The coast and the nearshore is a resource of extremely high value to the Baltic States and a location of major conflict of interests by different user groups. It is an important ecosystem that supports human wellbeing, incl. providing food and recreational opportunities. It also has an important commercial function, supporting trade, the movement of people, and recreation through the beaches, ports and marinas. It is the buffer between land and sea, with coastal erosion and integrity of the nearshore ecosystem being a particular concern.
The project SOLIDSHORE titled in Estonian: Läänemere idaranniku looduslike randade ja rannikuehitiste jätkusuutlik tulevik Solutions to current and future problems on natural and constructed shorelines, eastern Baltic Sea is financed from the European Economic Area (EEA) Financial Instrument 2014–2021 Baltic Research Programme (project EMP480).
This research brings together specialists from Tallinn University of Technology, Latvian Institute of Aquatic Ecology, Klaipeda University and Norwegian University of Science and Technology, each with their own internationally recognized expertise, to provide solutions to the current and future problems that already and will affect how we use coastal resources.
The major source of energy to the nearshore are waves. Many of the problems we experience (such as erosion and port siltation) relate to how sediment (mainly gravel, sand and mud) is moved. Much current knowledge comes from open ocean and cannot be directly applied to very different conditions of the Baltic Sea. This research will provide environmentally friendly solutions to coastal problems in ways that very specifically account for the wave, water level and sediment conditions in the eastern Baltic Sea and are transferable for all similar water bodies. This is accomplished using i) data and knowledge that we currently have to provide much better and higher resolution knowledge about waves than are presently available, ii) by measuring sediment transport using novel sensors developed at TalTech, iii) by applying the new knowledge to examine how the interactions of waves and sediment impact the natural shores and coastal structures, and iv) provide tools so that coastal managers can make use of the knowledge produced to estimate how vulnerable are single coastal sections.
The first half-year of the project has already led to several publications about our progress in reputable journals:
1. Pindsoo, K., Soomere, T. 2020. Spatial variability in trends in water level extremes in the Baltic Sea. Continental Shelf Research, 193, art. no. 104029, doi: 10.1016/j.csr.2019.104029.
Extreme water levels in the Baltic Sea have increased much faster than the global sea level rise. We employ long-term simulations with the Rossby Centre Ocean (RCO) circulation model in 1961–2005 for the quantification of (i) spatial variability of the increase rate of water level maxima in this water body and (ii) the contribution from different water level components to this increase. The increase rates of water level maxima vary from about 1.5 to 10 mm/yr. These values do not involve the vertical crust movements. The fastest increase in water level maxima occurred in the eastern Gulf of Finland (8–10 mm/yr), Gulf of Riga (6–9 mm/yr), near Klaipėda (6–8 mm/yr) and in the south-western Baltic Sea (5–7 mm/yr). Most of the increase in these locations stems from stronger local storm surges. The upsurge of the water level maxima on the shores of Sweden and in the eastern Gulf of Bothnia is typically 3–4 mm/yr and is almost fully governed by the joint impact of global sea level rise and increase in the maximum water volume of the entire sea.
2. Borisenko, I., Kondrat, V., Valaitis, E., Kelpsaite-Rimkiene, L., Urboniene, R.O. 2020. Application of the spatial statistic methods to coastal zone management: SE Baltic Sea coast case. Journal of Coastal Research, Special Issue 95, 753-758, doi: 10.2112/SI95-147.1.
The coastal zone is one of the most dynamic environments in the world. Climate change is having an undeniable influence on coastal areas. The main climatic factors driving change in the Baltic Sea coastal zone are wind, waves, storm surges and flooding. Shoreline change is affected by a multitude of complex processes operating at various time- and length-scales.
The presented work aims at clarification of the effects of different hydro meteorological factor to the short-term shoreline evolution at the Palanga beach. The analysis of the hydrometeorological factors, in order to assess the dependence of the beach response on the wind, sea level and wave characteristics with the focus on short term effects of the coastal protection structures in the rapid transition stage immediately after beach nourishment activities.
3. Rätsep, M., Parnell, K.E., Soomere, T. 2020. Detecting ship wakes for the study of coastal processes. Journal of Coastal Research, Special Issue No. 95, 1258–1262, doi: 10.2112/SI95-243.1.
Wakes from contemporary vessels may affect, and in some places dominate, coastal processes in the vicinity of major shipping lanes. The analysis of the properties and impact of wakes has generally been restricted to wakes that can be visually observed in raw data. In this work, spectral analysis of the time series of single-point measurements of water surface elevation from Tallinn Bay is used to highlight the structure of ship wakes using a Short Time Fourier Transform. This method makes it possible to determine the speed and distance of a vessel from the measurement site. Wakes are detected using an algorithm based on Gabor multipliers. The results are compared with vessel passages retrieved from the Automatic Identification System (AIS) data. The algorithm detects the majority of ship wakes that can be visually recognized in spectrograms and misses only those with low signal to noise ratio or those in close proximity to another vessel wake. The calculated speed and distance are consistent with the AIS data except for high-speed vessels sailing at ≥30 knots. The results indicate that by using these techniques the detection of vessel wakes from a single-point wave record is achievable under favorable weather conditions. The methods provide an option for mitigation of the impact of ship wakes in semi-enclosed water bodies.
4. Rätsep, M., Parnell, K.E., Soomere, T., Kruusmaa, M., Ristolainen, A., Tuhtan, J.A. 2020. Using spectrograms from underwater total pressure sensors to detect passing vessels in a coastal environment. Journal of Oceanic and Atmospheric Technology, 37(8), 1353–1363, doi: 10.1175/JTECH-D-19-0192.1.
Monitoring vessel traffic in coastal regions is a key element of maritime security. For this reason, additional ways of detecting moving vessels are explored by using the unique structure of their wake waves based on pressure measurements at the seabed. The experiments are performed at a distance of about 2 km from the sailing line using novel multisensor devices called ‘‘hydromasts’’ that track both pressure and near-bed water flow current velocities. The main tool for the analysis is a windowed Fourier transform that produces a spectrogram of the wake structure. It is shown that time series from the pressure sensors, measured at a frequency of 100 Hz, 0.2m above the seabed are a valid source of input data for the spectrogram technique. This technique portrays the properties of both divergent and transverse waves with an accuracy and resolution that is sufficient for the evaluation of the speed and distance of the detected vessels from the measurement device. All the detected passings are matched with vessels using automatic identification system (AIS) data. The use of several time series from synchronized multisensor systems substantially suppresses noise and improves the quality of the outcome compared to one-point measurements. Additional information about variations in the water flow in wakes provides a simple and reasonably accurate tool for rapid detection of ship passages.
5. Soomere, T., Pindsoo, K., Kudryavtseva, N., Eelsalu, M. 2020. Variability of distributions of wave set-up heights along a shoreline with complicated geometry. Ocean Science, 16, 1047–1065, doi: 10.5194/os-16-1-2020.
The phenomenon of wave set-up may substantially contribute to the formation of devastating coastal flooding in certain coastal areas. We study the appearance and properties of empirical probability density distributions of the occurrence of different set-up heights on an approximately 80 km long section of coastline near Tallinn in the Gulf of Finland, eastern Baltic Sea. The study area is often attacked by high waves propagating from various directions, and the typical approach angle of high waves varies considerably along the shore. The distributions in question are approximated by an exponential distribution with a quadratic polynomial as the exponent. Even though different segments of the study area have substantially different wave regimes, the leading term of this polynomial is usually small (between –0:005 and 0.005) and varies insignificantly along the study area. Consequently, the distribution of wave set-up heights substantially deviates from a Rayleigh or Weibull distribution (that usually reflect the distribution of different wave heights). In about three-quarters of the occasions, it is fairly well approximated by a standard exponential distribution. In about 25% of the coastal segments, it qualitatively matches a Wald (inverse Gaussian) distribution. The Kolmogorov–Smirnov test (D value) indicates that the inverse Gaussian distribution systematically better matches the empirical probability distributions of set-up heights than the Weibull, exponential, or Gaussian distributions.
6. [Joint publication of Estonian and Latvian teams] Männikus, R., Soomere, T., Viška, M. 2020. Variations in the mean, seasonal and extreme water level on the Latvian coast, the eastern Baltic Sea, during 1961–2018. Estuarine Coastal and Shelf Science, 245, art. no. 106827, doI: 10.1016/j.ecss.2020.106827.
High-resolution in situ water level data is one of the core sources for the identification and understanding the reaction of the sea to climate change. We analyse digitised recordings of water level measurements from all 10 currently functioning coastal tide gauges on the Latvian shores of the Baltic proper and in the Gulf of Riga for the period of 1961–2018. The frequency and temporal coverage of measurements vary greatly for these stations. The most complete hourly data are available from Liepaja on the Baltic proper coast and from Daugavgriva in the south-eastern bayhead of the Gulf of Riga. The water level regime is analysed from the viewpoint of (i) the entire range of water level variations, (ii) empirical probability distributions of different water levels, (iii) the seasonal course of water level, (iv) trends in the annual, seasonal, and monthly means and extremes of water level (in terms of the relative and uplift corrected absolute values), and (v) correlations of the main properties of water level with the North Atlantic Oscillation (NAO Gibraltar) index. The empirical probability distributions of different water levels have become narrower in 1991–2018 compared to 1961–1990 whereas very low water levels are now less frequent. The amplitude of the seasonal course has greatly decreased over these time intervals. The annual mean and maxima of water level have increased in 1961–2018. The rate of increase is smaller than the rate of increase in the sea level in the North Atlantic suggesting that changes in the local drivers of water level mitigate the sea level rise in Latvian waters. Variations in the NAO index can explain 1/3 of the annual variability of the main properties of water level and up to 2/3 of this variability in wintertime (December–March). The changes in the statistical properties of water level are consistent with alterations to the directional structure of strong winds.
7. [Joint publication of Lithuanian and Estonian teams] Kelpšaitė-Rimkienė, L., Parnell, K.E., Žaromskis, R., Kondrat, V. 2021. Cross-shore profile evolution after an extreme erosion event—Palanga, Lithuania. Journal of Marine Science and Engineering, 9, art. no. 38, https://doi.org/10.3390/jmse9010038
We report cross-shore profile evolution at Palanga, eastern Baltic Sea, where short period waves dominate. Cross-shore profile studies began directly after a significant coastal erosion event caused by storm “Anatol”, in December of 1999, and continued for a year. Further measurements were undertaken sixteen years later. Cross-shore profile changes were described, and cross-shore transport rates were calculated. A K-means clustering technique was applied to determine sections of the profile with the same development tendencies. Profile evolution was strongly influenced by the depth of closure which is constrained by a moraine layer, and the presence of a groyne. The method used divided the profile into four clusters: the first cluster in the deepest water represents profile evolution limited by the depth of closure, and the second and third are mainly affected by processes induced by wind, wave and water level changes. The most intensive sediment volume changes were observed directly after the coastal erosion event. The largest sand accumulation was in the fourth profile cluster, which includes the upper beach and dunes. Seaward extension of the dune system