IJC International St. Mary and Milk Rivers Study Board Final Draft Report (click … here)

Background:

The Milk River is naturally a much smaller river than the St. Mary River. Mean annual natural flow in the Milk River at Eastern Crossing is 108,000 acre-feet (1912-2022). (MRWC SOW) amounting to 15 percent of the mean annual natural flow of the St. Mary River near its mouth which is 715,000 acre-feet (OWC SOW).

According to apportionment provisions of the 1921 Order the United States is entitled to more water than Canada from the Milk River and vice versa for the St. Mary River. Under the existing Administrative Procedures and current level of infrastructure within the basin, the United States has not been able to fully access its entitlement of St. Mary River flows, and Canada has not been able to access its entitlement of Milk River flows. An analysis of data from 1950 through 2004 (AMTF 30 2006) indicated that the United States has accessed, on average, 62 percent of its entitlement of the St. Mary River annual volume, while Canada has accessed, on average, 25 percent of its entitlement of the Milk River annual volume (see Figure 7). This amounts to the US receiving ~100,000 acre-feet less than it is entitled from the St. Mary and about 30,000 acre-feet more than it is entitled from the Milk River. Canada receives ~100,000 acre-feet more than it is entitled from the St. Mary and ~30,000 acre-feet less than it is entitled from the Milk River. The US is entitled to 45% of the combined flow but receives 41%. Canada is entitled to 55% of the combined flows and receives 59%,

Similarly annual demand for irrigation water from the Milk River in Canada is less than three percent of the demand from the St. Mary River. Current irrigation demand for water diversion from the St. Mary River in Canada is for approximately 400,000 acre-feet annually to partially irrigate some of the 520,000 acres of cropland in the St. Mary and Raymond Irrigation Districts. A similar volume of water (422,000 acre-feet) is diverted from the Waterton and Belly rivers into the St. Mary Reservoir to augment supply for these districts. Diversion from the Milk River mainstem in Canada averages 4,000 acre-feet annually to irrigate 4,000 acres of cropland although water licences have been allocated for 8,000 acres (~11,000 acre-feet). Under current water management water is not available when required during the irrigation season in particularly dry years creating hardship for irrigation farmers along the Milk River in Canada.

Current irrigation demand from the Milk River in the United States downstream of Eastern Crossing is for about 246,000 acre-feet to irrigate 140,000 acres of cropland. There is some demand for additional water to increase water security for existing irrigators and for expansion.

SAGE Comments (as submitted):

The primary considerations for the International Joint Commission’s Study Board in recommending changes to current water management in sharing water from the St. Mary and Milk Rivers were to improve receipt of annual entitlements for both the US and Canada and to improve utilization of water entitlements in the basins. Climate change and water management models determined this is achievable through a combination of administrative and infrastructure alternatives.

• Modified annual balancing administrative option – Meaningful increase to US receipt of entitlement from the St. Mary River. Meets needs of existing Milk River irrigators. Acceptable to St. Mary River irrigators. Straightforward to implement.
• Rehabilitation of the 850 ft³/s US St. Mary Canal – Greatest positive improvement in US receipt of entitlement. Potential to improve supply to Canadian Milk River irrigators. Acceptable decrease in supply to St. Mary River irrigators.
• Control structures on Upper and Lower St. Mary Lakes – Requires feasibility analyses. Additional active storage would enhance operational flexibility, especially during drought. Benefits contingent on canal rehabilitation.
• Long-term storage development on the Milk River – Offstream reservoir (Miner’s Coulee) would provide modest improvement in Canada’s receipt of entitlement and increase water supply for Milk River irrigators. Or, onstream reservoir (Forks) would allow full receipt of Canada’s entitlement and increase water supply for Milk River irrigators.

In its draft report the Study Board concludes the recommendations “address water management challenges while supporting the long-term sustainability and cooperative management of the shared St. Mary and Milk River basins” (Section 7, p. 101/online 117). Long-term sustainability means balancing environment, society and the economy. However none of the recommendations have been seriously evaluated for environmental impacts hence the statement that long-term sustainability is supported is unsupported.

The Study Board made some attempts to include environmental considerations in its work. A performance indicator on bull trout population growth rates (July to September) in the St. Mary River was used to evaluate scenarios. Bull trout is a species at risk in Montana and Alberta. All options, including modified annual balancing and rehabilitation of the 850 ft³/s US St. Mary Canal show negative performance in some years. An Aquatic Ecosystems Technical Working Group was formed, however sufficient resources were not provided to complete compilation and review of background information on aquatic ecosystems in the basins let alone identify and address basic information gaps.

In contrast the Socio-Economic Analysis Technical Working Group had access to sufficient resources to compile and analyze relevant historical information and support a research project that included interviews of water users in both basins (heavily biased towards irrigation agriculture interests). IJC engaged in contracts with consultants for assessing the value of irrigation in Alberta and Montana (Acera Consult Inc. 2023, Westwater Research 2024). These studies appear to mask negative externalities and do not consider or value ecosystem services. It is disappointing that the simplistic ‘value of water’ determinations from these studies have been used to assess the economic costs and benefits of implementing the Study Board’s recommendations regarding administrative and structural options.

One key disappointment for those concerned about environmental implications of the Study Board’s recommendations is the addition, part way through the study, of the proposed Canadian Forks Reservoir as a structural option. This occurred despite knowledge of a prior feasibility study that assessed storage options in the Milk River basin in Canada and identified major technical issues, potential significant environmental impacts and a negative benefit-cost ratio (Klohn Crippen 2003) for all the storage options. That feasibility study is not referenced in the report even though its findings are relevant to the Study Board’s deliberations.

Further, regarding long-term storage development on the Milk River (Setion 6.2.4, p. 94/110) this could be interpreted as a statement about modelling results not a ‘recommendation’ of the Study Board. The concept of damming the Milk River in Alberta for Canada to receive its full, but relatively small, entitlement from that river raises major questions and challenges regarding river resilience, sustainable water and land use in a semi-arid environment, who benefits, who pays and shared governance of water management between two countries that are currently experiencing strained relations.  

Despite the absence of serious considerations regarding aquatic ecosystem health, the process was sound in modelling effects of administrative and infrastructure options on streamflow and water availability to meet entitlement and irrigation demand.  Water management models for both Montana (BLM Riverware) and Alberta (EPA WRMM) were used.  Results benefited from running a potential future hydroclimate scenario through one management model.  The visualization tools developed by the study team are very useful for interpreting the complex set of scenario modelling results.  

Governments at all levels are well-advised by the Study Board’s general recommendations regarding water management modelling (6.1.1), data analysis and visualization (6.1.2), infrastructure investments (6.1.3), integrating aquatic ecosystem considerations (6.1.4) and engagement of Advisory Groups following completion of the study (6.1.5).  Watershed Planning and Advisory Councils may have an important role in the last two general recommendations.

In particular integrating aquatic ecosystem considerations into future water apportionment decisions (p. 91/online 107) would go a long way towards advancing long-term sustainability. Specifically included are recommendations for:

• AOs in cooperation with interested to investigate opportunities to improve understanding of the impacts of water apportionment decisions on aquatic ecosystem considerations within the St. Mary and Milk River basins.
• AOs to consider integrating additional information, monitoring or analytical approaches (e.g. ecological flow relationships, seasonal flow requirements, ecological indicators)
• Advancing development of ecological flow relationships to identify critical thresholds, seasonal needs and management considerations for species and habitats of concern.