Multiphase gas transport in a shear zone

In the post-operational phase of a Low/Intermediate-Low radioactive waste repository, gas will be generated in the caverns due to anaerobic corrosion of metals, and also chemical and microbial degradation of organic substances. Previous investigations on gas migration have indicated that discrete water conducting features (e.g. shear zones) are mainly responsible for gas transport from the caverns through the geosphere. Two phase flow processes occur in these water conducting features; the continuity and spatial distribution of pore spaces, the pore size distribution and the interfacial forces of the three phases gas-water-rock have a significant influence on gas transport.The main difficulties to be resolved when simulating two-phase flow processes in fractured rock are:- The description of the internal heterogeneity of the individual water conducting features. The influence of channelling along preferential flow paths is even more important than for single phase fluid flow, because gas transport takes place more or less exclusively along the most transmissive channels. - The determination of effective mass exchange coefficients of the relevant components of the system. Mass exchange may occur between three phases (gas-water-rock). It depends on the spatial distribution of water and gas along the water conducting features (i.e. specific surface of contact areas between phases), and on the solubility and diffusivity of the different components, but also on a couple of state variables of liquid phase (initial content of dissolve/free gas, initial pressure).The work presented in this thesis aims to improve the understanding of the physics of single and multiphase transport phenomena, to be able to develop a quantitative description of gas transport in shear zones to overcome in a satisfactory way the problems described above.Postprint (published version

Multiphase gas transport in a shear zone

In the post-operational phase of a Low/Intermediate-Low radioactive waste repository, gas will be generated in the caverns due to anaerobic corrosion of metals, and also chemical and microbial degradation of organic substances. Previous investigations on gas migration have indicated that discrete water conducting features (e.g. shear zones) are mainly responsible for gas transport from the caverns through the geosphere. Two phase flow processes occur in these water conducting features; the continuity and spatial distribution of pore spaces, the pore size distribution and the interfacial forces of the three phases gas-water-rock have a significant influence on gas transport.The main difficulties to be resolved when simulating two-phase flow processes in fractured rock are:- The description of the internal heterogeneity of the individual water conducting features. The influence of channelling along preferential flow paths is even more important than for single phase fluid flow, because gas transport takes place more or less exclusively along the most transmissive channels. - The determination of effective mass exchange coefficients of the relevant components of the system. Mass exchange may occur between three phases (gas-water-rock). It depends on the spatial distribution of water and gas along the water conducting features (i.e. specific surface of contact areas between phases), and on the solubility and diffusivity of the different components, but also on a couple of state variables of liquid phase (initial content of dissolve/free gas, initial pressure).The work presented in this thesis aims to improve the understanding of the physics of single and multiphase transport phenomena, to be able to develop a quantitative description of gas transport in shear zones to overcome in a satisfactory way the problems described above

A front-fixing method for American option pricing on zero-coupon bond under the Hull and White model

ABSTRACT: A new efficient numerical method is proposed for valuation of American option on zero-coupon bond using Hull and White model. By applying the front-fixing transformation suggested by Holmes and Yang, the original free boundary problem is transformed into a new fixed boundary partial differential equation (PDE) problem, where the optimal stopping boundary is one of the unknowns of the problem. The numerical finite difference scheme for the transformed problem is constructed. Stability and convergence rate is studied empirically. Numerical simulation of the computation of both the option price and the optimal stopping boundary are illustrated with examples and the comparison with the Hull and White tree method.This work has been partially supported by the Ministerio de Ciencia, Innovación y Universidades, Spanish grant MTM2017-89664-P

Stochastic simulation of daily rainfall fields conditioned on atmospheric circulation patterns and orographic effects.

The objective of the current work is to present a methodology for simulation of stochastic spatial distributed rainfall fields at the daily time step. For this purpose, we develop a geo-stochastic rainfall generating process (SRGP) to generate spatially distributed rainfall fields at daily time scale, that respect the spatial correlation structure of historically observed precipitation, while taking into account important factors that influence the development of observed spatial patterns. For each day, a spatially distributed rainfall field is generated from a pre-specified SRGP, selected based on atmospheric synoptic conditions relevant for that day. Each SRGP is simulated by applying the concept of double kriging, as the product of the spatial amount of rainfall and the spatial occurrence of rainfall by sequential simulation (sequential Gaussian simulation and sequential indicator simulation respectively). The SRGP can account for spatial rainfall nonstationarity related to orographic effects, and can be incorporated as part of a downscaling technique in the context of climate change impact studies. A case study for the Upper Guadiana basin (Spain) is presented that shows the ability of the method to reproduce various spatio-temporal characteristics of precipitation.Peer ReviewedPostprint (published version

The Recharge Channels of the Sierra Nevada Range (Spain) and the Peruvian Andes as Ancient Nature-Based Solutions for the Ecological Transition

Nature-Based Solutions for Integrated Water Resources Management (NbS-IWRM) involve natural, or nature-mimicking, processes used to improve water availability in quantity and quality sustainably, reduce the risks of water-related disasters, enhance adaptation to climate change and increase both biodiversity and the social-ecological system’s resilience. United Nations and the European Commission promote their research as a cornerstone in the changeover to the Ecological Transition. In the Sierra Nevada range (Spain) and the Andean Cordillera, there is a paradigmatic and ancestral example of NbS-IWRM known as “careo channels” and “amunas”, respectively. They recharge slope aquifers in mountain areas and consist of an extensive network of channels that infiltrate the runoff water generated during the snow-thawing and rainy season into the upper parts of the slopes. The passage of water through the aquifers in the slope is used to regulate the water resources of the mountain areas and thus ensure the duration of water availability for the downstream local population and generate multiple ecosystem services. This form of water management is known asWater Sowing and Harvesting (WS&H). As shown in this work, it is a living example of a resilience and climate change adaptation tool that can be qualified as a nature-based solution.Organismo Autonomo Parques Nacionales from the Ministerio para la Transicion Ecologica y el Reto Demografico SPIP202102741 2768/2021Ibero-American Science and Technology for Development Programme (CYTED) 419RT0577"Severo Ochoa" extraordinary grants for excellence IGME-CSIC AECEX202

Isotopic and hydrogeochemical characterization of high-altitude karst aquifers in complex geological settings. The Ordesa and Monte Perdido National Park (Northern Spain) case study.

The Ordesa and Monte Perdido National Park, located in the Southern Pyrenees, constitutes the highest karst system in Western Europe. No previous studies regarding its geochemical and isotopic groundwater characterization are available in this area. This work presents the results of field and sampling campaigns carried out between July 2007 and September 2013. The groundwater presents high calcium bicarbonate contents due to the occurrence of upper Cretaceous and lower Paleocene-Eocene carbonate materials in the studied area. Other relevant processes include dissolution of anhydrite and/or gypsum and incongruent dissolution of Mg-limestone and dolomite. The water stable isotopes (δ18O, δ2H) showthat the oceanic fronts from the Atlantic Ocean are responsible for the high levels of precipitation. In autumn, winter, and spring, a deuterium excess is found in the rechargewater,which could be related to local atmospheric transport of low-altitude snow sublimation vapour and its later condensation on the snowsurface at higher altitude,where recharge ismostly produced. The recharge zones are mainly between 2500mand 3200ma.s.l. The tritiumcontent of the water suggests short groundwater transit times. The isotopic composition of dissolved sulphate points to the existence of regional fluxes mixed with local discharge in some of the springs. This work highlights the major role played by the altitude difference between the recharge and discharge zones in controlling the chemistry and the vertical variability of the isotopic composition in high-altitude karst aquifers

Vertical variation in the amplitude of the seasonal isotopic content of rainfall as a tool to jointly estimate the groundwater recharge zone and transit times in the Ordesa and Monte Perdido National Park aquifer system, north-eastern Spain

The time series of stable water isotope composition relative to meteorological stations and springs located in the high mountainous zone of the Ordesa and Monte Perdido National Park are analyzed in order to study how the seasonal isotopic content of precipitation propagates through the hydrogeological system in terms of the aquifer recharge zone elevation and transit time. The amplitude of the seasonal isotopic composition of precipitation and the mean isotopic content in rainfall vary along a vertical transect, with altitudinal slopes for d18O of 0.9‰/km for seasonal amplitude and - 2.2‰/km for isotopic content. The main recharge zone elevation for the sampled springs is between 1950 and 2600 m·a.s.l. The water transit time for the sampled springs ranges from 1.1 to 4.5 yr, with an average value of 1.85 yr and a standard deviation of 0.8 yr. The hydrological system tends to behave as a mixing reservoir.Peer ReviewedPostprint (author's final draft

Contribution of isotopic research techniques to characterize highmountain-Mediterranean karst aquifers: The Port del Comte (Eastern Pyrenees) aquifer.

Water resources in high mountain karst aquifers are usually characterized by high rainfall, recharge and discharge that leads to the sustainability of the downstream ecosystems. Nevertheless, these hydrological systems are vulnerable to the global change impact. The mean transit time (MTT) is a key parameter to describe the behavior of these hydrologic systems and also to assess their vulnerability. This work is focused on estimating MTT by using water stable isotopes in the framework of high-mountain karst systems with a very thick unsaturated zone (USZ). To this end, it is adapted to alpine zones an existing methodology that combines in a row a semi-distributed rainfall-runoff model used to estimate recharge time series, and a lumped-parameter model to obtain through a convolution integral. The methodology has been applied to the Port del Comte Massif (PCM) hydrological system (Southeastern Pyrenees, NE Spain), a karst aquifer system with an overlying1000 m thick USZ. Six catchment areas corresponding to most important springs of the system are considered. The obtained results show that hydrologically the behavior of the system can be described by an exponential flow model (EM), with MTT ranging between 1.9 and 2.9 years. These values are shorter than those obtained by considering a constant recharge rate along time, which is the easiest and most applied aquifer recharge hypothesis when estimating through lumped-parameter models. This methodology can be useful to improve the characterization and understanding of other high mountain karst aquifers with an overlying thick USZ that are common in many alpine zones elsewhere the globe

Identification of Natural and Anthropogenic Geochemical Processes Determining the Groundwater Quality in Port del Comte High Mountain Karst Aquifer (SE, Pyrenees)

The Port del Comte Massif (SE, Pyrenees) contains one of the most important vulnerable and strategic karst aquifers for supplying freshwater to the city of Barcelona (Spain). It is a fragile system, whose possible environmental impact is highly conditioned by land use. To improve the hydrogeological knowledge of the system, between September 2013 and October 2015, a detailed fieldwork was carried out for the revision of the geological model, the inventory of water points, and the in situ physico-chemical characterization on major elements and isotopes of up to a total of 43 springs, as well as precipitation water. This paper focuses on the characterization of the geochemical processes that allow explanation of the observed chemical variability of groundwater drained by the pristine aquifer system to determine the origin of salinity. The results show that the main process is the dissolution of calcite and dolomite, followed by gypsum and halite, and a minor cation exchange-like process. Sulfur and oxygen isotopes from dissolved sulfate in the studied springs point out a geogenic origin related to the dissolution of gypsum from Triassic and Tertiary materials, and that the contribution from anthropogenic sources, like fertilizers, is lower. Nitrate in groundwater is not an important issue, with a few localized cases related with agricultural activities. The multidisciplinary approach has allowed the development of a consistent hydrogeological conceptual model of the functioning of the aquifer system, which can be replicated in other places to understand the geogenic character of the hydrogeochemistry

Improvement on the bound of Hermite matrix polynomials

In this paper, we introduce an improved bound on the 2-norm of Hermite matrix polynomials. As a consequence, this estimate enables us to present and prove a matrix version of the Riemann-Lebesgue lemma for Fourier transforms. Finally, our theoretical results are used to develop a novel procedure for the computation of matrix exponentials with a priori bounds. A numerical example for a test matrix is provided. © 2010 Elsevier Inc. All rights reserved.This work has been partially supported by the Universidad Politecnica de Valencia under project PAID-06-07/3283 and the Generalitat Valenciana under project GVPRE/2008/340.Defez Candel, E.; Tung, MM.; Sastre, J. (2011). Improvement on the bound of Hermite matrix polynomials. Linear algebra and its applications. 434(8):1910-1919. https://doi.org/10.1016/j.laa.2010.12.015S19101919434