Spring Runoff Forecast March 1, Prepared by: Flow Forecasting & Operations Planning - Water Security Agency

Transcription

1 Spring Runoff Forecast March 1, 2019 Prepared by: Flow Forecasting & Operations Planning - Water Security Agency

2 General Overview The Water Security Agency (WSA) is preparing for 2019 spring runoff by issuing this runoff forecast. The spring runoff potential for the province, as of March 1, 2019, is shown in Figure 1. Forecasted peak levels for select lakes and reservoirs are included in Table 1, and peak flow estimates for select watercourses are included in Table 2. Fall conditions, snowpack water content, and rate of melt are the primary factors that influence snowmelt runoff. While we have a good understanding of the fall conditions and the snow accumulation season is nearing its end, it is much too early to be able to predict the conditions at melt. For this reason, this forecast assumes normal/average conditions going forward through to the conclusion of the spring runoff event. Above average snowmelt over the remaining weeks of winter and/or a rapid melt could increase runoff yields significantly. The converse is true for below normal snowfall going forward and/or a slow melt. As detailed in the WSA s Conditions at Freeze-up Report, which was released in November of 2019, the growing season precipitation last year was below average across all of southern and central Saskatchewan. In northern Saskatchewan, spring and summer precipitation was well above normal. Fall precipitation was more variable. In September, the dry area of the south and central Saskatchewan received near or above normal accumulations. Southern portions of the Qu Appelle River Basin, a good portion of the South Saskatchewan River Basin, most of the Cypress Hills, and the very northern portion of the province received below normal precipitation. Significant rainfall occurred over the Beaver River Basin where well above normal precipitation was received. October saw much less precipitation with most of the province experiencing below to well below normal precipitation, the exception was the southern portion of the province along the US border where normal accumulations were received. near normal runoff is expected. Above normal snowmelt runoff is anticipated in the Beaver River Basin and the North Saskatchewan River Basin above North Battleford due to wet conditions at freeze-up, and the presence of an ice layer under an above normal snowpack. Near normal snowmelt runoff is projected across the remained of the North Saskatchewan, Saskatchewan, and the Churchill River basins. Below normal runoff is expected over the far north. Some agricultural water supply issues began to emerge in late summer With below average 2019 snowmelt runoff projected across most of southern Saskatchewan, these water supply shortages may intensify and expand to additional areas in southern Saskatchewan and may begin to threaten some municipal water supplies. The snowpack over the alpine and foothill headwaters of the Saskatchewan River ranges from below normal, to normal at this time. Below average inflow is projected into Lake Diefenbaker from 2019 snowmelt. Rains over the mountain and foothill headwater areas in May and June have a significant effect on the overall inflow to the reservoir. Lake Diefenbaker is slightly below normal levels for this time of year and is expected to be close to full by the end of August if summer rainfall over the headwaters is near average. WSA will continue to monitor the 2019 spring runoff conditions across Saskatchewan. If warranted, further updates will be issued as the spring runoff progresses. Snow accumulations to date have been below average across most of the far north and southeastern Saskatchewan, with the exception of the very southeastern corner by the Manitoba and the US border where it is near normal. The remainder of the province has received cumulative winter precipitation that is near, or slightly above normal. As shown in Figure 1, snowmelt runoff is projected to be below to well below average across southern Saskatchewan, and the far north, with the exception of the far southwest corner, and the southeast along the Manitoba border where Cover Photo: Sucker Creek near Cypress Lake, February 20, 2019 Credit: Allana Howell, WSA March 2019 Runoff Outlook 1

3 The following descriptions provide some context to the categories of snowmelt runoff potential used to describe the potential for runoff from the spring snowmelt in Figure 1. Category Well Below Normal Below Normal Normal Above Normal Well Above Normal Very High Description Little to no runoff is expected Some runoff is expected Flows are expected to be average and will generally not exceed channel capacity in most reaches Flows from snowmelt runoff will exceed natural channel capacity in some areas Significant out of channel flow and some flooding will likely occur Significant flooding is likely to occur Approximate Frequency of Expected Flow << 1:2 year event < 1:2 year event 1:2 year event 1:5 year event 1:10 year event 1:25 year event or greater Above normal precipitation prior to runoff (especially if it occurs as rainfall) and/or a faster than normal melt could result in significantly higher runoff than presently forecasted. Mid-winter melt events or rain events on frozen soils can increase runoff yields and estimates from snowmelt accumulation. Below normal precipitation prior to runoff and/or a slow melt could result in significantly lower runoff than presently forecasted. Figure 1 applies to local runoff as opposed to the main stem river flows on major systems such as the Qu Appelle and Saskatchewan rivers. This forecast is based on limited data and should be used as a general guide for large geographical areas. Local conditions may vary significantly from the regional conditions and boundaries. Figure 1 should be considered as approximate. Ice jamming can result in out-of-bank flows and flooding, even for below normal flows. Figure 1: Spring Runoff Potential as of March 1, 2019 March 2019 Runoff Outlook 2

4 Fall Conditions Southern and central portions of Saskatchewan received below average rainfall in the spring and summer This resulted in some degree of drought like conditions across most of the grain belt. Fall brought some much-needed precipitation to southern and central Saskatchewan. Although the fall precipitation improved soil moisture conditions across most regions, available depressional/wetland storage volumes remain high following the very dry conditions in the spring and summer. This will reduce the spring runoff potential in these areas. Further north, conditions were wet throughout the Churchill River Basin as a result of the well above normal precipitation received in the spring and summer of This caused well above normal flows throughout the Churchill River system throughout the year. The Beaver River Basin also received above average rainfall in the fall, resulting in above normal flows throughout the system. The rest of the Churchill River Basin received below to average rainfall in the fall, which allowed flows to recede. Figure 2: Percent Normal Precipitation Aug. 3 to Oct. 31, 2018 March 2019 Runoff Outlook 3

5 Early Winter 2018/2019 Precipitation Point snowfall data, mapped as a percent of average, is provided in Figure 2. This map indicates that the western portion, the far south along the Canada-US border, and central Saskatchewan have received near, to slightly above normal, winter precipitation to date. The southeastern portion of the province, including parts of the agricultural portion of central Saskatchewan, along most of the Manitoba border, and the far north, are showing below normal snowfall accumulations. It is important to note that the map in Figure 3 is based on a relatively small number of sites across Saskatchewan, and due to the challenges of measuring point snowfall data in a windy environment and losses during the winter period, it may not represent the water equivalent available for runoff. Environment and Climate Change Canada produces a snow water equivalent (SWE) map generated using satellite passive microwave signals. Their February 22, 2019, map is provided as Figure 4. WSA completed point snow course surveys between February 25 and 28. This data, which is provided in Figure 5, is believed to be the best available information on current snow water equivalents. The southwestern area of the province, the extreme southeastern corner, along the US border, and the southern area of the boreal forest all have snowpacks that are near normal for this time of year. The rest of the southern agricultural areas of Saskatchewan and the far north are experiencing below normal snowpacks. Figure 3: Percent Normal Winter Precipitation November 1, 2018 to February 28, 2019 (Map Courtesy of Agriculture and Agri-Food Canada) March 2019 Runoff Outlook 4

6 Figure 4: March 1, 2019 Passive Microwave Snow Water Equivalent Map (Source: Environment and Climate Change Canada) Figure 5: WSA February 25-28, 2019, Snow Survey Data (mm of SWE) March 2019 Runoff Outlook 5

7 Long Range Forecasts Most long range forecast models are forecasting normal precipitation over the next three months, March 1 to May 31, with some expecting above normal precipitation over parts of the province, particularly over the north (Figure 6). Most long lead models are expecting above seasonal temperatures over the next three months over the province, but three are expecting below normal temperatures (Figure 7). With that said, it is important to note that seasonal weather forecasts are largely unreliable. Figure 7: Multi Model Ensemble Temperature Anomaly Forecast (March 1 to May 31, 2019) Map Courtesy of the US National Weather Service Water Supply Outlook Figure 6: Multi Model Ensemble Precipitation Anomaly Forecast (March 1 to May 31, 2019) Map Courtesy of the US National Weather Service Most reservoirs and dugouts went into winter at slightly below average levels. Consequently, with a below normal runoff, some surface water supplies are expected to be of concern in It is important to understand that the vast majority of prairie runoff occurs as a result of snowmelt. Summer rains typically only generate appreciable runoff when conditions are wet (approximately 10% of years). When soil conditions are dry, it takes significant rainfall to produce runoff; therefore, unless there is appreciable precipitation in March and April, it is likely there will be limited surface runoff in 2019 over much of southern Saskatchewan and the focus will need to be on storage during the spring melt. March 2019 Runoff Outlook 6

8 Summary of Major River Systems Souris Basin Rafferty Reservoirs and Grant Devine Lake were at, or below in the case of Rafferty, their normal drawdown levels prior to February 1. With near normal conditions at freeze-up in 2018 and below to near normal snow pack across much of the basin, non-flood operations are in effect and additional drawdown of these reservoirs is not expected to occur in Based on current conditions, WSA does not expect these reservoirs to reach their full supply levels in It is anticipated that reservoir releases during the spring runoff period will be limited to what may be required to meet international apportionment obligations. Detailed forecasts for the Souris River Basin are developed on or near the 1 st and 15 th of each month, beginning in February, up until the snowmelt runoff event. These forecasts can be found on Saskatchewan River Basin Winter inflows to Lake Diefenbaker have dropped below normal and Lake Diefenbaker water level is presently slightly below median for this time of year. As a result, the outflows have been reduced to below normal. Operations plans are to significantly reduce releases during March to limit any additional drawdown on the reservoir. Below normal releases are likely for both March and April. Snow pillows operated by Alberta Environment and Parks located at higher elevations within the alpine headwaters of the basin are showing near or slightly below average snowpack for the South Saskatchewan River headwaters, and above average (near the upper quartile) for the North Saskatchewan River. Snow courses completed at lower elevations in late January and early February also suggest an average to below average snowpack in the Bow and Oldman river basins, and a somewhat above normal snowpack in the Red Deer and North Saskatchewan river basins. The snowpack in the Rockies does not typically peaks until late May or early June at the upper altitudes; therefore, conditions can change between now and the melt. Additionally, high flows on the system are also largely driven by significant summer rainfall events in June and July. At this time, assuming near normal precipitation over southern Alberta, Lake Diefenbaker levels are expected to be near normal in summer Flows on the North Saskatchewan River are above normal for this time of year. This, combined with below normal outflows from Lake Diefenbaker, has resulted in slightly above average flows on the Saskatchewan River. With the planned reduced releases from Lake Diefenbaker in March and April, flows on the Saskatchewan are expected to drop to slightly below median by mid-march. Qu Appelle System Lakes in the Qu Appelle Valley downstream of Craven are at near normal levels for this time of year. The exception is Pasqua and Echo lakes which are about 0.3 m above normal levels. With dry fall conditions within the basin, WSA elected to leave some logs in the Echo Lake Control structure to increase the likelihood of desirable operating levels in the summer of The current expectation is for below to well below normal snowmelt runoff throughout the majority of the basin. Logs may be installed in some outlet structures in advance of the melt to maximize diversions into storage during the melt. If there is insufficient runoff to raise lakes levels into their desirable ranges, additional diversions into the system from Lake Diefenbaker via the Upper Qu Appelle Conveyance will be made. The controls structure located at the outlet of Round Lake will not be operated in 2019 as the Government of Canada does not possess adequate land control. Churchill System Flows in the Churchill System remain above normal in response to above normal rainfall during the spring and summer of The snowpack is near normal in the eastern portion of the basin and above average in the western portion of the basin. The wet conditions at freeze-up over the upper portion of the basin is expected to result in snowmelt runoff volumes that are slightly above normal across the Beaver River sub-basin. However, flood flows due to snowmelt runoff are unlikely based on current conditions. Quill Lakes The snowpack over the Quills Lake Basin ranges from below normal in the southwestern areas to near normal over the eastern and northern portions of the basin. With freeze-up moisture conditions in the basin being drier than normal in November 2018, the expectation is for a below normal snowmelt inflow into the Quill Lakes in The Quill Lakes are forecasted to peak near m in response to snowmelt inflows in 2019, which is an increase of about 0.09 m from the current level. This would be the lowest post-snowmelt runoff peak since the spring of March 2019 Runoff Outlook 7

9 Old Wives Lake Runoff potential is expected to be below normal for most of the Old Wives Lake basin in spring 2019 due to dry conditions at freeze-up in 2018 and below normal snowfall to date. Only upper portions of the Wood River are expected to experience near normal snowmelt runoff. WSA expects sufficient inflow to fill Thompson Lake from snowmelt inflows. Frenchman River Runoff yields from the basin s headwaters and areas south of the Frenchman River are expected to be higher than lower portions near Val Marie. The current expectation is for Eastend Reservoir, Huff Lake and Newton Lake to fill. Diversions into Cypress Lake from Belanger Creek are anticipated. Battle, Middle, Lodge Creeks With a near average snowpack in southeastern Albert and southwestern Saskatchewan, the expectation is that there will be average inflow into both Middle Creek Reservoir and Altawan Reservoir in Maple Creek Based on current conditions, near average inflow into all reservoirs in the Maple Creek Basin (Junction, McDougald, Harris, and Downie) is expected. Swift Current & Rush Lake Creeks The snowpack in the basin is near normal. With average fall conditions, a near normal runoff is expected. Highfield Reservoir is approximately 50% full and may not fill in Next Forecast The WSA will issue a Spring Snowmelt Forecast in early April unless runoff is underway. March 2019 Runoff Outlook 8

10 Lake 2019 March 1 st Level (metres) Table 1: Provincial Forecast for Saskatchewan March 2019 Forecast* 2019 Peak Spring Levels (metres) Shoreline 1 Level/FSL (metres) Normal Summer Level (metres) 2018 Peak (metres) Recorded Historical Extreme Level (metres) Year Anglin ** 2013 Big Quill (spill) Boundary Reservoir Buffalo Pound Candle Lake Cookson Reservoir Crooked ** 2014 Diefenbaker Echo and Pasqua Fishing Good Spirit ** 2010 Grant Devine ** 2011 Jackfish Katepwa and Mission La Ronge ** 2011 Last Mountain Moose Mountain Nickel Lake Rafferty ** 2011 Reindeer ** 1997 Round ** 2014 Wascana * These forecasted peaks are based on a typical spring precipitation and rate of melt. Above normal precipitation and/or rapid melt may result in significantly higher levels. ** Occurred after spring runoff during summer event(s). 1 The Shoreline Level and Full Supply Level refer to the highest elevation before spill occurs Spring Runoff Forecast 9

11 Basin and Location ASSINIBOINE RIVER BASIN Table 2: Spring Runoff Forecast March 2019 Forecast * (m 3 /s) Frequency 2018 Spring (m 3 /s) Historical Normal Year Recorded Maximum Spring Flow (m 3 /s) Flow (m 3 /s) Year Assiniboine River at Sturgis 20 <1: Whitesand River near Canora 30 <1: Assiniboine River at Kamsack 60 <1: QU APPELLE RIVER BASIN Qu Appelle River near Lumsden 25 <1: Qu Appelle River below Craven 15 <1: Qu Appelle River below Loon Creek 20 <1: Qu Appelle River near Hyde 35 1: Qu Appelle River near Welby 40 1: Moose Jaw River above Thunder Creek 15 <1: Moose Jaw River at Burdick 18 <1: Wascana Creek at Regina 10 1: Lanigan Creek above Boulder Lake 6 1: Pheasant Creek near Abernethy 6 1: Cutarm near Spy Hill 6 1: * These forecasted values are based on typical spring precipitation and typical rate of melt. Above normal precipitation and/or rapid melt may result in significantly higher flows. ** Occurred after spring runoff during summer event(s). Spring Runoff Forecast 10

12 Basin and Location March 2019 Forecast * (m 3 /s) Frequency 2018 Spring (m 3 /s) Historical Normal Year Recorded Maximum Spring Flow (m 3 /s) Flow (m 3 /s) Year BEAVER RIVER BASIN Beaver River near Dorintosh 175 1: LAKE WINNIPEGOSIS BASIN Red Deer River near Steen 20 1: Red Deer River near Erwood 150 1: NORTH SASKATCHEWAN RIVER BASIN North Saskatchewan River near Deer Creek : Eagle Creek near Environ 5 <1: North Saskatchewan River at Prince Albert : SASKATCHEWAN RIVER BASIN White Fox River near Garrick 30 1: Torch River near Love 50 1: Carrot River near Armley 75 1: Carrot River near Smoky Burn 220 1: SWIFT CURRENT CREEK BASIN Swift Current Creek below Rock Creek 15 1: Rushlake Creek above Highfield Reservoir 5 <1: * These forecasted values are based on typical spring precipitation and typical rate of melt. Above normal precipitation and/or rapid melt may result in significantly higher flows. ** Occurred after spring runoff during summer event(s). Spring Runoff Forecast 11

13 Basin and Location March 2019 Forecast * (m 3 /s) Frequency 2018 Spring (m 3 /s) Historical Normal Year Recorded Maximum Spring Flow (m 3 /s) Flow (m 3 /s) Year SOURIS RIVER BASIN Long Creek near Noonan 10 <1: Yellow Grass Ditch near Yellow Grass 5 <1: Souris River at Ralph 5 <1: Jewel Creek 2 <1: Moose Mountain above Grant Devine Lake 15 <1: Souris River near Sherwood 10 <1: SWIFT CURRENT CREEK BASIN Swift Current Creek below Rock Creek 15 1: Rushlake Creek above Highfield Reservoir 5 <1: OLD WIVES LAKE BASIN Notukeu Creek near Vanguard 20 1: Wood River near Lafleche 30 1: MISSOURI RIVER BASIN Battle Creek near Consul 3 1: Denniel Creek near Val Marie 10 1: East Poplar River above Cookson Reservoir 3 1: Frenchman River near Ravenscrag 30 1: * These forecasted values are based on typical spring precipitation and typical rate of melt. Above normal precipitation and/or rapid melt may result in significantly higher flows. ** Occurred after spring runoff during summer event(s). Spring Runoff Forecast 12