cannot be immediately reversed. The next best thing is to channel effort towards adapting to the changing realities- a new era of frequent storm events. In this commentary, therefore, I will first discuss adaptation strategies and then later talk about mitigation. Also, to keep the commentary compact, my reference point will be Lekki peninsula.

Adaptation Strategies:

Flood Walls as a First Line of Defense: A look at the map of Lekki shows how easily the development could become inundated during high tides or sustained rainfall. With the lagoon to the north and Atlantic Ocean to the south, the development is basically sandwiched between two bodies of water! Any rise in the level of water in both places as a result of high tide or sustained rainfall, continues to portend serious danger.

The first step to minimize inundation of Lekki by waters of the lagoon or Atlantic Ocean during severe storms or high tides is to follow the lead of the developers of Eko Atlantic. Immediately commence the design and construction of flood walls along the lagoon shoreline and even along the Atlantic Ocean shoreline. The wall will, in extreme and frequent rain conditions or high tides, hold back the lagoon and Atlantic Ocean water. That way, residents will only have the storm water generated within the development to deal with. In extreme storm conditions, even if the wall does not completely hold back all the water, it will hold it long enough for residents to safely evacuate. The Eko Atlantic development taking place next door to Lekki has an eight-kilometer sea wall going up. Reports so far is that the portion of the sea wall already constructed is performing as designed.

Upgrade Inadequate Drainage Systems and Build New Ones Where Needed to Meet The New Reality of Frequent Rainfall: Nigeria is disadvantaged from the get go on the issue of drainage. The country lacks well-planned and adequate storm drainage infrastructure. In many localities, storm water conveyance structures are non-existent so even small storms create flooding. Lekki is not an exception. While the flooding in Lekki lasted, authorities in Lagos posited that part of what caused it was that the lagoon level was high and so storm water that was supposed to flow into it from Lekki was backing up. From this writer’s perspective, the real problem is that drainage systems designed in the past to handle less severe and less frequent storms are no longer adequate in size to handle storm water generated by these mammoth and frequent storms. Furthermore, the number of drainage structures are no longer enough to adequately collect and convey storm water. This is because the many buildings and roads have created so much imperviousness in the landscape that excessive runoff has become the order of the day.

One of the steps to deal with this issue is to conduct a holistic hydrologic and hydraulic analysis of existing drainage systems like gutters, culverts, channels, swales, canals in Lekki. This is to determine the adequacy of the openings of existing storm systems vis a vis run off occasioned by increasing storms. Then effort should immediately be put in place to increase the sizes of the drainage systems and construct more conveyance structures in locations that may have been neglected in the past.

Continued in part 2…