Some time ago, in light of the growing interest by international stakeholders in the environment field regarding the water consumed by different power generation options, Hydro-Québec decided to give the matter some thought. Specifically, the company was interested in quantifying the net loss of water through evaporation at Eastmain 1 reservoir in the Baie-James region. To do so, the evaporation rate of the ecosystems present prior to flooding of the sites had to be deducted from the evaporation rate of the new reservoir.

In cooperation with McGill University, Hydro-Québec conducted studies whereby it measured the evaporation flows of aquatic and land ecosystems, using the eddy covariance technique. More than 25,000 measurements were taken over a five-year period. The company then evaluated evaporation throughout the region, taking into account the surfaces and quantity of evaporated water from each ecosystem present before and after the reservoir was created (bogs, forests, lakes, rivers, burn sites, reservoir).

Result: the process clearly showed that before the reservoir was created, the ecosystems were major sources of evaporation and evapotranspiration. Overall, the quantity of evaporated water from Eastmain 1 reservoir is slightly higher to that of the ecosystems present before the reservoir was created. Consequently, the reservoir's net loss of water through evaporation is low.

Résultat : l’exercice montre clairement que les écosystèmes, avant la création du réservoir, étaient des sources importantes d’évaporation et d’évapotranspiration. Dans l’ensemble, la quantité d’eau évaporée du réservoir de l’Eastmain 1 est légèrement supérieure à celle des écosystèmes qui l’ont précédé. Ainsi, la perte d’eau nette par évaporation du réservoir est faible.

Hydro Review. Studying Net Evaporation from Eastmain-1 Reservoir, 2014, 5 p [PDF 524 Kb]

Ian B. Strachan, Alain Tremblay, Luc Pelletier, Simon Tardif, Christian Turpin, Kelly A. Nugent. 2016. "Does the creation of a boreal hydroelectric reservoir result in a net change in evaporation?" Journal of Hydrology, Volume 540, p 886 – 899.