THE SPATIAL DISTRIBUTION OF LARGE WOODY DEBRIS AND ITS RELATIONSHIP WITH CHANNEL MORPHOLOGY IN THE BITTERROOT RIVER, MONTANA
Résumé
The spatial distribution of large woody debris (LWD) within a river channel has a complex, but influential, relationship with channel morphology. This study examines the spatial distribution of LWD, present as both jams and singular logs, and its relationship with the channel morphology of the Bitterroot River in western Montana. Using basic GIS digitising methods, the spatial distribution of LWD was assessed along a ten kilometre stretch of the river, spanning from Victor Crossing in the south to Crystal Lane in the north. The location of LWD was then evaluated in relation to certain channel features, including point bars, meander bends, midchannel bars and the flood plain. The most common area of LWD accumulations was on point bars, with 35% and 28% of jams and logs respectively, occurring here. Jams also commonly occurred on bare parts of islands; however a higher percentage of singular logs were located on the flood plain. Analysis of the size and orientation of LWD showed consistency with previous studies; the dominant orientation of individual logs was parallel to flow direction and larger LWD deposits were more likely to influence channel morphology. Based on the observed primary influence of LWD on flow deflection, sediment storage, pool formation and bank armouring, the secondary processes of stabilisation of planform morphology, meander cutoff and formation of depositional features were inferred.
Domaines
Environnement et Société
Origine : Fichiers produits par l'(les) auteur(s)