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1.
Permeability of Sands in the Coastal Areas of the Southern Baltic Sea: Mapping a Grain-size Related Sediment Property 总被引：1，自引：0，他引：1
We compared measurements of vertical permeability, grain size distribution, and porosity from sandy surface sediments in the southern Baltic Sea. Using this information we constructed maps reflecting the permeability within the study area. We found that the formula suggested by Krumbein and Monk (1942) overestimates measured permeabilites on average by a factor 2.6 for the area investigated. The results of a formula including porosity, as in the Carman-Kozeny relation (Carman, 1937), deviated even more from our observations. Vertical heterogeneity of the sediments between 0–10 cm depth and the content of fine particulate material were likely responsible for this phenomenon.Our findings suggest that sediments, classified by averagegrain size based nomenclature as sands, cannot generally be assumed to be highly permeable. Nevertheless, maps constructed mirror the distribution of the average grain size in two data sets we used. For the shallow southern Baltic and an assumed threshold for permeability-effects of2.5 × 10-12 m2, wecalculate >41% of the sea floor to be permeable. An additional 27% may be permeable, but were excluded from calculations due to poor sorting. 相似文献
2.
Gas production from shale formations by hydraulic fracturing has raised concerns about the effects on the quality of fresh groundwater. The migration of injected fracking fluids towards the surface was investigated in the North German Basin, based on the known standard lithology. This included cases with natural preferential pathways such as permeable fault zones and fracture networks. Conservative assumptions were applied in the simulation of flow and mass transport triggered by a high pressure boundary of up to 50 MPa excess pressure. The results show no significant fluid migration for a case with undisturbed cap rocks and a maximum of 41 m vertical transport within a permeable fault zone during the pressurization. Open fractures, if present, strongly control the flow field and migration; here vertical transport of fracking fluids reaches up to 200 m during hydraulic fracturing simulation. Long-term transport of the injected water was simulated for 300 years. The fracking fluid rises vertically within the fault zone up to 485 m due to buoyancy. Progressively, it is transported horizontally into sandstone layers, following the natural groundwater flow direction. In the long-term, the injected fluids are diluted to minor concentrations. Despite the presence of permeable pathways, the injected fracking fluids in the reported model did not reach near-surface aquifers, either during the hydraulic fracturing or in the long term. Therefore, the probability of impacts on shallow groundwater by the rise of fracking fluids from a deep shale-gas formation through the geological underground to the surface is small. 相似文献
3.
Jacek Rózkowski 《Environmental Geology》1998,33(4):274-278
A karst-fissured aquifer in the Upper Jurassic carbonate rocks of the Krakow Upland shows a very high yield (safe yield 117 000 m3/day) and belongs to the major groundwater basins (MGBs) of Poland. The uncovered character of the aquifer and its hydraulic
structure favor the intensive infiltration and migration of anthropogenic pollutants from the surface. This pollution is caused
by agriculture and industry in the proximity of Krakow and the Upper Silesian agglomeration. Progressive degradation of groundwater
quality on a regional scale results. Evaluation of the endangering of the aquifer studied is based on the analysis of the
time interval of vertical water percolation from the surface, the time interval of groundwater horizontal flow through the
aquifer and the duration of water residence in the aquifer derived from tritium data. Quaternary and Cretaceous overburden
occur in the Krakow Upland in addition to numerous outcrops of limestones. The time interval of vertical water percolation
in highly permeable limestones does not exceed 3 years and in the areas covered by overburden it is from several to 50 years.
The mean effective time interval of horizontal groundwater flow through the Upper Jurassic rocks along the flow paths ranges
from several months in the areas of direct drainage to over 15 years in the elevated areas of local groundwater divides. The
age of water in the rock matrix was determined using tritium data interpreted according to an exponential model and it ranges
from 70 years to over 130 years. In karst-fissured systems with a high retardation index (Rp=21) the effective time of water circulation in local drainage basins does not exceed 7 years.
The Krakow-Wieluń Upland is the most extensive and uniform karst region in Poland. It is a belt of Upper Jurassic limestone
extending from Krakcow in the southeast to Wieluń in the northwest on the northeast slope of the Silesian Upland. Residual
hills of Paleogene age separated by infilled karst depressions are the most characteristic features of the Krakow-Wieluń Upland.
More than 800 small caves are known in this area, but only two of them reach 1 km of aggregate passage length (Gazek and others
1992).
Received: 4 December 1996 · Accepted: 29 April 1997 相似文献
4.
We present values of velocity of ground water percolation (Vg) over large depth intervals, varying from shallow to deeper depths in Indaram area of Godavari sub-basin. The velocities have been estimated using available measured geothermal data. Sub-surface temperatures were measured in seven boreholes. Terrestrial heat flow values are calculated using temperature data and measured values of thermal conductivity of core samples. The results show that Vg is ～3.4 ×10?7 cm /sec in the top layers (70–150 m) and decreases to ～0.04×10?7 cm/sec in the deeper levels around 350 m depth and becomes negligibly small thereafter, thereby, indicating that the overall permeability of the sub-surface layers, due to the occurrence of successions of permeable, semi-permeable layers gets reduced to more or less zero at depths around 350 m. The value of Thermal Peclet Number, which is the ratio of the heat transfer through convection to that through conduction, naturally becomes negligible around this depth in the area. The observed consistency of the magnitude of heat flow through various deep sections is a clear indicator that water percolation is practically reduced to zero at depths around 320–400 m and that conduction is the dominant mechanism of heat transfer below the inferred depth section, while the upper layers are dominated by recharge at various depths by near surface water from streams at Indaram. 相似文献
5.
Arianna Bucci Diego Barbero Manuela Lasagna M. Gabriella Forno Domenico Antonio De Luca 《Environmental Earth Sciences》2017,76(5):221
This study investigated the thermal regime of shallow groundwater in the Turin area (NW Italy), where the large energy demand has motivated a new interest for renewable sources, such as the use of ground-source heat pumps for domestic heating and cooling. The vertical variability of the groundwater temperature between the ground surface and 10–20 m was detected: deeper temperatures were higher than shallow temperatures in spring, while a decrease with depth occurred in autumn. These variations are connected with the heating and cooling cycles of the ground surface due to the seasonal temperature oscillation. Variations below the seasonal oscillation are likely to be connected with the presence of advective heat transport due to the groundwater flow, according to the hydraulic features of a shallow aquifer. Temperature values mostly ranged between 12 and 14 °C in rural areas, while the values were between 14 and 16 °C below the Turin city. This groundwater warming is attributed to a widespread urban heat island phenomenon linked to warmer land surface temperatures in Turin city. Sparse warm outliers are connected with point heat sources and site-specific conditions of land and subsurface use, which may cause the aquifer temperature to rise. A relatively stable temperature below the seasonal fluctuation zone combined with high productivity and legislated limits for deeper groundwater use represent favourable conditions for a large-scale diffusion of groundwater heat pumps within the shallow aquifer. Moreover, this heat surplus should be regarded as a resource for future geothermal installations. 相似文献
6.
7.
The article discusses the effects of changing the parking situation in the surrounding of shopping centres on consumers store
choice behaviour. To get insight into these effects a hierarchical logit model of parking lot and store choice behaviour is
estimated and validated. The research is based on before-and-after data of supermarket visitors collected in a major regional
shopping centre in a suburban area in The Netherlands.
The model is estimated using the before data. At the level of the supermarkets the estimated hierarchical logit model performs
very well. The model is less accurate at the level of parking lots but still performs satisfactory. Significant attributes
are a constant representing the characteristics of the supermarket, the distance between supermarket and parking lot, the
number of parking spaces per parking lot, the location of the parking lot vis-à-vis the origin of the consumer, and the availability
of supermarket trolley facilities at the parking lot. Validating the model by reproducing the after data yields less satisfactory
results. Especially the model does not perform very well on predicting parking lot choice.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
8.
Mohammad A. Hoque Aftab A. Khan M. Shamsudduha Muhammad S. Hossain Tariqul Islam Shahid H. Chowdhury 《Environmental Geology》2009,56(8):1687-1695
This study investigated the relationship between near-surface lithology and the spatial variability of As concentrations using
sediment grain-size analysis and electromagnetic induction survey in the southeast Bangladesh. It has been observed that the
aquifers overlain by finer sediments have higher concentrations of As in groundwater, whereas As concentrations are remarkably
low in aquifers having permeable sandy materials or thinner silt/clay layer at the surface. The near-surface lithology acts
as a controlling factor for spatial distributions of groundwater As within the very shallow depths (<15 m). Shallow alluvial
aquifers can provide low-As drinking water in many areas of the country when tube wells are properly installed after investigation
of the overlying near-surface sediment attributes and hydraulic properties. 相似文献
9.
综合物探技术探测平果铝厂赤泥堆场岩溶发育特征 总被引：3，自引：3，他引：0
为了预测和评价赤泥堆场建成后对地下水环境造成的污染,利用等偏移地震反射法、高密度电法为主,自然电场法为辅的综合物探技术来探查堆场地下岩溶的发育特征和管道的分布状况。经上述3种物探技术综合探测,确定出堆场各处覆盖层的厚度,确认了5个断层破碎带及其走向,圈定了14个物探异常区,并初步探明了岩溶管道的分布和地下水的流向。同时综合物探技术与钻探成果揭示了研究区岩溶发育的特点是以浅部垂直型为主,浅层岩溶的发育深度大约在地表下0～10 m,深部岩溶也有少量发育,其发育深度约在地面下40～50 m,超过此深度后岩溶发育变弱。 相似文献
10.
The present study describes variations in the vertical fluxes measured concurrently with sediment traps at both a shallow
water (4 m) and a deeper water (7.5 m) position in a coastal lagoon in April 1995. A tripod equipped with five sediment traps
(trap openings at 0.35 m, 0.75 m, 1.05 m, 1.40 m, and 1.80 m above the seabed) was placed at the shallow water position. This
tripod was deployed three times during the study period and deployment periods varied between 2 d and 5 d. The second sediment
trap, placed at the deep water position in the central part of the lagoon, measured vertical flux for intervals of 12 h at
1.4 m above the seabed. The horizontal distance between the sediment traps was 8 km. The average maximum vertical flux at
the shallow water position reached 27.9 g m−2 d−1 during a period of high, westerly wind speeds, and a maximum vertical flux of 16.9 g m−2 d−1 was reached at the deep water position during a period of high, easterly wind speeds. Both strong resuspension events were
closely related to increased wave shear stress derived from surface waves. Maximum wave-induced resuspension rate was 10 times
higher at the shallow water position and 3.8 times higher at the deep water position compared with the net sedimentation rate
in the lagoon. Small resuspension events occurred at the shallow water position during periods of increased current shear
stress, Estimations of conditions for transport of sediment between shallow water and deep water showed that particles must
be resuspended to a height between 3 m and 4 m and that current speeds must be higher than about 0.1 m s−1. An average sedimentation rate of 3.8 g m−2 d−1 was obtained at the shallow water position during a period without wave shear stress and low current shear stress. This rate
measured by sediment traps is similar to a net sedimentation rate in the lagoon of 4.4 g m−2 d−1, which was determined by radiocarbon dating of a sediment core (Kristensen et al. 1995). 相似文献
11.
运城盆地峨眉台地前缘新庄村一带地表黄土塌陷严重，其演化过程及其发展趋势是评估地质灾害发生可能性及时限性急需解决的关键地质问题。以地表地质调查为基础，结合遥感资料解译及三分量共振成像技术，综合分析了新庄村黄土塌陷区近10 a来的发展过程及现今的内部结构。研究结果显示，峨眉台地前缘处于黄土与湖相沉积的过渡地带，地层序列兼具湖相与黄土沉积特征，纵向上砂层与黄土间互出现，奠定了黄土塌陷区的物质基础；遥感资料解译结果表明黄土塌陷区自2011年开始，经历了一个孕育至快速发展的过程；三分量共振成像技术对黄土塌陷内部结构监测数据表明，黄土内部已形成纵横交错的孔洞系统，说明新庄村一带地质结构奠定黄土塌陷的物质基础，峨眉台地前缘断裂活动形成的地表裂缝加速黄土塌陷的进程，该区已成为一个高风险的地质灾害易发区。研究成果为峨眉台地前缘地质灾害的预防提供了基础地质资料。 相似文献
12.
N. Ramaiah V. V. S. S. Sarma Mangesh Gauns M. Dileep Kumar M. Madhupratap 《Journal of Earth System Science》2000,109(4):443-451
Bacterial abundance and production, numbers, sizes and concentrations of transparent exopolymer particles (TEP) and total
organic carbon (TOC) were measured during the 1996 summer monsoon to understand the relationship between TEP, the most labile
particulate organic carbon, and bacteria. While high regional variability in the vertical distribution of TOC was discernible,
TEP concentrations were high in surface waters at 18–20°N along 64°E with concentrations well over 25 mg alginic acid equivalents
I−1 due to upwelling induced productivity. Their concentrations decreased with depth and were lower between 200 and 500 m. Bacterial
concentrations were up to 1.99 × 108 I–1 in the surface waters and decreased by an order of magnitude or more at depths below 500 m. A better relationship has been
found between bacterial abundance and concentrations of TEP than between bacteria and TOC, indicating that bacterial metabolism
is fueled by availability of TEP in the Arabian Sea. Assuming a carbon assimilation of 33%, bacterial carbon demand (BCD)
is estimated to be 1.017 to 4.035 g C m–2 d–1 in the surface waters. The observed TEP concentrations appear to be sufficient in meeting the surface and subsurface BCD
in the northern Arabian Sea. 相似文献
13.
本文从冀中坳陷束鹿凹陷潜山顶面不整合接触类型及分布规律、结构特征及输导类型出发，精细刻画了不整合面之下半风化岩石层的垂向岩溶分带特征。在此基础上对典型剖面烃源岩热演化、油气运移进行模拟，建立了研究区潜山油气的运聚模式。结果表明，束鹿凹陷潜山顶面不整合包括4种接触类型、5种结构模式，具有3种输导类型，其中斜坡区和洼槽区西部以侧向型为主，斜坡区局部构造高点与洼中隆为侧向+圈闭型，凸起区以侧向+垂向型为主。不整合面之下半风化岩石孔缝洞体系发育，垂向上可划分为表层岩溶带、垂直渗流带以及三个水平潜流带，具有多期岩溶旋回特征。潜山顶部发育的垂直渗流带是油气沿不整合面运移的主力输导层，而内幕发育的多期水平潜流带是油气向内幕运移的潜在通道。深、浅部烃源岩热演化的差异以及与薄层砾岩是否接触导致了斜坡区与洼中隆潜山油气充注的差异，形成了斜坡区晚期薄层砾岩高效中转、不整合侧向运移、水平潜流带向内幕输导、顺向断层向上输导、反向断层圈闭成藏的油气运聚模式。 相似文献
14.
斑岩铜矿浅部富矿岩浆房研究进展 总被引：6，自引：0，他引：6
在主流的斑岩铜矿模型中,矿床下方都有一个浅部富矿岩浆房,为矿床的最终形成提供成矿流体.国外近年来的大量研究揭示了其基本特征,即位于地表以下约5 km,其大小直接决定着最终矿床的规模,其形态为平卧状,相对封闭,生命周期较短(一般约2 Ma).岛弧或陆缘弧环境有利于浅部富矿岩浆房形成的条件是中等挤压应力状态或挤压后应力松驰... 相似文献
15.
Bottom water hypoxic events were observed in Narragansett Bay, Rhode Island during the summer of 2001 using a towed sensor, vertical casts at fixed stations, and continuous monitoring buoys. This combination of approaches allowed for both extensive spatial and temporal sampling. Oxygen concentrations below the U.S. Environmental Protection Agency (EPA) acute hypoxia criterion of 2.3 mg l?1 were observed in the northern parts of Narragansett Bay, including the Providence River. We estimate 39% of the area of the Providence River was affected by acute hypoxia between July and September 2001. All other regions experienced only small areas of acute hypoxia (<5%), and no acute hypoxia was observed from Quonset Point south. The area encompassing oxygen concentrations below the EPA chronic hypoxia criterion of 4.8 mg l?1 was much more extensive in the upper half of Narragansett Bay, sometimes covering the majority of the region, though it is unclear whether exposure to concentrations below this criterion persisted long enough to significantly affect marine species in these areas. Vertical profiles of dissolved oxygen typically exhibited a mid water oxygen minimum near the pycnocline, followed by a slight increase in oxygen with depth. The surface waters above the pycnocline were typically supersaturated with oxygen. The northern portions of the Bay where the most extensive hypoxia was observed corresponded to the regions with both the greatest thermohaline stratification, the highest nutrient inputs, and the highest primary productivity. 相似文献
16.
P. Van Rensbergen A. Rabaute A. Colpaert T. St. Ghislain M. Mathijs A. Bruggeman 《International Journal of Earth Sciences》2007,96(1):185-197
This study documents the suite of processes associated with source-to-seafloor fluid migration in the Connemara field area
on the basis of 3D seismic data, well logs, 2D high-resolution seismic profiles, subbottom profiles, short cores and sidescan
sonar data. The combination of datasets yields details about fluid migration pathways in the deep subsurface, in the unlithified
shallow subsurface and about the distribution of fluid and gas seeps (pockmarks) at the sea floor. The Connemara field area
is characterized by vertical fluid migration pathways (“seismic chimneys” or “gas chimneys”) that extend from the top of the
Jurassic sequence, cross-cutting the entire Cretaceous sequence to the Upper Tertiary deposits over a vertical distance of
up to 1.5 km. Their localization is mainly structurally controlled to the crest of tilted fault blocks along the main hydrocarbon
migration pathways. These chimneys are important conduits for focused vertical fluid/gas flow from the deep to the shallow
subsurface. However, gas seeps (pockmarks) at the sea floor are almost randomly distributed, which indicates a change from
focused to diffuse fluid/gas migration in shallow, unconsolidated sediment. Where the vertical chimneys reach up to unlithified
Eocene to Miocene sands, widespread deformation, interpreted as fluidization, occurs around the main conduit. This deformation
affects about 32% of the entire unconsolidated Tertiary section (Late Eocene – Miocene). A Plio-Pleistocene glaciomarine drift
with up to five horizons with iceberg ploughmarks seals the Tertiary sands. In the near surface sediments it is observed that
gas accumulation occurs preferentially at iceberg ploughmarks. It is inferred that lateral migration at five levels of randomly
oriented ploughmarks dispersed gas over larger areas and caused random pockmark distribution at the sea floor, independent
from the underlying focused migration pathways. This study demonstrates that fluid flow migration changes from structurally
controlled focused flow in the deep consolidated subsurface to diffuse flow, controlled by sediment variability, in the shallow
subsurface. This result is relevant to a better understanding of the distribution of seepage-induced features at the seafloor
related to focused hydrocarbon migration pathways known from industry data and fluid flow modeling. 相似文献
17.
A. Uddin M. Shamsudduha J.A. SaundersM.-K. Lee K.M. AhmedM.T. Chowdhury 《Applied Geochemistry》2011,26(4):470-483
Mineral assemblages (heavy and light fractions) and sedimentological characteristics of the Quaternary alluvial aquifers were examined in the central Bengal Basin where As concentrations in groundwater are highly variable in space but generally decrease downward. Chemical compositions of sediment samples from two vertical core profiles (2-150 m below ground level, bgl) were analyzed along with groundwater in moderately As-enriched aquifers in central Bangladesh (Manikganj district), and the As mobilization process in the alluvial aquifer is described. Heavy minerals such as biotite, magnetite, amphibole, apatite and authigenic goethite are abundant at shallow (<100 m below ground level (mbgl)) depths but less abundant at greater depths. It is interpreted that principal As-bearing minerals were derived from multiple sources, primarily from ophiolitic belts in the Indus-Tsangpo suture in the northeastern Himalayan and Indo-Burman Mountain ranges. Authigenic and amorphous Fe-(oxy)hydroxide minerals that are generally formed in river channels in the aerobic environment are the major secondary As-carriers in alluvial sediments. Reductive dissolution (mediated by Fe-reducing bacteria) of Fe-(oxy)hydroxide minerals under anoxic chemical conditions is the primary mechanism responsible for releasing As into groundwater. Authigenic siderite that precipitates under reducing environment at greater depths decreases Fe and possibly As concentrations in groundwater. Presence of Fe(III) minerals in aquifers shows that reduction of these minerals is incomplete and this can release more As if further Fe-reduction takes place with increased supplies of organic matter (reactive C). Absence of authigenic pyrite suggests that SO4 reduction (mediated by SO4-reducing bacteria) in Manikganj groundwater is limited in contrast to the southeastern Bengal Basin where precipitation of arsenian pyrite is thought to sequester As from groundwater. 相似文献
18.
An extension to the DRASTIC model is proposed in order to assess aquifer vulnerability to pollution. In contrast to the DRASTIC
model, which considers the unsaturated and saturated zones together and computes a global intrinsic vulnerability index, the
suggested approach discriminates between the aquifer vertical vulnerability (a concept related to the pollutant percolation)
and the groundwater susceptibility (a concept that depends on the behaviour and uses of the groundwater). This approach is
applied to the Haouz aquifer (Morocco) that supplies water to the Marrakech area. This aquifer is widely overexploited and
there is evidence that the groundwater quality is threatened by various sources of pollution. Evaluation of the vertical vulnerability
indicates that the aquifer mainly presents a moderate-to-weak vertical vulnerability. The zones potentially most favourable
to pollutant percolation are mainly located in Central Haouz, along or near the surface wadis. The aquifer susceptibility
is high in places located near the N’Fis, Baaja and Issil wadis. Everywhere else, low-to-moderate susceptibility is observed.
This new approach therefore enables areas of vertical vulnerability and areas of susceptibility to be delineated separately.
As a result, it constitutes a valuable decision-making tool for optimising the management of aquifer water resources and land-use
planning. 相似文献
19.
Anthropogenic marker evidence for accelerated sedimentation in Lake Illawarra,New South Wales,Australia 总被引：1，自引：0，他引：1
B. E. Chenhall I. Yassini A. M. Depers G. Caitcheon B. G. Jones G. E. Batley G. S. Ohmsen 《Environmental Geology》1995,26(2):124-135
The chronology of near-surface sediments in Lake Illawarra has been investigated using radiocarbon dating and anthropogenically derived substances including trace metals, ash, and137Cs. Sediments at depths about 1 m below the water-sediment interface ranged in age from Modern to 786 calendar years bp on the basis of radiocarbon dating ofNotospisula trigonella valves. Multiple marker (for example ash-trace metals) depth-concentration sediment profiles yielded estimates of sedimentation rate ranging from 3 to 5 mm yr–1 at Griffins Bay to more than 16 mm yr–1 at Macquarie Rivulet. Sedimentation rates of approximately 10 mm yr–1 appeared to be typical of the western and southwestern portions of the lagoon. Rates of sediment accretion, prior to catchment clearing, urbanization, and industrialization have been estimated at less than 1 mm yr–1, thus indicating a general tenfold increase in sediment accumulation adjacent to the western foreshore caused by catchment development. Accelerated sedimentation in shallow coastal lagoons constitutes significant environmental impacts including shoaling, degradation of seagrass beds, and increased turbidity with consequent loss of aesthetic appeal. Management policy should be directed at attempts to reduce the amount of sediment input by the construction of strategically placed sediment retention ponds. Siltation within the shallow embayments of Lake Illawarra could be ameliorated by a carefully planned program of dredging. 相似文献
20.
Seismic Facies in a Deepwater Area of a Marine Faulted Basin: Deepwater Area of the Paleogene Lingshui Formation in the Qiongdongnan Basin 总被引：1，自引：0，他引：1
In recent years, deep water areas have become popular exploration fields because of their abundant hydrocarbon resource potential. There are only relatively poor planar seismic profiles and no wells for deepwater areas of the Lingshui Formation in the Qiongdongnan Basin. A lot of faults developed and strata are fragmented due to high temperatures and high pressure, and this has resulted in dim sequence boundaries. Based on seismic data of the deepwater area and well data of bordering shallow water areas, Lingshui Formation was divided into four third class sequences; namely SI, SII, SIII and SIV, and the three-dimensional isochronous stratigraphic framework of the Lingshui Formation in the studied area was shaped. Based mainly on seismic attributes such as amplitude, continuity, internal structure and external shape, six typical seismic facies were identified, including mat-shaped, filling, wedge-shaped, foreset, moundy-shaped and lenticular-shaped, and a seismic facies distribution map was subsequently drawn. With studies on wells of bordering shallow water areas, regional sedimentary characteristics, and isopach map as references, sedimentary planar distribution features were analyzed. The deepwater area of the Lingshui Formation has mainly developed littoral and shallow sea. Sandstone bodies of fan delta, braided river delta, slope fan, basin floor fan, and turbidite fan are at an interdigitate junction to marine hydrocarbon source rocks and thus are favorable prospecting targets. 相似文献