Les vagues dans les retenues d'altitudes : analyse et méthodes pour la prévention

Le vent et l'impact d'un mouvement gravitaire rapide dans une retenue d'altitude, produisent des vagues dont la nature et l'amplitude dépendent des grandeurs de l'impactant (vent ou mouvement gravitaire rapide) et de la profondeur d'eau. Dans cet article, nous avons donné les principales lois d'échelle qui permettent d'évaluer le volume d'eau déplacé lors de l'interaction et l'onde hydrodynamique qui en résulte, en insistant non seulement sur l'amplitude des vagues mais aussi sur leurs natures. Le vent et les mouvements gravitaires lents produisent des ondes sinusoïdales alors que les mouvements gravitaires rapides produisent des ondes plus raides de type tsunami. L'extension des retenues d'altitude est limitée et les vagues produites rencontrent rapidement le parement du barrage (ou une berge). Elles génèrent une surélévation, dite run-up, dont l'amplitude dépend des caractéristiques de l'onde incidente et de la pente de la berge. Nous avons rassemblé suffisamment de données expérimentales et développé une analyse théorique pour montrer les similitudes et les différences qu'il y a entre les ondes sinusoïdales et les ondes solitaires en termes de run-up. Nous avons enfin choisi des formules simples et établi un abaque permettant à tout ingénieur de faire un premier diagnostic. / The load of the wind and the impact of rapid mass movements in a reservoir generate waves whose nature and properties depend on the magnitude of the load and the water depth in the reservoir. In this paper we summarized the main existing scaling laws allowing assessing the resulting hydrodynamic effects, focusing not only on the amplitude of the waves, but also on its nature. The wind and the slow movements produce sinusoidal waves while rapid mass movements produce steeper water waves such as tsunamis. Given the limited extension of the mountain lakes, the produced water waves rapidly meet the shores or the dam on which they generate a run-up whose amplitude depends on the characteristics of the incident wave and the slope of the shore. We have undertaken a theoretical analysis and collected several experimental data in order to show the similarities and the differences between the sinusoidal waves and the solitary waves in terms of run-up. We finally, choose simple formulas and produced a chart enabling any engineer to make a first diagnosis

Energy demands during a judo match and recovery

Objective: To assess energy demand during a judo match and the kinetics of recovery by measuring the metabolites of the oxypurine cascade, lipolytic activity, and glycolytic pathway. Methods: Venous blood samples were taken from 16 national judoists (mean (SEM) age 18.4 (1.6) years), before (T(1)) and three minutes (T(2)), one hour (T(3)), and 24 hours (T(4)) after a match. A seven day diet record was used to evaluate nutrient intake. Results: Nutrient analysis indicated that these athletes followed a low carbohydrate diet. Plasma lactate concentration had increased to 12.3 (1.8) mmol/l at the end of the match. An increase in the levels of extracellular markers of muscle adenine nucleotide catabolism, urea, and creatinine was observed at T(2), while uric acid levels remained unchanged. High concentrations of urea persisted for 24 hours during the recovery period. Ammonia, hypoxanthine, xanthine, and creatinine returned to control levels within the 24 hour recovery period. Uric acid concentrations rose from T(3) and had not returned to baseline 24 hours after the match. The levels of triglycerides, glycerol, and free fatty acids had increased significantly (p<0.05) after the match (T(2)) but returned to baseline values within 24 hours. Concentrations of high density lipoprotein cholesterol and total cholesterol were significantly increased after the match. Conclusions: These results show that a judo match induces both protein and lipid metabolism. Carbohydrate availability, training adaptation, and metabolic stress may explain the requirement for these types of metabolism

Competition and food restriction effects on oxidative stress in judo

International audienceWe examined the effects of weight loss induced by restricting energy and fluid intake on antioxidant status and oxidative stress of judo athletes. Twenty male judoka were randomly assigned to one of two groups (Group A: called diet, n = 10; height 174.8 +/- 1.9 cm, body weight 75.9 +/- 3.1 kg; they were asked to lose similar to 5% of their body weight through self-determined means during the week before the competition; Group 13: called control, n = 10; height 176.4 +/- 1.1 cm, body weight 73.3 +/- 6.3 kg maintained their body weight during the week before the competition). A battery of tests was performed during a baseline period (T-1) on the morning of a simulated competition (T-2) and 10 minutes after the end of the competition (T-3). These tests included assessment for body composition, determination of lag phase (Lp) before free radical induced oxidation, maximum rate of oxidation (R-max) during the propagating chain reaction and maximum amount of conjugated dienes (CDmax) accumulated after the propagation phase, and lipidic profile. Uric acid concentrations were also evaluated in plasma. Dietary data were collected using a 7-day diet record. We noted that the athletes followed a low carbohydrate diet whatever the period of the investigation. Concerning antioxidant nutrients, we can notice that mean nutritional intakes are in the normal range values for vitamin A, C and E at T-1 and T-2. Rapid weight loss induced a significant increase in Lp values (p < 0.05) and uric acid concentrations without alterations in oxidative stress. Our data also showed that the competition induced the same changes of oxidative-antioxidant status whatever the dietary intake during the seven days before the competition. Moreover, the effect of the competition on the antioxidant and oxidant parameters was more pronounced than the diet. Theses results could be linked to the food containing a large proportion of PUFA and a relative low proportion of carbohydrates

Géomorphologie des rivières de montagne

National audienceChapitre sur la géomorphologie des rivières de montagne