Arkansas v. Tennessee

Background

Two neighboring States, Arkansas and Tennessee, fought over where their common boundary runs in a part of a navigable river. The disagreement focused on whether the line should follow the middle of the main navigable channel or a line equidistant from the permanent banks, especially after a sudden 1876 change in the river’s course. Each State pointed to its own court decisions and later state acts and proposed commissions, and Tennessee had passed laws authorizing a commission or suit to settle the line.

Reasoning

The Court addressed whether a sudden change in the river (an avulsion) shifts the interstate boundary and whether long state practice had already fixed the line. Relying on prior decisions that adopt the thalweg rule — the middle of the main navigable channel — the Court rejected arguments that the rule disappears when a channel is abandoned. It held the avulsion of 1876 left the boundary in the middle of the former main channel as it existed at the relevant historical point (subject to later natural, gradual changes), and that state court decisions and recent legislation did not show sufficient long acquiescence to override that rule.

Real world impact

The Court ordered a three-person commission, to be named by the Court on counsel’s suggestion, to run, locate, and designate the boundary according to these principles. The commission will examine prior erosions and accretions and whether the old channel can be accurately located; its work may be reviewed by the Court. Land that has emerged or changed belongs to states under their property laws but cannot shift the interstate boundary.