Simulating meander evolution of the Geul River (the Netherlands) using a topographic steering model

Active meandering rivers are capable of reworking and removing large quantities of valuable land. Therefore, understanding the characteristics of meandering rivers and predicting future meander behaviour can be of great value for local authorities. In this study, we apply a topographic steering meander model to the Geul River (southern Netherlands), using field data to calibrate the model. The present channel characteristics of the Geul River were mapped in the field. Cut‐banks were classified as erosive, unstable or stable. The model outcomes were compared with these field data. Several model runs were carried out, using different sets of parameter values. After studying the results and using the field data, we introduced the concept of a variable channel width in the simulation model. In reality, the river has different channel widths varying from 8 to more than 15 m. These widths are a linear function of local curvature. The model runs using a variable channel width show that the model is capable of predicting locations of lateral migration in conformity with observed active lateral migration and erosive banks. With both models, the sediment reworking time of the floodplain can be calculated. Floodplain reworking times of 200–300 years were calculated. In combination with the lateral migration rate, this reworking time is an important element in catchment sediment budget calculations. Copyright © 2007 John Wiley & Sons, Ltd.     

A search for the optical and near-infrared counterpart of the accreting millisecond X-ray pulsar XTE J1751−305

We have obtained optical and near-infrared images of the field of the accreting millisecond X-ray pulsar XTE J1751−305. There are no stars in the 0.7-arcsec error circle (0.7 arcsec is the overall uncertainty arising from tying the optical and X-ray images and from the intrinsic uncertainty in the Chandra X-ray astrometric solution). We derive limiting magnitudes for the counterpart of   R > 23.1, I > 21.6, Z > 20.6, J > 19.6  and   K > 19.2  . We compare these upper limits with the magnitudes one would expect for simple models for the possible donor stars and the accretion disc subject to the reddening observed in X-rays for XTE J1751−305 and when put at the distance of the Galactic Centre (8.5 kpc). We conclude that our non-detection does not constrain any of the models for the accretion disc or possible donor stars. Deep, near-infrared images obtained during quiescence will, however, constrain possible models for the donor stars in this ultracompact system.     

The rate of grain release by pore-ice sublimation in cold-aeolian environments

Pore‐ice sublimation is a prerequisite for aeolian activity in cold environments where surface sediments hold significant amounts of frozen water. Few quantitative studies have defined the rate of grain release from cemented surfaces by pore‐ice sublimation. In 1996–1997, controlled field experiments at Presqu'ile Beach, Ontario, were implemented to measure sediment release from frozen surfaces. The release rates were compared to the local wind regime, ambient temperature and humidity. In additional field experiments, the effect of sediment water content on grain release by sublimation was examined. From the experimental results, an equation which predicts grain release based on local wind speed, ground temperature, humidity, and surface water content is proposed. Predicted release rates show reasonable agreement with natural deflation measured on the beach at Presqu'ile Provincial Park.     

Saltwater Upconing Due to Cyclic Pumping by Horizontal Wells in Freshwater Lenses

This article deals with the quantification of saltwater upconing below horizontal wells in freshwater lenses using analytical solutions as a computationally fast alternative to numerical simulations. Comparisons between analytical calculations and numerical simulations are presented regarding three aspects: (1) cyclic pumping; (2) dispersion; and (3) finite horizontal wells in a finite domain (a freshwater lens). Various hydrogeological conditions and pumping regimes within a dry half year are considered. The results show that the influence of elastic and phreatic storage (which are not taken into account in the analytical solutions) on the upconing of the interface is minimal. Furthermore, the analytical calculations based on the interface approach compare well with numerical simulations as long as the dimensionless interface upconing is below 1/3, which is in line with previous studies on steady pumping. Superimposing an analytical solution for mixing by dispersion below the well over an analytical solution based on the interface approach is appropriate in case the vertical flow velocity around the interface is nearly constant but should not be used for estimating the salinity of the pumped groundwater. The analytical calculations of interface upconing below a finite horizontal well compare well with the numerical simulations in case the distance between the horizontal well and the initial interface does not vary significantly along the well and in case the natural fluctuation of the freshwater lens is small. In order to maintain a low level of salinity in the well during a dry half year, the dimensionless analytically calculated interface upconing should stay below 0.25.     

Ore–Waste Discrimination in Epithermal Deposits Using Near-Infrared to Short-Wavelength Infrared (NIR-SWIR) Hyperspectral Imagery

Near-infrared (NIR) and short-wavelength infrared (SWIR) hyperspectral imagery can be used to detect certain alteration minerals. At epithermal deposits, the formation of alteration minerals is, in theory, related to the mineralisation of gold and silver. In order to provide foundations for developing sensor-based sorting applications at a mine that exploits such a deposit, it was investigated if NIR-SWIR hyperspectral imagery can be used to distinguish between ore and waste particles by characterising the alteration mineralogy. Maps were produced from the NIR-SWIR hyperspectral images of 827 drill core samples that show mineral occurrences, mineral absorption feature intensities and characteristics of the iron oxide mineralogy. Partial least squares discriminant analysis (PLS-DA) was applied to the information contained in these maps to investigate if this information can be used to discriminate between ore and waste. The results showed that NIR-SWIR hyperspectral imagery could be used to segment a population of waste samples by detecting occurrences of pyrophyllite, dickite and/or illite. This result can be explained by the fact that these minerals are commonly deposited further away from the ore-bearing epithermal veins, while the absence of SWIR-active minerals or detected occurrences of alunite are more closely associated with these structures. The ability to identify waste with NIR-SWIR spectral sensors means there is potential that sensor-based sorting can be used to remove this waste from mineral processing operations. Additional research is still required to assess the economic feasibility of such a sensor-based sorting application.

     

The Influence of Community Size and Location on Different Dimensions of Vulnerability: a case study of Australian coastal communities

ABSTRACT

Coastal communities are part of the Australian identity but little is known about their characteristics and their long-term prosperity prospects. Increased migration to coastal areas and increased exposure to extreme climatic events indicates a need for social and economic data to inform socio-ecological systems planning. Here, we undertake a geo-spatial analysis to develop a typology of Australian coastal communities and assess relative vulnerability to climate-driven environmental change for a range of social and economic indicators. The aim of this study is to understand how the vulnerability of Australian coastal communities varies with geographic location or community size, and in comparison to other community types. Results show that both the population size and location of a coastal community matter and that coastal communities overall are more vulnerable on some socio-economic dimensions to climate-driven environmental change than their rural equivalents. However, results also demonstrate that the smallest coastal communities are strong in some important aspects of the human, social and financial domains, putting them in a good position to deal with some changes. Scale-appropriate and context-specific social policies are needed to address identified socio-economic vulnerabilities, supported by a range of formal and informal institutional structures, such as strategies to improve education and female workforce participation, and encourage participation in volunteering to increase human and social capital.     

Characterisation of hydroclimatological trends and variability in the Lake Naivasha basin,Kenya

Recent hydro‐climatological trends and variability characteristics were investigated for the Lake Naivasha basin with the aim of understanding the changes in water balance components and their evolution over the past 50 years. Using a Bayesian change point analysis and modified Mann–Kendall tests, time series of annual mean, maximum, minimum, and seasonal precipitation and flow, as well as annual mean lake volumes, were analysed for the period 1960–2010 to uncover possible abrupt shifts and gradual trends. Double cumulative curve analysis was used to investigate the changes in hydrological response attributable to either human influence or climatic variability. The results indicate a significant decline in lake volumes at a mean rate of 9.35 × 10⁶ m³ year^?1. Most of the river gauging stations showed no evidence of trends in the annual mean and maximum flows as well as seasonal flows. Annual minimum flows, however, showed abrupt shifts and significant (upward/downward) trends at the main outlet stations. Precipitation in the basin showed no evidence of abrupt shifts, but a few stations showed gradual decline. The observed changes in precipitation could not explain the decline in both minimum flows and lake volumes. The findings show no evidence of any impact of climate change for the Lake Naivasha basin over the past 50 years. This implies that other factors, such as changes in land cover and infrastructure development, have been responsible for the observed changes in streamflow and lake volumes. Copyright © 2015 John Wiley & Sons, Ltd.     

The lateglacial Quercus expansion in the southern European Alps: rapid vegetation response to a late Allerød climate warming?

A pollen‐inferred vegetation shift, from pioneer birch–pine woodland to mixed pine–summergreen oak forests, in the southern Alpine forelands, is commonly attributed to a centennial‐scale warming that occurred between the Gerzensee Oscillation (GO) and the Younger Dryas. Two microtephra layers bracketing the Younger Dryas onset (the Laacher See Tephra and the Vedde Ash) improve the chronology at Lago Piccolo di Avigliana (northern Italy) and allowed accurate correlation with Central European records where the GO is clearly detected. We used pollen percentages, pollen accumulation rates (PARs) and plant macrofossils to assess the population dynamics of Quercus, and leaf‐cuticle analysis for a better taxonomic identification of Quercus. Our results indicate that the species that was locally present was probably Quercus robur. PARs suggest that the population expansion started as early as the Bølling and followed an exponential increase through time. We attribute this gradual shift to increasing summer temperatures and longer growing seasons which contrast with a gradually decreasing temperature trend as recorded in Greenland ice cores and in Central Europe. Breaks or set‐backs in the PAR record may indicate the biotic response to minor Lateglacial cooling events of different life‐history stages in the Quercus population. Copyright © 2011 John Wiley & Sons, Ltd.     

The Dynamics of Small Postglacial Lake Basins and the Nature of Their Archaeological Record: A Case Study of the Middle Palaeolithic Site Neumark‐Nord 2, Germany

Due to favorable conditions of preservation, sedimentary basins provide rich records of human behavior and its environmental context. The conditions for the preservation of archaeological material however vary between basin types (large, river‐fed or small, closed basins), while conditions also differ within a particular basin environment. The goal of this paper is to understand how the dynamics of a small postglacial basin such as Neumark‐Nord 2, a context that dominates the Eemian archaeological record, affected the archaeology situated at its basin margin. The approach used here is to correlate the archaeological record with reconstructions of patterns of deposition and the water conditions within the basin, using lithology, micromorphology, pollen, and macroremains from a transect running from the basin center to the margin. The results show that (1) find levels were exposed to overland flow‐induced winnowing, which vertically concentrated finds but did not cause significant transport, (2) find levels correspond to phases of increased water presence in the basin, and (3) lateral shifts in hominin activity areas may reflect adjustments in the water level. The research shows the importance of large‐scale archaeological excavations and a multidisciplinary sampling strategy that covers both the basin center and the margins, when studying postglacial basin localities like Neumark‐Nord 2.