Mapping wave set-up near a complex geometric urban coastline

Abstract

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.

Spatial variability in the trends in extreme storm surges and weekly-scale high water levels in the eastern Baltic Sea

“…The extensive spatial variation in the slopes of the trendlines of maximum water levels (Figs. 6-8) supports the conjecture that wind directions in strong storms may have changed in the northern Baltic Sea (Soomere et al, 2013). Further support to this hypothesis provides a decrease in the observed maxima of storm surge heights at Ristna.…”

“…The remarkable spatial variation shown here together with the conjecture about wind speeds, evidence of overall changes in wind directions from the literature and information extracted from the properties of air-flow over the Gulf of Finland suggest that wind directions in strong storms may have rotated over the time interval in question. A similar conjecture has been derived from the analysis of properties of wave-induced set-up (Soomere et al, 2013).…”

Combining airborne and terrestrial laser scanning to monitor coastal processes

“…1) develop in relatively rare conditions of a large, relatively young and shallow, micro-tidal, seasonally ice-covered water body of extremely complicated shape [1]. Their key driving mechanism is a highly intermittent wave regime that is accompanied by aperiodic variations of the water level, seasonal ice cover [2], and frequent presence of conditions favorable for unexpectedly high run-up [3] and set-up [4]. The most interesting coastal segment in this respect is the southern coast of the Gulf of Finland where the beaches mostly overlie ancient dunes in deeply indented bays that are geometrically sheltered from a large part of the directions of strong winds.…”