ABSTRACT: Exploring the physical environment of a subarctic estuary, the Nelson River Estuary, Hudson Bay, Canada.

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Abstract

The Nelson River, the largest contributor of freshwater inflows to Hudson Bay, is regulated for hydroelectric generation downstream of Lake Winnipeg, and is a major component of Manitoba Hydro’s hydraulic system. The Nelson River mouth, a large subarctic, mesotidal estuary, although well known for its important beluga whale gatherings, was until recently mostly unexplored, due to the remote location, difficult navigation conditions, a much shorter open-water season, compared to southern rivers, and a harsh regional climate.Manitoba Hydro, in collaboration with its consultants, have undertaken oceanographic studies of the Nelson River estuary to support environmental studies related to potential hydropower developments along the lower reaches of the Nelson River. These studies will provide the building blocks upon which the baseline for future development projects assessments will depend. Extensive survey programmes were carried out in the estuary over the summer-fall period in 2005, 2006 and 2007 by Manitoba Hydro to describe the existing physical environment and prevailing oceanographic processes. The approach used for the monitoring programme was specifically designed to extract essential information required to describe the physical environment of his large and complex estuary. Previous knowledge of the estuary indicated a tide dominated, homogeneous to partially-mixed environment with the presence of a stratified zone offshore whereas the information collected over three seasons (water levels, current patterns obtained from ADCP profilers, as well as temperature and conductivity gauging stations) reveals a relatively complex environment with three distinct zones each offering particular dynamics: the inner estuary submitted to tides with only occasional salt intrusions; a highly stratified middle estuary with cyclical current reversals in the bottom layer, and the well-mixed outer estuary open to Hudson Bay, characterized by a briny surface layer developing into a wide plume into the Bay. These physical processes are driven by strong opposing marine and fluvial forces. The presentation provides an overview of the main oceanographic processes governing the physical environment, circulation and mixing of water masses into Hudson Bay. Future studies include 3D numerical modelling of the estuary.

Bibliography of Canadian Geomorphology