首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 46 毫秒
1.
Abstract Long-term monitoring of temperature distribution in an active fault zone was carried out using the optical fiber temperature-sensing technique. An optical fiber cable was installed in a borehole drilled into the Nojima Fault in Awaji Island, south-west Japan, and the temperature profile to a depth of 1460 m had been measured for 2.5 years (July 1997–January 2000). Although the obtained temperature records showed small temporal variations due to drifts of the measurement system all along the cable, local temperature anomalies were detected at two depths. One at around 80 m seems to correspond to a fracture zone and may be attributed to groundwater flow in the fracture zone. This anomaly had been stable throughout the monitoring period, whereas the other anomaly at around 500 m was a transient one. The water level in the borehole could be estimated from the diurnal temperature variations in the uppermost part of the borehole and may provide information on the hydrological characteristics of the fault zone, which is connected to the borehole through perforations on the casing pipe. Except for these minor variations, the temperature profile had been very stable for 2.5 years. The conductive heat flow calculated from this profile and the thermal conductivity measured on core samples increases with depth, probably resulting from errors in thermal conductivity due to sampling problems and/or from advective heat transfer by regional groundwater flow. Assuming that the middle part of the borehole (less fractured granite layer) is least affected by these factors, heat flow at this site is estimated to be approximately 70 mW/m2.  相似文献   

2.
Abstract In order to make geophysical and geological investigations of the Nojima Fault on Awaji Island, Japan, three boreholes measuring 1800 m, 800 m and 500 m deep were drilled into the fault zone. The fault is one of the seismic source faults of the 1995 Hyogo-ken Nanbu earthquake of M 7.2. A new multicomponent borehole instrument was installed at the bottom of the 800 m borehole and continuous observations of crustal strain and tilt have been made using this instrument since May 1996. A high-pressure water injection experiment within the 1800 m borehole was done in February and March 1997 to study the geophysical response, behavior, permeability, and other aspects of the fault zone. The injection site was located approximately 140 m horizontally and 800 m vertically from the instrument. Associated with the water injection, contraction of approximately 0.7 × 10−7 str (almost parallel to the fault) and tilt of approximately 1 × 10-7 rad in the sense of upheaval toward the injection site were observed. In addition to these controlled experiments, the strainmeter and tiltmeter also recorded daily variations. We interpret strain and tilt changes to be related to groundwater discharge and increased ultra-micro seismicity induced by the injected water.  相似文献   

3.
尼泊尔MS8.1地震引起中国大陆大量地震观测井水位和水温的同震响应. 从宏观结果看, 在54个同时存在水位和水温同震效应的观测井中, 有51口观测井的变化类型为水位上升-水温上升、 水位下降-水温下降、 水位振荡-水温上升或下降(以下降为主), 井水位与井水温同震效应表现出良好的相关性, 这可能与地下水动力学作用有关; 有3口观测井的水位变化与水温变化方向相反, 且水温变化均为震后效应. 另外, 有1口观测井水位无变化而水温同震效应明显. 这些不同类型的同震变化与井孔条件、 水温梯度、 传感器位置及水位埋深等多种因素有关. 从微观结果看, 井水位同震效应出现的时间及变化幅度与井水温同震效应出现的时间及变化幅度之间的关联性比较复杂, 这与井孔条件和温度梯度等因素有关.   相似文献   

4.
Groundwater temperature is an important water quality parameter that affects species distributions in subsurface and surface environments. To investigate the response of subsurface temperature to atmospheric climate change, an analytical solution is derived for a one‐dimensional, transient conduction–advection equation and verified with numerical methods using the finite element code SUTRA. The solution can be directly applied to forward model the impact of future climate change on subsurface temperature profiles or inversely applied to produce a surface temperature history from measured borehole profiles. The initial conditions are represented using superimposed linear and exponential functions, and the boundary condition is expressed as an exponential function. This solution expands on a classic solution in which the initial and boundary conditions were restricted to linear functions. The exponential functions allow more flexibility in matching climate model projections (boundary conditions) and measured temperature–depth profiles (initial conditions). For example, measured borehole temperature data from the Sendai Plain and Tokyo, Japan, were used to demonstrate the improved accuracy of the exponential function for replicating temperature–depth profiles. Also, the improved accuracy of the exponential boundary condition was demonstrated using air temperature anomaly data from the Intergovernmental Panel on Climate Change. These air temperature anomalies were then used to forward model the effect of surficial thermal perturbations in subsurface environments with significant groundwater flow. The simulation results indicate that recharge can accelerate shallow subsurface warming, whereas upward groundwater discharge can enhance deeper subsurface warming. Additionally, the simulation results demonstrate that future groundwater temperatures obtained from the proposed analytical solution can deviate significantly from those produced with the classic solution. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

5.
Coastal groundwater discharge (CGD) plays an important role in coastal hydrogeological systems as they are a water resource that needs to be managed, particularly in wetland areas. Despite its importance, identifying and monitoring CGD often presents physical and logistical constraints, restraining the application of more traditional submarine groundwater discharge surveying techniques. Here we investigate the capability of electrical resistivity imaging (ERI) in the Peníscola wetland (Mediterranean coast, Spain). ERI surveying made it possible to identify and delineate an ascending regional groundwater flow of thermal and Ra‐enriched groundwater converging with local flows and seawater intrusion. The continuous inputs of Ra‐rich groundwater have induced high activities of Ra isotopes and 222Rn into the marsh area, becoming among the highest previously reported in wetlands and coastal lagoons. Geoelectrical imaging enabled inferring focused upward discharging areas, leaking from the aquifer roof through a confining unit and culminating as spring pools nourishing the wetland system. Forward modelling over idealized subsurface configurations, borehole datasets, potentiometric records from standpipe piezometers, petrophysical analysis, and four natural and independent tracers (224Ra, 222Rn, temperature and salinity) permitted assessing the geoelectrical model and a derived hydrogeological pattern. The research highlights the potential of ERI to improve hydrogeological characterization of subsurface processes in complex contexts, with different converging flows. Additionally, a hydrogeological conceptual model for a groundwater‐fed coastal wetland was proposed, based on the integration of surveying datasets. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

6.
注水井温度场模型及其数值模拟研究   总被引：5，自引：4，他引：1       下载免费PDF全文
油田注水开发中后期,井温测井在常规注水工艺的条件下,难以准确地反映注水剖面的实际情况．为此,本文根据注水井井筒与地层的传热机理,针对注水井多层注入的实际情况,建立了井筒及其周围地层的温度场数学模型．用该模型模拟计算了大庆油田某注水井的井下温度场分布,计算结果与实测结果接近,说明模型是适用的．通过对不同注入条件和地质条件的数值模拟,得出注水温度同井眼温度差别越大或注水速度越快,井温曲线越易于识别注入剖面．同时,对如何改善注水工艺,以提高井温测井识别注入剖面的能力提出了合理化建议．  相似文献   

7.
The Bohai Sea is a semi-enclosed inland sea with case-2 waters near the coast. A comprehensive set of optical data was collected during three cruises in June, August, and September 2005 in the Bohai Sea. The vertical profile measurements, such as chlorophyll concentration, water turbidity, downwelling irradiance, and diffuse attenuation coefficient, showed that the Bohai Sea was vertically stratified with a relative clear upper layer superimposed on a turbid lower layer. The upper layer was found to correspond to the euphotic zone and the deep chlorophyll maximum (DCM) occurs at the base of this layer. By tuning a semi-analytical model (24 and 25) for the Bohai Sea, we developed a method to derive water inherent optical properties and the depth of DCM from above-surface measurements. Assuming a ‘fake’ bottom in the stratified water, this new method retrieves the ‘fake’ bottom depth, which is highly correlated with the DCM depth. The average relative error between derived and measured values is 33.9% for phytoplankton absorption at 440 nm, 25.6% for colored detrital matter (detritus plus gelbstoff) absorption at 440 nm, and 24.2% for the DCM depth. This modified method can retrieve water inherent optical properties and monitor the depth of DCM in the Bohai Sea, and the method is also applicable to other stratified waters.  相似文献   

8.
This research (1) integrated a fluorescent dye injection and monitoring system for measuring the mixing of a fluorescent dye tracer (fluorescein) in permeable (sandy) sediments with a cabled ocean observatory, Kilo Nalu, Oahu, Hawaii, and (2) used this system to conduct remotely controlled in situ measurements of wave-enhanced porewater mixing in a physically well-characterized wave-dominated setting. Laboratory results indicated that the fiber-optic sensor is effective at measuring fluorescence-traced enhanced mixing in sandy sediments. Observed dye mixing, driven by paddle-generated surface waves in a laboratory wave channel was 2–3 orders of magnitude greater than molecular diffusion, and decreased with depth in the sediments. Similarly, field experiments used a remotely controlled submersible syringe pump for fluorescent tracer injection into sediment that was monitored with a fiber-optic sensor. These experiments were carried out at 10 m water depth, with mean wave heights of 0.3–1.5 m and periods of ∼15 s. At 15 cm sediment depth, transport rates of 0–5 cm h−1 were measured, with maximum dispersion coefficients 2–3 orders of magnitude faster than sedimentary molecular diffusion. Hydrodynamic measurements collected simultaneously via Kilo Nalu correlated with porewater transport, with significant wave height and diffusion having the strongest covariation.  相似文献   

9.
Large proportions of rainwater and snowmelt infiltrate into the subsurface before contributing to stream flow and stream water quality. Subsurface flow dynamics steer the transport and transformation of contaminants, carbon, weathering products and other biogeochemistry. The distribution of groundwater ages with depth is a key feature of these flow dynamics. Predicting these ages are a strong test of hypotheses about subsurface structures and time-varying processes. Chlorofluorocarbon (CFC)-based groundwater ages revealed an unexpected groundwater age stratification in a 0.47 km2 forested catchment called Svartberget in northern Sweden. An overall groundwater age stratification, representative for the Svartberget site, was derived by measuring CFCs from nine different wells with depths of 2–18 m close to the stream network. Immediately below the water table, CFC-based groundwater ages of already 30 years that increased with depth were found. Using complementary groundwater flow models, we could reproduce the observed groundwater age stratification and show that the 30 year lag in rejuvenation comes from return flow of groundwater at a subsurface discharge zone that evolves along the interface between two soil types. By comparing the observed groundwater age stratification with a simple analytical approximation, we show that the observed lag in rejuvenation can be a powerful indicator of the extent and structure of the subsurface discharge zone, while the vertical gradient of the age-depth-relationship can still be used as a proxy of the overall aquifer recharge even when sampled in the discharge zone. The single age stratification profile measured in the discharge zone, close to the aquifer outlet, can reveal the main structure of the groundwater flow pattern from recharge to discharge. This groundwater flow pattern provides information on the participation of groundwater in the hydrological cycle and indicates the lower boundary of hydrological connectivity.  相似文献   

10.
In the area near the village of Jazak (southern part of Fruška Gora mountain, Serbia), hydrogeological investigations were carried out for the purpose of finding a water supply source to provide an adequate volume of water for a mineral water bottling plant. The first exploratory borehole (IBJf-1) penetrated a water-bearing layer of Miocene organogenic limestones. This aquifer has a thickness of about 30 m and a yield of only 2.2 l/s, which falls short of the required water volume (5 l/s).The objective of further exploration was to define the attitude and extension of the aquifer and thus select a more favourable site for a new exploratory borehole that would secure the required volume of water. For this purpose, geophysical exploration was carried out in 2003 through vertical electrical sounding (VES) and high-resolution 3D reflection seismic methods. The VES measurements enabled determination of aquifer depth and indicated that the water-bearing strata extend over the entire area studied. However, because of the equivalence problem, it was not possible to determine the thickness of the water-bearing stratum based solely on the VES data. Thus, the 3D seismic method was used in the second stage of investigation. A low-cost 3D seismic survey was carried out with fixed receiver lines, using a vibrator as the source of the seismic waves.From the 3D seismic data it was possible to determine the aquifer thickness. The depth of the aquifer determined by interpretation of the 3D seismic data was in accordance with the depth determined by the VES method. Based on the assumption that the hydraulic conductivity of this formation is identical or similar over the entire area, as well as the fact that the first well showed the presence of a subartesian aquifer, we proposed drilling another borehole (IBJf-2) in the zone where the data indicated that the water-bearing stratum was much thicker. The data obtained by drilling and coring were in agreement with the predicted aquifer thickness. Pumping tests showed that the water discharge in borehole IBJf-2 was 6 l/s.The results show that the objective of delineating the groundwater body by combined application of two geophysical methods (VES and 3D seismic) was successfully performed.  相似文献   

11.
Upward discharge to surface water bodies can be quantified using analytical models based on temperature–depth (T-z) profiles. The use of sediment T-z profiles is attractive as discharge estimates can be obtained using point-in-time data that are collected inexpensively and rapidly. Previous studies have identified that T-z methods can only be applied at times of the year when there is significant difference between the streambed–water interface and deeper sediment temperatures (e.g., winter and summer). However, surface water temperatures also vary diurnally, and the influence of these variations on discharge estimates from T-z methods is poorly understood. For this study, synthetic T-z profiles were generated numerically using measured streambed interface temperature data to assess the influence of diurnal temperature variations on discharge estimation and provide insight into the suitable application of T-z methods. Results show that the time of day of data collection can have a substantial influence on vertical flux estimates using T-z methods. For low groundwater discharge fluxes (e.g., 0.1 m d−1), daily transience in streambed temperatures led to relatively large errors in estimated flow magnitude and direction. For higher discharge fluxes (1.5 m d−1), the influence of transient streambed temperatures on discharge estimates was strongly reduced. Discharge estimates from point-in-time T-z profiles were most accurate when the uppermost point in the T-z profile was near the bed interface daily mean (two time periods daily). Where temperature time series data are available, daily averaged T-z profiles can produce accurate discharge estimates across a wide range of discharge rates. Seasonality in shallow groundwater temperature generally had a negligible influence on vertical flow estimates. These findings can be used to plan field campaigns and provide guidance on the optimal application of T-z methods to quantify vertical groundwater discharge to surface water bodies.  相似文献   

12.
位于阿拉善高原的巴丹吉林沙漠分布有大量盐湖.为揭示盐湖分层特征以及地下水对盐湖水体的影响,选取沙漠腹地的第二大盐湖——苏木巴润吉林,对9月份湖水的温度和电导率剖面进行了观测.结果表明,尽管所测盐湖宽深比大于90,还是存在温跃层.温跃层的矿化度(TDS)为60~160 g/L,靠近湖底的水体存在TDS低值异常区,形成化跃层,推测为地下淡水集中排泄所致.这种湖底泉在其它较浅的盐湖水体中也存在,说明深、浅层地下水对盐湖水分及盐分都有贡献.温跃层水温随深度的变化近似符合静止水体的热传导规律,并没有受到地下水排泄热量的显著影响.研究区盐湖跃层的季节性变化还有待进一步研究.  相似文献   

13.
A large weighing lysimeter was installed at Yucheng Comprehensive Experimental Station, north China, for evapotranspiration and soil‐water–groundwater exchange studies. Features of the lysimeter include the following: (i) mass resolution equivalent to 0·016 mm of water to accurately and simultaneously determine hourly evapotranspiration, surface evaporation and groundwater recharge; (ii) a surface area of 3·14 m2 and a soil profile depth of 5·0 m to permit normal plant development, soil‐water extraction, soil‐water–groundwater exchanges, and fluctuations of groundwater level; (iii) a special supply–drainage system to simulate field conditions of groundwater within the lysimeter; (iv) a soil mass of about 30 Mg, including both unsaturated and saturated loam. The soil consists mainly of mealy sand and light loam. Monitoring the vegetated lysimeter during the growing period of winter wheat, from October 1998 through to June 1999, indicated that during the period groundwater evaporation contributed 16·6% of total evapotranspiration for a water‐table depth from 1·6 m to 2·4 m below ground surface. Too much irrigation reduced the amount of upward water flow from the groundwater table, and caused deep percolation to the groundwater. Data from neutron probe and tensiometers suggest that soil‐water‐content profiles and soil‐water‐potential profiles were strongly affected by shallow groundwater. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

14.
We estimated the effects of hydrogeological and surface temperature warming on subsurface thermal regime from the temperature-depth profiles and hydrological data of groundwater quality both in the quaternary and tertiary systems in the Sendai Plain as a preliminary step toward reconstruction of climate changes.Annual mean air temperature in the plain has increased about 1.5 °C in the last 70 years and this surface warming resulted in low or negative thermal gradient. However, anomaly of thermal gradient was recognized in not all temperature-depth profiles. Groundwater chemical compositions and stable isotope data (δD and δ18O) show that the groundwater flow system has marked difference between those of tertiary and quaternary systems. Calculated results of three dimensional groundwater flow and heat transport model ensure the above hypothesis and shows that thermal gradient changes at close to basement of the quaternary system. The differences in groundwater flow systems are expressed as subsurface thermal gradient anomalies in the temperature-depth profiles in the Sendai Plain. Furthermore, one-dimensional numerical analyze including the effect of surface warming indicates that calculated profile has departure from steady state line at depths in 60-80 m agree well with observed one.  相似文献   

15.
The Dead Sea is a closed lake, the water level of which is lowering at an alarming rate of about 1 m/year. Factors difficult to determine in its water balance are evaporation and groundwater inflow, some of which emanate as submarine groundwater discharge. A vertical buoyant jet generated by the difference in densities between the groundwater and the Dead Sea brine forms at submarine spring outlets. To characterize this flow field and to determine its volumetric discharge, a system was developed to measure the velocity and density of the ascending submarine groundwater across the center of the stream along several horizontal sections and equidistant depths while divers sampled the spring. This was also undertaken on an artificial submarine spring with a known discharge to determine the quality of the measurements and the accuracy of the method. The underwater widening of the flow is linear and independent of the volumetric spring discharge. The temperature of the Dead Sea brine at lower layers primarily determines the temperature of the surface of the upwelling, produced above the jet flow, as the origin of the main mass of water in the submarine jet flow is Dead Sea brine. Based on the measurements, a model is presented to evaluate the distribution of velocity and solute density in the flow field of an emanating buoyant jet. This model allows the calculation of the volumetric submarine discharge, merely requiring either the maximum flow velocity or the minimal density at a given depth.  相似文献   

16.
Underground temperature measurements in two shallow boreholes have been carried out by the Japanese Antarctic Research Expedition at Syowa Station, East Antarctica from April, 1981 to January, 1985. Two quartz thermometers were installed in the first borehole at depths of 2 and 5 m and three were in the second one at depths of 1, 4 and 6.8 m. The mean underground temperatures in the first borehole were −8.181 and −8.843°C at depths of 2 and 5 m, and in the second one −8.242 and −8.220°C at depths of 4 and 6.8 m. As the mean air temperature at Syowa Station was −10.8°C, the underground temperature in the 2 −6.8 m depth range is about two degrees higher than the air temperature. The thermal diffusivities of the observation area are determined by the same principle of the Ångström method, using long-term underground temperature records. The thermal diffusivity around Syowa Station is established to be about two times larger than those of ordinary igneous and metamorphic rocks measured in the laboratory. The thermal conductivity of the drilled cores and surrounding outcropping rocks are also measured by the transient method with temperature conditions at +23°C and −20°C. The thermal conductivities measured in various samples at −20°C are about 7% larger than those at +23°C. Thes tendency is consistent with the results of holocrystalline rock experiments.  相似文献   

17.
中国大陆科学钻探主孔动态地温测量   总被引：8，自引：2，他引：6       下载免费PDF全文
介绍了大陆科学钻探主孔完钻后4次的钻井测温数据,地温梯度随深度的变化趋势,系统的热导率测试结果及其温压校正. 地温测量显示,浅部（100m以上）的4次测量结果有较大的区别,而100m以下测量温度趋于一致.在900～1600m井段,温度略有波动,可能存在地下水活动.到了深部,温度与深度呈现良好的线性关系. 在0～500m,500～2700m,2700～3600m及3600m以下这4个井段范围内,地温梯度随深度降低或增加的趋势交替变化,平均地温梯度248±34℃/km. 198块岩芯样品测试结果表明,热导率变化范围在1711～36 W/(m·K),平均2716±0403 W/(m·K). 依据实测的温度-深度进行温压校正后,热导率为1989～3652 W/(m·K),平均2808±0363 W/（m·K）. 热导率随深度的变化趋势与地温梯度的变化趋势并不能完全相互补偿,表明影响地温梯度的其他因素不容忽视. 大陆科学钻探温度测量,为今后进一步研究超高压变质带深部地热场及其地球动力学含义提供了可靠的基础数据.  相似文献   

18.
Small‐scale heterogeneities and large changes in hydraulic gradient over short distances can create preferential groundwater flow paths that discharge to lakes. A 170 m2 grid within an area of springs and seeps along the shore of Shingobee Lake, Minnesota, was intensively instrumented to characterize groundwater‐lake interaction within underlying organic‐rich soil and sandy glacial sediments. Seepage meters in the lake and piezometer nests, installed at depths of 0·5 and 1·0 m below the ground surface and lakebed, were used to estimate groundwater flow. Statistical analysis of hydraulic conductivity estimated from slug tests indicated a range from 21 to 4·8 × 10?3 m day?1 and small spatial correlation. Although hydraulic gradients are overall upward and toward the lake, surface water that flows onto an area about 2 m onshore results in downward flow and localized recharge. Most flow occurred within 3 m of the shore through more permeable pathways. Seepage meter and Darcy law estimates of groundwater discharge agreed well within error limits. In the small area examined, discharge decreases irregularly with distance into the lake, indicating that sediment heterogeneity plays an important role in the distribution of groundwater discharge. Temperature gradients showed some relationship to discharge, but neither temperature profiles nor specific electrical conductance could provide a more convenient method to map groundwater–lake interaction. These results suggest that site‐specific data may be needed to evaluate local water budget and to protect the water quality and quantity of discharge‐dominated lakes. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

19.
《水文科学杂志》2013,58(2):316-326
Abstract

Nitrate contamination in groundwater originates mainly from excessive use of fertilizers and uncontrolled discharge to land of incompletely-treated wastewater associated with agricultural activities. A systematic field investigation was carried out in a sub-catchment of Dianchi Lake, Kunming, Yunnan, China, into the hydrological, biological and geological processes of nitrogen transport and transformation in the aeration zone and aquifer system. In situ experiments showed that the quantity of NO3-N recharged into groundwater was related to fertilization. Nitrification and denitrification behaved quite differently but were affected by moisture content and Eh value. The vertical infiltration rate was controlled by the groundwater table and hydraulic conductivity of the soil. The existence of a zero-flux plane reflected the dynamics of water fluxes in the soil profile and Eh was measured in the aeration zone. In response to these factors, the nitrification rate was greatest in the top soil and reduced with the depth of soil; it was 6.53 mg/(kg·h) in the vegetated plot and 0.2–0.3 mg/(kg·h) in the unvegetated one. The denitrification rate in the unvegetated plot was 6.36 mg/(kg·h), and it was 2.79 mg/(kg·h) in the vegetated one.  相似文献   

20.
The flow of groundwater beneath barrier islands has been cited as a possible pathway for salt water and chemical exchange between a protected embayment and the open sea. Evidence is presented that identifies an exchange of groundwater through a highly permeable paleoinlet along the barrier beach of Cavallino, which separates the northern Venice Lagoon from the Adriatic Sea. We utilized both point measurements of submarine groundwater discharge (SGD) and a geophysical investigation of the subsurface resistivity to analyze the movement of saline groundwater. Discharge of groundwater and associated nutrients, was higher at the site of a former inlet than at a similar site along the barrier and modulated by the difference in tidal water level between the lagoon and Adriatic Sea. If the measured conditions are typical, storm surge barriers could potentially result in a saline groundwater flow of up to 1.5×106 m3 d−1 into the lagoon.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号