Miramichi River - Geography

Geography

The Miramichi River watershed drains a territory comprising one-quarter of New Brunswick's territory, measuring approximately 13,000 km² of which 300 km² is an estuarine environment on the inner part of Miramichi Bay. The watershed roughly corresponds to Northumberland County, but also includes sections of Victoria County, Carleton County, and York County and smaller parts of Gloucester County and Sunbury County.

The Miramichi River meander length measures approximately 250 km and comprises two important branches, the Southwest Miramichi River and the Northwest Miramichi River, each having their respective tributaries. Nearly every bend in the river, from Push and Be Damned Rapids to the Turnip Patch has a distinctive name, reflecting the importance of the river to fishermen, canoeists, and lumbermen. Tides reach upriver in the Miramichi system to Sunny Corner on the Northwest Miramichi and to Quarryville on the Southwest Miramichi — a distance of approximately 70 km inland from the Gulf of St. Lawrence. The two branches combine at Newcastle where the river becomes navigable to ocean-going vessels.

The estuarine portion of the Miramichi River downriver from Newcastle in the city of Miramichi flows through a drowned river valley. Sea level rise in Miramichi Bay has flooded the mouth of the Miramichi River with saltwater. The estuary comprises the inner portion of Miramichi Bay and is protected from ocean storms in the Gulf of St. Lawrence by barrier islands. The estuary is significant in that it is a highly productive ecosystem, despite its relatively small size. The estuary receives the freshwater discharge from the Miramichi River and its tributaries, mixing with organic materials from the surrounding shorelines and the saltwater inundation from the Gulf of St. Lawrence, itself an estuary and the largest on the planet.

The estuary is a highly dynamic environment, ranging from the high outflows of freshwater during the spring freshet, to the low outflow and rising saltwater content during the summer period, to fall ocean storms and nor'easters which reshape the barrier islands and the old river channel which forms the navigation channel for ocean-going ships heading to ports at Chatham and Newcastle, to the winter covering of sea ice which encases the entire estuary. The inner bay measures only 4 m deep on average, with the navigation channel measuring only 6–10 m, resulting in significant warming of estuarine waters during the summer months. The diurnal tide cycle ranges only 1 m on average.