Procedures for Calculating Apportionable Flow for the Qu’Appelle River at the Saskatchewan/Manitoba Boundary

Background: The Prairie Provinces Water Board (PPWB) is the body that oversees the administration of the Master Agreement on Apportionment (MAA). Signed in 1969, the MAA is an agreement in place between Canada and the provinces of Alberta, Saskatchewan and Manitoba relating to the sharing of water in transboundary basins. The PPWB consists of representatives from Alberta, Saskatchewan, and Manitoba, as well as Environment and Climate Change Canada and Agriculture and Agri-Food Canada.

In order to facilitate collaboration on water sharing issues, the PPWB utilizes special committees related to various aspects of the MAA. The Committee on Hydrology (COH) is the committee that directly oversees aspects of the MAA related to water quantity, including the calculation of apportionable flows at the Alberta/Saskatchewan and Saskatchewan/Manitoba interprovincial boundaries.

Apportionable flow is the term used to describe the volume of water available at the boundary that is to be shared under the terms of the MAA. Apportionable flows are similar to naturalized flows in that they are an estimate of the volume of water that would have passed the interprovincial boundary under undeveloped conditions. They are, however, distinguished from natural flow in that they are calculated based on specific procedures that have been approved by the PPWB. These procedures are selected based on considerations such as data cost and availability, and the required level of accuracy for each basin. In striking this balance apportionable flow calculations may therefore not represent the same level of rigour that might normally be associated with a true natural flow estimate. Apportionable flow calculations, based on the PPWB approved calculation procedures, are completed by the PPWB Secretariat which is housed within the Transboundary Waters Unit of Environment and Climate Change Canada. Deviations from the approved apportionable flow calculation procedures are not permitted without approval of the Board.

The project depletion method is the name given to the apportionable flow calculation methodology that has been adopted by the PPWB for use in apportionment monitoring for most of the interprovincial basins. Project depletion method calculations are typically completed on a monthly time step. The method is based on adjusting the recorded flow at the apportionment point by adding and subtracting measured or estimated water inputs or withdrawals that have occurred within the basin. These include such things as: water put into or released from storage, evaporation losses from stored water, licensed water use, agricultural land drainage activities and inter basin diversions. All these items may also have routing adjustments applied to them to account for travel time between the location of their occurrence and the apportionment point.

Apportionment procedures for most basins were documented during the 1970s in a series of reports published by the PPWB. Some, but not all, basins have had additional studies. The apportionable flow calculations were subsequently moved into FORTRAN programs specific to each basin, which often resulted in modifications to the calculation procedures. An Excel workbook has been developed to complete the apportionable flow calculations for the Qu’Appelle River. The calculations in this workbook mirror the calculation procedures carried out by the former FORTRAN program.

In 2011 the PPWB COH embarked on a process of reviewing the apportionable flow calculation procedures for each of the basins subject to apportionment under the MAA. The COH’s target is that each basin will be reviewed approximately every ten years. The purpose of this review process is to ensure regular evaluation and improvement to the apportionable flow calculation procedures. Reviews for the North Saskatchewan River and Cold Lake at the Alberta/Saskatchewan boundary are complete and a review for the Saskatchewan River at the Saskatchewan/Manitoba boundary is underway. The Qu’Appelle River will be the fourth basin to undergo review.

The PPWB has recently begun utilizing a custom apportionable flow program called River Basin Assessment Tools (RBAT). The apportionable flow procedures recommended through this basin review will be implemented in the RBAT program. The Consultant completing the basin review will not be responsible for setting up the basin in RBAT, or require any knowledge in the use of this program, however, it is important to recognize that the use of this software may factor into the decision making process of the COH.