Rediscovery of the Endangered Carchi Andean Toad, Rhaebo colomai (Hoogmoed, 1985), in Ecuador, with comments on its conservation status and extinction risk

Since 1984 there have been no records of Rhaebo colomai (Hoogmoed, 1985) within the territory of Ecuador. This species was known from 2 localities in the province of Carchi, northwestern Ecuador, and the department of Nari��o, southwestern Colombia, which were reported in 1979 and 2015, respectively. We report the recent sightings of R. colomai at 3 new localities in Ecuador and discuss and evaluate this species��� extinction risk and conservation status

Transversal and longitudinal mixing in compound channels

none4An experimental campaign, based on particle image velocimetry (PIV) measurements of free-surface velocities, forms the basis for an analysis of the mixing processes which occur in a compound-channel flow. The flow mixing is characterized in terms of Lagrangian statistics (absolute dispersion and diffusivity) and of the related mean flow characteristics. Mixing properties strongly depend on the ratio rh between the main channel flow depth (h*mc) and the floodplain depth (h*fp), and three flow classes can be identified, namely shallow, intermediate, and deep flows. In the present study the large time asymptotic behavior of the mixing characteristics is analyzed in terms of the absolute diffusivity in order to characterize typical values of longitudinal and transversal diffusivity coefficients. Various sets of experiments, which cover a wide range of the governing physical parameters, have been performed and the asymptotic values of the absolute diffusivity have been evaluated. The results are then compared with several studies of flow dispersion for both the longitudinal diffusivity coefficient and the transversal turbulent mixing coefficient. The present results highlight a stronger dependence of such coefficients with the flow-depth ratio than with the flow regime (Froude number).Besio G.; Stocchino A.; Angiolani S.; Brocchini M.Besio, Giovanni; Stocchino, Alessandro; Angiolani, Sonia; Brocchini, Maurizi

Lagrangian mixing in Compound Channels

In a recent study Stocchino & Brocchini (2010) have investigated the dynamics of two dimensional large-scale vortices with vertical axis evolving in a straight compound channel under quasi-uniform \ub0ow conditions. They have showed that properties of quasi two dimensional turbulence strongly depend on the ratio rh between the main channel flow depth (h_mc) and the floodplain flow depth (h_f p). In the case of shallow flows, when the flow depth in the main channel largely exceeds the depth in the flood-plains, the macrovortices are generated owing to the vorticity production concentrated at the transition region, i.e. between the main channel and the floodplains. The source of vorticity was found to be related to the depth jump at the transition. Another fundamental property of this class of flow is that once the turbulence is fully developed, the typical size of the macrovortices is independent of the streamwise coordinate. In the present contribution, we discuss the results of a new extensive experimental campaign in terms of Lagrangian properties of the \ub0ow. Di\uaeerent Lagrangian measures of mixing (i.e. single and multiple particle statistics, FSLE) are introduced with the aim to characterize the mixing processes that occur in a compound channel for varying depth ratio (rh) and Froude number (Fr). The results suggest that the presence of the macrovortices at the transition region between the main channel and the \ub0ood plains delays the establishment of fully developed conditions, increasing the decorrelation time beyond which a Brownian regime is recovered. Moreover, the growth in time of the absolute dispersion is strongly influenced by the presence of long-lived macrovortices causing a non monotonic behaviour Moreover, the dependence of the relative diffusivity on the pair separation shows different behaviours as the flow ratio rh is increased characterized by a local dynamics

Lagrangian mixing in straight compound channels

Recently Stocchino & Brocchini (J. Fluid Mech., vol. 643, 2010, p. 425 have studied the dynamics of two-dimensional (2D) large-scale vortices with vertical axis evolving in a straight compound channel under quasi-uniform flow conditions. The mixing processes associated with such vortical structures are here analysed through the results of a dedicated experimental campaign. Time-resolved Eulerian surface velocity fields, measured using a 2D particle-image velocimetry system, form the basis for a Lagrangian analysis of the dispersive processes that occur in compound channels when the controlling physical parameters, i.e. the flow depth ratio (rh) and the Froude number (Fr) are changed. Lagrangian mixing is studied by means of various approaches based either on single-particle or multiple-particle statistics (relative and absolute statistics, probability density functions (p.d.f.s) of relative displacements and finite-scale Lyapunov exponents). Absolute statistics reveal that transitional macrovortices, typical of shallow flow conditions, strongly influence the growth in time of the total absolute dispersion, after the initial ballistic regime, leading to a nonmonotonic behaviour. In deep flow conditions, on the contrary, the absolute dispersion displays a monotonic growth because the generation of transitional macrovortices does not take place. In all cases an asymptotic diffusive regime is reached. Multiple-particle dynamics is controlled by rh and Fr. Different growth regimes of the relative diffusivity have been found depending on the flow conditions. This behaviour can be associated with different energy transfer processes and it is further confirmed by the p.d.f.s of relative displacements, which show a different asymptotical shape depending on the separation scales and the Froude number. Finally, an equilibrium regime is observed for all the experiments by analysing the decay of the finite-scale Lyapunov exponents with the particle separations