I have been doing some research.
If one looks at the Kariba lake level graphs published on the Zambesi River Authority website http://www.zaraho.org.zm/hydrology/lake-levels and projecting the graph for the period up to early January 2016, using last year’s graph, for the remainder of this year, the level will drop to just over 477.0M. This is about 0.75M higher than where it was in January 1996, the previous low, and still leaves 1.5M of generating capacity before hitting the 475.5M level, or 6 weeks of generation at current output.
The slope of the lake level graph from end of June to mid September does not suggest there has been any reduction in water take-off. However, the next lake level update may show a slowing down of the drop.
Interestingly, the Nehanda Radio website http://nehandaradio.com/2015/08/27/water-rationing-limits-kariba-power-generation/ quoted Zimbabwe Power Corporation in August saying that the water generation capacity available until the end of the year had to be reduced from 45 to 40 billion cubic M. This must be shared equally between Zambia and Zimbabwe, and when translated to actual power, the website quoted that 475Mw would be available to Zimbabwe and only 305Mw to Zambia….presumably each using the same water!! Which begs the questions, Why? Are the newer turbines on the Zambian side less efficient?