PREDICTION OF RIVER WATER TEMPERATURE USING A CONCEPTUAL-MODEL - CASE OF THE MOISIE RIVER

Hydro-Quebec is projecting to increase the hydroelectric production capacity of the St. Marguerite River by diversion of the tributaries Pekans and Carheil rivers of the Moisie River, the most productive salmon river of the whole Quebec. Along with substantial changes in hydrological regimes, this hydroelectric development is most likely to affect some physical environment factors such as the water temperature, which is of prime importance for the biotope and, in particular, for the salmon productivity. The objective of the present study is to simulate, over a long period of time, the river water temperatures under natural conditions as compare to those after the impoundment, to assess the consequences of the tributary diversion. We used the hydrological CEQUEAU model coupled with a temperature model. The temperature model developed is applicable to the ice-free period and calculates daily water temperatures in rivers by computing an energy budget to each element of the watershed. The energy budget considers the shortwave solar radiation, long-wave radiation, evaporation, and convection in the air as well as the advective heat of various inflows from surface runoff, interflow, and groundwaters. The estimation of the atmospheric thermal exchanges is based on the equations usually found in literature. The volumes of the various inflows are given by the hydrological model. The temperature model uses daily data for air temperature and monthly data for solar radiation, cloudiness, wind speed, and vapour pressure. The model has been applied to the Moisie River (Quebec), using the measured values for the calibration. Both observed and calculated values show good agreement. The model was also used to simulate, over the whole watershed, the water temperatures for the 1961-1989 period and after the diversion. The results show that the tributary diversion contributed to increase the water temperature of the Moisie River and that this increase is gradually attenuated as we progress downstream.