Water level of Akosombo Dam - Rejoinder

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I am very happy people have taken particular interest in the topic of Power Generation and finding alternate sources of Power Production. It has been the main topic on the news and in all the print and electronic media, after the drop of water level in the Akosombo Dam.

From my recent visit to the Akosombo Dam and my interest in this matter, I have tried to research on what people are talking about in the Media; to verify and also educate myself.

I read an article by one Kwaku Kwakyi, on Saturday, 30th September 2006. Recommending

Pumping downstream water back to the Dam or Constructing a “Smart Canal” to divert downstream water back to the Dam. I wish to comment on the issues he has raised as follows:

With his first recommendation, I think he wants to talk of embarking on a Pumped Storage Project. With this type of project, water is pumped from a lower reservoir downstream to an upper reservoir upstream during periods of low power demand, when there is an excess in electricity generation. This excess electricity generated would be made available for the pumping action.

This is normally done so that during periods when consumers switch on a lot of their appliances i.e. in the mornings when people are getting ready for work/school doing their ironing, cooking etc and also in the evenings when people return from work. The stored water is allowed to flow from the upper reservoir to the lower reservoir to produce additional power to complement the other sources of power production.

Saying a bit more about Pumped Storage facilities, it is a Net – Consumer of Energy that is to say, if for example a specific amount of water is used to produce say 3Mwatts of power, you would need 4Mwatts of power to pump the same amount of water back upstream. This means more energy is required in pumping than the energy in the same amount of water stored can produce electricity. So where lies the point. So therefore this system is employed in countries or Areas where there are large nuclear plants or other sources of generation apart from the Hydro. This would provide the excess power to lift water from the downstream to the main reservoir. You can clearly see that this is not the case with Ghana.

I also hope he wasn’t talking about an independent pump sitting somewhere to be doing the pumping, because in a situation like this even if we had excess power supply, you would need specially designed turbines called Reversible Pump Turbines which will be able to pump about the same quantity of water that the turbine would discharge when it is in operation. In this way it can meaningfully replenish the water lost in the Dam. Rather than using a relatively smaller pump which would not significantly refill the reservoir compared to the discharge. Note Just to give you an idea about turbine discharges, I would compare the discharge rate of one turbine at Akosombo to Ghana Water Company’s supply from Kpong Water Works to Accra - Tema area. Whilst one turbine at Akosombo discharges 287 m3 of water in one second the main supply from Ghana water Company at Kpong to Accra – Tema discharges 2.5m3 of water in a second. So if we are talking about pumped storage system, we should bear in mind the amount of water that needs to be returned in a given time to make the whole process useful.

Well the writer seemed to know that his first point was not feasible by saying and I quote “instead of using inadequate electricity to pump downstream water back to the Dam, VRA should try constructing a Smart Canal.” By talking about inadequate electricity I think he had even debunked his own suggestion.

He also made mention of constructing a “Smart Canal” where downstream water would be allowed to seek its own level and flow back into the Dam. This would mean trying to defy gravity and hence against the fundamental laws of Science. He should also consider the difference between the upstream and downstream levels which is between 240ft – 270ft above sea level for the upstream and the downstream is about 50ft above sea level. This gives us a head of about 200+ ft.

Water tends to flow from a higher elevation to a lower elevation due to difference in potential. Therefore trying to construct a physical structure to allow downstream water to flow back to the Dam would rather create a channel / gateway to allow water to flow from upstream to downstream since water finds its own level. This would therefore lead to the draining of the Dam and hence collapse of the Dam rather than saving it.

I think technically inclined Ghanaians should try and research into other sources of Power Production and help us come up with lasting and long term solutions to our problem and also hope that people read more and get their facts right rather than criticizing based on hear say.