Lots of talk on social media about the volume of the Falls at the moment - some are even claiming highest levels in seventy years - tourism media hype or reality? Zambezi River Authority data shows river levels at the Falls have experienced an early rise in levels, and levels are high, with flow rates exceeding 4,000 cubic metres a second, but within normal ranges and by no means exceptional. The trend is much as per 2019-20, which also experienced an early peak to similar levels, followed by a second peak in June - but not many people experienced the Falls during this high season due to the global pandemic (Victoria Falls Bits and Blogs, 23rd April 2020). It remains to be seen whether this year will follow with a similar second peak.
The 2017/8 flood cycle experienced a slightly higher peak, but later in May, while 2009/10 recorded a yet higher 'double peak' (but still below 5,000 cubic metres/second) and 2008/9 recorded an even higher early peak (exceeding 5,500 cubic metres/second). Individual years prior to this date are not shown, with the long-term mean indicated by the dashed red line (partially obscured by subsequent data), but the exceptional flood years of 1977/8 and 1968/9 are shown, when flow rates exceeded 6,000 and 8,000 cubic metres a second respectively. The highest recorded flood levels at the Falls was 9,346 cubic metres/second in March 1958 (not shown on hydrograph).
What is abundantly clear from the hydrograph is the extreme variability in seasonal flow over the Falls - from lows of 300 cubic metres/second to highs of 3,000 cubic metres/second, and huge variability in annual flood levels, reflecting variability in seasonal rainfall across the vast catchment area of the Upper Zambezi, covering western Zambia, including the vast Barotse Floodplains, and into south-eastern Angola (covering over 515,000 square kilomertres). What is of particular note from the hydrograph is that 2023-24 was an exceptionally 'flat' year, with peak flows hardly exceeding 1,000 cubic metres/second, and highlighting the extreme variability between flood years.
Data on river flow levels has been collected at the Victoria Falls since 1907, providing a huge data set of information on historical flow levels.
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The authors Moore et al (2007) recorded a mean annual flow at the Victoria Falls (!907-2002) of 1,087 cubic metres/second.
"Records of water level from the hydrological station at Victoria Falls, taken since 1907 are illustrated in Figure 15.11c. These indicate lower than normal years for 1907-46, above normal for the years 1947-81, and again below normal for 1982-1997. A major flood of 1958, during the construction of Kariba Dam, followed heavy rains in the upper catchment and also the local catchment below Victoria Falls. A coffer dam was overtopped and a road bridge washed away – at its peak some 9,000 m3 s−1 were passing over the Victoria Falls. In magnitude it was equivalent to the 1 in 100 year flood, which in turn is roughly half the probable maximum flood of 21,000 m3 s−1." (Moore et al, 2007)
References
Moore, A E, Fenton P.D, Cotterill F.P.D, Main, M.P. L. and Williams H.B. (2007) The Zambezi River. In Gupta, A [Editor] (2007) Large Rivers - Geomorphology and Management. Chapter 15. John Wiley & Sons, Ltd, England.
Victoria Falls Bits and Blogs (23rd April 2020)
