hydrological.net

How large northern rivers in Canada function under normal conditions is not fully understood, as most research has focused on temperate rivers. To complicate matters, most of these rivers are regulated by dams. Concern about the impacts of industrial effluents on Canadian northern rivers prompted the creation of the Northern River Basins Study. This study grew to investigate other factors in the healthy functioning of northern rivers in Canada, such as the drying of the Peace-Athabasca Delta. The Northern Rivers Basin Study attempted to investigate the effects of regulation on large northern rivers, specifically the Mackenzie River and its major tributaries: the Slave, Peace, and Athabasca Rivers. The Peace River is dammed at the W.A.C. Bennett Dam in British Columbia, constructed in 1968. As the delta began to dry up after the W.A.C. Bennett Dam was constructed, which dams the Peace River, it was suggested that the dam was responsible. Damming decreased the variability of flow in the river creating a much flatter hydrograph immediately downstream of the dam, and reduced the duration of ice cover. This effect was apparent but lessened further downstream the Peace River and in the Slave River. Changes in vegetation and channel morphology were also observed. Special consideration was given to the Peace-Athabasca Delta in northern Alberta, an important and unique freshwater ecosystem. It was discovered that the delta was drying up because it was not flooding, which is necessary to rejuvenate the perched basins in an environment where evaporation is higher than precipitation. Further investigation revealed that even record peak summer flows were not sufficient to restore the delta, and that only ice jam floods raised the water level high enough. The causes and characteristics of ice jam floods were investigated and the impact of the W.A.C. Bennett dam on ice jamming was also studied.

To investigate the influence of the dam, flow levels during spring break-up were studied and it was found that the contribution from the Peace River (measured directly past the dam) during spring break-up was higher after the dam was constructed than before, so another factor must be responsible for the lack of ice jam floods. Studies of the inputs from tributaries found that the Smoky River had previously been contributing a significant amount of discharge during the spring break-up but had not been doing so recently. Climate studies revealed two climate patterns in the area, one which caused high precipitation in the Smoky and one which did not, and found that the dry pattern had been dominating. To stimulate an ice jam flood, precipitation in the Smoky basin was monitored, and one year when it was high and the contribution from the Smoky during the spring break-up was estimated to be large, BC Hydro was asked to release extra water from the dam. They complied, and an ice jam flood was successfully triggered.