Transport of large woody debris in the presence of obstacles
Capacité de charge ; Cours d'eau ; Débris ligneux ; Expérimentation ; Géométrie hydraulique ; Obstacle ; Processus aléatoire
Flume experiments were carried out to investigate the motion of large woody debris (LWD) in rivers as influenced by the presence of obstacles. Non-rooted, defoliated LWD was modelled by placing properly scaled wooden dowels placed into controlled
water flow. The results provide the probability of lodging of the dowels and statistics of the distance travelled. Their relationships with flow rate and depth, dowel length and spatial density of the obstacles is explored. This yields a general
of the obstacle clast. Since none of the obstacle clasts was dispersed in 1989 and only two-thirds by 1990, obstacle clasts probably form a less significant delay to sediment entrainment than previously assumed and represent a relatively immobile component of bed
Boulder ; Experimentation ; Fluvial processes ; Morphometry ; Obstacle ; Quantitative analysis ; River bed ; Runoff ; Scouring ; Sediment transport ; Stream flow
The aims of this study are to identify variables as well as thresholds controlling different obstacle mark morphometries and to incorporate these into a simple statistical model. To achieve this, available field and laboratory studies on that topic
are reviewed first. Secondly, the results of laboratory flume experiments are analysed and compared with other available laboratory and field data. The results of this work have shown a significant relationship between the morphometry of fluvial obstacle marks
and obstacle Reynolds number, especially when morphometric variables were combined. Further validation, calibration and extension of this approach will help to adequately asses the influence of obstacles in the fluvial environment on micro- and meso-scale
Large roughness elements such as stones or plant stems (obstacles) influence the depth of overland flows in 2 ways. The first effect is a dynamic one, involving frictional retardation of the flow and associated reduction in flow speeds. The second
influence is static, and arises from the upward volumetric displacement of flow depth because of the submerged volume of the obstacles.To understand the true frictional drag arising from obstacles , a correction must be made for the volumetric displacement
A la différence du climat local, qui suppose la libre circulation des très basses couches de l'atmosphère, le microclimat est fortement influencé par la présence d'obstacles qui contrarient ladite circulation. Partant de cette définition, l'A
. distingue plusieurs types d'obstacles (sol, végétation, eau libre, construction humaine) et deux gammes microclimatiques (l'une au contact de l'atmosphère, l'autre à l'intérieur de l'obstacle). La 2partie étudie les facteurs de variation des microclimats
, qui sont les qualités propres de l'obstacle (densité, continuité, couleur), la distance à l'obstacle, la saison et le type de temps. La 3partie conclut à la nécessité de rechercher plusieurs familles d'échelles microclimatiques, pour lesquelles est
Bar'ery na puti geograficeskogo prognozirovanija (Les obstacles à l'établissement des prévisions géographiques)
Après avoir étudié les prévisions géographiques régionales et globales, les AA. font l'inventaire des obstacles rencontrés : ils concernent la géographie générale, la prospective, l'information et l'organisation de la direction. Ils indiquent les
Les obstacles au développement alternatif dans l'agriculture mexicaine
la dépendance alimentaire. L'A. examine les obstacles rencontrés par lesdites transformations à l'intérieur de ce qu'il appelle les options alternatives de développement rural. (OP).
Turkey's membership in the EEC : obstacles to economic integration
soumise à des conditions d'ordre politique et économique. L'A. examine en détail les principaux obstacles seulement économiques à l'adhésion de la Turquie à la CEE.