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71.
Prediction of areas prone to land degradation in agricultural catchments is a complex task. This is due to the difficulties encountered in data gathering over wide regions and in the translation of existing scientific knowledge to a quantitative and spatially explicit risk assessment system. This paper incorporates the use of remotely sensed data, terrain analysis and a multi‐criteria mechanism for evaluating risks of soil loss, water ponding, and sediment deposition in a mid‐size agricultural Mediterranean catchment, under 80 years of intensive cultivation. The research uses simulations to study the effect of topographic attributes, soil characteristics, vegetation cover, rainfall intensity and human activities on the three above‐mentioned processes. The results show that, from the methodological point of view, the integration of knowledge from several experts yields better predictive results than relying on a single expert, even the one found to be most consistent. Also, the use of a simple weighted linear combination was more useful than the more sophisticated computerized programming technique. From the phenomenological point of view, the increase in rainfall intensity and land‐use transformation from orchard to field‐crops has led to a significant increase in soil loss and sediment yield, while extreme changes in tillage direction have only yielded minor changes in water ponding. The developed system's predictive capabilities also show that the outcomes can be used as a basis for decisions on catchment management in regions of high environmental sensitivity. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
72.
Said Attia al Hagrey 《Pure and Applied Geophysics》2012,169(7):1283-1292
Modern optimization approaches for electrode configurations can significantly improve the resolution of 2.5D resistivity imaging surveys. This study presents a brief review of the 2.5D optimization approach, particularly for borehole–borehole surveys with applications for mapping virtual CO2 plumes sequestrated in deep saline reservoir formations. The applied algorithm searches for arrays that maximize the spatial resolution of the survey among the comprehensive dataset of best possible spatial resolution (i.e. least temporal resolution). A main goal of this study is to increase the temporal resolution of ERT borehole–borehole surveys by selecting optimized electrode configurations in order to minimise the required data acquisition time while sustaining a high spatial resolution. The optimized dataset starts with a base set and is iteratively increased based on the model resolution matrix (R ) until the required number of data points is achieved. Among four different optimization methods, the compare R (CR) method of the best resolution is applied to directly calculate R for each new array added to the optimized dataset. Small optimized datasets generated by this technique are only <5% of their comprehensive sets but of an average resolution ratio (R r) of >0.95 (i.e. almost the same resolution). With increasing the size of the optimized dataset (during its generation), the algorithm progressively enhances R r values in the central interwell region (of low sensitivities and low resolution) far higher than in the near borehole region (of high sensitivities). Also the inverted tomogram reliability increases by increasing the optimized data size. Briefly, the optimized arrays improve the resolution in the interwell region which is commonly low in borehole–borehole ERT studies. The inverted output model is evaluated quantitatively using the model difference relative to the input model. The results reflect the common smearing effects and artefacts of varying degrees that overpredict volumes, underpredict magnitudes and blur boundaries of the target anomalies. This input model is a synthetic resistivity model that was used to generate synthetic (forward solution) data used during the inversion. Applications on synthetic CO2 models show that the mapping resolution for optimized datasets is better than that for other highly resolving arrays of the same number of data points. Problems of smeared boundaries and thin layers are less visible in the optimized array than in the other highly resolving arrays. 相似文献
73.
Khadidja Abbes Louis Dorbath Catherine Dorbath Mohamed Djeddi Farida Ousadou Said Maouche Nassima Benkaci Abdennasser Slimani Said Larbes Djillali Bouziane 《Journal of Seismology》2016,20(2):655-667
A moderate Mw 4.9 earthquake struck the Beni Haoua (Algeria) coastal area on April 25, 2012. The mainshock was largely recorded by the accelerograph network of the Centre National de Recherche Appliquée en Génie Parasismique (CGS). The same day the earthquake occurred, eight mobile short period stations were deployed through the epicentral area. In this study, we use accelerogram and seismogram data recorded by these two networks. We combined the focal mechanism built from the first motion of P waves and from waveform inversion, and the distribution of aftershocks to well constrain the source parameters. The mainshock is located with a shallow focal depth, ~9 km, and the focal mechanism shows a nearly pure left lateral strike slip motion, with total seismic moment of 2.8?×?1016 N.m (Mw?=?4.9). The aftershocks mainly cluster on a narrow NS strip, starting at the coast up to 3–4 km inland. This cluster, almost vertical, is concentrated between 6 and 10 km depth. The second part of this work concerns the damage distribution and estimated intensity in the epicentral area. The damage distribution is discussed in connection with the observed maximum strong motion. The acceleration response spectrum with 5 % damping of the mainshock and aftershocks give the maximum amplitude in high frequency which directly affects the performance of the high-frequency structures. Finally, we tie this earthquake with the seismotectonic of the region, leading to conclude that it occurred on a N–S transform zone between two major compressional fault zones oriented NE–SW. 相似文献
74.
75.
Kamel Baddari Anatoly D. Frolov Victor Tourtchine Fayçal Rahmoune Said Makdeche 《Acta Geophysica》2015,63(1):62-102
Precursory stages of failure development in large rock samples were studied and simultaneous observations of the space-time variation of several physical fields were carried out under different stress-strain states. The failure process was studied in detail. A hierarchical structure of discreet rock medium was obtained after loading. It was found that the moisture reduced the rock strength, increased the microcrack distribution and influenced the shape of the failure physical precursors. The rise in temperature up to 400 °C affected the physical precursors at the intermediate and final stages of the failure. Significant variations were detected in the acoustic and electromagnetic emissions. The coalescence criterion was slightly depending on the rock moisture and temperature effect. The possibility of identifying the precursory stage of failure at different strain conditions by means of a complex parameter derived from the convolution of physical recorded data is shown. The obtained results point out the efficiency of the laboratory modelling of seismic processes. 相似文献
76.
The effect of adding olive oil cake to two sandy soils on their abilities to retain water was investigated under controlled conditions. Olive oil cake was applied to the soils in pots and rates equivalent to 0, 5, 10, and 20% by weigh of the air-dried soil. Pots were incubated for 3 weeks at controlled conditions.The results show that the addition of oil cake significantly increased (P 0·05) the ability of the two sandy soils studied to retain water under all applied tensions. However, treatments with highest percentage of oil cake applied, had significantly higher water retention compared to those which had less. In terms of available water, which was calculated as the difference in volumetric water content between field capacity (-33 KPa) and wilting point (1·5 MPa), the highest olive oil cake applied doubled this difference in comparison to the control. An effect of soil texture was also noted. Generally, the influence of olive oil cake on the available moisture percentage was more pronounced in sand than the sandy loam. 相似文献
77.
Ahmed Said Dahlan Dr. 《GeoJournal》1990,21(4):385-395
This case study examines Israeli resettlement policy and housing demolition measures practiced in the Gaza Strip. Since the Gaza Strip is distinguished by a huge concentration of dispossessed Palestinian refugees maintained in large camps, the Israeli authorities, from the early stage of the 1967 occupation of the area, have devoted major effort to breaking up the camps and relocating their inhabitants elsewhere. The Israeli authorities have applied a clear policy of systematic destruction of refugee shelters and initiation of resettlement schemes, aimed in the short run at making the refugee camps less congested, while in the long run, the policy appears designed to remove these camps from the landscape entirely, since they remain a constant reminder of Palestinian uprootedness and exile. To date, the Israeli strategy of demolishing the entire refugee camp network has failed to achieve its final objective. 相似文献
78.
Groundwater pollution risk mapping for the Eocene aquifer of the Oum Er-Rabia basin, Morocco 总被引:2,自引:0,他引:2
Said Ettazarini 《Environmental Geology》2006,51(3):341-347
Sustainable development requires the management and preservation of water resources indispensable for all human activities. When groundwater constitutes the main water resource, vulnerability maps therefore are an important tool for identifying zones of high pollution risk and taking preventive measures in potential pollution sites. The vulnerability assessment for the Eocene aquifer in the Moroccan basin of Oum Er-Rabia is based on the DRASTIC method that uses seven parameters summarizing climatic, geological, and hydrogeological conditions controlling the seepage of pollutant substances to groundwater. Vulnerability maps were produced by using GIS techniques and applying the “generic” and “agricultural” models according to the DRASTIC charter. Resulting maps revealed that the aquifer is highly vulnerable in the western part of the basin and areas being under high contamination risk are more extensive when the “agricultural” model was applied. 相似文献
79.
80.
The region of Ain Sefra is an arid region suffering from sand encroachment. In this study, we are calculating the shifted sand quantity and efficient wind directions during a period of 30 years (1985 to 2015) in order to classify the danger. The study shows that efficient winds in the region are characterized by their potential drift estimated at 220 till 329. This classifies the region as medium. Besides, the resultant drift potential is 76 to 99 with a migration coefficient of 0.3 which gives a medium classification to the zone and proves the Aeolian erosion complex system and its interrelation with other factors. Efficient winds generally blow from South-west to North-east with an angle of 234°. Furthermore, there are other directions causing sand drifting. Sand movement quantity is estimated between 23.03 and 15,224 m3/m/year according to effective wind threshold speed, which is 5 to 6 m/s. Autumn is the period when sand mobility is higher, but it decreases in winter. On the other hand, sand potential movement was well shown through satellite imagery between 1985 and 2015. Indeed, it closely corresponded to the previous study. It showed sand movement direction from South-west to North-east, and sand surface increase reached 16.44% of the global zone surface. Whereas, it decreased ??2.5% between 1985 and 2015. There is an important concentration of sand accumulation under the western mountain foothills along which sand moves. This shows that the ground particularities play a crucial role in this phenomenon. 相似文献