Research & Science Note 2: Study of Erosion and Sedimentation

The St. Mary—Milk River Diversion

The Milk River receives much of its annual flow volume from a diversion that transfers water from the St. Mary River into the Milk River just south of the Canada/USA border, near Babb, Montana. The St. Mary diversion was initiated as part of the Boundary Waters Treaty of 1909 between the United States and Canada and its subsequent intent was clarified by the 1921 Order . Construction of the St. Mary diversion was completed in 1917. The design capacity was 24.1 m3/s (850 cfs). The diversion works have since deteriorated to the extent that the current operating capacity is 18.4 m3/s to 19.1 m3/s (650 to 675 cfs). The U.S. is undertaking plans for rehabilitation and possible enlargement of the diversion works (up to 1000 cfs to 1200 cfs).