Eulerian flow velocities in the swash zone: Field data and model predictions

Measurements of Eulerian flow velocity obtained within the swash zone on a relatively steep beach face (gradient 1:23) are compared with an extended ballistic swash model. The model only requires a friction factor, beach slope and terminal bore velocity as input. The following model predictions matched well with observations: (1) The maximum Eulerian flow velocity is the shoreline velocity when it arrives at the fixed point of interest on the beach face; (2) at any location the time of flow reversal occurs prior to the shoreline reaching its maximum landward excursion; (3) the maximum flow velocity in the backwash is the velocity recorded as the shoreline recedes past the fixed point of interest (and this is less than the maximum uprush velocity); and (4) the duration of the uprush flow is shorter than the duration of the backwash flow. Previous studies have already confirmed that the ballistic swash model (including friction) can accurately predict shoreline motion and maximum run-up on steep beaches. This study shows that it is similarly successful in predicting Eulerian flow velocities during individual swash events. The model does not presently account for interacting swash, however, and so may be less appropriate on gently sloping beaches

Runup uncertainty on planar beaches

Parameterization of wave runup is of paramount importance for an assessment of coastal hazards. Parametric models employ wave (e.g., H-s and L-p) and beach (i.e., beta) parameters to estimate extreme runup (e.g., R-2%). Thus, recent studies have been devoted to improving such parameterizations by including additional information regarding wave forcing or beach morphology features. However, the effects of intra-wave dynamics, related to the random nature of the wave transformation process, on runup statistics have not been incorporated. This work employs a phase- and depth- resolving model, based on the Reynolds-averaged Navier-Stokes equations, to investigate different sources of variability associated with runup on planar beaches. The numerical model is validated with laboratory runup data. Subsequently, the role of both aleatory uncertainty and other known sources of runup variability (i.e., frequency spreading and bed roughness) is investigated. Model results show that aleatory uncertainty can be more important than the contributions from other sources of variability such as the bed roughness and frequency spreading. Ensemble results are employed to develop a new parametric model which uses the Hunt (J Waterw Port Coastal Ocean Eng 85:123-152, 1959) scaling parameter beta (HsLp)(1/2)

Ultrasensitive fluorescence-based methods for nucleic acid detection: towards amplification-free genetic analysis

Real time PCR is the mainstay of current nucleic acid assays, underpinning applications in forensic science, point-of-care diagnostics and detection of bioterrorism agents. Despite its broad utility, the search for new tests continues, inspired by second and third generation DNA sequencing technologies and fuelled by progress in single molecule fluorescence spectroscopy, nanotechnology and microfabrication. These new methods promise the direct detection of nucleic acids without the need for enzymatic amplification. In this feature article, we provide a chemist's perspective on this multidisciplinary area, introducing the concepts of single molecule detection then focussing on the selection of labels and probe chemistry suitable for generating a signal detectable by ultrasensitive fluorescence spectroscopy. Finally, we discuss the further developments that are required to incorporate these detection platforms into integrated ‘sample-in-answer-out’ instruments, capable of detecting many target sequences in a matter of minute