The FCT floods and emerging trends
The recent widespread floods in the FCT and surrounding areas is not unconnected with the manifestation of global climate change phenomenon which was never envisaged at the time the Abuja Master Plan was produced. The data used for the Master Plan’s preparation was the FCT ecological survey conducted in 1977. Unfortunately, from the early 70’s, the whole of Northern Nigeria was experiencing dry spell. Specifically, 1977 was among the drought years in the Northern region. That was the conclusion of a 1988 ABU B.Sc. research by this columnist, with the tittle “A Derived Drought Index for Northern Nigeria”. The data used for the research were collected from 1927 to 1983. The same work was published in “Samaru J. Agric Research” in 1992 and “Zaria Geographer” in 1993, by Oladipo E. O. and Shuaibu U, the columnist.
According to the data of the 70’s, the Master Plan captured raining season for the City site, between the midApril and mid-October. Contrarily, due to Climate Change, rainfall commences earlier, and lasts longer than these periods. Also, there is no deviation from the concentration of rainfall in the 3 months of July, August and September when 60 percent of the annual rainfall is received. However, there is increase in the intensity and the total amount received. The amount of rain which should fall within a span of one month can be concentrated in few hours, resulting to flash floods. A lot of places considered safe are washed away overnight. Rivers and stream channels overflow their banks, wiping out homes and farms. Structural fabrics of buildings are weakened leading to the devastating incidences of building collapse.
The data used for predictions are now superseded by the emerging trends. Flood mitigation measures proposed in the Master Plan are rendered inadequate, due to the higher amount of rainfall received. Engineering specifications, such as widths of drainage channels, sizes of bridges and culverts, and demarcations of areas liable to flooding while creation of new layouts by the Town Planners, becomes outdated and needs to be reviewed.
Meanwhile, proposal was made for hundred years flood regime to provide buffer zones for floods control along the stream channels traversing across the Capital City. Unfortunately, this provision is abused in various construction sites across the City. The abuse could arise from the point of creating the layout and allocation, because previously the notion of land bank was advanced to justify the conversion of some of the flood plains for residential uses. Abuse can also be made while granting building plans approval. On the other hand developers most especially, Mass Housing have the habits of development beyond the boundaries approved by the Development Control.
In Abuja, 472.2mm of rainfall was recorded between 19th July and 8th August 2019, with 226mm between the morning hours of 25th and the morning hours of 26th July alone. Thus, more than 50 percent of the total rainfall recorded in the previous year, fell in 20 days, with 24 percent within a space of 24 hours alone. That culminated to the flash floods at Lokogoma, Galadimawa, Kafe and many other Districts in the City. It led to destruction of properties and lives, and rendered families homeless. Runoff in stream channels that were very narrow and considered inconsequential, rapidly rose overnight and within few hours to the sizes of humongous rivers, flowing forcefully downstream.
It must be understood that urban floods can never be stopped and water can go from harmless to fatal in no time. However, the strategies required for adequate mitigation of the adverse consequences of urban floods are not large engineering solutions, but more on good land-use planning and stewardship. “We just need to move the water through our community quickly, with as little damage as possible.” This observation was made by David Driskell, the Executive Director for community planning and sustainability of Boulder in the District of Colorado.
The Big Thompson flood, the deadliest in Colorado history occurred in July 1976. Up to 14 inches or 356mm of rain, fell within 4 hours, and the Big Thompson River Canyon, just a short drive north of Boulder, swelled from 18 inches to 20 feet within minutes. The 31,000 cubic feet of water per second that raced down the canyon took 143 lives, washing some of the bodies 25 miles downstream.
Measures for mitigating such a disaster may appear daunting. However, Gilbert White a pioneer in the field of urban flood planning believes that cities should accommodate floods, rather than holding them in dams and embankments. Also, “Floods are acts of God, but flood losses are largely acts of man”. White provided the guide that pushed Boulder to adapt to the floods of the future, and it escaped disaster, without a single life lost from a bigger flood in September 2013.
What we need are studies and analyses of the flood patterns of our stream channels across the city and the implementation of floods adaptation measures for the mitigation of future occurrence akin to Boulder’s. Also, not putting stuff where they shouldn’t be.