Frequently Asked Questions: Surface Water Quantity

What are apportionable flows?

Apportionable flows are the flow levels that are subject to apportionment requirements in the Master Agreement on Apportionment to be delivered by Alberta to Saskatchewan (Schedule A) and by Saskatchewan to Manitoba (Schedule B). Apportionable flows are calculated, and are used to estimate the natural flow in a river that is referred to in the Master Agreement on Apportionment. Natural flow is the volume of flow that would occur in a particular river if that river had never been affected by human activity. Various methods are used to calculate apportionable flows that account for the amounts used by particular water uses in development projects (project depletion method), amount of water in storage in reservoirs/lakes, precipitation, evaporation losses and other factors. Apportionment computations vary for each river because the water uses and sources are specific to each river.

What is natural flow?

Natural flow is an important part of the Master Agreement on Apportionment's formula. Broadly defined, natural flow is the volume of flow that would occur in a particular river if theat river had never been affected by human activity. While calculating this amount can be difficult, the result is straightforward: all three provinces, even in drought periods, end up with approximately equal shares of the total water flow. It is then solely up to the provinces to decide how they will use their share of the water.

Please note that the methods used to determine apportionable flows have certain assumptions and limitations. Methodologies in monitoring and computation of data and information have also changed over the history of the PPWB. The user is cautioned in taking the measured natural (apportionable) flows out of context and using the data for other purposes. If you have any questions on interpreting data, please Contact Us.

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What is equitable sharing?

The Master Agreement on Apportionment calls for the equitable sharing of prairie waters. This means that water flows must not only meet the quantity required by the sharing formula over the years, but also must satisfy the provinces' need for a consistent water supply.

To achieve this consistent supply, the Prairie Provinces Water Board (PPWB) may recommend minimum flow requirements at interprovincial borders. For example, Alberta has to deliver a minimum flow of 42.5 CMS of the combined flow of the South Saskatchewan and Red Deer Rivers to Saskatchewan.

The PPWB also determines the frequency with which it estimates and reports natural flows.

How much water does Alberta have to deliver to Saskatchewan?

Under Schedule A of the Master Agreement on Apportionment, Alberta is entitled to 50 percent of the natural flow of an interprovincial river before it enters Saskatchewan. This formula is based on flow occuring over each year in all eastward flowing streams.

Exceptions occur to this simple formula of apportionment where interprovincial rivers cross the Canada-USA border where Canada has international commitments. Middle, Lodge and Battle Creeks are exceptions to this rule as they feed into the Milk River that crosses the USA border. Under the St Mary/Milk River International Joint Commission agreement, Canada is obligated to supply 50 percent of the Milk River to the USA, and the USA is obligated to supply 50 percent of the St Mary River to Canada. Thus, Saskatchewan would be treated unfairly if they had to deliver all of the flow that Alberta delivers to them. The Master Agreement on Apportionment is based on equitable sharing so Alberta is obligated to deliver 75 percent of the flows of Middle, Lodge and Battle Creeks to Saskatchewan so that Saskatchewan can use some of these waters, and Canada can still deliver 50 percent of the Milk River flow to the USA.

Moreover, the Province of Alberta is also required to deliver a minimum flow of 42.5 CMS of the combined flow of the South Saskatchewan and Red Deer Rivers to Saskatchewan. This minimum flow delivery is required to ensure that Saskatchewan has a consistent water supply, which is part of fulfilling the principle of equitable sharing of water that is fundamental to the Master Agreement on Apportionment.

How much water does Saskatchewan have to deliver to Manitoba?

Under Schedule B of the Master Agreement on Apportionment, Saskatchewan is entitled to 50 percent of the the water which enters the province from Alberta (Schedule A) and 50 percent of the flow arising within its border. Manitoba receives the remainder i.e., 50 percent of the river's natural flow. This formula is based on flow occuring over each year in all eastward flowing streams.

What are the benefits of apportionment requirements?

Both upstream and downstream provinces benefit from Apportionment requirements in the Master Agreement on Apportionment. With complete autonomy over how their water resources are to be used, upstream provinces are free to pursue long-term plans as long as they abide by the water-sharing formula. As a result, downstream provinces can make their water management plans with the knowledge they will be receiving a fair share of available water.

When does the Master Agreement on Apportionment terminate?

The Master Agreement on Apportionment is an on-going agreement with no end date. The only way the Agreement can terminate is if all Signatory Parties amend the Agreement.

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Page last modified: 20 August 2010

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