Railway-induced ground vibrations – a review of vehicle effects

This paper is a review of the effect of vehicle characteristics on ground- and track borne-vibrations from railways. It combines traditional theory with modern thinking and uses a range of numerical analysis and experimental results to provide a broad analysis of the subject area. First, the effect of different train types on vibration propagation is investigated. Then, despite not being the focus of this work, numerical approaches to vibration propagation modelling within the track and soil are briefly touched upon. Next an in-depth discussion is presented related to the evolution of numerical models, with analysis of the suitability of various modelling approaches for analysing vehicle effects. The differences between quasi-static and dynamic characteristics are also discussed with insights into defects such as wheel/rail irregularities. Additionally, as an appendix, a modest database of train types are presented along with detailed information related to their physical attributes. It is hoped that this information may provide assistance to future researchers attempting to simulate railway vehicle vibrations. It is concluded that train type and the contact conditions at the wheel/rail interface can be influential in the generation of vibration. Therefore, where possible, when using numerical approach, the vehicle should be modelled in detail. Additionally, it was found that there are a wide variety of modelling approaches capable of simulating train types effects. If non-linear behaviour needs to be included in the model, then time domain simulations are preferable, however if the system can be assumed linear then frequency domain simulations are suitable due to their reduced computational demand

Interacting Effects of Discharge and Channel Morphology on Transport of Semibuoyant Fish Eggs in Large, Altered River Systems

Habitat fragmentation and flow regulation are significant factors related to the decline and extinction of freshwater biota. Pelagic-broadcast spawning cyprinids require moving water and some length of unfragmented stream to complete their life cycle. However, it is unknown how discharge and habitat features interact at multiple spatial scales to alter the transport of semi-buoyant fish eggs. Our objective was to assess the relationship between downstream drift of semi-buoyant egg surrogates (gellan beads) and discharge and habitat complexity. We quantified transport time of a known quantity of beads using 2–3 sampling devices at each of seven locations on the North Canadian and Canadian rivers. Transport time was assessed based on median capture time (time at which 50% of beads were captured) and sampling period (time period when 2.5% and 97.5% of beads were captured). Habitat complexity was assessed by calculating width∶depth ratios at each site, and several habitat metrics determined using analyses of aerial photographs. Median time of egg capture was negatively correlated to site discharge. The temporal extent of the sampling period at each site was negatively correlated to both site discharge and habitat-patch dispersion. Our results highlight the role of discharge in driving transport times, but also indicate that higher dispersion of habitat patches relates to increased retention of beads within the river. These results could be used to target restoration activities or prioritize water use to create and maintain habitat complexity within large, fragmented river systems

Mixed-effects modelling of scale growth profiles predicts the occurrence of early and late fish migrants

Fish growth is commonly used as a proxy for fitness but this is only valid if individual growth variation can be interpreted inrelation to conspecifics’ performance. Unfortunately, assessing individual variation in growth rates is problematic undernatural conditions because subjects typically need to be marked, repeated measurements of body size are difficult to obtainin the field, and recaptures may be limited to a few time events which will generally vary among individuals. The analysis ofconsecutive growth rings (circuli) found on scales and other hard structures offers an alternative to mark and recapture forexamining individual growth variation in fish and other aquatic vertebrates where growth rings can be visualized, butaccounting for autocorrelations and seasonal growth stanzas has proved challenging. Here we show how mixed-effectsmodelling of scale growth increments (inter-circuli spacing) can be used to reconstruct the growth trajectories of sea trout(Salmo trutta) and correctly classify 89% of individuals into early or late seaward migrants (smolts). Early migrants grewfaster than late migrants during their first year of life in freshwater in two natural populations, suggesting that migrationinto the sea was triggered by ontogenetic (intrinsic) drivers, rather than by competition with conspecifics. Our studyhighlights the profound effects that early growth can have on age at migration of a paradigmatic fish migrant and illustrateshow the analysis of inter-circuli spacing can be used to reconstruct the detailed growth of individuals when these cannot bemarked or are only caught once