thalwegprincipe

Thalwegprinzip, or the thalweg principle, is a rule used in border delimitation along rivers. It designates the boundary between states to run along the thalweg—the line of deepest points in the bed of the watercourse, usually corresponding to the main navigable channel. In many cases the boundary is drawn as the centerline of the navigable channel within the river's banks, under the assumption that the deepest, most navigable part of the river best represents the route of flow and historic use.

Implementation varies by treaty and jurisdiction. Some agreements fix the boundary to the thalweg itself; others fix it to the centerline of the main navigable channel, which may be referred to as the thalweg, while some rely on fixed bank lines. The principle accommodates natural shifts in the river but often contains stabilization rules to prevent incessant changes in sovereignty.

Criticism and limitations include the dynamic nature of rivers. Since rivers migrate through erosion, sedimentation, floods, or engineering interventions, boundaries defined by the thalweg can shift over time and provoke disputes. In practice, many borders are adjusted by treaties, arbitration, or domestic law to balance navigation rights, security, and state sovereignty.

Origin and usage: The concept emerged in European public law and is widely cited in international boundary practice. The term is primarily used in German-speaking legal literature (Thalwegprinzip) though parallel concepts exist in other legal systems.

See also: Thalweg, Boundary delimitation, International water law.