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Levels and Flows for Rivers, Lakes, Reservoirs and Aquifers

Hydrologic Conditions and Outlook for Manitoba September 2006

Notes on this Publication

The Hydrologic Conditions and Outlook report for Manitoba is normally issued on a seasonal basis. The primary purpose of the report is to address low water conditions and the potential for water shortages. Reports are not issued during wet years such as 2005. A brief overview was issued in mid July, 2006 following dry spring weather conditions in southeastern Manitoba.

This report provides a summary of surface water and groundwater conditions as of early September, 2006 and provides information on anticipated lake, river, reservoir, aquifer and on-farm water supply conditions for the remainder of 2006.

This report may also be viewed on the Manitoba Water Stewardship web site located at http://www.gov.mb.ca/waterstewardship/water_info/lake_river/index.html

Manitoba Water Stewardship acknowledges the assistance of Environment Canada (Meteorological Service of Canada and Water Survey of Canada) for contributing climatological and hydrometric data used in this report, and that of Manitoba Hydro for providing data and forecasts for northern controlled lakes and streams. Saskatchewan Water Authority, U.S. National Weather Service, U.S. Geological Survey, U.S. Fish and Wildlife Service and Lake Of The Woods Control Board provided information on streams flowing from their jurisdiction into Manitoba. Information provided by regional offices of Manitoba Water Stewardship and Manitoba Conservation is also acknowledged.

All data provided in this publication is preliminary and subject to revision.

Technical questions or comments regarding this report may be directed to Manitoba's Hydrologic Forecast Centre at 204-945-6497, or by sending a message through the "contact us" feature on our web site.

The numerical portions of this report are in SI units, as surveys show that most of our users prefer these units. Conversions to metric may be made using the information below.

Equivalents of Measure

1.0 inch = 25.4 millimetres
1.0 foot = 0.3048 metres
1.0 cubic foot/second = 0.0283 cubic metres/second
1.0 acre-foot = 1.2335 cubic dekametres

September 14, 2006
Water Supply Conditions for Manitoba

Weather Conditions and Outlook
Runoff Prospects - Autumn 2006
River Flows
Reservoir Levels and Storages
Lake Levels
Groundwater Conditions
On-Farm Water Supplies
Report Updates

Figures

Weather Conditions and Outlook

The summer of 2006 was among the driest on record in southern Manitoba but was wetter than average in northern Manitoba. Dry weather began in southeastern Manitoba, including the Red River Valley, in April and continued unabated until mid September. Some portions of this area appear to have experienced the driest summer since the 1930's. The driest area was between Portage la Prairie and Winnipeg where rainfall since April 1 was as little as 30 % of normal. Extreme southeast Manitoba got some relief during the first two weeks of August when over 100 mm of rain fell in the Sprague area. Western Manitoba had at least average precipitation during May and June but unusually dry weather from July to mid September. Northern Manitoba (north of a line through the Pas and Norway House) experienced generally above average precipitation from April through mid September.

A map showing precipitation as a percent-of-normal for the period from April 1 to September 12, 2006 is provided. Individual percent-of-normal precipitation maps for April, May and June, July and August are also provided. These are also posted on the Water Stewardship web site in the "maps" folder

Temperatures were well above average during the summer of 2006 at most locations which, together with plentiful sunshine, resulting in above average water temperature in rivers, lakes and reservoirs.

The weather forecast for September 15-17 suggested that a large storm system could bring substantial precipitation to much of the Lake Winnipeg watershed from Alberta through NW Ontario. Hopefully this system will herald the end of the dry spell rather than a temporary deviation from it.

A long range weather outlook issued by Environment Canada in early September suggests somewhat above average precipitation in southern Manitoba and somewhat below average precipitation in northern Manitoba for the period from September to November, 2006. Temperatures for this period are expected to be average to somewhat above average. The U.S. Climate Prediction Center (NOAA) indicates that the world climate has been in an ENSO neutral phase so far this year but that a weak El Nino may develop early next year. El Nino's are associated with predominantly mild winters in most of Canada but their effect on precipitation is not well defined.

Runoff Prospects - Autumn 2006

The unusually dry weather in southern Manitoba this summer has resulted in low soil moisture levels in most areas. It is therefore likely that autumn rains will produce little or no runoff unless precipitation is well above average. A significant recharge of surface water supplies this autumn is therefore unlikely but not impossible. If dry weather continues this autumn soil moisture will be well below average at the start of next spring's runoff. This would greatly reduce runoff during the spring of 2007 although runoff could still be substantial depending on winter snow and spring rain. A minor recharge during the spring of 2007 could result in very low water levels in southern Manitoba later in the year.

Northern Manitoba is likely to experience average to above average runoff from autumn rains since antecedent moisture is high.

River Flows

Levels and flows of most rivers in southern Manitoba were well below average as of mid September. The Red River, Winnipeg River and the Souris River were all flowing at less than half their median flows for early September. Many smaller ephemeral streams in southern Manitoba had dried up or were down to near zero flow. However small streams have dried up many times before and water users do not depend on them for their supplies. The Assiniboine, Waterhen, and the Fairford rivers were exceptions with much above average flows this summer, due to a major spring recharge which produced high water storages in Shellmouth Reservoir and Lake Winnipegosis. However the Assiniboine River was declining rapidly during late August and September. Most rivers in northern Manitoba had above average flows as of mid September although the Saskatchewan River had only median flows.

A comparison of streamflows for September 7 for selected rivers is shown in Table 1. Flows are all above the extreme lows observed during the past 35 years. The Little Saskatchewan River is nearing the record low but is unlikely to stop flowing unless very dry weather continues this autumn. Many small streams that have dried up are at the record low for this time of year.

Plots of weekly flows for selected rivers in southern Manitoba are also provided herewith. These plots show observed flows along with lower decile, median and upper decile flows for the past 40 years.

Larger streams which provide water supplies for cities, towns, farms and industry will decline further this autumn if dry weather continues but should remain high enough to meet needs this fall and winter. A dry autumn could result in winter flows and levels of the Red River declining close to those observed during the winter of 2003-2004. During February 2004 the Emerson flow dipped to 400 cubic feet per second (cfs), well below the median February flow of 1340 cfs. The flow at Emerson on September 7, 2006 was 1170 cfs. Flows in the Assiniboine River could be somewhat below average this winter if the autumn is dry but should remain well within the desirable range. Souris River flows will likely decline to zero early this winter in the portion from Coulter to Melita but this is not unusual. Minor flows should persist from Hartney to Wawanesa due to groundwater discharge.

Additional smaller streams could dry up if dry weather continues this autumn. There is some concern that if a dry autumn is followed by a colder than average winter some streams which have not dried up could freeze up. However this will depend on snowcover and is not expected on the Red and Assiniboine rivers in any case.

Low flows on the Winnipeg River, Red River, Saskatchewan River (Alberta portion) and other streams flowing into Lake Winnipeg may impact on hydroelectric generation this autumn and winter.

Reservoir Levels and Storages

Most reservoirs operated by the province are lower than in recent years but are still well above previous lows set in the 1961, 1991 and 2003. This is in large part due to the fact that all reservoirs were full during the spring of 2006. A few reservoirs such as Stephenfield Reservoir and Lake Irwin are quite low due to extensive uses or releases in addition to low inflows this summer. Water uses were exceptionally high this summer due to the hot dry weather.

Reservoir levels, storages and outflows are shown in Table 2. Most reservoirs are at least 65% full and contain enough water to meet needs this autumn and winter and beyond. Shellmouth Reservoir has returned to its normal level for this time of year. Some recharge would be desirable on most reservoirs this autumn and a moderate recharge will be needed next spring to avoid difficulties on some reservoirs later in 2007.

Storage in Lake Diefenbaker is somewhat below average. The Saskatchewan Water Authority predicts outflows from now through February to be 85 % of normal based on average precipitation. Storages in the U.S. portion of the Red River watershed are close to normal for this time of year, except for some smaller reservoirs which are quite low.

Manitoba Water Stewardship will continue to operate control structures on reservoirs and lakes in order to maintain desirable levels while meeting local and downstream needs. Operation planning for major controlled lakes and reservoirs is ongoing and is based on current lake or reservoir and watershed conditions and on predicted inflows for various future weather conditions.

Lake Levels

Most lakes in southern Manitoba were at below average levels as of mid September due to low inflows, high evaporation and lack of significant precipitation this summer. Recent levels for 35 Manitoba lakes are provided in table 3 and table 4 titled "Southern Manitoba Lakes" and "Northern Manitoba Lakes". Target levels for these lakes and levels in recent years are also shown on these sheets.

Plots showing monthly mean levels for 15 selected lakes in southern Manitoba for the 35 year period from 1971 to 2005 are also provided to show how this year's levels compare to those of other years.

The level of Lake Winnipeg declined rapidly from this summer due to declining inflows, high net evaporation and relatively high outflows. The level of 713.2 in mid September was near the middle of the operating range of 711-715 feet and 2.4 feet lower than at the same time in 2005. Manitoba Hydro has been reducing outflows since mid August to slow the decline of the Lake. The lake could decline somewhat further this autumn if dry weather continues, but should decline little further once ice cover develops in December. While the present level is somewhat lower than the optimum, no particular problems are foreseen unless the 2007 spring recharge is well below average.

The level of Lake Manitoba as of mid September was in the middle of the operating range of 810.5-812.5 feet and one foot lower that at the same time last year. Inflows to the lake are still twice the normal due to continued above average levels on Lake Winnipegosis. The outflow at Fairford Dam was still more than three times the median as of mid September.

Lake of the Woods has been unusually low this summer due to the dry weather and was 2 feet below average as of mid September. The Lake of the Woods Control Board has been reducing outflows in an attempt to prevent further declines on the lake. The lake will likely recover to normal levels next spring although there is a chance it will not if dry weather continues.

Most smaller lakes in southern Manitoba were about 1 foot below average levels for mid September. It was not possible to maintain target levels on many lakes on the Whiteshell and elsewhere this summer due to the minimal inflows and high net evaporation. Big Whiteshell Lake, which is uncontrolled, is 2 feet below average. Moose Lake in extreme southeastern Manitoba was quite low during early August but recovered to normal later in the month due to local heavy rain. Stephenfield Lake and Lake Minnewasta are more than 3 feet below their full levels due to high direct uses and releases required to meet needs this summer. However both are very likely to fill next spring. A few lakes such as the Shoal Lakes in the southern Interlake and Whitewater Lake are still at above average levels, due to the fact they were very high this spring and have little or no outflow.

Northern Manitoba lakes were generally above average due to the much wetter weather conditions this summer. Most lakes in the vicinity of The Pas were near the top of the operating range. Saskatchewan Water Authority is maintaining above average outflows from Reindeer Lake to prevent further rises in the lake. Lakes in the Churchill River and Grass River were very high this summer but are declining due to drier weather during August. Lakes along the Nelson River system are above average or below average depending on their location relative to control structures. They have been associated with high flows on the Nelson River from late 2004 until July 2006 but have been reverting to levels associated with near normal flows since mid August.

For additional information on water levels and flows in northern Manitoba, visit the Manitoba Hydro web site at http://www.hydro.mb.ca/issues/water_regimes.shtml

Groundwater Conditions

Despite the very low rainfall conditions affecting much of southern Manitoba this summer, monitoring carried out by Manitoba Water Stewardship has shown that groundwater levels in major Manitoba aquifers have generally remained at or above historic normal elevations. Most groundwater systems react in a delayed manner to wet or dry cycles as compared to surface water systems. Consequently, groundwater levels in 2006 continue to reflect the influence of the substantial recharge to most aquifers which occurred in 2005 and, in some cases, over the past several years.

Groundwater levels in the Oak Lake, Assiniboine Delta, Winkler and Carbonate aquifers as of mid July, 2006, representing the major aquifer types in the southern part of the province, generally remain near or at above normal elevations although there have been substantial declines in water levels through the summer in the Carbonate aquifer east of Winnipeg. It is expected that the rate of decline in these areas will lessen over the fall and winter, with groundwater levels remaining well above the historic lows seen in the late 1980s to early 1990s. Plots showing hydrographs of representative groundwater levels in these aquifers are provided.

Groundwater supply issues may become more pronounced in parts of the province next year if little recharge occurs in the coming spring and early summer.

On-Farm Water Supplies

Manitoba's Water Services Board reports that groundwater levels in shallow dug wells and water levels in dugouts in parts of southern Manitoba may have declined or may decline to problem levels over the winter unless significant rainfall occurs this fall.

The Water Services Board continues to promote improvement of water sources and storage for drought prone areas, such as pipelines, cisterns, better dugouts and improved wells.

Report Updates

This report will not be updated this year unless the autumn is dry and serious concerns about water shortages develop.

In the meantime, weekly river reports, monthly lake reports and precipitation maps will continue to be provided as usual, and will be posted on the Manitoba Water Stewardship web site.

Figures

Hydrologic Forecast Centre
Water Branch,
Manitoba Water Stewardship