Realistically today, large amounts of irrigation water from so called Uganda’s lakes can only be drawn by pumping.
PART 8: IRRIGATION WATER SOURCING IN UGANDA: c) Surface water: Lakes and mini lakes
By Eng. Kant Ateenyi Kanyarusoke
Whereas river water evidently flows, lake water looks - by and large - stationary. Uganda's natural lakes are constantly being fed by rivers and underground water. During rain, surface runoffs and direct ‘hits' by rain drops supplement the two. The lakes hardly overfill because they are in turn drained by rivers (e.g. The Nile) and by seepage to aquifers deep below their ‘bottoms'. Hence, the water is really not stationary but in slow motion! Importantly, this is not all. Their large exposed surfaces receive direct sunshine which causes evaporation. Unlike rivers, protected by river banks and surrounding vegetation, wind blows the freshly made vapour away and hence keeps the evaporation going. A lot of water - especially in the rift valley lakes (e.g. up to seven litre per square metre from Lakes Edward and Albert) is lost this way on daily basis.
I have given you the above background so that you will appreciate the intricacies of withdrawing water from big and small lakes for irrigation. As expected, small lakes - unless very deep and in narrow valleys (e.g. crater lakes of Western Uganda) will suffer more than bigger ones. Food and Agriculture Organisation (FAO) of the UN advises that irrigation water withdrawal from small lakes should be started before end of the rainy season to avoid severe level drops or even drying up if done later. Such lakes in Uganda include, Kayumba, Kiija-nibarora, Mburo, Opeta, Wamala etc. And for completion sake, we can include artificial ones like Kabaka's and those we called ‘mini lakes': that is, river and valley dams in the last article. But there lies the first catch: it is at this time that the soil around the lake has a good amount of water. So where do we withdraw the water to? We will answer that question later.
Drawing lake water - In ancient times, Greeks pioneered use of channels and underground tunnels (aqueducts) to draw lake and reservoir water. Gravity drove the water through closable gates into the channels which gently sloped downward to points of use. However, it was the Romans about 2328 years ago (i.e. 312 BC) who ‘perfected' the art of building long ones - covering tens of kilometres - both above and underground. ‘Stationary' water could be drawn and distributed by gravity to the city (Rome), homes, and farms over a large area. It is supremacy in this art - and in road and drainage construction (essentially Civil Engineering) that enabled building of a great imperial empire - whose lasting effects still run the world order, millennia after its fall.
Realistically today, large amounts of irrigation water from so called (You will shortly see why ‘so called') Uganda's lakes can only be drawn by pumping. Then, it could be transported either through networks of pipelines or using water tankers to other reservoirs. We cannot use aqueducts partly because in today's era, they would be a lot more costly. Even if we were to mobilise and motivate the abundant ‘idle', the ‘under employed' or even the hundreds of thousands of ‘refugees' to dig them, we would encounter problems on land appropriation for the aqueducts. As we are seeing in other Civil Engineering projects, Uganda's present land tenure system is so bad, and many people, so opportunistic that it could take a decade or more to attempt to channel some water from L. Wamala to say, Kasambya in the same Mubende district. Or from Kioga to Nimule. Moreover, there is no certainty the water would arrive intact. And why should it anyway: Isn't it genuinely needed in between? The controversy of the latter question, together with a fear to upset the surrounding wetlands - in many countries leads to legal provisions that only properties adjoining the lake should use its water for irrigation. But in Uganda, it is such areas which least need irrigation. Areas like Karamoja with no major natural lakes need it more urgently. But we need not be tied to that norm - as the following examples show.
In China, Wu et al. (2008) report a 2005 water draw from L. Hounguan to drier parts of the Yangz river system with spectacular positive effects on the latter's ecosystem. Before you erroneously dismiss that as a practice in a ‘non democracy', consider this: In North America's great lakes region, agreement was reached in mid-2016 to pipe 31 Million litres a day from Lake Michigan to the city of Waukesha, about 30 km outside the region - on condition that the city released an equivalent of treated effluent water to the lake's in-feeding River Root.
So, we can actually pipe a limited amount of lake water to our dry regions, especially if we have sorted out our land tenure system. Which answers our earlier question on where to withdraw the water to: During rains on the lakes, pump it for tens of km to reservoirs in dry areas, especially those from which, are streams and/or rivers feeding into the lake. I will not go into land issues now. Interested readers should among other works, refer to Odrek Rwabwogo's 18 July 2016 article in The New Vision. However, we can briefly touch the issue of ‘internationally' shared lakes.
First of all, this author strongly abhors, condemns, and whenever possible, disregards subdivision of the continent as is now (e.g. see my "Divided, we are eaten" in The Independent, 27 Feb 2014). For Africa's northern Great lakes region, Omukama Kabalega was already on course to reunite it under one decentralised administration before Europeans arrived to stop and undo his work. In particular, Uganda's rift valley lakes were all in one political entity - and therefore, should never have worried us as to how to share the waters (and oil) with a western neighbour. But now here we are: the best we can do before using these waters the way I have described - is to consult and seek agreement from rulers of relatives that were once with us. Which brings me to a more radical approach: extensive harvest of rain water - before it even enters the ground. I discuss that in the next article which closes the engineering bit of this series.
Kant Ateenyi is a pan Africanist Engineering Don and CEO of Progressive Africa Solar Engineering Pty Ltd. in Cape Town.