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1.
The present work deals with the groundwater aquifer of the Lower Cretaceous sandstone and its sustainable development in Sinai. The studied aquifer system is the most promising groundwater system in Sinai due to its wide extension, hug storage, and good quality. The objective of this paper aims to elucidate the hydrogeological characteristics of the Lower Cretaceous aquifer. The aquifer system occurs under confined conditions. The top surface of the Lower Cretaceous dips steeply towards the southwest direction with step faults. The average sand percent of the penetrated aquifer attains 54%. The main direction of groundwater flow is generally from southwest and locally is concentric to the center of study area related to the influence of the graben block. The aquifer has a hydraulic gradient generally reaches 0.0011 m/m and attains 0.0028 in central portion of study area. The aquifer parameters (effective porosity, transmissivity, and hydraulic conductivity) increase towards the northeast direction with increasing of the sand percentage. Durov diagram plot revealed that the groundwater has been a final stage evolution represented by a NaCl water type. The groundwater salinity increases towards the central of study area coinciding with groundwater flow. The groundwater salinity of the Lower Cretaceous aquifer is brackish water and varies from 2,510 to 5,256 ppm and unsuitable for drinking and domestic purposes.  相似文献   

2.
The lithology of the studied aquifers has an important effect on their hydrogeologic setting. Moreover, the structural patterns have their imprint on the geologic setting and consequently the hydrogeologic conditions of the area. Lake Nasser recharges the groundwater in the study area by large amount of water increasing the groundwater level. A comparison of the depth to water in the same wells at two different periods (1998 and 2014 ) shows that the depth to water increases with average rise 11.1 m during 16 years. The constructed water table map shows that the groundwater flow is mainly towards the northwest direction reflecting recharge from Lake Nasser. The hydraulic parameters of the Abu Aggag and Sabaya sandstone aquifers are determined in the present work from pumping tests. The transmissivity of the studied aquifers reflects the moderate to high potentiality. The groundwater salinity of the studied aquifers is fresh water and varies from 353 to 983 ppm (part per million) and suitable for all purposes. It increases due to the west direction coinciding with groundwater flow direction. The main result of the present study shows that the seepage water from Lake Nasser attains 17 mcm/year.  相似文献   

3.
The geochemical processes controlling chemical composition of groundwater are studied using hydrochemical and isotopic data in Abdan-Dayer coastal plain, south of Iran. The salinity of groundwater in the coastal plain ranges from 1,000, a fresh end-member, to more than 50,000 μS cm?1, a saline end-member. Groundwater salinity increases from the recharge area toward areas with a shallow water table close to the Persian Gulf coast due to direct evaporation and sea water intrusion as confirmed by mixing binary diagrams, stable isotope content, and Br?/Cl? ratio. Groundwater flow pattern in the study area has been modified due to over-pumping of groundwater in recent years which resulted in further saline water migration toward fresh water and their mixing. The maximum mixing ratio is estimated about 15% in different parts of the study area according to chloride concentration.  相似文献   

4.
The El Minia governorate lies within the Nile Valley, surrounded by calcareous plateaus to the east and west. The present study focuses on the hydrogeochemistry of the Eocene limestone aquifer at some wadis in the east El Minia governorate, Eastern Desert, Egypt. Hydrogeologically, two main aquifers are encountered in the study area, namely the Maghagha marly limestone and the Samalut chalky limestone aquifers. The Maghagha aquifer is composed of alternating layers of marly limestone and shale with thicknesses ranging from 3.49 m to 177.05 m and a groundwater depth ranging from 8.5 m to 59.27 m which reflects low groundwater potentiality. The groundwater salinity representing this aquifer ranges from 603.5 mg/L to 978.5 mg/L, reflecting fresh water type. Samalut aquifer is made up of chalky, cavernous and fractured limestone with thickness ranging from 30 m to 205 m and groundwater depth ranging from 9 m to 86.77 m, which indicates good groundwater potential. The groundwater salinity of the concerned aquifer ranges from 349.7 mg/L to 2043.9 mg/L, reflecting fresh to possibly brackish water types. Groundwater in the study area is of meteoric water origin; recent recharge is mainly controlled through the presence of fractures and their densities. The majority of groundwater samples in the study area are suitable for drinking and irrigation purposes.  相似文献   

5.
To understand the impact of the influence of treated wastewater, a study was undertaken in the downstream side of Wadi Hanifa in the southern part of Riyadh City in Saudi Arabia. Chemical elements from 17 groundwater samples, 9 surface water samples (treated wastewater), and 14 soil samples were analyzed. Water facies analyses showed that both groundwater and surface water belong to the SO4-Cl class. However, the groundwater is characterized by high salinity (average value of 3547 mg/l), which may be result of the greater rock-water interaction and limited rainfall recharge. The NO3 values are also high in the groundwater samples (average value of 40 mg/l) and are mainly attributed to the agricultural practices in the study area. The surface water samples (treated wastewater from the plant) shows an average salinity value of 1232 mg/l and is better suited for irrigation purposes. Heavy elements analyzed in the soil samples show high concentrations of all the elements except Mn and Ni as compared to their background concentration. Enrichment factor and index of geoaccumulation calculated from the soil samples indicate that they are severely enriched with respect to Cd and Se. The spatial distribution maps were prepared based on kriging interpolation technique to estimate the concentrations of the analyzed elements at unknown locations. The treated wastewater in the study area is better suited for agricultural and domestic activities as compared to groundwater.  相似文献   

6.
The management of groundwater resources is very important in the semiarid Sahel region, which is experiencing rapid urban development. Impacts of urbanization on groundwater resources were investigated in the unconfined aquifer of the Continental Terminal beneath the city of Niamey, Niger, using water level and chemical data. Hydrodynamic and chemical changes are best described by a combination of factors including the historical development of the city, current land use, water-table depth and topography. Seasonal groundwater recharge occurs with high spatial variability, as indicated by water-level monitoring in all wells, but there was no interannual trend over the 5-year study period. Groundwater salinity shows high spatial variability and a minor rising trend. The highest salinity is in the old city centre, with Na–NO3 dominant, and it increases seasonally with recharge. Salinity is much lower and more variable in the suburbs (Ca–HCO3, Ca–NO3, and Na–NO3 dominant). Nitrate is the main ionic contaminant and is seasonally or permanently above the international guidelines for drinking water quality in 36 % of sampled wells, with a peak value of 112 mg L?1 NO3–N (8 meq L?1). Comparison of urban and rural sites indicates a long-term increase in groundwater recharge and nitrate enrichment in the urban area with serious implications for groundwater management in the region.  相似文献   

7.
Groundwater levels in hard-rock areas in India have shown very large declines in the recent past. The situation is becoming more critical due to a paucity of rainfall, limited surface water resources and an increasing pattern of groundwater extraction in these areas. Consequently, the Ground Water Department with the aid of World Bank has implemented the water structuring programme to mitigate groundwater scarcity and to develop a viable solution for sustainable development in the region. The present study has been undertaken to assess the impact of artificial groundwater recharge structures in the hard-rock area of Rajasthan, India. In this study groundwater level data (pre-monsoon and post-monsoon) of 85 dug-wells are used, spread over an area of 413.59 km2. The weathered and fractured gneissic basement rocks act as major aquifer in the area. Spatial maps for pre- and post-monsoon groundwater levels were prepared using the kriging interpolation technique with best fitted semi-variogram models (Spherical, Exponential and Gaussian). The groundwater recharge is calculated spatially using the water level fluctuation method. The entire study period (2004–2011) is divided into pre- (2004–2008) and post-intervention (2009–2011) periods. Based on the identical nature of total monsoon rainfall, two combinations of average (2007 and 2009) and more than average (2006 and 2010) rainfall years are selected from the pre- and post-intervention periods for further comparisons. All of the water harvesting structures are grouped into the following categories: as anicuts (masonry overflow structure); percolation tanks; subsurface barriers; and renovation of earthen ponds/nadis. A buffer of 100 m around the intervention site is taken for assessing the influence of these structures on groundwater recharge. The relationship between the monsoon rainfall and groundwater recharge is fitted by power and exponential functions for the periods of 2004–2008 and 2008–2011 with R 2 values of 0.95 and 0.98, respectively. The average groundwater recharge is found to be 18% of total monsoon rainfall prior to intervention and it became 28% during the post-intervention period. About 70.9% (293.43 km2) of the area during average rainfall and more than 95% (396.26 km2) of the area during above-average rainfalls show an increase in groundwater recharge after construction of water harvesting structures. The groundwater recharge pattern indicates a positive impact within the vicinity of intervention sites during both average and above-average rainfall. The anicuts are found to be the most effective recharge structures during periods of above-average rainfall, while subsurface barriers are responded well during average rainfall periods. In the hard-rock terrain, water harvesting structures produce significant increases in groundwater recharge. The geo-spatial techniques that are used are effective for evaluating the response of different artificial groundwater recharge techniques.  相似文献   

8.
The Cihanbeyli basin is located in the northern part of Konya in the Central Anatolian region, Turkey and is characterized by semi-arid climatic conditions and scarcity in water resources. The suitability of groundwater quality for drinking and agricultural purposes in the Cihanbeyli basin was assessed by measuring physicochemical parameters, including major cation and anion compositions, pH, total dissolved solid, electrical conductivity, and total hardness. For this purpose, 54 samples were collected from different sources viz. deep wells, shallow wells, and springs. Results from hydrochemical analyses reveal that groundwater is mostly affected by salty and gypsiferous lithologies. Evaporite minerals such as gypsum, anhydrite, and chloride salts make high contributions from the recharge areas (west, northwest, and southwest parts) toward the discharge area (central and eastern parts). High values of total dissolved solids in groundwater are associated with high concentrations of all major ions. A comparison of groundwater quality in relation to drinking water standards showed that most of the water samples are not suitable for drinking. Based on sodium absorption ratio values and percent sodium, salinity appears to be responsible for the poor groundwater quality, rendering most of the samples unsuitable for irrigation usage. It is concluded that evaporation and mineral dissolution are the main processes that determine major ion compositions.  相似文献   

9.
The integrated use of isotopic and hydrochemical tracers is an effective approach for investigating complex hydrological processes of groundwater. The stable isotope composition and hydrochemistry of the groundwater around Qinghai Lake were investigated to study the sources and recharge areas. Most of the groundwater points lie close to the local meteoric water line, indicating that the ground waters were recharged primarily from precipitation in the basin, though it had undergone varying degrees of evaporation. The hydrochemical analysis showed that the groundwater was mainly freshwater and that the hydrochemical type was Ca–Mg–HCO3; the results of the boomerang envelope model and solutes calculated indicated that the groundwater chemistry was mainly controlled by carbonate dissolution around Qinghai Lake. The recharge altitudes of groundwater were relatively low (at 3,400 m.a.s.l) on the northern shore of Qinghai Lake (locations G1 and G5), relatively high (above 3,900 m.a.s.l) on the southern shore (locations G3 and G4), and approximately 3,700 m.a.s.l on the western shore (location G2). Furthermore, groundwater samples from the fault zone (e.g., G3) would be recharged in part from fissure or inter-basin water. High salinity of groundwater on the western shore (location G2) was related with the evaporite dissolution, the groundwater is unsuitable for drinking, and the drinking water should be improved and enhanced in this area. Knowledge of our research can promote effective management of water resources in this cold and semiarid region and add new data to global groundwater database.  相似文献   

10.
Groundwater is a major source of supply for domestic and agricultural purposes, especially in arid and semi-arid regions. In this study, we followed the variations in water levels in the Souf oasis in the Algerian Sahara by measuring depths to groundwater across 65 points during the period from 2010 to 2015. Additionally, electrical conductivity (EC) was measured for assessing variations in groundwater salinity in the same groundwater monitoring network over the same time interval. The results from these investigations indicated that there are significant and continuous declines in the groundwater level across all study areas throughout the period of investigation. This is especially the case in the northern part of the study area where the water table declined by up to 18.2 m in Ghamra in 2015. Additionally, this study has indicated that the rate of decline of groundwater levels has increased from 0.29 m/year as an average in 2011 to 2.37 m/year in 2015, where the situation has become alarming. As a consequence of this, the depth to groundwater now exceeds 2 m over more than 77% of the study area, and only about 17% of the study area now has a water table depth that lies within the optimal depth interval for extractive uses (between 1 and 2 m). This decline in groundwater levels has been accompanied by a significant increase in the electrical conductivity values (salinity) of this water, and there is a strong correlation between these variables (R > 0.99). This alarming situation has been caused by the continuous over-exploitation and unsustainable management of this limited resource, especially by the agricultural sector. For a long time, this critical situation led to the demise of the agricultural world heritage cultivation system (Ghout) due to the increasing salinity of groundwater. Two solutions are proposed to manage the effects of groundwater depletion in the area: firstly, rationalizing groundwater use through effective groundwater allocation management measures, and secondly by implementing the reuse of treated wastewater as an alternative water source for agricultural use. This latter measure could be in two ways: either by direct use in irrigation to relieve pressure on the phreatic aquifer, or by artificial recharge of the phreatic aquifer.  相似文献   

11.
Korba aquifer is one of the most typical examples of overexploited coastal aquifer in the Mediterranean countries. In fact, from 1985, a considerable piezometric level drop, water salinization, and seawater intrusion were registered in the aquifer. In December 2008, Tunisian authorities initiated a general plan to groundwater management in order to augment groundwater resources, restore the piezometric levels, and improve water quality. The plan consists of artificial recharge of groundwater used treated wastewater through three infiltration basins. During the first 4 years (from December 2008 to December 2012), 1.41 Mm3 of treated wastewater was injected to the Korba aquifer. This study presents a hydrogeological assessment of groundwater evolution during the recharge processes. In this study, 32 piezometric and chemical surveys of 70 piezometers and observed wells are used to present hydrogeological investigation and water quality evolution of wastewater reuse through artificial recharge in Korba coastal aquifer. The piezometric evolution maps are used to specify the positive effect in groundwater level that exceeding 1.5 m in some regions. The interpretation of salinity evolution maps are used to indicate the improving of groundwater quality.  相似文献   

12.
An integrated approach was used to evaluate the impact of flash flood recharge on groundwater quality and its suitability for drinking, irrigation, livestock and poultry uses in the Wadi Baysh Basin, Western Saudi Arabia. Analyses of 182 groundwater samples, collected from the study area before and after a flash flood (FF) event, show that the average concentrations of TDS, Mg, Na, Cl, NO3 and EC decreased significantly after the event. The major water types (mixed CaMgCl, NaCl and CaCl) indicate that the infiltration of surface water from FF recharge has a great influence on groundwater chemistry. Drinking water suitability maps, created using WHO standards, indicate that wells located in the upstream region are suitable for drinking despite their high TDS and total hardness (TH) values. Groundwater in the coastal region is unsuitable due to its high salinity, high TH and high concentrations of major ions. The suitability of groundwater for irrigational use was assessed using salinity, sodium adsorption ratio, bicarbonate hazard, residual sodium carbonate, Kelly’s ratio, magnesium hazard, sodium percentage and permeability index values, which indicated that groundwater in the study region is suitable for most soils and crops. After FF, groundwater quality is improved by dilution, especially in the downstream region. USSL classification shows that the majority of the water samples are in the C3S1, C4S2, and C3S2 classes and are therefore suitable for the irrigation of salt-tolerant crops. Irrigational suitability maps suggest that wells in the upstream region are suitable for irrigation, whereas wells located near to the coast are unfit for irrigation. This study implies that construction of check dams in the dry valleys (wadies) may improve the groundwater quality in the area.  相似文献   

13.
The hydrogeochemical characteristics of shallow groundwater in the Grombalia region, northeastern Tunisia, were investigated to evaluate suitability for irrigation and other uses and to determine the main processes that control its chemical composition. A total of 21 groundwater samples were collected from existing wells in January–February 2015 and were analyzed for the major cations and anions concentrations. Conductivity, pH, T°, O2 and salinity were also measured. Interrelationships between chemical parameters were determined by using the scatter matrix method. The suitability of groundwater for irrigation and other uses was assessed by determining the sodium adsorption ratio, soluble-sodium percentage, total dissolved solids, total hardness, Kelly’s index and permeability index values of water samples. The spatial distribution of key parameters was assessed using a GIS-based spatial gridding technique. This analysis indicated that the chemical composition of groundwater in the study area is of Cl–SO4–Na–Ca mixed facies with concentrations of many chemical constituents exceeding known guideline values for irrigation. The salinity of groundwater is controlled by most dominant cation and anion (Na–Cl). A correlation analysis shows that Na+ is the dominant cation and that reverse ion exchange is a dominant process that controls the hydrogeochemical evolution of groundwater in the area. Geospatial mapping of hydrochemical parameters and indices analyzed with the USSL and Wilcox diagrams show distinctive areas of irrigation suitability. In contrast, 76.2% of samples fall in the highly doubtful to unsuitable category and indicate that the central and north-eastern parts of the study area are unsuitable for irrigation due to a high salinity and alkalinity.  相似文献   

14.
Groundwater availability depends on its accessibility, as well as on its quality. Factor analysis (FA) has been used to analyze quality problems and provide strategies for water resources exploitation. The present study demonstrated the use of factor analysis to evaluate temporal variations in groundwater quality and find latent sources of water pollution in coastal areas of Ramanathapuram District, Tamil Nadu, India. The data set included data of eleven water quality parameters viz., pH, electrical conductivity, salinity, total dissolved solids, total alkalinity, calcium hardness, magnesium hardness, total hardness, chloride and fluoride for two different seasons (pre- and post-monsoon) in 2012. FA of the two seasons resulted in two latent factors accounting for 80.38 % of total variance for pre-monsoon (summer) and 73.03 % for post-monsoon (winter) in the water quality data sets. The results obtained from FA prove that the groundwater quality in winter is better than that of summer. Langelier Saturation Index was used to find out scaling and corrosive tendency of the groundwater samples for the study area. Karl Pearson correlation matrix was used to study the correlation between the studied water quality parameters. Hence, the analysis suggests that FA techniques are useful tools for identification of influence of various quality parameters on overall nature of the groundwater.  相似文献   

15.
Shallow renewable groundwater sources have been used to satisfy the domestic needs and the irrigation in many parts of Saudi Arabia. Increased demand for water resulting from accelerated development activities has placed excess stress on the renewable sources especially in coastal aquifers of the western region of Saudi Arabia. It is expected that the current and future development activities will increase the rate of groundwater mining of the coastal aquifer near the major city Jeddah and surrounding communities unless management measures are implemented. The current groundwater development of Dahaban coastal aquifer located at alluvial fan at the confluence of three major Wadis is depleting the shallow renewable groundwater sources and causes deterioration of its quality. Numerical models are known tools to evaluate groundwater management scenarios under a variety of development options under different hydrogeological regimes. In this study, two models are applied—the MODFLOW for evaluating the hydrodynamic behaviors of the aquifer and MT3D salinity distribution to the costal aquifer near Dahaban town. The models’ simulation evaluates two development scenarios—the impact of excessive abstraction and the water salinity variation keeping abstraction at its current or increases in levels with or without groundwater recharge taking place. The simulation evaluated two scenarios covering a 25-year period—keeping the current abstraction at its current and the other scenario is increasing the well abstraction by 50% for dry condition (no recharge) and wet condition (with recharge). The analysis reveals that, under the first scenario, the continuation of the current pumping rates will result in depletion of the aquifer resulting in drying of many wells and quality deterioration at the level of 2,500 ppm. The results are associated with the corresponding salinity distribution in the region. Simulation of salinity in the region is a density-independent problem as salt concentration does not exceed 2,000 ppm, which is little value compared with sea salinity that amounts to 40,000 ppm. It is not recommended to increase the pumping rate than the current values. However, for the purpose of increasing water resources in the region, it is recommended to install new wells in virgin zones west of Dahaban main road. Maps of high/low potential groundwater and maps of salinity zones (more or less than 1,000 ppm) are provided and could be used to identify zones of high groundwater potential for the four studied scenarios. The implemented numerical simulation of Dahaban aquifer was undertaken to assess the water resources potential in order to reduce the depletion of sources in the future.  相似文献   

16.
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17.
Rock water interactions play an important role in the flow of groundwater. Groundwater samples were collected from deep production wells with depths ranging from 120 to 230 m. Complete chemical analysis of 40 groundwater samples was collected from the fractured limestone aquifer including major cations (Na+, K+, Ca2+, Mg2+) and major anions (Cl?, SO4 2?, HCO3 ?, CO3 2?). A geochemical modeling (NETPATH Software) was applied for environmental simulate net geochemical mass-balance reactions between initial and final waters along a hydrologic flow path. This program simulates selected evolutionary waters for every possible combination of the plausible phases that account for the composition of a selected set of chemical constraints in the system. The groundwater of the Eocene aquifer mainly belongs to fairly fresh water with salinity contents ranging from 228 to 3595 ppm. The measured groundwater levels range between 8 and 25 m near the river Nile to the limestone plateau (eastwards). Consequently, groundwater flows from east to westward toward the river Nile. Groundwater aquifer in the study area is mainly composed of fractured limestone; the saturated states of the PCO2, calcite, aragonite, dolomite, siderite, gypsum, anhydrite, hematite, and goethite in addition to H2 gas were estimated. The undersaturated state of carbon dioxide reflects closed conditions and very low probability of recent recharge, and it reveals also the high tendency of water to precipitates carbonate species. Undersaturation by carbonate minerals is only restricted to some pockets distributed on the different places of the aquifer in the study area. The majority of groundwater samples of Eocene aquifer in the study area indicated that groundwater is not suitable for irrigation with treatment and requires good drainage.  相似文献   

18.
A steady state groundwater flow simulation model was developed using available well data and general hydrogeological and geological information, for the Afram Plains area, Ghana. The hydrochemistry of groundwater from wells in the area was then evaluated to determine its suitability for irrigation and domestic uses. The assessment of the irrigation quality of groundwater from this area was based on salinity (EC) and sodium adsorption ratios (SAR), residual sodium carbonate (RSC), and permeability indices (PI). The simulation model reveals that groundwater in the Afram Plains area generally flows from the midsections in the neighborhood of Tease and surrounding areas, where significant recharge takes place, to the outer regions and discharges into the Volta Lake in the southern and eastern sections of the area. Flow magnitude and piezometric maps suggest that there is probably of less potential for groundwater extraction for sustainable irrigation in the central regions of the area, when compared to the other discharge areas. This study reveals that more than 70% of the samples analyzed fall within the C2–S1 category, referring to the medium level salinity and low sodium. Medium salinity waters may be used for irrigation on coarse textured soils with good permeability. About 15% of the data fall within the C3–S2 category, referring to water of high salinity and medium sodicity. High salinity, medium sodicity irrigation water cannot be used on fine-grained soils where drainage is restricted. This is because restricted flow is likely to result in the accumulation of salts in the root zones of crops, leading to salinity and soil clogging crisis. About 3% falls within the C3–S3 (high salinity, high sodicity) category. This category requires special soil management including improved drainage, heavy leaching and the use of chemical amendments on the water. Only one point plots within the extreme salinity–sodicity range. Concentrations of fluoride, arsenic and other natural elements in the area generally fall well within the world health standards for domestic water.  相似文献   

19.
城市化对地下水补给的影响已严重干扰了区域地下水均衡,引发了各种生态环境问题。在呼和浩特市自然地理及水文地质调查的基础上,运用GIS并结合地下水均衡计算的方法,探究城区扩张下以呼和浩特市为中心的研究区潜水补给量的变化。结果表明：从1986—2014年,研究区城镇面积扩大了约358倍。在城市化引起的地下水开采量增大、土地利用方式改变、景观河改造等因素影响下,研究区潜水疏干面积从119 1 km2扩大到10476 km2,年侧向补给量减少9 06115×104 m3;降水入渗补给量减少84385×104 m3;农灌水回渗补给量减少27944×104m3;河道渗漏补给量减少8638×104m3;城市供水管网漏失入渗量增加1 752×104m3。对比1986年和2014年,研究区潜水补给量从13 22501×104 m3减少至4 70703×104 m3,减少了644%,其中减少比例最大的是侧向补给量和降水入渗补给量。城市化使呼和浩特市潜水补给量大大缩减,迫切需要合理规划城市发展和地下水资源开采。  相似文献   

20.
Groundwater is the major source of water and a critical resource for socioeconomic development in semi-arid environments like the Johannesburg area. Environmental isotopes are employed in this study to characterise groundwater recharge and flow mechanisms in the bedrock aquifers of Johannesburg, which is known for polluted surface water. With the exception of boreholes near the Hartbeespoort Dam, groundwater in the study area was derived from meteoric water that has undergone some degree of evaporation before recharge, possibly via diffuse mechanisms. Boreholes that tap groundwater from the Transvaal Supergroup Formation show depletion in δ18O and δ2H values. This is attributed to diffuse recharge through weathering fractures at high elevation that are undergoing deep circulation or recharge from depleted rainfall from the high-latitude moisture sources. The influence of focused recharge from the Hartbeespoort Dam was observed in the boreholes north of the dam, possibly as a result of the north–south trending fault lines and the north-dipping fractures in the bedding planes of quartzites. This is also supported by a reservoir water budget method which indicated a mean annual net flux of 2,084,131 m3 from Hartbeespoort Dam recharging groundwater per annum. Using tritium in the dam and boreholes located at 750 m and 5400 m downstream, average groundwater flow velocity was estimated as 202 m/year. An open system was observed in shale, andesite and granitic-gneiss aquifers indicating soil CO2 as a dominant source of carbon (δ13C) in groundwater. A closed system was also observed in dolomitic aquifers indicating carbonate dissolution as the predominant source of carbon.  相似文献   

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