The concept of travelling bedload and its consequences for bedload computation in mountain streams

[Departement_IRSTEA]Eaux [TR1_IRSTEA]RIVAGE [Departement_IRSTEA]Eaux [TR1_IRSTEA]RIVAGEInternational audienceIn bedload transport modelling, it is usually presumed that transported material is fed by the bed itself. This may not be true in some mountain streams where the bed can be very coarse and immobile for the majority of common floods, whereas a finer material, supplied by bed-external sources, is efficiently transported during floods, with marginal morphological activities. This transport mode was introduced in an earlier paper as ‘travelling bedload’. It could be considered an extension of the washload concept of suspension, applied to bedload transport in high-energy, heavily armoured streams. Since this fine material is poorly represented in the bed surface, standard surface-based approaches are likely to strongly underestimate the true transport in such streams. This paper proposes a simple method to account for travelling bedload in bedload transport estimations. The method is tested on published datasets and on a typical Alpine stream, the Roize (Voreppe, France). The results, particularly on active streams that experience greater transport than expected from the grain sizes of their bed material, reinforce the necessity of accounting for the ‘travelling bedload concept’ in bedload computation. The method relevance is discussed regarding varying flood magnitudes, geomorphic responses and eventual anthropic origin of the ‘travelling bedload’ phenomena. To conclude, this paper considers how to compute bedload transport for a wide range of situations, ranging from sediment-starved cases to the general mobile bed alluvial case, including the intermediate situation of external source supply on armoured bed

Association between location of out-of-hospital cardiac arrest, on-scene socioeconomic status, and accessibility to public automated defibrillators in two large metropolitan areas in Canada and France

International audienceAimTo compare walking access times to automated external defibrillators (AEDs) between area-level quintiles of socioeconomic status (SES) in out-of-hospital cardiac arrest (OHCA) cases occurring in 2 major urban regions of Canada and France.MethodsThis was an international, multicenter, retrospective cohort study of adult, non-traumatic OHCA cases in the metropolitan Vancouver (Canada) and Rhône County (France) regions that occurred between 2014 and 2018. We calculated area-level SES for each case, using quintiles of country-specific scores (Q5=most deprived). We identified AED locations from local registries. The primary outcome was the simulated walking time from the OHCA location to the closest AED (continuous and dichotomized by a 3-minute 1-way threshold). We fit multivariate models to analyze the association between OHCA-to-AED walking time and outcomes (Q5 vs. others).ResultsA total of 6,187 and 3,239 cases were included from the Metro Vancouver and Rhône County areas, respectively. In Metro Vancouver Q5 areas (vs. Q1-Q4), areas, AEDs were farther from (79% over 400m from case vs. 67%, p<0.001) and required longer walking times to (97% above 3min vs. 91%, p<0.001) cases. In Rhône Q5 areas, AEDs were closer than in other areas (43% over 400m from case vs. 50%, p=0.01), yet similarly poorly accessible (85% above 3min vs. 86%, p=0.79). In multivariate models, AED access time ≥ 3min was associated with decreased odds of survival at hospital discharge in Metro Vancouver (odds ratio 0.41, 95% CI [0.23-0.74], p=0.003).ConclusionsAccessibility of public AEDs was globally poor in Metro Vancouver and Rhône, and even poorer in Metro Vancouver’s socioeconomically deprived areas