Just to continue the discussion on what I feel is an important on-going issue, I forward on my message to Gbenga yesterday with some minor additions. The articles and texts that have been referred to in other messages are very useful starting points but I would suggest that the issue demands updated discussion.

Great question Gbenga and one that has baffled policy makers and lawyers for centuries.

The first step is to see what the boundary treaty says about river movement (will the boundary follow the river or be fixed at a specific date etc.) If the treaty is silent, then it becomes a bit more tricky. The so-called general rules of accretion and avulsion may apply, in that unless parties can identify specific instances of avulsion, then the boundary will follow the river through accretion. I have been doing quite a bit of research on river boundaries looking at much of the juridical history of accretion and avulsion going back to Roman property law and I am not convinced that they are currently recognised as accepted principles in customary international law.  There is plenty of national jurisprudence on accretion/avulsion (particularly in the US Supreme Court and English common law) but state practice in international boundary treaties has not been universally consistent. The ICJ has been very cagey about accretion and avulsion, and the closest it has come to drawing any conclusions was in the land section of the El Salvador/Honduras case (and the decision on interpretation) when the Chamber failed to directly state that avulsion was a customary rule of international law. The only international decision/arbitral award I can find that refers directly to accretion and avulsion is the 1911 Chamizal arbitration, which itself was the Mexico-US boundary commissioners with a Canadian arbitrator. So without distinct ‘rules’ it becomes a matter of negotiation.

For me the most powerful argument is that if two states choose a thalweg (the main navigation channel – which I believe in legal terms is its proper definition) as a boundary, then the intention of both states when agreeing the boundary was to have equal access to navigation along the boundary river. In addition, I would be willing to bet that administrative practices since the original agreement have observed the river itself as the de facto boundary. However, if the river has shifted significantly then of course the state that believes it has ‘lost’ territory will naturally argue that the boundary should be along the course of the river at the date of the treaty. This gives rise to a multitude of administrative/management problems when the river no longer coincides with the boundary and you get bits of territory on the ‘wrong’ side of the river. Governments are obsessed with having a ‘fixed’ river boundary line even if it is just a line of coordinates, but they are just deluding themselves if they believe the river will not continue to move. This obsession with fixing a boundary river can be taken to ridiculous levels as the canalisation of the Rio Grande around Juarez/El Paso illustrates with disastrous environmental effects.

Apologies for the not so subtle marketing ploy but we had a fantastic discussion about these very issues at the last IBRU workshop Boundaries and Water back in July.

All the very best,

John