Set Of Piezometers Research Articles

A new small-scale experimental device for testing backward erosion piping

Abstract Backward erosion piping is driven by seepage forces acting on the soil grains at the downstream end of the seepage path. A new device for the laboratory testing of backward erosion progression was developed and tested. The device consists of a plexiglass prism at which the seepage path has been predefined. The prism was equipped with an inflow consisting of gravel separated from tested sand by a strainer. The hydraulic gradient along the seepage pipe was observed by a set of piezometers and pressure cells, and the seepage discharge was measured volumetrically. The transported sediment was trapped in a vertical cone located downstream from the device. The progression of the seepage path, the piezometric heads and the trapped material was observed by two synchronous cameras. 15 trial tests have been carried out to date, and from these, the interim results are presented.

Submarine slope destabilization and gully formation by water sapping: Physical simulation of an underestimated trigger of subaqueous sediment gravity flows

AbstractA laboratory tank experiment tested whether a subsurface flow from a confined aquifer causes slope instability and leads to the formation of pathways for sediment transfer from shallow to deep water when the subsurface flow discharges through the face of a subaqueous slope. A sandy slope with multilayer stratigraphy was built inside the tank, and a confined aquifer was simulated within the stratigraphy. To induce groundwater flow out of the face of the slope, water was injected in the proximal zone of the confined aquifer at progressive increased discharge. Sediment movement on the slope occurred by rolling of particles, fluidized flow, grain flow and slides. The fluctuation of phreatic pressure in the confined aquifer was measured by a set of piezometers, from which the hydraulic gradient generated by the water flow moving towards the slope was determined. This study determined that the mass movements started when the imposed injected flow rate was greater than the hydraulic conductivity capacity of the simulated aquifer, using the flow capacity calculated from the Darcy equation for porous media. The various physical parameters used in the experiment were found to scale well to natural prototypes. Moreover, the patterns of erosion and deposition in the physical simulation resembled natural features observed in seismic‐geomorphology maps and modern deep‐sea physiography. Therefore, water sapping by a confined aquifer flow is a potential mechanism for slope erosion and instability and for the formation of pathways connecting shallow‐water and deep‐water environments.

The AquiFR hydrometeorological modelling platform as a tool for improving groundwater resource monitoring over France: evaluation over a 60-year period

Abstract. The new AquiFR hydrometeorological modelling platform was developed to provide short-to-long-term forecasts for groundwater resource management in France. This study aims to describe and assess this new tool over a long period of 60 years. This platform gathers in a single numerical tool several hydrogeological models covering much of the French metropolitan area. A total of 11 aquifer systems are simulated through spatially distributed models using either the MARTHE (Modélisation d'Aquifères avec un maillage Rectangulaire, Transport et HydrodynamiquE; Modelling Aquifers with Rectangular cells, Transport and Hydrodynamics) groundwater modelling software programme or the EauDyssée hydrogeological platform. A total of 23 karstic systems are simulated by a lumped reservoir approach using the EROS (Ensemble de Rivières Organisés en Sous-bassins; set of rivers organized in sub-basins) software programme. AquiFR computes the groundwater level, the groundwater–surface-water exchanges and the river flows. A simulation covering a 60-year period from 1958 to 2018 is achieved in order to evaluate the performance of this platform. The 8 km resolution SAFRAN (Système d'Analyse Fournissant des Renseignements Adaptés à la Nivologie) meteorological analysis provides the atmospheric variables needed by the SURFEX (SURFace EXternalisée) land surface model in order to compute surface runoff and groundwater recharge used by the hydrogeological models. The assessment is based on more than 600 piezometers and more than 300 gauging stations corresponding to simulated rivers and outlets of karstic systems. For the simulated piezometric heads, 42 % and 60 % of the absolute biases are lower than 2 and 4 m respectively. The standardized piezometric level index (SPLI) was computed to assess the ability of AquiFR to identify extreme events such as groundwater floods or droughts in the long-term simulation over a set of piezometers used for groundwater resource management. A total of 56 % of the Nash–Sutcliffe efficiency (NSE; Ef) coefficient calculations between the observed and simulated SPLI time series are greater than 0.5. The quality of the results makes it possible to consider using the platform for real-time monitoring and seasonal forecasts of groundwater resources as well as for climate change impact assessments.

Spatial, vertical and temporal variation of arsenic in shallow aquifers of the Bengal Basin: Controlling geochemical processes

A detailed understanding of the geochemical processes that regulate the spatial, temporal and vertical variation of dissolved arsenic (As) in shallow aquifers (<50m) is a prerequisite for sustainable drinking water management in the Bengal Basin. The present study conducted at Chakdaha Block of the Nadia District, West Bengal, India, combined a high resolution hydrogeochemical monitoring study over 20months from two sets of piezometers (2×5) to the sediment geochemistry at areas with high (average: 146μg/L, n=5) and relatively low (average: 53.3μg/L, n=10) dissolved As concentrations in groundwater. The determination of the isotopic composition of δ2H and δ18O in groundwater of the two sites indicated the recharge of evaporative surface water to the aquifer. The concentrations of major aqueous solutes (Ca2+, Mg2+, Na+, K+, HCO3− and Cl−) and electrical conductivity were considerably higher in wells at the high As site compared to the low As site. Additionally, at the high As site, the major ions, Fe, SO42−, electrical conductivity, δ2H and δ18O showed markedly greater enrichment in the shallowest part (<24m) of the aquifer compared to the deeper part, reflecting vertical layering of groundwater composition within the aquifer. The oxidation of pyrites has been attributed to the high rate of mineral dissolution resulting in such greater enrichments in this part of the aquifer. In addition, the anthropogenic input with recharge water possibly increased the concentrations of Cl− in this part of the aquifer. The vertical layering of groundwater was absent in the aquifer at the low As site. The absence of such layering and relatively low major ion concentrations and electrical conductivity could be linked to the enhanced aquifer flushing and decreased water–sediment interactions influenced by local-scale groundwater abstraction. The seasonal variations of As concentrations in groundwater were observed only in the shallowest part of the aquifers (<30m). Furthermore, the As concentrations in groundwater at the uppermost part of the shallow aquifers (<21m) increased continuously over the monitoring period at both sites. This study supports the view that the reductive dissolution of Fe oxyhydroxides coupled with competitive PO43− sorption reactions in the aquifer sediment enriches As in groundwater of the Bengal Basin. However, the additional Fe released by the weathering of silicate minerals, especially biotite, or the precipitation of Fe as secondary mineral phases such as siderite, vivianite and acid volatile sulfides may result in the decoupling of As and Fe enrichment in groundwater. The redox zonation within the aquifer possibly regulates the vertical distribution of As in the groundwater.

Hydraulic conductivity field characterization from the joint inversion of hydraulic heads and self‐potential data

AbstractPumping tests can be used to estimate the hydraulic conductivity field from the inversion of hydraulic head data taken intrusively in a set of piezometers. Nevertheless, the inverse problem is strongly underdetermined. We propose to add more information by adding self‐potential data taken at the ground surface during pumping tests. These self‐potential data correspond to perturbations of the electrical field caused directly by the flow of the groundwater. The coupling is electrokinetic in nature that is due to the drag of the excess of electrical charges existing in the pore water. These self‐potential signals can be easily measured in field conditions with a set of the nonpolarizing electrodes installed at the ground surface. We used the adjoint‐state method for the estimation of the hydraulic conductivity field from measurements of both hydraulic heads and self potential during pumping tests. In addition, we use a recently developed petrophysical formulation of the streaming potential problem using an effective charge density of the pore water derived directly from the hydraulic conductivity. The geostatistical inverse framework is applied to five synthetic case studies with different number of wells and electrodes and thickness of the confining unit. To evaluate the benefits of incorporating the self‐potential data in the inverse problem, we compare the cases in which the data are combined or not. Incorporating the self‐potential information improves the estimate of hydraulic conductivity field in the case where the number of piezometers is limited. However, the uncertainty of the characterization of the hydraulic conductivity from the inversion of the self‐potential data is dependent on the quality of the distribution of the electrical conductivity used to solve the Poisson equation. Consequently, the approach discussed in this paper requires a precise estimate of the electrical conductivity distribution of the subsurface and requires therefore new strategies to be developed for the joint inversion of the hydraulic and electrical conductivity distributions.

Groundwater responses to controlled water releases in the limitrophe region of the Colorado River: Implications for management and restoration

Flow regulation and water diversion for irrigation have considerably affected the exchange of surface water between the Colorado River and its floodplains. However, the way in which both have impacted groundwater–surface water interactions is not completely understood. The objective of this study was to conduct a hydrologic analysis of the 2009–2010 winter flows released into the limitrophe region of the Colorado River in order to characterize the surface flows along this dry reach and, for the first time, study the impact of winter flows on the groundwater conditions in the area. The study used existing data on groundwater levels that was collected from regional piezometers on both sides of the limitrophe every five years from 1980 to 2005. Regional flow direction from NE to SW was observed in all years. A groundwater depression cone in the southwest part of the limitrophe was identified from 1980 to 1995. A general rise of groundwater levels was observed from 2000 to 2005 on both sides of the limitrophe, but during the same time period, a depression cone formed along the border between Arizona and Sonora, in the Mesa Arenosa on the Mexican side of the border. In order to identify the water table evolution within the limitrophe riparian zone, nine sets of piezometers were constructed in an arrangement perpendicular to the main river channel. Water table levels were measured automatically every 30min and were also manually measured periodically. Nine geohydrological cross sections were constructed using the topographic relief from LIDAR elevation points and depth to groundwater measurements during water discharges in the Colorado River channel at Morelos dam. Groundwater seepage from irrigation canals, irrigation returns, and river discharge flows were identified and the depth to groundwater and its influence on riparian vegetation was analyzed. A strong correlation between flow discharge (up to 60.49hm3 from November 2009 to April 2010) and groundwater elevation (average elevation change of 1.62m on January 22, 2010) in time and space was found. The percentage of water retained in the main river channel decreased from 100% in the first discharge event (December 12–13, 2009) to 36% after the last discharge event (April 9–17, 2010), due to remaining moisture in the unsaturated soil. The total volume of water retained, infiltrated, and evaporated, was 60% (36.6×106m3) of the total water discharged. The delay time of the groundwater front during a discharge event was on average 6:30, 20:06, and 28:53h from section 1 to section 2, 1–3, and 1–4 respectively. This historical study provides insight into how floods affect the groundwater system, which is the foundation for aquatic and riparian biodiversity. This issue is of increasing relevance given growing international interest in rehabilitating the riparian and aquatic ecosystems of the Colorado River delta through intentional flood releases.

Identifying connections in a fractured rock aquifer using ADFTs

Fractured rock aquifers are difficult to characterize because of their extremely heterogeneous nature. Developing an understanding of fracture network hydraulic properties in these aquifers is difficult and time consuming, and field testing techniques for determining the location and connectivity of fractures in these aquifers are limited. In the Clare Valley, South Australia, well interference is an important issue for a major viticultural area that uses a fractured aquifer. Five fracture sets exist in the aquifer, all dipping > 25 degrees . In this setting, we evaluate the ability of steady-state asymmetric dipole-flow tests (ADFTs) to determine the connections between a test well and a set of piezometers. The procedure involves dividing a test well into two chambers using a single packer and pumping fluid from the upper chamber to the lower chamber. By conducting a series of tests at different packer elevations, an "input" signal is generated in fracture zones connected to the test well. By monitoring the "output" response of the hydraulic dipole field at piezometers, the connectivity of the fractures between the test well and piezometers can be determined. Results indicate the test well used in this study is connected in a complex three-dimensional geometry, with drawdown occurring above and below areas of potentiometric buildup. The ADFT method demonstrates that the aquifer evaluated in this study cannot be modeled effectively on the well scale using continuum flow models.

Tillage and Split N-Fertilization Effects on Subsurface Drainage Water Quality and Crop Yields

ABSTRACT FIELD experiments were conducted to study the effects of no-till and conventional tillage, and single and slit N-fertilizer applications, for continuous corn production on the leaching of nitrate-nitrogen (NO3-N) through subsurface drainage water and below the root zone. The comparison between conventional and no-till was made by applying a single application of 175 kg-N/ha at the time of planting, and the comparison between single and split N applications was made for the no-tillage system. Six experimental plots, each drained with a single subsurface drain, were intercepted by installing sumps for measuring drain flow rates and collecting drainage water samples for NO3-N analyses. Also, four sets of piezometers were installed for deep water sampling. In the first year of the experiments, tillage and N-fertilizer management schemes did not significantly affect NO3-N concentrations in drainage. However, in the third year, the average NO3-N concentrations in drainage from conventional tillage plots were significantly greater than those of no-till plots when a single application of 175 kg-N/ha was made. The results of this study indicate that split N-applications totaling 125 kg/ha reduced NO3-N concentrations in drainage compared with a single, higher rate of application of 175 kg/ha for the no-tillage treatment.

Pore Water Pressures Measured in Sand Deposits During an Earthquake

A set of piezometers was embedded in sand deposits on a reclaimed island in Tokyo Bay and a seismograph was placed on the ground surface nearby in order to monitor simultaneously in-situ pore water pressures and horizontal accelerations during earthquakes. During the September 25, 1980 earthquake, the instruments registered increases in pore water pressures corresponding to 19% and 16% of the effective overburden pressure at depths of 6.0 M and 14.0 M, respectively. At the same time, a maximum horizontal acceleration of 95 gal was registered at the ground surface. Laboratory cyclic triaxial tests had been performed on undisturbed soil specimens obtained from this site using a large diameter sampler. Based on the laboratory test data, an estimate was made of the pore water pressures that might be produced in the deposit by seismic shaking of a maximum acceleration of 95 gal. The estimated values of pore water pressure were shown to be in good agreement with the pore water pressures registered during the earthquake. (Author/TRRL)