Rivière du Sud-Ouest (Saint Lawrence River tributary)

The Rivière du Sud-Ouest is a tributary of the southeast coast of the St. Lawrence River. This river flows in the administrative region of Bas-Saint-Laurent, in Quebec, in Canada, in the regional county municipalities of:

Rivière du Sud
Southwest river in Bic National Park
Location
CountryCanada
ProvinceQuebec
RegionChaudière-Appalaches
Regional County MunicipalityMontmagny Regional County Municipality
Physical characteristics
SourceLake Saint-Mathieu
 • locationSaint-Mathieu-de-Rioux
 • coordinates48.172053°N 68.99442°E / 48.172053; 68.99442
MouthSaint Lawrence River
 • location
Rimouski
 • coordinates
48.35695°N 68.75639°W / 48.35695; -68.75639
 • elevation
4 m (13 ft)
Length23 km (14 mi)
Basin features
Tributaries 
 • left(Upstream) Rossignol Creek, Lac des Coulombe outlet, Lac Fournier and Lac Caouette outlet, Ernest-Boucher stream.
 • right(Upstream) Morin stream, Beaver stream, Simon stream, Grand Lac Malobès outlet, Cold stream.

Geography

The Southwest river rises in the outlet of Lake Saint-Mathieu (length: 5.3 metres (17 ft); altitude: 114 metres (374 ft)), at Saint-Mathieu-de-Rioux. It then follows the St. Lawrence River in a northeast-southwest direction to flow into the Havre du Bic. During its course, it crosses Petit Lac Saint-Mathieu and Lac de la Station. Its two main tributaries are the outlet of Grand Lac Malobès and the Neigette River. A fall from a height of 18 metres (59 ft) is located near its mouth.[1]

The flow of the south-west river is generally slow, its course being located on a plateau whose average altitude is 105 kilometres (65 mi). The last eight kilometers show more rugged terrain.[2]

From the mouth of Lake Saint-Mathieu, the southwest river flows over 7.1 kilometres (4.4 mi) divided into the following segments:

Upper course of the river (segment of 12.1 kilometres (7.5 mi))

  • 0.2 kilometres (0.12 mi) towards the northeast, crossing under the bridge of the Ladrière road, to the southwest shore of Petit lac Saint-Mathieu;
  • 2.9 kilometres (1.8 mi) towards the north-east, crossing the full length of Petit lac Saint-Mathieu;
  • 2.3 kilometres (1.4 mi) towards the northeast, crossing the road to 5th rang, collecting the waters of the Neigette River (Les Basques), up to the route du 3th Rang Est;
  • 1.9 kilometres (1.2 mi) northwards, to the limit of Saint-Simon;
  • 2.6 kilometres (1.6 mi) towards the northeast, constituting the limit between Saint-Mathieu-de-Rioux and Saint-Simon;
  • 0.7 kilometres (0.43 mi) north-east, in Saint-Simon, to the road bridge of 2th rang Ouest;
  • 1.5 kilometres (0.93 mi) towards the northeast, forming the limit between Saint-Fabien and the town of Rimouski (sector Le Bic);

Upper course of the river (segment of 19.4 kilometres (12.1 mi))

  • 7.4 kilometres (4.6 mi) towards the northeast, in Rimouski, recovering the waters of the outlet of Lac des Coulombe (coming from the north), crossing Lac de la Station (length: 2.7 kilometres (1.7 mi); altitude: 106 metres (348 ft)) over its full length, to the dam located to the northeast;
  • 0.6 kilometres (0.37 mi) eastwards, to the bridge of 7th Avenue which crosses the village of Saint-Fabien;
  • 2.5 kilometres (1.6 mi) north-east, up to the confluence of the outlet of Grand Lac Malobès;
  • 5.1 kilometres (3.2 mi) north-east, passing under the Canadian National railway at the start of this segment, to the route 132 bridge;
  • 3.8 kilometres (2.4 mi) towards the north-east, crossing the Bay of Roses and passing under the bridge of Chemin du Petit Portage, to its confluence.[3]

Hydrology

The watershed has an area of 192 square kilometres (74 sq mi).

Toponymy

The toponym "south-west river" was formalized on December 5, 1968 at the Commission de toponymie du Québec.[4]

Fauna

The river hosts a small population of Atlantic salmon of around 40 spawners.[5] The latter goes up the river on 4 square kilometres (1.5 sq mi) where the fall of 18 metres (59 ft) constitutes an insurmountable obstacle. Salmon spend the first two years of their lives in the river.[6] The second species in abundance is generally the American eel, which unlike salmon, goes up the river over its entire length to Lake Saint-Mathieu.[7]

Notes and references
  1. Union québécoise pour la conservation de la nature 2004, p. 11-12
  2. Union québécoise pour la conservation de la nature 2004, p. 12
  3. "Atlas of Canada" map, edited by the Department of Natural Resources Canada.
  4. Commission de toponymie du Québec - Bank of place names - Toponym: Rivière du Sud-Ouest.
  5. Collectif Ulysse (2008). The national parks of Gaspésie and Bas-Saint-Laurent - collection=Ulysse Green Spaces. Ulysse Travel Guides. pp. 32–33. ISBN 978-2-89464-838-4.
  6. Union québécoise pour la conservation de la nature 2004, p. 17
  7. Union québécoise pour la conservation de la nature 2004, p. 18

Appendices

Bibliography
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