B.T. Mangeni (Uganda)
Lake Victoria level, Jinja releases, satellite altimetry, Agreed curve.
This paper analyses the operation of the Owen Falls (Nalubale) dam as a run-of-the river facility or according to what came to be known as the “Agreed Curve”. The outflows at Jinja had to be effected in such a way that the original relationship between the Jinja releases/outflow and the lake level was maintained as before the construction of the Owen Falls dam. Comparison of the trend of the Jinja releases and satellite Lake Victoria height variations was carried out from 1998 to 2004. Rainfall, evaporation and drought conditions for the same period were reviewed to assess their possible effects on the lake level. The results indicated that the operation of the dam according to the agreed curve was followed for most of the time varying the Jinja releases according to lake level as required until about 2001.Thereafter Jinja releases were progressively increased to the maximum ever in 2004 without regard to changes in lake levels. This meant that the operation of the dam/s was no longer based on the agreed curve after 2001. No significant influence on lake level could be deduced from changes in rainfall, evaporation and drought conditions as these remained essentially about average at least up to 2004. The conclusion from this analysis was therefore that the diminishing Lake Victoria level experienced from 2003 was mainly due to the departure from the original operation policy at the Nalubale dam which meant that more water than authorized by the agreed curve was being released.
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