Southern Africa Weather, Drought and Dam Levels April 2018

Posted on by livewiresa

The table below indicates how dam levels have changed over the last four and 52 weeks.

 Capacity      23.4.18     26.3.18     24.4.17
Dam million m3            %            %            %
Sterkfontein        2 617            96            95            90
Vaal        2 604           106            95           103
Bloemhof        1 240           104            78           102
Vanderkloof        3 171           102            58            63
Gariep        5 196           105            90            92
Free State total       15 971           100            80            85
Theewaterskloof           479            10,1            10,4          17,7
Voëlvlei           159            13,7            14,5          19,9
Berg River           127           36,2            45,0          31,9
Wemmershoek            59           44,9            44,2          36,2
Steenbras Lower            34           36,7            36,5          30,2
Steenbras Upper            32           62,9            81,7          51,7
W Cape total        1 853          16,0            18,3          21,6
kZN total        4 669            65            62            59
E Cape total        1 826            68            67            63
Limpopo total        1 508            77            70            78
Katse / Mohale (Lesotho)        2 376            57            54            55
Mpumalanga total        2 520            82            81            79
Total RSA and Lesotho       31 913            82            70            73

Those in the Western Cape are of the most interest due to the drought there and where even % points of capacity become significant, especially of the Theewaterskloof dam. The six dams identified in the Western Cape are those which supply Cape Town and in total have moved from 23.0% of capacity a year ago to 21.9% four weeks ago and 19.7% on 23 April. This shows that looking at Theewaterskloof on its own, despite its relative size, is not a true indication. The small change in the overall position from a year ago on the face of it seems quite encouraging given that last winter was so dry. Hopefully the last three years’ really abnormal rainfall figures won’t be repeated. On the optimistic side there have been a couple of reasonable cold fronts this week so that whereas rainfall for the year to date as at 23 April was only 7.5mm (compared to the 40 year median figure of 74mm) there have now been good rains, and even flooding. This is following the recent pattern of negligible rain for seven or more months around the summer period and winter rains having to provide virtually all the runoff.

In contrast the Free State dams are now at 100% of capacity following the good March rains. This extends even to the country’s second largest dam, the Vanderkloof, pictured below, which was only a little over half full four weeks ago, representing an increase of 1.4 billion m3. This increase would have been enough to raise the level of the Western Cape’s 20 leading dams from 16 to 91% of capacity. The increase in all the Free State dams in the four weeks is equal to 172% of the Western Cape’s total installed capacity. This helps emphasise the fragility of Cape Town which can access less than half the Western Cape capacity.

vdk2

The Lesotho dams, despite being on or fairly close to the headwaters of the Orange and Vaal river systems which feed the Free State dams, continue to disappoint at only 57% of capacity and leads one to wonder what combination of circumstances would be necessary to achieve 100%, given two years of good summer rains. The kZN and Eastern Cape dams continue their recent steady trend of rarely  moving much outside the 60 to 70% of capacity band. The region’s overall figure of 82% of capacity is good news for most but not all of the country.

Sources: http://www.dwa.gov.za; http://www.csag.uct.ac.za; https://www.vanderkloofdam.co.za

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