Controls on the persistence of water in perched basins of the Peace-Athabasca Delta, northern Canada

One of the world's largest freshwater deltas, the Peace-Athabasca Delta (PAD), is located in northern Alberta, Canada. The landscape consists of three separate deltas that enclose large lakes. The purpose of this study was to determine the hydroclimatic controls on the persistence of water within perched basins. To accomplish this goal, climatological and hydrological field and modelling studies were conducted at three spatial scales: perched basin, delta and contributing basin environment.; Water-balance simulations for a typical basin perched basin situated next to a lake revealed that the duration of ponded water was sensitive to the prevailing local hydroclimatology (cool-dry, warm-wet, etc.) and that a basin usually dried-up within a decade after a recharge event. Groundwater flow through the levee was insignificant to the overall balance of water. The annual drawdown of water was predominantly controlled by evaporation in excess of precipitation. The maintenance of aquatic conditions within perched basins was therefore dependent on occasional floodwater inputs.; A comparison study revealed that the most elevated perched basins located in the perimeter deltas were recharged by extremely high ice-induced backwaters. Overbanking of delta channels during the open-water period required the generation of an extremely large floodwave and the areas affected were limited to the less elevated perched basins. Perched basins located within the inner delta zone were inundated when the central lakes expanded beyond their normal shoreline. Comparison of the regulated to the naturalized system revealed that impoundment of the Peace River has led to reduced open-water flood levels on channels of the Peace Delta and has also diminished the potential for lake expansion into contiguous areas. Overall, ice-induced backwater was a more effective mechanism for inundating perched basins because less flow was required to produce extreme water levels and more extensive areas were affected as compared to open-water conditions.; A regional flow analysis in the Peace and Athabasca Basins revealed that runoff driving ice-jam and open-water floods originated from distinct regions of the contributing basins. Peak break-up backwater levels near the delta resulted predominantly from snowmelt runoff in sub basins that drain the plains and foothill regions closest to the deltas. High waters in the delta channel and lakes during the open-water period were generated by rainfall and snowmelt runoff originating from more elevated foothill and mountain areas where orographic effects enhanced the amount of precipitation. As a result of the impoundment of the Peace River headwaters, the generation of peak open-water flow has become more dependent on the unregulated portions of the basin below the dam and less so on the productive mountain region. (Abstract shortened by UMI.)...