Scour at the head of a vertical-wall breakwater

This paper presents the results of an experimental investigation on the near-bed flow patterns, the bed shear stress amplification and scour around the head of a vertical-wall breakwater, using regular waves. The Keulegan-Carpenter number (KC), based on the diameter of the breakwater head, is found to be the major parameter that governs the flow and the equilibrium scour depth. Basic flow structures are identified as function of KC. The scour depth is found to increase with increasing the Keulegan-Carpenter number. The necessary extent of the conventional stone protection is studied. An empirical formula is worked out for the width of the protection layer as function of KC. Also, the effects of head shape, the angle of attack and the presence of a co-directional current are investigated. The results indicate that the scour depth is increased considerably in the presence of a current. Likewise, the scour depth is increased when the head shape is changed from a round shape to a sharp-edged one. It is found that the angle of attack is also an influencing factor as regards the scour depth.     

The Late Silurian Age of the Reference Aralaul Granosyenites–Granite Massif (Northern Kazakhstan)

This work presents the results of U–Pb geochronological studies of alkaline granites of the Aralaul complex of Northern Kazakhstan, which allow one to substantiate their Late Silurian (420 ± 4 Ma) age. Taking into consideration the previously obtained data, we propose a new development scheme of Paleozoic granitoid magmatism in Northern Kazakhstan, which includes Late Ordovician granite–granodiorite (Zerenda and Krykkuduk), Early Silurian granite–leucogranite (Borovoe and Karabulak), Late Silurian granosyenites–granite (Aralaul), and Early Devonian (Balkashino and Orlinogorsk) complexes.     

Estimation of uncertainties in eigenspectral estimates from decaying geophysical time series

Summary. The response of many dynamical systems to an impulse is a linear combination of decaying cosines. The frequencies of the cosines have generally been estimated in geophysics by periodogram analysis and little formal indication of uncertainty has been provided. This work presents an estimation procedure by the methods of complex demodulation and nonlinear regression that specifically incorporates in the basic model the decaying aspect of the cosines (periodogram analysis does not). The use of plots of the instantaneous phase as a function of time is shown to greatly enhance resolution. Expressions for the variances of eigenfrequencies, amplitudes, phases and damping constants Q are derived by non-linear least-squares. The results are illustrated, for the problem of the free oscillations of the Earth, by computations with the record made at Trieste of the Chilean earthquake of 1960 May 22. Sample values are periods and standard errors of 737.79 ± 0.13 s, 506.25 ± 0.13 s and 429.60 ± 0.14 s for ₀ T ₈, ₀ T ₁₃ and ₀ T ₁₆ with Q values and standard errors of 200 ± 14, 230 ± 28 and 215 ± 30, respectively.     

Crystal features of supergene gold at Hannan South,Western Australia

Deep weathering of basalt-hosted sulphidic gold mineralisation has resulted in remobilisation of the gold and the formation of a supergene deposit. The deposit occurs beneath an ephemeral lake system and is at least partially saturated by highly saline groundwater. A general downward movement of an iron redox front associated with the weathering has controlled the distribution of the gold and its morphology. It is unusual in that the high fineness gold crystals formed are coarse and well-preserved. Small octahedra, up to 50 μm, are the most abundant form of gold crystals but large, up to 3 mm, octahedral plates are common. Crystal morphology variations described here suggest that the gold is initially precipitated as euhedral octahedra and plates. Subsequent dissolution and recrystallisation associated with fluctuations in the chemical environment above the redox front has led to the development of the more common irregular dendritic or wire gold forms observed in other supergene deposits.     

Characterization of groundwater chemistry under the influence of lithologic and anthropogenic factors along a climatic gradient in Upper Cauvery basin, South India

Hydrogeological and climatic effect on chemical behavior of groundwater along a climatic gradient is studied along a river basin. ‘Semi-arid’ (500–800 mm of mean annual rainfall), ‘sub-humid’ (800–1,200 mm/year) and ‘humid’ (1,200–1,500 mm/year) are the climatic zones chosen along the granito-gneissic plains of Kabini basin in South India for the present analysis. Data on groundwater chemistry is initially checked for its quality using NICB ratio (<±5 %), EC versus TZ+ (~0.85 correlation), EC versus TDS and EC versus TH analysis. Groundwater in the three climatic zones is ‘hard’ to ‘very hard’ in terms of Ca–Mg hardness. Polluted wells are identified (>40 % of pollution) and eliminated for the characterization. Piper’s diagram with mean concentrations indicates the evolution of CaNaHCO₃ (semi-arid) from CaHCO₃ (humid zone) along the climatic gradient. Carbonates dominate other anions and strong acids exceeded weak acids in the region. Mule Hole SEW, an experimental watershed in sub-humid zone, is characterized initially using hydrogeochemistry and is observed to be a replica of entire sub-humid zone (with 25 wells). Extension of the studies for the entire basin (120 wells) showed a chemical gradient along the climatic gradient with sub-humid zone bridging semi-arid and humid zones. Ca/Na molar ratio varies by more than 100 times from semi-arid to humid zones. Semi-arid zone is more silicaceous than sub-humid while humid zone is more carbonaceous (Ca/Cl ~14). Along the climatic gradient, groundwater is undersaturated (humid), saturated (sub-humid) and slightly supersaturated (semi-arid) with calcite and dolomite. Concentration–depth profiles are in support of the geological stratification i.e., ~18 m of saprolite and ~25 m of fracture rock with parent gneiss beneath. All the wells are classified into four groups based on groundwater fluctuations and further into ‘deep’ and ‘shallow’ based on the depth to groundwater. Higher the fluctuations, larger is its impact on groundwater chemistry. Actual seasonal patterns are identified using ‘recharge–discharge’ concept based on rainfall intensity instead of traditional monsoon–non-monsoon concept. Non-pumped wells have low Na/Cl and Ca/Cl ratios in recharge period than in discharge period (Dilution). Few other wells, which are subjected to pumping, still exhibit dilution chemistry though water level fluctuations are high due to annual recharge. Other wells which do not receive sufficient rainfall and are constantly pumped showed high concentrations in recharge period rather than in discharge period (Anti-dilution). In summary, recharge–discharge concept demarcates the pumped wells from natural deep wells thus, characterizing the basin.     

Statistical characteristics of polar lows over the Nordic Seas based on satellite passive microwave data

Izvestiya, Atmospheric and Oceanic Physics - In this study polar lows over the Nordic Seas for the period of 1995–2008 have been detected and studied using the Special Sensor Microwave Imager...     

Micromechanical approach to effective viscoelastic properties of micro‐fractured geomaterials

The aim of this paper is to formulate a micromechanics‐based approach to non‐aging viscoelastic behavior of materials with randomly distributed micro‐fractures. Unlike cracks, fractures are discontinuities that are able to transfer stresses and can therefore be regarded from a mechanical viewpoint as interfaces endowed with a specific behavior under normal and shear loading. Making use of the elastic‐viscoelastic correspondence principle together with a Mori‐Tanka homogenization scheme, the effective viscoelastic behavior is assessed from properties of the material constituents and damage parameters related to density and size of fractures. It is notably shown that the homogenized behavior thus formulated can be described in most cases by means of a generalized Maxwell rheological model. For practical implementation in structural analyses, an approximate model for the isotropic homogenized fractured medium is formulated within the class of Burger models. Although the approximation is basically developed for short‐term and long‐term behaviors, numerical applications indicate that the approximate Burger model accurately reproduce the homogenized viscoelastic behavior also in the transient conditions.     

Hydrodynamic and geochemical conditions of the formation of stratiform Zn-Pb ore mineralization by chloride solutions

Ore mineralization is formed by postsedimentary (concentrated by evaporation to stage SW2) chloride brines metamorphosed in hydrogeochemical systems that are closed with respect to CO₂, evolve according to “calcic” trend, and have high 2mCa²⁺ > mHCO ₃ ^? + 2mCO ₃ ^2? ratios. In these situations at high R/W ratios (10–100) and temperatures (100–200°C), these brines concentrate ore elements (Zn, Pb, Fe, and Mn) that are geochemical analogues of Ca. The sulfide precipitation of these elements occurs under the effect of carbonate rocks at the abiogenic sulfate reduction of S(VI) of the original brines at low Eh values, which are created in carbonate rocks at higher (>100°C) temperatures. This origin of sulfide mineralization is intensified at decreasing R/W ratios during the dilution of the original brines by elision waters and an increase in the temperature. The hydrodynamics of these ore-forming brines is controlled by the elision hydrogeological regime, which is defined in hydrogeological structures by the geostatic pressure. The brines migrate into the zones of geochemical barriers during the relaxation of hydrogeological structures toward their equilibrium hydrostatic state. Hydrogeological structures, optimal for the precipitation of ore mineralization, are hydrodynamically active and able to maintain a steady (during 10⁵-10⁶ years) inflow of ore-forming brines into the zones of geochemical barriers and the maximum number of water-exchange cycles at these barriers. Modern analogues of these structures are miogeosyncline foredeeps with Cl-Na-Ca chloride brines with high concentrations of ore elements and overall flow rates ranging from 0.n to n m³/year. Stagnate hydrogeological platform structures in hydrostatic equilibrium cannot ensure water exchange needed for ore formation, and, hence, the brines of these structures are not able to deposit the ore elements contained in them, in spite of the high concentrations of these elements.