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.

Most cities in temperate climate zones, including Tallinn, face the threat of torrential rains and resultant floods, which cause extensive damage to city economies. The main causes of floods are climatic; however, unreasonable building activity and insufficiently developed and maintained drainage systems also contribute to this problem. The percentage of impervious pavement has increased with the consolidation of buildings and road networks. Rainwater drainage is an important issue in a number of different areas of human activity ranging from town planning and environmental protection to building, maintenance and operation of rainwater drainage systems. Hence, to deal with the rainwater drainage issue, it is necessary to develop an integrated and scientifically justified strategy. The present study represents a constituent part of the relevant strategy development process. The authors pay special attention to options for increasing rainwater percolation in different environmental conditions, including geological setting, topography and different soil filtration properties.