Hello Gbenga, another useful work is that by L.J. Bouchez, "The Fixing of Boundaries in International Boundary Rivers", International and Comparative Law Quarterly, Vol. 12 (3), 1963, in  particular pp. 799 ff. The mobility of the boundary-thalweg  will, in the end, depend on the provisions of the applicable treaty (or specific legal regime that may have come into existence): this may (or may not) set a 'mobile' boundary, and to different degrees. There have been cases where this 'mobility' also applied to frontier changes that were not so gradual (see footnote 85 of the above-mentioned article for some interesting examples). In the total absence of  clear-cut treaty or customary provisions, the general 'trend', as I understand it, is that the boundary fixed on the thalweg will change with the thalweg if these changes occur in a gradual and continuous manner (i.e. the requirements usually associated with accretion).
 
Fabio

Da: Anton Florian Zeilinger <[log in to unmask]>
A: [log in to unmask]
Inviato: Mer 22 settembre 2010, 12:33:42
Oggetto: Re: [INT-BOUNDARIES] Thalweg boundaries

Dear Gbenga,

yes, indeed, I would concur that in principle the "thalweg" boundary is generally recognized as a dynamic boundary, if the changes are "gradual and imperceptible". See the excellent treatise by Hyde, Notes on Rivers as Boundaries, 6 (1912) AJIL 901 (Granted, it's almost a hundred years old, but still valid, in my opinion).

This is, for instance, relatively clear from the ICJ's judgment in the Case Concerning Kasikili/Sedudu Island (Botswana/Namibia) of 1999, especially para. 24-25 and para. 88-89. The court fixed the boundary at "the line of deepest soundings" in the northern channel around the island. Notably it did not refer to a historic date (e.g. the 1890 treaty) for fixing the boundary, but just referred to this line in general. If it had intended to fix fix the border at the historic date of 1890, it would have had to say so explicitly, in my opinion.

However, I should also point to the Frontier Dispute (Benin/Niger) judgment of 1995, where the boundary was fixed by the principle of uti possidetis on the basis of colonial effectivités. Here the Chamber set the boundary at the "main navigable channel of the River Niger as it existed at the dates of independence", see para. 103.

I should also like to point you to the US Supreme Court's opinion in the case of New Hampshire v. Maine, 532 US 742 (2001) where it had to interpret a 1740 decree and determined the middle of the main channel of navigation as the boundary.

Kind regards,

Anton Zeilinger
Vienna, Austria








Date: Wed, 22 Sep 2010 09:29:53 +0100
From: [log in to unmask]
Subject: Thalweg boundaries
To: [log in to unmask]

Dear Colleagues,
 
A Court judgment refers to the thalweg of a river as the boundary between two countries based on a Century old treaty. In the determination of that boundary does a demarcation team look for the thalweg as it was a century ago or is it the thalweg of the river today that applies? My instinct says thalweg boundaries are dynamic but are there contrary views or am I plain wrong?
 
Best regards
 
Dr. Gbenga Oduntan
Lecturer in International Commercial Law,
Kent Law School,
Eliot College,
University of Kent,
Canterbury,
Kent CT2 7NS, UK.

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