Ninth International Conference on Permafrost ... - IARC Research

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Modeling Permafrost Evolution and Impact on Hydrogeology at the Meuse/Haute-Marne Sedimentary Site (Northeast France) During the Last 120,000 YearsVanessa Teles, Emmanuel Mouche, Christophe Grenier, Damien RegnierLaboratoire des Sciences du Climat et de l’Environnement, UMR CEA-CNRS-UVSQ, FranceJacques Brulhet, Hakim BenaberrahmaneAndra, Agence nationale pour la gestion des déchets radioactifs, FranceIntroductionThe Callovo-Oxfordian layer in the eastern part of theParisian Basin (France) was recognized as a potential nuclearwaste repository layer. To evaluate transfers from the hostformation to the biosphere, it is important to understand thetemporal evolution of the hydraulic boundary conditions ofthe clayey layer, which means to understand the evolution ofthe whole hydrogeological system. The Callovo-Oxfordianunit is part of the Parisian Basin consisting of piled upsedimentary units ranging over thousands of meters indepth at maximum and covering the northern half of France.Besides this specific sedimentary geological structure, pastpermafrost extension differs from Nordic situations, becauseice cover remained here very limited in time and depth soonfollowed by a cold and dry steppic landscape.A few years ago, Andra (National Agency for NuclearWaste Management) launched a research program on thegeoprospective of the MHM (Meuse/Haute-Marne) site,including the study of the impact of glacial cycles on theunderground flow patterns (Andra 2005, Andra 2004,Brulhet 2004).Recent efforts to study the impact of permafrost onunderground flow patterns, modeling of permafrost extensionthrough geological times as well as on going activities, arereported here involving the LSCE (Laboratoire des Sciencesdu Climat et de l’Environnement) team. This work followsa former phase of pure hydrological modeling of the MHMsite.The studies conducted at LSCE are presented here along3 major issues: (1) impact of permafrost reconstruction onhydrogeology during the last 120,000 years; (2) 3D thermalmodeling of permafrost extensions based on solar radiationevolution (120,000-year period); and (3) coupled thermohydrologicalmodeling and role of small-scale surface andsubsurface units (valley vs. hill, river, lake, aquifer).The thermal and hydrodynamic simulations have beenperformed with the Cast3M code, developed and implementedby the CEA (Atomic Energy Commission), using finiteelementor mixed hybrid finite-element formulations.The extension of the modeled zone is 75 km x 80 km,involving the actual present-time topography and rivers, aswell as geological layers (from bottom to surface: Dogger,Callovo-Oxfordien, Oxfordien-Calcaire, Kimmérigien,Cretacé-Barrois) corresponding for the latter to roughly a500 m depth.Impact of Permafrost Reconstruction onHydrogeology During the Last 120,000 YearsThe idea behind this first modeling phase (refer to Teles& Mouche 2005) consists in taking reconstructions ofpermafrost extensions over the last 100,000 years, transferit into permeability information, and simulate transient flowon the MHM domain with adequate boundary conditions.More precisely, reconstructions from Van Vliet (2004)concerning the MHM region were considered. They involvefive development stages with associated time periods:present conditions for 10,000 years BP, installation of athin permafrost (starting 95 BP), permafrost on hills withfree valleys (from 75,000 years BP on), thick continuouspermafrost (starting 20,000 years BP), relict permafrost(from 13,000 years BP). Three-dimensional simulationsof transient flow were conducted starting from initialconditions close to present state. Freezing causes a stop inthe infiltration as permafrost develops, so surface boundaryconditions are changed from imposed heads assumed closeto the local altitude to no flow conditions. Furthermore, the3D permeability field is modified to account for the presenceof permafrost. Practically speaking, permeability tensors areassociated with each mesh element corresponding verticallyto harmonic mean between permafrost permeability(arbitrary put at 10 -13 m/s) and actual geological formationpermeability; horizontally, arithmetic mean was considered.Consequently, vertical flow is limited, whereas horizontalflow is directly a function of the vertical fraction of unfrozenformation thickness.Results show that the flow velocities are reduced ascompared with present-state conditions in all geologicalformations during permafrost phases. This is the result of thestop in the recharge as well as reduction in the permeability.Flow velocity in the aquifers not directly concernedthemselves by freezing is roughly reduced by a factor oftwo.It should be stressed here, nevertheless, that conditionsinferred at the MHM site for the last glacial cycle are verydifferent from conditions reconstructed for more Nordiclocations, where the ice thickness was large and lead to amechanical load onto the geological units. Consequently,increased pressure boosted access of water to deeper zones,though recharge from the surface was actually stopped. Thesituation at the MHM site is considered best represented asa mere stop in recharge, leading to a pure aquifer drainagesituation for deeper units.311
Ni n t h In t e r n at i o n a l Co n f e r e n c e o n Pe r m a f r o s t3D Thermal Modeling of PermafrostExtensions from Solar Radiation Evolution(Last 120,000 Years)In a second step (refer to Teles & Mouche 2006), focuswas put on the modeling of transient evolution of permafrostextension. Former 3D geometrical features were retainedfor a thermal modeling approach and identical 100,000-yeartime period. A purely conductive model was consideredwith actual geological formation thermal properties,imposed bottom geothermal flux, and transient imposedsurface temperature. The latter followed the normalizedvariation in solar radiation over the time period accordingto Berger (1978). The modeling of permafrost extensionwas attempted considering the following refined points: (1)Imposed surface temperature was made dependant fromthe actual altitude and incident solar radiation (Šafanda1999). (2) Ground level solar radiation was considereddependant on incident solar radiation, topographic slope andsurface orientation (Senkova & Rontu 2003). (3) Imposedsurface temperature was affected a positive correction whencorresponding to a river mesh to account for heat exchangeresulting in the reduction of permafrost development underrivers (the coefficient was chosen constant and its valueassessed based on model sensitivity analysis). Simulationresults were finally compared to a vertical reconstruction of0°C isotherm for a deep borehole location. These referencevalues correspond to a best expert view resulting from insitu analysis, naturalistic considerations, as well as 1Dvertical thermal modeling including phase change effects(cf. Courbouleix et al. 1998).This study remains preliminary in the sense that the 3Dmodel was not further complexified to account for phasechangephenomena and heat advection due to water flow.This is attempted in the third modeling phase. Nevertheless,results show that qualitative evolution of the 0°C isothermcould be well simulated, although quantitative fit requiresbetter constraints on the solar radiation forcing history. Thisis a critical point, since literature shows that uncertaintiesin solar radiation histories resulting from existing scenariosremain large, whereas the sensitivity of the thermal model tothis input data is very large. For two models considered in thestudy only differing roughly by a factor of two, permafrostextensions were very different. Consequently, care should beput in the future in increasing the robustness of this forcingterm.including topographic variability (valleys vs. hills); and(3) addressing the issue of spatial and temporal upscaling(e.g., periodic thermal stress, daily, yearly, cycles) to achieveregional modeling for a 120,000-year time period.These efforts will serve to organize the various mechanismsinto a hierarchy, and finally improve the physical andnumerical modeling of the impact of glacial cycles on thehydrogeology at the MHM site over geological time scales.ReferencesAndra. 2005. Dossier 2005. Argile, Référentiel du site deMeuse / Haute-Marne, Tome 3. Document Andra n°C.RP.ADS.04.0022.B.Andra. 2004. Site Meuse/Haute-Marne, Géothermie.Inventaire des nouvelles données. Note TechniqueAndra n° C.NT.ASMG.04.0001.Berger, A. 1978. Long-term variations of daily insolationand Quaternary climatic changes. Journal of theAtmospheric Sciences 35(12): 2362-2367.Brulhet, J. 2004. L’évolution géodynamique (tectoniqueet climatique) et son impact sur l’hydrogéologieet l’environnement de surface. Site MHM. NoteTechnique Andra n° C.NT.ASMG.03.106.B: 84 pp.Courbouleix, S., Gros, Y., Clet, M., Coutard, J.P., Lautridou,J.P., Van Vliet-Lanoe, B., Dupas, A. & Cames-Pintaux,A.M. 1998. Simulation de la profondeur du pergélisolau cours du dernier cycle climatique. Utilisation deséchantillons du sondage EST106, Rapport Andra n°D.RP.0ANT.98.011.Šafanda, J, 1999. Groundwater surface temperature asa function of slope angle and slope orientation.Tectonophysics 306: 367-375.Senkova, A.V. & Rontu, L. 2003. A Study of the RadiationParametrization for Sloping Surfaces. St. Petersburg:Baltic HIRLAM Worshop, 79-82.Teles, V. & Mouche, E. 2005. Analyse de sensibilité de laprésence d’un pergélisol continu et discontinu surl’hydrogéologie du secteur, Site MHM. RapportAndra n° C.RP.12CEA.05.001.Teles, V. & Mouche, E. 2006. Site MHM, Modélisationtridimensionnelle de la distribution du pergélisolau cours d’un cycle climatique. Rapport Andra n°C.RP.12CEA.06.001.Van Vliet-Lanoë, B. 2004. Modèle conceptuel du pergélisol,Site MHM. Rapport Andra n° C.RP.0UST.04.002.Coupled Thermo-Hydrological Modeling ofSmall-Scale UnitsOngoing efforts consist in (1) developing a coupledTH (Thermo-Hydro) numerical model within our Cast3Mcode including thermal conduction, convection, and phasechange; (2) answering the issue of the level of heat fluxactually transmitted to the underground while consideringvarious surface- and subsurface-specific units leading toheat exchange like water bodies (river, lake, aquifer), or312
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ContentsPreface ...................
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Mapping and Modeling the Distributi
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Satellite Observations of Frozen Gr
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xiiIce Wedge Thermal Regime in Nort
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xivPermafrost Response to Dynamics
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NICOP SponsorsUniversitiesUniversit
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Deep Permafrost Studies at the Lupi
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Effect of Fire on Pond Dynamics in
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Cryological Status of Russian Soils
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Acoustical Surveys of Methane Plume
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Permafrost Delineation Near Fairban
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Preparatory Work for a Permanent Ge
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A Provisional Soil Map of the Trans
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Martian Permafrost Depths from Orbi
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Time Series Analyses of Active Micr
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Impact of Permafrost Degradation on
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DC Resistivity Soundings Across a P
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Modeling Thermal and Moisture Regim
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A Provisional Permafrost Map of the
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Alpine Permafrost Distribution at M
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Cryogenic Formations of the Caucasu
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Modeling Potential Climatic Change
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A Hypothesis: A Condition of Growth
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Modeled Continual Surface Water Sto
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Freeze/Thaw Properties of Tundra So
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Discontinuous Permafrost Distributi
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Thermal Regime Within an Arctic Was
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Seasonal and Interannual Variabilit
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Twelve-Year Thaw Progression Data f
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Continued Permafrost Warming in Nor
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Landsliding Following Forest Fire o
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A Permafrost Model Incorporating Dy
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Seasonal Sources of Soil Respiratio
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Greenland Permafrost Temperature Si
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The Importance of Snow Cover Evolut
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The Account of Long-Term Air Temper
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The Combined Isotopic Analysis of L
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Adaptating and Managing Nunavik’s
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Human Experience of Cryospheric Cha
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HiRISE Observations of Fractured Mo
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A Soil Freeze-Thaw Model Through th
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Mapping and Modeling the Distributi
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First Results of Ground Surface Tem
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Historical Changes in the Seasonall
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Rock Glaciers in the Kåfjord Area,
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Snowpack Evolution on Permafrost, N
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Climate Change in Permafrost Region
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Maximizing Construction Season in a
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Pleistocene Sand-Wedge, Composite-W
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