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  • 1.
    Bosson, Emma
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Selroos, Jan-Olof
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Stigsson, Martin
    Gustafsson, Lars-Göran
    Destouni, Georgia
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Exchange and pathways of deep and shallow groundwater in different climate and permafrost conditions using the Forsmark site, Sweden, as an example catchment2012In: Hydrogeology Journal, ISSN 1431-2174, E-ISSN 1435-0157, Vol. 21, no 1, p. 225-237Article in journal (Refereed)
    Abstract [en]

    This study simulates and quantifies the exchange and the pathways of deep and shallow groundwaterflow and solute transport under different climate and permafrost conditions, considering the example field case of the coastal Forsmark catchment in Sweden. A number of simulation scenarios for different climate and permafrost condition combinations have been performed with the three-dimensional groundwater flow and transport model MIKE SHE. Results show generally decreasing vertical groundwater flow with depth, and smaller vertical flow under permafrost conditions than under unfrozen conditions. Also the overall pattern of both the vertical and the horizontal groundwater flow, and the water exchange between the deep and shallow groundwater systems, change dramatically in the presence of permafrost relative to unfrozen conditions. However, although the vertical groundwater flow decreases significantly in the presence of permafrost, there is still an exchange of water between the unfrozen groundwater system below the permafrost and the shallow groundwater in the active layer, via taliks. ‘Through taliks’ tend to prevail in areas that constitute groundwater discharge zones under unfrozen conditions, which then mostly shift to net recharge zones (through taliks with net downward flow) under permafrost conditions.

  • 2.
    Frampton, Andrew
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Painter, Scott L.
    Destouni, Georgia
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Permafrost degradation and subsurface-flow changes caused by surface warming trends2012In: Hydrogeology Journal, ISSN 1431-2174, E-ISSN 1435-0157, Vol. 21, no 1, p. 271-280Article in journal (Refereed)
    Abstract [en]

    Change dynamics of permafrost thaw, andassociated changes in subsurface flow and seepage into surface water, are analysed for different warming trends in soil temperature at the ground surface with a three-phase two-component flow system coupled to heat transport. Changes in annual, seasonal and extreme flows are analysed for three warming-temperature trends, representing simplified climate change scenarios. The results support previous studies of reduced temporal variability of groundwater flow across all investigated trends. Decreased intra-annual flow variability may thus serve asan early indicator of permafrost degradation before longer term changes in mean flows are notable. This is advantageous since hydrological data are considerably easier to obtain, may be available in longer time series, and generally reflect larger-scale conditions than direct permafrost observations. The results further show that permafrost degradation first leads to increasing water discharge, which then decreases as the permafrost degradation progresses further to total thaw. The most pronounced changes occur for minimum annual flows. The configuration considered represents subsurface discharge from a generic heterogeneous soil-type domain.

  • 3.
    Selroos, Jan-Olof
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Painter, Scott
    Effect of transport-pathway simplifications on projected releases of radionuclides from a nuclear waste repository (Sweden)2012In: Hydrogeology Journal, ISSN 1431-2174, E-ISSN 1435-0157, Vol. 20, no 8, p. 1467-1481Article in journal (Refereed)
    Abstract [en]

    The Swedish Nuclear Fuel and Waste Management Company has recently submitted an application for alicense to construct a final repository for spent nuclear fuel, at approximately 500m depth in crystalline bedrock. Migration pathways through the geosphere barrier are geometrically complex, with segments in fractured rock, deformation zones, backfilled tunnels, and near-surface soils. Several simplifications of these complex migration pathways were used in the assessments of repository performance that supported the license application. Specifically, in the geosphere transport calculations, radionuclide transport in soils and tunnels was neglected, and deformation zones were assumed to have transport characteristics of fractured rock. The effects of these simplifications on the projected performance of the geosphere barrier system are addressed. Geosphere performance is shown to be sensitive to how transport characteristics of deformation zones are conceptualized and incorporated into the model. Incorporation of advective groundwater travel time within backfilled tunnels reduces radiological dose from non-sorbing radionuclides such as I-129, while sorption in near-surface soils reduces radiological doses from sorbing radionuclides such as Ra-226. These results help quantify the degree to which geosphere performance was pessimistically assessed, and provide some guidance on how future studies to reduce uncertainty in geosphere performance may be focused.

  • 4.
    Sjöberg, Ylva
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Frampton, Andrew
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Lyon, Steve W.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Using streamflow characteristics to explore permafrost thawing in northern Swedish catchments2012In: Hydrogeology Journal, ISSN 1431-2174, E-ISSN 1435-0157, Vol. 21, no 1, p. 121-131Article in journal (Refereed)
    Abstract [en]

    The recent and rapid warming of the Arcticleads to thawing of permafrost, which influences andchanges subsurface water-flow systems in such landscapes.This study explores the utility of catchments as“sentinels of change” by considering long-term dischargedata from 17 stations on unregulated rivers in northernSweden and analyzing trends in annual minimum dischargeand recession flow characteristics. For the catchmentsconsidered, the annual minimum discharge hasincreased significantly (based on the Mann Kendall test ata 95% confidence level) in nine of the catchments anddecreased significantly in one catchment. Consideringchanges in recession-flow characteristics, seven catchmentsshowed significant trends consistent with permafrostthawing while two catchments showed significanttrends in the opposite direction. These results aremechanistically consistent with generic physically basedmodeling studies and the geological setting, as thecatchments considered span the spatial limit of permafrostextent. This study illuminates the potential for usinghydrologic observations to monitor changes in catchmentscalepermafrost. Further, this opens the door for researchto isolate the mechanisms behind the different trendsobserved and to gauge their ability to reflect actualpermafrost conditions at the catchment scale.

  • 5. Vidstrand, Patrik
    et al.
    Follin, Sven
    Selroos, Jan-Olof
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Swedish Nuclear Fuel and Waste Management Company (SKB), Sweden.
    Näslund, Jens-Ove
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Swedish Nuclear Fuel and Waste Management Company (SKB), Sweden.
    Groundwater flow modeling of periods with periglacial and glacial climate conditions for the safety assessment of the proposed high-level nuclear waste repository site at Forsmark, Sweden2014In: Hydrogeology Journal, ISSN 1431-2174, E-ISSN 1435-0157, Vol. 22, no 6, p. 1251-1267Article in journal (Refereed)
    Abstract [en]

    The impact of periglacial and glacial climate conditions on groundwater flow in fractured crystalline rock is studied by means of groundwater flow modeling of the Forsmark site, which was recently proposed as a repository site for the disposal of spent high-level nuclear fuel in Sweden. The employed model uses a thermal-hydraulically coupled approach for permafrost modeling and discusses changes in groundwater flow implied by the climate conditions found over northern Europe at different times during the last glacial cycle (Weichselian glaciation). It is concluded that discharge of particles released at repository depth occurs very close to the ice-sheet margin in the absence of permafrost. If permafrost is included, the greater part discharges into taliks in the periglacial area. During a glacial cycle, hydraulic gradients at repository depth reach their maximum values when the ice-sheet margin passes over the site; at this time, also, the interface between fresh and saline waters is distorted the most. The combined effect of advances and retreats during several glaciations has not been studied in the present work; however, the results indicate that hydrochemical conditions at depth in the groundwater flow model are almost restored after a single event of ice-sheet advance and retreat.

  • 6. Vidstrand, Patrik
    et al.
    Follin, Sven
    Selroos, Jan-Olof
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Näslund, Jens-Ove
    Rhén, Ingvar
    Modeling of groundwater flow at depth in crystalline rock beneath a moving ice-sheet margin, exemplified by the Fennoscandian Shield, Sweden2012In: Hydrogeology Journal, ISSN 1431-2174, E-ISSN 1435-0157, Vol. 21, no 1, p. 239-255Article in journal (Refereed)
    Abstract [en]

    On-going geological disposal programs for spent nuclear fuel have generated strong demands for investigation and characterization of deep-lying groundwater systems. Because of the long time scales for which radiological safety needs to be demonstrated in safety assessment applications, an analysis of the hydrogeological performance of the geosphere system during glacial climate conditions is needed. Groundwater flow at depth in crystalline rock during the passage of an ice-sheet margin is discussed based on performed groundwater-flow modeling of two bedrock sites, Forsmark and Laxemar, in the Fennoscandian Shield, Sweden. The modeled ice sheet mimics the Weichselian ice sheet during its last major advance and retreat over northern Europe. The paper elaborates and analyzes different choices of top boundary conditions at the ice sheet–subsurface interface (e.g. ice-sheet thickness and ice-margin velocity) and in the proglacial area (presence or lack of permafrost) and relates these choices to available groundwater-flow-model hydraulic output and prevailing conceptual hydrogeochemical models of the salinity evolution at the two sites. It is concluded that the choice of boundary conditions has a strong impact on results and that the studied sites behave differently for identical boundary conditions due to differences in their structural-hydraulic properties.

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