Procedures for the Division of the Waters of St. Mary and Milk Rivers

Abstract

The apportionment of the waters of the St. Mary River and Milk River, including its tributaries, is governed by the Boundary Waters Treaty of 1909 which specifies the proportion of the natural flow to which each country is entitled. The subsequent Order of the International Joint Commission dated October 4, 1921 gives general procedural guidelines for determining natural flow. The natural flow computations are performed on an interim basis to provide the real-time information needed for the effective operation of reservoirs and to ensure that each country receives its share of the natural flow on a continuing basis. In order to provide real-time information it is necessary to use preliminary data including approximations, therefore, the natural flow computations are repeated annually when all input data become available. The annual computations represent a final account of the apportionment and are included in the annual report to the International Joint Commission (IJC). Because the procedures, assumptions and approximations used in determining the natural flow have evolved with time but have never been documented to any extent, it was decided to document the methods currently used to compute natural flow. Thus the intent of this report is three-fold: to document the current procedures and assumptions used in determining natural flow; to provide some insight into the philosophy or reason for certain procedures or assumptions; to act as a user's manual for computing natural flow on an interim and annual basis. In order to best satisfy these requirements, the report is dividedinto separate sections on each of the St. Mary River, Milk River and the Eastern Tributaries. The 1909 Boundary Waters Treaty and the 1921 Order of the International Joint Commission are appended to the report.