Macrobenthic associations in a South Atlantic Brazilian enclosed bay: the historical influence of shrimp trawling

This study characterized the macrobenthos of Tijucas Bay and related the distribution and dominance patterns with historical trawling activities. Fifteen sampling sites were established in the bay and were sampled in summer and winter for the characterization of the macrobenthos. To evaluate the trawling effects, three passages were established at each site with control and impacted areas analyzed before and after trawl-net action in impacted area. Seasonal differences occurred in macrobenthos, possibly influenced by rainfall where the relative water level of the Tijucas River was directly associated with the discharge of freshwater and particulate matter. The associations identified in the bay were distinct in comparison with the Zimbros Embayment. The trawling assessment showed no significant variation in the macrobenthos after the trawl, possibly due to decades of shrimp exploitation in the bay. Trawling and instable environmental conditions inside the bay make the establishment of a stable macrobenthic community difficult.     

Consolidation and deformation around stone columns: Numerical evaluation of analytical solutions

Coupled finite element analyses of the consolidation and deformation around stone columns have been performed to assess the accuracy of different analytical solutions. The numerical model reproduces the hypotheses of the closed-form solutions. In the model, a rigid load is applied to a unit cell formed by a fully penetrating column and its surrounding soil, and simple elastic or elasto-plastic soil models are used. The surface settlement, the dissipation of the pore pressure and the vertical stress concentration on the column are studied. These soil responses are accurately estimated with closed-form solutions that properly include the radial and plastic strains in the column. However, the surrounding soil does not yield for usual conditions, which reasonably justifies the elastic soil behavior assumed in the analytical solutions. The differences between drained and consolidation analyses are also evaluated. Comparing the numerical results with the closed-form solutions illustrates the implications of the assumptions of each approach.     

Risk perception and evacuation decisions of Florida tourists under hurricane threats: a stated preference analysis

Though most hurricane evacuation studies have focused on residents, tourists are also a vulnerable population. To assess their perceptions of risk and evacuation likelihood under different hurricane conditions, we surveyed 448 tourists visiting central Florida. Respondents viewed four maps emulating track forecast cones produced by the National Hurricane Center and text information featuring variations of storm intensity, coast of landfall, centerline position relative to the survey site, time until landfall, and event duration. We performed chi-square tests to determine which hurricane conditions, and aspects of tourists such as their demographics and previous hurricane experience, most likely influenced their ratings of risk and evacuation likelihood for respondents located on Pinellas County beaches or inland near Orlando, FL. Highly rated scenarios featured a Category 4 hurricane making landfall along the Gulf Coast with the centerline passing over the sampling site. Overall, tourists that indicated the highest risk and evacuation ratings were not previously affected by a hurricane, had a trip duration of less than 6 days, and had checked for the possibility of a hurricane strike before departure. However, results for other tourist attributes differed between tourists in coastal and inland locations. We found that although somewhat knowledgeable about hurricanes, tourists misinterpreted the track forecast cone and hurricane conditions, which led to a lower perception of risk and subsequent likelihood to evacuate. Tourists, particularly those from outside of Florida, need to be better educated about the risks they face from hurricanes that make landfall.     

Influence of sieving time on the efficiency and accuracy of grain‐size analysis of beach and dune sands

Grain size is a fundamental property of sediments and is commonly used to describe sedimentary facies and classify sedimentary environments. Among the various conventional techniques utilized to determine grain‐size frequency distributions, sieving is the most widely applied procedure. The accuracy of such analyses is, among other factors, strongly dependent on the sieving time. However, despite a substantial amount of research in this field, optimal sieving times for different types of sediments have, to date, not been established. In this article, the influence of sieving time on grain‐size analyses of medium‐grained microtidal and mesotidal beach and dune sands has been determined. To assess the precision of important textural parameters, such as median grain size, sorting, skewness and kurtosis, an error analysis was carried out for different sieving times (2, 5, 10, 15 and 20 minutes). After calibrating the analytical and sampling methodologies, significant deviations were registered when sieving time was less than 10 minutes. However, such deviations were very small and grain‐size distributions remained almost identical for sieving times of 10 minutes and longer, relative errors being as low as 0% in some cases.     

Les flux de matières dissoutes et particulaires exportés des Andes par le Rio Béni (Amazonie Bolivienne), en période de crue

Résumén

Le Rio Béni est l’un des principaux formateurs andins du Rio Madeira, le plus important des affluents méridionaux de l’Amazone. La station hydrométrique de “Angosto del Bala” sur le Rio Béni contrôle un bassin andin de 67500 km², aux caractéristiques géomorpho-climatiques très contrastées.

Afin de connaître l’évolution temporelle des teneurs relatives des éléments des phases dissoutes et particulaires, un suivi hydrologique et hydrogéochimique a été réalisé à cette station en mars 1988, période de hautes eaux où une crue de fréquence annuelle a été observée. Les résultats obtenus montrent l’existence d’une grande variabilité temporelle des concentrations, mais présentant un cortège hydrogéochimique stable au cours de la crue.

Enfin, l’importance quantitative de cette période de hautes eaux sur le bilan moyen annuel des flux exportés est souligné.     

Assessing the impact of future climate change on groundwater recharge in Galicia-Costa, Spain

Climate change can impact the hydrological processes of a watershed and may result in problems with future water supply for large sections of the population. Results from the FP5 PRUDENCE project suggest significant changes in temperature and precipitation over Europe. In this study, the Soil and Water Assessment Tool (SWAT) model was used to assess the potential impacts of climate change on groundwater recharge in the hydrological district of Galicia-Costa, Spain. Climate projections from two general circulation models and eight different regional climate models were used for the assessment and two climate-change scenarios were evaluated. Calibration and validation of the model were performed using a daily time-step in four representative catchments in the district. The effects on modeled mean annual groundwater recharge are small, partly due to the greater stomatal efficiency of plants in response to increased CO₂ concentration. However, climate change strongly influences the temporal variability of modeled groundwater recharge. Recharge may concentrate in the winter season and dramatically decrease in the summer–autumn season. As a result, the dry-season duration may be increased on average by almost 30 % for the A2 emission scenario, exacerbating the current problems in water supply.     

Facies Recognition Using Multifractal Hurst Analysis: Applications to Well-Log Data

Well-log (radioactivity, density and resistivity) analysis constitutes a standard approach for inferring lithology from wells. However, due to inherent complexity of the signals (such as highly heterogeneous deep-water sedimentary sequences) lithology recognition is not straightforward. We used a rescaled range analysis, calibrated with cores, to recognize lithological patterns from signal recorded along wireline logs. The detected intervals coincide with zones of visual electro-facies associations proposed by geologist well-log interpreters. In addition, we propose a rescaled range multifractal analysis to identify ranges of well-log signal complexities, which could be related to sedimentary process variations at specific stratigraphic order cycles.     

Comments on “Confirmation of beach accretion by grain-size trend analysis: Camposoto beach, Cádiz, SW Spain” by E. Poizot et al. (2013) Geo-Marine Letters 33(4)

This Discussion provides comments on the application of grain-size trend analysis to Camposoto beach (SW Spain) reported by Poizot et al. (2013) in Geo-Marine Letters 33(4):263–272. Some of their results are updated or complemented by existing data from other studies carried out on Camposoto and other nearby beaches. For example, a detailed breakdown of beach nourishment volumes and costs is presented, and the influence of a horizontal reef flat on the tilting of the beach profile around the mean or the low water level is highlighted. Moreover, data from the displacement of dyed samples are used to evaluate the relationship between sediment transport speed (v_a) and current speed (V), the corresponding ratio being consistent with the range of values reported by several other authors. Finally, some minor, although still significant, differences are detected in some granulometric parameters as well as in the profile shape. Determining the reason for these discrepancies could enhance our current knowledge about the factors controlling short-term beach profile responses.     

Numerical study on the effect of submerged depth on the horizontal plate wave energy converter

The growing search for clean and renewable energy sources has given rise to the studies of exploring sea wave energy. This paper is concerned with the numerical evaluation of the main operational principle of a submerged plate employed for the conversion of wave energy into electrical one. The numerical model used to solve the conservation equations of mass, momentum and transport of volume fraction is based on the finite volume method （FVM）. In order to tackle with the flow of mixture of air-water and its interaction with the device, the multiphase model volume of fluid （VOF） is employed. The purpose of this study is the evaluation of a numerical model for improvement of the knowledge about the submerged plate wave energy converter, as well as the investigation of the effect of the distance from the plate to the bottom of the sea （HP） on the performance of the converter. The simulations for several distances of the plate from the seabed show that the optimal efficiency is 64%, which is obtained for HP=0.53 m （88% of the depth）. This efficiency is 17% larger than that found in the worst case （HP=0.46 m, 77% of the depth）.     

Response surfaces of vulnerability to climate change: the Colorado River Basin,the High Plains,and California

We quantify the vulnerability of water supply to shortage for the Colorado River Basin and basins of the High Plains and California and assess the sensitivity of their water supply system to future changes in the statistical variability of supply and demand. We do so for current conditions and future socio-economic scenarios within a probabilistic framework that incorporates the inherent uncertainties in the drivers of vulnerability. Our analysis indicates that the most sensitive basins to both current and future variability of demand and supply are the Central California and the San Joaquin-Tulare basins. Large sensitivity is also found for the Kansas basin of the High Plains. Within the Colorado River Basin, the Lower Colorado and Gila were found to be the most vulnerable and sensitive sub-basins. By accounting for future uncertainty within the above probabilistic framework, this study unveils and isolates the individual responses of a given basin to changes in the statistical properties of demand and supply and offers a valuable tool for the identification of policy strategies and adaptation measures.