botswana/namibia - Cour international de Justice

350. The northern channel carries the larger flow because it has greater capacity (see
paragraphs 385 and 386). Flow in a channel is a product of cross-section area (a product of
the width and depth of the channel) and mean velocity through the cross-section. As Professor
Sefe explains:-
"The word "main" has both hydrological and geomorphological connotations relating to the
velocity of flow, hence discharge. So it connotes the ability of the river to transport debris in
terms of particle size (i.e. its competence, Mackin 1948); and the maximum load (sediment of
particular grain size) a stream can carry (i.e. its capacity as defined by Gilbert 1914). As
energy in a river is proportional to the product of the mass (i.e. size and the bed-slope), the
larger of two tributaries is considered the main channel."5 (Botswana Memorial, Appendix to
Chapter VII, First Opinion of Professor Sefe, page 5).
[5. Note that capacity as used by Gilbert refers only to its geomorphic usage. However, as a stream derives its
energy from the volume of flow in the channel, a hydrological connotation is also implied in Gilbert's usage.
Thus, hydrologically speaking, 'capacity' refers to volume of flow which is the product of depth, width and
velocity of flow.]
351. To sum up, on the basis of the six propositions and criteria set out above, the Chobe
River is a mature perennial river with continuous downstream flow at the bifurcation of the
island through the northern and western channel, that flow being measured by navigability
and competence to carry flow. As the thalweg, the shipping channel and the one through
which the greater flow takes place, the northern and western channel is clearly the main
channel within the meaning of Article III of the Anglo-German Agreement of 1890.
(F) The Report of the Sedimentological Study of Kasikili/Sedudu Island
352. A Sedimentological Study of Kasikili/Sedudu Island was carried out in December 1996
by Professor F.T.K. Sefe of the University of Botswana with the assistance of Mr I.M. Muzila
B.Sc. (C. Engineering), Principal Hydrological Engineer, Government of Botswana. The
results and analysis are set out in the Report in Appendix 3, Volume II, of this Counter-
Memorial and show the location, composition, category, size and date of particles in the
extraction of cores from 13 bore-holes on Kasikili/Sedudu Island. The position of the boreholes
is shown on the attached plan and at Table 1 (Coordinates of the Sample Sites).
353. The Study provides evidence in support of the following propositions:-
(i) Kasikili/Sedudu Island consists of two layers, a dark top layer consisting of a clay, silt and
mud admixture extending to about 1.5 metres in depth, and a bottom layer of sand, sampled
from 1.50 to 5.00 metres in depth (Table 2);
(ii) the two layer profile suggests two distinct processes;
(iii) deposition of sand, clay and mud to a depth of 1.50 metres, would require a very low
energy environment with very low flow velocity with flow being laminar;
(iv) the complete absence of sand in this top layer suggests that the deposition process was
never interrupted in any major way and indicates that the low energy environment, and the
present alignment of the Chobe River with the north channel carrying the major flow of water,
occurred thousand of years ago;