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Response of the Ha! Ha! River to the flood of July 1996 in the Saguenay region of Quebec: Large-scale avulsion in a glaciated valley.

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Lapointe, Michel F.; Secretan, Yves; Driscoll, Steve; Bergeron, Normand; Leclerc, Michel (1998). Response of the Ha! Ha! River to the flood of July 1996 in the Saguenay region of Quebec: Large-scale avulsion in a glaciated valley. Water Resources Research , vol. 34 , nº 9. p. 2383-2392. DOI: 10.1029/98WR01550.

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Résumé

Modifications to valley form due to extreme flooding in the lower 34 km of the Ha! Ha! River were analyzed. Heavy regional precipitation in July 1996 triggered extreme runoff and the catastrophic drainage of Ha! Ha! Lake, producing discharges of 1100 m³/s, 8 times the 100‐year flood. Dominant valley modifications, revealed by comparing preflood and postflood topographies derived photogrammetrically, were related to two large‐scale avulsions; in particular, a deep retrogressive incision which bypassed the 30‐m‐high Perron Falls, exporting 6 × 10⁶ m³ of glacial stratified drift from a 2‐km section of valley and producing massive sedimentation in the reach downstream. Reconstructed maximum flow power values support the existence of a 300 W/m² threshold for major scouring of the alluvial valley bottom. The evidence highlights the potential for massive scour and fill and reorganization of the long profile, with potentially catastrophic effects on infrastructure, during extreme floods in glaciated valley settings.

Type de document: Article
Mots-clés libres: avulsion; catastrophic event; erosion; flooding; glacial landform
Centre: Centre Eau Terre Environnement
Date de dépôt: 29 nov. 2019 15:15
Dernière modification: 29 nov. 2019 15:15
URI: http://espace.inrs.ca/id/eprint/9457

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