Application of grain size trend analysis for the determination of sediment transport pathways in intertidal areas

In this paper, we apply the Gao and Collins procedure of grain size trend analysis for the first time in an intertidal sedimentary system. Our purpose is to evaluate a reliable method to determine residual transport directions in intertidal environments, where sediment movement is not well understood. Residual transport patterns can be determined by grain size trend analysis if the following criteria are applied: (1) a single sediment transport unit must be precisely defined and investigated; (2) the thickness of sampling has to be chosen in order to investigate the most recent sedimentary event; and (3) a regular mesh grid is sampled to avoid bias in the calculation of grain size trends.The Gao and Collins method was undertaken simultaneously with a topographic survey and a tracer experiment, during consecutive meteorological conditions of fair weather and a storm event. The topographic changes observed between these two situations and the directions of sediment movement deduced from tracer tracking are coherent with the residual transport pattern calculated from the grain size trend analysis. The method was tested on a ridge and runnel system which corresponds to the intertidal part of a macrotidal beach, called La Salie beach, located along the southwest French coast, in a high wave energy environment. This study permits us to recognize two different residual transport patterns for this intertidal ridge and runnel system; one for fair weather and a second for storm conditions. During fair weather, specific sites are subject to sand accretion, while during storm conditions these sand stocks are subsequently spread out over the whole area, and remain partly on the beach

Comparative demography and diversity of small mammals in precordilleran temperate rainforests of Southern Chile

Small mammals were studied in two southern Chilean temperate rainforests in the precordillean Andes during 2 low-rainfall years following the 1982 El Niño event. Forests had somewhat different levels of canopy, shrub, and herbaceous cover, and species richness of trees but most of the same plants. Most captures were of four sigmodontine rodents, Akodon olivaceus, Abrothrix longipilis, Abrothrix sanborni, and Oligoryzomys longicaudatus; five other species and a putative hybrid were recorded. Maximum numbers were in January-July (late summer to winter) and lower numbers in August-December (late winter to early summer). All species had seasonal reproduction in September-April (spring to autumn). A. olivaceus and A. longipilis generally were long-lived, whereas survival rates were low for O. longicaudatus. Responses after the 1982 El Niño were small, and some populations increased during 1984. Populations of A. olivaceus fluctuated more than those of A. longipilis; those of A. sanborni were low and O. longicaudatus was sporadic and irruptive. Lower-elevational Chilean and precordilleran Argentine forests have similar species composition, but differences in demography and dominance of the former by more widespread, omnivorous A. olivaceus, animalivorous-fungivorous Abrothrix, and granivorous O. longicaudatus. Opportunities for immigration may explain greater homogeneity of populations of small mammals in Chilean rainforests relative to Argentine ones. Although responses to El Niño and subsequent droughts were weak, flowering episodes of bamboo (Chusquea) can have strong effects due to increased availability of food

Basic parameters of three star clusters in the Small Magellanic Cloud: Kron 11, Kron 63 and NGC 121

We present observations for three star clusters, Kron 11, Kron 63 and NGC 121, in the Small Magellanic Cloud. We have studied their structure and derived their fundamental parameters by means of their luminosity functions, their colour magnitude diagrams and the Padova suite of isochrones. NGC 121 is a well-studied object, for which we confirm previous evidence about its old age and low-metal content, and have found that it is an undergoing mass segregation. Kron 11 and Kron 63 are poorly populated clusters which had never been studied so far. Kron 11 is several gigayears younger than NGC 121, while Kron 63 is basically a very young star aggregate. Both clusters are immersed in dense stellar fields which share the same population properties, suggesting that in their cases, cluster ages are consistent with typical ages of field stars.Instituto de Astrofísica de La PlataFacultad de Ciencias Astronómicas y Geofísica

Basic parameters of three star clusters in the Small Magellanic Cloud: Kron 11, Kron 63 and NGC 121

We present observations for three star clusters, Kron 11, Kron 63 and NGC 121, in the Small Magellanic Cloud. We have studied their structure and derived their fundamental parameters by means of their luminosity functions, their colour magnitude diagrams and the Padova suite of isochrones. NGC 121 is a well-studied object, for which we confirm previous evidence about its old age and low-metal content, and have found that it is an undergoing mass segregation. Kron 11 and Kron 63 are poorly populated clusters which had never been studied so far. Kron 11 is several gigayears younger than NGC 121, while Kron 63 is basically a very young star aggregate. Both clusters are immersed in dense stellar fields which share the same population properties, suggesting that in their cases, cluster ages are consistent with typical ages of field stars.Instituto de Astrofísica de La PlataFacultad de Ciencias Astronómicas y Geofísica

A method to characterize the different extreme waves for islands exposed to various wave regimes: a case study devoted to Reunion Island

This paper outlines a new approach devoted to the analysis of extreme waves in presence of several wave regimes. It entails discriminating the different wave regimes from offshore wave data using classification algorithms, before conducting the extreme wave analysis for each regime separately. The concept is applied to the pilot site of Reunion Island which is affected by three main wave regimes: southern waves, trade-wind waves and cyclonic waves. Several extreme wave scenarios are determined for each regime, based on real historical cases (for cyclonic waves) and extreme value analysis (for non-cyclonic waves). For each scenario, the nearshore wave characteristics are modelled all around Reunion Island and the linear theory equations are used to back calculate the equivalent deep-water wave characteristics for each portion of the coast. The relative exposure of the coastline to the extreme waves of each regime is determined by comparing the equivalent deep-water wave characteristics. <br><br> This method provides a practical framework to perform an analysis of extremes within a complex environment presenting several sources of extreme waves. First, at a particular coastal location, it allows for inter-comparison between various kinds of extreme waves that are generated by different processes and that may occur at different periods of the year. Then, it enables us to analyse the alongshore variability in wave exposition, which is a good indicator of potential runup extreme values. For the case of Reunion Island, cyclonic waves are dominant offshore around the island, with equivalent deep-water wave heights up to 18 m for the northern part. Nevertheless, due to nearshore wave refraction, southern waves may become as energetic as cyclonic waves on the western part of the island and induce similar impacts in terms of runup and submersion. This method can be easily transposed to other case studies and can be adapted, depending on the data availability

Longshore sediment movements from tracers and models, Praia de Faro, South Portugal

This work aims to improve the knowledge of sediment circulation in the coastal zone, focusing on the quantification of sediment movement due to longshore drift. The studied field site is the Praia de Faro beach on the Peninsula do Ancão in Algarve (Portugal), which is located on the updrift coast of the Barra Nova tidal inlet. The main objective of the study was to quantify the sediment transport rate that will enter in the inlet system.Measurements were undertaken during low hydrodynamic conditions prevailing in this area and permitted to estimate a longshore transport rate of 2.6–4.2 m/s, consistent with other transport estimations in Algarve. Four theoretical models for longshore transport rate calculation were confronted to tracer results to choose a extrapolation tool. Kamphuis (1991) formula appeared to be the more appropriate in this area. It was used to extrapolate the results in order to be compared to the observed morphological evolution. The calculated short term sediment flux (10500 m3/month) corresponds to the accretion on the updrift swash platform of the Barra Nova tidal inlet and is thus considered to be the contribution of the adjacent coast to this system. Moreover, the estimated longshore transport rate permit us to predict a spit progradation of 60–70 m/year. This result is consistent with the observed migration rate of the Barra Nova inlet during the last 25 years. This study shows that, with a good knowledge of the environmental context, sediment fluxes obtained by sand tracers are accurate enough to estimate the long term longshore transport and long term morphological response of a stretch of shoreline

Integrated approach for coastal hazards and risks in Sri Lanka

The devastating impact of the tsunami of 26 December 2004 on the shores of the Indian Ocean recalled the importance of knowledge and the taking into account of coastal hazards. Sri Lanka was one of the countries most affected by this tsunami (e.g. 30 000 dead, 1 million people homeless and 70% of the fishing fleet destroyed). Following this tsunami, as part of the French post-tsunami aid, a project to establish a Geographical Information System (GIS) on coastal hazards and risks was funded. This project aims to define, at a pilot site, a methodology for multiple coastal hazards assessment that might be useful for the post-tsunami reconstruction and for development planning. This methodology could be applied to the whole coastline of Sri Lanka. <br><br> The multi-hazard approach deals with very different coastal processes in terms of dynamics as well as in terms of return period. The first elements of this study are presented here. We used a set of tools integrating a GIS, numerical simulations and risk scenario modelling. While this action occurred in response to the crisis caused by the tsunami, it was decided to integrate other coastal hazards into the study. Although less dramatic than the tsunami these remain responsible for loss of life and damage. Furthermore, the establishment of such a system could not ignore the longer-term effects of climate change on coastal hazards in Sri Lanka. <br><br> This GIS integrates the physical and demographic data available in Sri Lanka that is useful for assessing the coastal hazards and risks. In addition, these data have been used in numerical modelling of the waves generated during periods of monsoon as well as for the December 2004 tsunami. Risk scenarios have also been assessed for test areas and validated by field data acquired during the project. The results obtained from the models can be further integrated into the GIS and contribute to its enrichment and to help in better assessment and mitigation of these risks. <br><br> The coastal-hazards-and-risks GIS coupled with modelling thus appears to be a very useful tool that can constitute the skeleton of a coastal zone management system. Decision makers will be able to make informed choices with regards to hazards during reconstruction and urban planning projects

Basic parameters of three star clusters in the Small Magellanic Cloud: Kron 11, Kron 63 and NGC 121

We present observations for three star clusters, Kron 11, Kron 63 and NGC 121, in the Small Magellanic Cloud. We have studied their structure and derived their fundamental parameters by means of their luminosity functions, their color magnitude diagrams and the Padova suite of isochrones. NGC 121 is a well studied object, for which we confirm previous evidence about its old age and low metal content, and have found that it is undergoing mass segregation. Kron 11 and Kron 63 are poorly populated clusters which had never been studied so far. Kron 11 is several gigayears younger than NGC 121, while Kron 63 is basically a very young star aggregate. Both clusters are immersed in dense stellar fields which share the same population properties, suggesting that in their cases, cluster ages are consistent with typical ages of field stars.Comment: 9 pages; 7 figures, MNRAS pape