Land, Water, People

Significance

Many people would agree that the Milk River watershed is a unique and significant part of Alberta, Saskatchewan and Montana.

Location

The Milk River watershed is the only watershed in Canada that drains to the Gulf of Mexico. There are 480 km (298 mi) of shared international border between Canada and the United States.

The Milk River Watershed

The Milk River watershed spans an area of 59,857 km2 (5,985,653 ha; 14,790,813 acres) in Alberta, Saskatchewan and Montana. The Milk River and its tributaries intricately connect the two provinces and the state as they share similar experience with climate, water quantity, water quality and other aspects of the ecosystem. The topographic limits for the watershed are the Rocky Mountains on the Blackfeet Reservation in the west, Montana, the Milk River Ridge that extends from the Rocky Mountains northeastward in Alberta, to the Cypress Hills, (Alberta and Saskatchewan) and Wood Mountains in the north (Saskatchewan). The Sweetgrass Hills, Bears Paw and Little Rocky Mountains form the limit in the south (Montana). Elevations vary considerably in the watershed from west to east and reflect topographical features. The highest peak is found in the west at Glacier National Park in the Rocky Mountains (2,663 m or 8,737 ft) and the lowest elevation is located at the confluence of the Milk and Missouri rivers (619 m or 2,031 ft). At the point where the Milk River flows across the Canada-United States border, the elevation is 819 m (2,687 ft), the lowest elevation in southern Alberta.

The mainstem Milk River rises in the grasslands of Montana and flows northward into Alberta before flowing eastward a distance of about 288 km (179 mi) parallel to the Canada-United States border. The river then flows south and returns to Montana where it flows through Fresno Reservoir and continues to flow southeast a distance of 710 km (441 mi) before joining the Missouri River.

Important tributaries include the North Fork of the Milk River that is often mistaken for the mainstem Milk River as it generally contains higher flows that are sustained by the St. Mary River Diversion in Montana. From the Canada-United States border, the North Fork flows a distance of 96 km (60 mi) before meeting the mainstem of the Milk River west of Del Bonita, Alberta. In Saskatchewan, substantial flows are delivered to the Milk River via three major tributaries: Lodge Creek, Battle Creek and the Frenchman River, that originate in the Cypress Hills. Lodge Creek and Battle Creek flow south across the Saskatchewan-Montana border and continue to flow south into the Milk River near Chinook, while the Frenchman River joins the Milk River further downstream near Hinsdale, Montana.

“The water of this river possesses a peculiar whiteness, being about the colour of a cup of tea with the admixture of a tablespoon of milk. From the colour of its water, we called it the Milk River.” (Meriweather Lewis and William Clark, May 8, 1805)

Trends in human population are often cited as an indicator of watershed health as they describe the social “quality of life” aspect of watersheds. In many watersheds in North America, urbanization is occurring rapidly, resulting in land use changes from a rural landscape to more centralized urban centres. The Milk River watershed remains rural and the total population is relatively small. In Alberta, the total population in the watershed is 2,534, showing a -9.1% population decline since 2008.

The Milk River provides water for various purposes such as municipal, domestic, agricultural and recreational activity; however, irrigation is the main water use across the watershed. Since the Milk River is considered an arid basin (meaning that evaporation exceeds precipitation), various storages and diversions are operated in the watershed mainly in Saskatchewan and Montana to meet irrigation demand. Such infrastructure is not available in the Alberta portion of the Milk River; however the St. Mary River Diversion augments Milk River natural flows during the irrigation season, typically from the beginning of March to the end of October.

The natural flow of the Milk River in Alberta in winter months is low and may approach zero in the lower reaches in times of drought. Flow depths across the channel width can be less than 0.1 m, limiting the movement of larger fish and increasing the potential for isolated pools that are disconnected from the main channel (Golder Associates 2010; AMEC Earth and Environmental 2011).