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Impact of landscape topography and quaternary overburden on the performance of a geological repository of nuclear waste
KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
2008 (English)In: Nuclear Technology, ISSN 0029-5450, E-ISSN 1943-7471, Vol. 163, 165-179 p.Article in journal (Refereed) Published
Abstract [en]

The topographical driving forces for groundwater on different spatial scales in several ways influence the performance of a repository for nuclear waste located at large depth in crystalline bedrock. We show that the relation between local topographical characteristics (topographical steepness and wavelengths) in the area of a repository (kilometer scale) and the large-scale (hundreds of kilometers) surroundings, together with repository depth, are the primary controls of residence time distributions and the discharge pattern of radionuclides released from an underground repository. In addition, the topography affects the groundwater flow at repository depth and, therefore, influences the long-time degradation of the repository. In the areas studied, all located in Sweden, the local topography mainly controls the groundwater flow down to a depth of ∼500 m, which is the suggested depth of the Swedish repository. The importance of the large-scale topography increases with depth but even at depth where local-scale topography is dominant, the continental-scale topography affects length and depth of flow paths as well as groundwater velocities. The impact of large-scale topography is particularly clear in areas where the steepness of local-scale landforms is relatively small. The study also shows that quaternary deposits (bedrock overburden) may have a significant impact on the overall residence times in the underground because of their hydraulic and sorption properties. This effect is fiirther enhanced by the fact that flow paths originating from repository depth generally emerge in topographical lows with relatively deep layers of quaternary deposits. The findings of this study underscore the need to consider multiscale topographical characteristics as well as bedrock overburden in assessments of radiological consequences of underground repositories.

Place, publisher, year, edition, pages
2008. Vol. 163, 165-179 p.
Keyword [en]
Nuclear waste repository; Quaternary overburden; Topography
National Category
Water Engineering
Identifiers
URN: urn:nbn:se:kth:diva-11168ISI: 000257277400017Scopus ID: 2-s2.0-50549091633OAI: oai:DiVA.org:kth-11168DiVA: diva2:236803
Note
QC 20100802Available from: 2009-09-25 Created: 2009-09-25 Last updated: 2017-12-13Bibliographically approved
In thesis
1. Topographic Control of Groundwater Flow
Open this publication in new window or tab >>Topographic Control of Groundwater Flow
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Gravity is the main driving force for groundwater flow, and both landscape topography and geology distribute the effects of gravity on groundwater flow.  The groundwater table defines the distribution of the potential energy of the water. In humid regions where the bedrock permeability is relatively low and the soil depth is sufficiently shallow, the groundwater table closely follows the landscape topography and, thus, the topography controls the groundwater circulation in these regions. In this thesis, I investigate multi-scale topography-controlled groundwater flow, with the goal of systematizing the spatial distribution of groundwater flow and assessing geological parameters of importance for groundwater circulation.  Both exact solutions and numerical models are utilized for analyzing topography-controlled groundwater flow. The more complex numerical models are used to explore the importance of various simplifications of the exact solutions. The exact solutions are based on spectral representation of the topography and superpositioning of unit solutions to the groundwater flow field. This approach is an efficient way to analyze multi-scaled topography-controlled groundwater flow because the impact of individual topographic scales on the groundwater flow can be analyzed separately.  The results presented here indicate that topography is fractal and affects groundwater flow cells at wide range of spatial scales. We show that the fractal nature of the land surface produces fractal distributions of the subsurface flow patterns. This underlying similarity in hydrological processes also yields a single scale-independent distribution of subsurface water residence times which have been found in distributions of solute efflux from watersheds. Geological trends modify the topographic control of the groundwater circulation pattern and this thesis presents exact solutions explaining the impact of geological layering, depth-decaying and anisotropic hydraulic conductivity on the groundwater flow field. For instance, layers of Quaternary deposits and decaying permeability with depth both increase the importance of smaller topographic scales and creates groundwater flow fields where a larger portion of the water occupies smaller and shallower circulation cells, in comparison to homogeneous systems.

Abstract [sv]

Gravitationen är den mest betydelsefulla drivkraften för grundvattenströmning. Topografin och geologin fördelar vattnets potentiella energi i landskapet. Grundvattenytans läge definierar vattnets potentiella energi, vilket är ett randvillkor för grundvattnets strömningsfält. I humida områden med en relativt tät berggrund och tillräckligt tunna jordlager, följer grundvattenytan landskapets topografi. Därav följer att grundvattenströmningen är styrd av topografin i dessa områden. I denna avhandling belyser jag den flerskaliga topografistyrda grundvattenströmningen. Min målsättning har varit att kvantitativt bestämma grundvattenströmningens rumsliga fördelning samt att undersöka hur olika geologiska parametrar påverkar grundvattencirkulationen. Jag har använt såväl numeriska modeller som analytiska lösningar, för att undersöka hur topografin styr grundvattenströmningen. De numeriska modellerna är mer komplexa än de analytiska lösningarna och kan därför användas för att undersöka betydelserna av olika förenklingar som finns i de analytiska lösningarna. De analytiska lösningarna är baserade på spektralanalys av topografin, samt superponering av enhetslösningar, där varje enhetslösning beskriver hur en specifik topografisk skala påverkar grundvattnets strömningsfält. Detta är ett effektivt tillvägagångssätt för att undersöka flerskaliga effekter av topografin, eftersom påverkan av varje enskild topografisk skala kan studeras separat. Resultaten som presenteras indikerar att topografin är fraktal och att den ger upphov till cirkulationsceller av varierande storlek som även dessa är av en fraktal natur. Denna grundläggande fördelning i grundvattnets strömningsfält ger upphov till att grundvattnets uppehållstid i marken följer ett självlikformigt mönster och kan förklara uppmätta tidsvariationer av lösta ämnens koncentrationer i vattendrag efter regn. Geologiska trender påverkar hur grundvattenströmningen styrs av topografin. De exakta lösningar som presenteras här, beskriver hur geologiska lager samt djupavtagande och anisotropisk hydraulisk konduktivitet påvekar grundvattnets strömning. Exempelvis är betydelsen av mindre topografiska skalor viktigare i områden med kvartära avlagringar och en berggrund med djupavtagande konduktivitet, än i områden med homogen bergrund utan kvartära avlagringar. Dessutom är en större andel strömmande vatten belägen närmare markytan i de förstnämnda områdena.

Place, publisher, year, edition, pages
Stockholm: KTH, 2009. xiv, 44 p.
Series
Trita-LWR. PHD, ISSN 1650-8602 ; 1052
Keyword
Groundwater, Modeling, Topography, Spectral analysis, Fourier series, Exact solu-tions, Multi-scale, Grundvatten, Modellering, Topografi, Spektralanalys, Fourier serier, Analytisk lösning, Flerskalig
National Category
Oceanography, Hydrology, Water Resources Other Environmental Engineering
Identifiers
urn:nbn:se:kth:diva-11153 (URN)978-91-7415-377-4 (ISBN)
Public defence
2009-10-14, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20100802Available from: 2009-09-25 Created: 2009-09-23 Last updated: 2010-08-02Bibliographically approved

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