Water Supply Assessment Report (pdf, 8 mb)

This study quantifies the natural water supply to the North Saskatchewan River and its spatial, seasonal and annual variability.

Executive Summary

North Saskatchewan Watershed Alliance (NSWA) contracted Golder Associates Limited (Golder) to assess the water supply and its variability in the North Saskatchewan River Basin (NSRB) under natural hydrologic conditions and present climatic conditions.

The NSRB was divided into seven (7) hydrologic regions to account for the spatial variability in factors influencing water yield. The hydrologic regions were delineated such that the hydrologic responses were essentially similar within each region, but different from region to region. The annual yield for each hydrologic region was estimated as the average of the annual yields of gauged watersheds located completely within the hydrologic region, if available. Thirty-four hydrometric stations within the NSRB were included in the analysis. For the assessment of natural water yield, only those data series or portions thereof that have been collected under natural flow conditions were considered.

A key aspect of the water yield assessment in the NSRB was the estimation of water yield in watersheds with non-contributing areas. The calculation of water yield for each hydrologic region and sub-basins in the NSRB was based on the effective drainage areas of gauged watersheds and on effective drainage areas within each hydrologic region or sub-basin. The noncontributing areas as delineated by the Prairie Farm and Rehabilitation Administration (PFRA) of Agriculture and Agri-Food Canada (AAFC) for the NSRB were used.

Monthly yields were determined by first estimating the average percentage of the annual yield at each station within a hydrologic region, with priority given to stations wholly contained within the hydrologic region and to stations with winter flow records. The average monthly percentage was then used with the annual yield estimated for a hydrologic region to estimate a typical monthly yield for that region. The coefficients of variation and skewness for the annual yield of a hydrologic region were used to estimate the 10th, 25th, 75th and 90th percentiles on the basis that the annual yield series followed a log-normal distribution.

The annual and monthly yields for each sub-basin as defined by NSWA were also estimated from the annual yield of each hydrologic region that is included in each sub-basin and the proportion of each hydrologic region within each sub-basin. 

The mean annual natural discharge of the NSR at the Alberta/Saskatchewan boundary is about 7,510 million m3 (Mm³), which is equivalent to an annual yield of 179 mm during average hydrologic conditions. The cumulative annual yield (volume) at the same location for the 10th, 25th, 75th and 90th percentile hydrologic conditions are 122, 142, 205 and 248 mm (5,110 Mm³, 5,930 Mm³, 8,600 Mm³, and 10,400 Mm³), respectively. The headwater hydrologic region, with an area of 4,110 km2 compared to the NSRB’s gross drainage area of 56,860 km2, contributes almost half (3,600 Mm³) of the annual cumulative yield of the NSRB at the boundary. The portion of the NSRB downstream of Edmonton contributes less than 300 Mm³ of flow volume to the annual cumulative volume of the NSRB at the boundary. The mean annual natural discharge of the NSR near Edmonton and at the downstream outlet of the Strawberry sub-basin is 7,080 Mm³. The cumulative annual discharge at the same location for the 10th, 25th, 75th and 90th percentile hydrologic conditions are 4,990 Mm³, 5,740 Mm³, 8,030 Mm³, and 9,470 Mm³, respectively.

The most upstream hydrologic region has the highest annual yield at 870 mm, while the easternmost hydrologic regions near the Alberta/Saskatchewan boundary have the lowest annual yields at 35 mm and 25 mm, respectively. These low yields are a reflection of the low precipitation, relatively higher temperature and higher evapotranspiration, and large noncontributing areas in the eastern half of the NSRB. The peak monthly yield from the hydrologic regions in the eastern half of the NSRB occurs in April as a result of snow melt as temperatures begin to increase in spring. In contrast, the peak monthly yield from the hydrologic regions in the western half of the NSRB, particularly those along the eastern slopes of the Rocky Mountains, occur in July because of the gradual rise in temperature during spring and early summer at these high elevations. The peak monthly cumulative yield at the Alberta/Saskatchewan boundary occurs in July and seems to follow the pattern shown by the hydrologic regions in the western half of the NSRB. This is an expected result as the western hydrologic regions generate most of the yield in the NSRB.

The results of an analysis of flow records on the NSR indicate that the approach and results of the water supply assessment for the NSRB as described above are valid.