UPDATED 2006  SPRING FLOODING OUTLOOK
Flooding Potential Increased: Spring Weather Key Factor

Hydrologic Forecast Centre,
Manitoba Water Stewardship

Manitoba Water Stewardship acknowledges the assistance of Water Survey Of Canada and Manitoba Hydro in contributing data for this report.

March 24, 2006 - The Hydrologic Forecast Centre of Manitoba Water Stewardship has released an updated flood outlook for the spring of 2006. 

The spring flood potential has increased in most areas of southern Manitoba since the first 2006 outlook was issued in late February, mainly due to heavy snowfall in early March.

The potential for minor flooding remains in northern Manitoba. 

Spring flooding potential is highest in western Manitoba from the Riding Mountain area to The Pas when snow cover is at near-record levels.

There is also a potential for flooding in the Red River watershed, portions of the Assiniboine River watershed, on the Saskatchewan River and in the Interlake.

The extent and severity of flooding will be determined by spring weather conditions. 

A gradual melt with little precipitation would result in only minor flooding. 

A quick melt with above-average precipitation could result in serious flooding in many areas of Manitoba.

Soil Conditions:
An aerial survey conducted in early November 2005 showed that topsoil moisture was average to above average in most portions of southern Manitoba.  A Manitoba Agriculture, Food and Rural Initiatives field
survey in late October 2005 also showed that topsoil and subsoil moisture are generally above average.  However, soil moisture is below average in the Dauphin and Westlake areas and in portions of the western Interlake.  In northern Manitoba, moisture conditions are estimated at 150 to 200 per cent of normal in most areas because of the heavy rain which fell in the late summer and autumn. 

Snow Cover and Winter Precipitation:
An airborne snow survey and a conventional surface survey were conducted in mid-March 2006. Water content of the snowpack ranged generally:

* from 75 to 100 mm (150 to 200 per cent of normal) in southeastern Manitoba and the Interlake;
* up to 175 mm (175 to 225 per cent of normal) in the Duck Mountains in western Manitoba;
* less than 25 mm (25 to 50 per cent of normal) in southwestern Manitoba; and
* from 100 to 170 mm (150 to 200 per cent of normal) in the The Pas region.

The surface survey by Manitoba Water Stewardship shows that snow cover is more than double or 200 per cent of normal in many areas from Neepawa north to The Pas.  
 
Spring Run-off: 
Above-average run-off is expected in southeastern Manitoba, northern Manitoba, the eastern Interlake and in western Manitoba from the Riding Mountain to The Pas areas.  Most other areas should experience average to below-average spring run-off based on normal weather.  

Potential for flooding along major rivers is largely dependent on weather conditions in the next few months. 

Ice jamming remains difficult to predict, however, ice breaking using the Amphibex ice breaker along the Red River north of Winnipeg is ongoing and is being considered for other areas prone to ice jamming.

Many lakes are still at above-average levels from the unusually heavy precipitation in 2005. Lakes above average levels could be susceptible to shoreline flooding if above-average spring run-off develops in their
watersheds.  Manitoba Hydro has maintained the maximum possible outflow from Lake Winnipeg since January 2005 within constraints required to prevent ice-related difficulties.

Daily flood reports will be available once spring run-off is underway. The Hydrologic Forecast Centre, Water Science and Management Branch, Manitoba Water Stewardship will keep a close watch on watershed conditions.  The full technical report is available at: http://www.gov.mb.ca/waterstewardship/.


SPECIFIC RIVER AND LAKE FORECASTS ARE ATTACHED.

Second 2006 Spring Flooding Outlook for Rivers and Lakes

River Forecasts:
The spring flood outlook is based on three weather scenarios based on probabilities of additional snowmelt rates and spring rain based on statistics for the past 40 years.  These have been considered within the context of existing watershed conditions for run-off and hydrologic forecasting.  The terms favourable, average and unfavourable refer to the lower-decile, median and upper-decile conditions. 

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 in eastern Saskatchewan was obtained from the Saskatchewan Water Authority. 

Red River Main Stem:
There is a potential for flooding due to high soil moisture and moderate snow cover in most of the watershed including the U.S. portion. 
* Favourable weather (one-in-10 chance):  crests from Emerson to the floodway inlet would be similar to those of the spring of 2005 with minimal flooding. 
* Average weather:  peak levels would be similar to April 2001. Flooding would occur within several miles of the river from Letellier to Morris, somewhat greater than July 2005. Flooding of low-lying areas from Morris to the floodway inlet would be similar to July 2005. Floodway operation should keep the crest in downtown Winnipeg from exceeding 19 feet. 
* Unfavourable weather:  a serious flood similar in magnitude to that of 1996 could develop. This scenario is based on a rapid melt, additional precipitation of at least 50 mm during the snowmelt run-off
period and an unfavourable north-south timing of run-off.  The 1996 flood was a few feet lower than the 1979 flood and much lower than the 1997 flood.  The 1996 flood is the fourth-highest flood after the 1997, 1950 and 1979 floods.  This scenario should produce serious flooding along the Red River from Emerson to the floodway inlet.  The peak stage in downtown Winnipeg would be held to 19.5 feet by operation of flood-control works. 

Serious ice jamming from Selkirk to Breezy Point appears unlikely this spring due to below-average ice thicknesses and the ice-breaking activities of the Amphibex.  An ice survey conducted in mid-March indicated ice thickness of close to half a metre or 1.6 feet from Lockport to Breezy Point.  The normal ice thickness in the late winter is 0.8m or 2.6 ft.

Red River Tributaries:
Minor flooding of low-lying agricultural lands, especially on eastern tributaries, is likely even with favourable weather.  Flooding would become more significant with average spring weather and could reach 2004 levels.  The unfavourable weather scenario could produce serious flooding on the eastern tributaries and the La Salle River although still generally less than that of 1974, 1979 and 1997.  Western tributaries would also experience considerable flooding under this scenario but it should be well below record levels.  Flooding is unlikely on the Pembina River with average weather but minor flooding
could develop with the unfavourable weather scenario.

Assiniboine River Main Stem:
* Flooding along the Assiniboine River should be avoided with favourable weather from now on.
* With average weather, flooding of valley lands would occur from Millwood to Brandon. Operation of the Shellmouth Reservoir and the Portage Diversion should prevent flooding in the Shellmouth area and
from Portage la Prairie to Winnipeg. 
* An unfavourable weather scenario (one-in-10 chance) would result in significant flooding along the Assiniboine River with crests similar or somewhat greater than those of April 2005.  Operation of the Portage Diversion would prevent serious flooding from Portage la Prairie to Winnipeg, although brief flooding due to ice jams could occur.

Assiniboine River Tributaries:
* With favourable weather, flooding should be limited to the Shell River and the headwater areas of the Little Saskatchewan River and Birdtail Creek.
* With average spring weather, flooding on these streams could become more significant and some flooding could also occur on tributaries from Shellmouth to St. Lazare.
* Unfavourable weather (one-in-10 chance) would result in serious flooding on the Shell River and the Little Saskatchewan River and would require some diking of low-lying buildings at Minnedosa.  Flooding would also occur on many other tributaries except western and southern tributaries from St. Lazare to Brandon.  Sturgeon Creek could produce agricultural flooding and could overtop Ness Avenue in Winnipeg under this scenario.

Souris River:
* Flooding is not expected along the Souris River with favourable weather.         
* Median weather could produce minor flooding of agricultural lands in the Coulter area. 

* Unfavourable weather (one-in-10 chance) could produce minor flooding from the U.S. boundary to Hartney, but still somewhat less than that of last spring. 
* Eastern tributaries from Waskada Creek to Elgin Creek could reach near bank-full levels under the unfavourable weather scenario. Western tributaries would remain well within their banks. 

Interlake Region:
* With favourable weather, some overland flooding would occur in low-lying areas but streams should remain within their banks.
* With average weather, minor flooding could occur on the Fisher River, greater than 2005 but less than in 2004.  Considerable flooding of low-lying areas is likely, especially around marshes and small lakes
such as the Shoal Lakes.  This would be in part due to the high-water levels remaining from 2005.
* The unfavourable weather scenario (one-in-10 chance) could produce serious flooding on the Fisher River and other streams in the eastern Interlake, at least as great as in 2001 but still less than in
1979.  There would also be extensive overland flooding.  Agricultural flooding near the Shoal Lakes would increase in extent and could threaten some homes and farm buildings. 
* The Dauphin River remains high due to above-average flows and significant ice conditions on the river.  Flows in the river are not expected to increase significantly during breakup since Lake Manitoba and Lake St. Martin, the source of the flows, will rise only slightly before the ice disappears.  No change in log settings at Fairford Dam is planned at this time. The threat of spring flooding on the Dauphin River is quite low although temporary flooding is a possibility if ice jams develop. 

Eastern Region:
* Minor localized flooding is expected with average future weather conditions.
* The unfavourable weather scenario could see considerable overland flooding as well as flooding of low areas along the Brokenhead, Whitemouth and Birch rivers and streams in Whiteshell Provincial Park. 
* Above-average levels are likely on the Winnipeg River but levels should be lower than last spring with average weather.  The unfavourable scenario could produce a repeat of the unusually high levels observed in the Nutimik area in 2005. 

Westlake-Dauphin-Swan River Region:
Snow cover is up to two times or 200 per cent of normal on the Riding, Duck and Porcupine mountains.  Snow on the high ground often melts slowly over a period of several weeks to a month.  Occasionally it melts very quickly in a few days.  The flood threat for streams flowing off the high terrain is highly related to the melt rate as well as to additional precipitation. 

Soil moisture is below average in the Dauphin Lake watershed and the Westlake region but somewhat above average in the Swan River 
* With favourable weather flooding would be relatively minor. 
* Average weather conditions could produce considerable flooding on streams flowing off the high ground on the Riding, Duck and Porcupine mountains.  This flooding would occur mainly in low-lying areas.
Below-average soil moisture in the Westlake and Dauphin areas should absorb much of the snowpack and prevent serious overland flooding or over-bank flows.  However, over-bank flows are likely in the Dead Lake
Drain area south of Gladstone, in portions of the Turtle River watershed and on some streams flowing eastward off Duck Mountain.  Levels on the Whitemud River at Westbourne should be similar to those of 2001.
* The adverse weather scenario (one-in-10 chance) could produce serious flooding on most streams in the region with a rapid melt in the highland areas with daily high temperatures of  plus 15 or higher for at least five consecutive days.  Flooding could also develop on the Swan River but it is unlikely the Town of Swan River would be affected. Flooding in the Whitemud River watershed including the Big Grass River and Big Grass Marsh could reach near 1979 levels. The Village of MacGregor could sustain flooding and some diking might be required at Gladstone and Westbourne.  There is a possibility that a partial dike closure may be required on the Turtle River at Ste. Rose under this scenario.

The Pas Region:
Soil moisture and snow cover are unusually high in the lower Saskatchewan, Carrot and Red Deer river watersheds.  The portion of the Saskatchewan River watershed lying in east-central Saskatchewan often
produces the main spring crest at The Pas.  This area has very high soil moisture from last autumn's heavy rains and has 150 to 200 per cent of normal snow cover.  The presence of river ice during the snowmelt crest raises river levels and increases the chance of flooding.  There would be a 20-per-cent chance of flooding at Rall's Island even with river ice moving out in advance of the flow crest.
* With favourable weather, unusually-high river levels would occur but flooding would be relatively minor and diking would not be required.

* With average weather conditions, including near-normal ice breakup, above bank-full flows would occur in the Pasquia Valley and some flooding would occur along the Carrot River and the Red Deer River.
Flooding at Rall's Island could occur if river ice is still in place when the flow crest arrives.  The possibility of breaking the ice downstream of Rall's Island with the Amphibex is being explored.  Some diking of properties at Opasquiak Cree Nation (OCN) and the Bracken area may be necessary.
* With adverse weather, serious flooding of record proportions could occur on the Saskatchewan, Carrot, Red Deer and Pasquia rivers. Serious flooding would occur in the OCN and Bracken area of the Carrot
River and in the Pasquia Polder area.  Diking would be required to protect properties near the rivers and much pumping would be needed in the Pasquia area. 

Northern Manitoba:
Run-off in northern Manitoba (north of latitude 54) is likely to be somewhat above average based on normal weather conditions from now on. While snow cover appears to be close to average, soil moisture and depression storage is well above average due to heavy rain last summer and autumn.  Localized flooding of low-lying areas is likely to occur. 

Flooding is not expected along the Churchill River and the Nelson River this spring and early summer under the average weather scenario as both rivers would experience relatively minor rises.  The unfavourable weather scenario (one-in-10 chance) could produce significant flooding of low-lying areas and lake shores in northern Manitoba, although not likely as great as that of the late summer and autumn of 2005.  Levels of the Churchill River and the Nelson River would still be lower than those of 2005.  Manitoba Hydro may have more specific information for certain areas in northern Manitoba.

Lake Forecast:
Many lakes are still at above-average levels as a result of the unusually heavy precipitation in 2005 and are susceptible to shoreline flooding if above-average spring run-off develops in their watersheds. 

Smaller lakes in southern Manitoba including the Whiteshell are unlikely to be seriously high in 2006 unless the unfavourable weather scenario unfolds. 

Lakes in the vicinity of The Pas and in northern Manitoba are likely to be higher than desirable due to the presently high levels and the significant run-off expected this spring.  Lakes along the Nelson River
will most likely be above the desirable range although likely lower than last summer.  Lakes along the Churchill River should be above average but much lower than the record levels of last autumn. 

Lake Winnipeg
Strong wind storms, which are more probable in the fall, could again pose a threat of shoreline flooding on large lakes in 2006, especially if the unfavourable spring weather scenario unfolds and is followed by
adverse summer weather.  However, this scenario is unlikely to be repeated in 2006.  The present Lake Winnipeg level of 714.3 feet is still 1.4 feet above average.  With average weather conditions, the lake
is expected to crest at about 714.8 feet in June.  This level would be similar to the wind-eliminated levels during the windstorms in the autumn of 2005. There is a one-in-10 chance that the lake may rise to
715.5 feet if the unfavourable weather scenario unfolds.  The highest level without wind in 2005 was 716.6 feet in August.  Manitoba Hydro has maintained the maximum possible outflow from the lake since January 2005 within constraints required to prevent ice related difficulties.  The wind-eliminated forecasts given above are preliminary estimates made in consultation with Manitoba Hydro.

The chance of flooding along the Lake Winnipeg shoreline this spring and summer is relatively low since strong winds seldom occur during this time when the level without wind will likely be at its highest.  The
one-in-10-year increase in levels due to wind set-up and wave uprush at Gimli is only three feet during the spring and summer as compared to six feet in the autumn. 

Lake Manitoba
Lake Manitoba is likely to rise to 812.4 feet by late spring based on average weather, a rise of about half a foot from the present level. Continued high outflows at Fairford Dam will help control the lake level.  The level would rise half a foot above the top of the operating range (810.5 to 812.5 feet) under the adverse weather scenario. Flooding along the Lake Manitoba shoreline due to wind set-up is unlikely this spring, as the strength of spring and summer winds is usually much lower than that of the autumn. 

The full report is available at http://www.gov.mb.ca/waterstewardship/.

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