Managing Director of Reo-Habilis Construction Limited and the immediate past president of the Nigerian Institute of Building, Kunle Awobodu, has spoken on why compounds should not be fully floored to reduce flooding, among other related issues

He said whenever it rains, water is expected to percolate into the soil so that there will be less natural runoff that can flood the environment, adding that in a situation where the compound floor is concreted, percolation of rainwater into the unsaturated zone is hindered. Hence, the water escapes through the external drainage adjoining the compound.

“Consequently, the volume of runoff from many compounds laid with impervious flooring materials could flood the whole area, especially when the street has equally been tarred or concreted for smooth movement of vehicles. For instance, I observed, some time ago, a natural process of reducing excess water in the compound. At a site in Ogun State, during the installation of a roller or sliding gate, there came a sudden downpour. The outlet for the runoff was to be constructed immediately after the gate was installed.

“The apprehension of flooding was doused by the internal drainage assisted with the hydraulic conductivity of the soil. The excess rainwater from the roof was absorbed by the soil. If the floor of the compound had been laid with concrete or paved with interlocking stones, flooding would have taken place.

“The experience remains etched in my memory. It demonstrated the water retention process in the ground. It underscored the danger inherent in creating barriers between water and the soil. When the ground is deprived of porosity, flood develops.

“Assuming the building had been completed and floored with concrete or interlocking blocks, the water could have gone into the street drainage and from there be transported to lower parts and when the volume of water is quite massive, it will flood the lower part. I think that’s the problem NEMA was trying to explain, which is true, to be frank. But then, this type of problem occurs majorly in developed areas and what should be done is to create clusters of gardens. The earth needs rain to absolve moisture as not all water should be allowed to flow into the drainage system. The absence of this simple method is a major problem that leads to flooding.

“Also, residential development in an area at times can prevent the natural absorption of water into the ground. For example, when the drainage is concreted, the roads are concreted or tarred and many compound floors are constructed with interlocked bricks, the little narrow path that should be reserved for flowers and kerbs for large flower paths or trees are destroyed.

“If you look at the pattern of colonial buildings even in Lagos, they have a large compound and hardly concrete all the space but leave large areas for flowers, trees and the like. It is only the road within the compound that they will either tar or concrete so that the soil can absolve rainwater that can flood the environment,” he said.

Speaking on what a property owner do to avoid flooding of his compound after rainfall, he said, “the natural and ecological system is an effective method to prevent flooding in a locality. Therefore, it is important to expose part of the ground in the compound to retain the umbilical cord to the groundwater reserves. Flood introduces dampness in the foundation of the building which could cause high moisture content in walls through capillary action. This undermines the structural integrity of the building.

“The inclusion of gardens or green areas in the landscape of the compound is crucial to the enhancement of the environment. A damp-proof course or electro-osmosis damp-proofing system will be inevitable in places where flooding has become perennial,” he added. (Story adapted from The PUNCH)

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