Perspective of agricultural water safety under combined future changes in crop water requirements and climate conditions in China

Theoretical and Applied Climatology - Agricultural water safety is foreseen to have more turmoil in the future, and this concern will be driven by agricultural production growth, population growth,...     

Aquifer vulnerability assessment using the DRASTIC model at Russeifa landfill,northeast Jordan

Groundwater is inherently susceptible to contamination from anthropogenic activities and remediation is very difficult and expensive. Prevention of contamination is hence critical in effective groundwater management. In this paper an attempt has been made to assess aquifer vulnerability at the Russeifa solid waste landfill. This disposal site is placed at the most important aquifer in Jordan, which is known as Amman-Wadi Sir (B2/A7). The daily-generated leachate within the landfill is about 160 m³/day and there is no system for collecting and treating this leachate. Therefore, the leachate infiltrates to groundwater and degrades the quality of the groundwater. The area is strongly vulnerable to pollution due to the presence of intensive agricultural activity, the solid waste disposal site and industries. Increasing groundwater demand makes the protection of the aquifer from pollution crucial. Physical and hydrogeological characteristics make the aquifer susceptible to pollution. The vulnerability of groundwater to contamination in the study area was quantified using the DRASTIC model. The DRASTIC model uses the following seven parameters: depth to water, recharge, aquifer media, soil media, topography, impact on vadose zone and hydraulic conductivity. The water level data were measured in the observation wells within the disposal site. The recharge is derived based on precipitation, land use and soil characteristics. The aquifer media was obtained from a geological map of the area. The topography is obtained from the Natural Resources Authority of Jordan, 1:50,000 scale topographic map. The impact on the vadose zone is defined by the soil permeability and depth to water. The hydraulic conductivity was obtained from the field pumping tests. The calculated DRASTIC index number indicates a moderate pollution potential for the study area.     

An empirical attenuation relationship for Northwestern Turkey ground motion using a random effects approach

Using a random effects model that takes into consideration the correlation of data recorded by a single seismic event, a database consisting of 195 recordings from 17 recent events is employed to develop empirical attenuation relationships for the geometric mean of horizontal peak ground acceleration and 5-percent damped spectral acceleration (S_a). The recordings employed are obtained from strong motion stations operating in Northwestern Turkey and resulted from events that include the Kocaeli (M_w=7.4) and the Düzce (M_w=7.1) earthquakes and their aftershocks as well as other events. By studying differences in standard errors, the random effects model is compared with a fixed effects model that does not account for distinctions between intra- and inter-event variability. Effects of local site conditions are included in the empirical relationships developed. The dependence on frequency of the various model parameters is also studied. Frequency-dependent attenuation coefficients for the proposed random effects models developed are summarized in tables to facilitate their use.     

Secondary circulation induced by flow curvature and Coriolis effects around headlands and islands

Previous studies have shown that flow curvature in river bends generates a secondary circulation in the plane normal to the mean flow direction. A similar circulation pattern is shown to exist in oceanic situations when flows are subject to curvature, mainly due to interaction with topographic features. However, it is shown that, due to differences between oceanic conditions and river bends, theory and prediction methods based on the assumptions for river bends are invalid for oceanic flows. Via scaling arguments based on the equations of motion, that include both the effects of flow curvature and the Coriolis force, parameters that govern the different flow regimes are identified. The maximum strength of the secondary flow is derived for each flow regime and is verified using a three-dimensional (3-D) numerical model applied to an idealized island. It is also shown that upwelling, due to the generation of secondary flow, occurs off the tips of the headland or island, and its influence can extend far downstream.Responsible Editor: Richard Signell     

Effects of T-shape groin parameters on beach accretion

The effects of various groin parameters (length, head length and opening) and wave parameters (wave height, wave period and wave angle) on the accretion of the area protected by T-shape groins are studied in a physical model. The model studies are performed using regular waves in a basin. A numerical model which depends primarily on a CERC model is employed to examine the effects of some of the above parameters. Good agreement is found in the results of physical and numerical models. The results of a numerical model are compared with field data obtained by deep sounding measurements at Of coasts, Trabzon Province, Turkey. The finding from this study may be employed in designing T-shape groins.     

On the importance of boundary layer calculations instead of viscous correction in heavily loaded marine propellers while using a surface panel method

A surface panel method is employed for the thin boundary layer calculation of heavily loaded marine propellers in steady state conditions. Employing the surface panel method, known as the “Morino Method”, the flow field around the propeller is represented by an unknown potential. The majority of the flow field is governed by the potential theory while the viscosity is assumed to be largely confined to thin shear layer on the propeller surface. The boundary layer calculations are performed by using Cebeci-Smith two dimensional model and the local skin friction coefficients and blowing velocities are obtained along the pre-computed on-body streamlines. It is shown that the prediction of torque of the propeller is improved when the boundary layer calculations are used instead of the boundary layer corrections based on the formulae established for the flat plates.     

Structure of Mesozoic oceanic crust in the vicinity of the Cape Verde Islands from seismic reflection profiles

Multichannel seismic reflection profile data have been used to determine the internal structure of Mesozoic oceanic crust in the vicinity of the Cape Verde islands. The data show the oceanic crust to be characterized by both dipping and sub-horizontal reflectors. Several lines of evidence argue against the reflectors being scattering artifacts arising, for example, from rough basement topography. Instead, the reflectors are attributed to tectonic and magmatic processes associated with the accretion of oceanic crust at the Mid-Atlantic Ridge. The upper crust shows variable reflectivity due to both dipping and sub-horizontal events. We interpret the dipping reflectors, which have been identified on both ridge-normal and ridge-parallel profiles, as sub-surface expressions of normal faults that formed at or near the Mid-Atlantic Ridge. There is no evidence that the faults are caused by loading of the oceanic crust by either the Cape Verde islands or their associated topographic swell. Some faults, however, can be traced into the overlying sediments suggesting they may have been re-activated since their formation at the ridge. The origin of the sub-horizontal reflectors is not as clear. We believe them to be boundaries of different igneous lithologies, such as that between basalts and gabbros. The lower crust is highly reflective in some areas, whereas in others only a few dipping and sub-horizontal reflectors are observed. Some of the dipping reflectors can be traced into the upper crust, suggesting they are also normal faults. Others, however, appear to be confined to the lower crust. The sub-horizontal, discontinuous, reflectors about 2.0–2.5 seconds two-way travel time below the top of oceanic basement are attributed to the Moho.     

Effects of salinity and clay type on oil-mineral aggregation

Effects of salinity and clay type on the aggregation process of crude oil and clay particles (oil-mineral aggregates--OMA) were studied in the laboratory. OMA were generated by shaking various oil/clay mixtures in water at 20 degrees C and at a pre-determined energy level. Shape, median and maximum sizes, size distribution and concentration of oil droplets forming OMA were measured using epi-fluorescence microscopy. Results showed that the median and maximum sizes and the concentration of mineral-stabilized droplets increase rapidly when salinity increases from zero to a critical aggregation salinity in the range of 1.2-3.5 ppt. The magnitude of the increase of droplet size is controlled by clay type, while the increase of droplet concentration is influenced by oil type. Size distributions of oil droplets are self-similar, but their magnitudes depend on salinity and oil type. The effect of salinity on droplet size distribution is strongly influenced by clay type. Empirical relationships are derived to calculate concentration and size distribution of mineral-stabilized droplets.     

The Aegir Rift: Crustal Structure of an Extinct Spreading Axis

Two seismic refraction and gravity lines were obtained along and normal to the axis of the Aegir Rift, an extinct spreading centre in the Norway Basin. Velocity-depth solutions and crustal structure models are derived from ocean-bottom records using two-dimensional ray tracing and synthetic seismogram modelling techniques. Gravity data are used to generate models consistent with the lateral variations in thickness of the layers in the crustal models. The resulting models require considerable degree of lateral inhomogeneity along and perpendicular to the rift axis. Crust within the extinct spreading centre is found to be thinner and of low P-wave velocity when compared with the crust sampled off-axis. To explain reduced velocities of the lower crust we suggest that, due to the relationship between fracturing and seismic velocity, the decreasing spreading rate leading up to extinction let the mechanically strong layer thicken, so that faulting and fracturing extended to greater depths . Low velocities are also observed in the uppermost mantle underlying the extinct spreading ridge. This zone is attributed to hydrothermal alteration of upper mantle peridotites. Furthermore, after spreading ceased 32-26 my ago, ongoing passive hydrothermal circulation was accompanied by the precipitation of alteration products in open void spaces, thereby decreasing the porosity and increasing the velocity. Consequently the typical low velocities of layer 2 found at active mid-ocean ridges have been replaced by values typical of mature oceanic crust.