排序方式： 共有13条查询结果，搜索用时 0 毫秒
11.
The inter-relationship between coastal sub-aquifers and the Mediterranean Sea, deduced from radioactive isotopes analysis 总被引：3，自引：1，他引：2
Radioactive isotopes were used to estimate the rate of seawater intrusion into the coastal aquifer of Israel, the connection between the different sub-aquifers, and the connection between the sub-aquifers and the sea. This was done by dating both fresh and saline groundwaters from the vicinity of the shoreline, which were analyzed for their 14C and tritium content together with their chemical and stable isotope composition. The results indicate that the distinct sub-aquifers differ in their water chemistry and age. The saline groundwater in the lower sub-aquifers is older than ca. 10,000 years, as evidenced by the absence of tritium and low 14C activity (<12 PMC). On the other hand, saline groundwaters in the upper sub-aquifers contain tritium and are thus younger than 50 years, indicating recent intrusion of seawater. The ages of the saline groundwaters become younger upward from the lower sub-aquifers to the upper ones, reflecting the sea-level rise since the last glacial period. The older ages also imply slow groundwater flow in the lower sub-aquifers. The fresh groundwaters in most cases in the lower sub-aquifers were found to be older than ca. 10,000 years and this implies that the flow to the sea is blocked or restricted. 相似文献
12.
In coastal aquifers, significant vertical hydraulic gradients are formed where fresh water and underlying salt water discharge together upward to the seafloor. Monitoring boreholes may act as "short circuits" along these vertical gradients, connecting between the higher and the lower hydraulic head zones. When a sea tide is introduced, the fluctuations of both the water table and the depth of the mixing zone are also biased due to this effect. This problem is intensified in places of long-screen monitoring boreholes, which are common in many places in the world. For example, all approximately 500 boreholes of the fresh water-salt water mixing zone in the coastal aquifer of Israel are installed with 10 to 50 m long screens. We present field measurements of these fluctuations, along with a three-dimensional numerical model. We find that the in-well fluctuation magnitude of the mixing zone is an order of magnitude larger than that in the porous media of the actual aquifer. The primary parameters that affect the magnitude of this bias are the anisotropy of the aquifer conductivity and the borehole hydraulic parameters. With no sea tide, borehole interference is higher for the anisotropic case because the vertical hydraulic gradients are high. When tides are introduced, the amplitude of the mixing zone fluctuation is higher for the isotropic case because the overall effective hydraulic conductivity is greater than the conductivity in the anisotropic case. In the aquifer, the fresh water-salt water mixing zone fluctuations are dampened, and tens of meters inland from the shoreline, the fluctuations are on the order of few centimeters. 相似文献
13.
Gabay Ran Shalev Eyal Yechieli Yoseph Sagy Amir Weisbrod Noam 《Hydrogeology Journal》2014,22(2):425-440
Fault zone architecture plays an important role in flow regimes of hydrological systems. Fault zones can act as conduits, barriers, or conduits/barrier systems depending on their spatial architecture. The goal of this study is to determine the fault-zone permeability structure and its effect on the local hydrogeological system in the Dead Sea fault system. Permeability was measured on small-scale outcrop plug samples at four faults along the Dead Sea fault system, and large-scale slug tests in four boreholes, in different parts of the fault, at Yair fault in Israel. The research results show that values in the damage zone are two to five orders of magnitude higher than those of the fault core (~3.5?×?10?10, 1?×?10?15 m2 respectively), resulting in an anisotropic permeability structure for the overall fault zone and preferable flow parallel to the fault. A set of injection tests in the Yair fault damage zone revealed a water-pressure-dependent behavior. The permeability of this zone increases when employing a higher water pressure in the fault fracture-dominated damage zone, due to the reopening of fractures. 相似文献