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Secondary currents in groundwater
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water. ÅF Industry AB.
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The thesis concerns the small vertical water movements created by thermal convection and the Coriolis force acting on groundwater flows. These small flows are of importance to vertical transports of temperature, nutrients and contaminants that would not be spread in the way they are. The first part analyzes thermally driven, seasonal groundwater convection by numerical simulation. The second part shows that the Coriolis force also induces secondary currents in groundwater flow through different vertical permeability distributions. Density driven convection occurs during the autumn in southern Sweden when the ambient air temperature cools the mean groundwater temperature from about 10ºC. When the shallow groundwater is cooled by the ambient air its increased density makes this water sink, slowly increasing in temperature, while pressing the warmer water upwards creating a convection cell. The process is ongoing as long as there is a thermal gradient between ground surface and the groundwater. Under favorable conditions convection can reach a depth of 6m. Such density-driven water movements occur most easily in more permeable soil. In northern Sweden, the situation is reversed, since the mean groundwater temperature is below 4ºC, at which water is at its density maximum. So, in springtime when the uppermost groundwater is heated to 4ºC by the warmer air the convection process starts. Here, the sinking groundwater does not reach the same depth, less than one meter. The Coriolis force has been considered too small to have any effect on groundwater flow, though its importance in meteorology and oceanography is well established. These theories have been applied using numerical simulations of groundwater flow. The numerical model has been validated by simulating some earlier studies of Coriolis forces in fluids. Furthermore the model has been extended to include porous media. It has been shown that secondary currents occur in nonlinear vertical permeability distributions. For simulations of constant and linear distributions no secondary currents have been seen. The development is more pronounced in confined aquifers. The structure of the bottom of the aquifer  affects  how the secondary currents arise. It was shown that both temperature gradients and the Coriolis force form secondary currents in groundwater and a general conclusion is that groundwater flow is more complex than previously assumed.

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2017. , p. 70
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
Keyword [en]
Groundwater
National Category
Oceanography, Hydrology and Water Resources
Research subject
Water Resources Engineering
Identifiers
URN: urn:nbn:se:ltu:diva-66411ISBN: 978-91-7790-006-1 (print)ISBN: 978-91-7790-007-8 (electronic)OAI: oai:DiVA.org:ltu-66411DiVA, id: diva2:1156293
Public defence
2017-12-15, F1031, Luleå, 10:00 (English)
Opponent
Supervisors
Available from: 2017-11-14 Created: 2017-11-11 Last updated: 2018-01-13Bibliographically approved
List of papers
1. Earth’s rotation induces vertical ground water flow
Open this publication in new window or tab >>Earth’s rotation induces vertical ground water flow
2007 (English)Conference paper, Oral presentation only (Other academic)
Abstract [en]

It is well established that the Coriolis Force deflects wind and water currents. However, its influence on groundwater flow is neglected. Earth’s rotation causes inertia circles in groundwater that create vortices ending up in different local pressure zones, similar to the high and low pressures in air. High pressure zones in groundwater induce, under certain conditions, a vertical flow up to the surface. This could be the missing link where hydrostatic pressure is not sufficient to explain springs in deserts, mountains and on islands in the sea. Here, simulations on the Coriolis force acting on groundwater flows are presented.

Keyword
Earth sciences - Atmosphere and hydrosphere sciences, Geovetenskap - Atmosfärs- och hydrosfärsvetenskap
National Category
Water Engineering
Research subject
Water Resources Engineering
Identifiers
urn:nbn:se:ltu:diva-40081 (URN)f0f6605d-e991-4321-aa3c-7ddc5d0caacf (Local ID)f0f6605d-e991-4321-aa3c-7ddc5d0caacf (Archive number)f0f6605d-e991-4321-aa3c-7ddc5d0caacf (OAI)
Conference
International Workshop on Natural Energies : 03/08/2007 - 05/08/2007
Note
Godkänd; 2007; 20121107 (bon)Available from: 2016-10-03 Created: 2016-10-03 Last updated: 2017-11-25Bibliographically approved
2. Seasonal groundwater turnover in the north and south of Sweden
Open this publication in new window or tab >>Seasonal groundwater turnover in the north and south of Sweden
2007 (English)Conference paper, Oral presentation only (Other academic)
Abstract [en]

Nutrient leakage from agricultural areas in Sweden mainly occurs during the autumn in the south and during the spring in the north. The infiltration of nutrients also reaches greater depths in the south. An occurring “seasonal groundwater turnover” similar to that in lakes is the suggested mechanism. This thermal convection results from changing temperatures (densities). The 10oC groundwater in southern Sweden becomes denser as it is cooled from the surface in the autumn, while the corresponding convection in the North occurs during the spring. Performed simulations show how seasonal temperature variations, under certain conditions, initiate and drive thermal convection.

National Category
Water Engineering
Research subject
Water Resources Engineering
Identifiers
urn:nbn:se:ltu:diva-39243 (URN)de452dcd-a627-4023-865a-de0f283e4db5 (Local ID)de452dcd-a627-4023-865a-de0f283e4db5 (Archive number)de452dcd-a627-4023-865a-de0f283e4db5 (OAI)
Conference
International Workshop on Natural Energies : 03/08/2007 - 05/08/2007
Note
Godkänd; 2007; 20121107 (bon)Available from: 2016-10-03 Created: 2016-10-03 Last updated: 2017-11-25Bibliographically approved
3. Temperature-driven groundwater convection in cold climates
Open this publication in new window or tab >>Temperature-driven groundwater convection in cold climates
2016 (English)In: Hydrogeology Journal, ISSN 1431-2174, E-ISSN 1435-0157, Vol. 24, no 5, p. 1245-1253Article in journal (Refereed) Published
Abstract [en]

The aim was to study density-driven groundwater flow and analyse groundwater mixing because of seasonal changes in groundwater temperature. Here, density-driven convection in groundwater was studied by numerical simulations in a subarctic climate, i.e. where the water temperature was < 4 A degrees C. The effects of soil permeability and groundwater temperature (i.e. viscosity and density) were determined. The influence of impermeable obstacles in otherwise homogeneous ground was also studied. An initial disturbance in the form of a horizontal groundwater flow was necessary to start the convection. Transient solutions describe the development of convective cells in the groundwater and it took 22 days before fully developed convection patterns were formed. The thermal convection reached a maximum depth of 1.0 m in soil of low permeability (2.71 center dot 10(-9) m(2)). At groundwater temperature close to its density maximum (4 A degrees C), the physical size (in m) of the convection cells was reduced. Small stones or frost lenses in the ground slightly affect the convective flow, while larger obstacles change the size and shape of the convection cells. Performed simulations show that "seasonal groundwater turnover" occurs. This knowledge may be useful in the prevention of nutrient leakage to underlying groundwater from soils, especially in agricultural areas where no natural vertical groundwater flow is evident. An application in northern Sweden is discussed.

National Category
Water Engineering
Research subject
Water Resources Engineering
Identifiers
urn:nbn:se:ltu:diva-5568 (URN)10.1007/s10040-016-1420-0 (DOI)000380090000013 ()2-s2.0-84965070759 (Scopus ID)3b2b798a-1169-414f-b7ce-a3133e98639b (Local ID)3b2b798a-1169-414f-b7ce-a3133e98639b (Archive number)3b2b798a-1169-414f-b7ce-a3133e98639b (OAI)
Note

Validerad; 2016; Nivå 2; 2016-08-17 (inah)

Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2017-11-24Bibliographically approved
4. Seasonal groundwater turnover
Open this publication in new window or tab >>Seasonal groundwater turnover
2006 (English)In: Nordic Hydrology, ISSN 0029-1277, E-ISSN 1996-9694, Vol. 37, no 1, p. 31-39Article in journal (Refereed) Published
Abstract [en]

Seasonal air temperature variations and corresponding changes in groundwater temperature cause convective movements in groundwater similar to the seasonal turnover in lakes. Numerical simulations were performed to investigate the natural conditions for thermally driven groundwater convection to take place. Thermally driven convection could be triggered by a horizontal groundwater flow, Convection then starts at a considerably lower Rayleigh number (Ra) than the general critical Rayleigh number (Ra assuming that 10 degrees C groundwater is cooled to 4 degrees C, i.e. heated from below convection in porous media, This study supports the hypothesis that seasonal temperature variations, under certain conditions, initiate and drive thermal convection.

National Category
Water Engineering
Research subject
Water Resources Engineering
Identifiers
urn:nbn:se:ltu:diva-15162 (URN)10.2166/nh.2005.028 (DOI)ea4a3600-9207-11db-8975-000ea68e967b (Local ID)ea4a3600-9207-11db-8975-000ea68e967b (Archive number)ea4a3600-9207-11db-8975-000ea68e967b (OAI)
Note
Validerad; 2006; 20061006 (pafi)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2017-11-24Bibliographically approved

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