Coastal Placer Deposits of Central Tamil Nadu, India     

N. Angusamy  J. Dajkumar Sahayam  M. Suresh Gandhi  G. Victor Rajamanickam 《Marine Georesources & Geotechnology》2005,23(3):137-174

Placer mineral exploration has been undertaken along the beach of Central Tamil Nadu coast from Pondicherry to Vedaranyam. On the basis of the drainage network, geomorphology, and the coastal environment, the study area has been grouped into three sectors, North, Central, and South. Heavy mineral by Wt% shows a slightly higher abundance in the Northern sector, an enrichment of opaques in the Central sector from stations between Poompuhar and Karaikal, and a total depletion in the Southern sector. An abundance of heavies in the Northern sector is considered to be the result of a higher wave energy, and the cymatogenic downwarping of the basin during the present transgression. An enrichment of heavies in the Central sector from Poompuhar to Karaikal is attributable to the reworking of the beach ridges, which were submerged during the present transgression, and to the role of density sorting. A depletion of heavies in the Southern sector is accounted for by the absence of a terrigenous supply and the prevalence of wave shadow conditions throughout the year. The nature of the heavy mineral assemblage reflects the derivation of sediments principally from khondalites, granites, metamorphic rocks and paleo-sediments. Factor analysis also supplements the predominant role of a density factor in the segregation of heavy minerals in the study area. A five-stage model is proposed for the formation of placer deposits in the study region. The present study has disclosed rich concentrations of ilmenites in the central sector between Poompuhar and Karaikal that can be commercially exploited.  相似文献   

The Beach Environment in Mexico as a Potential Source of Placer Minerals     

Mayumy Cabrera-Ramirez  Arturo Carranza-Edwards 《Marine Georesources & Geotechnology》2002,20(3):187-198

The potential of Mexico for placer minerals in beach sediments has been analyzed, taking into consideration the geomorphic, tectonic, and lithologic conditions of nine different coastal regions. Besides, the textural characteristics of average size and degree of classification, carbonate content was also considered as a measure of terrigenous influence. It is concluded that mineral bearing rocks in the source area, and well-classified fine sands, poor in carbonates, in the beach area represent the major potential for placer minerals. Favorable conditions for placer minerals may be present in Regions 2 and 3 in the Central and Southern portion of the Gulf of Mexico coast, and have their highest potential in Regions 6, 7, 8, and 9 in the Gulf of California and along the Western mainland coast from the Colorado River in the North to the Guatamalan border in the South.  相似文献   

岬间海滩剖面短期变化的动力作用分析   总被引：4，自引：0，他引：4  

戴志军  陈子燊  李春初 《海洋科学》2001,25(11):38-41

根据粤东寮嘴口岬间海滩重复测量的剖面数据及实测波，风资料，运用交叉谱等方法分析了寮河口海滩剖面短期变化过程的主要动力作用，结果表明海滩短期的变化过程主要是响应风应力，波浪及台风大浪动力的作用。  相似文献   

弧形海岸中间过渡带海滩剖面的地貌动态分析   总被引：1，自引：0，他引：1  

陈子燊  李春初 《海洋科学》1990,14(2):6-12

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Even–odd analysis on a complex shoreline     

Todd L. Walton  Jr 《Ocean Engineering》2002,29(6):711-719

An even–odd signal decomposition is performed on a complex shoreline having a longshore sediment transport gradient. The expected impact of erosion due to a navigation channel and structures is discussed and implications of the transport gradient on the decomposed shoreline signal are noted.  相似文献   

Multidirectional wave transformation around detached breakwaters     

S. Ilic  A.J. van der Westhuysen  J.A. Roelvink  A.J. Chadwick 《Coastal Engineering》2007

The performance of the new wave diffraction feature of the shallow-water spectral model SWAN, particularly its ability to predict the multidirectional wave transformation around shore-parallel emerged breakwaters is examined using laboratory and field data. Comparison between model predictions and field measurements of directional spectra was used to identify the importance of various wave transformation processes in the evolution of the directional wave field. First, the model was evaluated against laboratory measurements of diffracted multidirectional waves around a breakwater shoulder. Excellent agreement between the model predictions and measurements was found for broad frequency and directional spectra. The performance of the model worsened with decreasing frequency and directional spread. Next, the performance of the model with regard to diffraction–refraction was assessed for directional wave spectra around detached breakwaters. Seven different field cases were considered: three wind–sea spectra with broad frequency and directional distributions, each coming from a different direction; two swell–sea bimodal spectra; and two swell spectra with narrow frequency and directional distributions. The new diffraction functionality in SWAN improved the prediction of wave heights around shore-parallel breakwaters. Processes such as beach reflection and wave transmission through breakwaters seem to have a significant role on transformation of swell waves behind the breakwaters. Bottom friction and wave–current interactions were less important, while the difference in frequency and directional distribution might be associated with seiching.  相似文献   

Application of empirical models to bay-shaped beaches in Portugal     

Filipa S.B.F. Oliveira  Olalla M. Barreiro 《Coastal Engineering》2010

Three models were applied to analyse the planform of bay-shaped Portuguese beaches. They are based on empirical mathematical functions: the logarithmic spiral bay equation, the hyperbolic-tangent bay equation, and the parabolic bay equation. These models were applied to analyse the fitting to the beach planform of 42 beaches on the Portuguese Atlantic coast which was calculated through the validation against the waterline extracted from rectified aerial photographs. The logarithmic spiral model fits well the curved zone of the beaches, in particular small beaches with two headlands. Despite the good fitting of the hyperbolic-tangent model for one headland beach, its process of approximation to the solution was less intuitive than the processes of the other two models, therefore its application was more exhaustive. A comparative analysis between the logarithmic spiral model and the hyperbolic-tangent model revealed the best fit of the first. The application of the parabolic model allowed to conclude that despite the majority of the beaches analysed being in dynamic equilibrium condition due to the high energy wave regime of the Portuguese Atlantic coast, their planform was very close to the planform in static equilibrium condition due to the high dynamics of the coastal environment.  相似文献   

Statistical simulation of wave climate and extreme beach erosion     

D.P. Callaghan  P. Nielsen  A. Short  R. Ranasinghe 《Coastal Engineering》2008

Recent developments in extreme values modelling have been used to develop a framework for determining the coastal erosion hazard on sandy coastlines. This framework quantitatively reproduced the extreme beach erosion volumes obtained from field measurements at Narrabeen Beach, Australia. This encouraging finding was achieved using Kriebel and Dean's [Kriebel, D.L. and Dean, R.G., 1993. Convolution method for time-dependent beach profile response. Journal of Waterway, Port, Coastal and Ocean Engineering, 119(2): 204–226.] simple beach erosion and accretion model. The method includes allowances for joint probability between all basic erosion variates including; wave height, period and direction, event duration, tidal anomalies and event spacing. A new formulation for the dependency between wave height and period has been developed. It includes the physical wave steepness limitation. Event grouping, where significantly more erosion can occur from two closely spaced storms is handled by temporally simulating the synthetic wave climate and the resulting beach erosion and accretion.  相似文献   

On the design of beach nourishment projects using static equilibrium concepts: Application to the Spanish coast     

Mauricio González  Raul Medina  Miguel Losada 《Coastal Engineering》2010

The concept of equilibrium plan form and equilibrium profile has been widely used as an engineering tool in order to design beach nourishment projects. The scope of this paper is to further explore this “equilibrium beach” concept in crenulated bays, as a long-term tool for beach nourishment projects. The proposed methodology is based on González and Medina (2001) and combines the static equilibrium plan and profile for long-term analysis. This methodology includes a modified equilibrium plan form, which is able to define the orientation of the local wave front in the diffracting point, and also to locate the downcoast starting point of the static equilibrium beach from which the parabolic plan form of Hsu and Evans (1989) is valid. This methodology permits the application of any equilibrium profile formulation. An example of the application of this methodology and long-term formulations to the design of the Spanish nourishment project of Poniente Beach (Gijón) is presented. Ten years after its construction, the beach has still got a static equilibrium and remains pretty close to the predicted equilibrium beach in plan and profile.  相似文献   

Spatial Variations in Particle Size and Magnetite Concentration on Cedar Beach: Implications for Grain-Sorting Processes, Western Lake Erie, Canada   总被引：1，自引：0，他引：1  

ZHANG Shuwei  Maria T. CIOPPA  ZHANG Shihong 《《地质学报》英文版》2010,84(6):1520-1532

<正>This study examined spatial variations in the concentration,grain size and heavy mineral assemblages on Cedar Beach(Lake Erie,Canada).Magnetic studies of heavy mineral-enriched,dark-reddish sands present on the beach showed that magnetite(～150μm) is the dominant magnetic mineral.Surficial magnetic susceptibility values defined three zones:a lakeward region close to the water line(Zone 1),the upper swash zone(Zone 2) and the region landwards of the upper swash zone (Zone 3).Zone 2 showed the highest bulk and mass susceptibility(κ,χ) and the highest mass percentage of smaller grain-size(250μm) fractions in the bulk sand sample.Susceptibility(i.e.κandχ) values decreased and grain size coarsened from Zone 2 lakewards(into Zone 1) and landwards (into Zone 3),and correlated with the distribution of the heavy mineral assemblage,most probably reflecting preferential separation of large,less dense particles by waves and currents both along and across the beach.The eroded western section of Cedar Beach showed much higher concentrations of heavy minerals including magnetite,and finer sand grain sizes than the accreting eastern section, suggesting that magnetic techniques could be used as a rapid,cost-effective way of examining erosion along sensitive coastline areas.  相似文献