Goal 1: Achieve Apportionment Requirements

In general, under the Master Agreement on Apportionment, Alberta is entitled to 50 percent of the natural flow of a transboundary river before it enters Saskatchewan; Saskatchewan is entitled to 50 percent of the water which enters the province from Alberta and 50 percent of the flow arising within its borders. Manitoba receives the remainder. This formula is based on flow occurring over the course of a 12-month period in all eastward flowing streams. Exceptions to this formula occur to meet the principle of equitable sharing as discussed below.


Natural flow is an important concept within the Master Agreement. Broadly defined, the term refers to the flow of water that would occur in a particular river if that river had never been affected by the activities of people. Calculating natural flow amount then allows the PPWB to determine the share of the flow available to each of the provinces. The volume of flow subject to the Master Agreement are called apportionable flows. Rivers at the Alberta-Saskatchewan boundary receive apportionable flows that are received by Saskatchewan from Alberta. Rivers at the Saskatchewan-Manitoba boundary receive apportionable flows that are the sum of the water received by Saskatchewan from Alberta and natural flow arising in Saskatchewan.


Equitable Sharing: Striving for Fairness

The Master Agreement calls for an equitable sharing of prairie waters. Water flows must not only meet the quantity required by the sharing formula over the year, but also must satisfy the provinces' need for a consistent water supply. To implement the principle of equitable sharing, two types of exceptions are found to the simple 50% formula of apportionment.

The first exception occurs where interprovincial rivers cross the Canada-USA border and Canada has international commitments. Under the St Mary/Milk River 1921 Order (International Joint Commission), 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 they can use some of these waters, and Canada can still deliver 50 percent of the Milk River flow to the USA.


The second exception occurs when the Prairie Provinces Water Board (PPWB) recommends minimum flow requirements at interprovincial borders to ensure consistent water supply. 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. 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.


Calculating Apportionment Flows

Calculating flows to assess whether apportionment requirements have been met is a complex process. The PPWB Secretariat computes apportionable flows at 12 PPWB locations using the methodology that is recommended by the Committee on Hydrology (COH), a permanent committee of the PPWB, and approved by the Board. Stream flow is monitored by Environment and Climate Change Canada - Water Survey of Canada and other partners along the Alberta-Saskatchewan and Saskatchewan-Manitoba boundaries (see Where We Monitor). These flow data and additional hydrometric, meteorological and water use data are used by the PPWB Secretariat to calculate apportionable flows. Indeed, data are used from 104 stations (85 hydrometric and 19 meteorological) that are located in 5 major river basins, although many of the sites are in the South Saskatchewan and Assiniboine River basins. Natural flows are first calculated for each river and then apportionable flows are estimated by applying the apportionment formula to determine the share of each province. Natural flow is calculated using the project depletion method that incorporates the relevant factors specific to each river eg., upstream flow rates and volumes, additions and subtractions of water uses by infrastructure developments, the amount of water in storage reservoirs, meteorological factors such as precipitation and evaporation, etc. This approach estimates the natural flow that is the flow of water that would occur on a particular river if the river had never been affected by the activities of people. The methods used to estimate natural flows have certain assumptions and limitations such that these data should not be taken out of context.


Currently, the PPWB calculates apportionable flows at 12 water quantity monitoring sites at interprovincial borders. However, the Master Agreement covers all eastward flowing streams, including those where the water flow is currently not monitored. Other river basins may be added to the monitoring and apportionment list when water uses in an upstream province become significant. The PPWB reviews water uses from time to time on various river reaches to assess whether formal apportionment flows should be monitored and calculated.


The PPWB determines how often and when apportionable flows are calculated and reported. Currently, apportionable flows are reported each year in the Annual Report that is submitted to the Ministers responsible for the Master Agreement on Apportionment. Quarterly Reports are distributed to Member Agencies that report apportionable flows for each Quarter on the South Saskatchewan River; Middle, Lodge and Battle Creeks; and Cold Lake. Both of these types of reports show apportionable flows for each month throughout the year.


Apportionable and recorded flow data are provided for each river in the Water Quantity Monitoring Sites and Data submenu.


To maintain accurate apportionable flows, the COH reviews water apportionment problems and advises the board on possible solutions. Another important task of the COH includes reviewing proposed projects that could have a significant impact on water quantity and apportionment at provincial boundaries. Indeed, the methods used to estimate apportionable flows have changed over the years to continually refine the process.


Promote public awareness of the need for and benefits of interprovincial water management and the PPWB's mandate.