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Ben Gurion University of the Negev (2014)

The Morpho-textural characterization of dryland braided channels and their humid counterparts : hydrological regime as a key driver

Storz-Peretz, Yael

Titre : The Morpho-textural characterization of dryland braided channels and their humid counterparts : hydrological regime as a key driver

Auteur : Storz-Peretz, Yael

Université de soutenance : Ben Gurion University of the Negev

Grade : Doctor of Philosophy (PhD) 2014

Résumé partiel
Studies of gravel braided streams have been conducted mainly in humid braided systems or flume simulations thereof. The differences in hydrologic regime between arid and humid climates are responsible for differences in the textural character of braided channel beds. Dryland rivers have bare catchments, short-lived hydrographs with typically rapid rises, followed by a slower, recession (yet rapid in comparison to humid rivers) lasting only several hours as well as unarmored channel beds, which are responsible for very high bedload discharges, thereby increasing the likelihood for braiding. Humid perennial rivers differ in hydrograph characteristics : base flow, moderate rise and a slow flow recession, the latter responsible for the development of armoring on the channel bed. Even though braided rivers in humid environments were extensively studied, no linkage has been undertaken between texture and morphological elements of the braided cell, nor in poorly studied braided systems in drylands. Also, in drylands scour holes are not evidenced in the field, raising the question whether they are generate at all in drylands. The main objective of this thesis is to characterize the morpho-texture of braid-cells, formed by different braiding processes in the dryland braided systems, compare them to their humid counterparts and to understand the impact of the hydrological regime on the morpho-texture of braided rivers. The secondary objective of this study is to find a simple and rapid method to characterize the texture of the bed subsurface, thereby determining its Grain Size Distribution (GSD) and enabling the calculation of armoring. GSD is a key indicator in stratigraphy and geomorphology ; it is a basic tool used by a variety of disciplines : geology, geomorphology, archeology, ecology and engineering. Modern techniques including AGS (Automatic Grain Sizing) were recently developed to analyze GSD of surfaces in a rapid and effortless manner. Yet, the traditional method, time consuming and laborious, is still in use for the determination of the GSD of coarse-grained sedimentary deposits and of the near-subsurface of landforms, principally river beds. The AGS technique applied to the stratigraphic record and to the subsurface is examined herein. Braid-cells in arid areas were measured in the ephemeral braided Wadis Ze’elim, Rahaf and Roded located in the SE, hyper-arid Syrian-African Rift Valley, Israel. AGS was examined on vertical exposures in Wadi Rahaf and Ze’elim. Braided rivers in humid environments, Bléone located in the French Pre-Alps and Cimoliana and Saisera, located in NE Italy, were measured as well.

Mots clés : Braided rivers, hydrological regime, perennial, ephemeral, morphotexture, armoring, confluence zone, GSD, AGS, stratigraphy, conglomerate

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Page publiée le 1er avril 2015, mise à jour le 12 septembre 2017