Abstract. Wave induced set-up is a process that leads to increased water levels in coastal regions. When coupled with storm conditions, wave set-up -or, for brevity, set-up -can significantly increase the risk of flooding or structural damage and therefore is of particular importance when considering coastal management or issues related to the planning of nearshore infrastructures. Here, we investigate the effects of set-up in the coastal region of the Gulf of Finland in the Baltic Sea, close to Tallinn, Estonia, although the results will have wider relevance for many other areas. Due to a lack of continuous wave data we employ modelling to provide input data using a calculation scheme based on a high-resolution (470 m) spectral wave model WAM to replicate spatial patterns of wave properties based on high-quality, instrumentmeasured wind data from the neighbourhood of the study site. The results indicate that for the specific geometry of coastline under consideration, there is a variation in set-up which is strongly affected by wind direction. The maximum set-up values are up to 70-80 cm in selected locations. This is more than 50 % of the all-time maximum water level and thus may serve as a substantial source of marine hazard for several low-lying regions around the city. Wind directions during storms have changed in recent years and, with climate variability potentially increasing, these results will encourage further tests which may be used in a policy setting regarding defences or other structures in and around coastlines. In particular, with urban development now taking place in many coastal regions (including the one within this study) these results have implications for local planners. They may also be incorporated into new storm warning systems.
Abstract. Wave set-up is a process that leads to increased water levels in coastal regions. When coupled with storm conditions, set-up can significantly increase the risk of flooding or structural damage and therefore is of particular importance when considering coastal management or issues of planning related to near-shore infrastructures. Here, we investigate the effects of wave set-up in the coastal region of the Gulf of Finland in the Baltic Sea close to Tallinn, Estonia, although the results will have wider relevance for other areas. Due to a lack of continuous wave data we employ modelling to provide input data using a calculation scheme based on a high-resolution (470 m), spectral wave model WAM to replicate spatial patterns of wave properties based on high-quality, instrument measured wind data from the neighbourhood of the study site. The results indicate that for the specific geometry of coastline under consideration, there is a variation in set-up which is strongly affected by wind direction. The maximum set-up values are up to 70–80 cm in selected locations. This is more than 50% of the all-time maximum water level and thus may serve as a substantial source of marine hazard for several low-lying regions around the city. Wind directions during storms have changed in recent years and, with climate variability potentially increasing, these results will encourage for further tests which may be used in a policy setting regarding defences or other structures in and around coastlines. In particular, with urban development now taking place in many coastal regions (including the one within this study) these results have implications for local planners. They may also be incorporated into new storm warning systems.
We show that undesired remote impacts of changes in the location of the waterfront may occur in fairly mild wave conditions. As an example, we analyse the consequences of a moderate reclamation action in the bayhead of Tallinn Bay, the Baltic Sea. The planned changes are fairly small: the waterfront will be shifted by a few tens of metres owing to the construction of a new major traffic junction. The potential impacts are established using generic concepts of the nature of coastal processes and a detailed reconstruction of the local wave climate. The main properties of closure depths and magnitude and direction of wave-driven alongshore transport in the entire bay are established using a triplenested high-resolution version of the wave model WAM that is forced for 32 years by high-quality marine winds. It is demonstrated that the planned reclamation area currently serves as a convergence point of alongshore sediment transport. Even though the closure depth is only about 2 m, the presence of fine sand gives rise to a relatively wide equilibrium beach profile. The seaward end of this profile is currently close to the entrance to a major harbour about 0.5 km from the activity area. The pattern of sediment motions is such that even a minor shift in the coastline may lead to considerable increase in the transport of sand into the harbour entrance. We evaluate the time scale for this process based on laser scanning data about sand accumulation rates and the concept of equilibrium beach profile, and discuss the ways of preventive mitigation of the consequences of reclamation.
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