CHAPTER NINE THE SOUTH SASKATCHEWAN RIVER SUB-BASIN The State of the Saskatchewan River Basin 113 Chapter Nine - The South Saskatchewan River Sub-basin Figure 9.1. The South Saskatchewan River Sub-basin Water Quality Stations 114 From the Mountains to the Sea Chapter Nine - The South Saskatchewan River Sub-basin CHAPTER NINE THE SOUTH SASKATCHEWAN RIVER SUB-BASIN The South Saskatchewan River sub-basin, shown in Figure 9.1, originates in mixed grasslands at the confluence of the Bow and Oldman rivers. The sub-basin comprises the river reach of the South Saskatchewan River and its associated drainage area. The South Saskatchewan River flows east to Medicine Hat then turns northeast to the Saskatchewan boundary. The river receives some tributary flow from small streams rising on the slopes of the Cypress Hills. Shortly after crossing the interprovincial boundary, it is joined by the Red Deer River. Flowing east, the river enters Lake Diefenbaker – a Sub-basin Summary 225 km-long reservoir created by the Gardiner Dam Characteristics and the Qu’Appelle Dam. This large reservoir has a • plains to boreal transition surface area of 430 km2 and a shoreline length of • length – 998 km 800 km. The river flows northeast from the reservoir 2 • gross drainage area – 59 508 km through moist mixed grasslands to Saskatoon. • effective drainage area – 13 277 km2 It continues through aspen parkland and the boreal Hydrology plain to its confluence with the North Saskatchewan • reliable flow on mainstem River. • ephemeral flow on plains tributaries • highly regulated Open grasslands dominate the upper portion of the Water Quality sub-basin. Downstream of Gardiner Dam, aspen trees • good for mainstem can be found around wetlands, in coulees, and in the • poor for plains tributaries river valley. The lower portion of the sub-basin Biodiversity contains aspen groves and natural grasslands, which • riparian zones healthy, but problems then give way to continuous forest. The soils of the • loss of wetlands sub-basin are highly diversified but generally can be Key Issues considered brown or dark brown. Weakly developed • interprovincial water apportionment soils along the river valley form significant sand-dune • municipal effluents complexes upstream of Lake Diefenbaker. Ninety • agricultural point sources percent of the sub-basin is taken up by cropland or • drought rangeland, either native or improved pasture.1 • shoreline erosion, Lake Diefenbaker The State of the Saskatchewan River Basin 115 Chapter Nine - The South Saskatchewan River Sub-basin The sub-basin has a population of about 300 000, of the small streams originating on the slopes of the with major centres being Medicine Hat, Swift Cypress Hills do not join the South Saskatchewan Current and Saskatoon. Canadian Forces Base River. They flow into Many Island Lake – a terminal Suffield – a 2690 km2 block of unplowed grassland – lake. Of the 59 508 km2 surface area of this sub- is on the west bank of the river in Alberta; some of basin, only 13 277 km2 contribute to flow in a the base extends into the Red Deer River sub-basin. median year. The annual hydrograph is typical of the There are four First Nations reserves downstream of mountain-fed streams of the Saskatchewan River Lake Diefenbaker. basin: that is, it rises to a June peak because of snowmelt runoff from the mountains. Protected areas in this sub-basin include a portion of Cypress Hills Interprovincial Park, three provincial The annual precipitation through most of this sub- parks on Lake Diefenbaker, two provincial parks basin ranges from 300 to 350 mm, although it downstream of the Lake, and Batoche National increases to over 400 mm in the boreal transition Historic Site. A 458 km2 portion of Canadian Forces zone near the confluence with the North Base Suffield is a National Wildlife Area. The riparian Saskatchewan River. About 75 percent of annual woodland of the South Saskatchewan River from the precipitation falls as rain, with most of that confluence with the Red Deer River to the Leader area occurring in May through August. These spring and is the largest area of deciduous woodland between summer rains contribute little to runoff on the the Cypress Hills and the aspen parkland. The sub- plains. Spring snowmelt drives the plains runoff. basin is dotted with small wetlands. PFRA data reveal Figure 9.2 shows the typical annual hydrograph for 121 452 ha of existing wetlands.2 The lower sub-basin Swift Current Creek. The annual runoff produced by from Outlook to The Forks contains much of the sub- the prairie streams is highly variable and unreliable. basin’s wetland area. There are also significant waterfowl nesting and staging areas in the sub-basin. Flows entering the South Saskatchewan River sub- basin have been modified by upstream dams and Economic activity includes a broad mix of agricultural diversions. Within Saskatchewan, the flow of the activities, with both irrigated and dryland crop South Saskatchewan River is significantly modified production, and livestock. Near Saskatoon, there are by Lake Diefenbaker. This large reservoir, completed several dairy operations, while the upper half of the in 1967, can store more water than all the reservoirs sub-basin features oil and gas production. There are in Alberta combined. The total storage is 9.4 million seven potash mines that depend on the sub-basin’s cubic decameters of water, more than the median water supply, although one is not in the sub-basin. annual flow of the river. The live, or usable, storage of the reservoir is 4.3 million cubic decameters. This HYDROLOGY storage is greater than the combined live storage of all upstream reservoirs. At the time of construction, The South Saskatchewan River sub-basin extends from Lake Diefenbaker was the largest constructed lake in the confluence of the Bow and Oldman rivers at an Canada. Gardiner Dam is one of the largest earth- elevation of 740 m to its confluence with the North filled dams in the world. Saskatchewan River at an elevation of 400 m. As described in Chapter Four, almost 90 percent of the Lake Diefenbaker is operated on an annual cycle, flow in the river originates in the water towers. The capturing mountain runoff and releasing it during river channel serves simply as a conveyance channel. the remainder of the year. Water stored in the There are no large tributaries in over 1000 km of river reservoir is used for municipal and industrial water channel. Tributary inflow in this sub-basin accounts needs, irrigation, recreation, hydroelectric generation, for only two percent of the annual flow, one-half of and maintenance of downstream flows. The reservoir that being the flow from Swift Current Creek. Some also provides some flood control for downstream 116 From the Mountains to the Sea Chapter Nine - The South Saskatchewan River Sub-basin 8 900 7 800 700 6 600 3 3 5 Pre-dam (m /s) (m /s) 500 4 400 3 300 Discharge Discharge 2 Post-dam 200 1 100 0 0 Jan Feb Mar Apr MayJun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr MayJun Jul Aug Sep Oct Nov Dec Month Month Figure 9.2. Swift Current Creek – Average Daily Flows. Figure 9.3. Effects of River Regulation Downstream of Gardiner Dam. communities. Because of hydroelectric installations at supplies. The best estimate of inflow to Lake Gardiner Dam and downstream on the Saskatchewan Diefenbaker for 2080 is for an 8.5 percent reduction River, water is released to meet peak power demands, in annual inflow. The uncertainty band is wide, especially in the winter. The natural hydrograph of the however, with the range in inflow values being river has therefore been significantly altered as shown in Figure 9.3. Winter flows have increased, which aids assimilation of municipal effluent at Saskatoon. Spring “The Greatest Marine Disaster in flushing flows are almost entirely absent and overall the History of Saskatoon” flow volumes are depleted by upstream diversions. Steamboats rarely used the South Saskatchewan Within this sub-basin, the flows of Swift Current Creek River because the shallow waters made for have also been modified by dams and diversions. unreliable service. Not to be deterred, the Medicine Hat hotelier and Scottish nobleman Horatio Ross Reservoir capacity is affected by sediment inflows, commissioned a new boat in 1906-07 to connect particularly during spring runoff, and by shoreline the newly completed railway at Medicine Hat to erosion. These processes may affect the live storage points downstream. The sternwheeler, the S.S. City of the reservoir or the unusable storage, known as of Medicine Hat, was 40 m long and had a draft of the dead storage. In the case of Lake Diefenbaker, only 0.6 m. over a 15-year period following construction, live On June 7, 1908 the boat proceeded downstream storage decreased by 1.5 percent. This is made up of during the high water and tricky currents of the a one percent loss from delta formation at the upper spring flood. It cleared the Grand Trunk Railway end of the reservoir and a half percent loss from Bridge at Saskatoon and was gingerly attempting shoreline erosion and slumping. Sediments flowing the passage under the Canadian Northern Railway into the reservoir come from the South Bridge when its rudder and sternwheel became Saskatchewan River itself; the contribution from entangled in a submerged telegraph line. Swift Current Creek is negligible.3 The captain lost control and the ship drifted downstream striking the pier of the Traffic Bridge. The effects of climate change on water availability in The ship rode up the pier and wrecked. All on the South Saskatchewan River have been examined. board but the ship’s engineer clambered on to The climate in 2080 is expected to be warmer and the bridge.