Effect of selection and sequencing of representative wave conditions on process-based predictions of equilibrium embayed beach morphology     

Christopher J. Daly  Karin R. Bryan  Mauricio R. Gonzalez  Antonio H. F. Klein  Christian Winter 《Ocean Dynamics》2014,64(6):863-877

In order to decrease the simulation time of morphodynamic models, often-complex wave climates are reduced to a few representative wave conditions (RWC). When applied to embayed beaches, a test of whether a reduced wave climate is representative or not is to see whether it can recreate the observed equilibrium (long-term averaged) bathymetry of the bay. In this study, the wave climate experienced at Milagro Beach, Tarragona, Spain was discretized into ‘average’ and ‘extreme’ RWCs. Process-based morphodynamic simulations were sequenced and merged based on ‘persistent’ and ‘transient’ forcing conditions, the results of which were used to estimate the equilibrium bathymetry of the bay. Results show that the effect of extreme wave events appeared to have less influence on the equilibrium of the bay compared to average conditions of longer overall duration. Additionally, the persistent seasonal variation of the wave climate produces pronounced beach rotation and tends to accumulate sediment at the extremities of the beach, rather than in the central sections. It is, therefore, important to account for directional variability and persistence in the selection and sequencing of representative wave conditions as is it essential for accurately balancing the effects beach rotation events.  相似文献   

Methods for estimating the velocities of the Brazil Current in the pre-salt reservoir area off southeast Brazil (23∘ S–26∘ S)     

Tiago Carrilho Biló  Ilson Carlos Almeida da Silveira  Wellington Ceccopieri Belo  Belmiro Mendes de Castro  Alberto Ricardo Piola 《Ocean Dynamics》2014,64(10):1431-1446

The Brazil Current (BC) is likely the least observed and investigated subtropical western boundary current in the world. This study proposes a simple and systematic methodology to estimate quasi-synoptic cross-sectional speeds of the BC within the Santos Basin (23^° S–26^° S) based on the dynamic method using several combinations of data: Conductivity, temperature, and depth (CTD), temperature profiles, CTD and vessel-mounted Acoustic Doppler Current Profiler (VMADCP), and temperature profiles and VMADCP. All of the geostrophic estimates agree well with lowered Acoustic Doppler Current Profiler (LADCP) velocity observations and yield volume transports of -5.56 ±1.31 and 2.50 ±1.01 Sv for the BC and the Intermediate Western Boundary Current (IWBC), respectively. The LADCP data revealed that the BC flows southwestward and is ～100 km wide, 500 m deep, and has a volume transport of approximately -5.75 ±1.53 Sv and a maximum speed of 0.59 m s^?1. Underneath the BC, the IWBC flows northeastward and has a vertical extent of approximately 1,300 m, a width of ～60 km, a maximum velocity of ～0.22 m s?¹, and a volume transport of 4.11 ± 2.01 Sv. Our analysis indicates that in the absence of the observed velocities, the isopycnal (σ ₀) of 26.82 kg m^?3 (～500 dbar) is an adequate level of no motion for use in geostrophic calculations. Additionally, a simple linear relationship between the temperature and the specific volume anomaly can be used for a reliable first estimate of the BC-IWBC system in temperature-only transects.  相似文献   

Coastal vulnerability assessment based on video wave run-up observations at a mesotidal,steep-sloped beach     

Michalis Ioannis Vousdoukas  Dagmara Wziatek  Luis Pedro Almeida 《Ocean Dynamics》2012,62(1):123-137

Coastal imagery obtained from a coastal video monitoring station installed at Faro Beach, S. Portugal, was combined with topographic data from 40 surveys to generate a total of 456 timestack images. The timestack images were processed in an open-access, freely available graphical user interface (GUI) software, developed to extract and process time series of the cross-shore position of the swash extrema. The generated dataset of 2% wave run-up exceedence values R ₂ was used to form empirical formulas, using as input typical hydrodynamic and coastal morphological parameters, generating a best-fit case RMS error of 0.39 m. The R ₂ prediction capacity was improved when the shore-normal wind speed component and/or the tidal elevation η _tide were included in the parameterizations, further reducing the RMS errors to 0.364 m. Introducing the tidal level appeared to allow a more accurate representation of the increased wave energy dissipation during low tides, while the negative trend between R ₂ and the shore-normal wind speed component is probably related to the wind effect on wave breaking. The ratio of the infragravity-to-incident frequency energy contributions to the total swash spectra was in general lower than the ones reported in the literature E _infra/E _inci > 0.8, since low-frequency contributions at the steep, reflective Faro Beach become more significant mainly during storm conditions. An additional parameterization for the total run-up elevation was derived considering only 222 measurements for which η _total,2 exceeded 2 m above MSL and the best-fit case resulted in RMS error of 0.41 m. The equation was applied to predict overwash along Faro Beach for four extreme storm scenarios and the predicted overwash beach sections, corresponded to a percentage of the total length ranging from 36% to 75%.  相似文献   

Sediments Quality Assessment of Jacarepaguá Lagoon: The Venue of the 2011 Rock in Rio     

José Tavares Araruna Júnior  Paula Elias Benedetti  Patrício José Moreira Pires  Ricardo Froitzheim Rinelli de Almeida 《洁净——土壤、空气、水》2012,40(9):906-910

In order to aid in the efforts of the 2016 Olympic Games, the organizers of 2011 Rock in Rio decided to build a permanent venue next to the Olympic Park. The area is problematic from the geotechnical point of view since it presents soils with low shear strength, low permeability, and high plasticity, so major soil improvement works were carried out. Bored soil–cement columns were placed to increase soil shear strength and reduce compressibility. A meter thick fill composed of gneiss residual soil was placed and trenches were digged to drain rainwater. However, earlier studies conducted on Jacarepaguá Lagoon have detected the presence of heavy metals in these sediments. In this study, an environmental survey on the Jacarepaguá Lagoon sediments took place in order to choose a place where its sediments could be dredged to be later used in the drainage facilities. The results indicated areas where the threshold level 1 (low probability of adverse effects) issued by the general procedures for sediments quality assessments for dredging purposes, Resolution no 344 of the Brazilian Federal Government, was surpassed. Levels above the limits established for cadmium (Cd), lead (Pb), copper (Cu), nickel (Ni), and zinc (Zn) were detected. Based on this consideration the State Environmental Agency issued a permit allowing the organizers of 2011 Rock in Rio to dredge an area close to City of Rock in order to obtain coarse sediments for the drainage facilities. In addition, it was found that those sediments were ideal for this application since their hydraulic conductivity is on the order of 10^?2 cm/s.  相似文献   

Strong ground-motion relations for Mexican interplate earthquakes     

Danny Arroyo  Daniel García  Mario Ordaz  Mauricio Alexander Mora  Shri Krishna Singh 《Journal of Seismology》2010,14(4):769-785

We derive strong ground-motion relations for horizontal components of pseudo-acceleration response spectra from Mexican interplate earthquakes at rock sites (NEHRP B class) in the forearc region. The functional form is obtained from the analytical solution of a circular finite-source model. For the regression analysis we use a recently proposed multivariate Bayesian technique. The resulting model has similar accuracy as those models derived from regional and worldwide subduction-zone databases. However, there are significant differences in the estimations computed from our model and other models. First, our results reveal that attenuation in Mexico tends to be stronger than that of worldwide relations, especially for large events. Second, our model predicts ground motions for large earthquakes at close distances to the source that are considerably larger than the estimations of global models. Lack of data in this range makes it difficult to identify the most appropriate model for this scenario. Nevertheless, according to the available data at the city of Acapulco, our model seems to estimate seismic hazard more adequately than the other models. These new relations may be useful in computing seismic hazard for the Mexican forearc region, where no similar equations had been yet proposed.  相似文献   

An assessment of the Brazil Current baroclinic structure and variability near 22° S in Distinct Ocean Forecasting and Analysis Systems   总被引：1，自引：1，他引：0  

Mateus O. Lima  Mauro Cirano  Mauricio M. Mata  Marlos Goes  Gustavo Goni  Molly Baringer 《Ocean Dynamics》2016,66(6-7):893-916

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Unfolding relations between land cover and farm management: high nature value assessment in complex silvo-pastoral systems     

Mara Almeida  Carlos Guerra  Teresa Pinto-Correia 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(2):97-108

The high nature value (HNV) concept, proposed by the European Environment Agency, recognizes that specific farming systems support high biodiversity levels, mainly as a result of extensive management practices. The Portuguese montado is one of the most significant HNV systems in southern Europe. However, considering the great complexity characterizing these systems both in land management and in landscape structure, a specific context-oriented methodology to assess which montado areas are likely to be classified as HNV farmland is needed. In this sense, the aim of this study is to explore a methodological approach which makes it possible to assess land management pressures through land cover information on these complex silvo-pastoral systems. The proposed methodology was tested through a local case study in a montado area in southern Portugal, assessing the relation between management practices and a vegetation cover index. Results show that in similar montado areas different land management strategies varying in stocking density, but also in type of grazing animals and shrub control practices, configure different vegetation cycles. These results indicate there is a way to develop a straightforward methodology to assess the HNV value of Mediterranean silvo-pastoral systems based on land cover indicators. These would make it possible to assess the HNV of montado areas with direct and objective information and independent of farmer’s surveys or other farm-based data.  相似文献   

Social change and land tenure regimes in Mexico     

Mauricio Herrera Rodriguez 《GeoJournal》2012,77(5):633-649

This paper argues that the changing land tenure legislation in Mexico is a concrete reflection of generalized societal attitudes towards indigenous and traditional peasants. It contends that the 1992 neoliberal land-reform mimics the progress-oriented liberal project of the ninettenth century and continues a market-centered modernization process underway since the 1940s, which has been legitimized by an overt institutional disdain and discrimination against indigenous people, peasants and their ways of life. It concludes that this process of assimilation or eradication of traditional agro-ecosystems, cultural diversity and social organization will further increase the vulnerability of Mexican peasants to economic and cultural change. As peasants engage in market-controlled business ventures in the rural areas, migrate to cities, rent or sell their lands, they simultaneously adapt to new values and envision new strategies for subsistence that are increasingly mediated by political-economic forces largely beyond their sphere of influence.  相似文献   

Integrated provenance analysis of a convergent retroarc foreland system: U–Pb ages,heavy minerals,Nd isotopes,and sandstone compositions of the Middle Magdalena Valley basin,northern Andes,Colombia     

Junsheng Nie  Brian K. Horton  Joel E. Saylor  Andrés Mora  Maria Mange  Carmala N. Garzione  Asish Basu  Christopher J. Moreno  Victor Caballero  Mauricio Parra 《Earth》2012,110(1-4):111-126

Sediment provenance analysis remains a powerful method for testing hypotheses on the temporal and spatial evolution of uplifted source regions, but issues such as recycling, nonunique sources, and pre- and post-depositional modifications may complicate interpretation of results from individual provenance techniques. Convergent retroarc systems commonly contain sediment sources that are sufficiently diverse (continental magmatic arc, fold–thrust belt, and stable craton) to enable explicit provenance assessments. In this paper, we combine detrital zircon U–Pb geochronology, heavy mineral identification, Nd isotopic analyses, conventional sandstone petrography, and paleocurrent measurements to reconstruct the clastic provenance history of a long-lived sedimentary basin now exposed in an intermontane zone of the northern Andean hinterland of Colombia. The Middle Magdalena Valley basin, situated between the Central Cordillera and Eastern Cordillera, contains a 5–10 km-thick succession of Upper Cretaceous to Quaternary fill. The integrated techniques show a pronounced change in provenance during the Paleocene transition from the lower to upper Lisama Formation. We interpret this as a shift from an eastern cratonic source to a western Andean source composed of magmatic-arc rocks uplifted during initial shortening of the Central Cordillera. The appearance of detrital chloritoid and a shift to more negative ε_Nd(t=0) values in middle Eocene strata of the middle La Paz Formation are attributed to shortening-related exhumation of a continental basement block (La Cira–Infantas paleohigh), now buried, along the axis of the Magdalena Valley. The diverse provenance proxies also show distinct changes during middle to late Eocene deposition of the Esmeraldas Formation that likely reflect initial rock uplift and exhumation of the fold–thrust belt defining the Eastern Cordillera. Upsection, detrital zircon U–Pb ages and heavy mineral assemblages for Oligocene and younger clastic deposits indicate that the Mesozoic sedimentary cover of the Eastern Cordillera was recycled during continued Cenozoic shortening. Our multidisciplinary provenance study refines the tectonic history of the Colombian Andes and demonstrates that uncertainties related to sediment recycling, nonunique sources, source heterogeneity, and climate in interpreting provenance data can be minimized via an integrated approach.  相似文献   

Sources and behavior of arsenic and trace elements in groundwater and surface water in the Poopó Lake Basin,Bolivian Altiplano     

Oswaldo Eduardo Ramos Ramos  Luis Fernando Cáceres  Mauricio Rodolfo Ormachea Muñoz  Prosun Bhattacharya  Israel Quino  Jorge Quintanilla  Ondra Sracek  Roger Thunvik  Jochen Bundschuh  Maria Eugenia García 《Environmental Earth Sciences》2012,66(3):793-807

Water management in semiarid and arid catchments such as the Poopó Lake Basin requires improved understanding of the complex behavior of the various contaminants, which affect the drinking water quality and considered as crucial for sustainable development of the region. Mechanisms of arsenic (As) release in the surface and groundwater were studied. Hydrochemical data for surface water (4 samples) and groundwater (28 samples) were collected in a small watershed in the Poopó catchment at the highland of the Bolivian Andes (Altiplano). All of them show high electrical conductivity values and moderately oxidizing conditions. The surface water contains high concentration of sulfate and the trace elements As, Zn and Pb in the zone affected by acid mine drainage. There is a large variability of the concentration of As and of the trace elements in the groundwater in the five different regions within the Poopó catchment. The metal concentrations sensitive to changes of redox state and results of speciation modeling suggest that As (V) is a predominant aqueous species, which conforms to the prevailing oxidizing conditions in the shallow groundwater environment. Two generalized trends for As distribution were identified in groundwater: (a) high concentrations are found in the arid zone (100–250 μg/L) in the southern (region III) and in the northwestern (region V) regions, and (b) low concentrations (<50 μg/L) are found in the remaining part of the basin (region I, II and IV). However, the spatial distribution within these regions needs to be investigated further. A conclusion from the present study is that there are multiple sources of As as well as other trace elements (such as Cd, Mn and Zn) in the Poopó Lake Basin. Among the sources and the processes which led to the mobility of As and other trace metals in the region are: (a) weathering of sulfide minerals, (b) oxidation of pyrite and/or arsenopyrite in mineralized areas and (c) desorption from hydrous ferric oxide (HFO) surfaces. In non-mining areas, volcanic ash is suggested to be a significant source of As.  相似文献