Flood Warning Continues for Assiniboine River
A flood watch has been issued by Manitoba Water Stewardship for all of southern Manitoba, south of a line through Duck Mountain and Bissett, due to potential heavy rain this weekend.
Environment Canada indicates that rainfall of 25 to 50 millimetres (one to two inches) is possible tonight and Saturday in western Manitoba and Saturday to Sunday in central and eastern Manitoba. Thunderstorms with intense rain are possible and any rain would fall on very wet ground and could result in heavy run-off and flash flooding. There is potential for smaller streams to overflow in areas already hard hit by recent storms and for larger rivers to rise significantly next week.
A flood warning continues for the Assiniboine River valley from Shellmouth to Brandon.
Portions of the Souris and Pembina river watersheds received up to 40 mm (1.6 in.) of rain last evening and the watershed upstream of Shellmouth Dam received 10 to 15 mm (0.4 to 0.6 in.).
Duck Mountain and Eastern Riding Mountain
· Overland flooding is subsiding but could become more extensive this weekend with over-bank flows on streams that are already high from previous rains. This situation will be closely monitored.
· The Shellmouth Reservoir level rose seven centimetres (2.8 in.) since yesterday morning and stood at 430.17 metres
(1,411.33 feet) this morning. The conduit flow was reduced from 850 cubic feet per second (cfs) to 700 cfs during the 24-hour period ending at 9 a.m. today. Gate changes were made to try to keep the total outflow from exceeding 3,700 cfs, which is the minimum outflow achievable in recent days. This will be more difficult, if not impossible due to additional recent rain and the prospect of more rain this weekend. The spillway flow this morning was 3,050 cfs, while the total outflow was 3,750 cfs. The computed inflow this morning was 6,000 cfs. The reservoir is expected to crest at 430.26 m (1,411.5 ft.) on June 28, based on little precipitation for the next 10 days. This is the first time the spillway has been overtopped during the summer in 40 years of operation. The spillway elevation is 429.31 m (1,408.5 ft.).
· Most tributaries of the Assiniboine River from Shellmouth to Brandon have crested but remain very high and could rise significantly with additional rain. The Qu’Appelle River will continue to rise until next week. Predicted crests in the portion from Shellmouth to Portage la Prairie are unchanged and flooding of lower portions of the valley next week is likely. The forecast will be revised if heavy rain falls this weekend. Flooding of valley lands from Shellmouth to Millwood will continue for the next few weeks. Much will depend on rainfall during the next 10 days. Crests are expected at Miniota on June 28 to 30, Virden on June 30 to July 1 and Brandon on July 3 to 4.
· The Portage Diversion continues to be operated to reduce levels in Winnipeg, which have risen above 3.4 m (11 ft.). The diversion flow this morning was 5,143 cfs while the flow at Southport (downstream of the control structure) was 3,210 cfs.
· Operation of the Red River Floodway has been temporarily halted due to rising flows on the Red River resulting from last week’s rain in the Red River valley. The flow at the floodway inlet this morning was 23,500 cfs. Red River levels from Emerson to St. Norbert are expected to rise about another 0.15 m (0.5 ft.) without additional rain. Operation of the control structure to lower river levels from Ste. Agathe to the floodway inlet will likely resume next week unless significant additional rain develops on the weekend. There is a potential for significant rises if more than 25 mm (one in.) of rain develops this weekend.
· The river level in downtown Winnipeg declined slightly to 3.5 m (11.36 ft.) at 9 a.m. this morning. The level should decline further as the full effect of Portage Diversion operation reaches Winnipeg. Significant rises could occur if the weekend rain falls as presently forecasted. The natural level without operation of major flood control works was 3.95 m (12.95 ft.) this morning.
Souris and Pembina Rivers
· Heavy rain in the Souris River watershed in Saskatchewan and North Dakota will result in significant rises of the Souris River in Manitoba during the next few weeks. Based on a U.S. National Weather Service forecast for Westhope, a rise of up to 1.22 m (four ft.) could occur from now until early July. Flooding of agricultural lands in the Coulter area will increase substantially. Larger rises are likely if heavy rain falls this weekend.
· Heavy run-off from downpours in the headwaters of the Pembina River last week caused significant rises on Pelican and Rock lakes. Pelican Lake levels area being lowered by operation of the outlet control works. The level of Rock Lake has risen
0.49 m (1.6 ft.) since last week and stood at 406.33 m (1,333.10 ft.) this morning, about 0.6 m (two ft.) above the summer target level. A further rise of about 0.3 m (one ft.) is expected without additional rain, but larger rises would occur if heavy rain develops this weekend. Some flooding of low-lying properties has been reported.
· Very wet conditions continue in a large portion of southern Manitoba from a Swan River to Gypsumville line south to the U.S. boundary, with overland flooding in low-lying areas. The flooding is gradually receding in most areas, but additional rain will extend the flooding and cause it to worsen. There is concern about the forecast of rain on the weekend, which could aggravate the flooding situation.