Damming the Nile and Reservoir Induced Seismicity

By Kant Ateenyi Kanyarusoke

Is Karuma dam on track now? Perhaps yes. Bujagali took ages to come on. But opponents of damming will not give up! Through local compatriots like Oweyaaga Afunaduula (New Vision, 8 July 13), they are opening a new front – in the form of Reservoir Induced Seismicity (RIS) – to stop dam building on the Nile.

In this article, I will address four things: One – current scientific thinking on the subject; two – current recommended engineering practice in design of dams in earthquake-prone areas; three – question intentions of opponents when they do not provide alternatives to damming; and finally, hazard a motive in light of experiences elsewhere. Hopefully, I reassure Ugandans that we should move full throttle in building Karuma Dam and any other on the Nile.

Reservoir Induced Seismicity (RIS) is a condition where earthquakes are thought to be helped by filling of a big, deep ‘hole’ – or reservoir on the surface with water. The quakes are not caused by the reservoir but by pre-existing conditions in the rocks below.

Because they originate several kilometres below the surface, there is still much debate between Mechanical/Civil and Geotechnical Engineers as to whether RIS should be an issue. The late Dr. Kanuri L Rao, India’s celebrated “father of Water management and Agriculture”, for example, compared the weight of water in a reservoir to that of a fly on an elephant’s back. Yet even this is a gross overestimate of the water effect.

Geotechnical engineers on the other hand have suggested two different mechanisms by which the water could help an earthquake. These are illustrated in the sketches below. One is for a condition when the reservoir is directly above a fault line in the crust below.

It is supposed that the weight of water adds to stresses in the rocks below, leading to fractures at interface and therefore slippage followed by the earthquake. It is said that these quakes occur when the reservoir is filling very quickly, thus causing a kind of ‘jerking’ or rapid loading failure.

Mechanical and civil engineers counter this by looking at the shock absorbing effect of the soil and rocks between the fault plane and the reservoir floor. The rocks would have to be very solid and almost uniform all way to the slippage plane.

The plane itself would have to be nearer to the surface – which would perhaps result from using a very deep valley filled with water as a reservoir.  Bujagali and Karuma are using ‘run of river’ reservoirs. So, this mechanism – even if it were true – cannot be at play.

The second mechanism suggested is by lubrication of rocks at slippage planes. This is for areas away from the reservoir through seepage. Again, for this to be of effect, the reservoir has to be very deep so as to create enough pressure to drive water through all the crevices; it has to be leaking; the rocks below and/or in its sides have to be porous or have connected openings up to the slippage plane below.

It is said the earthquakes in this case do not occur immediately on filling but later – having given enough time for water to percolate. Not all these conditions are present for Bujagali and Karuma.

After suggesting these still debatable mechanisms, and realising their possible limitations, Geotechs have provided limits of strengths of the earthquakes from RIS. They are intended to guide the civils/mechs and the public in design and construction of structures and systems in areas near affected dams.

It is said that the RIS quakes are normally small. Only dams exceeding 100 meters in height or those holding at least 500 Million cubic metres of water are thought capable to cause a RIS of magnitude 5 on the Richter scale.

Disagreements notwithstanding, engineers are obliged to be cautious in design. The internationally accepted practice in earthquake prone areas is: Take full care of “RIS when the dam height is over 100 m”. In that case, the design has to follow the earthquake proofing code.

For Bujagali, the dam is 30 m high while the mean reservoir depth is minimal. For Karuma, the dam height is 20 m while the reservoir depth averages a mere 2.9 m. Even then, the Environment Impact Assessment reports that “full earthquake protection” was followed in design.

Clearly, the dams – or any other that may later be built along the Nile in Uganda – fall well within the internationally recognised ‘safe’ height category. It is erroneous and misleading to compare them with the likes of Kariba (128 m), Zipingpu, (150 m), or even Ethiopia’s Milleneum Renaissance (170 m).

But even if they were that high: what alternatives do the environmentalists – of whom our compatriot Afunaduula is one – suggest? Thermal plants are ‘poison’ to these people.

Nuclear plants are a No-go area; Geothermal plants are actually worse than hydro – from a seismicity point of view; Large wind and Solar plants – apart from being expensive initially and erratic in operation – are accused of ‘uglifying’ the landscape and of interfering with bird flights; Wave energy is limited in Uganda; Fuel cell technology is still new and will soon be condemned for using drinking water.

So how do we power our country to the so called ‘First world’ status by 2040? Within the remaining 27 years, we need to add over 54 GW to the grid if we have to live like the present 1st world residents. Where will this electricity come from?

Perhaps the answers lie in our compatriot’s unease with China’s dominance in winning contracts on the continent. Perhaps not – in which case – register my apologies. But if the former, would it be any different if Europeans or Africans or even Jesus of the Bible built these dams to specification?

Here below is a short live story about people whose interest is either profiteering on others’ weaknesses or keeping them in perpetual darkness. It is about the US$ 1.7 billion, 1.2 GW, 135 meter high Ilisu dam on the Tigris river in Turkey (Note the cost and contrast with Bujagali’s US$0.8 billion and Karuma’s US$2.2 bilion).

The Ilisu dam reservoir covers 313 km2 at an average depth of 9.4 meters. Because of the huge area and consequential relocation of thousands of homesteads, the British who had at first agreed to part-fund it pulled out: thanks to some local environmentalists – partnering with outsiders from as far as Brazil, half a globe away!

Then Germans, Austrians and the Swiss followed the British. European firms who were to supply equipment and construct it pulled out in 2009 – citing over 150 non-conformities to ‘international’ standards. Now the shocker: In 2011 Turkey decided to fund it using own resources with help of three of its banks.

With no design or implementation changes, the European firms resurfaced – and this time with funds! Siemens rushed to buy the civil engineering firm that had won the construction contract. Andritz – which had withheld turbines came running and panting.

Local pressure groups were ignored and left to nurse their injured evil egos of darkness. As of April 2013, the project was 55% complete. It is expected to be commissioned in 2014. But costs are being revised towards US$2 billion!

The moral of this true story is that where darkness is concerned, we are on our own. Therefore we should be free to choose whoever gives us the best deal. Also, local compatriots should avoid being entangled in other people’s scavenging fights.

Kant Kanyarusoke is a Pan Africanist Solar Engineer, Member of ASHRAE and of South Africa Society of Engineering Education (SASEE).