botswana/namibia - Cour international de Justice

(v) The mud-peat deposits in the area of the island adjacent to the northern channel are of later
date, ranging in age 1,400 years to 1,890 years, while the older materials are to be found along
the centre of the island and the southern channel. This suggests that they were laid down later
than the rest of the island. The one exception is Bore Hole 9 immediately south of the lagoon
in the southern channel, where the sample was also of relatively younger materials.
(vi) the lower layer of sand indicates a higher energy period of fluvial erosion and deposition
of sediments;
(vii) in the lower layer of sand there is a predominance of angular and sub-angular particles.
This indicates that the sediments have not undergone rounding by abrasion in transport and
hence were found in situ;
(viii) the evidence indicates that these sands are of local origin. A method sensitive enough
for discriminating between different processes of sediment deposition, known as the sorting
measure or the inclusive standard deviation, applied to the samples, supports their originating
from the local area; the standard deviation values do not accord with values for river sands;
(ix) the local source is the sand in the ridges to the south of the Chobe River;
(x) these sands were brought by bank erosion into an ancient river approximately occupying
the position of the current southern channel;
(xi) the increased sediment load vis-à-vis the available energy silted up the southern channel,
necessitating a change in alignment of the river to its present form along the northern channel;
(xii) the processes described above are "recent" only in geological terms, occurring between
10,000 and 3,000 years ago;
(xiii) the existence of the present environment in the Chobe River for many thousands of
years is supported by the Sedimentological Report's analysis as to type and size of the
particles of the lower layer sampled from the 13 bore-holes. That analysis indicates a
predominance of saltating population in the particles and of medium to fine sand categories.
The predominance of both indicates a depositional environment in which flow velocities are
moderate. Saltating particles are those transported in a hopping fashion, being too large to
remain buoyant for long and too small to be transported as bedload by rolling. They are
mobilised by moderate flow velocities. The mean grain size in a deposit is largely a function
of the energy of the processes controlling transport and deposition. Medium to fine sand
particles suggest an energy-limited environment , where reworking of sediments or the
importation of sediments from outside the locality is restricted;
(xiv) there is a very limited presence of rolling and coarse particles in the samples at any of
the depths cored and, where they do occur, their location is likely to be indicative of overbank
flow during floods. Rolling population requires a larger energy to mobilise than sediments in
the saltating and suspension categories. Overbank flow during floods is likely to mobilise
rolling sediments, but, equally, when flow slackens towards the end of the flood, these large
sediments are the first to be deposited. Consistent with such high flow, some 10,000 years ago
or more, is the presence in limited quantity of rolling particles at 1.50 to 2.00 metres depth at
Bore-holes Nos.12 and 1 at the western and eastern bifurcation points of the Island, at
Boreholes Nos. 3 in the northern channel and at Borehole 8 in the southern channel. At the