Early Spring Conditions Overview in the Ottawa River Basin

OTTAWA/GATINEAU, Wednesday March 16, 2022 — The Ottawa River Regulating Committee monitors the Ottawa River basin closely in preparation for the spring freshet. Overall, weather conditions this winter have been close to normal in most locations of the basin. With above seasonal temperatures forecast for this week and rainfall over the southern portion of the basin later this week, levels and flows are expected to start increasing in the lower Ottawa River. This Early Spring Conditions Overview is a summary of current conditions in the Ottawa River basin prior to the onset of the freshet. Sometime over the next few weeks, as flows and water levels begin to rise in the Ottawa River, the Regulating Committee will publish a Press Release announcing the onset of freshet.

Current Snowpack Conditions:

• December was characterized by below average precipitation and mild weather, while temperatures in January were colder than normal with above average precipitation in the central and southern parts of the basin and below average precipitation in the southeastern part. Thus, at the end of January (figure to the left below), the snow water content, or the quantity of water held in the snowpack, was close to normal in most locations, except in the southeastern portion where it was below average. February brought close to normal temperatures and precipitation with snow-water quantities increasing from south to north.
• Above zero temperatures combined with rain occurred on two occasions in February, but these milder weather conditions were too short lived to result in a substantial thaw. As a result, the snow cover still contained close to normal water content over a large part of the basin at the end of February (figure to the right below). Below and above average water content was observed in the southern and northern parts of the basin respectively at that time.

Reservoir Regulation Strategy / Current Level and Flow Conditions:

• The principal reservoirs located in the northern part of the Ottawa River basin are essentially empty as shown in the figure below and are ready to retain spring runoff once the freshet begins in those upstream areas.
  • The levels and flows on the main stem of the river from Lake Timiskaming down to the Montreal area have been below normal in most locations over the last few weeks due to below average baseflow (which is groundwater discharging back to the stream system) and the absence of a substantive thaw this winter. With warm weather forecasted in the short term and rainfall forecasted for March 19 over a portion of the basin, levels and flows are expected to increase slightly over the next few days. Flows and levels are expected to remain close to normal for this time of the year over the coming week, based on the current short-term weather forecast.

Longer-term Overview:

• While there is higher than average water content in the snow pack in the northern headwater areas of the Ottawa, Gatineau and Lièvre rivers, these areas drain into large reservoirs where it is possible to retain a large portion of the runoff.
• It is too early to forecast peak river conditions, including the timing of the start of the spring freshet and the magnitude of the peak. At this time, there are no indicators of concern; the snow over a large part of the basin has near-average water content, and flows and levels in several locations along the main stem of the river are below average. Additionally, the weather forecast calls for a return to seasonally cooler weather in the coming week, which is a positive indicator for a slow start to the freshet season.