Transient three-dimensional modeling of riverbank filtration at Grind well field, Germany

Riverbank filtration (RBF) is a proven treatment step in a multi-barrier method of drinking-water supply at many sites. RBF wells induce a large amount of river water to infiltrate the river base and travel towards the wells, giving the opportunity for mixing of infiltrated surface water and groundwater. Assessment of raw water quality plays an important role in planning and operating a RBF well field. In this context, the determination of the catchment area (and land uses within the catchment) and the ratio of bank filtrate (BF) to raw groundwater (GW) are two prior steps. Transient model simulations were performed in order to study the hydraulic conditions at the RBF well field at Grind near Düsseldorf, Germany. The BF/GW ratio was determined to be 75/25. The flood events in winter, in particular, showed the BF/GW ratio to have high variation. Transient path lines in the well field were used for delineation of the catchment area.     

Hydraulic analysis of a radial collector well for riverbank filtration near Nakdong River, South Korea

A radial collector well is used for the extraction of a large amount of groundwater without causing a deep drawdown at the well??s center, and it is appropriate for the supply of municipal water through riverbank filtration (RBF). Flow path changes caused by water extraction through a radial collector well were simulated to estimate the amount of river water induction at a RBF site associated with Nakdong River in South Korea. The structure of the screened horizontal arms of a radial collector well was examined with respect to effective riverbank filtration. The relative ratio of the river water induced to the radial collector well compared to the total groundwater extraction was estimated to be 27?C52%. The amount of induced river water varies with the distance of a horizontal arm from the river, indicating that the location and structure of the collector well is significant for RBF. In all simulation cases, the maximum drawdown of the groundwater level near the collector well was 2.1?m, which is not significant considering the substantial pumping rate at the study site. It was concluded that RBF radial collector wells can be used at the study site for a sustainable water supply.     

Groundwater management by riverbank filtration and an infiltration channel: the case of Obrenovac, Serbia

The Vi? Bare groundwater source is used to supply water to the population and industry of Obrenovac, one of the municipalities of Belgrade (the capital of Serbia). It is a typical riverbank filtration site; exploitation is performed through 30 drilled wells and two radial wells located in the meander of the Sava River. The established hydraulic connection between the river and tapped aquifer is so great that the river regime has a dominant influence on the aquifer. As a consequence of this, water-delivery reduction occurs in the dry months (summer–autumn), when the population needs water the most. Based on the data associated with the river’s gauges, precipitation, quantity of pumped water and groundwater-level fluctuation, a simulation of the groundwater regime for non-steady-state flow conditions has been undertaken through a numerical model. To overcome problems of water shortage during the dry season, the possibility of artificial recharge using an infiltration channel, made up of two connected parts, was analyzed. During the dry months, 80 % of the wells receive water partly from the infiltration channel. In this way, possibilities for extracting additional water are created. The application of this concept is discussed.     

Model reconstruction of nitrate pollution of riverbank filtration using 15N and 18O data,Karany, Czech Republic

Stable isotopes of O (δ¹⁸O) in water and N (δ¹⁵N) in ${\text{NO}}_3^{-}$ have been used as natural indigenous groundwater tracers for sources of water and of ${\text{NO}}_3^{-}$ at two riverbank filtration (RBF) water supply systems. Both RBF systems (Skorkov and Sojovice) have wells in unconsolidated Quaternary sediments close to the Jizera River (Czech Republic) that have been affected by increasing ${\text{NO}}_3^{-}$ concentrations. The area is underlain by Turonian sandstones and marls that form a deeper bedrock aquifer. Sources of ${\text{NO}}_3^{-}$ are local sewerage systems and landfills (point sources) and seasonal application of manure and inorganic fertilizers (diffuse sources).At RBF Skorkov recharge to wells can be modelled using a two-component model with 60% river water contribution and 40% of very shallow groundwater with an average residence time of one month. During periods of abundant precipitation, groundwater originates entirely from the unsaturated zone of the Quaternary aquifer; extensive pumping for over 40 a has created new, bypassing flow paths that preferentially drain the contaminated unsaturated zone. During dry periods, wells are recharged by longer residence time groundwater from the Quaternary aquifer.At RBF Sojovice there is an additional recharge component of groundwater from the Turonian aquifer, which is sandier at this locality; this contains denitrified ${\text{NO}}_3^{-}$ with highly positive δ¹⁵N values.     

Quantification of River Nile/Quaternary aquifer exchanges via riverbank filtration by hydrochemical and biological indicators,Assiut, Egypt

This study approach seeks to characterize the hydraulic interactions between the Nile and the Quaternary aquifer via riverbank filtration (RBF) in Abu Tieg area, Assuit Governorate. The substantial removal/reduction of the most problematic substances during percolation of Nile water into abstraction wells was investigated using physico-chemical and biological indicators. Four sites with 11 municipal wells (20–750 m from the Nile) tapping the alluvial aquifer that is fed by the riverbank infiltrate were monitored. Bank-filtrated water was compared with those of the Nile and groundwater. Results showed that infiltrated Nile water ratio into the wells ranged from 39 to 80% reflecting the effect of distance from the Nile. Removal efficiency of total algal, total and faecal coliforms in bank-filtered water was 99.9%, while turbidity removal ranged from 93 to 98%. Fe, Mn and Zn in the bank-filtered water were relatively higher than those in the Nile, but were still under the allowable standards except those of Mn. LSI and WQI for the bank-filtered water indicated that the water was ranked as non-corrosive and of excellent quality. Comparison of physico-chemical and microbiological characteristics of the bank-filtered water with those of the Nile and groundwater showed the high efficiency of RBF as a treatment technology with minimal cost compared to conventional methods.     

Procedure for the evaluation of lithogeochemical anomalies in large-scale mineral exploration

The objective of geochemical exploration is to detect anomalous concentrations of ore elements and evaluate their ore potential. Methods for the detection and evaluation of geochemical anomalies related to exposed deposits are now rather well developed. Recent successes in the development of geochemical exploration methods for blind and shallowly covered hydrothermal mineralization deserve special consideration. They are based on the characteristic features of composition and on the arrangement of primary geochemical haloes. Primary haloes are normally much larger than orebodies proper and thus extend the effective area for anomaly evaluation several fold as compared with ore occurrences themselves.     

Performance evaluation of environmentally compatible stormwater filtration systems

A horizontal flow multimedia stormwater filter was developed and tested for hydraulic efficiency and pollutant removal efficiency. Suitability of different natural fibres such as jute, sisal, hemp, coir and oil palm was studied as filter media. Furthermore, the efficacy of different fabric filter screens made up of both woven and nonwoven textiles was also assessed. A new terminology, Universal Performance Index, was introduced. Analysis of these indices showed that jute medium, nonwoven sisal screen and media proportion 1:1:1 performed better. All of the filter combinations exhibited 100 % sediment removal at lower sediment concentration in the inflow. Percentage of discarded flow versus reference flow for the stormwater filter combinations showed that the device performed better at lower flow rates. It was also observed that the hydraulic efficiency was directly proportional to the slope and inversely proportional to the cross-sectional area of the filter. Hydraulic efficiency showed a diminishing trend as the sediment level in inflow increases. By using matrix ranking method, the gravel–coir fibre–sand filter in 1:1:1 proportion with woven sisal hemp screens was selected as the best filter combination. The field evaluation of the filter showed 97.24 % efficiency in normalizing pH and 13.27 % efficiency in reducing electrical conductivity. The removal percentages of magnesium and sodium were 32 and 34 %, respectively. But higher removal efficiencies above 70 % were recorded for total solids, nitrates and sulphates.     

The impact of sewage-contaminated river water on groundwater ammonium and arsenic concentrations at a riverbank filtration site in central Delhi,India

The groundwater abstracted at a well field near the Yamuna River in Central Delhi, India, has elevated ammonium (NH₄ ⁺) concentrations up to 35 mg/L and arsenic (As) concentrations up to 0.146 mg/L, constituting a problem with the provision of safe drinking and irrigation water. Infiltrating sewage-contaminated river water is the primary source of the NH₄ ⁺ contamination in the aquifer, leading to reducing conditions which probably trigger the release of geogenic As. These conclusions are based on the evaluation of six 8–27-m deep drillings, and 13 surface-water and 69 groundwater samples collected during seven field campaigns (2012–2013). Results indicate that losing stream conditions prevail and the river water infiltrates into the shallow floodplain aquifer (up to 16 m thickness), which consists of a 1–2-m thick layer of calcareous nodules (locally known as kankar) overlain by medium sand. Because of its higher hydraulic conductivity (3.7 × 10^?3 m/s, as opposed to 3.5 × 10^?4 m/s in the sand), the kankar layer serves as the main pathway for the infiltrating water. However, the NH₄ ⁺ plume front advances more rapidly in the sand layer because of its significantly lower cation exchange capacity. Elevated As concentrations were only observed within the NH₄ ⁺ plume indicating a causal connection with the infiltrating reducing river water.     

Eastern Altantic fracture zones as potential disposal sites for radioactive waste

Disposal of radioactive waste in the sea floor of fracture zones associated with the flanks of the Mid-Atlantic Ridge may be a satisfactory alternative to land disposal. Effective physiographic, sedimentary, chemical, and oceanographic barriers exist in these aseismic deep canyons, especially in the eastern Atlantic. In addition, the major producers of radioactive wastes are likely to be near the Atlantic Ocean. If such a disposal strategy is adopted, intensive study of the sedimentologic and oceanographic properties of oceanic fracture zones will be necessary.     

采空区上方修建大型建筑物地基稳定性评价

地表移动变形随时间的稳定性及剩余变形问题一直是采动覆岩沉陷研究的重要方面。笔者分析了采动地表移动变形的时间过程,探讨了地表沉陷的延续时间及地表剩余沉陷的预计方法,给出了采空区上方修建大型建筑物地基稳定性评价的指标,对采空区上建设建筑物提出了相应的技术措施。     

Delineation of potential sites for groundwater recharge using a GIS-based decision support system

In arid and semi-arid regions without perennial water sources such as rivers or lakes, almost all water supply needs are met by groundwater. Groundwater recharge (GWR) is critical to maintain the abundance of groundwater. This paper presents a methodology based on a decision support system (DSS) that combines remote sensing, field survey and geographic information system techniques to identify suitable GWR areas. The DSS was implemented to obtain suitability maps and to evaluate the existing GWR in the study area. The DSS inputs comprised maps of rainfall surplus, slope, potential runoff coefficient, land cover/use and soil texture. The spatial extents of GWR suitability areas were identified by a hierarchical process analysis that considered five layers. The model generated a GWR map with four categories of suitability: excellent, good, moderate and poor and unsuitable. The spatial distribution of these categories showed that 0.08 and 32.3 % of the study area was classified as excellent and good for GWR, respectively, while 63.2 and 4.42 % of the area was classified as moderate and poor and unsuitable, respectively. Most of the areas with excellent to good suitability have slopes of between 4 and 8 % and are intensively cultivated areas. The major soil type in the excellent to good areas is loam, followed by clay loam, and the rainfall in these areas ranges from 150 to 260 mm. Another suitability model, in which all criteria were assigned equal influence, generated a suitability map in which 0.1 % of the study area was rated as excellent, 10.9 % as good, 82 % as moderate and 7 % as poor and unsuitable. The locations of existing GWR dams were compared with the locations indicated on the generated suitability map using the proximity analysis tool in ArcGIS 10.1. Most (77 %) of the existing GWR structures that were categorised as successful were within the excellent and good areas, followed by moderately suitable (23 %).     

Methodology for groundwater recharge assessment in carbonate aquifers: application to pilot sites in southern Spain

Aquifer recharge can be determined by conventional methods such as hydrodynamic or hydrologic balance calculations, or numerical, hydrochemical or isotopic models. Such methods are usually developed with respect to detrital aquifers and are then used on carbonate aquifers without taking into consideration their hydrogeological particularities. Moreover, such methods are not always easy to apply, sometimes requiring data that are not available. Neither do they enable determination of the spatial distribution of the recharge. For eight regions in southern Spain, the APLIS method has been used to estimate the mean annual recharge in carbonate aquifers, expressed as a percentage of precipitation, based on the variables altitude, slope, lithology, infiltration landform, and soil type. The aquifers are representative of a broad range of climatic and geologic conditions. Maps of the above variables have been drawn for each aquifer, using a geographic information system; thus they can be superimposed to obtain the mean value and spatial distribution of the recharge. The recharge values for the eight aquifers are similar to those previously calculated by conventional methods and confirmed by discharge values, which corroborates the validity of the method.     

Assessment of the potential for bank filtration in a water-stressed megacity (Delhi,India)

In the densely populated semi-arid territory around Delhi, the water demand is rising continuously, while the surface- and groundwater resources are threatened by contamination and overexploitation. This is a typical scenario in many newly industrialising and developing countries, where new approaches for a responsible resources management have to be found. Bank filtration holds a great potential, thus being a low tech method and benefiting from the storage and contaminant attenuation capacity of the natural soil/rock. For this study, three field sites have been constructed to investigate bank filtration in different environments in and around the megacity with a main focus on inorganic contaminants. Hydraulic heads, temperature gradients and hydrochemistry of surface water and groundwater were analysed in three different seasons. Depending on site-specific conditions, distinct hydrogeological conditions were observed and both positive and negative effects on water quality were identified. Most concerning issues are the impact of anthropogenic ammonia, the mixing with ambient saline groundwater and the mobilisation of arsenic during the reductive dissolution of manganese- and iron-(hydr)oxides. Positive aspects are the dilution of contaminants during the mixing of waters from different sources, the sorption of arsenic, denitrification, and the precipitation of fluoride under favourable conditions.     

考虑卸荷作用的黄土湿陷性评价方法研究

卸荷作用会导致湿陷性黄土部分湿陷量未发生,但目前黄土湿陷性评价方法中未考虑卸荷因素的影响。推导并建立了卸荷条件下黄土湿陷系数的表达式,并通过卸荷湿陷试验确定了表达式中的参数取值。首先定义湿陷完成比、卸荷应力比分别用来表征卸荷作用发生前黄土湿陷变形的完成程度及卸荷作用发生时卸荷量的大小。运用湿陷完成比及卸荷应力比推导出卸荷湿陷系数的计算公式。该公式揭示出卸荷湿陷系数是对湿陷系数一定程度的折减,而该折减与湿陷完成比及卸荷应力比有关。随后进行黄土在不同湿陷完成比和卸荷应力比下的卸荷湿陷试验,得到上述条件下黄土卸荷湿陷量的取值。对试验结果进行分析得到卸荷湿陷系数的具体表达式。该公式可用于计算在不同初始压力下,任意湿陷完成比及卸荷应力比下的卸荷湿陷系数。通过对比卸荷湿陷系数的试验值与计算值验证了所推公式的合理性及准确性。得到了考虑卸荷作用的黄土湿陷性影响系数的确定方法,进一步总结了卸荷作用对黄土湿陷性的影响规律。     

Quantification of riverbank erosion and application in risk analysis

The estimation of river bank erosion requires the knowledge of both local hydrodynamic and erodibility characteristics. Models exist in literature that allow the estimation of the river bank shear stress, the fundamental parameter in evaluating the retreat given the discharge flow and the geometry of the river channel. In this study, two hydrodynamic models (1-D and 2-D) were combined with three shear stress models in order to obtain an estimation of the retreat on a study case on the river Cecina in Tuscany, Central Italy. A calibration of the models was performed based on observations from aerial photos of the region over a period of 10 years (1994–2004), and the results of the different combinations of the models are discussed and compared. A framework was developed for the risk analysis of land loss due to bank erosion based on the analyses of discharge flow time series and an excess shear stress erosion model. An application to the study case is provided by using the results of fluvial erosion modelling.     

Conjunction effect of stream water level and groundwater flow for riverbank stability analysis

Variations in pore-water pressure determined by the groundwater table within a riverbank have been investigated and recognized as an essential factor in determining riverbank stability with respect to mass failure. However, the effect of pore-water pressure is taken into account for most of the existing riverbank stability models under some simplified assumptions, and the limitations of predicting ability may arise. To avoid the unrealistic estimation of pore-water pressure distribution, the new approach proposed here is to couple riverbank stability with groundwater flow modeling, and apply this to tackle the conjunction effect between river stage and groundwater table. Moreover, riverbank material characteristics and the influence of infiltration can be taken into consideration via groundwater flow modeling. Two hypothetical examples, stage rising and stage falling, are used to investigate the capabilities of the present study and two representative methods. The simulated results show that riverbank failure is triggered particularly during the falling stage, which has been pointed out by other researchers as well. Furthermore, the riverbank material characteristics predominantly control the occurrence of failure and should be considered regarding assessment of riverbank stability. Additionally, the effects of parameters indicate that riverbanks with soil properties of low permeability or high specific yield with great infiltration intensity during the falling stage have a tendency to riverbank failure.     

渐进坍塌型崩岸的力学机制及模拟

针对渐进坍塌型崩岸,从土力学和河流动力学两方面理论出发,建立了岸坡稳定的力学模式,结合室内概化模拟试验和数值计算,分析了岸坡稳定或破坏的力学机制,揭示了缓坡出现崩岸的原因。结果表明,岸坡坡脚未受水流冲失时,若坡内渗流出逸坡降小于渗透破坏的临界坡降,岸坡处于稳定状态,当坡脚被水流冲失后,渗流渗径缩短,水土结合处坡面出逸坡降增大,大于临界坡降时则出现渗透破坏,引起局部小幅度土体崩塌,其后部土体失去支撑而陆续产生失稳破坏,随着时间的延长,土体崩塌现象逐步向后发展,最终导致岸坡整体崩塌破坏。     

Liquefaction potential evaluation for subsurface soil layers of Delhi region

The study area Delhi is second most populous city and third largest urban area in the world. Though the area lies in seismic high damage risk zone, number of high rise building and construction of mega structure at several sites of the city increase rapidly. In this study field Standard Penetration Test (SPT) values of soil collected from 750 boreholes data were analyzed to identify liquefiable sub-surface soil layers. Finally, liquefaction susceptible sub-surface maps of the region at various depth (20 m, 15 m, 12 m, 9 m, 6 m and 3 m) from ground level is prepared. The outcome of this study will be useful input for preliminary foundation and designing of earthquake resistant high rise building and seismic microzonation studies of Delhi.     

Lake bank filtration at Nainital,India: water-quality evaluation

There are different water-supply schemes in Uttarakhand, India to tap the water from streams, rivers and lakes. At Nainital, seven tube-wells (depths 22.6–36.7 m), located at a distance of <100 m from the lake, are being used to abstract (1) lake water after passage through the soil and (2) subsurface water/groundwater flowing towards the lake. Water samples from the lake and tube-wells were analyzed in monsoon and non-monsoon periods from 1997 to 2006. Total dissolved solids, EC, alkalinity and hardness were found to be marginally greater in tube-well waters. The difference in hydrochemistry of tube-well water was mainly due to variation in flow regimes during monsoon and non-monsoon periods. Results clearly indicate that lake water as such is not potable as it contains unacceptable levels of organic matter in terms of COD (~44 mg/L), coliforms (~15.6 × 10⁴ MPN/100 mL) and nutrients. Coliform bacteria and COD have not been detected in any of the tube-well water samples over the years. Lake water, treated by sand filters did not conform to drinking water standards. These investigations have led to the closure of the treatment facility and installation of two tube-wells in addition to the existing five tube-wells.

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Résumé  Il existe divers projets d’alimentation en eau dans l’état d’Uttarakhand, Inde, afin de capter l’eau de ruisseaux, de rivières et de lacs. A Nainital, sept puits tubés (profondeur de 22.6–36.7 m), situés à une distance < à 100 m du lac, sont utilisés pour prélever (1) de l’eau du lac après transit à travers le sol et (2) de l’eau de sub-surface/eau souterraine s’écoulant vers le lac. Des échantillons d’eau du lac et des puits tubés ont été analysés en périodes de mousson et de celles sans mousson 1997 à 2006. Résidu sec, C.E., alcalinité et dureté ont été trouvés marginalement supérieurs dans l’eau des puits tubés. La différence d’hydrochimie de l’eau des puits tubés était surtout due à la variation des régimes d’écoulement pendant les périodes de mousson et de celles sans mousson. Les résultats indiquent clairement que l’eau du lac en tant que telle n’est pas potable car elle contient des teneurs inacceptables de matière organique en termes de COD (~44 mg/L), de coliformes (~15.6 × 10⁴ MPN/100 mL) et d’éléments nutritifs. Des bactéries coliformes et du COD n’ont été détectés dans aucun des échantillons d’eau de puits tubés au fil des années. L’eau du lac traitée par des filtres à sable ne se conformait pas aux normes de l’eau potable. Ces recherches ont conduit à la fermeture de l’installation de traitement et à l’implantation de deux puits tubés en plus des cinq puits existants.

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Resumen  En el estado de Uttarakhand, India, existen diferentes esquemas de abastecimiento de agua que explotan agua de arroyos, ríos y lagos. En Nainital, siete pozos (profundidades entre 22.6–36.7 m), ubicados a una distancia de <100 m del lago, se usan para extraer (1) agua del lago luego de su pasaje a través del suelo y (2) agua superficial y subterránea que fluye hacia el lago. En períodos de monzón y de no monzón de 1997 a 2006 se han analizado muestras de agua del lago y de las captaciones. Se halló que el agua de los pozos es ligeramente mayor en términos del total de sólidos disueltos, la conductividad eléctrica, la alcalinidad y la dureza. La diferencia en la hidroquímica del agua de las perforaciones se debe principalmente a la variación de los regímenes de flujo durante los períodos de monzón y de no monzón. Los resultados claramente indican que el agua del lago no es potable por su contenido inaceptable de materia orgánica medida como demanda de carbono orgánico/oxígeno –DCO- (~44 mg/L), coliformes (~15.6 × 10⁴ NMP/100 mL) y nutrientes. En el período, no se han detectado bacterias coliformes ni DCO en las muestras de agua de las captaciones. El agua del lago, tratada con filtros de arena, no conformó los estándares de agua para bebida. Estas investigaciones han demostrado la necesidad de clausurar las instalaciones de tratamiento y la adición de dos captaciones a las cinco ya existentes.

     

Identifying potential sites for artificial groundwater recharge in sub-watershed of River Kanhan,India

Groundwater is an important decentralized source of drinking water. Being underground, it is relatively less susceptible to contamination. In addition to domestic needs, it is extensively used for irrigation and industrial purposes. It is therefore necessary to implement groundwater recharge systems by capturing the rainwater runoff. In the present study, GIS-based hydrological assessment of watershed has been used to identify the potential sites for locating the groundwater recharge structures. Based on land use, soil and topography, rainfall runoff modelling was carried out in GIS for a sub-watershed of River Kanhan, in Nagpur District, Maharashtra State, India. Five potential sites with maximum flow accumulation were delineated using the rational method for peak runoff estimation. As the groundwater recharge potential also depends on the geological and geomorphological characteristics of land, analytic hierarchy process (AHP) with expert’s judgement was used for ranking the sites. The criteria considered in AHP were geological features, i.e. lineament density, depth to bedrock and soil cover; geomorphological features, i.e. drainage density, slope, landforms and land use/land cover; and water table level fluctuation. The site P5 with maximum flow accumulation and sandstone rock formation was ranked first. The site P1, where catchment has well-developed drainage and geological formation shows rock with secondary porosity, was ranked second.