Flooding In Accra has been reduced to engineering the drainage system.
My informed knowledge of the problem is way beyond dredging the Odaw River.
There are about five fundamental challenges which cause flooding in Accra.
Hydrology, Infrastructure, Topography, Urbanisation and Attitude.
Accra is a very flat and low lying city surrounded by hills.
Over 89 years ago, the colonial administration realised that when the rains come down the hills, the runoff struggles to get to the sea quick enough and the ripple effect was causing flooding.
So they decided to create holding pans along the seven or so streams that drain the city from east to west.
These holding pans included the wetlands and mangroves closer to the sea because of their holding and percolating capacity.
Unfortunately all the seven or so holding pans have been built up.
So now the water has no choice than to take its natural course to the sea.
Unfortunately due to the almost zero gradient at the point of discharge, the rate of flow into the sea is higher than the rate of discharge causing excess water to flow backwards.
Twenty years ago the worst affected areas were Adabraka Official Town, Circle, Asylum Down, etc.
Today, the ripple effect goes as far back as Achimota, Taifa, Dome, Madina etc.
We cannot do much about the topography of Accra and we have not done much about the haphazard settlements in the holding pans and river beds.
Accra soils are clay in nature in many places what that means is that the percolating capacity or the spongy effect of the soil is severely reduced because the clay holds water.
These days if it rains on Saturday for more than two hours and rains again for another two hours on Monday, you are likely to experience flooding because the clay soil will still be retaining water from Saturday making it difficult for easy absorption or percolating.
Added to this phenomenon is the fact that while the hills and green areas provided some relief by breaking the flow of water and absorbing part, the hills have almost all been cleared of vegetation and replaced with buildings whose roofs and concrete compounds allow the water to even run faster towards the sea.
I always made the point that the N1 from Mallam to Tetteh Quarshie has no green median to aid percolating rain water. The whole road is designed to discharge surface run off into the sea.
Our refuge for drainage has become the sea which because of topography lacks the capacity to receive effectively.
With drainage infrastructure, it is a very capital intensive activity and we only do it piecemeal. In effect while portions of Alajo, West Airport, Dzorwulu, Odaw, etc may be lined, the areas not lined carry a fair amount of natural sand and silt in the drain not to mention the millions of plastic waste dumped into the open drains.
The sins of Oyarifa, Mcarthy Hill, Ashongman, Taifa, East Legon are visited on Osu, Adabraka, Circle, Asylum Down, Kaneshie First Light, Dzorwulu etc.
Obviously the carrying capacity of the drains designed 40 years ago is inadequate in 2023.
But the solution is more than civil engineering.
I saw a NADMO notice asking affected persons to go to higher ground. It’s a normal practice in settlement planning to provide civic spaces on higher ground in case of emergencies or disasters but Accra is all flat land to a large extent.
A ROOT CAUSE OF
FLOODING IN ACCRA
Ghana has six designated Ramsar sites. These are wetlands designated under the criteria of the Ramsar Convention on Wetlands, an international treaty that seeks to protect them.
In Ghana, these sites are mainly along the coast and are meant to be protected as set out in the convention. But the sites have become targets for property developers whose activities are leading to a decline in the flood resilience of many parts of Accra.
Wetlands are considered under the Ramsar Convention “areas of marsh, fen, peatlands or water, whether natural or artificial, permanent or temporary, with water that is static or flowing, fresh, brackish or salt, including areas of marine water the depth of which at low tide does not exceed six metres.”
Ghana is a signatory to the convention and the first wetland designated was the Owabi Wildlife Sanctuary Ramsar Site. Wetland areas in Ghana cover all the country’s beaches, mangrove areas, river buffer zones and low-lying land that is flooded by water, at times to a depth of about six metres.
Wetlands are important in many ways and are relevant to almost every aspect of human life. They serve as a buffer for floods as they absorb water. They also help reduce the impact of drought as they replenish groundwater by releasing that trapped water slowly into aquifers (the rocks that hold water underground). The holding capacity of wetlands helps control floods and prevents water logging of crops. Mangroves also reduce the impact of storm surges, and protect the coast from erosion.
Wetlands serve as breeding and nursery grounds for several species of marine fish, which are a source of people’s livelihood (both as fisher-folk and in the downstream fish value chain). They also provide medicinal plants and building materials as well as household items such as mats.
Several species of animals and plants need wetland conditions to survive. All of these animals and plants have intrinsic value too, in that they give people pleasure. Wetlands are very peaceful places.
Wetlands are targeted for commercial and residential development in urban areas where there is a shortage of land or in areas where the wetland is seen as prime land for tourist development along the coast.
In the urban setting, wetlands are usually the last places to be developed.
So in a place like Accra, wetlands in low lying flooded areas are being targeted because almost every space has been encroached as a result of ill considered developments (sometimes with the indiscriminate allocation of building permits by local authorities).
Wetlands are not suitable to build on. Wetlands soil is waterlogged, often acidic or saline and has high clay content. It is therefore unstable. Building on this soil is not the wisest thing to do: the buildings are never strong. Even after adding chemicals to the cement and concrete, you find that groundwater in the wetlands erodes the foundations. Filling up the wetland by piling ‘material’ on it does not help, as this material act like a wick bringing corrosive chemicals to the surface.
Landowners know this, but continue with their developments.
The major impact especially in urban areas is tied to fact that the wetlands lose their function of acting as a sponge. Wetlands soak up the excess runoff and then release it slowly. This stops high water levels rising, and flooding. The loss of the greenbelt and urban wetlands in Accra has reduced the ability of wetlands to retain water when there is unusually heavy rain.
To build in a wetland you usually need to fill it. You have to add material to build it up. The water that would have previously occupied that space is displaced and needs to go somewhere else. So you may have built years ago and feel your building is safe. However, the water that is been displaced will result in flooding. The result is that infrastructure such as roads which were previously never flooded now become flooded.
To restore a wetland after it has been encroached on does not just involve removing a building. You have to take away the material that has been put there, in some cases illegally, then you have to try to seed the wetland with the correct types of plants and hope that the animals will come to reestablish it. It is a long, expensive process.
Probably the simplest wetlands to restore are the mangroves along the coast. But even then, the problems caused by erosion, sea level rise, plastic pollution and increased sedimentation because of the runoff are difficult to turn around.
Wetlands are being restored in parts of Europe and North America, because authorities realised that the value of having a wetland was greater than the development that was there. But this action is rooted in behavioural and attitudinal change.
Ghana needs people to stop doing the damage. Then we can see how to remove some of those buildings which are in waterways, how to open culverts, how to plant trees to increase infiltration (the flow of water from above ground into the subsurface). And how to get people to stop paving their entire compounds with tiles which increase water runoff.
It’s everyone’s problem. And everyone can benefit from solving it.[The writer is an Environmental Scientist]
BY CHRISTOPHER GORDON