EDITORIAL COMMENT: Irrigation needs to be used fully, wisely Dam building and irrigation have now been turned into a major budget item every year, so we not only accelerate construction but also end this stop-start problem that bedevilled the work before 2018. 

Drought has always been a danger in Zimbabwe according to the rainfall records we have now going back in some detail for over 120 years and even further in a limited number of areas, but they are becoming more frequent and are likely to become more so with global warming.

At the same time we are seeing more cyclone activity in the Indian Ocean and again will see more of this. 

Over the last few years we have two cyclone records fall, Cyclone Idai was the most violent cyclone for many decades at least and now Cyclone Freddie has been the longest lasting cyclone. Neither record is expected to remain for that long.

In some ways the two main climate dangers can compensate each other, but only so long as we keep building big dams. 

Droughts, and we have seen back-to-back droughts, mean we need to store water for more than a year. That is, we need to have water stored to get the winter wheat harvest in and still have enough for the next summer season if rainfall is bad.

At the same time big dams can suddenly fill fast if they are in the path of a cyclone, not something that will happen every year, but when it does the water reserves can be built up. 

This was part of the design of Lake Mutirikwi several decades ago. The engineers found an incredible site, where a reasonable dam wall could impound a very large lake.

But it took around 15 years to fill, and the design engineer came in for a lot of ribbing and abuse during those years. Then a cyclone moved over the Lowveld and it suddenly filled over a couple of months. 

The engineer had studied annual Lowveld rainfall and had seen the spikes from the occasional cyclone and built to catch the next one. In those days there were a lot rarer, but he eventually got what he was building for. 

This sort of design work is likely to become increasingly important, and will have the useful by-product of controlling floods. 

A near empty large lake on a river filling quickly will stop flood waters racing downstream and creating severe damage.

At the moment there are close to a dozen large dams in various stages of construction with at least two now being commissioned each year and the commissioning rate likely to rise as more of the dams ordered by the Second Republic, rather than just finishing dams ordered and work suspended some years ago which helped to kickstart the present rate dam commissioning.

Equally important is using this water. This year irrigation will exceed 100 000ha and with the acceleration of commissioning dams and the accompanying irrigation the 350 000ha target by the end of 2025 is achievable.

We need to remember that irrigation water is not free, but fortunately the ministry for agriculture is also the ministry for water so the experts should be able to work out which crops on which schemes will produce the sort of profit needed to cover irrigation costs and still leave the farmers will thick wallets, and to help them make sure every drop of irrigation water counts and adds to those profits. 

Dam building and irrigation have now been turned into a major budget item every year, so we not only accelerate construction but also end this stop-start problem that bedevilled the work before 2018. 

The giant Gwayi-Shangani Dam in Matabeleland North is one of the best examples, a major and urgent undertaking ordered fairly early in the Second Republic and coming on stream at the end of this year.

The principal purpose of Gwayi Shangani is to supply Bulawayo with adequate water for a major industrial city, end the eternal water crisis in Zimbabwe’s second largest metropolitan area and open up the expansion, not just the resuscitation, of what used to be the industrial centre of the country. 

The impounded lake will be large enough to divert water for irrigation, since the Gwayi river system and its tributaries, the Shangani being the lead one, drain a large area of that province. 

The irrigation will need careful planning since water will be a lot cheaper near the dam rather than after it has been pumped for several hundred kilometres.

This cost of raw water is not going to be a problem in Bulawayo, where each house and each factory needs only modest quantities and there will be savings on treating almost pure water that will help offset the pumping costs. 

Zinwa has already made it clear that it sees a lot of irrigation water near the Bulawayo pipeline terminus, as well as some on the way, coming from the small dams to the south and east of Bulawayo being reassigned primarily for irrigation. 

The urban connections might have to be retained for an emergency, but generally this water can grow food, which Bulawayo will largely eat and use.

Besides the small dams there is also the major borehole operation at the Nyamandlovu Aquifer, and those megalitres a day can now be diverted to farmers. 

So a good chunk of the greenbelt along the pipeline will come from diversion of present urban water, rather than using pipeline water. The pipeline can also provide water for cost-efficient high-value cropping along its route, although the growing number of industrial and other urban centres will create their own high-value demand.

While supplies are good for the moment for both urban and farming use, it is likely that the second phase, the extension of the pipeline to the Zambezi, will be needed before the 80 years now predicted. 

Successful delivery of decent water supplies is likely to accelerate growth in Matabeleland region since that has always been the critical factor.

While we use the Zambezi catchment and Zambezi water to generate power, the amount needed for urban, industrial and irrigation is a small fraction. While lake Gwayi Shangani will block off much of Matabeleland North’s contribution to the Zambezi, it was never that large. 

The lake might be the third largest interior dam but its entire capacity, the inflows from a year’s runoff, is just enough to keep both Kariba power stations going for a few hours. 

While the water is important for industrialists, urban people and farmers it will not be missed by the power stations.

Once again it takes a few years to build a large dam, but we are now with an assembly line so they will be commissioned at regular intervals. 

Now they have to be used wisely and carefully, both to ensure water lasts through future droughts and secondly to ensure that farmers can extract every dollar possible from whatever they spend on that water.

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