Meso-scale modeling of aeolian sediment transport in coastal areas

Measurement and modelling of aeolian sediment supply from the beach to coastal foredunes on a scale of months to years is complicated by the presence of a number of factors which may act to limit sediment supply from the surface and transport by wind, including: surface moisture, snow and ice cover, gravel lags, flotsam and jetsam, and fetch distance. Prediction of sand supply based on hourly average wind speed and using standard transport equations typically overestimate sand supply by up to an order of magnitude compared to measured deposition. The collection of a time series of hourly data on wind speed and direction, sediment transport, beach surface moisture, beach width and the presence of snow and ice over a period of nine months has provided new insights into the dynamics of transport events driving sediment from the beach toward the foredune at Greenwich Dunes, Prince Edward Island National Park, Canada. This paper summarizes the key aspects of aeolian sediment movement for the period and utilises the data set to explore the development of a modelling approach that can be applied to improve prediction of sand supply to coastal dunes over periods of months and years The main hypothesis of the modelling approach is that there is a limited number of key factors that control both the occurrence and the magnitude of transport events. These factors may be used to isolate significant transport periods over the year. The impacts of nearshore processes are included in the model as part of the dynamics of coastal dunes, as are transport limiting factors and tradeoffs between fetch distances, angle of wind approach, and beach dimensions. A simple analytical procedure, based on previously published equations, is carried out to assess the general viability of the conceptual approach. Results show that the combination of filtering of the time series and the incorporation of moisture and fetch effects in the calculation of transport for isolated events result in improved predictions of sediment deposited at the dune area. Predicted net deposition is of the same order of magnitude as measured deposition, and much less than that predicted by models based solely on wind speed and direction.