Sediment processes and flow reversal in the undular tidal bore of the Garonne River (France)

A tidal bore is a series of waves propagating upstream as the tidal flow turns to rising, and the bore front corresponds to the leading edge of the tidal wave in a funnel shaped estuarine zone with macro-tidal conditions. Some field observations were conducted in the tidal bore of the Garonne River on 7 June 2012 in the Arcins channel, a few weeks after a major flood. The tidal bore was a flat undular bore with a Froude number close to unity: $\hbox {Fr}_{1} = 1.02$ and 1.19 (morning and afternoon respectively). A key feature of the study was the simultaneous recording of the water elevation, instantaneous velocity components and suspended sediment concentration (SSC) estimates, together with a detailed characterisation of the sediment bed materials. The sediment was some silty material ( $\hbox {d}_{50} \approx 13~\upmu \hbox {m}$ ) which exhibited some non-Newtonion thixotropic behaviour. The velocity and SSC estimate were recorded simultaneously at high frequency, enabling a quantitative estimate of the suspended sediment flux at the end of the ebb tide and during the early flood tide. The net sediment flux per unit area was directed upstream after the bore, and its magnitude was much larger than that at end of ebb tide. The field observations highlighted a number of unusual features on the morning of 7 June 2012. These included (a) a slight rise in water elevation starting about 70 s prior to the front, (b) a delayed flow reversal about 50 s after the bore front, (c) some large fluctuations in suspended sediment concentration (SSC) about 100 s after the bore front and (d) a transient water elevation lowering about 10 min after the bore front passage. The measurements of water temperature and salinity showed nearly identical results before and after the tidal bore, with no evidence of saline and thermal front during the study.     

Using small triangular baffles to facilitate upstream fish passage in standard box culverts

Environmental Fluid Mechanics - A culvert is a covered channel to pass streams and floodwaters through an embankment. The ecological impact of culverts has been recognised, in particular in terms...     

Minimizing Impacts of Maintenance Dredged Material Disposal in the Coastal Environment: A Habitat Approach

At present, coastal disposal of maintenance dredged material constitutes one of the most important problems in coastal zone management and in some coastal areas represents the major anthropogenic disturbance to the benthos. In this review we first propose, based on the classic literature, that macrofaunal communities typical of environmentally stressed habitats are more resilient than those of more environmentally stable habitats, and we outline the macrofaunal successional changes following a disturbance. Second, from a review and analysis of the published and unpublished literature on macrofaunal recovery following maintenance dredged material deposition in the coastal environment, we compare the successional sequences and recovery rates in euhaline and polyhaline systems. The review reveals that invertebrate recovery following dredged material disposal in relatively unstressed marine environments generally takes between 1 and 4 years, while in more naturally stressed areas, recovery is generally achieved within 9 months, although deeper polyhaline habitats can take up to 2 years to recover. Differences in recovery times are attributed to the number of successional stages required to regain the original community composition and that species typical of naturally unstressed assemblages do not possess life-history traits to allow rapid recolonization of disturbances. In the last section of this review, the management implications of these findings are discussed in terms of minimizing dredged material disposal impacts on fisheries resources. Since the natural disturbance regime appears to be very important in determining the response of a benthic community following dredged material disposal, it is recommended that when predicting the potential environmental impact of an operation, the nature of the physical environment in combination with the status (and role) of associated marine benthic communities should be considered.     

Mutual interactions in bioelectromagnetics

This paper discusses mutual interactions phenomena especially in the case of Transverse ElectroMagnetic (TEM) cell applications as an exposure system in technical and biomedical studies. In many publications is described problem of influence of an object upon the electromagnetic field (EMF) distribution inside a exposure system while inverse effect—influence of exposure system on tested object is overlooked. The problem plays primary role if a correlation between investigations carried out in an enclosure (e.g. TEM cell) and that in the free space is looked for.     

Computer-assisted navigation and the acquisition of route and survey knowledge

The incidental acquisition of spatial orientation knowledge when using a pedestrian navigation assistance system for wayfinding was compared to incidental learning during map-based wayfinding. First-time visitors to a real environment (a zoo) took a guided tour. In the navigation assistance conditions, users were provided with direction information and view-based pictures of the current intersection at each decision point, presented on a hand-held computer. In the map-based condition, participants derived route segments from a map (each segment comprising three or four intersections), and then walked the partial routes from memory. After walking, unexpected tests on route memory and survey knowledge were administered. Navigation assistance users showed good route knowledge and poor survey knowledge. In contrast, map users showed better survey knowledge and nearly perfect route knowledge. Variations of information presentation within navigation assistance conditions (auditory vs. visual direction command, additional presentation of allocentric spatial information) was not effective. Results are explained with an active encoding principle. Only information that is actually encoded, transformed, and/or memorized during the primary wayfinding activity, is incidentally learned. Since navigation assistance systems do not require users to encode, transform, and memorize spatial information, the spatial orientation knowledge of navigation assistance users is poor.