Lake Victoria and the Flow of the Yala River

Abstract

WITH reference to Dr. Hale Carpenter's letter (NATURE, August 30, p. 311) on the subject of Lake Victoria and the flow of the Yala River, the following considerations occur to me. There is a fairly regular diurnal fluctuation in the waters of the lake. At the head of the Kavirondo Gulf the average level is a few inches higher in the afternoon than in the morning. On the open shore of the lake at Entebbe the variation is naturally smaller, but the figures given by Dr. Carpenter (which appear to be in metres) show a trace of it. I attributed this variation to the alternation of land and lake breezes, which drive the water away from the shore during the night and early morning and towards the shore during the afternoon. From this factor alone one would expect the direction of flow between the Yala swamp and the lake to be from the swamp in the morning and towards it in the afternoon, i.e. the reverse of that found by Dr. Carpenter. If the channels between swamp and lake are short and deep, there might be a regular circulation of the water. The diurnal variation of temperature in a shallow swamp is much greater than that in the main body of lake water. The swamp water cooled during the night would flow towards the lake as a bottom current and would be replaced by a surface flow from the lake to the swamp, the latter only being observed by Dr. Carpenter. In the afternoon the heated swamp waters would flow towards the lake as a surface current and the cooler lake water would form the bottom current.