Borehole-based study of CO2-rich air transport in the vadose zone of a Mediterranean karst system (Malaga, southern Spain)

2020 ◽  
Author(s):  
Lucía Ojeda ◽  
José Benavente ◽  
Iñaki Vadillo ◽  
Cristina Liñán ◽  
Enrique P. Sanchez-Cañete
Keyword(s):  
Vadose Zone ◽  
Karst Aquifer ◽  
Field Measurements ◽  
Temporal Variations ◽  
Groundwater Levels ◽  
Sources And Sinks ◽  
Global Carbon Budget ◽  
Vertical Heterogeneity ◽  
Test Linking ◽  
Karst Systems

<p>The characterization of CO<sub>2 </sub>transport, and other C compounds (CH<sub>4</sub>, DIC, organic matter, etc.), in the vadose zone of a karst aquifer is key in order to quantify sources and sinks of carbon. In karst environments, most of the studies are focused on the dynamics of CO<sub>2</sub> in caves, but only a few studies are related to field measurements of the CO<sub>2</sub> content in boreholes, which provides direct insights about the vadose zone. Located at the east of the Nerja Cave (Malaga, Andalusia), one of the most important tourist caves in Spain, the vadose zone was accessed by 9 boreholes drilled into the vadose zone of a Triassic carbonate aquifer, with depths ranging between 15 and 30 m. The karst network in the study area is characterized by a great vertical heterogeneity, with significant cavities and voids at specific intervals. Groundwater levels at different altitudes are a consequence of this heterogeneity. Similarly, CO<sub>2</sub> distribution and transport are clearly determined by the complex karst network.</p><p>Our study aims to identify significant horizontal gradients of CO<sub>2</sub> in the karst vadose air, both spatial and temporally. We present monthly measurements of CO<sub>2</sub> concentration, relative humidity, air temperature and <sup>222</sup>Rn inside boreholes. In addition, we present CO<sub>2</sub> results from an 18 hours-atmospheric air injection test. Linking them to the geophysical knowledge of voids in the study area, the results allow us to identify lateral fluxes of CO<sub>2</sub>-rich air in the vadose zone and how these fluxes are favoured by the incidence of the main karst discontinuity orientations. We observe different ventilation patterns:  in spring the vadose air seems to be stored in specific orientations, while in summer there is a lower convective ventilation. The results contribute to explain the temporal variations of the chemical composition of recharge water in karst systems, as well as to support studies on the global carbon budget.</p>

scholarly journals Simulation of Groundwater Flow in Fractured-Karst Aquifer with a Coupled Model in Maling Reservoir, China

2021 ◽  
Vol 11 (4) ◽  
pp. 1888
Author(s):  
Jinbang Cai ◽  
Yue Su ◽  
Huan Shen ◽  
Yong Huang
Keyword(s):  
Groundwater Flow ◽  
Water Level ◽  
Karst Aquifer ◽  
Coupled Model ◽  
Geometrical Parameters ◽  
Underground Powerhouse ◽  
Groundwater Levels ◽  
Seepage Control ◽  
Fractured Medium ◽  
Karst Systems

A coupled model has been developed to simulate groundwater flow in fractured karst systems according to the complex geological and karst hydrogeological conditions of the dam site, where a 3D mathematical model based on Boussinesq equation was used to describe the movement of groundwater flow in fractured medium, and a 1D conduit model for karst medium. The model was solved with the continuous hydraulic heads at the common boundaries. The hydraulic conductivities of karst medium were determined by geometrical parameters and flux of pipes. Furthermore, the permeability parameters for fractured medium were calibrated by the measured and calculated groundwater levels. The calibrated model was employed to predict the variation of groundwater flow field and leakage from the karst pipes and underground powerhouse during the reservoir operation. The simulated results showed that the groundwater level of the powerhouse had decreased by about 2–5 m. The water level of conveyance pipeline had risen by 10–20 m, and the water level on both banks had risen by 15–25 m. The leakage of karst conduits for impervious failure was larger than that for normal seepage control. In addition, the leakage of the powerhouse was estimated to be about 1000–3000 m3/d, and the seepage control of karst pipes had little influence on the leakage of underground powerhouse.

scholarly journals CO2 dynamics and heterogeneity in a cave atmosphere: role of ventilation patterns and airflow pathways

2021 ◽  
Author(s):  
Lovel Kukuljan ◽  
Franci Gabrovšek ◽  
Matthew D. Covington ◽  
Vanessa E. Johnston
Keyword(s):  
Temporal Variations ◽  
Observation Point ◽  
Spatially Distributed ◽  
Combined Action ◽  
Karst Systems ◽  
The Relationship ◽  
Co2 Dynamics ◽  
Global Carbon

AbstractUnderstanding the dynamics and distribution of CO2 in the subsurface atmosphere of carbonate karst massifs provides important insights into dissolution and precipitation processes, the role of karst systems in the global carbon cycle, and the use of speleothems for paleoclimate reconstructions. We discuss long-term microclimatic observations in a passage of Postojna Cave, Slovenia, focusing on high spatial and temporal variations of pCO2. We show (1) that the airflow through the massif is determined by the combined action of the chimney effect and external winds and (2) that the relationship between the direction of the airflow, the geometry of the airflow pathways, and the position of the observation point explains the observed variations of pCO2. Namely, in the terminal chamber of the passage, the pCO2 is low and uniform during updraft, when outside air flows to the site through a system of large open galleries. When the airflow reverses direction to downdraft, the chamber is fed by inlets with diverse flow rates and pCO2, which enter via small conduits and fractures embedded in a CO2-rich vadose zone. If the spatial distribution of inlets and outlets produces minimal mixing between low and high pCO2 inflows, high and persistent gradients in pCO2 are formed. Such is the case in the chamber, where vertical gradients of up to 1000 ppm/m are observed during downdraft. The results presented in this work provide new insights into the dynamics and composition of the subsurface atmosphere and demonstrate the importance of long-term and spatially distributed observations.

Geophysical measurements in an abandoned old railway tunnel located in a karst area

2021 ◽  
Author(s):  
Enzo Rizzo ◽  
Luigi Capozzoli ◽  
Gregory De Martino ◽  
Giacomo Fornasari ◽  
Valeria Giampaolo
Keyword(s):  
Karst Aquifer ◽  
Geophysical Methods ◽  
Water Reservoir ◽  
Test Site ◽  
Point Of View ◽  
Karst Area ◽  
Fluid Circulation ◽  
Railway Tunnel ◽  
Interdisciplinary Field ◽  
Karst Systems

<p>Carbonate aquifers in karst systems are very important water reservoir and are recognized as the most difficult to characterize. The purpose of this article is to present a project aimed to understand the circulation of fluids in carbonate reservoirs through innovative hydrogeophysical methodologies both in the laboratory and in the field. The test site is located in the Castel di Lepre karst system, which is disposed in the Mezo-Cenozoic carbonate substratum of the Monti della Maddalena ridge (Southern Appenines). In the karst area are located several caves, but the presence of an artificial tunnel (disused railway tunnel) could give the opportunity to characterize the whole area and the fluid circulation by multisensors geophysical sensors installed inside the karst aquifer. This natural laboratory permits to define an Applied Geophysics strategy developing several main topics from an engineering to hydrogeological point of view. Firstly, the geophysical investigations conducted, without altering the structure and in a fast manner, obtains important information concerning the construction of the tunnel, and the interaction between the infrastructure and surrounding rock, in that area that we define infrastructural critical zone. The study conducted aims to highlight the potential and any limitations of the use of geophysical techniques applied to infrastructures, emphasizing the emerging role of urban geophysics for the importance and topicality of its contents as well as the important innovations that the use of these techniques they can contribute to the hazardous processes. Secondly, the geophysical methods are used as a tool to characterize the fluid circulation by hydrogeophysal sensors installed inside the karst aquifer. The hydrogeophysics arose as an interdisciplinary field that focuses on the improved understanding of hydrological processes through geophysical observation. These approaches aimed at mitigating the detrimental effects of environmental problems.</p>

Predicting preferential flow and water table fluctuations in karst systems using film-flow theory and source-responsive models

2021 ◽  
Author(s):  
Torsten Noffz ◽  
Jannes Kordilla ◽  
Alireza Kavousi ◽  
Thomas Reimann ◽  
Martin Sauter ◽  
...  
Keyword(s):  
Water Table ◽  
Vadose Zone ◽  
Water Resource Management ◽  
Preferential Flow ◽  
Film Flow ◽  
Dry Valleys ◽  
Diffuse Infiltration ◽  
Water Table Fluctuations ◽  
Aquifer Systems ◽  
Karst Systems

<p>The locally focused dissolution of the rock material (e.g., below dolines and dry valleys) in karst systems and in general percolating clusters of fractures in consolidated aquifer systems trigger the development of preferential flow paths in the vadose zone. Rainfall events may initiate rapid mass fluxes via macropores and fractures (e.g., as gravitationally-driven films) that lead to source-responsive water table fluctuations and comparably short residence times within the vadose zone. The degree of partitioning into a slow diffuse infiltration component and a rapid localized part depends, amongst others, on the hydraulic interaction of porous matrix and fracture domain as well as the geometrical characteristics of the fracture systems (e.g., persistence, connectivity) that are often difficult to obtain or unknown under most field conditions. Given their importance in water-resource management, specifically in arid and semi-arid regions (e.g., Mediterranean), it is desirable to recover such infiltration dynamics in porous-fractured systems with physically-based yet not overparameterized models. Here, we simulate water table fluctuations in a karst catchment in southwest Germany (Gallusquelle) using a source-responsive film flow model based on borehole and precipitation data. The model takes into account interfacial connectivity between slow and fast domain as well as phreatic zone discharge via classical recession analysis. This case study shows the potential importance of preferential flows while modeling water table responses in karst systems and recognizes the need for formulations other than those applied for a diffuse bulk fractured domain where infiltration patterns are assumed to be homogeneous without formation of infiltration instabilities along preferential pathways.</p>

scholarly journals A numerical geotechnical model for computing soil slides at banks of water reservoirs

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Nils Reidar B. Olsen ◽  
Stefan Haun
Keyword(s):  
Numerical Model ◽  
Water Level ◽  
Stokes Equations ◽  
Limit Equilibrium ◽  
Three Dimensional ◽  
Field Measurements ◽  
Navier Stokes ◽  
Adaptive Grids ◽  
Groundwater Levels ◽  
Before And After

AbstractSoil slides can occur when the water level in a lake or a reservoir is lowered. This may take place in situations when a reservoir is flushed to remove sediments. The current study describes a three-dimensional numerical model used for the simulation of reservoir flushing that includes the slide movements. The geotechnical failure algorithms start with modelling the groundwater levels at the banks of the reservoir. A limit equilibrium approach is further used to find the location of the slides. The actual movement of the sediments is computed by assuming the soil to be a viscous liquid and by solving the Navier–Stokes equations. The resulting bed elevation changes from the slides are computed in adaptive grids that change as a function of water level, bed erosion and slide movements. The numerical model is tested on the Bodendorf reservoir in Austria, where field measurements are available of the bank elevations before and after a flushing operation. The results from the numerical simulations are compared with these observations. A parameter test shows that the results are very sensitive to the cohesion and less sensitive to the E and G modules of the soil.

scholarly journals Taking into Account both Explicit Conduits and the Unsaturated Zone in Karst Reservoir Hybrid Models: Impact on the Outlet Hydrograph

Water ◽  
2020 ◽  
Vol 12 (11) ◽  
pp. 3221
Author(s):  
Lucie Dal Soglio ◽  
Charles Danquigny ◽  
Naomi Mazzilli ◽  
Christophe Emblanch ◽  
Gérard Massonnat
Keyword(s):  
Unsaturated Zone ◽  
Numerical Models ◽  
Karst Aquifer ◽  
Hybrid Models ◽  
Model Parameters ◽  
Transit Times ◽  
The Matrix ◽  
Karst Reservoir ◽  
Karst Systems ◽  
The One

The main outlets of karst systems are springs, the hydrographs of which are largely affected by flow processes in the unsaturated zone. These processes differ between the epikarst and transmission zone on the one hand and the matrix and conduit on the other hand. However, numerical models rarely consider the unsaturated zone, let alone distinguishing its subsystems. Likewise, few models represent conduits through a second medium, and even fewer do this explicitly with discrete features. This paper focuses on the interest of hybrid models that take into account both unsaturated subsystems and discrete conduits to simulate the reservoir-scale response, especially the outlet hydrograph. In a synthetic karst aquifer model, we performed simulations for several parameter sets and showed the ability of hybrid models to simulate the overall response of complex karst aquifers. Varying parameters affect the pathway distribution and transit times, which results in a large variety of hydrograph shapes. We propose a classification of hydrographs and selected characteristics, which proves useful for analysing the results. The relationships between model parameters and hydrograph characteristics are not all linear; some of them have local extrema or threshold limits. The numerous simulations help to assess the sensitivity of hydrograph characteristics to the different parameters and, conversely, to identify the key parameters which can be manipulated to enhance the modelling of field cases.

scholarly journals Modeling of Artificial Groundwater Recharge by Wells: A Model Stratified Porous Medium

Mathematics ◽  
2020 ◽  
Vol 8 (10) ◽  
pp. 1764 ◽  
Author(s):  
Carlos Fuentes ◽  
Carlos Chávez ◽  
Antonio Quevedo ◽  
Josué Trejo-Alonso ◽  
Sebastián Fuentes
Keyword(s):  
Decision Making ◽  
Porous Medium ◽  
Artificial Recharge ◽  
Cost Benefit ◽  
Field Measurements ◽  
Stratified Media ◽  
Artificial Groundwater Recharge ◽  
Industrial Activities ◽  
Groundwater Levels ◽  
The Cost

In recent years, groundwater levels have been decreasing due to the demand in agricultural and industrial activities, as well as the population that has grown exponentially in cities. One method of controlling the progressive lowering of the water table is the artificial recharge of water through wells. With this practice, it is possible to control the amount of water that enters the aquifer through field measurements. However, the construction of these wells is costly in some areas, in addition to the fact that most models only simulate the well as if it were a homogeneous profile and the base equations are restricted. In this work, the amount of infiltrated water by a well is modeled using a stratified media of the porous media methodology. The results obtained can help decision-making by evaluating the cost benefit of the construction of wells to a certain location for the recharge of aquifers.

Influence of canopy structure on the understory environment in tall, old-growth, conifer forests

2000 ◽  
Vol 30 (8) ◽  
pp. 1231-1245 ◽  
Author(s):  
Robert Van Pelt ◽  
Jerry F Franklin
Keyword(s):  
Leaf Area ◽  
Canopy Structure ◽  
Field Measurements ◽  
Horizontal Distribution ◽  
Shrub Cover ◽  
Old Growth ◽  
Light Levels ◽  
Vertical Heterogeneity ◽  
Canopy Volume ◽  
Old Growth Forests

The effect of the spatial distribution of trees and foliage on understory conditions was examined in six tall old-growth forests along the Pacific Coast: two sites each in Washington, Oregon, and California. Detailed field measurements of crown parameters were collected on over 9000 trees encompassing over 14.5 ha in the stands. Crown parameters were used to construct a spatially explicit model useful in analyzing the variability of crown distributions in both vertical and horizontal dimensions. Sapwood measurements of over 400 trees in combination with published equations and 240 hemispherical photos were used to assess leaf area and understory light levels, respectively. Shrub and herb cover was used as a biological indicator of growing conditions in the understory. Although leaf area is often assumed to be correlated with the amount of light penetrating the canopy, this is not the case in tall, old-growth forests. The semivariance of the horizontal distribution of canopy volume was strongly correlated with shrub cover and understory light levels and was an overall predictor of canopy structure. This variability gives rise to potentially higher understory light levels and shrub cover values when compared with a forest lacking this vertical heterogeneity and may allow the stand to support a higher volume of foliage.

scholarly journals Temporal variations in flow velocity at Finsterwalderbreen, a Svalbard surge-type glacier

2005 ◽  
Vol 42 ◽  
pp. 71-76 ◽  
Author(s):  
Anne-Marie Nuttall ◽  
Richard Hodgkins
Keyword(s):  
Flow Velocity ◽  
Climate Changes ◽  
Field Measurements ◽  
Temporal Variations ◽  
Aerial Photographs ◽  
Velocity Data ◽  
Glacier Surface ◽  
Basal Sliding ◽  
Hydrological System ◽  
Interannual Fluctuations

AbstractInter- and intra-annual velocity variations are well known on alpine glaciers, but their importance for Arctic glaciers has only been recognized more recently. This paper presents flow velocity data from Finsterwalderbreen, a 35 km2 polythermal surge-type glacier in southern Svalbard that is presently ∼100 years into its quiescent phase. Field measurements of glacier surface velocities are available from 1950-52 and 1994-97, and mean velocities for the last decade are estimated for the lower glacier using cables drilled to the glacier bed. These velocities show substantial seasonal variations indicating that basal sliding is an important component of surface velocities and interannual fluctuations of up to 75%, possibly indicating variations in subglacial water storage. Several lines of evidence indicate that this glacier has an extensive subglacial hydrological system, generally considered to be a prerequisite for surge-type glaciers, which is at least partly pressurized. Information on surface morphology from 1898 onwards shows that the glacier has experienced continuous retreat since the last surge in about 1910, and has now retreated ∼1.5 km further back than its previous pre-surge position in 1898. Tracking of moraine loops on terrestrial and aerial photographs acquired over a 100 year period indicates that the surge period of Finsterwalderbreen may be lengthening in response to climate changes.

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