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51.
Changes to the groundwater system, from 1888 to present, in a highly-urbanized coastal area in Hong Kong, China 总被引:3,自引:1,他引:2
Historical groundwater levels in a coastal region of Hong Kong Island (China) were reviewed and compared with data collected recently to reveal changes to the groundwater regime over the last century. The coastal springs and seeps have disappeared and the lower boundary of the seepage zone has moved uphill. Groundwater was found to be flowing upward along the boundary of natural slopes and urbanized areas. Artesian flows were commonly noted in the deep piezometers in the lower urbanized areas. Moreover, an overall rise in water levels in a 10-year period was observed in the urbanized areas, except in areas with good drainage. Extensive urbanization since the 1950s has included large-scale land reclamation, deep foundations of high-rise buildings, an underground transport system, water mains and horizontal drains in slopes; the effect has been a slow but gradual increase in the water level of the hillslope groundwater system. Further urbanization activities such as the westward extension of the underground transport system and new major drainage systems in the slopes, should be assessed for possible further changes to the groundwater system. The results presented here may serve as reference for other highly-urbanized coastal areas in the world. 相似文献
52.
The long-term trends in the occurrence frequency of pre-summer daytime and nocturnal extreme hourly rainfall(EXHR) during 1988-2018 in Hong Kong and their spatial distributions are examined and analyzed. Despite a significant increasing trend observed in the occurrence frequency of pre-summer EXHRs during the investigated period,the increase in daytime and nocturnal EXHRs show distinct spatial patterns. Nocturnal EXHRs show uniform increasing trends over the entire Hong Kong. However, the increa... 相似文献
53.
Chloride as tracer of solute transport in the aquifer–aquitard system in the Pearl River Delta,China
A 1D numerical model is constructed to investigate the impact of sedimentation and sea level changes on transport of Cl? in the aquifer–aquitard system in the Pearl River Delta (PRD), China. The model simulates the evolution of the vertical Cl? concentration profiles during the Holocene. Sedimentation is modeled as a moving boundary problem. Chloride concentration profiles are reconstructed for nine boreholes, covering a wide area of the PRD, from northwest to southeast. Satisfactory agreement is obtained between simulated and measured Cl? concentration profiles. Diffusion solely is adequate to reproduce the vertical Cl? concentration profiles, which indicates that diffusion is the regionally dominant vertical transport mechanism across the aquitards in the PRD. The estimated effective diffusion coefficients of the aquitards range from 2.0?×?10–11 to 2.0?×?10–10 m2/s. The effective diffusion coefficients of the aquifers range from 3.0?×?10–11 to 4.0?×?10–10 m2/s. Advective transport tends to underestimate Cl? concentrations in the aquitard and overestimate Cl? concentrations in the basal aquifer. The results of this study will help understand the mechanisms of solute transport in the PRD and other deltas with similar geological and hydrogeological characteristics. 相似文献
54.
Transfer zones and fault reactivation in inverted rift basins: Insights from physical modelling 总被引:2,自引:0,他引:2
Elena A. Konstantinovskaya Lyal B. Harris Jimmy Poulin Gennady M. Ivanov 《Tectonophysics》2007,441(1-4):1-26
Carbonate mylonites with varying proportions of second-phase minerals were collected at positions of increasing metamorphic grade along the basal thrust of the Morcles nappe (Helvetic nappes, Switzerland). Variations of temperature, stress, and strain rate, changes in chemistry of solid and fluid phases, and differing degrees of strain localization and annealing were tracked by measuring the shapes, mean sizes, and size distributions of both matrix and second-phase grains, as well as crystal preferred orientation (CPO) of the matrix. Field structures suggest that strain rate was constant along the fault. The mean and distribution of the calcite grain sizes were affected most profoundly by temperature: Increased temperature, presumably accompanied by decreased stress, correlated with larger mean sizes and wider size distributions. At a given location, the matrix grains in mylonites with more second-phase particles are, on average, smaller, have narrower size distributions, and have more elongate shapes. For example, mylonites with 50 vol.% of second phases have matrix grain sizes half that of pure mylonites. Changes in calcite chemistry and the presence of synkinematic fluids seemed to influence microfabric only weakly. Temporal variations in conditions, such as exhumation-induced cooling, apparently provoke changes in temperature, stress, and strain rate along the nappe. These changes result in further strain localization during retrograde conditions and cause the grain size to be reduced by an additional 50%. The matrix CPO strengthens with increasing temperature or strain, but weakens and rotates with increasing second-phase content. These fabric changes suggest differing rates of grain growth, grain size reduction, and development of CPO owing to variations in the deformation conditions and, perhaps, mechanisms. To interpret natural mylonite structures or to extrapolate mechanical data to natural situations requires careful characterization of the microfabric, and, in particular, second-phase minerals. 相似文献
55.
A Permanent Multilevel Monitoring and Sampling System in the Coastal Groundwater Mixing Zones
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To study the spatial and temporal variability of water dynamics and chemical reactions within the coastal groundwater mixing zones (CGMZs), high‐resolution periodical and spatial groundwater sampling within CGMZs is needed. However, current samplers and sampling systems may require heavy driving machines to install. There is also possible contamination from the metal materials for current samplers and sampling systems. Here, a permanent multilevel sampling system is designed to sample coastal groundwater within CGMZs. This cost‐effective system consists of metal‐free materials and can be installed easily. The system is tested in Po Sam Pai and Tingkok, Tolo Harbor and Hong Kong. Major ions, nutrients, stable isotopes and radium and radon isotopes were analyzed and the data provided scientific information to study the fresh‐saltwater interface fluctuations, and temporal variations and spatial heterogeneity of geochemical processes occurred within CGMZs. The reliable spatial and temporal data from the sampling system demonstrate that the system functions well and can provide scientific data for coastal aquifer studies. 相似文献
56.
Alix Toulier Jean-Lambert Join Pierre Staménoff Yoan Benoit Geneviève Lebeau Maxime Gautier Caroline Gorge Eric Gayer Emmanuel Cordier Victor Kbidi Guillaume Payen Magali David Sophie Ferreira François Bonnardot Julien Bonnier Stéphane Martel Jimmy Gonthier Emilie Roulleau Jean-Pierre Cammas Dominique Strasberg Olivier Flores Fabrice R. Fontaine Thomas Giambelluca Claudine Ah-Peng 《水文研究》2024,38(2):e15061
Tropical volcanic islands are biodiversity hotspots where the Critical Zone (CZ) still remains poorly studied. In such steep topographic environments associated with extreme climatic events (cyclones), deployment and maintenance of monitoring equipment is highly challenging. While a few Critical Zone Observatories (CZOS) are located in tropical volcanic regions, none of them includes a Tropical Montane Cloud Forest (TMCF) at the watershed scale. We present here the dataset of the first observatory from the French network of critical zone observatories (OZCAR) located in an insular tropical and volcanic context, integrating a ‘Tropical Montane Cloud Forest’: The ERORUN-STAFOR observatory. This collaborative observatory is located in the northern part of La Réunion island (Indian Ocean) within the 45.0 km2 watershed of Rivière des Pluies (i.e., Rainfall river) which hosts the TMCF of Plaines des Fougères, one of the best preserved natural habitats in La Réunion Island. Since 2014, the ERORUN-STAFOR monitoring in collaboration with local partners collected a multidisciplinary dataset with a constant improvement of the instrumentation over time. At the watershed scale and in its vicinity, the ERORUN-STAFOR observatory includes 10 measurement stations covering the upstream, midstream and downstream part of the watershed. The stations record a total of 48 different variables through continuous (sensors) or periodic (sampling) monitoring. The dataset consists of continuous time series variables related to (i) meteorology, including precipitation, air temperature, relative humidity, wind speed and direction, net radiation, atmospheric pressure, cloud water flux, irradiance, leaf wetness and soil temperature, (ii) hydrology, including water level and temperature, discharge and electrical conductivity (EC) of stream, (iii) hydrogeology, including (ground)water level, water temperature and EC in two piezometers and one horizontally drilled groundwater gallery completed by soil moisture measurements under the canopy. The dataset is completed by periodic time series variables related to (iv) hydrogeochemistry, including field parameters and water analysis results. The periodic sampling survey provides chemical and isotopic compositions of rainfall, groundwater, and stream water at different locations of this watershed. The ERORUN-STAFOR monitoring dataset extends from 2014 to 2022 with an acquisition frequency from 10 min to hourly for the sensor variables and from weekly to monthly frequency for the sampling. Despite the frequent maintenance of the monitoring sites, several data gaps exist due to the remote location of some sites and instrument destruction by cyclones. Preliminary results show that the Rivière des Pluies watershed is characterized by high annual precipitation (>3000 mm y−1) and a fast hydrologic response to precipitation (≈2 h basin lag time). The long-term evolution of the deep groundwater recharge is mainly driven by the occurrence of cyclone events with a seasonal groundwater response. The water chemical results support existing hydrogeological conceptual models suggesting a deep infiltration of the upstream infiltrated rainfall. The TMCF of Plaine des Fougères shows a high water storage capacity (>2000% for the Bryophytes) that makes this one a significant input of water to groundwater recharge which still needs to be quantified. This observatory is a unique research site in an insular volcanic tropical environment offering three windows of observation for the study of critical zone processes through upstream-midstream-downstream measurements sites. This high-resolution dataset is valuable to assess the response of volcanic tropical watersheds and aquifers at both event and long-term scales (i.e., global change). It will also provide insights in the hydrogeological conceptual model of volcanic islands, including the significant role of the TMCFs in the recharge processes as well as the watershed hydrosedimentary responses to extreme climatic events and their respective evolution under changing climatic conditions. All data sets are available at https://doi.org/10.5281/zenodo.7983138 . 相似文献
57.
58.
Chunlei LIU Yazhu YANG Xiaoqing LIAO Ning CAO Jimmy LIU Niansen OU Richard P.ALLAN Liang JIN Ni CHEN Rong ZHENG 《大气科学进展》2022,39(11):1941-1955
The change in ocean net surface heat flux plays an important role in the climate system. It is closely related to the ocean heat content change and ocean heat transport, particularly over the North Atlantic, where the ocean loses heat to the atmosphere, affecting the AMOC(Atlantic Meridional Overturning Circulation) variability and hence the global climate.However, the difference between simulated surface heat fluxes is still large due to poorly represented dynamical processes involving multisca... 相似文献
59.
The present paper gives a brief overview of the CLASH project, making reference to other relevant papers in this issue and elsewhere. Emphasis is put on the two main objectives of the project and how these objectives were realised: development of a generic prediction method for wave overtopping and guidance on possible scale/model effects for wave overtopping. 相似文献
60.
Byakatonda Jimmy Parida B. P. Moalafhi Ditiro B. Kenabatho Piet K. Lesolle David 《Natural Hazards》2020,101(1):255-274
Natural Hazards - The objective, accurate and rapid quantification of agricultural drought is the key component of effective drought planning and management mechanism. The present study proposed a... 相似文献