River Update #4 - South AB Rivers Continue To See Rising Levels, Hat Takes precautions

A couple of Hatters discuss the river levels at the Strathcona Park boat launch Tuesday in Medicine Hat. The boat launch and trails along the South Sask. River are now closed as a precautionary measure. (Photo Alex McCuaig)

Water levels at the Oldman reservoir are stabilizing and two of the three watercourses which feed it are experiencing reduced streamflows as the river basin is feeling the aftereffects of sustained precipitation.

The Oldman reservoir is sitting at a little less than 97 per cent capacity mid-afternoon Tuesday, sustaining a 350 m³/s outflow, the majority of which is coming from the dam spillway.

Streamflows on the upper Oldman are continuing to rise while both the Castle and Crowsnest rivers that make up the three major tributaries or the reservoir have both seen reduced levels Tuesday afternoon.

The Pikkani Nation is reporting the Brocket area has a 400 m³/s full bank and conditions should stay below that level following Oldman dam operators sustaining outflows to 350 m³/s. 

The floodgates are open at the Oldman dam. (Photo Courtesy of Heritage Acres)

Pincher Creek, which flows into the Oldman downstream of the reservoir but upstream from Brocket, is also seeing reduced streamflows Tuesday afternoon.

Downstream communities, however, have yet to feel the full impact of swelling watercourses which have been the result of sustained and at times heavy precipitation over the past few days in Alberta.

On Tuesday, Medicine Hat joined the list of communities warning residents of the dangers of the high streamflows on southern Alberta watercourses at the South Saskatchewan nears 1,000 m³/s.

The city has closed several riverside park spaces and trails along with its boat launches but states it doesn’t anticipate any flooding.

The South Saskatchewan River which flows through the community is running close to 950 m³/s Tuesday afternoon and is continuing to rise, still being feed from the Bow which has yet to crest downstream of Calgary and the continuing situation on the Oldman.

One of a number of logs floating down the South Saskatchewan River Tuesday as high streamflows are picking up flotsam and jetsam from banks. (Photo Thomas Fougere)

The Oldman River is also being feed by the St. Mary and Belly just upstream which are contributing to rising streamflows in Lethbridge.

As of Tuesday afternoon, streamflows are topping 670 m³/s on the Oldman at Lethbridge.

The St. Mary reservoir is at more than 98 per cent capacity and has opened its spillway, stabilizing outflows at around 250 m³/s. The streamflows on the Belly River are continuing to rise, closing in on 900 m³/s Tuesday afternoon. 

The high-water mark for the South Saskatchewan River at Medicine Hat in the past decade is 1130 m³/s in 2020 but a far cry from 2013’s record daily average high of 4,440 m³/s on June 24, 2013. That day saw the river peak at 5,040 m³/s, according to federal hydrometric data.

The highest instantaneous recorded instantaneous streamflow on record came in 1995’s flood when it peaked at 5,110 m³/s but with a daily average of 4,200 m³/s, according to the federal data set which began collection records at Medicine Hat in 1911.

A high streamflow advisory continues throughout the Bow, Oldman and South Saskatchewan rivers as of Tuesday afternoon.