Pb-210 and Cs-137 distribution in Burullus lagoon sediments of Nile river delta, Egypt: sedimentation rate after Aswan High Dam

This paper examines the Burullus lagoon deposits of the Nile delta coast and the distribution of Pb-210 and Cs-137. Three vibrocores from the lagoon have revealed densely concentrated shell fragments of brackish water origin in the upper (<ca. 15cm, in general) core sediments. Pb-210 and Cs-137 are in general measurable above this sediment core horizon, but, the rest downcore remains as an irregular distribution pattern, probably incurred due to secondary sediment transport or seawater seepage related processes. The present study of Pb-210 and Cs-137 and associated sediment nature of Burullus lagoon prefers sediments of <15 cm in vibrocores to after Aswan High Dam constructed in 1964, with sedimentation rate of 0.42-0.56 cm/a.     

Mapping flood susceptibility in an arid region of southern Iraq using ensemble machine learning classifiers: a comparative study

This study examined the efficacy of three machine ensemble classifiers, namely, random forest, rotation forest and AdaBoost, in assessing flood susceptibility in an arid region of southern Iraq. A dataset was created from flooded and non-flooded areas to train and validate the ensemble classifiers using a binary classification scheme (1—flood, 0—non-flood). The prepared dataset was then partitioned into two sets with a 70/30 ratio: 70% (2478 pixels) for training and 30% (1062 pixels) for testing. A total of 10 influential flood factors were selected and prepared based on data availability and a literature review. The selected factors were surface elevation, slope, plain curvature, topographic wetness index, stream power index, distance to rivers, drainage density, lithology, soil and land use/land cover. The information gain ratio was first utilised to explore the predictive abilities of the factors. The predictive performances of the three ensemble models were compared using six statistical measures: sensitivity, specificity, accuracy, kappa, root mean square error and area under the operating characteristics curve. The results revealed that the AdaBoost classifier was the best in terms of the statistical measures, followed by the random forest and rotation forest models. A flood susceptibility map was prepared based on the result of each classifier and classified into five zones: very low, low, moderate, high and very high. For the model with the best performance, i.e., the AdaBoost model, these zones were distributed over an area of 6002 km² (44%) for the very low–low zone, 2477 km² (18%) for the moderate zone and 5048 km² (40%) for the high–very high zones. This study proved the high capabilities of ensemble machine learning classifiers to decipher flood susceptibility zones in an arid region.     

Spatio‐temporal evaluation of the groundwater quality in Kafr Al‐Zayat District,Egypt

Eighteen groundwater well sites located in Kafr Al‐Zayat (Egypt) were sampled monthly from January 2009 to November 2011 for microbial content, Mn⁺², Fe⁺², total dissolved solids (TDS), total hardness, NO₃^?, and turbidity. The data were analyzed combining the integrated use of factor and cluster analyses as well as the geostatistical semi‐variogram modeling. The prime objectives were to assess the groundwater suitability for drinking, to document the factors governing the spatio‐tempral variability, and to recognize distinctive groundwater quality patterns to help enable effective sustainability and proactive management of the limited resource. The groundwater microbial, Mn⁺², Fe⁺², TDS, and total hardness contents violated the drinking water local standards while the turbidity and the nitrate content complied with them. Factor analysis indicated that the microbial content is the most influential factor raising the variability potential followed, in decreasing order, by Mn²⁺, Fe²⁺, TDS, NO₃^?, turbidity, and finally the total hardness. Turbidity resulting from urban and agricultural runoff was strongly associated with most of the quality parameters. Quality parameters fluctuate sporadically without concrete pattern in space and time while their variability scores peak in November every year. Three spatially distinctive quality patterns were recognized that were consistent with and affected by the cumulative effects of the local topography, depth to water table, thickness of the silty clay (cap layer), surface water, and groundwater flow direction and hence the recharge from contaminated surface canals and agricultural drains. Copyright © 2013 John Wiley & Sons, Ltd.     

Erratum: Trace Elements in Sediments and Mussels – Spatial Distribution,Chemical Partitioning,and Risk Assessment

Sediment samples were collected from 30 different locations in Abu Qir Bay (Mediterranean Sea), East Alexandria, Egypt and analyzed for trace elements. The highest concentrations of most of the elements were observed in the nearshore stations in the vicinity of the major anthropogenic activities as industrial settlements, wastewater discharges, and agricultural drainage. In addition, mussel samples of Mactra corallina and Tapes decussata were collected corresponding to the sediment samples. Concentrations of As, Cd, Cr, Mn, and Zn in the mussel tissues were higher than concentrations in sediments, thus indicating their relatively high bioavailability. Sequential extraction procedure was performed on selected sediment samples. Significant correlations were observed between the concentrations of Cu, Mn, Pb, and Zn in the exchangeable fraction of the sediments and the corresponding tissues of M. corallina. The output of the risk assessment applied on the sediments revealed that adverse ecological effects to benthic species could occur and that a higher level of risk is expected from the exposure to Cd, Cr, Hg, and Zn. No adverse carcinogenic or non‐carcinogenic human health effects are expected from the consumption of the two mussel species from Abu Qir Bay.     

Natural and human-induced sinkhole hazards in Saudi Arabia: distribution,investigation, causes and impacts

Approximately 60 % of the 2,150,000 km² area of Saudi Arabia is underlain by soluble sediments (carbonate and evaporite rock formations, salt diapirs, sabkha deposits). Despite its hyper-arid climate, a wide variety of recent sinkholes have been reported in numerous areas, involving significant property losses. Human activities, most notably groundwater extraction, have induced unstable conditions on pre-existing cavities. This work provides an overview of the sinkhole hazard in Saudi Arabia, a scarcely explored topic. It identifies the main karst formations and the distribution of the most problematic sinkhole areas, illustrated through several case studies covering the wide spectrum of subsidence mechanisms. Some of the main investigation methods are presented through selected examples, including remote sensing, trenching and geophysics. Based on the available data, the main causal factors are identified and further actions that should be undertaken to better assess and manage the risk are discussed.     

Stochastic Forecasting Models of the Monthly Streamflow for the Blue Nile at Eldiem Station

Egypt is almost totally dependent on the River Nile for satisfying about 95% of its water requirements. The River Nile has three main tributaries: White Nile, Blue Nile, and River Atbara. The Blue Nile contributes about 60% of total annual flow reached the River Nile at Aswan High Dam. The goal of this research is to develop a reliable stochastic model for the monthly streamflow of the Blue Nile at Eldiem station, where the Grand Ethiopian Renaissance Dam (GERD) is currently under construction with a storage capacity of about 74 billion m³. The developed model may help to carry out a reliable study on the filling scenarios of GERD reservoir and to minimize its expected negative side effects on Sudan and Egypt. The linear models: Deseasonalized AutoRegressive Moving Average (DARMA) model, Periodic AutoRegressive Moving Average (PARMA) model and Seasonal AutoRegressive Integrated Moving Average (SARIMA) model; and the nonlinear Artificial Neural Network (ANN) model are selected for modeling monthly streamflow at Eldiem station. The performance of various models during calibration and validation were evaluated using the statistical indices: Mean Absolute Error, Root Mean Square Error and coefficient of determination (R2) which indicate the strength of fitting between observed and forecasted values. The results show that the performance of the nonlinear model (ANN) was much better than all investigated linear models (DARMA, PARMA and SARIMA) in forecasting the monthly flow discharges at Eldiem station.     

Discriminating Weathering Degree by Integrating Optical Sensor and SAR Satellite Images for Potential Mapping of Groundwater Resources in Basement Aquifers of Semiarid Regions

Natural Resources Research - Unlike in coastal and sedimentary basins, regional-scale exploration of groundwater resources using only geophysical methods is costlier in consolidated rocks such as...     

The diffraction of linear waves by a uniform vertical cylinder with cosine-type radial perturbations

The interaction of linear waves with a uniform, bottom-mounted, surface-piercing cylinder whose diameter exhibits a cosine-type variation is investigated. Two solution methods are presented. One method is based on a perturbation theory, using a perturbation parameter defined in terms of the surface geometry of the cylinder. The analysis includes terms up to the first-order in this parameter, where the zeroth-order solution corresponds to a circular cylinder. The velocity potentials at the zeroth and first orders are expressed as eigenfunction expansions involving unknown coefficients that are subsequently determined through the cylinder boundary conditions. The second method is based on Green's theorem and gives rise to an integral equation for the fluid velocity potential on the cylinder surface. A comparison between the results of these two methods has proved that they are in good agreement for small values of the perturbation parameter. Numerical results are presented that illustrate the influence of the magnitude and frequency of these perturbations on the resulting hydrodynamic force and the wave runup on the cylinder.     

Estimation of ship motions using closed-form expressions

A semi-analytical approach is used to derive frequency response functions for the wave-induced motions for monohull ships. The results are given as closed-form expressions and the required input information for the procedure is restricted to the main dimensions: length, breadth, draught, block coefficient and water plane area together with speed and heading. The formulas make it simple to obtain quick estimates of the wave-induced motions and accelerations in the conceptual design phase and to perform a sensitivity study of the variation with main dimensions and operational profile.     

Desertification in the Arab Region: analysis of current status and trends

The total area of the Arab Region is about 14·2 million km², 90% of it lies within arid, semi-arid and dry sub-humid areas. The area is characterized by harsh environment, fragile ecosystems and limited water resources and arable lands. Throughout its long history these lands were the main source of grain and animal production.By the end of this century and in spite of the national, regional and international efforts to combat desertification and mitigate the effect of drought and desiccation, desertification is still one of the major environmental problems in the Arab Region. The rapid increase in population by some 3% annually, considered among the highest worldwide, along with the changing of consumption patterns and life styles, resulting in increasing food demand, have hastened land degradation in this arid environment.Land degradation in the Arab Region due to misuse is widespread and is proceeding at accelerating rates. Failures of resource management policies are aggravated by overgrazing, overexploitation of water and land resources, overcultivation of marginal lands, deforestation, and the use of inappropriate technologies.This paper attempts to provide:

• A synthesis and analysis of the status of desertification in the Arab Region.

• Identification of the major causes and trends of land degradation.

• Highlighting the limitations and constraints on combating desertification in the Arab Region.