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1.
The combination of layer resistivity and thickness in the so called Da-zarrouk parameters S (longitudinal conductance) and R (transverse resistance) have proved useful in the evaluation of the transmissivities of the aquifers around Owerri and environs. The area is underlain by the unconsolidated to semi-consolidated coastal Benin Formation. The surface direct current electrical resistivity method was used in the study. Seven Vertical Electrical Soundings (VES) data by the Schlumberger array was acquired in the area. A maximum current electrode spacing (AB) of 1000 m was used for data acquisition. Four of the soundings were carried out near existing boreholes. Computer modelled interpretative methods was utilized in processing the data. Results show that the depth to the water level is shallow around Ife and Egbu areas with a mean depth of 30 m. Semi-deep aquifers were encountered around Okpalla and AVU areas with a mean depth of 90 m while very deep aquifers were sensed around Owerri and Obinze areas with a mean depth of 125 m. Aquifer thicknesses in the study area range from 8 m at Ife and 117 m at Owerri. The diagnostic Kσ = constant value have proved so useful in calculating transmisivities and hydraulic conductivities of all the sounding locations including areas where no boreholes exist. Hydraulic conductivity varies between 6.19m/day at Ife and 24.7 m/day at Obinze. Transmissivity values also very between 51.39 m2/day at Ife and 1379.56 m2/day at Owerri. It is hoped that the results would help in long term planning of groundwater exploitation schemes within the study area.  相似文献   

2.
A regional lithostratigraphic and hydraulic interpretation is presented for the upper 0–300 m of the Benin Formation where groundwater is abstracted in the Rivers State, Nigeria.The aquifers are predominantly sand beds with minor clays, lignite, and conglomerate intercalations. The sands are very fine to coarse grained, subangular to subrounded, poor to fairly well sorted and mostly lithic arenites. A maximum thickness greater than 50 m is developed in places and vertical stacking is common. Most of the conglomerate beds have a matrix support fabric and appear restricted to the east as the lignite beds. An east-west trending belt, about central to the state, seems to contain more clay interbeds.The transmissivity values for the aquifers range from 1.05 × 10–2 to 11.3 × 10–2 m2/sec, while the coefficient of storage varies between 1.07 × 10–4 and 3.53 × 10–4 and specific capacity values lie between 19.01 and 139.8 m3/h/m drawdown. These values suggest that the aquifers have very good capacity to transmit groundwater. The static water level map shows a north-to-south regional groundwater flow pattern except in the northeast (Imo River catchment area) where the flow is northeast to southwest. The groundwater quality is very good and compares favorably with WHO standards for drinking water. However, relatively high iron and chloride values are localized in time and space.Deposition of the aquifer materials is thought to have occurred in alluvial fan, fluvial channel, tidal channel, intertidal flat, beach, and related microenvironments.  相似文献   

3.
In this paper, fist-order reliability method (FORM) is used to evaluate the impacts of uncertainties posed by traditional deterministic models on the environment in Jining, China. Because of groundwater contamination in shallow aquifer, and an increase in water demand, the new wells target the confined aquifer with constant pumping rate of 5,000 m3/d. Using Theis equation, the groundwater drawdown is analyzed to determine whether the confined aquifer will be contaminated. Although the piezometric level is higher than the phreatic level by 11.0 m, the risk of drawdown is still 19.49% when the pumping rate of 5,000 m3/d is maintained for 2 years. The deterministic model indicates a drawdown of 8.94 m which is lower than the maximum tolerance drawdown of 11.0 m. The sensitivity and uncertainty analysis reveal that the model result is more sensitive to transmissivity than specific yield, while the reliability analysis offers significant information for the decision makers. This approach exposes and minimizes the risk of undesirable consequences such as groundwater contamination.  相似文献   

4.
Modeling of groundwater flow for Mujib aquifer, Jordan   总被引：4，自引：0，他引：4  
Jordan is an arid country with very limited water resources. Groundwater is the main source for its water supply. Mujib aquifer is located in the central part of Jordan and is a major source of drinking water for Amman, Madaba and Karak cities. High abstraction rates from Mujib aquifer during the previous years lead to a major decline in water levels and deterioration in groundwater quality. Therefore, proper groundwater management of Mujib aquifer is necessary; and groundwater flow modeling is essential for proper management. For this purpose, Modflow was used to build a groundwater flow model to simulate the behavior of the flow system under different stresses. The model was calibrated for steady state condition by matching observed and simulated initial head counter lines. Drawdown data for the period 1985–1995 were used to calibrate the transient model by matching simulated drawdown with the observed one. Then, the transient model was validated by using drawdown data for the period 1996–2002. The results of the calibrated model showed that the horizontal hydraulic conductivity of the B2/A7 aquifer ranges between 0.001 and 40m/d. Calibrated specific yield ranges from 0.0001 to 0.15. The water balance for the steady state condition of Mujib aquifer indicated that the total annual direct recharge is 20.4 × 106m3, the total annual inflow is 13.0 × 106 m3, springs discharge is 15.3 × 106 m3, and total annual outflow is 18.7 × 106 m3. Different scenarios were considered to predict aquifer system response under different conditions. The results of the sensitivity analysis show that the model is highly sensitive to horizontal hydraulic conductivity and anisotropy and with lower level to the recharge rates. Also the model is sensitive to specific yield  相似文献   

5.
Land subsidence in Bangkok, Thailand   总被引：9，自引：0，他引：9  
Land subsidence from deep well pumping has been affecting Bangkok for the past 35 years. Its impact is particularly critical because of the flat low-lying topography and the presence of a thick soft clay layer at the ground surface that augment flood risk and foundation engineering problems, respectively. The subsidence reached its most critical state in the early 1980s when it occurred at a rate as high as 120 mm/year. The rate decreased in the subsequent period but the subsidence-affected area expanded following the growth of the city. Despite various attempts implemented to remedy the crisis, groundwater pumping from the thick aquifer system underneath the city continued to increase from 1.2 million m3/day in the early 1980s to more than 2.0 million m3/day at the turn of the century. Piezometric levels in the main aquifer layers had been drawn down by as much as 65 m. Monitoring data showed a clear correlation between the subsidence and piezometric drawdown. The data suggested that for 1 m3 of groundwater pumped out in Bangkok Plain, approximately 0.10 m3 of ground loss occurred at the surface. Significant development has been made in numerical methods for prediction of differential settlements between building foundations caused by the piezometric drawdown in the aquifers. The strict mitigation measures adopted recently, comprising a pricing policy for groundwater management, an expansion of tap water supply, and strict enforcement of groundwater laws, have resulted in a marked drop in groundwater use. However, the land subsidence will continue for a long while owing to the time-dependent consolidation behavior of the soft clay layer and clay aquitards.  相似文献   

6.
Vertical electrical soundings technique was used to evaluate the aquifer characteristics and distribution in the northern part of Paiko in Nigeria. A total of thirty vertical electrical soundings were carried out using ABEM SAS4000 Terrameter, and the data was analyzed both manually and with software (Resist software). The result revealed the aquifer resistivity and thickness to vary from 10.9 to 80,368 Ωm, and 1.06 to 72 m, respectively. Also, hydraulic conductivity ranges from 0.010267 to 41.61928 m/day while transmissivity values range from 0.035215 to 70.09302 m2. The hydrogeological maps (hydraulic conductivity and transmissivity image maps) showed the variations of these parameters in the study area and that the southwestern part of the area has prolific aquifer.  相似文献   

7.
Phu Le Vo 《GeoJournal》2007,70(1):75-89
The management of water resources is an unfinished effort of the international community. Rapid urbanization has transcended the management capacity of governments in developing countries. Since the renovation policy launched in 1986, Ho Chi Minh City, Vietnam, has experienced the fastest urbanization and industrialization process. This has placed severe constraints on the use of water resources and management capacity of the local government. The abstraction of groundwater has exceeded the limiting volume (520,000 m3/day) and the annual drawdown of water table is 2–3 m. In addition, the quality of urban water bodies is increasingly exacerbated by a huge volume of untreated industrial and domestic wastewater. These are hampering water demand, use and the capacity of the municipal authority in managing water resources. The purpose of this paper is to analyze the impact of urbanization on water resources. Current issues and challenges in the management practices of water resources are discussed. It will propose a new paradigm of water management in Ho Chi Minh City.  相似文献   

8.
Canelles landslide: modelling rapid drawdown and fast potential sliding   总被引：4，自引：0，他引：4  
A large landslide (40 × 106 m3) was reactivated on the left bank of Canelles reservoir, Spain. The instability was made evident after a considerable reduction of the reservoir level. The drawdown took place during the summer of 2006 after several years of high water levels. The drawdown velocity reached values between 0.5 and 1.2 m/day (registered at low elevations). The paper reports the geological and geotechnical investigations performed to define the movement. The geometry of the slip surface was established from the detailed analysis of the continuous cores recovered in deep borings and from limited information provided by inclinometers. Deep piezometric records provided also valuable information on the pore water pressure in the vicinity of the failure surface. These data allowed validating a flow–deformation coupled calculation model, which takes into account the changes in water level that occurred 4  years previous to the failure as well as the average rainfall. The analysis indicates that the most likely reason for the instability is the rapid drawdown that took place during the summer of 2006. The potential sudden acceleration of the slide is also analysed in the paper introducing coupled thermal hydraulic and mechanical effects that may develop at the basal shearing surface of the sliding mass. The results indicate that the slide velocity may reach values around 16 m/s when displacement reaches 250 m.  相似文献   

9.
During the formation and development of glacial meltwater runoff, hydrochemical erosion is abundant, especially the hydrolysis of K/Na feldspar and carbonates, which can consume H+ in the water, promote the formation of bicarbonate by dissolving atmospheric CO2, and affect the regional carbon cycle. From July 21, 2015, to July 18, 2017, the CO2 concentration and flux were observed by the eddy covariance (EC) method in the relatively flat and open moraine cover area of Koxkar Glacier in western Mt. Tianshan, China. We found that: (1) atmospheric CO2 fluxes ranged from ??408.95 to 81.58 mmol m?2 day?1 (average ? 58.68 mmol m?2 day?1), suggesting that the study area is a significant carbon sink, (2) the CO2 flux footprint contribution areas were primarily within 150 m of the EC station, averaging total contribution rates of 93.30%, 91.39%, and 90.17% of the CO2 flux in the snow accumulation, snow melting, and glacial melting periods, respectively. Therefore, the contribution areas with significant influences on CO2 flux observed at EC stations were concentrated, demonstrating that grassland CO2 flux around the glaciers had little effect at the EC stations, (3) in the predominant wind direction, under stable daytime atmospheric stratification, the measurement of CO2 flux, as interpreted by the Agroscope Reckenholz Tanikon footprint tool, was 79.09% ± 1.84% in the contribution area. This was slightly more than seen at night, but significantly lower than the average under unstable atmospheric stratification across the three periods of interest (89%). The average distance of the farthest point of the flux footprint under steady state atmospheric conditions was 202.61?±?69.33 m, markedly greater than that under non-steady state conditions (68.55?±?10.34 m). This also indicates that the CO2 flux observed using EC was affected primarily by hydrochemical erosion reactions in the glacier area, (4) a good negative correlation was found between net glacier exchange (NGE) of CO2 and air temperature on precipitation-free days. Strong ice and snow ablation could promote hydrochemical reactions of soluble substances in the debris area and accelerated sinking of atmospheric CO2. Precipitation events might reduce snow and ice melting, driven by reduced regional temperatures. However, a connection between NGE and precipitation, when less than 8.8 mm per day, was not obvious. When precipitation was greater than 8.8 mm per day, NGE decreased with increasing precipitation, (5) graphically, the slope of NGE, related to daily runoff, followed a trend: snow melting period?>?snow accumulation period?>?early glacial ablation period?>?late glacier ablation period?>?dramatic glacier ablation period. The slope was relatively large during snow melting, likely because of CO2 sinking caused by water–rock interactions. The chemical reaction during elution in the snow layer might also promote atmospheric CO2 drawdown. At the same time, the damping effect of snow cover and the almost-closed glacier hydrographic channel inhibited the formation of regional runoff, possibly providing sufficient time for the chemical reaction, thus promoting further CO2 drawdown.  相似文献   

10.
The Miocene Siwalik Group (upsection, the Chinji, Nagri, and Dhok Pathan Formations) in northern Pakistan records fluvial and lacustrine environments within the Himalayan foreland basin. Thick (5 m to tens of metres) sandstones are composed of channel bar and fill deposits of low-sinuousity (1·08–1·19), single-channel meandering and braided rivers which formed large, low-gradient sediment fans (or ‘megafans’). River flow was dominantly toward the south-east and likely perennial. Palaeohydraulic reconstructions indicate that Chinji and Dhok Pathan rivers were small relative to Nagri rivers. Bankfull channel depths of Chinji and Dhok Pathan rivers were generally ≤ 15 m, and up to 33 m for Nagri rivers. Widths of channel segments (including single channels of meandering rivers and individual channels around braid bars) were 320–710 m for Chinji rivers, 320–1050 m for Nagri rivers, and 270–340 m for Dhok Pathan rivers. Mean channel bed slopes were on the order of 0·000056–0·00011. Bankfull discharges of channel segments for Chinji and Dhok Pathan rivers were generally 700–800 m3s?1, with full river discharges possibly up to 2400 m3s?1. Bankfull discharges of channel segments for Nagri rivers were generally 1800–3500 m3s?1, with discharges of some larger channel segments possibly on the order of 9000–32 000 m3s?1. Full river discharges of some of the largest Nagri braided rivers may have been twice these values. Thin (decimetres to a few metres) sandstones represent deposits of levees, crevasse channels and splays, floodplain channels, and large sheet floods. Laminated mudstones represent floodplain and lacustrine deposits. Lakes were both perennial and short-lived, and likely less than 10 m deep with maximum fetches on the order of a few tens of kilometres. Trace fossils and body fossils within all facies indicate the former existence of terrestrial vertebrates, molluscs (bivalves and gastropods), arthropods (including insects), worms, aquatic fauna (e.g. fish, turtles, crocodiles), trees, bushes, grasses, and aquatic flora. Palaeoenvironmental reconstructions are consistent with previous palaeoclimatic interpretations of monsoonal conditions.  相似文献   

11.
In the Afram Plains area, groundwater is the main source of water supply for most uses. The area is underlain by aquifers of the southern Voltaian sedimentary basin, which are predominantly sandstones, mudstones, conglomerates and shale. Ordinary least squares regression analysis using 41 well-test data from aquifers in the Afram Plains portion of the Voltaian system reveals that transmissivity, T, exists in a non-linear relationship with specific capacity, Sc. The analysis reveals that T = 0.769Sc1.075 with R 2 = 0.83 for aquifers in the area. The mudstone/conglomerate aquifer in the area appears to be the most variable in terms of both specific capacity and transmissivity with transmissivity ranging from 0.18 to 197.7 m2/day and 0.5 and 148.5 m3/day/m, respectively. Horizontal fractures and joints resulting from secondary fracturing appear to be the main determinants of both transmissivity and specific capacity in the area. PHREEQC modeling and mineral stability diagrams indicate that groundwater quality in the Afram Plains area is controlled by the incongruent weathering of silicate minerals in the aquifers. These processes concentrate calcium, sodium, magnesium, potassium, bicarbonate ion and quartz, leading to calcite, dolomite and aragonite supersaturation at most locations. Hierarchical cluster analysis performed on the raw chemical data reveals two main water types or facies: the calcium–sodium–chloride–bicarbonate facies, and the magnesium–potassium–sulfate–nitrate facies for the southern and northern sections of the Afram Plains area, respectively.  相似文献   

12.
The current study aimed to evaluate hydrogeologically the Nubian sandstone aquifer in El-Bahariya Oasis. It represents the main water-bearing horizon in the study area and consists of continental elastic sediments, mainly sandstone alternating with shale and clays. The general flow lines are directed from SW to NE direction, as detected from the constructed potentiometric head contour map. The piezometric surface reaches 149 m in El-Heiz area at the southern part, while it reaches 90 m at the northern, reflecting higher pressure head of the aquifer in the southern part. The map also illustrates that the southern part is considered as the most promising location for development. The structural elements play an important role in the deposition and distribution of the sedimentary succession of the Nubian sandstone sediments. Consequently, this sedimentary pattern affects the occurrences and movements of the groundwater within the aquifer system. Along the structurally high areas, in the study area, the piezometric head increases, while the reverse is recorded along the structurally low areas. The step-drawdown tests data were carried out by calculating the aquifer loss coefficient (B) and the well loss constant (C). The B values are smaller compared with C values, indicating that the aquifer under pressure has a behavior of leaky aquifer; therefore, it shows hydraulic connection with surrounding formation. The values of well efficiency range from 78.50% to 87.76%. Analysis of 12 pumping test data (constant discharge tests) was carried out in order to calculate the Nubian aquifer hydraulic parameters (transmissivity, hydraulic conductivity, and storage coefficient). The transmissivity values decrease from 3,045 m2/day in the southern part (El-Heiz area) to 236 m2/day in the northeastern part (El-Harra area). Accordingly, the aquifer classified as a high to moderate potentiality. Transmissivity contour map observes gradual increase of transmissivity values from the southern to northeastern direction. This may be due to the increase of shale or clay content in the concerned aquifer in that direction. The storage coefficient values range between 1.04 × 10?4 and 5.22 × 10?3, as obtained from the results of pumping test analysis, which ensure that the Nubian sandstone aquifer is classified as semi-confined to confined aquifer type. The S values show a decrease from southwest to northeast direction as detected from S-map. The hydraulic conductivity values vary from to 0.46 m/day in the northern part to 10.88 m/day in the southern part with an average of 5.67 m/day. According to the classification based on K values, the aquifer is mainly composed of coarse sand.  相似文献   

13.
During the last 25 years, rapid and unplanned land reclamation activity has been carried out in the areas located in both south and east of Wadi El - Natrun Depression of Egypt. Accordingly, negative effects on groundwater levels and vulnerability are frequently caused by localized high levels of abstraction and the return-flow of polluted irrigation water respectively. A groundwater model is a computational method that presents an approximation of an underground water system. In this study the groundwater system is simulated both in quantity and quality by using Mass Balance Transfer Model (NETPATH), Groundwater Modeling System (GMS) and DRASTIC Model to investigate the water - rock interactions, groundwater levels drawdown and vulnerability respectively. Three main geochemical processes namely dedolomitisation, dissolution of halite and silicate weathering were estimated during the flow path. The present over-abstraction of groundwater (105.84 million m3/year) has induced a general head drawdown from 3 to 40 m in years 2015 and 2050 respectively. Best estimate using a 3D GMS hydraulic model was (157000 m3/day) a strategy proposed for the management of groundwater without critical depletion (second scenario). The results document the extent to which a high drawdown can greatly reach 4 m by the end of simulation year 2050. The vulnerability maps of groundwater were constructed using the DRASTIC index method. The results indicated that, the southeastern and central portions of the study area are having high vulnerability rate (> 110). Modified DRASTIC map showed many more dominant high risk areas in the eastern parts of the study area that were low risk, which may be attributed to return flow of polluted irrigation water.  相似文献   

14.
The River Gash Basin is filled by the Quaternary alluvial deposits, unconformably overlying the basement rocks. The alluvial deposits are composed mainly of unconsolidated layers of gravel, sand, silt, and clays. The aquifer is unconfined and is laterally bounded by the impermeable Neogene clays. The methods used in this study include the carry out of pumping tests and the analysis of well inventory data in addition to the river discharge rates and other meteorological data. The average annual discharge of the River Gash is estimated to be 1,056?×?106 m3 at El Gera gage station (upstream) and 587?×?106 m3 at Salam-Alikum gage station (downstream). The annual loss mounts up to 40% of the total discharge. The water loss is attributed to infiltration and evapotranspiration. The present study proofs that the hydraulic conductivity ranges from 36 to 105 m/day, whereas the transmissivity ranges from 328 to 1,677 m2/day. The monitoring of groundwater level measurements indicates that the water table rises during the rainy season by 9 m in the upstream and 6 m in the midstream areas. The storage capacity of the upper and middle parts of the River Gash Basin is calculated as 502?×?106 m3. The groundwater input reach 386.11?×?106 m3/year, while the groundwater output is calculated as 365.98?×?106 m3/year. The estimated difference between the input and output water quantities in the upper and middle parts of the River Gash Basin demonstrates a positive groundwater budget by about 20?×?106 m3/year  相似文献   

15.
The Central Ground Water Board (CGWB) constructed 72 bore wells down to a targeted depth of 208 m in Nanded district, Maharashtra which is mainly underlain by hard rocks, namely basalts and granites. The yield of these bore wells varies from 0.10 litres/second (l/s) to 25 l/s and depth of weathering varies from less than 1 m to 24 meters below ground level (m bgl). The shallowest and the deepest aquifer zones are encountered at 7 and 172 m bgl respectively and majority of the productive aquifer zones are encountered within 100 meter (m) depth. Most productive zones are fractured basalts, fractured and weathered granites and 31 % of the zones are encountered within 25 m, 36 % within 25–50 m, 24 % within 50–100 m, 8 % within 100–150 m and less than 1 % within 150–173 m depth ranges. Out of the three major sets of lineaments, the NE-SW trending lineaments are more productive, and a maximum of five fracture zones are encountered in all. Surface geophysical studies (profiling) reveal that wherever the ratio between high resistivity and low resistivity is high, the discharge is high, and where the ratio is low the discharge is low. The depth to water level in these bore wells are in the range of 1.5–47.5 m bgl (below ground level). The transmissivity (T) and Storativity (S) values of 21 wells range from 3 to 593 m2/day and 6.5 × 10?6 to 7.32 × 10?2 respectively. The groundwater from the area is mostly of Ca-Na-HCO3-Cl, Ca-Na-HCO3, Ca-HCO3-Cl, Na-HCO3, Na-HCO3-Cl, Na-Cl, Ca-HCO3 types in the descending order of dominance and a few are found to be unsuitable for drinking. At a few sites, drilling down to the targeted depth of 200 m couldn’t be completed due to highly fractured nature of formations, hydraulic backpressure, occurrences of saturated intertrappean beds and high magnetic nature of formations.  相似文献   

16.
The load bearing capacity of soils in Otukpa area of Benue state, Nigeria was evaluated by characterizing the geotechnical, geophysical and structural properties of the soil. The evaluation was necessary because aside the area holding good prospect for future increase in human population, sparsely distributed low-weight buildings in the area have cracks and other signs of failure. Remote sensing/GIS, geophysical and geotechnical approaches were integrated to achieve the objective. 2-D tomography and processed remotely sensed data confirmed the presence of areas of strength especially to the north. Stratigraphy of the northern portion consist of four layers; loose top soil (0-0.26m), compact clayey sand (0.26m-3.33m), dry clayey sand (3.33m-74.21m) and saturated clayey sands (74.21m-201.58m) While the stratigraphy in the south is slightly different; compact topsoil (0-1.2m), loose sand (1.2m-10.81m), compact sand (10.82m-19.71m) and compact clay sand (19.71m-56.03m). The plastic limit range from 11-17% with average specific gravity of 2.64g/cm3. Permeability ranges from 7.8×10-6m/sec to 3.36×10-4m/sec while volume compressibility under 250kN ranges from 7.27×10-5m2/kN to 1.3×10-4m2/kN and the rate of consolidation under 250kN is within 12.43 m2/year to 1.33m2/year. MDD peaks at 1.85g/cm3 at an OMC of 12.11% and is lowest at 1.67g/cm3 at an OMC of 11.99%. UCS ranges from 31-45kN/m2 while shear strength is between 258.81kN/m2 to 338 kN/m2. Due to the variability of engineering properties of soils, the southern part of the area is preferred for locating the buildings. Generally, careful foundation design in the area is necessary.  相似文献   

17.
In Dakhla oasis, Western Desert of Egypt, groundwater is the only resource for all anthropogenic activities. During the last 50 years, the Nubian Sandstone Aquifer System (NSAS) has been undergoing serious stress through withdrawing its storage. Plans for expanding the agricultural areas in Dakhla oasis were given by the government. This article is an attempt to investigate the best management option that meets development ambitions and groundwater availability. Based on a calibrated regional three-dimensional groundwater flow model for the NSAS using FEFLOW, a refined (high resolution) local scale model was developed to simulate and predict the impact of applying the actual and planned extractions rates on Dakhla oasis. Five management scenarios were suggested. The application of the actual extraction rate of 1.2 × 106 m3/day for the oasis for the next 90 years resulted in a drawdown of 75 m and a depth to groundwater up to 75 m with an annual change in hydraulic head of 0.57 m. At the end of this simulation, only a few wells at the west of the oasis will still be free flowing. The application of the planned extraction rate (1.7 × 106 m3/day) resulted in great depths to groundwater (>100 m) and formed huge cones of depressions that connected together to cover the whole oasis and extend further beyond its borders. It was found that the best option for groundwater management in the oasis is the implementation of an extraction rate of 1.46 × 106 m3/day, as the depths to groundwater will never exceed the 100 m limit.  相似文献   

18.
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19.
A spatial relationship between high capacity municipal production wells (>5,000 m3/day), completed in a deep bedrock aquifer, and a buried bedrock valley was recognized in the city of Guelph, southwestern Ontario, Canada. Most production wells are completed in a discrete zone, ～60 m below ground surface, within flat-lying dolostones of the Silurian Amabel Formation. Thick overburden and limited subsurface data make characterization of the karstic aquifer difficult. This study integrates hydrogeologic data with models of karst formation, deriving a conceptual model of porosity development as it relates to valley incision. Bedrock valley incision likely occurred prior to the early Wisconsinan age (>60–75 ka). Incision created steep hydraulic gradients within the flat-lying bedrock, and provided the driving force required to integrate regional groundwater flow into karst conduits that drained at the base of the valley. Dissolution in production zone dolostones was favoured over dissolution in shallower bedrock due to abundant bedding plane partings and fossiliferous facies with high intercrystalline porosity. Burial of the valley during subsequent ice advances reduced the valley’s hydraulic influence and the efficacy of the flow system to cause dissolution. The high capacity municipal wells near the buried bedrock valley tap into the now dormant karst aquifer system.  相似文献   

20.
The composition of river water, sediments, and pore waters (down to 30 cm below the bed) of Las Catonas Stream was studied to analyze the distribution of trace elements in a peri-urban site. The Las Catonas Stream is one of the main tributaries of Reconquista River, a highly polluted water course in the Buenos Aires Province, Argentina. The semi-consolidated Quaternary sediments of the Luján Formation are the main source of sediments for Las Catonas Stream. The coarse-grained fraction in the sediments is mainly composed of tosca (calcretes), intraclasts, bone fragments, glass shards, quartz, and aggregates of fine-grained sediments together with considerably amounts of vegetal remains. The clay minerals are illite, illite–smectite, smectite, and kaolinite. For the clay-sized fraction, the external surface area values are mostly between 70 and 110 m2g?1, although the fraction at 15 cm below the bottom of the river shows a lower surface area of 12 m2g?1. The N2 adsorption–desorption isotherms at 77 K for this sample display a behavior indicative of non-porous or macroporous material, whereas the samples above and below present a typical behavior of mesoporous materials with pores between parallel plates (slit-shaped). As, Cr, Cu, and Cd concentrations increase down to 15 cm depth in the sediments, where the highest trace element and total organic carbon (TOC) concentrations were found, and then decrease toward the bottom of the core. Except for As, the levels of the other heavy metals show higher concentration in surficial waters than in pore waters. Distribution coefficients between the sediments, pore water, and surficial water phases indicate that As is released from the sediments to the pore and surficial waters. Cu content strongly correlates with TOC (mainly from vegetal remains), suggesting that this element is mainly bound to the organic phase.  相似文献   

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