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排序方式: 共有210条查询结果,搜索用时 15 毫秒
31.
Rainfall-induced erosion involves the detachment of soil particles by raindrop impact and their transport by the combined action of the shallow surface runoff and raindrop impact.Although temporal variation in rainfall intensity(pattern)during natural rainstorms is a common phenomenon,the available information is inadequate to understand its effects on runoff and rainfall-induced erosion processes.To address this issue,four simulated rainfall patterns(constant,increasing,decreasing,and increasing-decreasing)with the same total kinetic energy were designed.Two soil types(sandy and sandy loam)were subjected to simulated rainfall using 15 cm×30 cm long detachment trays under infiltration conditions.For each simulation,runoff and sediment concentration were sampled at regular intervals.No obvious difference was observed in runoff across the two soil types,but there were significant differences in soil losses among the different rainfall patterns and stages.For varying-intensity rainfall patterns,the dominant sediment transport mechanism was not only influenced by raindrop detachment but also was affected by raindrop-induced shallow flow transport.Moreover,the efficiency of equations that predict the interrill erosion rate increased when the integrated raindrop impact and surface runoff rate were applied.Although the processes of interrill erosion are complex,the findings in this study may provide useful insight for developing models that predict the effects of rainfall pattern on runoff and erosion. 相似文献
32.
Abdalla Sirag Norashidah Mohamed Nor Siong Hook Law Nik Mustapha Raja Abdullah Miloud Lacheheb 《GeoJournal》2017,82(6):1247-1261
The current paper examines the relationship between health financing (public and out-of-pocket health financing), CO2 emission and health outcomes in 35 Sub-Saharan African countries for the period of 1995–2012. The panel unit root and cointegration tests are conducted as pre-tests, followed by the estimation of the parameters using the FM-OLS and DOLS techniques. The findings of the study show the importance of public health financing as one of the major factors that lead to better health outcomes, whereas the out-of-pocket expenditure is found to be harmful to population health since it leads to increase under-5 mortality rate. Although the results show a negative relationship between CO2 and health outcomes, still these results remain inclusive. In addition, the findings reveal the importance of socioeconomic factors such as income and education as key determinants of health outcomes. 相似文献
33.
Osman A. E. Abdalla 《Arabian Journal of Geosciences》2009,2(4):321-335
The present study assesses groundwater resources in the semiarid central Sudan, where 20 deep productive wells were installed
to supply a major city in the region, El Obeid. The wells, which has an average 20 L/s discharge each, are taping a deep semiconfined
to confined aquifer of fluvial silisiclastics deposited in the Tertiary–Pleistocene. Groundwater modeling was used as a technique
to interpret the hydrologic system in arid to semiarid central Sudan and to simulate the future influence of the project on
the hydrogeologic system. The simulation confirmed that steady-state flow conditions have been currently reached as indicated
by consistency of computed heads. It also calibrated the values of the conductivity and recharge and ensured the sustainability
of the El Obeid water supply project. A total of 3.5 × 107 m3/year can be continually extracted from the deep aquifer to supply El Obeid city without endangering the groundwater resources
in the region. The decline in water level will not exceed 25 m during the first 10 years, while indefinite continuous pumping
will affect only the vicinity of the wells in a circle of 30 km diameter. Therefore, aquifer storage capacity and hydraulic
properties encourage further groundwater exploitation. The present use of groundwater is extremely lower than the present
demand, and it can potentially cover future demands without introducing significant changes to the system. The increase of
pumping cost due to the decline in head subsequent to project operation was found to be minimal and of local effect. 相似文献
34.
Khadija Semhi Osman A. E. Abdalla Salah Al Khirbash Tabisam Khan Salim Asaidi Sardar Farooq 《Arabian Journal of Geosciences》2009,2(2):143-150
Groundwater samples from six wells and various species of plants from soils developed on ophiolites were collected from an arid area (AlKhod area, Oman) and analyzed for trace elements including rare earth elements (REEs). The distribution patterns of REEs in plants indicated an enrichment in middle REEs (MREEs?=?Sm to Dy) and heavy REEs (HREEs?=?Ho to Lu), when they are normalized to the REE composition of the Post Archean Australian Shale (PAAS), with a significant negative anomaly in Ce and a positive anomaly in Eu. Compared to Oman ophiolites, the REEs in different species of plants are depleted in Ce and enriched in MREEs and slightly enriched in light REE (LREE?=?from La to Nd). Relative to PAAS, the distribution of REEs in groundwaters revealed similar patterns to the REE distribution in plants. The distribution patterns of REEs in plants relative to those in waters are nearly flat. These patterns suggest that the transfer of REEs from soil solutions to the groundwaters in Oman occurs without any significant fractionation. 相似文献
35.
Fluid inclusions in the leucosomes of Wadi Feiran migmatites showed that CO
2
, H2O and (H2O-CO2) fluids were likely to have been present when partial melting began in these rocks. Low salinity, aqueous fluid, to a lesser
extent, CO2-rich fluids are the most abundant fluids. The present study suggests that high-density CO2 inclusions were formed at the earliest stage, while H2O inclusions were formed at the late stage. In an intermediate stage, low-density CO2 and H2O, CO2 inclusions were formed. At the early stage of uplift and during melt crystallization, the CO2-bearing vapour was trapped at grain boundaries. At the late stage of uplift, H2O released at the time of crystallization of the melt was trapped as inclusions. 相似文献
36.
Salah Saleh 《Pure and Applied Geophysics》2013,170(12):2037-2074
Crustal and lithospheric thicknesses of the southeastern Mediterranean Basin region were determined using 3D Bouguer and elevation data analysis. The model is based on the assumption of local isostatic equilibrium. The calculated regional and residual Bouguer anomaly maps were employed for highlighting both deep and shallow structures. Generally, the regional field in the area under study is considered to be mainly influenced by the density contrast between the crust and upper mantle. Use of the gravity and topographic data with earthquake focal depths has improved both the geometry and the density distribution in the 3-D calculated profiles. The oceanic-continental boundary, the basement relief, Moho depth and lithosphere-asthenosphere boundary maps were estimated. The results point to the occurrence of thick continental crust areas with a thickness of approximately 32 km in northern Egypt. Below the coastal regions, the thickness of crust decreases abruptly (transition zone). An inverse correlation between sediment and crustal thicknesses shows up from the study. Furthermore, our density model reveals the existence of a continental crustal zone below the Eratosthenes Seamount block. Nevertheless, the crustal type beneath the Levantine basin is typically oceanic; this is covered by sedimentary sequences more than 14 km thick. The modeled Moho map shows a depth of 28–30 km below Cyprus and a depth of 26–28 km beneath the south Florence Rise in the northern west. However, the Moho lies at a constant shallow depth of 22–24 km below the Levantine Basin, which indicates thinning of the crust beneath this region. The Moho map reveals also a maximum depth of about 33–35 km beneath both the northern Egypt and northern Sinai, both of which are of the continental crust. The resulting mantle density anomalies suggest important variations of the lithosphere-asthenosphere boundary (LAB) topography, indicating prominent lithospheric mantle thinning beneath south Cyprus (LAB ~90 km depth), followed by thickening beneath the Eratosthenes seamount, Florence Rise, Levantine Basin and reaching to maximum thickness below Cyprian Arc (LAB ~115–120 km depth), and further followed by thinning in the north African margin plate and north Sinai subplate (LAB ~90–95 km depth). According to our density model profiles, we find that almost all earthquakes in the study area occurred along the western and central segments of the Cyprian arc while they almost disappear along the eastern segment. The active subduction zone in the Cyprian Arc is associated with large negative anomalies due to its low velocity upper mantle zone, which might be an indication of a serpentinized mantle. This means that collision between Cyprus and the Eratosthenes Seamount block is marked by seismic activity. Additionally, this block is in the process of dynamically subsiding, breaking-up and being underthrusted beneath Cyprus to the north and thrusted onto the Levantine Basin to the south. 相似文献
37.
Gold Valley is typical of intermountain basins in Death Valley National Park (DVNP), California (USA). Using water-balance calculations, a GIS-based analytical model has been developed to estimate precipitational infiltration rates from catchment-scale topographic data (elevation and slope). The calculations indicate that groundwater recharge mainly takes place at high elevations (>1,100?m) during winter (average 1.78?mm/yr). A resistivity survey suggests that groundwater accumulates in upstream compartmentalized reservoirs and that the groundwater flows through basin fill and fractured bedrock. This explains the relationship between the upstream precipitational infiltration in Gold Valley and the downstream spring flow in Willow Creek. To verify the ability of local recharge to support high-flux springs in DVNP, a GIS-based model was also applied to the Furnace Creek catchment. The results produced insufficient total volume of precipitational infiltration to support flow from the main high-flux springs in DVNP under current climatic conditions. This study introduces a GIS-based infiltration model that can be integrated into the Death Valley regional groundwater flow model to estimate precipitational infiltration recharge. In addition, the GIS-based model can efficiently estimate local precipitational infiltration in similar intermountain basins in arid regions provided that the validity of the model is verified. 相似文献
38.
Groundwater recharge in arid areas induced by tropical cyclones: lessons learned from Gonu 2007 in Sultanate of Oman 总被引:4,自引:1,他引:3
Younger groundwater found in some Omani aquifers is a result of recent recharge from cyclonic and storm events [Weyhenmeyer
et al. (Science 287:842–845, 2000); Young et al. (J Appl Geophys 57:43–61, 2004)]. The analysis of the meteorological data in Oman indicates an anomalous rainfall on a decadal interval whereas cyclones
frequency is expected to increase due to global climatic changes. The cyclone Gonu has severely struck the eastern Omani coasts
in 2007 resulting in devastating floods. Huge volume of water (3,672 mm3) spread over the coastal plain calling for an assessment of potential groundwater recharge subsequent to this event. The
present study evaluates groundwater recharge with respect to Gonu 2007 to assess the potential of recharge induced by such
cyclones in the arid zones. The hydrographs of several piezometers sited along the coastal plain in Muscat Province have been
studied and variation in water table rise has been analyzed. Significant water table rise is indicated for areas with geological
and structural settings favoring rapid infiltration of water yielding considerable groundwater mound, whereas piezometers
located in less favorable zones show minimum rise of water table. However, soon after the floods the aquifer hydrodynamics
has readjusted to attain equilibrium and the groundwater mound dissipated. The cumulative rise of the water table on an areal
extent does not exceed a few centimeters indicating lesser volume of recharge. Comparatively, recharge from frequent precipitation
along favorable zones produces more significant recharge compared with cyclonic events where surface water residence time
is shorter to allow for efficient infiltration. 相似文献
39.
El Bahariya Oasis is a part of the great groundwater reservoir of the Western Desert of Egypt. The different stratigraphic units, the water-bearing zones, aquifer potentiality conditions, and the favorable locations for drilling new wells were evaluated by carrying out 24 Schlumberger vertical electrical soundings (VESs), along with the data of some wells drilled in the near vicinity of the measuring sites. The results of the interpreted field data revealed the presence of ten distinctive subsurface geoelectric layers; a thin surface, dry loose sand and gravel, sandy clay and shale interclations, saturated coarse sand layer, shale and clay, and saturated fine sandstone and saturated coarse sandstone. The aquifer is a multilayer aquifer with different thicknesses represented by the fourth, sixth, eighth, and tenth geoelectric layers. Results also revealed that the thicknesses of the water-bearing horizons increase towards the east direction, consequently the aquifer potentiality increases. Therefore, the best production well locations are in that direction. Depth to water starts from 40 m at VES no. 14 and increases gradually toward the east to reach 66 m at VES no. 5. Hydrogeochemical analysis of two groundwater samples taken from Ein El Ezza and well no. 2 showed that groundwater in the study area is suitable for agricultural purposes but not for human consumption due to the high iron content. Recommendations concerning site selection for drilling new productive groundwater wells are given. 相似文献
40.