Back grounder
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SECOND SPRING FLOOD OUTLOOK
FOR MANITOBA
Snow Cover and Winter Precipitation
Manitoba Water Stewardship conducted an aerial snow survey over the Red, Assiniboine and Souris
river watersheds and a surface-based survey in mid-March. These surveys showed that the water
content of the snowpack was slightly above average in most areas of southern Manitoba except the
extreme southeast where it was below average.
The snow water content was well above average from Duck Mountain north to Flin Flon. Snow
samples may not always be representative of an area due to redistribution of snow by wind and
differences in land use, topography and vegetation.
Spring Run-off
The 2007 spring run-off is expected to be below average in much of southern Manitoba. Dry soils
resulting from the drought-like conditions last summer should absorb most of the meltwater, leaving a
smaller than usual percentage for run-off. A gradual melt would reduce run-off but a fast melt would
increase run-off.
Above-average run-off is expected in many areas north of a line through Dauphin and Berens River,
where soil moisture and snow cover are average to above average.
Spring run-off is influenced by melt rate and future precipitation.
River Forecasts
The spring flood outlook is based on three future weather scenarios relating to additional snow, melt
rates and spring rain. These scenarios are based on climate statistics for the past 40 years.
The weather scenarios are referred to as favourable, average and unfavourable and relate to the
statistical lower decile, median and upper decile conditions, respectively. There is a one-in-ten
chance of the weather being favourable or better, and of it being unfavourable or worse.
Peak discharges and water levels have been computed for the Red, Assiniboine and Souris rivers
based on tributary forecasts and flood routing. Information on expected peak flows for the Red River
at Pembina N.D., and for the Souris River at Westhope N.D., was obtained from the U.S. National
Weather Service. Information on probable run-off and flows in eastern Saskatchewan was obtained
from the Saskatchewan Water Authority.
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-2Red River Main Stem
Anticipated spring peak stages have increased up to five feet from the February forecast due to
above-average precipitation in late February and March. Run-off is well underway in portions south
of Grand Forks and is expected to begin in Manitoba during the last week of March unless cooler
weather develops.
The Red River is expected to remain within its banks and only a minor operation of the Red River
Floodway will be required unless above-average precipitation develops.

The unfavourable weather scenario would produce minor over-bank flows in the portion of the Red
River from Emerson to just south of Morris. Operation of the Red River Floodway would keep the
crest in downtown Winnipeg from exceeding 17.5 feet. Construction on the floodway channel will
not interfere with floodway operations.

Serious ice jamming from Selkirk to Breezy Point appears unlikely this spring. An ice survey
conducted in mid-March showed that the ice thickness is near average. Relatively low river flows
will reduce the chance of serious ice jamming. The threat of ice jams near the Breezy Point area
has been further reduced by icebreaking with the Amphibex icebreaking machine.
Red River Tributaries
Flooding is not expected on Red River tributaries with average weather. This includes the Pembina
River. Unfavourable weather could produce minor localized flooding. Temporary localized flooding
may occur due to ice or snow-blocked channels.
Run-off has begun in the upper Pembina River near Killarney where some flooding has occurred near
PR 253 due to ice action. Run-off is likely to begin this weekend or early next week on most
tributaries.
Assiniboine River Main Stem
Flooding along the Assiniboine River will be narrowly avoided with a gradual melt and little additional
precipitation.
The run-off potential into the Shellmouth Reservoir remains high.

Drawdown of the reservoir continues with record high outflows for this time of year of
1,700 cubic feet per second.

The intent is to draw the reservoir down to about 1,386 feet, below which fish kill becomes a
concern. It is anticipated this will provide sufficient storage to prevent over-bank flows from the
Shellmouth Dam to Millwood unless heavy spring precipitation develops.
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-3With average weather conditions, the Shellmouth Reservoir would successfully store spring inflows
and a minor operation of the Portage Diversion would prevent flooding from Portage la Prairie to
Winnipeg.

With average weather, minor over-bank flows would occur from St. Lazare to Griswold during
April, largely due to an expected early high crest on the Qu’Appelle River. Operation of the
Shellmouth Reservoir would reduce flooding and limit flooding to the month of April without
overtopping of the spillway.

Unfavourable weather would result in significant flooding along the Assiniboine River from
Shellmouth to Brandon with crests similar or higher than to those of 2006.

The Shellmouth Reservoir would be operated to pass enough flow to prevent overtopping of the
spillway. Flooding along the Assiniboine River would end before mid-May unless very heavy
precipitation, similar to that of 2006, develops over the basin upstream of Brandon.
There would be no flooding downstream of Brandon due to low flows in the Souris River. Operation
of the Portage Diversion would prevent flooding from Portage la Prairie to Winnipeg. The Amphibex
icebreaker will be deployed to break ice on the Portage Diversion channel near Lake Manitoba to
prevent ice jams and potential related flooding.
Assiniboine River Tributaries
Despite the above-average snow cover from March storms, flooding is not expected with average
weather. Relatively dry soils are expected to absorb most of the meltwater.
With unfavourable weather, flooding could occur along the Qu’Appelle River, the Shell River and
Scissor Creek near McCauley.
Temporary localized flooding could occur in low areas elsewhere, especially where channels may be
blocked by ice or snow.
Souris River
There has been substantial additional snow on western tributaries of the Souris River in Manitoba.
However, due to very dry soil conditions, much of the meltwater is expected to soak into the ground.

With average weather conditions, flooding is not expected along the Souris River.

Unfavourable weather conditions could produce minor flooding from Coulter to Melita, similar to
that of 2006.

Minor localized flooding of Souris River tributaries could develop with unfavourable weather.
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-4Interlake Region
Additional precipitation since late February is below average in most areas.

With average weather, streams in the Interlake should experience little or no flooding. Flooding
adjacent to the Shoal Lakes, which is still ongoing, would spread somewhat.

With unfavourable weather, near bank-full flows could appear on the Fisher River including Peguis
Townsite. Other streams would likely remain within their banks unless ice jams develop.

Flooding of agricultural lands near the Shoal Lakes would increase significantly with unfavourable
weather.

With unfavourable weather, peak flows in the Fairford and Dauphin rivers would be similar to
those of 2006 when levels were high but flooding was avoided during the ice-free period.
Eastern Region
Both soil moisture and snow cover are below average in the Sandilands area east to Ontario
including the Whiteshell.

Flooding is not expected with average weather and is unlikely even with the unfavourable weather
scenario.

Spring flows on the Winnipeg, Brokenhead, Whitemouth and Whiteshell rivers are expected to be
well below average this spring unless heavy precipitation develops.
Westlake-Dauphin Region
With normal weather, flooding is not expected on the Whitemud River and its tributaries, nor on
streams flowing into Dauphin Lake with the possible exception of the Big Grass River.

The unfavourable weather scenario could produce minor flooding on streams in the region
especially if there is a rapid melt in the high terrain of Riding Mountain.

Flooding on the Whitemud River would still be less than last year even with somewhat
unfavourable weather. Manitoba Water Stewardship will be breaking ice in the lower Whitemud
River to reduce the chance of ice jam flooding at Westbourne.
Duck Mountain to The Pas
Both snow cover and soil moisture are well-above-average in this area. Snowfall since late February
has been close to average maintaining a high flood potential. The extent and severity of flooding will
be very sensitive to additional precipitation, since a large portion of additional snow or rain will
become run-off.
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-5Red Deer River
With average weather conditions, the flood potential remains high but is not as high as in 2006. The
expected crest on the Red Deer River has been reduced from that issued in February based on
information provided by the Saskatchewan Water Authority.

With normal weather, the inflow to Red Deer Lake will be only half of the extreme value observed
in 2006 but the river would be at the top of its banks.

The unfavourable weather scenario would still produce less inflow than that of 2006 but there
would be significant over-bank flows.
Swan River
The flood potential remains high. With average weather, the crest at Swan River should be 0.5 to
one feet lower than last year when flooding in Swan River was narrowly avoided. Unfavourable
weather could produce a crest similar to or higher than that of last year.
Carrot River
Conditions in the Carrot River are similar to those at this time in 2006. With average weather, the
spring crest should be slightly lower than last spring. It is likely that diking at Opaskwayak Cree
Nations west of the The Pas will be required again. Unfavourable weather could produce a nearrecord high crest west of The Pas, about half a foot higher than last spring.
Saskatchewan River
The Saskatchewan Water Authority reports that the spring run-off potential in the Saskatchewan
portion is greater than in 2006. The authority will be operating reservoirs to minimize peak outflows
from Tobin Lake. Additional precipitation, breakup conditions and ice action both in Saskatchewan
and at The Pas will influence the flooding potential.

The 2007 crest at The Pas for the normal weather condition is expected to be slightly lower than
last year assuming that ice jamming will not be extensive.

The unfavourable weather scenario has the potential to produce a crest somewhat in excess of
the 854.6 foot crest observed last spring, based on ice action also being somewhat in excess of
average

Ice jams are quite common in the Ralls Island area of The Pas. The occurrence and severity of
ice jams this spring will be a very significant factor in determining the crest.

Manitoba Water Stewardship is planning to deploy the Amphibex to break ice in the Ralls Island
area, which will reduce the chance of a serious ice jam.

Flooding of the Saskeram area on the Pasquia River southwest of The Pas is likely to occur again
this spring with levels similar to those of 2006. Provincial crews are preparing to pump water in
order to reduce levels and minimize flooding.
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-6Streams flowing off Duck Mountain and Porcupine Mountain
Snow cover is 200 per cent in the Porcupine Mountain area and up to 300 per cent in the Duck
Mountain area and soil moisture is somewhat above average.
There is a potential for flooding on streams flowing off the high ground, especially if a rapid melt
occurs resulting from daytime temperatures of 15 to 20 degrees Celsius and strong winds and rain
develop. Some flooding could occur even with average weather due to snow and ice-blocked
channels.
Northern Manitoba
Run-off in northern Manitoba (north of latitude 54) is likely to be generally above average. However
flooding is unlikely on the Churchill or the Nelson rivers.
Lake Forecast
Lake Winnipeg is low this year due to dry conditions last summer. A smaller-than-usual rise is likely
this spring due to below-average inflows from the Winnipeg and Red rivers. With average weather
conditions, the lake may rise to little more than 713 feet by early summer, which is about one foot
lower than average. The level was even lower during the last drought in 2003 when the July level
was 712.2 feet.
Lake Winnipegosis is likely to rise nearly as high as last year even with average weather from now
on. Flooding of low-lying agricultural lands adjacent to the lake is expected again this year.
The level of Lake Manitoba should be somewhat lower than in 2006 unless unfavourable weather
develops. Inflows from the Portage Diversion should be significantly less than in 2006. The lake is
expected to remain within the operating range of 710.5 to 712.5 feet. Lake St. Martin is expected to
be well above average but somewhat lower than last year.
Lake of the Woods and many other lakes in the Whiteshell area had below-average levels last
summer. Many lakes in this region are likely to be low again unless precipitation is above average
from now through June.
Most smaller lakes in southwestern and western Manitoba are at below-average levels due to dry
weather last summer. Most are expected to rise to near-normal levels by the end of spring run-off.
The level of Red Deer Lake is presently about one foot above average due to the wet conditions in
the watershed and ice in the outlet channel. The lake is forecast to crest about three feet below the
2006 crest. There is a one-in-ten chance that it could rise to within one foot of last years crest.
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-7Lakes in the vicinity of The Pas are at above-average levels and are likely to rise higher than
desirable this spring. Last spring’s flooding of low-lying lands near these lakes is likely to be repeated
this spring.
Levels of Reindeer Lake and most other lakes in far northern Manitoba are expected to be at average
or above-average levels after the 2007 spring run-off.
The full report is available on the Water Stewardship web site at:
http://www.gov.mb.ca/waterstewardship/. Click on Flood Information, Forecasts for Rivers Lakes and
Reservoirs.