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排序方式： 共有115条查询结果，搜索用时 375 毫秒
81.
Marine intrusion is the most serious problem facing the coastal Jorf shallow aquifer, located in south‐eastern Tunisia on the Mediterranean Sea. Jorf Aquifer is intensively exploited to supply the growing needs of agriculture and domestic sectors. This work proposes a multidisciplinary investigation, involving hydro‐geochemical, geoelectrical survey and geostatistical techniques for modelling the saltwater intrusion. For this purpose, 36 water samples were conducted and analysed. Electric conductivity, pH, total dissolved solids and major ions were measured and analysed. Pie and Durov Diagrams, Q‐mode hierarchical cluster and geostatistical analysis were considered to identify the main groundwater mineralization processes. Results revealed that the Na‐Cl‐Ca‐SO4 is the dominant water type suggesting that dissolution of halite and gypsum was the main mineralization source of groundwater in the central and southern part of study area. However, saltwater intrusion was shown to control groundwater quality essentially in coastal areas. Variographic analyses were used to select the variographic model that best fits the spatial development of apparent resistivity. Kriged apparent resistivity profiles showed an abnormal decrease of resistivity values in the coastal zone, implying highly saline water because of seawater intrusion. Apparent resistivity values also decrease considerably in the faulted areas, suggesting a contribution of faults to seawater intrusion. Finally, saltwater mixing ratio was computed for each sample, and a refined seawater intrusion map was developed. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
82.
83.
Sea level in the Mediterranean Sea: seasonal adjustment and trend extraction within the framework of SSA 总被引：1，自引：0，他引：1
The sea level change is a crucial indicator of our climate. The spatial sampling offered by satellite altimetry and its continuity during the past years are the major assets to provide an improved vision of the Mediterranean sea level changes. In this paper, an automatic signal extraction approach, based on Singular Spectrum Analysis (SSA), is utilized for analysis and seasonal adjustment of the Mediterranean Sea level series. This automatic approach enables us to overcome the difficulties of visual identification of trend constituents that sometimes we encounter when using the conventional SSA method. The results indicate that the Mediterranean mean sea level is dominated by several harmonic components. The annual signal is particularly strong and almost covers 73.62 % of the original sea level series variation whiles its amplitude is about 15 cm. The extracted trend also indicates that the Mediterranean main sea level has significantly been raised during the period 1993–2012 by 2.44?±?0.4 mm yr?1. As an important consequence, considering the current situation, if this trend continues, the Mediterranean Sea level will be raised about 22 cm by the end of this century, which makes a dramatic effect on several issues such as land, flora, fauna, and people activities established along the Mediterranean coastlines. 相似文献
84.
The authors derived the normalized difference vegetation index (NDVI) from the NOAA/AVHRR Land dataset, at a spatial resolution of 8km and 15-day intervals, to investigate the vegetation variations in China during the period from 1982 to 2001. Then, GIS is used to examine the relationship between precipitation and the Normalized Difference Vegetation Index (NDVI) in China, and the value of NDVI is taken as a tool for drought monitoring. The results showed that in the study period, China’s vegetation cover had tended to increase, compared to the early 1980s; mean annual NDVI increased 3.8%. The agricultural regions (Henan, Hebei, Anhui and Shandong) and the west of China are marked by an increase, while the eastern coastal regions are marked by a decrease. The correlation between monthly NDVI and monthly precipitation/temperature in the period 1982 to 2001 is significantly positive (R2=0.80, R2=0.84); indicating the close coupling between climate conditions (precipitation and temperature) and land surface response patterns over China. Examination of NDVI time series reveals two periods: (1) 1982–1989, marked by low values below average NDVI and persistence of drought with a signature large-scale drought during the 1982 and 1989; and (2) 1990–2001, marked by a wetter trend with region-wide high values above average NDVI and a maximum level occurring in 1994 and 1998. 相似文献
85.
Abstract This paper refers to the quantification and prediction of the sedimentation rate of 26 hillside-dam reservoirs in Central Tunisia. The objectives of the study are to develop a simple and practical methodology to identify controlling factors of sedimentation, and to propose a regionalization from the study sites. Principal component analysis (PCA) and complementary multi-dimensional statistical methods are used to relate highly variable area-specific sediment yield to hydro-morphometric, lithological, geomorphological and anthropogenic characteristics of catchments. It appears that catchment area is not the main controlling factor of sedimentation in the studied area. The overall slope index, drainage network characteristics and runoff parameters are also important in characterizing sediment yield. Applied to the annual sedimentation rate series, PCA resulted in retaining the first three principal axes, explaining 65% of the total variance. Statistical methods showed that the overall slope index, the total drainage length, the compacity index and the runoff parameters are as important for the sedimentation quantification. This allowed a graphical clustering of the study zone into three distinct groups having similar behaviours: (i) watersheds characterized by high sediment transport rates and high runoff coefficients, (ii) basins distinguished by relatively low values of both flow discharge and sediment transport rates, and (iii) watersheds with an intermediate sediment yield, especially characterized by relatively high relief. In a second step, a multiple regression model including the four characteristic catchment properties was developed, presenting a valuable tool to predict area-specific sediment yield from catchments in central Tunisia. This model shows reasonable efficiency with an absolute prediction error of 81%. Citation Ayadi, I., Abida, H., Djebbar, Y. & Mahjoub, M. R. (2010) Sediment yield variability in central Tunisia: a quantitative analysis of its controlling factors. Hydrol. Sci. J. 55(3), 446–458. 相似文献
86.
87.
Surface Matching and Change Detection Using a Modified Hough Transformation for Robust Parameter Estimation 总被引：3，自引：0，他引：3
Many photogrammetric and GIS applications, such as city modelling, change detection and object recognition, deal with surfaces. Change detection involves looking for differences between two surface models that are obtained from different sensors, for example an optical sensor and a laser scanner, or by the same sensor at different epochs. Surfaces obtained through a sampling process may also have to be compared for future processing (for example transformation parameter estimation and change detection). Surface matching is therefore an essential task in these applications. The matching of surfaces involves two steps. The first step deals with finding the correspondences between two surface points and/or patches. The second step requires the determination of transformation parameters between the two surfaces. However, since most surfaces consist of randomly distributed discrete points and may have different reference systems, finding the correspondences cannot be achieved without knowing the transformation parameters between the two surfaces. Conversely, deriving the transformation parameters requires the knowledge of the correspondence between the two point sets. The suggested approach for surface matching deals with randomly distributed data sets without the need for error prone interpolation and requires no point-to-point correspondence between the two surfaces under consideration. This research simultaneously solves for the correspondence and the transformation parameters using a Modified Iterated Hough Transform for robust parameter estimation. Several experiments are conducted to prove the feasibility and the robustness of the suggested approach, even when a high percentage of change exists. 相似文献
88.
Impacts of irrigation with treated wastewater effluents on soils and groundwater aquifer in the vicinity of Sidi Abid Region
(Tunisia) are evaluated. The groundwater aquifer was monitored by several piezometers, where monthly water levels were registered
and groundwater salinity was evaluated. This resulted in characterizing the spatial and temporal evolution of the hydrochemical
and hydrodynamic properties of the aquifer, showing thereby the impact of artificial recharge. Piezometric maps for pre-recharge
and post-recharge situations were developed and a comparison study of both piezometric situations was considered. The piezometric
evolution map showed a generalized rise of the piezometric level in the vicinity of the irrigation zone. The extent of recharge
was shown to increase with time as the groundwater level increase, which was localized in the vicinity of the irrigation area,
reached more extended zones. Several groundwater samples were withdrawn from wells and piezometers and analyzed. Examining
the corresponding physical and chemical parameters showed an increase in the concentrations of nutrients (28 mg/l for NO3 and 3.97 mg/l for NH4) in the groundwater aquifer below the irrigation zone, which confirms again the infiltration of treated wastewater effluents.
The evolution of soil salinity was examined through chemical analysis of soil samples. Electric conductivities of soils were
generally shown to be less than 4 mS/cm while the irrigation water has an electric conductivity that may reach 6.63 mS/cm.
This might be explained by the phenomenon of dilution and the capacity of soils to evacuate salts downward. 相似文献
89.
Golian Mohsen Katibeh Homayoon Najafi Zeinab Saadat Habib Saffarzadeh Ali Ahmadi Aboozar Khazaei Mahdi Sametzadeh Ershad 《Hydrogeology Journal》2021,29(6):2171-2186
The Dena rainstorm in Iran in March and April 2019 caused about US$ 8.3?×?109 damage in the country; however, it resulted in the replenishment of half of the dam reservoirs and 35% of ponds and lakes. Also, it increased the volume of groundwater stored in aquifers by 3.6?×?109 m3. In arid and semiarid regions such as most parts of Iran, which usually face water scarcity, getting water from rainstorms is essential for replenishing water resources. This research aims to quantify the direct and indirect effects of the Dena rainstorm on the replenishment of Iran’s groundwater storage using the groundwater balance method and water-table fluctuation method. Studies showed that the main mechanisms for replenishment of groundwater storage due to the rainstorm included increases in precipitation recharge, surface runoff recharge, and artificial recharge, and reductions in irrigation withdrawal and evapotranspiration, while the contribution of each factor is estimated to be about 23, 28, 2, 15, and 32%, respectively.
相似文献90.