Evaluation of rain gauge network in arid regions using geostatistical approach: case study in northern Oman

A geostatistical approach based on ordinary kriging is presented for the evaluation and the augmentation of an existing rain gauge network. The evaluation is based on estimating the percentage of the area that achieves a targeted level of acceptable accuracy. The variances of kriging estimation erros at un-gauged locations were assumed to be normally distributed. Kriging estimation erros with a probability that equals to or exceeds a given threshold value of acceptance probability were assumed to have satisfactory accuracies. The percentage of the area that achieved the targeted probability of acceptance is delineated and used to judge the overall performance of the existing rain gauge network. A study area in northern Oman located in Sohar governorate is selected as the pilot case. The area has 34 rain gauges and it is characterized by a terrain surface that varies from coastal plain to mountains. For a threshold value of 0.85, and 0.90 of acceptance probability, the existing network achieved area of acceptable probability of 88.71 and 77.72 %, respectively. For a success criterion of 80 %, the existing rain gauge network indicated acceptable performance for acceptance probability threshold of 0.85 and inadequate performance is noticed in the case of probability threshold of 0.90, which necessitated further network augmentation. A sequential algorithm for ranking and prioritization of the existing rain gauges is used to classify the existing rain gauges into base and non-base rain gauges. The base rain gauge network for mean annual rainfall comprised about 29 of the existing rain gauges. The identified non-base rain gauges were sequentially relocated to achieve higher levels of percentage of area with acceptable accuracy. The percentage of area with acceptable accuracy increased from 88.71 % for the original rain gauge network to about 94.51 % for the augmented network by adding four rain gages at probability acceptance threshold of 0.85. It also increased from 77.72 % for the existing network to 90.50 % for the augmented rain gauge network at acceptance threshold of 0.9.     

Effect of the damping and excitation on the identification of the hydrodynamic parameters for an underwater robotic vehicle

The main objective of this work is to investigate the effects of the damping level as well as different excitation forms on the overall prediction of the hydrodynamic parameters in the equations describing the coupled heave and pitch motions for an Underwater Robotic Vehicle (URV) sailing near the sea surface in random waves. The response of an underwater vehicle heaving and pitching in random waves having wide-band and narrow-band spectra are generated. The RDLRNNT technique is used to identify the hydrodynamic parameters in the equations. The technique is based on a combination of a multiple linear regression algorithm and a neural networks technique. The combination of the classical parametric identification techniques and the neural networks technique provides robust results and does not require a large amount of computer time. The identification technique would be particularly useful in identifying the parameters for both moderately and lightly damped motions under the action of unknown excitations effected by a realistic sea. It is shown that the developed technique produces reliable results for the parameters in the equations describing the coupled heave and pitch motions for a URV.     

Improved Pile Geometry to Reduce Negative Skin Friction on Single Driven Pile and Pile Groups Subjected to Lateral Loads

Geotechnical and Geological Engineering - Negative skin friction on piles represents a severe problem when piles were installed in soft clay due to consolidation process. It reduces the bearing...     

Effect of Soil Improvement Techniques on Increasing the Lateral Resistance of Single Piles in Soft Clay (Numerical Investigation)

Geotechnical and Geological Engineering - Soft clay soil extends in many areas all over the world. The construction on soft clay is one of the most important problems in engineering practice. When...     

Chemical Fractionation of Aluminium in the Sediments of El-Burullus Lagoon of Nile Delta,Egypt

A five step sequential extraction technique, following Tessier’s protocol has been applied to determine the chemical association of aluminium with major sedimentary phases (exchangeable, carbonate, manganese and iron oxides, organic and residual fraction) in four short sediment cores collected from El-Burullus lagoon of the Nile delta, Egypt. This study is a first approach of chemical fractionation of aluminium in one of the protective areas of the Mediterranean Sea of Egypt. The total metal content was also determined. The results of the fractionation study indicated that aluminium was mainly associated with the residual fraction (>95%). The organic and Fe–Mn oxide fractions were the next important phases. The exchangeable and carbonate fractions were less than 1%, limiting its potential toxicity as a pollutant. The geochemical analysis of aluminium forms reflected the lithogenic origin of this metal in the study area.     

Sustainable Development Goals (SDGs) Associated with Groundwater Over-Exploitation Vulnerability: Geographic Information System-Based Multi-criteria Decision Analysis

Natural Resources Research - Groundwater over-exploitation is related to various environmental, economic, and social aspects, which should be addressed comprehensively to support a sustainable...     

Geophone‐ground coupling with flat bases

Seismic acquisition can be costly and inefficient when using spiked geophones. In most cases, such as the desert, the most practical solution is the use of flat bases, where geophone‐ground coupling is based on an optimal choice of the mass and area of contact between the receiver and the ground. This optimization is necessary since areas covered by sand are loose sediments and poor coupling occurs. Other cases include ground coupling in stiff pavements, for instance urban areas and ocean‐bottom nodes. We consider three different approaches to analyse coupling and model the geophone with a flat base (plate) resting on an elastic half‐space. Two existing models, based on the full‐wave theory, which we refer to as the Wolf and Hoover‐O'Brien models, predict a different behaviour with respect to the novel method introduced in this work. This method is based on the transmission coefficient of upgoing waves impinging in the geophone‐ground contact, where the ground is described as an anelastic half‐space. The boundary conditions at the contact have already been used to model fractures and are shown here to provide the equation of the damped oscillator. This fracture‐contact model depends on the stiffness characteristic of the contact between the geophone base plate and the ground. The transmission coefficient from the ground to the plate increases for increasing weight and decreasing base plate area. The new model predicts that the resonant frequency is independent of the geophone weight and plate radius, while the recorded energy increases with increasing weight and decreasing base plate area (as shown from our own experiments and measurements by Krohn) which is contrary to the theories developed by Wolf and Hoover‐O'Brien. The transient response is obtained by an inverse Fourier transform. Optimal geophone‐ground coupling and energy transmission are required, the first concept meaning that the geophone is following the motion of the ground and the second one that the signal is detectable. As a final example, we simulate seismic acquisition based on the novel theory, showing the differences between optimal and poor ground‐to‐geophone energy transmission.     

Site specific probabilistic seismic hazard analysis at Dubai Creek on the west coast of UAE

A probabilistic seismic hazard analysis (PSHA) was conducted to establish the hazard spectra for a site located at Dubai Creek on the west coast of the United Arab Emirates (UAE). The PSHA considered all the seismogenic sources that affect the site, including plate boundaries such as the Makran subduction zone, the Zagros fold-thrust region and the transition fault system between them; and local crustal faults in UAE. PSHA indicated that local faults dominate the hazard. The peak ground acceleration (PGA) for the 475-year return period spectrum is 0.17 g and 0.33 g for the 2,475-year return period spectrum. The hazard spectra are then employed to establish rock ground motions using the spectral matching technique.     

Hydrochemical evolution and variation of groundwater and its environmental impact at Sohag, Egypt

Groundwater resources of Sohag, Egypt are currently threatened by contamination from agricultural and urbanization activities. Groundwater in Sohag area has a special significance where it is the second source for fresh water used for agricultural, domestic, and industrial purposes. Due to growing population, agriculture expansion, and urbanization, groundwater quality assessment needs more attention to cope with the increasing water demand in this arid zones and limited water resources. The aim of this paper is to address the integrated role of geochemical processes, agriculture and urbanization in evolution of groundwater composition, and their impact on groundwater quality to help in management and protection of groundwater resources of study area using geochemical modeling techniques and geographical information systems. Spatial variation of groundwater hydrochemical properties, rock–water interaction, ion exchange, and assessment of groundwater quality were investigated. Results indicated that groundwater properties are varied spatially and its evolution in the study area is generally controlled by the prevailed geochemical processes represented by leaching, dissolution, and precipitation of salts and minerals, ion exchange, in addition to human activities represented by agriculture and urbanization as well as climatic and poor drainage conditions. Management alternatives should be followed in the study area to avoid degradation of groundwater quality and provide sustainable development.     

Recent warming trend in the coastal region of Qatar

The objective of this study was to analyze long-term temperature-related phenomena in the eastern portion of the Middle East, focusing on the coastal region of Qatar. Extreme temperature indices were examined, which were defined by the Expert Team on Climate Change Detection and Indices, for Doha, Qatar; these indices were then compared with those from neighboring countries. The trends were calculated for a 30-year period (1983–2012), using hourly data obtained from the National Climatic Data Center. The results showed spatially consistent warming trends throughout the region. For Doha, 11 of the 12 indices studied showed significant warming trends. In particular, the warming trends were represented by an increase in the number of warm days and nights and a decrease in the number of cool nights and days. The high-temperature extremes during the night have risen at more than twice the rate of their corresponding daytime extremes. The intensity and frequency of hot days have increased, and the minimum temperature indices exhibited a higher rate of warming. The climatic changes in Doha are consistent with the region-wide heat-up in recent decades across the Middle East. However, the rapid economic expansion, increase of population since the 1990s, and urban effects in the region are thought to have intensified the rapidly warming climate pattern observed in Doha since the turn of the century.