Field observations on hydrodynamic and coastal geomorphic processes off Harilaid Peninsula (Baltic Sea) in winter and spring 2006–2007

Investigations of multi-layer current regime, variations in sea level and wave parameters using a bottom-mounted RDCP (Recording Doppler Current Profiler) during 20 December 2006–23 May 2007 were integrated with surveys on changes of shorelines and contours of beach ridges at nearby Harilaid Peninsula (Saaremaa Island). A W-storm with a maximum average wind speed of 23 m s⁻¹ occurred on 14–15 January with an accompanying sea level rise of at least 100 cm and a significant wave height of 3.2 m at the 14 m deep RDCP mooring site. It appeared that in practically tideless Estonian coastal waters, Doppler-based “vertical velocity” measurements reflect mainly site-dependent equilibrium between resuspension and sedimentation. The mooring site, 1.5 km off the Kelba Spit of Harilaid, was located in the accumulation zone, where downward fluxes dominated and fine sand settled. As a result of storms in January and April, the distal part of the accumulative gravel spit advanced by 50 m, whereas a 30–50 m retreat of the shoreline in the western and northern parts occurred at Cape Kiipsaare. The location of the beach ridges shows that the development of the spit occurs through relatively short-period but infrequent storm events, roughly 2–3 times each decade.     

Time Effects in Rock Mechanics by N. D. Cristescu and U. Hunsche,Wiley Series in Materials,Modelling and Computation,John Wiley & Sons,Chichester, New York,Weinheim, Brisbane,Singapore, Toronto, 1998, viii + 342 p., $115 (U.S.), ISBN 0-471-95517-5

Mathematical Geosciences -     

Stability and tightness evaluation of bedded rock salt formations for underground gas/oil storage

The presence of interfaces has a critical influence on the stability and tightness of underground gas/oil storages. In China, these energy storages are constructed mainly in bedded salt formations and are widely distributed. Therefore, it is necessary to study the sedimentary rhythm and mechanical characteristics of the interfaces between beds. The petrologic study of core samples from exploratory wells in Yunying Salt Mine, Hubei Provence, China, reveals a sedimentary rhythm and multiple interfaces of bedded salt formations: (1) Mudstone–anhydrite–glauberite–Glauber’s salt–salt rock–mudstone are periodically deposited in sequences. Chemical deposition, the predominant formation mechanism, and mechanical deposition appear alternately and result in the formation of sedimentary multicycles; (2) depending on whether a certain component of the rhythm is lacking or not, interfaces are divided into sequential depositional interfaces and intermittent depositional interfaces. Depending on the deposition frequency, interfaces can also be classified into dominant interfaces and secondary interfaces. Depending on whether the mineral composition changes gradually or abruptly, interfaces can be divided into gradual transition interfaces and discrete discontinuous interfaces. Based on the classification of the interfaces together with scanning electron microscope analyses, the cementation state and strength of the interfaces are discussed. Both field investigations and laboratory tests show that the strengths of the chemical deposition interfaces are higher than those of the mechanical deposition interfaces. Specifically, interfaces of mudstone and rock salt are mostly weak. Taking into account the presence of weak interfaces, the strength of interbedded salt formations around caverns can be represented by a U-shaped lower-bound strength envelope curve, which means that shear failure may occur more easily at the haunches of the cavern. Therefore, when setting the range of the internal operating pressures, more attention should be paid to the shear strength of the weak interlayers and weak interfaces, in particular those at the haunches of the cavern, to ensure the stability and tightness of underground gas/oil stores.     

Climatology of precipitation extremes in Estonia using the method of moving precipitation totals

A method of moving precipitation totals is described and applied for the analysis of precipitation extremes in Estonia. Numbers of extremely wet and extremely dry days and other indices of precipitation extremes were calculated using the daily precipitation data measured at 51 stations over Estonia during 1957–2009. Mean regularities of spatial and seasonal distribution were determined. Long-term changes were detected using Sen's method and Mann–Kendall test. The highest risk of heavy precipitation is in the regions of higher mean precipitation on the uplands and on the belt of higher precipitation in the western part of continental Estonia. Wet spells have their sharp maxima in July and August. The highest risk of droughts is observed in the coastal regions of West Estonia. In the coastal area, droughts appear mostly in the first half of summer, while in the eastern Estonia, they are usually observed during the second half of summer. Extreme precipitation events have become more frequent and intense. Statistically significant increasing trends were, first of all, found in the time series of winter extreme precipitation indices. In summer and autumn, trends existed in some indices, but in spring, there were no trends at all. There were no trends in time series of dryness indices in Estonia in 1957–2009.     

Book Review: Cavity Expansion Methods in Geomechanics. By Hai-Sui Yu. Kluwer Academic Publishers,Dordrecht, 2000, 385 pp., $170.00 (U.S.), ISBN 0-412-79990-1, (hb)

Mathematical Geosciences -     

A regression approach to the mapping of bio-physical characteristics of surface sediment using in situ and airborne hyperspectral acquisitions

Remote sensing has been successfully utilized to distinguish and quantify sediment properties in the intertidal environment. Classification approaches of imagery are popular and powerful yet can lead to site- and case-specific results. Such specificity creates challenges for temporal studies. Thus, this paper investigates the use of regression models to quantify sediment properties instead of classifying them. Two regression approaches, namely multiple regression (MR) and support vector regression (SVR), are used in this study for the retrieval of bio-physical variables of intertidal surface sediment of the IJzermonding, a Belgian nature reserve. In the regression analysis, mud content, chlorophyll a concentration, organic matter content, and soil moisture are estimated using radiometric variables of two airborne sensors, namely airborne hyperspectral sensor (AHS) and airborne prism experiment (APEX) and and using field hyperspectral acquisitions by analytical spectral device (ASD). The performance of the two regression approaches is best for the estimation of moisture content. SVR attains the highest accuracy without feature reduction while MR achieves good results when feature reduction is carried out. Sediment property maps are successfully obtained using the models and hyperspectral imagery where SVR used with all bands achieves the best performance. The study also involves the extraction of weights identifying the contribution of each band of the images in the quantification of each sediment property when MR and principal component analysis are used.     

THE IMPACT OF CLIMATE CHANGE ON THE SNOW COVER PATTERN IN ESTONIA

The paper deals with problems of temporal and spatial variability of snow cover duration, of correlation between snow cover and winter mean air temperature patterns and of the impact of climate change on the snow cover pattern in Estonia. Snow cover fields are presented in form of IDRISI raster images. Snow cover duration measured at ca 100 stations and observation points have been interpolated into raster cells. On the base of time series of raster images, a map of mean territorial distribution of snow cover duration is calculated. Estonia is characterized by a great spatial variability of snow cover mostly caused by the influence of the Baltic Sea. General regularities of snow cover pattern are determined. A 104-year time series of spatial mean values of snow cover duration is composed and analyzed. A decreasing trend and periodical fluctuations have detected. Standardized principal component analysis is used for the time series of IDRISI raster images. It enables to study the influence of different factors on the formation of snow cover fields and territorial extent of coherent fluctuations. Correlation between snow cover duration and winter mean air temperature fields is analyzed. A spatial regression model is created for estimation of the influence of climate change on snow cover pattern in Estonia. Using incremental climate change scenarios (2 °C, 4 °C and 6 °C of warming in winter) mean decrease of snow cover duration in different regions in Estonia is calculated. According to results of model calculation, the highest decrease of snow cover duration will be take place on islands and in the coastal region of West Estonia. A permanent snow cover may not form at all. In the areas with maximum snow cover duration in North-East and South-East Estonia, that decrease should be much lower.