botswana/namibia - Cour international de Justice

282. This statement is somewhat contradicted later by Namibia in its Memorial where it
admits to normal flow in the months of April to July and describes a more complicated flow
pattern:
"Thus, during the first part of the flood season, water actually moves from the Zambezi into
and up the Chobe from the Mambova Rapids. This occurs in the months from January to
March. During that period the movement of the waters of the Chobe is upstream, i.e. the
reverse of what would normally be expected. As the floods begin to subside, this flow
reverses, and from April to July the waters flow in the normal direction downstream to its
confluence with the Zambezi." (Namibian Memorial, p.22, para.62).
"By August, however, the levels of water in the Chobe River fall below the height of the
rapids at Mambova. From August until December, the water in the two channels in the region
around the island is stagnant. (Namibian Memorial, p.22,para.65).
283. This misrepresents the flow along the Chobe. As stated in the Memorial of Botswana,
(paragraphs 26 to 29), flow along the Chobe is a result of the runoff from the catchment area
of the system and follows the pattern of the rainfall regime which occurs over certain seasons
of the year. The Chobe is a mature river; it maintains a flow independent of the Zambezi
except in floods. Minimum velocity during the dry season is in the order of 0.5 metre per
second.
284. In October rains falling in the Angolan Highlands begin to fill the upper reaches of the
river and water levels rise through the following months until they reach their maximum in
the months of April/May. Thereafter they decline until August. At the lower end of the Chobe
a minimum flow is maintained, with a level of 925.6 metres being recorded at the Kasane
Gauging Station. In the dry season in the months of August and September, the base flow is
maintained by flow from the cross-channels linking the Chobe with the Zambezi River, and
equals any losses artificial or natural, such as evaporation (see below, paragraph 295).
285. Recent discharge figures taken in the vicinity of Kasikili/Sedudu Island show volumes of
15.660 to 21.790 cubic metres per second over the months of March and April 1997 in the
northern channel, compared to volumes of 3.127 to 5.478 cubic metres per second in the
southern channel (Counter-Memorial, Appendix 2, Second Opinion of Professor Sefe, p.80,
para.103, Table 7).
286. In the dry season the flow from the Kasai channel can result in some upstream flow. Its
effect in the northern channel is to retain rather than cause to flow upstream the normal down
gradient flow. The longterm flow over the whole Chobe system is not overridden by the local
and temporary back flow caused by the Kasai channel.
287. Professor Alexander relies on back flow to support the southern channel as the channel
with the larger volume and flow of water and to challenge the classification of the Chobe as a
river. Movement against the gradient cannot make the channel experiencing such temporary
reversal of flow a river flowing in that direction. Reversal of flow happens in rivers as well as
estuaries at times of high tide. The temporary reversal of the hydraulic gradient does not
affect the river bed gradient; channels experiencing this reversal of hydraulic gradient become
temporary storage channels, soon to resume down slope flow when the hydraulic gradient
returns to normal.