Field observation of flow in a fracture intersecting unsaturated chalk

Dahan, Ofer; Nativ, Ronit; Adar, Eilon; Berkowitz, Brian; Ronen, Zeev

doi:10.1029/1999wr900198

Cited by 98 publications

(62 citation statements)

References 14 publications

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“…While fractures in the vadose zone are usually considered as preferential flow paths that serve mainly as water conduits for deep and fast water percolation (Dahan et al, 1999(Dahan et al, , 2000Zhou et al, 2006;Ireson et al, 2009), recent studies have shown that they can serve as air conduits that enhance aeration and water evaporation in deep sections of the vadose zone (Nachshon et al, 2008;Kamai et al, 2009;Weisbrod et al, 2009). It has been shown that, in arid environments, the density gradients between the air within a fracture void (light, wet and warm air) and the atmospheric air (cooler, drier and heavier (denser)) trigger air convection within the void, which enhances water evaporation and salt accumulation in the sediment surrounding the fracture walls (Weisbrod and Dragila, 2006;Kamai et al, 2009).…”

Section: Introductionmentioning

confidence: 99%

Desiccation-crack-induced salinization in deep clay sediment

Baram

Ronen

Kurtzman

et al. 2013

Hydrol. Earth Syst. Sci.

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Abstract.A study on water infiltration and solute transport in a clayey vadose zone underlying a dairy farm waste source was conducted to assess the impact of desiccation cracks on subsurface evaporation and salinization. The study is based on five years of continuous measurements of the temporal variation in the vadose zone water content and on the chemical and isotopic composition of the sediment and pore water in it. The isotopic composition of water stable isotopes (δ 18 O and δ 2 H) in water and sediment samples, from the area where desiccation crack networks prevail, indicated subsurface evaporation down to ∼ 3.5 m below land surface, and vertical and lateral preferential transport of water, following erratic preferential infiltration events. Chloride (Cl − ) concentrations in the vadose zone pore water substantially increased with depth, evidence of deep subsurface evaporation and down flushing of concentrated solutions from the evaporation zones during preferential infiltration events. These observations led to development of a desiccation-crack-induced salinization (DCIS) conceptual model. DCIS suggests that thermally driven convective air flow in the desiccation cracks induces evaporation and salinization in relatively deep sections of the subsurface. This conceptual model supports previous conceptual models on vadose zone and groundwater salinization in fractured rock in arid environments and extends its validity to clayey soils in semi-arid environments.

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Section: Introductionmentioning

confidence: 99%

Desiccation-crack-induced salinization in deep clay sediment

Baram

Ronen

Kurtzman

et al. 2013

Hydrol. Earth Syst. Sci.

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“…Although the basic information that allows adequate characterization of flow and transport in a well-defined medium is relatively well known, the processes occurring in natural heterogeneous environments are still far from being clearly described or properly predicted. Apparently, the difficulty in characterizing water flow and contaminant transport in natural unsaturated zones at the field scale is intimately related to the instability of unsaturated flow [7][8][9][10]. In laboratory experiments where the flow characteristics through a welldefined medium may be controlled, accurate measurements and consequent close calibration of transport models may be achieved.…”

Section: Vadose-zone Monitoring Technologymentioning

confidence: 99%

Real-time monitoring of the vadose zone as a key to groundwater protection from pollution hazard

Dahan¹

2015

WIT Transactions on Ecology and the Environment

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Minimization subsurface pollution is very dependent on reliable and effective monitoring tools. Today, most monitoring programs are based on observation wells that enable collection of hydrological and chemical information from the saturated part of the subsurface. As a result, identification of pollution in wells is clear evidence that the contaminants already crossed the entire vadose-zone and accumulated in the aquifer. Accordingly, an effective monitoring program must include monitoring means that provide real-time information in the unsaturated zone. Such monitoring programs may provide "early warning" for potential pollution processes that may risk groundwater quality. A vadose-zone monitoring system (VMS), which was developed recently, allows continuous monitoring of the hydrological and chemical properties of percolating water in the deep vadose zone. Data which is collected by the system allows direct measurements of the water percolation fluxes and detects the chemical evolution of the percolating water across the entire unsaturated domain. The VMS is designed for long term continuous operation in a time scale of years to decades. To date, the system has been successfully implemented in several studies on water flow and contaminant transport in various hydrological and geological setups. These include research projects on: (a) floodwater infiltration and groundwater recharge from stream channels and reservoirs, (b) impact of various agricultural regimes on quality and quantity of groundwater recharge, (c) subsurface pollution of dairy farms, (d) chemical evolution of landfill leachates, and (e) control of remediation operations in contaminated sites.

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“…Many observations of irregular and fast -developing wetting patterns, suggest that preferential flow commences before macropores are filled (Nimmo and Mitchell, 2013). However, experimental studies have shown that flow proceeds along localized preferential flow paths (e.g., Dahan et al, 1999;Nicholl et al,1994;Su et al, 1999). For example, an infiltration experiment on a single, in situ, unsaturated fracture in the Negev Chalk, Israel, showed that 70% of water flux was transmitted through less than 20% of the studied fracture openings (Dahan et al, 1999).…”

Section: Conceptual Models Of Infiltration In Unsaturated Chalkmentioning

confidence: 99%

“…However, experimental studies have shown that flow proceeds along localized preferential flow paths (e.g., Dahan et al, 1999;Nicholl et al,1994;Su et al, 1999). For example, an infiltration experiment on a single, in situ, unsaturated fracture in the Negev Chalk, Israel, showed that 70% of water flux was transmitted through less than 20% of the studied fracture openings (Dahan et al, 1999). To account for these inconsistencies, hypotheses related to fluid films on fracture surfaces have been proposed (Tokunaga and Wan, 1997).…”

Section: Conceptual Models Of Infiltration In Unsaturated Chalkmentioning

confidence: 99%

Kinematic diffusion approach to describe recharge phenomena in unsaturated fractured chalk

Pastore

Cherubini

Giasi

2017

Journal of Hydrology and Hydromechanics

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When dealing with groundwater resources, a better knowledge of the hydrological processes governing flow in the unsaturated zone would improve the assessment of the natural aquifer recharge and its vulnerability to contamination. In North West Europe groundwater from unconfined chalk aquifers constitutes a major water resource, therefore the need for a good hydrological understanding of the chalk unsaturated zone is essential, as it is the main control for aquifer recharge. In the North Paris Basin, much of the recharge must pass through a regional chalk bed that is composed of a porous matrix with embedded fractures. The case study regards the role of the thick unsaturated zone of the Cretaceous chalk aquifer in Picardy (North of France) that controls the hydraulic response to rainfall. In order to describe the flow rate that reaches the water table, the kinematic diffusion theory has been applied that treats the unsaturated water flow equation as a wave equation composed of diffusive and gravitational components. The kinematic diffusion model has proved to be a convenient method to study groundwater recharge processes in that it was able to provide a satisfactory fitting both for rising and falling periods of water table fluctuation. It has also proved to give an answer to the question whether unsaturated flow can be described using the theory of kinematic waves. The answer to the question depends principally on the status of soil moisture. For higher values of hydraulic Peclet number (increasing saturation), the pressure wave velocities dominate and the preferential flow paths is provided by the shallow fractures in the vadose zone. With decreasing values of hydraulic Peclet number (increasing water tension), rapid wave velocities are mostly due to the diffusion of the flow wave. Diffusive phenomena are provided by matrix and fracture-matrix interaction.The use of a kinematic wave in this context constitutes a good simplified approach especially in cases when there is a lack of information concerning the hydraulic properties of the fractures/macropores close to saturation.

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Field observation of flow in a fracture intersecting unsaturated chalk

Cited by 98 publications

References 14 publications

Desiccation-crack-induced salinization in deep clay sediment

Desiccation-crack-induced salinization in deep clay sediment

Real-time monitoring of the vadose zone as a key to groundwater protection from pollution hazard

Kinematic diffusion approach to describe recharge phenomena in unsaturated fractured chalk

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