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World Court Digest

II. Substantive International Law - Second Partv
1.2. Boundaries
1.2.1.Land Boundaries

¤ Kasikili/Sedudu Island
Judgment of 13 December 1999

[pp. ] 21. ... As far as the region covered by the present case is concerned, this provision locates the dividing line between the spheres of influence of the contracting parties in the "main channel" of the River Chobe; however, neither this, nor any other provision of the Treaty, furnishes criteria enabling that "main channel" to be identified. It must also be noted that the English version refers to the "centre" of the main channel, while the German version uses the term "thalweg" of that channel (Thalweg des Hauptlaufes).

22. Throughout the proceedings, the Parties have expressed differing opinions regarding the method to be applied for the purpose of interpreting these expressions. Botswana contends that:

"[i]n a bifurcated stretch of river, such as the Chobe River in the vicinity of Kasikili/Sedudu Island, both channels will have their respective thalwege. However, the thalweg of the main channel will be at a lower elevation than the thalweg of the other channel. Only the thalweg of the main channel can be logically connected to the thalweg of the channel upstream of the point of bifurcation and downstream of the point of reunion."

Botswana maintains that, in order to establish the line of the boundary around Kasikili/Sedudu Island, it is sufficient to determine the thalweg of the Chobe; it is that which identifies the main channel of the river. For Botswana, the words "des Hauptlaufes" therefore add nothing to the text.

23. For Namibia, however, the task of the Court is first to identify the main channel of the Chobe around Kasikili/Sedudu Island, and then to determine where the centre of this channel lies:

"The 'main channel' must be found first; the 'centre' can necessarily only be found afterward. This point is equally pertinent to the German translation of the formula' ... im Thalweg des Hauptlaufes ...' In the same way as with the English text, the search must first be for the 'Hauptlauf' and for the 'Thalweg' only after the 'Hauptlauf' has been found. The 'Hauptlauf' cannot be identified by first seeking to find the 'Thalweg'."

24. The Court notes that various definitions of the term "thalweg" are found in treaties delimiting boundaries and that the concepts of the thalweg of a watercourse and the centre of a watercourse are not equivalent. The word "thalweg" has variously been taken to mean "the most suitable channel for navigation" on the river, the line "determined by the line of deepest soundings", or "the median line of the main channel followed by boatmen travelling downstream". Treaties or conventions which define boundaries in watercourses nowadays usually refer to the thalweg as the boundary when the watercourse is navigable and to the median line between the two banks when it is not, although it cannot be said that practice has been fully consistent.

25. The Court further notes that at the time of the conclusion of the 1890 Treaty, it may be that the terms "centre of the [main] channel" and "Thalweg" des Hauptlaufes were used interchangeably. In this respect, it is of interest to note that, some three years before the conclusion of the 1890 Treaty, the Institut de droit international stated the following in Article 3, paragraph 2, of the "Draft concerning the international regulation of fluvial navigation", adopted at Heidelberg an 9 September 1887: "The boundary of States separated by a river is indicated by the thalweg, that is to say, the median line of the channel" (Annuaire de l'Institut de droit international, 1887-1888, p. 182), the term "channel" being understood to refer to the passage open to navigation in the bed of the river, as is clear from the title of the draft. Indeed, the parties to the 1890 Treaty themselves used the terms "centre of the channel" and "thalweg" as synonyms, one being understood as the translation of the other (see paragraph 46 below).

The Court observes, moreover, that in the course of the proceedings, Botswana and Namibia did not themselves express any real difference of opinion on this subject. The Court will accordingly treat the words "centre of the main channel" in Article III, paragraph 2, of the 1890 Treaty as having the same meaning as the words "Thalweg des Hauptlaufes" (cf. 1969 Vienna Convention on the Law of Treaties, Article 33, paragraph 3, under which "the terms of the treaty are presumed to have the same meaning in each authentic text").

[pp. ] 29. The Parties to the dispute agree on many of the criteria for identifying the "main channel", but disagree on the relevance and applicability of several of those criteria.

For Botswana, the relevant criteria are as follows: greatest depth and width; bed profile configuration; navigability; greater flow of water. Botswana also lays stress, in the following terms, on the importance, from the standpoint of identification of the main channel, of "channel capacity", "flow velocity" and "volume of flow":

"channel capacity - This is determined by width and depth of the channel and in the discharge equation it is represented by cross-sectional area. From the cross-section survey and the analysis of satellite imagery, it is clear that the northern channel is deeper than the southern channel ... .

flow velocity - Flow velocity is a function of bed slope, hydraulic radius and roughness coefficient. ... the northern channel has a steeper bed slope; both of its banks are smooth (compared to the southern channel), therefore velocity will be higher in that channel.

volume of flow - Volume of flow in a channel is computed as the product of channel capacity (cross-section area) and mean velocity through the cross-section."

Namibia acknowledges that

"[p]ossible criteria for identifying the main channel in a river with more than one channel are the channel with the greatest width, or the greatest depth, or the channel that carries the largest proportion of the annual flow of the river. In many cases the main channel will have all three of these characteristics."

It adds, however, referring to the sharp variations in the level of the Chobe's waters, that:

"neither width nor depth are suitable criteria for determining which channel is the main channel."

Namibia nevertheless further states the following:

"Various criteria may be employed; these include width, depth, velocity, discharge, and sediment transport capacity. Since discharge is the product of width, mean depth and mean velocity, and is a determinant of transport capacity, it is the most straightforward and general criterion."

Among the possible criteria, Namibia therefore attaches the greatest weight to the amount of flow: according to Namibia, the main channel is the one "that carries the largest proportion of the annual flow of the river". Namibia also emphasized that another key task was to identify the channel that is "most used for river traffic".

30. The Court finds that it cannot rely on one single criterion in order to identify the main channel of the Chobe around Kasikili/Sedudu Island, because the natural features of a river may vary markedly along its course and from one case to another. The scientific works which define the concept of "main channel" frequently refer to various criteria: thus, in the Dictionnaire français d'hydrologie de surface avec equivalents en anglais, espagnol, allemand (Masson, 1986), the "main channel" is "the widest, deepest channel, in particular the one which carries the greatest flow of water" (p. 66); according to the Water and Wastewater Control Engineering Glossary (Joint Editorial Board Representing the American Public Health Association, American Society of Civil Engineers, American Water Works Association and Water Pollution Control Federation, 1969), the "main channel" is "the middle, deepest or most navigable channel" (p. 197). Similarly, in the Rio Palena Arbitration, the arbitral tribunal appointed by the Queen of England applied several criteria in determining the major channel of a boundary river (Argentina-Chile Frontier Case (1966), United Nations, Reports of International Arbitral Awards (RIAA), Vol. XVI, pp. 177-180; International Law Reports (ILR), Vol. 38, pp. 94-98). The Court notes that the Parties have expressed their views on one or another aspect of the criteria mentioned in paragraph 29 above, distinguishing between them or placing emphasis on their complementarity and their relationship with other criteria. It will take into account all of these criteria.

[p. ] 87. In view of the absence of any map officially reflecting the intentions of the parties to the 1890 Treaty and of any express or tacit agreement between them or their successors concerning the validity of the boundary depicted in a map (cf. Temple of Preah Vihear, Judgment, Merits, I.C.J Reports 1962, pp. 33-35), and in the light of the uncertainty and inconsistency of the cartographic material submitted to it, the Court considers itself unable to draw conclusions from the map evidence produced in this case. That evidence cannot therefore "endors[e] a conclusion at which a court has arrived by other means unconnected with the maps" (Frontier Dispute (Burkina Faso/Republic of Mali), I.C.J. Reports 1986, p. 583, para. 56), nor can it alter the results of the Court's textual interpretation of the 1890 Treaty.

[p. S.O. Oda] 26. The 1890 Treaty is an instrument which determined the respective spheres of influence of the Parties in this region of Africa but which certainly did not fix national boundaries there between the territories of Germany and Great Britain. The limit of the German sphere of influence was fixed as the "centre of the main channel of the Chobe River", but in that Treaty no concrete boundary line was indicated in this geographically complex area. The determination of the boundary, which would certainly have had the effect of determining the legal status of Kasikili/Sedudu Island, was at that time a matter far removed from the actual purpose of the Treaty.

[p. S.O. Oda] 59. After an examination of certain incidents that occurred in the area, as well as the correspondence between the authorities of the northern bank and southern bank and certain surveys conducted in the course of the past hundred years, I conclude that the northern channel of the Chobe River had been regarded, implicitly or explicitly, as the boundary separating the authorities on the northern and southern banks, and that Kasikili/Sedudu Island had been regarded as being under the authority of the south, despite the occasional use of the Island by tribespeople from the northern side.

The Judgment, however, refers to these same past practices as if they might serve to assist it in interpreting the 1890 Anglo-German Treaty as provided for in the Vienna Convention on the Law of Treaties, and the Court came to the conclusion that those practices were not in fact capable of constituting "subsequent practice" or "subsequent agreement" within the meaning of the Vienna Convention. I would emphasize once more that in my view this case is not one directly related to the application of the provisions of the Vienna Convention on the Law of Treaties to the 1890 Anglo-German Treaty, to which later Treaty neither Botswana nor Namibia is a party.

I refer above to these past practices, as decisive factors in assisting the Court to determine the course of the boundary in the Chobe River and, hence, to determine the status of Kasikili/Sedudu Island as a part of the territory of Botswana.

[pp. D.O. Weeramantry] 91. A court reaching such a conclusion as that Kasikili/Sedudu Island belongs to Namibia cannot end its responsibilities with the mechanical exercise of a geometric delineation of boundaries on the ground.

I have already advanced the illustration of a sacred site which is one and entire, but which may need to be divided in two if merely geometrical considerations are to be followed. Likewise, a village may be separated from a grazing ground which for centuries had been integral to it, or the village itself may be divided into two parts whose residents thus became citizens of two different States, however closely they may be connected. It would be a diminution of a court's inherent jurisdiction if it were expected in such hypothetical circumstances to turn its glance away from these very real and vital problems and proceed with the task of delineation as if it were a purely geometrical exercise. Charged as it is with the application of equity to the problem before it, a court would not proceed in this fashion.

If there is a natural reserve which, in the interests of the ecosystem and of biological diversity cannot be divided without lasting damage, this is a factor which the Court can no less ignore than a sacred site or archaeological preserve which must be maintained in its integrity if it is to be preserved.

92. There is more than one way in which equitable considerations can be given effect in such situations.

One is that the Court should consider itself empowered to make a slight deviation from the strict geometric path indicated by the boundary treaty, but always preserving a balance between the entitlements of the two parties to the enjoyment of this precious asset.

Another is to constitute, in the larger interests of both parties and indeed of the world community, a joint régime over the area so that neither party is deprived of its use. In this category, a multitude of possibilities and precedents are available which I shall briefly consider later.

93. I may observe here that the division of a sacred site or ecological preserve into two discrete portions is a procedure likely to produce tension between the Parties in the future, as that which was considered to be a common resource on both sides of the border is then available to neither Party, and the entire asset is under risk of destruction through the process of division. Indeed, in an extreme case, as where a geometrical line of partition passes through the most holy place of a sacred site, the imperative need for such discretion on the part of the Court is obvious.

That the Court has such a power, and indeed a duty in an extreme case, is thus beyond dispute. Whether a given situation is an appropriate one for the use of its equitable power is a matter for the Court's discretion.

In the present state of recognition of the importance of ecological considerations, and having regard to the importance of this natural reserve as stressed to us by both Parties at the oral hearings, a decision in favour of Namibia would trigger the exercise of such discretion.

[p. D.O. Weeramantry] 98. The emphasis, therefore, was on areas of interest rather than linear boundaries. A major difference between boundary treaties, stricto sensu, and zones of influence treaties is that zones of influence treaties deal with spatial zones while boundary treaties involve points or lines that have no breadth. Consequently, there is a precision and definiteness attending a boundary treaty which distinguishes it from the generalized nature of a treaty dealing with spheres of influence. In the expressive language of Brownlie, a boundary treaty "draws precision and clarity in its train". The same cannot be said for spheres of influence treaties.

This is not a conclusive factor in the present case, but is not without its implications in the particular circumstances here, for

(a) it gives the Court greater flexibility in the definition of the boundary in question, while of course not departing from the terms of the Treaty;

(b) it gives the Court greater scope for the application of equitable principles;

(c) it widens the latitude available to the Court for making provision for the integrity and preservation of important features such as environmental preserves; and

(d) it enables the Court to take into account such factors as that one interpretation will draw a line between a given people and the land which they have traditionally used over a long period of time, while the other will not, thereby inclining the Court towards the former interpretation, if it be possible within the terms of the Treaty.

99. In the present case, this factor makes easier the resolution in favour of Namibia of the doubt regarding interpretation. It would also incline the Court against a formalistic interpretation which deprives a people of land which they have used over the generations without any acknowledgment of any other sovereignty over it and without any assertion of right by the State claiming such sovereignty. A zones of influence treaty would permit more flexibility in this regard than a treaty dealing strictly with boundaries.

To attach the Island which the Masubia had long regarded and used as theirs to another sovereign State upon a literal interpretation of a zones of influence treaty would perhaps represent an overly formalistic approach to an essentially human problem.

100. At the same time, the additional leeway resulting from this fact would make it easier for the Court, in holding with Namibia, to make appropriate provision in its Order for preserving in its integrity as one comprehensive whole the wildlife habitat which comprises both the Island and the Chobe Game Park to the south. The Court would be able to exercise its equitable powers to require Namibia to enter into a joint régime with Botswana in order to ensure the integrity of this habitat.

[p. D.O. Fleischhauer] 5. As to object and purpose of the 1890 Treaty, I would like to first observe that the 1890 Treaty is a bilateral treaty and that, as is often the case with bilateral treaties, object and purpose pursued with the Treaty by its parties follow fairly clearly from its text. The object of the 1890 Treaty were the spheres of influence of the two contracting parties in Africa and the purpose was their agreed delimitation (Arts. I-IV of the Treaty) in order to secure the respect by each of the parties of the sphere of the other (Art. VII). Although the delimitations provided for in the Treaty have evolved to become existing boundaries between African States, including the boundary between Namibia and Botswana, the Treaty has not to be regarded as a boundary treaty in the technical sense; the Treaty was meant to keep the political relations between the two contracting States undisturbed by rivalry in Africa. This cannot be overlooked in its interpretation; the Treaty must not be understood as meaning a comprehensive settlement of all questions regarding the actual course of the delimitations it establishes. It seems quite compatible with the Treaty's object and purpose that, in certain places, it sets forth only in broad lines where the delimitation of the spheres of interests runs but leaves the fixation of its course in detail to the future application of the Treaty.

[p. D.O. Fleischhauer] The Court should however have gone into the conditions under which title to territory may be acquired by prescription, far enough to state that South Africa could not have acquired title to the Island by prescription. South Africa, whose presence in the Caprivi Strip including the Island lasted longer than the presence there of Germany or Britain, prior to the termination of the Mandate by the General Assembly in 1966 exercised authority there not à titre de souverain but à titre de mandataire. As mandatory, South Africa certainly was vested by virtue of the Mandate instrument of 17 December 1920 (League of Nations Journal Officiel, 2nd Year, No. 1, p. 89) with the "full power of administration and legislation over the territory subject to the present Mandate as an integral portion of the Union of South Africa"; however, as the Court observes in its Advisory Opinion on the International Status of South West Africa (I.C.J. Reports 1950, p. 128, at p. 132):

"On the other hand, the Mandatory was to observe a number of obligations, and the Council of the League was to supervise the administration and see to it that these obligations were fulfilled."

And the Court added:

"The terms of this Mandate, as well as the provisions of Article 22 of the Covenant and the principles embodied therein, show that the creation of this new international institution did not involve any cession of territory or transfer of sovereignty to the Union of South Africa. The Union Government was to exercise an international function of administration on behalf of the League, with the object of promoting the well-being and development of the inhabitants." (Ibid.)

This perception of the nature of the Mandate is incompatible with acquisitive prescription working in favour of the Mandatory. After the termination of the Mandate, the continued presence of South Africa in South West Africa (Namibia) was no longer "peaceful", i.e., uncontested, as is confirmed by Security Council resolution 276 (1970) and by the Courts Advisory Opinion on the Legal Consequences for States of the Continued Presence of South Africa in Namibia (South West Africa) notwithstanding Security Council Resolution 276 (1970) (I.C.J. Reports 1971, p. 16).

[pp. D.O. Parra-Anguren] 42. Consequently, after the confirmation of the creation of the mandate by the Council of the League of Nations in 1920, the Union of South Africa could not dispose by its own actions of the territory of South West Africa, as it had been determined by the subsequent practice of the parties to the 1890 Anglo-German Agreement.

43. For this reason, 1914 is the latest date to be taken into account for the determination of the subsequent practice of the parties, Germany and Great Britain, in regard to the interpretation of Article III of the 1890 Anglo-German Agreement. In fact, no subsequent practice could exist on the part of Germany after September 1914 when the Eastern Caprivi was occupied by Southern Rhodesia. During the existence of the mandate the Union of South Africa had no competence either to enter into any express agreement to delimit the international boundary of South West Africa or to modify the prevailing subsequent practice with regard to the interpretation of Article III of the 1890 Anglo-German Agreement. Consequently, in my opinion, the subsequent practice of the parties for the purpose of interpreting the Anglo-German Agreement should be determined on the basis of the situation existing up to September 1914.