Water Supply Conditions and Outlook June 4, 2018

Transcription

1 Water Supply Conditions and Outlook June 4, 2018 Flow Forecasting & Operations Planning Water Security Agency

2 Overview Water supply conditions across Saskatchewan are generally good with most reservoir and lake levels close to typical levels for this time of year. However there are some southcentral areas with dry soil conditions and low reservoir levels. Precipitation in April and May was generally below average across all of Saskatchewan. In late May and early June significant rainfall was received over eastern Saskatchewan. Streamflows across the province are generally near normal for this time of year with the exception of the southeast where flows are above normal in response to recent rainfall. Flows on the Saskatchewan River system are currently near average, but flow on the South Saskatchewan River is projected to drop off noticeably due to below average rainfall over southern Alberta. Dry conditions over southern Alberta results in less rainfall runoff into the South Saskatchewan River and increases irrigation water use. Flows and levels on the Churchill River System are above average for this time of year in many locations, mainly due to high rainfall last spring and summer. All operable lakes within the Qu Appelle River System are projected to be within their desirable summer operating ranges through summer

3 2018 Rainfall Precipitation in April and May was well below normal across Saskatchewan as shown in Figure 1. However, as shown in Figure 2, significant rainfall was received during the last few days of May and the first few days of June. This rain alleviated dry conditions over eastern areas of the province and, despite the dry conditions prior to the events, resulted in some localized flooding where accumulations were highest. Most areas in western Saskatchewan have received minimal rainfall in Figure 1: April 1 to May 31, 2018, Percent of Normal Precipitation (Map courtesy of Agriculture and Agri-Food Canada) 2

4 Figure 2: Weekly Precipitation - May 28 to June 3,

5 Soil Moisture Conditions Figure 3 shows cropland topsoil moisture conditions as of June 4, The rain in late May and early June has improved moisture conditions over the eastern half of southern Saskatchewan. The southwest portion of the province remains dry. The satellite derived moisture conditions map (Figure 4) supports the topsoil moisture conditions map and observed rainfall accumulations, with below average conditions across the southwest portion of the grainbelt. On their May 31, 2018, drought conditions map (Figure 5), Agriculture and Agri-food Canada had identified much of southern Saskatchewan as being Abnormally Dry with pockets identified as experiencing Moderate drought conditions. Rainfall in early June has likely improved conditions over the eastern half of the province. Figure 3: Cropland Topsoil Moisture Conditions as of June 4, 2018 (Map Courtesy of the Ministry of Agriculture) 4

6 Figure 4: Difference from Long Term Average Percent Saturated Surface Soil Moisture May 28-June 3, 2018 (Map courtesy of Agriculture and Agri-Food Canada) 5

7 Figure 5: Canadian Drought Monitor May 31, 2018 (Map courtesy of Agriculture and Agri-Food Canada) Long Range Forecasts Most long range forecast are currently expecting below to near normal precipitation over the province between June 1 and August 31 and above normal temperatures, Multi-model ensemble maps for precipitation and temperature over the next three months, which are the average result of seven seasonal weather forecasts, are shown in Figure 6 and 7 respectively. It is important to keep in mind that seasonal weather forecasts are statistically unreliable. 6

8 Figure 6: North American Multi-Model Ensemble Precipitation Anomaly Outlook for June 1-August 31, 2017 (Map Courtesy of the US National Weather Service) Figure 7: North American Multi-Model Ensemble Temperature Anomaly Outlook for June 1-August 31, 2018 (Map Courtesy of the US National Weather Service) 7

9 Detailed Water Supply Condition Table 1 provides a summary of the current levels and storages of the major water supply reservoirs in Saskatchewan. Most reservoirs were above median levels as of June 1, Many of the reservoirs in southeastern and southcentral Saskatchewan are below their full supply levels and at lower than normal levels as a result of below normal snowmelt runoff and hot and dry conditions during the summer of This includes Avonlea, Cookson, Boundary, Nickle, Rafferty and Grant Devine lakes/reservoirs. Smaller private dugouts and reservoirs throughout southcentral and southeast areas are also low (Figure 8), particularly near Weyburn. Rain in late May and early June likely provided some relief, particularly in the Moose Mountain Creek and Antler River basin, including nearly bringing Grant Devine Lake up to its full supply level in early June. 8

10 Table 1: Water Supply Reservoir Current Condition Report Reservoir Date of Observation Current Elevation (m) Full Supply Level (m) Departure from Full Supply (m) Current Storage (dam 3 ) Current Percent Full Lower Quartile Elevation (m) Median Elevation (m) Upper Quartile Elevation (m) Grant Devine June 1, ,000 93% Altawan June 1, ,560 84% Avonlea June 1, ,530 74% Boundary June 1, ,700 90% Buffalo Pound June 1, , % Cookson June 1, ,000 81% Cypress June 1, ,000 94% Downie* May 31, ,100 91% Duncairn* May 31, ,000 98% Diefenbaker June 1, ,460,000 90% Eastend June 1, ,130 84% Highfield* May 31, ,000 87% Huff June 1, ,660 62% Junction* May 31, , % Lafleche/Thompson* May 31, ,900 99% Newton June 1, ,950 81% Nickle June 1, ,970 68% Rafferty June 1, ,000 90% *Data courtesy of Agriculture and Agri-Food Canada 9

11 Figure 8: Water Supply Impact Map as of May 31, 2018 (Map courtesy of Agriculture and Agri-Food Canada) 10

12 Discharge - m 3 /s Water Supply Outlook Conditions as of June 4, 2018 Major River Systems Saskatchewan River System Flows entering the province on both the North and South Saskatchewan rivers are near average for this time of year. At the beginning of May the snowpack over the alpine headwaters of the basins was at above normal levels. Significant melt occurred in May, approximately 2-3 weeks earlier than typical. Lake Diefenbaker entered the month of June at an elevation that was about 1.5 metres above normal for this time of year as a result of above normal prairie and foothill runoff in April and early mountain snowmelt in May. However, with dry conditions persisting over southern Alberta, inflows to the reservoir are dropping and are expected to continue to do so through the first half of June. To safeguard against low summer outflows and lower than desirable summer lake levels, outflows at Gardiner Dam will be reduced beginning June 7. Figures 7, 8, and 9 show recorded and projected inflow, elevation and outflow to Lake Diefenbaker Apr 1 May 1 Jun 1 Jul 1 Aug 1 Sep 1 Oct 1 Nov 1 Dec 1 Observed 10-Day Forecast 6-Month Forecast Low Inflow Estimate Mid. Inflow Estimate High Inflow Estimate Lower Quartile Median Upper Quartile Figure 7: Lake Diefenbaker Observed and Forecasted Inflows 11

13 Discharge - m 3 /s Elevation - m Water Supply Outlook Conditions as of June 4, Apr 1 May 1 Jun 1 Jul 1 Aug 1 Sep 1 Oct 1 Nov 1 Dec 1 Observed 10-Day Forecast 6-Month Forecast Low Inflow Estimate Mid. Inflow Estimate High Inflow Estimate Lower Quartile Median Upper Quartile Figure 8: Lake Diefenbaker Observed and Forecasted Elevations Apr 1 May 1 Jun 1 Jul 1 Aug 1 Sep 1 Oct 1 Nov 1 Dec 1 Observed 10-Day Forecast 6-Month Forecast Low Inflow Estimate Mid. Inflow Estimate High Inflow Estimate Lower Quartile Median Upper Quartile Figure 9: Lake Diefenbaker Observed and Forecasted Outflows 12

14 Qu Appelle River Buffalo Pound, Last Mountain, Pasqua, Echo, Mission, Katepwa and Crooked lakes are all near the upper end of their desirable summer operating ranges. The significant rainfall in early June resulted in levels slightly higher than desirable at Buffalo Pound, Last Mountain, Pasqua-Echo, and Crooked lakes, Structure operations took place throughout the system between June 4-6 to return the lakes to their summer operating ranges. We anticipate that all lakes on the Qu Appelle River System will be maintained within their desirable summer operating ranges through the summer of 2018 with Round Lake being the only exception. The WSA will not be operating the control structure at the outlet of Round Lake until the Federal Government obtains appropriate land control. Peak spring observed levels and projected July 1 levels for the major lakes along the Qu Appelle River are listed in Table 2. Table 2: Qu Appelle Lakes 2018 Levels and Operating Ranges (metres) Lake 2018 Spring June 1, Projected July Desirable Summer Peak , 2018 Operating Range Buffalo Pound Last Mountain Pasqua-Echo Mission-Katepwa Crooked Round Souris River Flows within the Souris River Basin, including the Long and Moose Mountain creek subbasins, were near normal levels following what was a well below normal snowmelt runoff event. The major reservoirs did not reach their full supply levels. The significant rainfall in early June has generated streamflow in the Moose Mountain Creek watershed as well as the upper and lower Souris River watershed. As a result, Grant Devine reservoir is expected to reach its full supply level in June and Nickle Lake is receiving inflow. 13

15 Quill Lakes 2018 spring runoff raised the Quill Lakes back up to within a few centimeters of the recorded high levels set in Flows in the tributaries have receded to near zero and some evaporation is occurring, so the lake has leveled off. Typically average net evaporation in the summer months will drop the lake approximately 25 cm. If below average rainfall occurs in 2018 the decline could be larger. Conversely, if above average rainfall occurs the lake may rise further. Churchill The Churchill River continues to flow at above average levels due to the extremely high rainfall received in the spring and summer of Lac La Ronge went into spring at a relatively low level due to repair work at the outlet structure in This spring the outlet structure has been closed to reduce outflow to help bring the lake back up to a desirable level of m. Southwest Snowmelt runoff within the southwest was generally above normal, resulting in most reservoirs within the Battle, Frenchman, Lodge, Swift Current, Maple Creek, Rush Lake, and Old Wives Lake watersheds filling. The only two reservoirs that did not fill were Middle Creek Reservoir, which rarely fills, and Harris Reservoir in the Maple Creek Basin. Irrigation deliveries for forage crops began within these basins in May. Most projects finished taking water in May, but some projects are expected to continue taking water through the first half of June. 14

16 Lake June 1 Level (metres) Table 3: Lake Level Summary Summer 2018 Projected Level (metres) Normal Summer Level (metres) Recorded Historical Extreme Level Year (metres) Grant Devine ** 2011 Anglin ** 2013 Big Quill ** 2017 Boundary Reservoir Buffalo Pound Candle Lake Cookson Reservoir Crooked ** 2014 Echo and Pasqua Fishing Good Spirit ** 2010 Jackfish Katepwa and Mission La Ronge ** 2011 Last Mountain Moose Mountain Rafferty ** 2011 Round *** ** 2014 **Occurred after spring runoff during summer event(s) *** with outlet structure operated. Under natural conditions the normal summer level is 441.2m Ongoing Water Supply Outlook The WSA will issue Water Supply Conditions Reports monthly until November,