NDLI: Effects of tectonic structures, salt solution mining, and density-driven groundwater hydraulics on evaporite dissolution (Switzerland)

Content Provider	Springer Nature Link
Author	Zechner, Eric Konz, Markus Younes, Anis Huggenberger, Peter
Copyright Year	2011
Abstract	Subsurface dissolution (subrosion) of evaporites such as halite and gypsum can lead to extensive land subsidence. Recent land subsidences have been surveyed at six separate locations in northwestern Switzerland. The diameters of the affected surface areas range from 100 to 1,500 m, and corresponding subsidence rates reached more than 100 mm/year. Based on a geometrical model, three sites could be outlined where land subsidence can likely be attributed to salt solution mining. The effects of increased hydrostatic gradient due to both groundwater withdrawal and fluid density contrasts were evaluated in more detail for the remaining sites with a series of 2D density-coupled solute-transport simulations along an approximately 1,000-m-long and 150-m-deep 2D cross section. Simulation results indicate that the upconing process of saline groundwater into the main aquifer occurs under different distributions of subsurface parameters and hydraulic boundary conditions. For the presented setup, the simulations also revealed that the most sensitive factor for the dissolution rate is the structure or dip of the halite formation, which leads to an increase of dissolution rate with increasing dip. Due to the increased density of the brine, an intrinsic flow dynamic develops which follows the direction of the dip.La dissolution de subsurface (subrosion) d’évaporites telles la halite et le gypse peuvent conduire à une subsidence étendue du terrain. Des subsidences récentes ont été suivies sur six sites distincts au Nord-Ouest de la Suisse. Les diamètres des domaines affectés s’échelonnent de 100 à 1,500 m, et les taux de subsidence respectifs atteignent plus de 100 mm/an. Sur la base d’un modèle géométrique, trois sites ont pu être délimités où la subsidence peut vraisemblablement être attribuée à une cavitation par solution salée. Les effets d’un gradient hydrostatique, augmentés à la fois par prélèvement sur la nappe et contraste de densité de fluide, ont été évalués de façon plus détaillée sur d’autres sites avec une série de simulations 2D de transport de soluté couplé à la densité le long d’un profil 2D long de 1,000 m sur une hauteur de 150 m. Les résultats de la simulation indiquent que le processus de cavitation de l’eau saline de nappe à l’intérieur de l’aquifère principal se produit sous différentes conditions de paramètres de subsurface et conditions hydrauliques aux limites. Dans le cas présenté les simulations ont aussi révélé que le facteur le plus sensible du taux de dissolution est le pendage de la halite, qui conduit à un accroissement du taux de dissolution. En raison de l’accroissement de la densité de la saumure une dynamique intrinsèque d’écoulement se développe suivant la direction du pendage.La disolución subsuperficial (suberosion) de las evaporitas tales como halita y yeso pueden conducir a extensas subsidencias del terreno. Se han relevado recientes subsidencias del terreno en seis sitios en el noroeste de Suiza. Los diámetros de las áreas de las superficies afectadas varían desde 100 a 1,500 m, y los correspondientes ritmos de subsidencia alcanzaron más de 100 mm/año. Basado en un modelo geométrico, se pudieron esquematizar tres sitios donde la subsidencia del terreno puede probablemente ser atribuida a la minería de las soluciones salinas. Se evaluaron los efectos del gradiente hidrostático incrementado debido tanto a los contrastes de la extracción del agua subterránea y como de la densidad del fluido más detalladamente para los sitios restantes dentro de una serie de simulaciones 2D de transporte de soluto de densidad acoplada a lo largo de una sección transversal bidimensional de 1,000-m de longitud y 150-m de profundidad. Los resultados de la simulación indican que el proceso de ascenso vertical en forma de cono del agua subterránea salina en el acuífero principal ocurre bajo diferentes distribuciones de los parámetros subsuperficiales y las condiciones de contorno hidráulicas. Para la presente disposición las simulaciones también revelaron que el factor más sensitivo para el ritmo de disolución es la estructura y la inclinación de la formación de halita, lo que conduce a un incremento del ritmo de disolución con el incremento de la inclinación. Debido al incremento de la densidad de la salmuera se desarrolla un flujo intrínseco dinámico que sigue la dirección de la inclinación.A dissolução subsuperfícial (suberosão) de evaporitos, tais como a halite e o gesso, pode levar a um extenso processo de subsidência. Têm sido recentemente observados fenómenos de subsidência em seis diferentes locais na região noroeste da Suíça. Os diâmetros das áreas afectadas variam entre os 100 e os 1,500 m e as taxas de subsidência correspondentes atingem mais de 100 mm/ano. Com base num modelo geométrico, são apontados três locais onde a subsidência pode ser atribuída à mineração por dissolução de sal-gema. Os efeitos do aumento do gradiente hidráulico devido à extracção de água e ao contraste da densidade de fluidos foram avaliados em mais pormenor para os restantes locais, através de um modelo 2D de simulação de transporte de solutos de densidade-acoplada aplicado ao longo de uma secção transversal 2D com cerca de 1,000 m de comprimento e 150 m de profundidade. Os resultados das simulações indicam que o processo de ascensão de água subterrânea salina para o aquífero principal ocorre sob diferentes condições de parâmetros hidráulicos e diferentes condições fronteira. Para as condições analisadas, as simulações revelaram ainda que o factor mais sensível para a taxa de dissolução é a estrutura ou o pendor da formação de halite, levando a um aumento da taxa de dissolução com o aumento do pendor. Devido ao aumento de densidade da salmoura, desenvolve-se uma dinâmica de escoamento intrínseca, que segue a direcção do pendor.
Starting Page	1323
Ending Page	1334
Page Count	12
File Format	PDF
ISSN	14312174
Journal	Hydrogeology Journal
Volume Number	19
Issue Number	7
e-ISSN	14350157
Language	Portuguese
Publisher	Springer-Verlag
Publisher Date	2011-08-10
Publisher Institution	International Association of Hydrogeologists
Publisher Place	Berlin, Heidelberg
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Subrosion Tectonics Numerical modeling Density-driven solute transport Switzerland Waste Water Technology Water Pollution Control Water Management Aquatic Pollution Geology Hydrogeology
Content Type	Text
Resource Type	Article
Subject	Earth and Planetary Sciences Water Science and Technology

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