Modeling tidal sand wave dynamics in response to dredging interventions

Tidal sand waves are large scale bed forms observed in many tidally dominates sandy shallow seas, such as the North Sea. They often interfere with offshore human activities, such as navigation, because they are dynamic, are frequently surveyed and dredged. For both, surveying frequencies and dredging strategies, knowledge on sand wave recovery is required.<br/

Modeling wave and wind climate effects on tidal sand wave dynamics:A North Sea case study

To obtain site-specific wave and wind climate averaged sand wave dynamics, we combine an idealized linear stability model with 20 years of wave and wind data taken from the Euro Platform in the North Sea. The model output results in a wave and wind climate-averaged growth and migration rate. The results show that waves and wind affect particularly migration and to a much smaller extent the growth rate. Seasonal variations in wave and wind conditions during winter and summer periods result in seasonal variations in sand wave dynamics, in particular during winter the migration rate is larger, the growth rates are lower and the preferred wavelength is larger compared to summer. Medium wave and wind conditions are responsible for two thirds of the migration rate, while these conditions occur roughly only one third of the time. Extreme wave and wind conditions result in only a moderate contribution to the migration rate. Furthermore, we see a seasonal variation in migration as well as reasonable correlation with observed migration rates for the intervals between surveys in the period 1996–2010. Our work shows that storms are able to affect sand wave migration, and cause variability in migration rate

CFD Evaluation of airflow patterns around beachhouses with different wind facing sides

The attractiveness of beaches to people has led, in many places, to the construction of buildings at the beach-dune interface. Buildings change the local airflow patterns which, in turn, alter the sediment transport pathways and magnitudes. This induces erosion and deposition patterns around the structures.In this study, a numerical model is developed using the open-source computational fluid dynamics solver OpenFOAM. First, the impact of wind facing surface on the near-surface airflow patterns is investigated. Second, the near-surface horizontal divergence of the velocity field is calculated to interpret the impact of changes in airflow patterns on potential erosion and deposition patterns around the buildings

Modelling the vertical grain size sorting process in aeolian sediment transport using the discrete element method

We present a model study of the aeolian saltation process where sediment samples are studied for the size selective transport processes. The discrete element method is used to simulate the sediment particles of different sizes, coupled with a fluid boundary layer model to capture the driving wind forces. Sediment samples with identical median grain size, but with systematically varying size distributions were simulated to investigate under various wind shear rates which sediment fractions are transported. The presented model results show - well in line with other research - that the median grain size is an appropriate sediment sample parameter to quantify the total rate of sediment transport. However, our results show that this does not determine what fractions of sediment are in transport. The larger the standard deviation in the sediment size distribution the smaller the median grain size becomes of the sediment that is in transport compared to the median grain size present at the bed

The influence of storms on sand wave evolution: a nonlinear idealized modeling approach

We present a new 2DV nonlinear process-based morphodynamic model to investigate the effects of storms, specifically wind-driven flow and wind waves, on finite amplitude tidal sand wave evolution. Simulations are performed on periodic domains of two lengths: (i) on a 350-m domain, comparable to the wavelength of observed sand waves, we study the evolution toward equilibrium shapes, and (ii) on a 4-km domain, we study the evolution from a randomly perturbed seabed. Our model results demonstrate that both wind-driven flow and wind waves reduce sand wave height and tend to increase wavelength. Wind-driven flow breaks the tidal symmetry, resulting in horizontal sand wave asymmetry and migration. Waves alone do not induce migration but can enhance migration induced by, for example, tidal asymmetry and wind-driven flow. On the 350-m domain, we further find that migration rates decrease with increasing sand wave height. However, in an irregular sand wave field, large sand waves tend to overtake the smaller ones, suggesting a complicated interaction among neighboring bed forms. The above results concern steady state storm conditions. However, since storms occur on an intermittent basis, we also simulated a synthetic storm climate consisting of alternating short periods of storm conditions and long periods of fair-weather conditions. Simulations reveal a dynamic equilibrium with sand wave heights significantly below those obtained for tide-only conditions, also for relatively short storm duration. Our work identifies mechanisms that explain why sand wave heights are generally overpredicted by numerical models that do not include storm processes