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Temperature-driven groundwater convection in cold climates
Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Arkitektur och vatten.
Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Arkitektur och vatten.ORCID-id: 0000-0001-7144-9778
Rekke forfattare: 22016 (engelsk)Inngår i: Hydrogeology Journal, ISSN 1431-2174, E-ISSN 1435-0157, Vol. 24, nr 5, s. 1245-1253Artikkel i tidsskrift (Fagfellevurdert) 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.

sted, utgiver, år, opplag, sider
2016. Vol. 24, nr 5, s. 1245-1253
HSV kategori
Forskningsprogram
Vattenteknik
Identifikatorer
URN: urn:nbn:se:ltu:diva-5568DOI: 10.1007/s10040-016-1420-0ISI: 000380090000013Scopus ID: 2-s2.0-84965070759Lokal ID: 3b2b798a-1169-414f-b7ce-a3133e98639bOAI: oai:DiVA.org:ltu-5568DiVA, id: diva2:978442
Merknad

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

Tilgjengelig fra: 2016-09-29 Laget: 2016-09-29 Sist oppdatert: 2018-07-10bibliografisk kontrollert
Inngår i avhandling
1. Secondary currents in groundwater
Åpne denne publikasjonen i ny fane eller vindu >>Secondary currents in groundwater
2017 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
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.

sted, utgiver, år, opplag, sider
Luleå: Luleå University of Technology, 2017. s. 70
Serie
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
Emneord
Groundwater
HSV kategori
Forskningsprogram
Vattenteknik
Identifikatorer
urn:nbn:se:ltu:diva-66411 (URN)978-91-7790-006-1 (ISBN)978-91-7790-007-8 (ISBN)
Disputas
2017-12-15, F1031, Luleå, 10:00 (engelsk)
Opponent
Veileder
Tilgjengelig fra: 2017-11-14 Laget: 2017-11-11 Sist oppdatert: 2018-01-13bibliografisk kontrollert

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