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Tuesday, November 19, 2013

Harare`s Water Crisis

Harare`s Water Crisis
Harare is presently in the grips of its seasonal drawdown problems, with numerous enquiries being made relating to reduced water yields, drying up of boreholes etc, sometimes in surprising areas. Ground water is under stress as next to no recharge will have taken place this past season. In Chisipite we received a total of 774mm rainfall, with only 34mm coming in February - the critical part of the season. Harare's average precipitation is 850mm, and we require at least 2 to 3 above-average rainfall seasons (+1000mm) with good distribution to make a difference to ground water recharge. Recharge to the resource is only 2 to at best 5% of annual precipitation. The rest goes to runoff, evapotranspiration etc. Therefore excessive abstraction (more that is mined than is replenished) can tip the balance on available water supply. Users have to be aware that the water table is not a 'lake' but, in Harare and most of Zimbabwe where 'hard rocks' prevail, it is restricted superficially to the weathered and fractured zone. Massive bedrock does not store or transmit ground water, and it is only on rare occasions that open fractures are present to depth below say 60 to 100 metres. Therefore drilling to depth is not usually the answer, and can be a costly experiment. We hear about the odd success, but not the many failures. A column of water in a borehole where there is no deep fracturing will draw down to pump intake just as easily, and the energy costs to get the contained volume to a header tank may well double. Users therefore have to be self regulatory in their abstraction and usage of ground water in the common interest. Collectively they have to appreciate the fallibility of their resource, despite the magic of recharge. Your message should be for them to stop using excessive water on gardens, verges and other nonessentials, and to think positively in their community interest through self discipline and forethought. It is not only the elevated areas of Glen Lorne, Greystone Park, Kamfinsa, Greendale North, and Ballantyne Park that are suffering drawdown problems, but also parts of Mount Pleasant centred on the International School, parts of Vainona, especially the north, the area surrounding Borrowdale Village and parts of Chisipite, Gun Hill etc are also feeling the pinch, some surprisingly.

Harare's ground water is under stress and its users must act responsibly if this city is to survive its inability to provide and reticulate the available water supply and to develop new sources. Kunzvi Dam was scheduled to be on line by 2004 and the Shavanohwe addition shortly thereafter. That plan is not in sight.

Some thoughts
Tim Broderick

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