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The Threshold Concept Framework is used to initiate a dialogue on an empirically supported pedagogy that focuses on students’ conceptual understanding required for solving application-based problems. The present paper uses a triangulation approach to identify the threshold concept in a third-year undergraduate civil engineering course on open channel hydraulics. Evidence from teachers, students, and assessment data point to ‘critical flow’ as the threshold concept – a concept that is transformative, integrative, and troublesome. Identifying the threshold concept by engaging various course stakeholders in a dialogue about conceptual understanding and capabilities makes learning visible for all participants in the process. Implementing this approach can result in an empirically driven rationale for adjusting pedagogies and assessments to foster enhanced student learning outcomes. [ABSTRACT FROM PUBLISHER]

Abstract: A temporal stochastic modelling method for predicting exceedance probabilities of the beach barrier elevations fronting intermittently closed and open coastal lagoons is developed. The method incorporates synthetic tides generated from measured tidal harmonics, and randomly sampled values relating to rainfall, beach face slope, lake opening period, and wave height, direction and period. Samples are derived from distributions of each of these parameters formed from standard long term data records. The method is applied to Tabourie Lake, on the south coast of New South Wales. This entrance is sheltered from the dominant wave climate by an island close to shore, the impact of which is separately assessed by phase averaged wave modelling. The barrier elevation is determined from the 2% run-up level arising from constructive waves. The sensitivity of results to a variety of assumptions is tested. The methodology is applied to determine the probabilistic distribution of barrier heights for both stationary and non-stationary (i.e. sea level rise (SLR)) scenarios. Such probabilities can be adopted in a risk based assessment of catchment flooding behind an enclosing barrier for present conditions, or provide management guidelines for future climate scenario, i.e. changes in rainfall, wave climate, sea level. The model can also be used to investigate different management strategies and how these alter the barrier elevation for given probabilities of exceedance. [Copyright &y& Elsevier]

Abstract: To unravel the relation between hydrodynamic forcing and the dynamics of the tidal flat–salt-marsh ecosystem, we compared hydrodynamic forcing in terms of proxies relevant to bed sediment motion for four tidal flat–salt-marsh ecosystems that were contrasting in terms of wind exposure (sheltered vs. exposed) and lateral development (shrinking vs. expanding). Wave and current field measurements on these four contrasting tidal flat and salt-marsh ecosystems indicated that the hydrodynamic forcing on the bottom sediment (bed shear stress) was strongly influenced by wind-generated waves, more so than by tidal- or wind-drive currents. The measurements further showed that the hydrodynamic forcing decreased considerably landward of the marsh cliff, highlighting a transition from vigorous (tidal flat and pioneer zone) to sluggish (mature marsh) fluid forcing. Spatial wave modeling using measured wind, revealed that the time-integrated wave forcing on the intertidal mudflat in front of the marsh (i.e., the potential bed sediment pickup) was a factor two higher for salt marshes that are laterally shrinking than for laterally expanding marshes, regardless of whether these marshes were exposed to or sheltered from the wind. The same result could not be obtained from a straightforward wind speed and fetch length approach for estimating wave forcing. This confirmed that wave force estimates required spatial modeling to be consistent with the sites trends of shrinking or expanding marshes and wind exposure is not enough to characterize the wave forcing at these sites. Seasonal changes in wave forcing identified from wind measurements potentially provide an alternative mechanism for marsh cliff formation. During the calm summer, fine sediments switches from the water column to the bed. During the following winter, fine sediment is retained within the vegetated regions while being returned to the water column from the bare tidal flats. The continuous slow upward growth of vegetated areas combined with the seasonal cyclic tidal flat elevations, could, during winter, cause a discontinuity at the bare/vegetated boundary. If this discontinuity grows large enough for plant die-off to occur, then a small cliff will form. [Copyright &y& Elsevier]

Abstract: Recent developments in extreme values modelling have been used to develop a framework for determining the coastal erosion hazard on sandy coastlines. This framework quantitatively reproduced the extreme beach erosion volumes obtained from field measurements at Narrabeen Beach, Australia. This encouraging finding was achieved using Kriebel and Dean''s [Kriebel, D.L. and Dean, R.G., 1993. Convolution method for time-dependent beach profile response. Journal of Waterway, Port, Coastal and Ocean Engineering, 119(2): 204–226.] simple beach erosion and accretion model. The method includes allowances for joint probability between all basic erosion variates including; wave height, period and direction, event duration, tidal anomalies and event spacing. A new formulation for the dependency between wave height and period has been developed. It includes the physical wave steepness limitation. Event grouping, where significantly more erosion can occur from two closely spaced storms is handled by temporally simulating the synthetic wave climate and the resulting beach erosion and accretion. [Copyright &y& Elsevier]

Reef-protected beaches are vulnerable to the effects of sea level rise and degradation of their associated fringing reefs. The SWAN hydrodynamic wave model is combined with classical theory describing the planform of beaches in equilibrium with the wave forcing to estimate the reef top hydrodynamics and the shoreline configuration in the lee of the reefs. Open access Bayesian Belief Networks with high accuracy and simple user interfaces have been built to communicate the results. The BBN enable end users to access all the model results and to compare different scenario to determine how changes in the wave climate or reef elevation change the shoreline configuration. The results show that recession of the shoreline in the lee of fringing reefs due to sea level rise may be much greater than that expected on open coast beaches. Loss of reef flat elevation can also lead to severe shoreline erosion. • Bayesian Belief Networks are constructed for end-users to model complex coastal processes. • Models include the hydrodynamics and shoreline response behind fringing reefs. • The impact of climate change and reef degradation is considered. • Results are communicated using open-access BBNKeywords. • End-user experience was used to develop accurate and transparent networks. [ABSTRACT FROM AUTHOR]

The development of slosh suppression blocks is an important step forward for mitigating sloshing in floating closed containment fish tanks and makes the tanks suitable for operating in a broader range of wave conditions. This experimental study investigates the motion and sloshing response of a scaled floating rigid containment tank model under regular wave action in a wave flume. The tank is fitted with slosh suppression blocks of different dimensions to investigate their effectiveness in mitigating sloshing while considering the state of the internal fluid for fish well-being. This study shows that by sacrificing moderately higher sloshing amplitudes at lower excitation periods, slosh suppression blocks are able to reduce the overall sloshing amplitudes and mitigate the build-up to large sloshing amplitudes. By letting fluid overtop onto the slosh suppression block disturbances to the main fluid volume are minimised, thereby preserving a calm living environment for the fish below. Effective slosh mitigation allows for deploying these closed containment systems in higher energy fish farming sites as the aquaculture industry expands operations into more spacious offshore sites. • Mitigate sloshing in closed containment aquaculture systems. • Floating closed containment fish farms in waves. • Fish farming in exposed farming sites. • Damp fluid oscillations with slosh suppression blocks via overtopping. • Create a calm, controlled and low-energy environment for fish wellbeing. [ABSTRACT FROM AUTHOR]

In this study, we explain contradictory previous observations of the contribution of coherent wave organised motion to the downward transfer of momentum through wave Reynolds stresses ( ρ u ˜ w ˜ ¯ ) below wind waves. The generation of non-zero u ˜ w ˜ ¯ is potentially significant because 1) the turbulent mixing is not then the only momentum transport mechanism under wind waves as was previously assumed, 2) this provides a wave-current energy exchange pathway that could explain inconsistencies in measured air- and water-side wind-wave energy transfer and 3) it can be a critical term in the wave-current coupling formulation under wind waves. However, such a mechanism for momentum transfer has generally been ignored, since contradictory observations were reported. Here, two new sets of wind-wave laboratory experiments are reported. For the first set, contradictory u ˜ w ˜ ¯ were observed, as in previous literature. Investigating the sources of such inconsistency, we examined spatial inhomogeneity due to wave reflection through a second set of experiments, by varying instrument location and additionally considering random waves. The results resolve the inconsistencies observed in the first set of experiments and previous measurements. In addition, we emphasise the contribution of secondary circulation cells in momentum transfer under wind waves. [ABSTRACT FROM AUTHOR]

Traditional methods for assessing coastal hazards have not typically incorporated a rigorous treatment of uncertainty. Such treatment is necessary to enable risk assessments which are now required by emerging risk based coastal zone management/planning frameworks. While unresolved issues remain, relating to the availability of sufficient data for comprehensive uncertainty assessments, this will hopefully improve in coming decades. Here, we present a modelling framework which integrates geological, engineering and economic approaches for assessing the climate change driven economic risk to coastal developments. The framework incorporates means for combining results from models that focus on the decadal to century time scales at which coasts evolve, and those that focus on the short term and seasonal time scales (storm bite and recovery). This paper demonstrates the functionality of the framework in deriving probabilistic coastal hazard lines and their subsequent use to establish an economically optimal setback line for development at a case study site; the Narrabeen–Collaroy embayment in Sydney, New South Wales. [ABSTRACT FROM AUTHOR]

This paper introduces a new concept to mitigate sloshing, tailored to floating closed containment aquaculture systems, termed slosh suppression blocks. Slosh suppression blocks reduce the natural sloshing periods by contracting the free surface area without any significant reduction of the operational volume in the tank, and can be retrofitted to existing systems. Sloshing energy is dissipated on top of the suppression blocks, out of the fluid domain to reduce the spread of turbulent eddies in the main body of the fluid in the tank. The fundamental idea and working principles of the slosh suppression blocks are illustrated with an experimental setup representing a 2D section of a closed-containment system under forced horizontal excitations. Maximum sloshing amplitudes are compared for 25 different test configurations for a range of excitation frequencies, using cubic slosh suppression blocks of different sizes. For selected configurations, the fluid's internal state is assessed by visualising the fluid motions both experimentally and by numerical simulations. The results show that slosh suppression blocks reduce the total sloshing volume and turbulent motions within the main body of the tank, providing a much calmer, controlled low energy living environment which is regarded essential for fish wellbeing. It is found that positioning the top of the slosh suppression blocks flush with the still water level mitigates and damps internal sloshing most effectively. To quantify and characterise the degree of slosh suppression, three slosh indices are introduced; the slosh reduction index, the slosh overtopping index and the slosh free surface index. The novel concept of slosh suppression blocks provides an important step forward in the design of floating closed containment aquaculture tanks that minimises sloshing and internal fluid motions in energetic environments. [ABSTRACT FROM AUTHOR]

Li, F., van Gelder, P.H.A.J.M., Callaghan, D.P., Jongejan, R.B., den Hijer, C. and Ranasinghe, R., 2013. Probabilistic modelling of wave climate and predicting dune erosion considering sea level rise Knowledge about future oceanographic events will assist governments to better manage risk in coastal zones, a crucial task in the light of projected sea level rise, population growth and economic development. In this study, a 31-year data set of deep water wave climate parameters and bathymetry measurements (yearly cross-shore transect surveys) at Noordwijk, the Netherlands, were analyzed (1) to jointly estimate storm events variates of deep water wave conditions, and (2) to probabilistically compute dune erosion volume and the resulting coastal retreat distance with the simulated wave climate and plausible local sea level rise scenarios by 2100. The probabilistic coastline retreat models were applied and adjusted to the study site. Based on the outcomes of this application, a modeling technique can be established to propose a framework for probabilistically describing the coastal risk along the Dutch coast. [ABSTRACT FROM AUTHOR]

A new methodology is proposed to estimate storm demand and dune recession by clustered and non-clustered events, to determine if the morphological response to storm clusters results in greater beach erosion than that from individual storms that have the same average recurrence interval (ARI) or return period. The method is tested using a numerical morphodynamic model that combines both cross-shore and longshore beach profile evolution processes, forced by a 2D wave transformation model, and is applied as an example within a 20 km long coastal cell at an erosion hotspot at Old Bar, NSW mid-north coast, Australia. Wave and water level data hindcast in previous modelling (Davies et al., 2017) were used to provide two thousand different synthetic wave and tide records of 100 years duration for input to a nested nearshore 2D SWAN model that provides wave conditions at the 12 m depth contour. An open-source shoreline evolution model was used with these wave conditions to model cross-shore and longshore beach profile evolution, and was calibrated and verified against long-term dune recession observations. After a 50 year model spin up, 50 years of storm demand (change in sub-aerial beach volume) and dune toe position were simulated and ranked to form natural estimators for the 50, 25, 16, 12.5 and 10 year return period of individual events, together with confidence limits. The storm demand analysis was then repeated to find the return period of clustered and non-clustered morphological events. Morphological clusters are defined here by considering the response of the beach, rather than the forcing, with a sensitivity analysis of the influence of different recovery thresholds between storms also investigated. The new analysis approach provides storm demand versus return period curves for the combined population of clustered and non-clustered events, as well as a curve for the total population of individual events. In this approach, non-clustered events can be interpreted as the response to isolated storms. For clustered and non-clustered morphological events the expected storm demand for a 50-year return period is approximately 25% greater than that for individual events. Alternatively, for clustered and non-clustered events the magnitude of the storm demand that occurs at a return period of 17 years is the same as that which occurs at a return period of 50 years for individual events. However, further analysis shows that for a 50-year return period, the expected storm demand for the population of non-clustered events is similar to that of the clustered events, although the size of the population of the latter is much greater. Hence, isolated storms can generate the same storm demand as storm clusters, but there is a much higher probability that a given storm demand is generated by a morphologically clustered event. • Morphological modelling investigates beach erosion due to storm clusters. • A hybrid cross-shore and longshore beach profile evolution model is used. • Clustering leads to greater beach erosion for the same return period event. • Extreme erosion is much more likely to occur due to a clustered event. [ABSTRACT FROM AUTHOR]

Novel series of experiments are presented that demonstrate morphological hysteresis in the evolution to equilibrium of beach profiles under sequences of different wave climates. The experiments were conducted in a wave flume at medium scale using both monochromatic and random waves, representing 2D conditions. Beach profiles were obtained with high spatial resolution at frequent intervals with a laser profiler, from which shoreline location, bar position and sediment transport rates were derived. Experiments were conducted for sequences of wave climates, where a sequence comprised of 6–13 sequential tests, each commencing with the beach profile from the preceding test. Each test was run until equilibrium conditions were obtained and had a constant wave height, increased or decreased relative to the preceding test. Cyclical conditions were also included, with erosive and accretive wave conditions of short durations alternating through multiple cycles, so that equilibrium conditions were not reached during a test. With a sequence of increasing wave heights, the relationship between the shoreline position and the bulk cross-shore sediment transport, at equilibrium, was non-monotonic, indicating a maximum in the landward sediment transport rate. For test series comprised of a sequence of increasing wave heights followed by a sequence of decreasing wave heights, morphological hysteresis was observed in the equilibrium shoreline position and bulk cross-shore sediment transport, such that shoreline recession, or offshore transport, continued in some instances after reductions in wave height. This is inconsistent with classical equilibrium type shoreline evolution models. However, when equilibrium conditions were not reached, in the cyclic sequences, no such morphological hysteresis was observed and a dynamic equilibrium is reached. The morphological hysteresis occurs because of the decay, stranding, or increased relative depth, of the breaker bar following a reduction in wave height, often in conjunction with a new breaker bar generated by further offshore transport in the inner surf zone. Similar sequences of morphological response are evident in field data and larger scale tests in the literature. Finally, it is shown that the morphological hysteresis can be explained using the classical equilibrium beach state model of Wright et al. (1985) by introducing the concept of a subsequent alternate active beach state, which may occur following a change in wave conditions. [ABSTRACT FROM AUTHOR]

Abstract: Due to the unprecedented growth in population and economic development along the coastal zone all over the world, knowledge about future extreme oceanographic events will assist in ensuring human and property safety. This will be a task with increasing significance in the light of projected climate change impacts. A joint estimation of extreme storm events' variates of deep water wave conditions was performed. It can be used for multivariate descriptions of wave climate variates, such as wave height, period, steepness, and storm duration. The storm sequences can be simulated and extrapolated from limited observational data for optimal structure protection strategies and various disaster risk analysis, like erosion or overtopping. The analysis not only shows the effectiveness of the proposed statistical approaches for improving multivariate modelling of the storm parameters but also highlights the most compatible approach for the Dutch wave climate data from 1979 to 2009. We used the Monte-Carlo method and four methods to construct the dependency structures, based on copula functions, physical relationship and extreme value theory. The marginal probabilistic distribution functions of wave climate variables and the joint probability were then obtained. The simulated data group performs a reasonable similarity to the field measurements according to the goodness-of-fit test, and the Gaussian copula model was found to be the best wave climate simulation method for the Dutch coast. [Copyright &y& Elsevier]

Abstract: There is a growing recognition of the important role of scale-dependent feedback for biogeomorphological landscape formation, where organisms locally improve survival and growth but at the same time negatively affect organisms at larger distance. However, little is known on how scale-dependent bio-geomorphic feedback is influenced by organism traits in combination with abiotic forcing. This was studied by measuring in a flume, the flow patterns around patches of three contrasting marsh species (Spartina anglica, Puccinellia maritima and Salicornia procumbens), using the flow acceleration around vegetation patches and deceleration within vegetation patches as quantitative proxy for the negative and positive feedback to the vegetation performance. The importance of external forcing was assessed by comparing three realistic current velocities: 0.1, 0.2 and 0.3ms−1. Our results showed that the dense clonal growth of stiff Spartina anglica shoots caused strongest flow deviations, irrespective of the applied current velocity. In contrast, the more sparsely growing, shorter stiff shoots of Salicornia procumbens induced much less flow deviation, allowing more water to pass through and over the vegetation canopy. The dense but highly flexible shoots of Puccinellia maritima caused strong flow deviations at low velocities, which diminished at higher velocities due to bending of the vegetation. Overall, these hydrodynamic results demonstrate that plant species traits interact with environmental conditions in creating scale-dependent feedbacks explaining why the effects of vegetation on landscape formation in saltmarshes are species specific. [Copyright &y& Elsevier]