Grotian Traditions, Thalwegs and Winner Take All

Rivers are a natural boundaries and a pretty obvious way to determine who controls land on either bank, not withstanding occasional riverbed shifts. However rivers are also natural resources in their own right. They provide drinking water, irrigation, food and transportation. Those who control territory abutting a river naturally want to own and control access to the precious water coursing past. Methods have been devised to prevent or resolve disputes but there are only two basic approaches with minor variations. Either one landowner will control the river entirely or residents on opposing banks will find a way to split it. This can be established by negotiation, tradition, logic, adjudication, luck, force or by any other reason, but it all boils down to either sharing control or not.

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The Potomac River boundary is an example of “one side owns all.” In this instance Maryland and the District of Columbia own the river. Virginia, their cross-border neighbor does not. This arrangement traces its roots to a 1632 Royal Charter that continued to be applied across the centuries. It can be seen clearly in the map above where the border extends all the way to the Virginia shoreline. It sounds like such an elegantly simple solution but water rarely remains constant for long. Even in what would seemingly be a cut-and-dried instance, agreements are necessary to fix upon certain points such as the low-tide mark, the crossing of Virginia tributaries flowing into the river, and landform changes taking place during cycles of drought and flood. Disputes continue to flare into the modern era as water becomes an increasingly valuable commodity.

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It’s more common for neighbors to share ownership as in the case of the Columbia River between Oregon and Washington shown above. An early method involved an equal split right down the middle based on fundamentals of natural law advocated by Hugo Grotius in the early 17th Century. Such Grotian theories formed the underpinning of international law and provided a rational basis for dispute resolution and economic efficiency. However as in the example here, and indeed for most river boundaries, the Grotian model has not been applied. Notice how some of the islands fall within Oregon and others in Washington as the border zigzags between the Columbia’s riverbanks. That’s because river borders in the modern era generally follow the thalweg.

“For navigable rivers, which are commonly used for demarcating international boundaries, the legal rule dictates that the boundary line follow the middle of the thalweg, or the navigable channel through which the current flows downstream. If the river is not navigable, the older, Groation rule applies in which the boundary runs down the middle of the stream.” – Joyner, Christopher C. International Law in the 21st Century: Rules for Global Governance. Lanham MD: Rowman & Littlefield, 2005. 43.

So the thalweg is the midpoint of the deepest contiguous line along the bottom of a riverbed, and is also generally its point of greatest flow and natural direction. It is derived from the German words Tal meaning valley, and Weg, meaning way, and is alternately called the “valley line.” Since rivers twist and turn, and currents drop sediment in some locations and erode them in others, it’s no wonder that the thalweg usually swings back and forth between riverbanks.

Got all that? This will be useful for future posts.

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