A depth‐integrated,coupled SPH model for flow‐like landslides and related phenomena

In the past decades, flow‐like catastrophic landslides caused many victims and important economic damage around the world. It is therefore important to predict their path, velocity and depth in order to provide adequate mitigation and protection measures. This paper presents a model that incorporates coupling between pore pressures and the solid skeleton inside the avalanching mass. A depth‐integrated, coupled, mathematical model is derived from the velocity–pressure version of the Biot–Zienkiewicz model, which is used in soil dynamics. The equations are complemented with simple rheological equations describing soil behaviour and are discretized using the SPH method. The accuracy of the model is assessed using a series of benchmarks, and then it is applied to back‐analyse the propagation stage of some catastrophic flow‐like slope movements for which field data are available. Copyright © 2008 John Wiley & Sons, Ltd.     

Porosity-reducing and porosity-enhancing diagenetic factors for some carbonate microfacies: a guide for petrophysical facies discrimination

The present study deals with the petrographical and petrophysical properties of the Aptian–Albian Risan Aneiza Formation in north Sinai, Egypt. Cementation and aggrading neomorphism are the main porosity-reducing factors for Risan Aneiza Formation, whereas dissolution and leaching out are the main porosity-enhancing factors. Dolomitization, on the other hand, played a multistage role as a porosity-reducing factor in the initial invasion stage by Mg-bearing solutions and in the final pervasive stage, while it played an enhancing role in the selective dolomitization midway stage. Mostly, the mentioned pore types were later reduced by cementation with sparite and dolosparite as well as by aggrading neomorphism. Based on the governing effect of diagenetic factors on the petrophysical behavior and their enhancing or reducing effect on the pore volume, the Risan Aneiza Formation has to be classified into seven petrophysical facies; each one has its characteristic petrophysical features and behavior. The petrophysical behavior of the studied facies has been examined by measuring porosity, density, permeability, and electrical resistivity. The reservoir quality index reveals that the petrophysical features of the studied facies can be explained based on their petrographical features, indicating bad reservoir properties for the Risan Aneiza samples. Studying the petrophysical facies behavior indicates that the permeability and formation resistivity factors are mostly dependent on the effective porosity and, to some extent, on the electric tortuosity. Precautions must be taken into consideration in extrapolating the present conclusion to the subsurface extensions, e.g., similarity of the mineralogical composition, the diagenetic history stage, as well as the geopressure.     

Derivation of short-duration design rainfalls using daily rainfall statistics

Design rainfall intensity–frequency–duration data are a basic input to many water-related development projects. To derive design rainfalls, one needs long period of recorded rainfall data. Although daily rainfall data are generally widely available, short-duration rainfall data are scarce. For many urban applications, design rainfalls for much shorter durations are needed, which cannot be obtained directly from daily read rainfall data. This paper presents a simple approach that can be adopted to derive design rainfalls of short durations using daily rainfall data and other physio-climatic characteristics using a novel ‘index frequency combined with parameter regression technique’. This uses L moments to reduce the impacts of sampling variability in the analysis. Furthermore, this adopts generalised least squares regression to account for the inter-station correlation of the rainfall data in the analysis. The proposed method is applied to a pilot data set consisting of 203 rainfall stations across Australia. An independent Monte Carlo cross-validation test shows that the proposed method is capable of generating consistent and accurate design rainfall estimates from 6-min to 12-h duration. The developed technique can be adapted to other countries where there is a scarcity of short-duration rainfall data, but daily rainfall data are abundant.     

On the recent global mean sea level changes: Trend extraction and El Niño's impact

The spatial sampling offered by TOPEX and Jason series of satellite radar altimeters and its continuity during the last twenty years are major assets to provide an improved vision of the global mean sea level (GMSL). The objective of this paper is to examine the recent GMSL variations (1993–2012) and to investigate the correlation between the GMSL and ENSO (El Niño-southern oscillation) episodes. For this purpose, a mean sea level anomalies time series, obtained from TOPEX, Jason-1 and Jason-2 measurements, is used to determine the trend of GMSL changes by using a simplified form of an unobserved components model (namely UCM). Then, to investigate the impact of the ENSO phenomenon on the GMSL changes, we considered the sea surface temperature anomalies (SSTA) index over the Niño3 region (5N–5S 150W–90W). Cross wavelet transform and wavelet coherence analysis are performed to expose common power between the GMSL changes and the SSTA index and their relative phase in the time–frequency space. The results indicate that there are in the estimated GMSL's trend a number of fluctuations over short periods that are least partly related to the El Niño/La Niña episodes. Cross wavelet transform and wavelet coherence analysis indicate that a significant correlation between GMSL and ENSO occurred during 1997–1998, 2006–2007, 2009–2010 El Niño events and 2007–2008 and 2010–2011 La Niña ones. All these areas show in-phase relationship, suggesting that GMSL and SSTA index vary synchronously.     

Impacts of dolomitization on the petrophysical properties of El-Halal Formation, North Sinai, Egypt

The Cenomanian marine sequence in north Sinai is mostly represented by El-Halal Formation. Petrographically, it is composed of four microfacies, namely: (1) dolomitic micrite, (2) dolomicrite, (3) dolowackestone and (4) dolosparite. The assigned pore volume (10–25%) could be differentiated into: micro intercrystalline pore spaces, micro to meso vugs and micro pore channels. The present pore spaces are frequently reduced by drusy and/or xenotopic dolosparite and micro sparry calcite. El-Halal Formation has been deposited in a restricted marine platform (SMF-23, FZ-8) with a progressive shallowing sea level upward. The diagenetic history has been controlled by cementation, dolomitization, aggrading neomorphism and creation of authigenic illite. Petrophysically, the studied samples could be grouped into three petrophysical facies: (1) dolomitic micrite/dolomicrite facies, (2) dolowackestone and (3) dolosparite. The permeability (ave. 3.54, 12.9 and 0.49 md, respectively) is dependent on the pore channel radius (ave. 1.03, 1.92 and 0.19 μm, respectively) and porosity (ave. 22.1%, 25.8% and 11.4%, respectively); it could be related to the electrical tortuosity as well (ave. 3.28, 1.40 and 5.06, respectively). The apparent formation resistivity factor was measured at five consequent saline concentrations of 6, 30, 60, 90 and 120 kppm and the true one has been calculated. It is controlled by the effective porosity and electrical tortuosity. Though dolomitization has an enhancing effect on the studied petrophysical features, it had a reducing effect in its first stages of invasion through filling the pore spaces and in the last stages through the aggrading neomorphism.     

Trends in global and regional sea level from satellite altimetry within the framework of auto-SSA

The sea level change is a crucial indicator of our climate. The spatial sampling offered by satellite altimetry and its continuity during the last 18 years are major assets to provide an improved vision of the sea level changes. In this paper, we analyze the University of Colorado database of sea level time series to determine the trends for 18 large ocean regions by means of the automatic trend extraction approach in the framework of the singular spectrum analysis technique. Our global sea level trend estimate of 3.19 mm/year for the period from 1993 to 2010 is comparable with the 3.20-mm/year sea level rise since 1993 calculated by AVISO Altimetry. However, the trends from the different ocean regions show dissimilar patterns. The major contributions to the global sea level rise during 1993–2010 are from the Indian Ocean (3.78?±?0.08 mm/year).     

A study on selection of probability distributions for at-site flood frequency analysis in Australia

The most direct method of design flood estimation is at-site flood frequency analysis, which relies on a relatively long period of recorded streamflow data at a given site. Selection of an appropriate probability distribution and associated parameter estimation procedure is of prime importance in at-site flood frequency analysis. The choice of the probability distribution for a given application is generally made arbitrarily as there is no sound physical basis to justify the selection. In this study, an attempt is made to investigate the suitability of as many as fifteen different probability distributions and three parameter estimation methods based on a large Australian annual maximum flood data set. A total of four goodness-of-fit tests are adopted, i.e., the Akaike information criterion, the Bayesian information criterion, Anderson–Darling test, and Kolmogorov–Smirnov test, to identify the best-fit probability distributions. Furthermore, the L-moments ratio diagram is used to make a visual assessment of the alternative distributions. It has been found that a single distribution cannot be specified as the best-fit distribution for all the Australian states as it was recommended in the Australian rainfall and runoff 1987. The log-Pearson 3, generalized extreme value, and generalized Pareto distributions have been identified as the top three best-fit distributions. It is thus recommended that these three distributions should be compared as a minimum in practical applications when making the final selection of the best-fit probability distribution in a given application in Australia.     

Quantification of the Attenuation of Storm Surge Components by a Coastal Wetland of the US Mid Atlantic

Coastal wetlands are receiving increased consideration as natural defenses for coastal communities from storm surge. However, there are gaps in storm surge measurements collected in marsh areas during extreme events as well as understanding of storm surge processes. The present study evaluates the importance and variation of different processes (i.e., wave, current, and water level dynamics with respect of the marsh topography and vegetation characteristics) involved in a storm surge over a marsh, assesses how these processes contribute to storm surge attenuation, and quantifies the storm surge attenuation in field conditions. During the Fall of 2015, morphology and vegetation surveys were conducted along a marsh transect in a coastal marsh located at the mouth of the Chesapeake Bay, mainly composed of Spartina alterniflora and Spartina patens. Hydrodynamic surveys were conducted during two storm events. Collected data included wave characteristics, current velocity and direction, and water levels. Data analysis focused on the understanding of the cross-shore evolution of waves, currents and water level, and their influence on the overall storm surge attenuation. Results indicate that the marsh area, despite its short length, attenuates waves and reduces current velocity and water level. Tides have a dominant influence on current direction and velocity, but the presence of vegetation and the marsh morphology contribute to a strong reduction of current velocity over the marsh platform relative to the currents at the marsh front. Wave attenuation varies across the tide cycle which implies a link between wave attenuation and water level and, consequently, storm surge height. Storm surge reduction, here assessed through high water level (HWL) attenuation, is linked to wave attenuation across the front edge of the marsh; this positive trend highlights the reduction of water level height induced by wave setup reduction during wave propagation across the marsh front edge. Water level attenuation rates observed here have a greater range than the rates observed or modeled by other authors, and our results suggest that this is linked to the strong influence of waves in storm surge attenuation over coastal areas.