Definition of thalweg in US English:



  • A line connecting the lowest points of successive cross-sections along the course of a valley or river.

    • ‘Along all three of the Maine/New Brunswick boundary rivers, the actual boundary follows the middle of the main channel, but it is only on the St. Croix that the term thalweg is expressly used.’
    • ‘The common boundary between the States of Arkansas and Mississippi in the Mississippi River is the thalweg, which is the middle of the main navigable channel followed as the principal course of downstream navigation.’
    • ‘A river adjusts to variations in seasonal changes in volumetric flow by means of its thalweg (the thread of fastest flowing water), its flood plains, and its underground flow.’
    • ‘Where a large river separates two countries or states, the boundary is commonly drawn along the thalweg, which is the continuous line of deepest soundings along the main channel of the river.’
    • ‘Article 2 of the Treaty of Washington, April 11, 1908, states that the boundary along the St. Croix River shall ‘follow the center of the main channel or thalweg as naturally existing.’’


Mid 19th century: from German, from obsolete Thal ‘valley, dale’ + Weg ‘way’.