Impacts des cônes latéraux sur le fonctionnement hydrodynamique et morphosédimentaire actuel des fonds de vallées prérifaines : cas de l'Oued Larbâa (Maroc) / Impact of lateral fans on the current hydrodynamic and morphosedimentary characteristics of valley bottoms : the case of the Larbâa wadi (Morocco)

Abstract

: Impact of lateral fans on the current hydrodynamic and morphosedimentary characteristics of valley bottoms : the case of the Larbâa wadi (Morocco). Situated in a marly formation, in a region which is semi-arid and particularly sensitive to erosion processes, the valley bottom of the Larbâa wadi is marked by the presence of several lateral outwash fans of different ages. These fans operate intermittently, under the influence of exceptional rainfall events that may occur annually. With heavy rainfall, the fans invade the bed of the wadi thereby hindering its longitudinal flow. Under the pressure of heavy liquid and solid flows injected into the river by the fans, the main stream migrates across the valley bottom. As a result, the morphogenic dynamic processes show reverse trends in the meanders, leading to bank erosion and slipping on the slopes. These morphogenic processes warrant careful examination if we are to understand the present-day dynamic processes affecting deposition within fans, the changing state of fans in the valley bottom, and the flood risks they generate. The present survey analyses these impacts based on the observed relationship between climatic factors (rainfall), hydrodynamic aspects (lateral erosion, slope destabilization, etc.), sedimentary processes (granulometry, lithology and stratigraphy of deposits) and morphological aspects (types and measurements of fans, and their geometric relationship with the present alluvial plain and the actual bed of the wadi).

Dynamique Hydro-Erosive Actuelle Des Bassins Versants Endoreiques De La Region De Niamey (Sud-Ouest Du Niger)

“…Cependant, l'accumulation des sédiments entraine la disparition des cuvettes de mi-versant qui sont remplacées progressivement par des cônes d'épandage. Lors des averses, ces cônes, qualifiés de signaux de connectivité (Cossart, Lissak, & Viel, 2017) peuvent désynchroniser le continuum hydrosédimentaire en divers points des bassins en envahissant le lit des cours d'eau et en entravant les écoulements longitudinaux des principaux systèmes hydrographiques (Taous et al, 2004). C'est ce qui explique l'intensité des dynamiques morphogéniques et l'instabilité spatiale du lit des cours d'eau dans le secteur d'étude.…”