Recognising the importance of understanding sediment dynamics to evaluate the status of a coastal lagoon environment, this work has been focused on the investigation of the hydrodynamic and sediment transport processes occurring in such basins. In order to describe the lagoon system, a modelling approach combining hydrodynamics, waves and sediment dynamics has been developed. The framework of the numerical model consists of a finite element hydrodynamic model, a third generation finite element spectral wave model and a sediment transport and morphodynamic model for both cohesive and non-cohesive sediments. The model adopts the finite element technique for spatial integration, which has the advantage to describe more accurately complicated bathymetry and irregular boundaries for shallow water areas. The developed model has been applied to test cases and to a very shallow tidal lagoon, the Venice Lagoon, Italy. Numerical results show good agreement with water level, waves and turbidity measurements collected in several monitoring stations inside the Lagoon of Venice. Such a model represents an indispensable tool in analysing coastal problems and assessing morphological impacts of human interference. 相似文献
Evaluating yearly net migration for the Federal Republic of Germany establishes the importance of demographic restructuring and government policies as explanations for the counterurbanization phenomenon. Counterurbanization, the spatial demographic deconcentration of regional population, is measured as an inverse relationship between the net migration rate and population sizes of functional urban regions. A counterurbanization pattern filtered-down from older to younger age-groups of the population, and appears related to an increasing preference for small-sized regions with natural amenities. For foreigners, a counterurbanization direction of movement can be explained by changes in immigration laws. While counterurbanization may be slowing down during the 1980s in certain developed countries, such as the United States, in the Federal Republic the phenomenon intensifies throughout the 1970–84 time period. Based on broad national demographic changes in combination with agespecific patterns of movement, this strong counterurbanization trend should continue well into the future. 相似文献
The incorporation of hydrogen in enstatite in a hydrous system containing various amounts of NaCl was investigated at 25 kbar.
The hydrogen content in enstatite shows a clear negative correlation to the NaCl-concentration in the system. The most favourable
explanation is the reduction of water fugacity due to dilution. Other reasons for the limited hydrogen incorporation at high
NaCl levels, such as a significant influence of Na+ on the defect chemistry or an exchange between OH- and Cl−in enstatite, appear much less important. A partition coefficient DNaEn/Fluid = 0.0013 could be determined, demonstrating that Na is less incompatible in enstatite than H. The new results support the
idea that dissolved components have to be considered when the total hydrogen storage capacity in nominally anhydrous minerals
is estimated, especially in geological settings with high levels of halogens, such as subduction zones. 相似文献
The Jervois region of the Arunta Inlier, central Australia, contains para- and orthogneisses that underwent low-pressure
amphibolite facies metamorphism (P = 200–300 MPa, T = 520–600 °C). Marble layers cut by metre-wide quartz + garnet ± epidote veins comprise calcite, quartz, epidote, clinopyroxene,
grandite garnet, and locally wollastonite. The marbles also contain locally discordant decimetre-thick garnet and epidote
skarn layers. The mineral assemblages imply that the rocks were infiltrated by water-rich fluids (XCO2 = 0.1–0.3) at ∼600 °C. The fluids were probably derived from the quartz-garnet vein systems that represent conduits for fluids
exsolved from crystallizing pegmatites emplaced close to the metamorphic peak. At one locality, the marble has calcite (Cc)
δ18O values of 9–18‰ and garnet (Gnt) δ18O values of 10–14‰. The δ18O(Gnt) values are only poorly correlated with δ18O(Cc), and the δ18O values of some garnet cores are higher than the rims. The isotopic disequilibrium indicates that garnet grew before the
δ18O values of the rock were reset. The marbles contain ≤15% garnet and, for water-rich fluids, garnet-forming reactions are
predicted to propagate faster than O-isotopes are reset. The Sm-Nd and Pb-Pb ages of garnets imply that fluid flow occurred
at 1750–1720 Ma. There are no significant age differences between garnet cores and rims, suggesting that fluid flow was relatively
rapid. Texturally late epidote has δ18O values of 1.5–6.2‰ implying δ18O(H2O) values of 2–7‰. Waters with such low-δ18O values are probably at least partly meteoric in origin, and the epidote may be recording the late influx of meteoric water
into a cooling hydrothermal system.
Received: 29 April 1996 / Accepted: 12 March 1997 相似文献
Detailed analysis of basal organic deposits underlying Hammock River marsh, Connecticut allowed documentation of water-level changes that occurred between 13,000 and 6000 yrs B.P. Four main periods of groundwater- and lake-level movements and related environmental changes can be identified.
1. (1) 12,500-10,200 yrs B.P. (lake stage): very rapid rise of the groundwater table of about 2 to 3 m, resulting in a shallow lake, followed by a more gradual rise of about 2.5 to 1.5 m.
2. (2) 10,200-7000 yrs B.P. (freshwater marsh, stage 1): slow overall rise of the water table interrupted by a drop of at least 1 m between about 9500 and 9000 yrs B.P. and of at least 0.8 m between about 8000 and 7500 yrs B.P., each event leading to oxidation and maceration of organic material.
3. (3) 7000-6400 yrs B.P. (complete desiccation of the swamp): rapid fall of the water table of at least 3.9 m. causing large-scale down-wasting of the accumulated peat.
4. (4) After 6400 yrs B.P. (freshwater marsh, stage 2): rapid rise of the water table.
The water-table rise of period 1 and the lowering of period 3 are attributed to predominantly local causes, while the groundwater fluctuations during period 2 are probably climate-related. The final water-level increase reflects the influence of Holocene relative sea-level rise. 相似文献
A cloud-ocean planetary boundary layer (OPBL) feedback mechanism is presented and tested in this paper. Water vapor, evaporated from the ocean surface or transported by the large-scale air flow, often forms convective clouds under a conditionally unstable lapse rate. The variable cloud cover and rainfall may have positive and negative feedback with the ocean mixed layer temperature and salinity structure. The coupling of the simplified Kuo’s (1965) cumulus cloud model to the Kraus-Turner’s (1967) ocean mixed layer model shows the existence of this feedback mechanism. The theory also predicts the generation of low frequency oscillation in the atmosphere and oceans. 相似文献
Precompacted annular clay blocks surrounding a casing with a heater were emplaced in a borehole with 20 cm diameter and 2.8 m depth in granite. The heater was in operation for 8 months and raised the temperature of the clay to 176°C close to the casing. At the extraction the clay was completely water-saturated close to the rock and it had experienced an increased water content also close to the hot casing.
Mineralogical changes of the Ca-smectite clay were indicated by a slight increase in CEC and by an XRD-based conclusion that the content of low-charge smectite increased, while the initial content of kaolinite was reduced. 相似文献
Canister embedment of highly compacted Na bentonite forms a low-permeable medium of significant homogeneity both macro- and microscopically. However, despite the fact that a large part of the porewater is in interlamellar positions and not mobile by ordinary hydraulic gradients, there are still a number of pore passages that let water and gas through even at very high bulk densities. A preliminary model for flow and diffusion has been outlined on the basis of generalized, quantitative microstructural data and basic physical relationships. It accounts for actually recorded hydraulic and gas conductivities as well as for commonly measured swelling pressures. Qualitatively, it is in agreement also with published ion diffusion data. 相似文献