Low Hydraulic Gradients Research Articles

Preclearing hydrology of the Western Australia wheatbelt: Target for the future?

The wheatbelt of Western Australia largely corresponds to a zone of ancient drainage, characterised by highly variable rainfall, long dry summers, low hydraulic gradients, intermittent surface flows and high regolith salt loads. The accumulation and distribution of salt, the rudimentary aquifers with deep watertables, the intermittent flooding and subsequent transpiration of water from the valley sediments, and the low yields of water reaching the ocean were a product of the underlying physical environment and vegetation types capable of using deeply infiltrated water through the dry season. The hydrological and hydrogeochemical changes induced by widespread clearing of this vegetation for dryland agriculture are profound and enduring. Run-off onto and through the valley floors has increased by a factor of five; combined with local rainfall on these valley floors, the resulting increase in groundwater recharge is filling the deep sedimentary materials and bringing highly saline water to the surface. Diffuse recharge has also increased on the slopes and ridges, with saline watertables rising in these lateritic formations as well, providing additional hydraulic heads forcing groundwater towards the valleys. The resulting increase in the groundwater discharge areas is projected to greatly increase flooding risk downstream into the future. A variety of natural, built and agricultural assets are either already impacted or at risk to these phenomena. It is hypothesised that restoring the original hydraulic and hydrological functions of the system will lead to its recovery. This raises several issues: can we design remedies in terms of restoring the original rates of flux (recharge, runoff, etc) or in terms of the original balances (recharge less than aquifer discharge, input of salt into the root zone equal to output)? Secondly, to what degree can revegetation or engineering now restore these original conditions? Finally, we examine the potential for the landscape to recover to its original hydrological and hydrogeochemical state once salinised. Given the advanced state of saline watertable development, with its implications for successful revegetation and restoration of valley transpiration, the changes in soil structure and chemistry, and the immediate implications to valued assets, we posit that an aim of restoring the landscape solely with revegetation, either in terms of rates or balances, is not feasible or even possible. To a degree, one can only restore certain aspects of the original balance via revegetation combined with discharge enhancement and flood mitigation.

Hydrogeology and Water Resource Potential of Neogene Sediments in the Tualatin Basin and Comparison with the Neighboring Portland Basin, Northwest Oregon

Research Article| April 01, 2003 Hydrogeology and Water Resource Potential of Neogene Sediments in the Tualatin Basin and Comparison with the Neighboring Portland Basin, Northwest Oregon DOYLE C. WILSON DOYLE C. WILSON 1Geology Department, Portland State University, Portland, OR 97207-0751 1Current address: Mohave Community College, 1977 W. Acoma Blvd., Lake Havasu City, AZ 86403 Search for other works by this author on: GSW Google Scholar Author and Article Information DOYLE C. WILSON 1Current address: Mohave Community College, 1977 W. Acoma Blvd., Lake Havasu City, AZ 86403 1Geology Department, Portland State University, Portland, OR 97207-0751 Publisher: Association of Environmental & Engineering Geologists First Online: 02 Mar 2017 Online ISSN: 1558-9161 Print ISSN: 1078-7275 Copyright © 2003 Geological Society of America Environmental & Engineering Geoscience (2003) 9 (4): 327–338. https://doi.org/10.2113/9.4.327 Article history First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation DOYLE C. WILSON; Hydrogeology and Water Resource Potential of Neogene Sediments in the Tualatin Basin and Comparison with the Neighboring Portland Basin, Northwest Oregon. Environmental & Engineering Geoscience 2003;; 9 (4): 327–338. doi: https://doi.org/10.2113/9.4.327 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyEnvironmental & Engineering Geoscience Search Advanced Search Abstract Hydrogeologic properties of the Neogene Hillsboro Formation and Willamette Silt in the Tualatin basin are evaluated to provide a foundation for future groundwater use in the Portland, Oregon, metropolitan area, and are then compared to hydrogeological conditions in the neighboring Portland basin. Catastrophic flood deposits of the Willamette Silt in the Tualatin Valley have low hydraulic conductivities and well yields below 7 gpm (26.5 lpm). Fluvial sand aquifers within the Hillsboro Formation compose only 20 percent of the 1,400-ft (450-m) thick unit and most contain a significant quantity of silt and clay, with hydraulic conductivities on the order of 2–30 ft/day (0.6–6 m/day). Water quality is good, yet low well yields (6–100 gpm; 23–380 lpm), a low hydraulic gradient within the basin, and geochemical data point to residence times of tens to hundreds of years and slow recharge to the system. A numerical simulation verifies slow groundwater velocities and the presence of local and regional flow regimes. Aquifers of the Hillsboro Formation are limited to domestic use, and model simulations of hypothetical well fields show that these aquifers would not support large-scale withdrawals. High-yield aquifers of the coarse-grained Troutdale Formation in the Portland basin contrast sharply with those of the Hillsboro Formation and Willamette Silt in that they can be separated into multiple hydrogeologic units, have high hydraulic conductivities, and can be used for municipal purposes. Such drastic differences in hydrogeologic characteristics within a metropolitan area require different strategies involving groundwater use or remediation. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Wetland restoration and nitrate reduction: the example of the peri-urban wetland of Vitoria-Gasteiz (Basque Country, North Spain)

Abstract. Changes in land use and agricultural intensification caused wetlands on the quaternary aquifer of Vitoria-Gasteiz (Basque Country) to disappear some years ago and nitrate concentration in groundwaters increased very quickly. The Basque Government recently declared the East Sector of this aquifer a Vulnerable Zone according to the 91/676/CEE European Directive. Recently, the wetlands have been restored through the closure of the main drainage ditches, the consequent elevation of the water table and the abondonment of agricultural practices near the wetlands. This is the case of the Zurbano wetland. Restoration has allowed the recovery of its biogeochemical function, which has reduced nitrate concentrations in waters. Nitrate concentrations which exceed 50 mg l–1 in groundwaters entering into the wetland are less than 10 mg l–1 at the outlet. Conditions in the wetland are conducive to the loss of nitrates: organic matter rich wetted soils, clay presence allowing a local semiconfined flow and very low hydraulic gradient. Water quality monitoring at several points around the wetland showed the processes involved in nitrate loss, although some aspects still remain unresolved. However, during storm events, the wetland effectively reduces the nitrate concentration entering the Alegria River, the most important river on the quaternary aquifer. Keywords: restored wetland functionality, nitrate losses, Basque Country

新第三紀堆積岩に対する低動水勾配での透水係数に関する一考察

In this study, we have studied on the non linearity of hydraulic conductivity for Neogene sedimentary rocks under low hydraulic gradient. The behavior was tested not only by laboratory test but also in situ test taking account for accuracy under low hydralic condition. It's found that the non-Darcy is dominant in the hydraulic gradient less than 5 at the laboratory test. Also at the in situ test the non-Darcy behavior was found. We proposed the model of the flow under low hydraulic gradient using capillary model taking account of Bingham flow. This model is based on the assumption that the molecule of water is absorbed by the surface of micro condition. It was found that the non-Darcy behavior was well simulated when all capillary have a narrow (10-8m) space.

Lower Miocene gypsum palaeokarst in the Madrid Basin (central Spain): dissolution diagenesis, morphological relics and karst end‐products

Abstract The Miocene sedimentary record of the Madrid Basin displays several examples of palaeokarstic surfaces sculpted within evaporite formations. One of these palaeokarstic surfaces represents the boundary between two main lithostratigraphic units, the Miocene Lower and Intermediate units of the Madrid Basin. The palaeokarst formed in lacustrine gypsum deposits of Aragonian age and corresponds to a surface palaeokarst (epikarst), further buried by terrigenous deposits of the overlying unit. Karst features are recognized up to 5·5 m beneath the gypsum surface. Exokarst and endokarst zones are distinguished by the spatial distribution of solution features, i.e. karren, dolines, pits, conduits and caves, and collapse breccias, sedimentary fills and alteration of the original gypsum across the karst profiles. The development of the gypsum palaeokarst began after drying out of a saline lake basin, as supported by recognition of root tubes, later converted to cylindrical and funnel‐shaped pits, at the top of the karstic profiles. The existence of a shallow water table along with low hydraulic gradients was the main factor controlling the karst evolution, and explains the limited depth reached by both exokarst and endokarst features. Synsedimentary fill of the karst system by roughly laminated to massive clay mudstone with subordinate carbonate and clastic gypsum reflects a punctuated sedimentation regime probably related to episodic heavy rainfalls typical of arid to semi‐arid climates. Duration of karstification is of the order of several thousands of years, which is consistent with previous statements that gypsum karstification can develop rapidly over geologically short time periods.

Hydrogeochemical and isotopic evidence of groundwater salinization in a coastal aquifer: a case study in Jeju volcanic island, Korea

In order to identify the origin of saline groundwater in the eastern part of Jeju volcanic island, Korea, a hydrogeochemical and isotopic study has been carried out for 18 observation wells located in east and southeast coastal regions. The total dissolved solid contents of groundwaters are highly variable (77–21,782 mg/l). Oxygen, hydrogen, sulfur, and strontium isotopic data clearly show that the saline water results from mixing of groundwater with seawater. Strontium isotopic compositions and Br/Cl and I/Cl ratios strongly suggest that the source of salinity is modern seawater intrusion. Hydrogeochemical characteristics based on bivariate diagrams of major and minor ions show that changes in the chemical composition of groundwater are mainly controlled by the salinization process followed by cation-exchange reactions. The highly permeable aquifers at the east coastal region are characterized by low hydraulic gradient and discharge rate and high hydraulic conductivity as compared with other regions. These properties enhance the salinization of groundwater observed in the study area. Based on the Cl, Br, and δ 18O data, seawater was determined to have intruded inland some 2.5 km from the coastline. Considering the poor correlation of sampling depth and Cl concentrations observed, the position of seawater-freshwater interface is not uniformly distributed in the study area, due to heterogeneities of the basaltic aquifers.

The geochemical dynamics of oxidising mine tailings at Laver, northern Sweden

The former Cu mine Laver in northern Sweden was selected for a study of the geochemical processes in mine tailings. The Laver mine was in operation between 1936 and 1946, producing approximately 1.2 Mt of tailings. This study of the tailings at Laver includes time series of groundwater and surface water chemistry, chemical and mineralogical studies of the tailings sand and geophysical investigations. The results allow a good understanding of the dynamic geochemical processes taking place within the tailings. Oxidation of sulphide minerals in the tailings has led to the development of a distinct chemical zonation. Metals released from oxidation and weathering of sulphide minerals are retained within the tailings impoundment. This retention mechanism is today very efficient and only 5–10% of the released masses of metals reaches the surface water system. Zn, Cd, Co and Ni are probably secondarily bound to the tailings with adsorption in a large mass of non-weathered tailings. Cu, on the other hand, is enriched in a distinct zone just below the front of oxidation. This distinct Cu-enrichment suggests precipitation of a secondary mineral phase, probably covellite. The downward movement of the front of oxidation advances at a rate of 2.8 cm/a, and displaces the secondary zone with Cu-enrichment at the same rate. When the oxidation front reaches the groundwater table, the oxidation of sulphide minerals will almost completely stop. The Cu-enrichment will, in this case, probably partly go into solution and be transported away by the groundwater movement. The seepage of acid water from the oxidation front will consume pH-buffering capacity of the tailings and the groundwater will eventually become more acidic. Such a low pH-environment in the tailings will force the adsorbed Zn, Cd, Co and Ni to go into solution and be transported away. A front of water with low pH and high concentrations of metals has been detected and is moving towards the outlets of the tailing impoundment. Due to the low hydraulic gradient and conductivity, the front of acid metal-rich water will be delayed in time by 10–30 years before it reaches the recipient.

Evolution of groundwater systems at the European coastline

Abstract An overview is given of the status and origin of fresh and saline groundwaters in the sedimentary aquifers at or near the present European coastline. Results are presented as six regional maps summarizing, as far as possible, the conditions likely to have existed at the end of the Pleistocene, after the impact of glaciation, when groundwaters might be expected to have reached their maximum offshore evolution prior to the encroachment of sea water during the Holocene marine transgression. In the eastern Baltic, the groundwater evolution was different to other European regions in that freshwater heads were higher than the present day, promoting recharge during much of the Late Pleistocene. Near the North Sea coasts, there is generally evidence of freshwater movement to depths of 100–150 m but the absence of deeper freshwater (palaeowater) storage may relate to the low hydraulic gradients in the North Sea Basin. In the southeastern part of the North Sea brackish palaeowater is found between Tertiary marine sediments c . 300 m below the island of Rømø, 10 km off the Danish west coast. Freshwater of Pleistocene and Holocene ages is found in aquifers at the English Channel coast in several areas, to depths in excess of −300 m; offshore flow in the Late Pleistocene took place towards the central palaeovalley and some of this groundwater may be preserved off the present coastline. In the two Atlantic coastal areas of France and Portugal-Spain a contrast exists due to the proximity of the continental margin and different hydraulic gradients. In Portugal, freshwaters are found at the coastline, and probably offshore, that contain evidence of recharge during the lowered sea levels. In most of the southwestern Atlantic coast of Spain, fresh recent groundwater discharges along and beyond the coastline, while in the old estuary of the Guadalquivir River, saline Holocene water still encroaches the sediments. On the Mediterranean coast of France and Spain some salinity encroachment took place during sea-level rise. In most of the Spanish aquifers fresh recent groundwater has substituted for palaeowater, except for the low-lying areas (Ebro Delta, Inca-Sa Pobla Plain) where brackish Holocene water is still present.

Évolution spatio-temporelle des teneurs isotopiques ( δ2H– δ18O) des eaux de la cuvette lacustre du fleuve Niger (Mali)

The Niger inland delta is a flooded zone of major economic importance. Evaporation is higher than precipitation and the flooded surfaces depend on Niger and Bani Rivers’ inflow. Rainwater data pointed to an isotopic variability due to various climatic conditions and rainfall origins. In the upper basin, values are influenced by groundwater, sub-surface storage and direct runoff in turn affected by high evaporation rates during the low water stage. Because of low hydraulic gradient, the isotopic variations are dominated by evaporation. Nevertheless, the spatial evolution is not as important as expected. A vapour re-equilibration with the river surface can reduce isotope fractionation.

A method to determine hydraulic conductivity of clayey material under low hydraulic gradients

Based on the column tracer test, we develop a new method to determine the hydraulic conductivity of saturated bentonite under low hydraulic gradient or low flow rate. Derived from Darcy's law and one‐dimensional solute transport equation, this method further evaluates hydraulic conductivity through measuring solute concentrations, rather than through flow rates. In order to examine the proposed method, two types of experimental data drawn from a review of the literature are adopted, and four sorts of accuracy‐test data are employed. The results of accuracy‐tests indicate a good consistency with an error margin of 5.5%. Our experimental results also show that hydraulic conductivities from the tracer method are more precise than those from the flow rate method.

A Tracer Method to Determine Hydraulic Conductivity and Effective Porosity of Saturated Clays Under Low Gradients

AbstractBased on the column tracer test, we developed a research method to determine the hydraulic conductivity and effective porosity of saturated clays under low hydraulic gradients or small flow rates. Derived from Darcy's law and the solute transport equation, this method evaluates the hydraulic conductivity through measuring solute concentrations rather than by measuring flow rates. And the effective porosity is determined by applying an analytical solution of the one‐dimensional uniform flow equation.Two types of experimental data drawn from a review of the literature and four sorts of accuracy test data carried out in the laboratory are used to examine the proposed method. The reproducibilities of accuracy tests for hydraulic conductivity determination indicate a consistency within a 5.5% error margin. The experimental results further indicate that hydraulic conductivities determined using the tracer method are more precise than those from the conventional flowmeter method. In addition, with the assistance of the proposed tracer method, we argue that the effective porosities may be overestimated as shown in the drawn example cases due to mistaking total pore volumes as the effective pores. The results of the accuracy tests further indicate that the effective porosities of saturated clay specimens are significantly smaller than the total porosities, at least when the samples are allowed to swell freely.

Hydraulic conductivity of clays in confined tests under low hydraulic gradients

Clay barriers normally function at hydraulic gradients much lower than are commonly used in laboratory tests for hydraulic conductivity. This paper describes low-gradient tests on compacted illite, Na-bentonite, and sand-bentonite specimens at a range of dry densities. The tests examined the effects of deionized or saline pore fluid, the initial degree of saturation at the time of compaction, and back-pressuring to achieve saturation during permeation. No "critical" or "threshold" gradients were observed. In low-density materials, "transitional" gradients defined two separate regions of Darcian flow. Low flow rates and low hydraulic conductivities were associated with hydraulic gradients below the transitional gradient. Higher conductivities were associated with gradients above the transitional gradient. Hydraulic conductivities decreased with increasing initial density. They appeared independent of initial degree of saturation or back-pressuring. Tests on Na-rich bentonite showed that deionized and saline permeants produced similar hydraulic conductivities. Measured hydraulic conductivities were in reasonable agreement with values computed using the Poiseuille and Kozeny-Carman equations. Key words: hydraulic conductivity, gradient, Darcian, illite, bentonite.

Hydraulic conductivity of clays in confined tests under low hydraulic gradients

Hydraulic conductivity of clays in confined tests under low hydraulic gradients

TOWARDS ACHIEVING FUNCTIONAL ECOSYSTEM MIMICRY WITH RESPECT TO WATER CYCLING IN SOUTHERN AUSTRALIAN AGRICULTURE

The southern Australian landscape is characterised by large climatic variability and an old, weathered surface with generally low hydraulic gradients. Many of these landscapes are prone to salinisation. The original ecosystems have strategies to cope with this environment in ways which minimise runoff and groundwater recharge. Replacement of these ecosystems with conventional agriculture has resulted in large-scale disruption of the natural water cycle with severe environmental, economic and social consequences. Sustainable agricultural systems aimed at mimicking natural hydrology must either minimise groundwater recharge over most of this landscape or intercept groundwater discharge in lower parts of the landscape prior to salinisation to restore the original hydrological balance. Empirical and theoretical analyses suggest that however vegetation is managed in the landscape, effective water balance control will be achieved only at a leaf area index approaching that of the natural state, indicating revegetation of most or all parts of the catchment with either trees or plants with similar ecohydrological characteristics as trees. There are at present few economically- attractive agricultural systems able to achieve hydrologic mimicry likely to be adopted at the necessary scale.

Removal of pooled dense, nonaqueous phase liquid from saturated porous media using upward gradient alcohol floods

Laboratory experiments employing 90% by volume alcohol solutions are used to compare the abilities of ethanol and 1‐propanol to remove pooled tetrachloroethene (PCE) from saturated porous media using low upward hydraulic gradients. Equilibrium ternary phase diagrams measured for the systems water/PCE/ethanol and water/PCE/1‐propanol indicate that for alcohol concentrations below the miscibility envelope, 1‐propanol will partition predominantly into the dense, nonaqueous phase liquid (DNAPL) phase while ethanol remains in the aqueous phase. Interfacial tension and phase density measurements show that while both systems demonstrate a reduction in interfacial tension with increasing alcohol content, the density difference between the aqueous and DNAPL phases is only reduced for the 1‐propanol system. Two‐dimensional experiments in saturated porous media using alcohol floods ranging in size from 0.125 pore volumes (PV) to 1.0 PV recovered between 5.7% and 98.7% of the PCE mass. The removal mechanisms for the ethanol floods included enhanced dissolution followed by miscible displacement, while the 1‐propanol floods removed PCE by DNAPL swelling and interfacial tension reduction leading to immiscible displacement followed by miscible displacement. Recovery results and effluent composition histories indicate that hydrodynamic instabilities and dispersion cause significant alcohol slug deterioration and confirm the necessity of using an appropriate size alcohol slug of sufficient concentration for efficient PCE mass recovery.

Modeling Impact of Small Kansas Landfills on Underlying Aquifers

Small landfills are exempt from compliance with Resource Conservation and Recovery Act Subtitle D standards for liner and leachate collection. We investigate the ramifications of this exemption under western Kansas semi-arid environments and explore the conditions under which naturally occurring geologic settings provide sufficient protection against ground-water contamination. The methodology we employed was to run water budget simulations using the Hydrologic Evaluation of Landfill Performance (HELP) model, and fate and transport simulations using the Multimedia Exposure Assessment Model (MULTIMED) for several western Kansas small landfill scenarios in combination with extensive sensitivity analyses. We demonstrate that requiring landfill cover, leachate collection system (LCS), and compacted soil liner will reduce leachate production by 56%, whereas requiring only a cover without LCS and liner will reduce leachate by half as much. The most vulnerable small landfills are shown to be the ones with no vegetative cover underlain by both a relatively thin vadose zone and aquifer, and which overlie an aquifer characterized by cool temperatures and low hydraulic gradients. The aquifer-related physical and chemical parameters proved to be more important than vadose zone and biodegradation parameters in controlling leachate concentrations at the point of compliance.

Rigorous Theoretical Analysis of a Flow Pump Permeability Test

Abstract With the growing importance of environmental issues in our society, extremely low-permeability geotechnical materials are being studied increasingly for their long-term stability and effectiveness in retarding the transport of hazardous wastes. Relatively rapid measurements of the permeability and specific storage of the materials, using relatively low hydraulic gradients, can be obtained with a constant flow pump and the corresponding theoretical analysis proposed by Morin and Olsen (1987). However, the accuracy of this method is limited because their theoretical analysis does not take into account the storage capacity of the experimental system. This paper presents a more general theoretical analysis and shows how it can be used to determine not only the permeability and specific storage of a test specimen, but also the storage capacity of the experimental system. Experimental data are presented that illustrate the accuracy and efficiency of the general theoretical analysis.

Measurement of hydraulic conductivity in oil sand tailings slurries

Fine tails, the resulting fine waste from oil sand processing, undergoes large-strain consolidation in tailings ponds. Its consolidation behaviour must be analyzed using a large-strain consolidation theory, which requires the determination of the relationship between the void ratio and hydraulic conductivity. Conventional measurement techniques are not suitable for fine tails, and a special slurry consolidometer, with a clamping device to prevent seepage-induced consolidation, was designed to determine the hydraulic conductivity of the fine tails and nonsegregating fine tails – sand slurries. The hydraulic conductivity of slurries is not constant but decreases with time to a steady-state value. Hydraulic conductivity is also influenced by the hydraulic gradient and bitumen content. It is shown that a low hydraulic gradient, less than 0.2, is necessary to counteract the effect of the bitumen and to represent tailings pond conditions. The hydraulic conductivity of fine tails – sand mixes is controlled by the fines void ratio, hence, fines content. The hydraulic conductivity of chemically amended nonsegregating tailings can be lower than that of fine tails. However, acid–lime or acid – fly ash amended nonsegregating tailings have similar hydraulic conductivity values in terms of fines void ratio. The hydraulic conductivity of nonsegregating tailings appears to be governed by fines content and by the nature of the fines aggregation caused by the chemical additive. Key words: tailings, slurries, hydraulic conductivity, slurry consolidometer, nonsegregating tailings, oil sands.

A capillary flow meter for measuring the hydraulic conductivity of clay under low gradients

The measurement of water flow through clay at low hydraulic gradients (<1) is a very difficult task requiring several months to accomplish in a laboratory. A capillary flow meter, capable of measuring extremely low flow rates through clay samples under low imposed hydraulic gradients, has been designed and tested. Flux as low as 10–12 m·s–1 was successfully measured using this flow meter. To minimize the contaminatiion effects, perchloroethylene, which has self-cleaning ability, mixed with Sudan IV was used as the bubble liquid in the capillary flow meter. Glass and Teflon® valves were fused to the inflow and outflow capillary tubes to permit these components to be flushed with cleaning agents and distilled water. The movement of the menisci through the capillary tube was used as a measure of the volume flow rate through the sample. A sensitive differential pressure transducer was connected between the inflow and outflow end of the clay sample to measure the imposed hydraulic head difference. This flow meter has been independently calibrated against a conventional constant head permeameter. Once the clay samples have stabilized in a permeameter, oedometer, or a triaxial cell, multiple flow measurements under low hydraulic gradients can be done in less than an hour. Key words: nonlinear flow, saturated hydraulic conductivity, non-Darcy flow, ultra-low flow meter.

Hydrological exchange and sediment characteristics in a riverbank: relationship between heavy metals and invertebrate community structure

The first metre of bed sediments of the Rhône River functions as a filter for fluxes of heavy metals and epigean organisms between surface and interstitial environments. To study the efficacy of this bank filtration, three sampling stations were established at increasing distances from pumping wells, resulting in a gradient of hydraulic characteristics. Station A, a permanent downwelling area with very high hydraulic gradients, low hydraulic conductivity, low oxygen content, and rather high metal concentrations contained a fauna exclusively composed of epigean organisms. At station B, intermediate hydraulic gradients, high hydraulic conductivity near the surface, and variable direction of water exchanges resulted in well-oxygenated pore water and a diversified fauna with hypogean and epigean species. Finally, at station C, low hydraulic gradient, low hydraulic conductivity, low water exchange, and high sediment metal concentrations resulted in low pore-water oxygen concentrations and low interstitial fauna density and diversity. At this site, low oxygen content and low biodiversity were related to the clogging of shallow sediments and low filtration efficiency. Thus, bank filtration efficiency, a property that depends mainly on natural or human-induced hydraulic gradients and sediment granulometry, determines pore-water chemistry, metal distribution, and faunal composition in the shallow interstitial environments of the Rhône River.