Towards medium-term (order of months) morphodynamic modelling of the Teign estuary, UK

The main objective of this paper is to address the principal mechanisms involved in the medium-term (order of months to years) morphodynamic evolution of estuaries through the application of a process-based numerical modelling. The Teign estuary (Teignmouth, UK) is the selected site. The system is forced by the macrotidal semi-diurnal tide in the English Channel and is perturbed to a minor extent by high river discharge events (freshets). Although waves have a definite influence on the adjacent coastal area, Wells (Teignmouth Quay Development Environmental Statement: Changes to Physical Processes. Report R.984c:140. ABP Marine Environmental Research Ltd., Southampton, 2002b) suggested that swell waves do not enter the estuary. Hence, wave effects are neglected in this study, as only tides and the river discharge are taken into account. The sediment grain size is highly variable, but mainly sandy. Within the frame of the COAST3D project (), four bathymetric surveys of the adjacent coastal area were carried out at a nearly weekly intervals. The outer estuary and the adjacent coastal area were also surveyed every 6 months as part of the COASTVIEW project (). Based on these data and on continuously measured parameters, such as water level, waves, wind and river discharge, numerical modelling of the morphodynamic processes can be tested. To replicate the morphological changes in the medium-term within a feasible simulation time, forcing conditions are reduced through the use of an input reduction method (called ensemble technique). In this study, simulations are based on the coupling between Telemac-2D and its non-cohesive sediment transport module, Sisyphe (version 5.3 for both modules). Three different sediment transport formulae were tested: (1) Engelund and Hansen (A monograph on sediment transport in alluvial streams, 3rd edn. Technological University of Denmark, Copenhagen, 1967) including the modifications proposed by Chollet and Cunge (J Hydraul Eng 17(1):1–13, 1979); (2) Bijker (Mechanics of sediment transport by the combination of waves and current. In: Design and reliability of coastal structures. 23rd international conference on Coastal Engineering, pp 147–173, 1968) and (3) Soulsby (Dynamics of Marine Sands. A manual for practical applications. HR Wallingford, Wallingford, p 142, 1997) modified version of van Rijn [J Hydraul Eng 110(10):1431–1456, 1984a, J Hydraul Eng 110(11):1613–1641, 1984b] formulation. Both a qualitative (i.e. visual comparison) and a quantitative tool [Brier Skill Score (BSS); described in Sutherland et al. in Coast Eng 51:917–939, 2004b] are applied to assess the similarity of simulations when compared to model predictions and observations. Tests confirmed the reliability and time efficiency of the ensemble technique, since it reproduced very well the results of a reference run, a computation based on the observed boundary conditions. For the spring-neap cycle modelled, the BSS was of 0.91 (a perfect modelling would have a BSS of 1), with a reduction in the simulation time on the order of 80%. For the 6-month-period simulation, results were also excellent: BSS=0.92 and a computer time reduction of 85%. In principle, this method has the advantage of being applied to any process-based numerical model.     

Ice flow direction during late Paleozoic glaciation in western Paraná Basin, Brazil

The recent discovery of ice-striated surfaces associated with the late Paleozoic Aquidauana Formation suggests that glaciers coming from southwest Africa reached westernmost parts of the Paraná Basin in central Brazil. Abrasion features were developed by glaciers moving from SSE towards NNW, mainly on an unconsolidated bed. These records expand to about 1,050,000 km², the coverage of the late Paleozoic glaciation in the region of the Paraná Basin in Western Gondwana.

Resumen

A recente descoberta de superfícies estriadas associadas à Formação Aquidauana, de idade permocarbonífera, sugere que as geleiras provenientes do sudoeste da África alcançaram as porções ocidentais da Bacia do Paraná, na região central do Brasil. As feições de abrasão foram geradas pelo deslocamento de geleiras de SSE para NNW, principalmente sobre substrato inconsolidado. Estes novos registros evidenciam que a glaciação neopaleozóica cobriu uma área de pelo menos de 1.050.000 km² na região ocupada pela Bacia do Paraná no Gondwana Ocidental.     

The generation ofK indices from digitally recorded magnetic data

TheK index was developed by Bartels and is a measure of geomagnetic activity. The important feature of this index is that it is a measure of solar activity superimposed on the regular daily variation.It is the most used estimate of activity being of particular interest to researchers in ionospheric physics and telecommunications.In response to increased availability of digital data from magnetic observatories and their demand by the scientific community it becomes desireable to check whetherK indices produced from magnetograms plotted from digital data are consistent with those handscaled from La Cour charts.This paper presents results of these comparisons and also reports on several methods tested to produce theK index directly from the digital data.Handscaled indices from digital plots are suitable for producing theK index. Computations using digital data do not reproduceK as defined by Bartels precisely but do provide an equivalent index which is satisfactory for most user and research purposes.     

Estimation Of Apparent Transmissivity From Capacity Testing Of Boreholes In Bedrock Aquifers

Several theoretical and semi-empirical studies indicate a near linear relationship between the specific capacity (F) of boreholes in bedrock aquifers and apparent transmissivity (T) of the form T=F/!, where !=c. 0.9. For several boreholes in Hvaler and Trondheim, Norway, the specific capacity of individual fractures has been determined by plotting Q_A (the yield of water from the aquifer during pumping or recovery) against s (drawdown). Individual apparent fracture transmissivities can be calculated, as can average apparent hydraulic conductivities for individual borehole sections. The method presented is easily performed, requires modest amounts of data, is not mathematically difficult, and is believed to yield at least an order-of-magnitude estimate of transmissivity. Given that hydraulic conductivity in bedrock aquifers can range over seven or eight orders of magnitude, even such a coarse estimate can be of significant use. This is verified by comparison of hydraulic conductivities derived from testing of boreholes in Hvaler with conductivities deduced from water leakage into a nearby subsea tunnel in the same lithology. Résumé: Plusieurs études théoriques et semi-empiriques font envisager un relation pratiquement linéaire entre la capacité d'emmagasinement spécifique (F) de forages dans des aquifères de socle et la transmissivité apparente (T), de la forme T = F/a, où a = 0,9 c. Pour plusieurs forages de Hvaler et de Trondheim (Norvège), la capacité spécifique de fractures individuelles a été déterminée à partir de la relation Q (débit d'alimentation de l'aquifère au cours du pompage ou de la remontée) en fonction de s (rabattement). On a pu calculer les transmissivités individuelles apparentes des fractures et, quand c'était possible, les conductivités hydrauliques apparentes moyennes de portion de forages. La méthode proposée est facile à mettre en oeuvre; elle demande peu de données, n'est pas difficile mathématiquement et parait donner au moins un ordre de grandeur de la transmissivité. Etant donné que la conductivité hydraulique dans les aquifères de socle peut couvrir 7 ou 8 ordres de grandeur, une estimation, même grossière comme coll-ci, peut être significative. Ceci est vérifié en effectuant la comparasion entre les conductivités hydrauliques, obtenues en testant les forages de Hvaler, et celles déduites de l'étude de fuites dans un tunnel sous-marin voisin, dans les mêmes formations géologiques.     

Coral reef ecosystems protect shore from high-energy waves under climate change scenarios

Coral reefs and other coastal ecosystems such as seagrasses and mangroves are widely recognized to provide protection against the devastating effects of strong waves associated with tsunamis and storms. The predicted warming climate brings to fore the role of these ecosystems in providing protection against stronger typhoons that can result in more devastating waves of greater amplitude. We performed a model simulation of storm generated waves on a Philippine reef, which is located along the path of tropical storms, i.e., at least 10 typhoons on the average pass through the study site yearly. A model to simulate wave propagation was developed using Simulating Waves Nearshore (SWAN) and DELFT3D-WAVE computer simulation software. Scenarios involving local monsoonal wind forcing and storm conditions were simulated. In addition, as climate change may also result to increased relative sea level, a 0.3 m and 1 m rise in sea level scenarios were also used in the wave model simulations. Results showed that the extensive reef system in the site helped dissipate wave energy that in turn reduced wave run-up on land. A significant reduction in wave energy was observed in both climate change, i.e., stronger wind and higher sea level, and non-climate change scenarios. This present study was conducted in a reef whose coral cover is in excellent condition (i.e., 50 to 80% coral cover). Estimates of coral reef growth are in the same order of magnitude as estimates of relative sea level rise based on tide gauge and satellite altimeter data, thus it is possible that the role of reefs in attenuating wave energy may be maintained if coral reef growth can keep up with the change in sea level. Nonetheless, to maintain reef growth, it is imperative to manage coral reef ecosystems sustainably and to eliminate the stressors that are within human control. Minimizing activities such as illegal and destructive blast and poison fishing methods, pollution and siltation, is crucial to minimize the impacts of high-energy waves that may increase with climate change.     

Wave Generation from Explosions in Rock Cavities

—?We have developed a measurement method to monitor P- and S-waves generated from laboratory-scale explosions in meter-sized rock samples at a series of stations, as well as invented a device to drill spherical cavities in rock, with diameters up to 10?centimeters. We applied these to experiments in Bedford limestone in which spherical/cylindrical explosives (0.2 to 1.9?g) were centrally placed in 1.2- to 3-cm diameter cavities. Stress waves generated by the explosions were recorded within a radius of 25?cm. The radial stress wave records and post-explosion studies demonstrate that S-waves are generated from explosions in cavities as a result of both wave mode-conversion from the cavity wall and crack propagation in rocks. The experimental results of wave generation from the explosions in spherical and cylindrical cavities demonstrate the cavity geometrical effect on the resulting wave pattern. The P- and S-waves generated by explosions and crack propagation in rocks are analyzed. A simple analytic model for P-wave generation is proposed to explain the differences of P-wave-induced displacement histories between the observed waveforms and those predicted by a step-pressure source. Generally, the qualitative predictions of this model fit the observations. The present results demonstrate the importance of rock cracking and cavities in P- and S-wave generation.     

Paleomagnetism of early Aphebian diabase dykes from the slave structural province, Canada

Early Aphebian dykes (lowermost Proterozoic) intrude the Archean terrain of the Slave Structural Province of the Canadian Shield and paleomagnetic results from them are reported. The Dogrib dykes, with an Rb/Sr age of 2692 ± 80 mm.y., have directions of magnetization directed toward the NW without reversals (16 sites; 309, + 37; α₉₅ = 4°; pole 35S, 050W). The Indin dykes, with an Rb/Sr age of 2093 ± 86 mm.y., have magnetization directed toward the SE with reversals (13 sites; 131, + 58; α₉₅ = 8°; pole 19N, 076W). Other, less well-documented data from a third dyke swarm (the “X” dykes) and a basic sill (the Duck Lake Sill), are also presented, and a very tentative polar path for the Slave Province in the earlier Proterozoic is given. This path is not greatly different from a similar very tentative early Aphebian polar path from the Archean Superior Province, considering the uncertainties in the paleomagnetic and age determinations. We interpret this to mean either that the intervening Hudsonian Structural Province (−1850 m.y.) was not the site of a wide plate-style opening and closing ocean, or if it was, the two bounding Archean cratons returned approximately to their original relative position.