The heavy rains this past week in western Manitoba are producing dramatic effects in the Assiniboine Basin and on the Whitemud River. The province has opened the Portage Diversion to restrict flows on the Assiniboine east of Portage to about 10,000 cfs, with the surplus diverted to Lake Manitoba. Flows on the Assiniboine exceeded 15,000 cfs this week. The flow in the Diversion is currently 4,273 cfs. If the flow on the Assiniboine subsides this week, the effect of opening the Diversion on the level of Lake Manitoba will be negligible (a flow of 5,000 cfs raises the lake level about 7/10ths of an inch each week). Flows on the Whitemud have jumped substantially to 2,243 cfs from near zero last week, and will go higher this week. The province expects that Whitemud flows will be higher than in 2011. The flow on the Assiniboine has jumped sharply this week and is currently registering 12,360 cfs at Holland and 9,041 cfs at Headingly. It looks like the river has crested at Holland is now starting to fall. On Lake Manitoba the gauge at Westbourne is malfunctioning, so there is no estimate of the average lake level. Outflow at Fairford is 2,896 cfs. Inflow from the Waterhen River is 4,520 cfs. The level of the Shellmouth Reservoir is unchanged from last week to 1402.41 feet.
River update
Time: 8:00 PM July 5, 2020
Portage Diversion: 4,273 cfs
Assiniboine at Holland: 12,360 cfs cfs
Assiniboine at Headingly: 9,041 cfs
Waterhen: 4,520 cfs
Whitemud: 2,243 cfs
Fairford: 2,896 cfs
Dauphin: 3,323 cfs
Lake update
Time: 8:00 PM July 5, 2020
Steep Rock: 811.58 ft
Westbourne: gauge malfunction
Mean level Lake Manitoba: no data
Lake Manitoba desired operating range: 810.5 to 812.5 ft
Lake St. Martin: 798.21 ft
Lake St. Martin desired operating range: 797.0 to 800.0 ft
Lake Winnipegosis: 831.37 ft
Shellmouth Reservoir: 1402.41 ft
Extracted from the Environment and Climate Change Canada Real-time Hydrometric Data web site (https://wateroffice.ec.gc.ca/mainmenu/real_time_data_index_e.html) on July 6, 2020.