In English. Summaries in Estonian

Proceedings of the Estonian Academy of Sciences.



Volume 50 No. 2 June 2001


Guest editorial; 83–84

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Hydrodynamical and geological investigations of possible deep harbour sites in north-western Saaremaa Island: Overview and conclusions; 85–98

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Jüri ELKEN, Jüri KASK, Tarmo KÕUTS, Uno LIIV, Rein PERENS, and Tarmo SOOMERE

Abstract. Saaremaa is the largest Estonian island located to the west of Estonian mainland. A new deep harbour, need for which is stated in the Saaremaa County development plan, is possible only in the north-western part of the island that is environmentally sensitive and belongs partly to the area of Vilsandi National Park. This part of the island is known as wintering area of Steller’s Eider and the sanctuary for seals. Environmental impact assessment of the harbour site selection indicated environmental risks at all the considered sites. Discussion of the assessment results led to additional hydrodynamical and geological investigations of the three harbour location alternatives on the Tagamõisa Peninsula: Undva (Uudepanga Bay), Suuriku-Kuriku (entrance of Tagalaht Bay), and Vaigu (central part of Tagalaht Bay). The investigations contained geological and hydrographic field work and modelling of currents and waves. The results revealed that due to dominating cyclonic circulation and small current speeds in the Uudepanga Bay, the risk of oil pollution from the Undva harbour to nearby Vilsandi National Park is rather low. The risk of polluting Steller’s Eider wintering area in the north from the harbour site is somewhat higher, but still small. Vaigu has a favourable wave regime, but the bedrock is covered by a sand layer amounting to 10 m thickness. The waves exceed critical value for sand movement frequently, indicating the need for repeated dredging of ship channels. In addition, contaminant dispersal from Vaigu has the worst pattern. Suuriku-Kuriku has been found the most suitable location for the deep harbour. The expected tough wave regime is not so critical because the high-wave wind directions are rather seldom. As a location of the deep harbour, Undva was found somewhat less favourable and Vaigu considerably less favourable.

Key words: Saaremaa Island, harbour, environmental impact assessment, geological setting, currents, waves, oil drift, sediment transport, hydrogeological conditions, modelling.

Comparison of geological settings at possible deep harbour sites, north-western Saaremaa Island; 99–125

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Jüri KASK, Helle PERENS, Rein PERENS, Sten SUUROJA, and Andres KASK

Abstract. The investigations carried out on Tagamõisa Peninsula (north-western Saaremaa Island, West Estonian Archipelago) were aimed at finding the deep harbour site with most favourable hydrogeological and geological conditions. Three possible sites were studied: Undva on the eastern coast of Uudepanga Bay, and Suuriku-Kuriku and Vaigu on the western coast of the Tagalaht Bay. The investigations show that in spite of active shore processes between Suuriku and Kuriku cliffs, geological and hydrogeological conditions for establishing the deep harbour are somewhat more favourable in this area than at Undva (dredging volumes as well as the amount of filling material needed for jetties and quays were not considered). At Undva dredging would be more work-consuming and to obtain fresh high quality drinking water is more complicated. Vaigu is less favourable because in the harbour basin area a thick layer of sand occurs on the seafloor.

Key words: deep harbour, Saaremaa Island, geological setting, bathymetric surveying, soil properties, hydrogeological conditions.

Variability of currents in bays of Tagalaht and Uudepanga; 126–140

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Tarmo KÕUTS and Janek LAANEARU

Abstract. The variability of the hydrodynamical fields in the sea around the Tagamõisa Cape, the north-western coast of the Saaremaa Island, has been investigated from August to November 2000 measuring currents and stratification. The time series of the forcing parameters, such as the sea level, wind, and currents are presented, and the primary relationships between them have been established. The horizontal fields and the progressive vector diagrams of the currents are constructed. The measured currents in the Tagalaht Bay are significantly dependent on the forcing factors and reveal predominantly a two-layer character. During the dominating southern winds the surface flow to the north, which carries water out from the bay, is compensated by the undercurrent, causing in such a way intensive ventilation of the bay. The two-layer shallow-water model was used to calculate the vertical structure of the currents by integrating the equation of motion through upper and lower layers and eliminating the local sea level forcing term. In the Uudepanga Bay the dominating southern winds cause anticlockwise circulation and the currents reveal predominantly the one-layer structure.

Key words: Baltic Sea, Saaremaa, bay current circulation, wind forcing.

Modelling of coastal circulation and oil drift at possible deep harbour sites, north-western Saaremaa Island; 141–156

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Abstract. In a short-term project related to the environmental impact assessment of the possible locations of a deep harbour in the north-western Saaremaa Island, Estonia, the oil drift probability was investigated by applying Lagrangian particle tracking on the currents from the coastal circulation model. In a four-step nested three-dimensional circulation model, the coarsest grid covered the whole Baltic Sea area with a 4 mi grid step. One-way nesting with the use of sponge layers refined each subsequent grid by a factor of four, reaching on the finest grid the 1/16 mi grid step. Due to unstratified conditions in the bays and to the need for computational efficiency, the Bryan–Cox–Killworth model was recoded for barotropic conditions and implicit timestepping. Calibration run, using forcing data from the local wind measurements that were near the coast corrected by fetch dependent wind speed reduction, gave satisfactory agreement with direct current observations. Using the calibrated model, time series of the current patterns were calculated for a 32 week period in 1991 using the gridded wind fields over the Baltic Sea. Further, the oil drift probability was calculated by recollecting on the grid counter the number of particles reaching a specific grid point after 24 h of drift. If the harbour will be located near the Vilsandi National Park, then probability of oil spill drift to the coasts of the protected territory is low. However, the risk of oil contamination of the nearby wintering areas of globally endangered Steller’s Eider remains. The Suuriku-Kuriku site was found to be the most suitable harbour location with the least consequences of oil spill drift.

Key words: coastal circulation, circulation model, oil spill, environmental impact assessment, Baltic Sea.

Wave regimes and anomalies off north-western Saaremaa Island; 157–173

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Abstract. Properties of the saturated wave field in the neighbourhood of possible sites of the Saaremaa deep harbour during typical (about 15 m/s) and extreme (about 25 m/s) storms, forced by steady winds, are analysed on the basis of the wave model WAM. The toughest wave regime is at Undva (Uudepanga Bay, probability of occurrence of waves exceeding 3 m is 1%), slightly better at Suuriku-Kuriku (0.6%) and the mildest at Vaigu (0.13%). Directional distribution of wave heights in typical and extreme storms is highly anisotropic. The highest waves correspond to NNW storms. Remarkable wave height anomalies may occur in the neighbourhood of the harbour sites. The anomalies emerge only during very strong storms and may serve as a major navigation danger.

Key words: wave modelling, local wave climate, surface waves, wave height anomalies.

Saaremaa deep harbour layout design and computer simulation of the wave climate and sediment transport; 174–192

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Toomas LIIV and Uno LIIV

Abstract. The layouts for the three proposed sites for the Saaremaa Island deep harbour were designed at Corson Consulting. The layouts were designed on the basis of geological, hydro­meteorological, and wave and current conditions. Emphasis was given to the impact of the future harbour on nature. The layouts were used as the basis for wave and velocity field calculations using program MIKE 21. Wave and velocity characteristics were determined for wind directions that are significant for the harbour sites. SandCalc 2.0 was applied for calculation of wave generated shear stresses on the bottom of the seabed around the harbour sites taking into account the local bed characteristics. The calculated shear stresses were used for the analysis of the sediment processes. The results indicate that Suuriku-Kuriku site is the most favourable site for the harbour. The proposed layout protects satisfactorily the harbour basin from most wind directions. The movement of the alluvial material into the harbour basin does not generate problems due to the characteristics of the seabed. Calculation shows that at Suuriku-Kuriku less dredging work is needed than at the other sites.

Key words: harbours, wave climate, sediment transport, MIKE 21.