River Report #3 – Mountain Tap Turned on But Not a Lot Coming Out
A beaver den’s entrance lays exposed as South Saskatchewan River levels remain low. (Photo Alex McCuaig)
The spring snowpack melt is underway, but it’s not forecast to be an especially heavy flow of water coming down southern Alberta rivers without a push from significant precipitation.
Conditions are favourable for tempered on-crop agricultural draws from southern Alberta rivers this month with moderate temperatures, descent soil moisture and some precipitation hitting the region.
The South Saskatchewan River at Medicine Hat has continued to be in the red zone over the past week, falling well below the water conservation objective (WCO) which has gone from 68 cubic metres a second on May 8 to 132 cubic metres per second on May 15. Those WCOs have risen in conjunction with calculated natural flow rates which have nearly doubled in the past seven days with the deficit coming from upstream draws.
While those numbers have risen, steamflows at Medicine Hat have been constant, dipping below the instream objective (IO) of 42.5 cubic metres a second on May 8, hitting a seven-day high of 66 cubic metres on May 11 before dropping to 47 today.
The Bow River at the forks of the Oldman has been dancing along the bottom end of seasonal norms since the beginning of April. Its current streamflow is sitting at 35 cubic metres a second.
The South Saskatchewan River at the northeastern edge of Medicine Hat (Photo Alex McCuaig)
The Oldman River at the forks has been under pressure, failing to meet its WCO over the past seven days with its peak streamflow over that time coming today at 31 cubic metres a second.
The Oldman River at Lethbridge is also under pressure falling well below its WCO streamflow of 106 cubic metres a second. It also dipped under its IO of 20 cubic metres a second for a couple of days in the past week. As of Thursday morning, it’s sitting at 27 cubic metres per second.
The Oldman Reservoir was buoyed by a short, sharp increase in volumes of water from its three main tributaries earlier this week, pushing storage levels just past the 60 per cent capacity level while increasing downstream releases.
Broccoli sprouts at a city irrigated farm. (Photo Alex McCuaig)
But the mountain snowpack reporting stations are pointing to an earlier and quicker than usual release of melt water.
South Racehorse Creek station north of Coleman peaked at a little less than 300 mm of snow water equivalent in the first half of April. It’s currently sitting at less than 8 mm.
Garnier Creek station at the headwaters of Castle River reported its highest level of 550 mm of snow water equivalent at the very beginning of May. It’s currently sitting at 300 mm.
Anticipated mountain snowpack runoffs from Banff to the US border are forecast to be below to much below normal.
The Belly and St. Mary rivers aren’t yet helping the Oldman Basin downstream of the Oldman Reservoir with both running at the bottom end of seasonal norms.
Despite the low streamflow rates on the Oldman, reservoirs are filling up.
St. Mary Reservoir is nearing 75 per cent capacity, Milk River Ridge is at 63 per cent capacity with Waterton at 46 percent.
West Block St. Mary River Irrigation District (SMRID) reservoirs Chin and Stafford are at 76 and 95 per cent capacity respectively.
SMIRD Central Block reservoirs are reporting Fincastle Lake at 84 per cent capacity with Taber, Horsefly and Grassey all in the mid 60 per cent range.
Eastern Block reservoirs. 40-Mile, Murray and Sauder (Rattlesnake) are at a combined 83 per cent of capacity.
Graphic courtesy of Alberta’s River Forecast Centre
Both the Bow River Irrigation District (BRID) and Eastern Irrigation District (EID) are posting descent reservoir levels heading into the growing season.
The EID’s Lake Newell, Crawling Valley and Snake Lake are reporting a combined 93 per cent of capacity.
BRID’s McGregor, Travers and Little Bow reservoirs are at a combined 86 per cent of capacity.
Sub-surface moisture levels in the southern region are reported to 91 per cent to be in either fair or good with seeding progress well above the five year average with more than 50 per cent complete.
Some rain is forecast across southern Alberta over the Victoria Day long weekend with the western half of the region expected to see more than the eastern portion.
June is southern Alberta’s wettest month.