CONTENTS & ABSTRACTS
InEnglish. Summaries in Estonian
Proceedings of the Estonian Academy of Sciences.
Engineering
Volume 9 No. 3September 2003
Special issue on wave studies in Tallinn Bay
Guesteditorial; 155–156
Rein Raudsep
Anexperimental study of wind waves and ship wakes in Tallinn Bay;157–184
Tarmo Soomere and Kalev Rannat
Abstract. The results of a fieldstudy of wind waves and ship wakes in the coastal area of Tallinn Bay in theyears 2001–2002 are described. The main goal was to identify the typical andextreme parameters of ship wakes and to describe their energetic properties indifferent coastal areas. The basic features of wind wave fields in differentwind conditions are estimated. The structure of the wake patterns of fastferries, the maximum and typical values of wake heights and their spatialvariability are analysed. Waves caused by fast ferries generally are higherthan those excited by hydrofoils or conventional ferries. Their daily maximumheight typically exceeds 1 m and may reach in extreme cases 1.7–2.3 mat a depth of 5 m at the eastern coast of the bay. The highest wavecomponents frequently have periods of 10–15 s. Waves with such propertiesdo not occur in natural conditions in the area in question. The spatialvariation of the average energy density of the ship waves and its flux isrelatively small in Tallinn Bay. The daily average frequency spectra ofship-generated waves show that different parts of the coastal zone are affectedby waves with largely different properties.
Key words: wind waves, high-speedcraft, wake wash, wave measurements, wave spectra, semi-enclosed seas.
Geologicalsetting of areas endangered by waves generated by fast ferries in Tallinn Bay;185–208
Jüri Kask, Aado Talpas, Andres Kask, andKlaus Schwarzer
Abstract. The paper considers the distribution of bottom deposits inTallinn Bay in connection with the general geological setting. The shoressubject to intense ship wash (western coast of the Viimsi Peninsula, SW coastof Aegna Island, and eastern coast of Naissaar Island) are discussed in greaterdetail. Distribution of bottom deposits is determined by the location oferosion areas and seafloor topography. The shores of the bay are mostly coveredwith coarse material washed out from glacial deposits, which reduces theinfluence of the waves. During the periods with low water level the wavesgenerated by fast ferries influence deeper parts of the nearshore.
Key words: Tallinn Bay, fast ferries, shore, bottom deposits.
Possibilitiesof reconstruction of the wind regime over Tallinn Bay;209–219
Sirje Keevallik
Abstract. An attempt has been made to reconstruct the wind regime over TallinnBay from coastal data. For this purpose, two ideal sites exist – Tallinnharbour and Naissaar Island. They describe the transformation of open seaconditions to the coastal ones. The average wind speed is 5.1 m/s atNaissaar decreasing to the value of 4.7 m/s near the harbour. The mostprobable wind direction is SW at the entrance of the bay and south for theinner part of it. Strong winds (11 m/s and more) blow mostly from SW atNaissaar and mostly from NW at Tallinn harbour. Such a difference is obviouslycaused by the topography of the bay as it is open to the NW; other directionsare sheltered by islands and peninsulas. The secondary maximum of the strongwind directional distribution at NE seems to be similar for the whole bay. TheSE and south winds are mostly weak. As these stations do not function any more,regressions were calculated to estimate the wind vector components on the bayfrom Harku and Kalbådagrund data. It has been shown that the zonal component ofthe sea winds in winter, spring, and autumn can be reconstructed from the Harkudata. The same cannot be said about the meridional component. To restore themeridional component at Naissaar, Kalbådagrund data offer a better opportunity.The conclusion is that possibilities of reconstruction of the wind fieldproperties based on Harku data are very limited.
Key words: wind regime, Tallinn Bay.
Fastferries as a new key forcing factor in Tallinn Bay;220–242
Tarmo Soomere, Jüri Elken, Jüri Kask, SirjeKeevallik, Tarmo Kõuts, Jaan Metsaveer, and Pearu Peterson
Abstract. The role ofship-generated waves in the total wave activity in Tallinn Bay, a semi-enclosedbasin of the Gulf of Finland, is analysed. The heights of ship waves aremoderate. Since the seabed in the vicinity of the shoreline is mostly coveredwith a pebble and cobble pavement which protects the shore from furthererosion, the influence of the ship waves is negligible near the shoreline.Owing to the high density of fast ferry traffic, the annual mean energy of shipwaves is 5–8% from the wind wave energy and the ship-induced wave energy flux(wave power) is 18–35% from the wind wave power. The highest components of shipwakes have the heights about 1 m and frequently periods of 10–15 s.Such waves do not occur in natural conditions in the area in question. Theycause unusually high near-bottom velocities at the depths of 5–20 m. Thus,the fast ferry traffic is a new forcing component of vital impact on the localecosystem that may cause considerable intensification of beach processes aswell as enhanced vertical mixing in the water body. It may have significantinfluence on the aquatic biota.
Key words: fast ferries, ship wash, Gulf of Finland, wave measurements.
