Accra drainage bombshell!
Media channels beamed dramatic images of the Accra floods across the world recently. Available records suggest the flooding is repetitive. It occurs at the same locations when rainfall events reach a particular threshold of intensity and duration.
As we wait for the next episode of flooding or disaster, I would like to look at the situation from a technical angle, and as an observer.
Undeniably, flooding causes far-reaching adverse impacts in the affected areas. It cripples the transport network, businesses are unable to function and it brings life to a standstill.
Prolonged ponding of surface water in the middle of town has the potential to damage underground services as well as structural foundations of buildings and other infrastructure in the vicinity permanently. In tropical climates, residual health risks due to the nuisance of pollution and spread of infectious diseases persist well after the clean-up process is complete.
Sadly and inevitably, humans perish when urban floods, which are a great disturbance to daily life, occur. The deprived or the vulnerable in society, including women and children bear the worst of the ensuing misery. Two important but simple questions need prompt and unequivocal answers:
1. Why should the same locations flood not just once, not twice but every year?
2. Where are the responsible municipal and civil engineers of the Accra City Council?
Municipal administrators and their supporting technical staff who should be accountable appear to have relinquished their responsibilities and allowed flooding to become a perennial problem in the City of Accra. This constitutes an abandonment of responsibility, or in other words, dereliction of duty.
Presently and strangely enough, the victims have no insurance cover. Whilst the populace become destitute, the municipal engineers continue to enjoy life as normal, drive in their big official vehicles and are only interested in doing nothing than doing anything. The state pays no compensation to the victims and the engineers answer no questions.
The recurrent flooding in Accra is not such a complex and an extraordinary problem to require the outstanding expertise of rocket scientists to resolve. It is a normal drainage problem that civil engineers elsewhere encounter day in, day out, and deal with as just another job.
Ghanaians need a moment to contemplate and ask questions about whether the people entrusted with the responsibility of ensuring the smooth running of the city are up to the task.
Let me examine briefly the concept of drainage design in a non-technical language. Basic drainage design involves essentially:
a. Determining the intensity of rainfall that occurs in a catchment over a particular duration;
b. Providing facilities for collecting the anticipated runoff; and
c. Conveying the runoff to an outfall in a receiving water body, as efficiently as reasonably practicable.
In accordance with the recommended best practice, it is mandatory to minimise the impact on the receiving environment in terms of water quality and flood risk.
Rainfall intensities vary so much so that the assessment of the capacity of drainage systems requires a knowledge of the likelihood of a particular rainfall event occurring. The statistical methods for doing this can be onerous but certainly not beyond the capabilities of our experts.
Nowadays, computer programmes and clear-cut procedures are available for generating the critical rainfall for design. From an economic perspective however, it is impractical to provide a system with an infinite capacity. This would be a drainage network that never runs full and never floods no matter what the elements throw at it.
Therefore, the various organisations, stakeholders and municipal authorities provide guidance on performance expectations of their drainage assets. In the UK, drainage systems in all-purpose roads have the capacity to withstand 1 in 5-year rainfall events.
This means that the estimated recurrent interval of a storm that would cause the drains to run at full capacity is 5 years. Drains in urban and residential areas in the UK have capacity for 30-year rainfall events. Of course, decision makers incorporate additional mitigation and redundancies to help avoid, reduce or remedy the likelihood of flooding.
For example, inclusion of the effects of climate change and global warming is a non-negotiable condition to achieving approval. Different rules apply for sensitive infrastructure such as airports, tunnels, power plants, etc. Notwithstanding, drainage design is not rocket science and above all, water flows downhill!
As an example, the Kwame Nkrumah circle is one of the areas that floods regularly. The simple at-grade roundabout has now become a three-level grade separated interchange. Such a junction would encounter major planning hurdles to get it off the ground in most established cities due to the potential short and long-term environmental disbenefits. It may even be exacerbating or contributing to the recurrent flooding scenarios.
The extensive bridge deck with blacktop significantly increases the amount of surface water runoff well over the previous situation. The intercepted water now travels faster over the artificial surfacing and has a higher peak flow.
This change in the flow regime alone is probably sufficient to overwhelm the receiving watercourse down the line. Those whose decisions and actions determine the operational efficiency of the city’s infrastructure, perhaps, take their eyes off the ball far too often, and they do so at will with impunity.
Drainage standards in Ghana have not changed since the colonial times. Roads in our towns and cities have open longitudinal channels running on both sides. These are in the “combined sewers” category because they carry both surface water and used water during periods of rainfall and dry weather conditions, respectively.
The dry weather flow in the longitudinal channels cannot be anything other than concentrated sewage. It is wastewater originating from the factories, hotels, restaurants, hospitals and clinics, bathrooms, urinals, etc.
The wastewater is primarily a toxic filth and every Ghanaian knows that it contains faecal matter and pathogenic bacteria that may be very harmful. We also know that the drains have a characteristic air quality issue and negatively impact on the “ambience” in our towns and cities.
Yet these open longitudinal drains laden with toxic waste, including potential excrement and putrefied organic matter, run alongside the high streets. They are in the markets where residents go for fresh consumables, and in the hospitals where the sick and the infirm go for treatment.
Young children cross these channels, usually using improvised footbridges on their way to and from school. We order our kebabs and takeaways from food vendors in stalls or kiosks lined along the open drains.
The overseers of our cities are short-changing and brainwashing us to believe that these open longitudinal channels serve a useful purpose and are indispensable. Rather, they are key “incident black spots” on both sides of our roads and the harm they cause far outweighs their usefulness.
During the night, “dumsor” compounds the situation and makes living and working around the drains even more precarious. When it rains, the flows within these channels have sufficient energy, and are capable of sweeping humans away. The drains are not only a significant hazard to pedestrians but to motorised traffic and, in fact, all categories of road users.
Elsewhere, they would be set behind safety barriers or vehicle restraint systems to protect errant vehicles, and their installation in pedestrian areas would be inconceivable. These open drains would not pass operational road safety audits in any modern city.
Accra requires a robust long-term drainage and sewerage solution to alleviate the detrimental impacts of recurrent flooding. The option adopted should comprise a dedicated sealed pipe network for foul water and a separate system for surface water runoff. Regrettably, politicians do not see drainage in our cities as an essential part of the infrastructure to merit coverage in their manifestos.
Our cities cannot continue to expand without a sewerage system. Moreover, drainage and the quality of sanitation in an area are inextricably entwined. Accra municipal authority and their engineers have a moral responsibility to future-proof the city against flooding for the next generation, so that the children yet unborn can enjoy a befitting livelihood.
Let us initiate a process of change by decommissioning and replacing the open channel drains with piped systems buried beneath the roads. It would suffice to start modestly and gradually expand the network outwards, concentrating the initial efforts at key locations:
1. Open markets: To eliminate and prevent the display and selling of foodstuffs and meat around open sewers.
2. At taxi ranks, bus stops and lorry parks or locations with substantial pedestrian traffic and around schools: To eliminate the “trip hazard” and minimise the likelihood of falls. It will be a welcome relief to the mobility impaired, including all non-motorised road users.
3. At hospitals and clinics: For the sake of hygiene. The open channel drains in our towns and cities, including those in Accra have outlived their usefulness and are therefore not fit for purpose. We should be worried about the associated environmental impacts, deplorable air quality and the unsatisfactory sanitation.
Our politicians, municipal administrators and their supporting engineers are in a quagmire of conflicting decisions. They do not seem to appreciate that the expanding infrastructure changes the “drainage dynamics” and exposes our cities to needless flood risks. The longer it takes to fix the drains, the more costly and painful the solution would be.