No sooner than we got to the neighbourhood of the property did we realise the presence of a one-metre deep canal about 25 metres from this property which qualifies to be property of reference to represent the fair (to best) case scenario for the residents of Chief Natufe locality, near Bode Thomas Junction, Surulere, Lagos. The problem became apparent. It was the typical drainage problem usually associated with most highbrow areas in Lagos – flooding and high groundwater table! Lagos state is a low-lying coastal region occupying 180km of Nigeria’s estimated 900km coastline. The low-lying land, wet-lands and water occupy 78% of the entire land mass of the state, a fact that a considerable part of Surulere represents.
It is therefore not a surprise that this part of Lagos, like many other typical lagoon front-inspired areas of the state, revealed discouraging factors such as the nuisance of high groundwater table and flooding, though it was being surveyed in a dry season when the water level ought to have drawn down according to geological principles. This makes it crucial for any intending resident or real estate investor to be wary of the direct implications of any drainage catchment failure that this situation signifies. With such failures come the attendant ones such as backflows of plumbing flow and artificial surfeit of septic tanks issues, capillarity and seepage flows into living apartments, etc. All the aforementioned are yet only hydraulic cum geotechnical issues which be solved by civil engineers, albeit at a rather inefficient cost.
Below are common signs to watch out for when inspecting flood-prone areas, for an inexpert real estate investor or intending resident. They are based on the deductions from our own inspection:
1. Nearness of a water body is one of the issues to look out for. Water in the natural aquifers will take the colour of a nearby water body except deliberate geophysical attempts are made to find deeper and clearer aquifers.
2. When a nearby property is abandoned to flood or water bodies like this, visible impressions of marks left by flood impingement on enclosed building walls reveal flood proneness.
3. General Depth of water level in dug wells, in that neighbourhood (should be deeper that 4 metres below ground surface).
4. When well walls in the neighbourhood reveal a poorly compacted soil strata arrangement, soil inadequacies can be revealed this way, with little observation.
5. Visible vertical cracks on walls of nearby buildings may be signs of deeper structural cracks emanating from perhaps a differential foundational settlement which is usually the effect of water on foundation.
Apart from the aforementioned issues, there are other structural defects which occur as a result of the settling of the foundation of the buildings of such areas. Usually, the effect of water in wetlands is that of compromising the cohesiveness and internal friction of the soil. These two factors are indispensable in the make-up of the bearing capacity necessary for the support of structures. When these foundation prerequisites are defied without compensating for them in the design of the foundation, it results in problems such as foundation settlement, uniform or differential. For the property of reference which I had earlier mentioned, there had not been adequate consideration for the effect of water on the foundation; hence a differential foundation settlement that has resulted in side-to-side structural cracks on the building. The design life of such building is diminished; so also is the value.
If the foundation is destroyed, what really can even the best geotechnical engineers do? And I mean, what can they do in terms of economic and safety considerations?