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Accueil du site → Doctorat → Canada → Sequential scouring, alternating patterns of erosion and deposition, laboratory experiments and mathematical modelling

University of Toronto Canada (1998)

Sequential scouring, alternating patterns of erosion and deposition, laboratory experiments and mathematical modelling

Brun, Soren Erik

Titre : Sequential scouring, alternating patterns of erosion and deposition, laboratory experiments and mathematical modelling

Auteur : Brun, Soren Erik.

Université de soutenance : University of Toronto

Grade : Doctor of Philosophy 1998

Résumé
Erosion and deposition by flowing water commonly produce patterns of soi1 type, topography and vegetation. Sometimes they produce distinctive, spatial pattems whereby erosion and deposition altemate downslope. These altemathg pattems are common in arid and semi-arid regions on gentle dopes with low rainfaii amounts and are typicaiiy associated with banded vegetation. Scour and fiil processes in natural alluvial nvers commonly produce ri£Eie-pool sequences. A similar, but smder-scale, pattern of erosion and deposition was produced by this study - sequentiai scouring. Sequential scou g is best desnibed as senes of scour chutes separated by deposition zones. These pattems of scour and deposition exhibit quasi-periodic behaviour and have 2 to 6 m distances between successive deposition zones. Scour chutes are smdl erosional channels which are not deeply incised, are not associated with headcuts and have non-vertical sidewaiis. Deposition zones are lobate deposits where the thickest portion of the deposit occurs near the head of the deposit. Scour chutes are generally 5 - 10 cm wide and less than 1 cm deep, while deposition zones are between 20 -50 cm wide. The purpose of this research was to : 1) produce sequential scouring in the laboratory : 2) detede the relationship between initial microtopography and the initiation of scour and deposition ; 3) investigate the downslope sediment sorting associated with sequential scouring ; 4) detemllne the optimal conditions for the occurrence of sequential scouring ; 5) determine the interactions between scour and deposition ; and 6) produce a one-dimensional mathematicai mode1 for sirnulating sequential scouring . The uiitiation of sequential scouring was strongly intluenced by local convexities and concavities in the initiai surfiice. Through tirne, deposition zones becarne dorninated by coarser soi1 material, while scour chutes were typified by fker sedirnents. The variations in surface material aitered downslope surface roughness and flow conditions. Strong positive feedback mechanisms developed which caused downslope variations in water and sediment fluxes. The interactions between scour and deposition produced a system which varied spatiaiiy and temporaily. The mathematical mode1 adequately sirnulated the initiation and development of sequentiai scouring as it reproduced the quasi- periodic behaviour, positive feedbacks and interactions between scour and deposition associated with sequentiai scouring.

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