Bathymetric control of surf zone retention on a rip-channelled beach

Simulations from a numerical model address the impact of nearshore morphology on surf zone retention on, open coast, rip-channelled beaches exposed to shore-normal waves. In the model, rip channels are regularly spaced alongshore with a given spacing λ. For a given reference case bathymetry (λ= 200 m), rip current circulations retain floating material at a hourly rate R of about 80 % which is in line with most existing field and laboratory studies in similar settings. The influence of a surf zone rip-channel morphology on surf zone retention is evaluated by a number of morphologic parameters. Results show that rip spacing is important. The ratio of the surf zone width X _s to rip spacing λ controls surf zone retention with R rapidly increasing with increasing X _s /λ up to a threshold of about 1 above which R levels off to become asymptotic to 100 %. The impact of the presence of a rip head bar is profound but nonlinear. The onset of wave breaking across the rip head bar drives a weak seaward located circulation providing major pathways for surface water exiting the surf zone compartment. Additional simulations suggest that alongshore variations in the offshore bathymetry are important. Patterns in the wave field enforced by wave refraction and potentially wave breaking across offshore bathymetric anomalies can provide a conduit for transporting floating material out of the surf zone and into the inner shelf region. This has major implications for surf zone flushing by inner-bar rips on multiple-barred beaches and on beaches facing bathymetric anomalies on the inner shelf.     

Detecting changing river temperatures in England and Wales

Changes in water temperature can have important consequences for aquatic ecosystems, with some species being sensitive even to small shifts in temperature during some or all of their life cycle. While many studies report increasing regional and global air temperatures, evidence of changes in river water temperature has, thus far, been site specific and often from sites heavily influenced by human activities that themselves could lead to warming. Here we present a tiered assessment of changing river water temperature covering England and Wales with data from 2773 locations. We use novel statistical approaches to detect trends in irregularly sampled spot measurements taken between 1990 and 2006. During this 17‐year period, on average, mean water temperature increased by 0.03 °C per year (±0.002 °C), and positive changes in water temperature were observed at 2385 (86%) sites. Examination of catchments where there has been limited human influence on hydrological response shows that changes in river flow have had little influence on these water temperature trends. In the absence of other systematic influences on water temperature, it is inferred that anthropogenically driven climate change is driving some of this trend in water temperature. © 2014 The Authors. Hydrological Processes published by John Wiley & Sons Ltd.     

Hubbert’s Legacy: A Review of Curve-Fitting Methods to Estimate Ultimately Recoverable Resources

A growing number of commentators are forecasting a near-term peak and subsequent terminal decline in the global production of conventional oil as a result of the physical depletion of the resource. These forecasts frequently rely on the estimates of the ultimately recoverable resources (URR) of different regions, obtained through the use of curve-fitting to historical trends in discovery or production. Curve-fitting was originally pioneered by M. King Hubbert in the context of an earlier debate about the future of the US oil production. However, despite their widespread use, curve-fitting techniques remain the subject of considerable controversy. This article classifies and explains these techniques and identifies both their relative suitability in different circumstances and the level of confidence that may be placed in their results. This article discusses the interpretation and importance of the URR estimates, indicates the relationship between curve fitting and other methods of estimating the URR and classifies the techniques into three groups. It then investigates each group in turn, indicating their historical origins, contemporary application and major strengths and weaknesses. The article then uses illustrative data from a number of oil-producing regions to assess whether these techniques produce consistent results as well as highlight some of the statistical issues raised and suggesting how they may be addressed. The article concludes that the applicability of curve-fitting techniques is more limited than adherents claim and that the confidence bounds on the results are wider than usually assumed.     

Peck公式在我国隧道施工地面变形预测中的适用性分析

在目前众多的预测地铁隧道开挖引起的地表位移的经验方法中，Peck于1969年提出的高斯方程最简便，也是目前应用最为广泛的方法。由于这一公式是基于有限地区的实测资料提出的，因此，在某个地区应用前首先应该进行基于当地实测资料的验证工作。国内地铁建设工作起步相对较晚，在土中开挖的浅埋隧道工程引起的地层变形实测资料比较缺乏，因此，目前对Peck公式在国内各地区的适用性还没有定论。近年来，随着地铁建设热潮的兴起，各地逐渐积累了一些实测资料，但仍比较零散，也没有形成比较统一的结论。通过对搜集到的国内8个地区30多组观测数据的分析，评价这一方法在不同地区的适用性，并对相关计算参数提出初步建议值。     

H_2O Megamasers: Accretion Disks, Jet Interaction, Outflows or Massive Star Formation?

The 25 years following the serendipitous discovery of megamasers have seen tremendous progress in the study of luminous extragalactic H₂O emission. Single-dish monitoring and high-resolution interferometry have been used to identify sites of massive star formation, to study the interaction of nuclear jets with dense molecular gas and to investigate the circumnuclear environment of active galactic nuclei (AGN). Accretion disks with radii of 0.1–3 pc were mapped and masses of nuclear engines of order 10⁶–10⁸ M were determined. So far, 50 extragalactic H₂O maser sources have been detected, but few have been studied in detail.     

VLBI observations of GNSS-satellites: from scheduling to analysis

The possibility of observing satellites with the very long baseline interferometry (VLBI) technique has been discussed for several years in the geodetic community, with observations of either existing satellites of the global navigation satellite systems or of satellites dedicated to realise a space tie. Such observations were carried out using the Australian telescopes in Hobart and Ceduna which, for the first time, integrated all the necessary steps: planning the observations (automated scheduling), correlation of the data and the generation of a series of time delay observables suitable for a subsequent geodetic analysis. We report on the development of new and the adaptation of existing routines for observing and data processing, focusing on technology development. The aim was to use methods that are routinely used in geodetic VLBI. A series of test experiments of up to six hours duration was performed, allowing to improve the observations from session to session and revealing new problems still to be solved. The newly developed procedures and programs now enable more observations. Further development assumed, this bears the prospect of being directly applied to the observation of dedicated space-tie satellites.     

Mass transport in porous rocks

The physical processes by which materials may move within porous rocks are briefly reviewed. In impermeable rocks diffusion through the solid rock limits mass transfer. Diffusion coefficients in solids are typically of the order 10^–15 to 10^–8 cm²/sec and temperature-dependent. When there is no fluid convection in a permeable rock, diffusion through liquid-filled pores, with diffusion coefficients of the order 10^–6 cm²/sec, will be the dominant mass transport process. Fluid convection in permeable rocks can increase mass transfer rates by many orders of magnitude. The pressure gradient in the fluid, fluid viscosity, and the specific permeability of the rock are dominant in determining the fluid velocity and mass transfer rates. The role of these transport processes in the deposition and leaching of orebodies in porous rocks is discussed.

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Zusammenfassung Massenbewegung in undurchlässigem Gestein ist durch die Diffusion durch das feste Gestein begrenzt. Die temperaturabhängigen Diffusionskoeffizienten in Festkörpern sind von der Größenordnung 10^–15 bis 10^–8 cm²/sek. Wo keine Flüssigkeitskonvektion in einem durchlässigen Gestein stattfindet, ist Diffusion durch flüssigkeitshaltige Poren, mit Diffusionskoeffizienten von der Größenordnung 10^–6 cm²/sek., der wichtigste Massentransport-Prozeß. Der Massentransport durch durchlässiges Gestein kann durch Flüssigkeitskonvektion um viele GrÖßenordnungen vergrößert werden. Der Druckgradient in der Flüssigkeit, die Viskosität der Flüssigkeit und die spezifische Permeabilität des Gesteins sind die wichtigsten Faktoren, welche die Geschwindigkeit und Menge des Massentransportes bestimmen. Das Wesen dieser Transportprozesse bei der Ablagerung und Auslaugung von Erzlagerstätten wird diskutiert.