The Rapides River flows from north to south for, falling from an altitude of to sea level. The river mouth forms a small bay wide and long that opens into the Sept Îles Bay past Père-Conan island. The mouth of the Rapides River is in the municipality of Sept-Îles in the Sept-Rivières Regional County Municipality. It enters Sept-Îles bay to the west of the community of Sept-Îles. The origin of the name is not known. It was made official on 5 December 1968. The Aylmer-Whittom Park at the mouth of the river, also known as Squirrel Park, is an area of natural mixed woodland, dominated by spruce and lichen. There are several trails through the park, and two observation towers to observe the bay and the birds that nest there. One tower has observation binoculars. There is a miniature village for children.
Description
According to the Dictionnaire des rivières et lacs de la province de Québec,
Basin
The Rapides River basin cover. It is elongated along a north–south axis, long and wide. It lies between the basins of the Sainte-Marguerite River to the west and the Moisie River to the east. The basin is partly in the unorganized territory of Lac-Walker and partly in the municipality of Sept-Îles. Part of the basin is in the Zec Matimek, which covers of the western side. Most of the watershed is on a high plateau with deep valleys in which steep slopes can rise for more than. The highest point is at an altitude of in the north of the watershed. The piedmont area between the coastal plan and the plateau is about wide. It contains rounded rocky hills up to high. The coastal plain in the south is less than wide, and is fairly flat, rising to about of elevation. The bedrock is mainly magmatic, deformed to some extent, including migmatite, anorthosite, gabbronorite and granodioritic or granitoidgneiss. On the plateau the bedrock is usually exposed, although in some areas there is undifferentiated glacial till no more than deep. Some of the valleys hold glaciofluvial sediments. In the piedmont and the coastal plain large amounts of silt and clay were deposited by the Goldthwait Sea after the glaciers retreated. As the land rebounded from the weight of the ice and the sea retreated, these fine sediments were covered by coarse sandy estuarine and deltaic sediments.
Hydrology
The rivers and streams in the northern plateau follow angular courses dictated by fractures in the bedrock, which are fairly rectilinear and constrained by narrow valleys. Downstream the watercourses meander in the soft deposits of the piedmont and coastal plain. The main tributaries of the Rapides River are the Desmeules, Deschênes and Champion rivers, which drain the northeast, southeast and southwest parts of the watershed. The Bouleau waterfall on the Rapides River is above its confluence with the Desmeules River. There are three waterfalls in the lower section of the river between the outlet of Lake Rapides and the river mouth, the Outarde at, the Grosse Chute at and the Cran de Fer at from the mouth. The river basin includes several large and irregular-shaped lakes, Lake Grand Rapides at, Lake Rapides at, Lake Curot at, Lake Tortellier at and Lake Hingan at. Waterbodies cover 8.31% of the basin. Ombrotrophicpeat bogscover 0.95% of the area, mostly on the coastal plain with its flat relief and fine sediments. A gauging station from the Rapides River's mouth made continuous measurements from 1947 to 1983. It showed an annual average flow of, varying during the year from.
