Showing papers by "Philippe Davy published in 2006"
TL;DR: In this paper, the authors define the scaling nature of fracture networks that is likely quantified by power-law length distributions whose exponent fixes the contribution of large fractures versus small ones, and define the flow models, including equivalent permeability, that are appropriate for multiscale fracture networks.
Abstract: Abstract The paper aims at defining the flow models, including equivalent permeability, that are appropriate for multiscale fracture networks. As a prerequisite of the flow analysis, we define the scaling nature of fracture networks that is likely quantified by power-law length distributions whose exponent fixes the contribution of large fractures versus small ones. Despite the absence of any characteristic length scale of the power-law model, the flow structure appears to contain three length scales at the very maximum: the connecting scale, the channelling scale, and the homogenization scale, above which the equivalent permeability tends to a constant value. These scales, including their existence, depend on the fracture length distribution and on the transmissivity distribution per fracture. They are basic in defining the flow properties of fracture networks.
79 citations
TL;DR: The connection between the Ebro basin and the Mediterranean Sea has been investigated in this paper, showing that this connection did not exist before the Messinian salinity crisis but is effective from the Pliocene because of progressive regressive erosion.
57 citations
TL;DR: In this article, the authors used the ros model to simulate both erosional and depositional processes in rivers and obtained the best fit between numerical results and geological data for a nonlinear relation between incision and drainage area and for a small transport length of sediment.
Abstract: [1] After a base level drop, rivers are the first components of the landscape to respond by incising into topography. A base level drop results in a knickpoint in the downstream part of river longitudinal profiles. Whether knickpoints are preserved or erased during the upstream propagation of incision is still debated. Preservation and erasure of knickpoints are two end-member processes that work in natural systems at different timescales, different length scales, and different places. The huge (1500 m) and fast (tens of kiloyears) sea level drop in the Mediterranean during the Messinian resulted in the fast propagation of incision far inland. This is especially the case in the Rhone Valley (southern France) where the knickpoint is 300 km from the Mediterranean coast. Numerical modeling of this event has been performed using the ros model, which simulates both erosional and depositional processes in rivers. The best fit between numerical results and geological data is obtained for a nonlinear relation between incision and drainage area and for a small transport length of sediment. This small transport length, at least 2 orders of magnitude lower than the length of the Rhone, suggests that the longitudinal profile relaxed in a diffusive way, so that the initial knickpoint was not preserved. Finally, after a base level fall, the propagation of fluvial incision is very fast at geological timescales (hundreds of kiloyears). Despite this, the diffusive response implies that the time required for restoration of an equilibrium profile is very long.
51 citations
TL;DR: In this paper, the chemical evolution of water during the exploitation of a fractured aquifer in a NO3-rich agricultural environment was studied, and the changes in SO42 and NO3 were attributed to the development of equilibrium between the physical flow parameters and the chemical kinetics of autotrophic denitrification processes.
50 citations
TL;DR: It is proposed that the database structure could be used as a template for designing databases for complex sites, such that any type of geolocalized data obtained from wells, hydrological stations, and meteorological stations can be handled.
Abstract: In most cases, analysis and modeling of flow and transport dynamics in ground water systems require long-term, high-quality, and multisource data sets. This paper discusses the structure of a multisite database (the H+ database) developed within the scope of the ERO program (French Environmental Research Observatory, http://www.ore.fr). The database provides an interface between field experimentalists and modelers, which can be used on a daily basis. The database structure enables the storage of a large number of data and data types collected from a given site or multiple-site network. The database is well suited to the integration, backup, and retrieval of data for flow and transport modeling in heterogeneous aquifers. It relies on the definition of standards and uses a templated structure, such that any type of geolocalized data obtained from wells, hydrological stations, and meteorological stations can be handled. New types of platforms other than wells, hydrological stations, and meteorological stations, and new types of experiments and/or parameters could easily be added without modifying the database structure. Thus, we propose that the database structure could be used as a template for designing databases for complex sites. An example application is the H+ database, which gathers data collected from a network of hydrogeological sites associated with the French Environmental Research Observatory.
39 citations
TL;DR: In this paper, the authors derived the angular correction that has to be applied to borehole fracture intensities to recover the actual three-dimensional distribution when the fracture networks have a length distribution.
Abstract: We derive the angular correction that has to be applied to borehole fracture intensities to recover the actual three-dimensional distribution when the fracture networks have a length distribution. We assume that the fracture intensity is calculated from the fractures that fully transect the core. Because of the length distribution, the classical Terzaghi correction, which involves the cosine of fracture dip, is no longer valid. Solutions have been calculated in the specific case of fractal fracture networks with power law length distribution. We show that the Terzaghi correction may significantly overestimate the frequency of fractures subparallel to the borehole. The correction procedure proposed here was tested on a fracture database recorded at a study site for a repository of spent nuclear fuel located in SE Sweden, with three outcrop maps and three boreholes. A consistency between the dip distributions of outcrops and boreholes was achieved when applying the angular correcting term calculated with the power law length distribution deduced from outcrop maps.
36 citations
Journal Article•
TL;DR: In this article, the authors investigated the effect of rainstorms and monoculture on Burgundian vineyards, which induced a high level of erosion in the arable soil layer.
Abstract: Burgundian vineyards are affected by erosion phenomena that induce sediment transfer along hillslopes. The vineyard under study has occupied the western Bressan rift border for 1000 years, benefiting from marly limestone bedrock and its silt-sand covering. The combined effects of rainstorms and monoculture on slopes reaching 25°, induce a high level of erosion in the arable soil layer. Quantification of erosion rates on a pluri-decennial scale, using vine roots'as a palaeo-surface marker, has been performed on three parcels on three sites along the Cotes-de-Nuits and Cotes-de-Beaune. Assessed erosion rates of around 1 mm.yr-1 characterise current erosive dynamics involving a critical situation for soil sustainability, and consequently for terroir conservation.
18 citations
01 Jan 2006
TL;DR: In this article, the authors define the scaling nature of fracture networks that is likely quantified by power-law length distributions whose exponent fixes the contribution of large fractures versus small ones, and define the flow models, including equivalent permeability, that are appropriate for multiscale fracture networks.
Abstract: The paper aims at defining the flow models, including equivalent permeability, that are appropriate for multiscale fracture networks. As a prerequisite of the flow analysis, we define the scaling nature of fracture networks that is likely quantified by power-law length distributions whose exponent fixes the contribution of large fractures versus small ones. Despite the absence of any characteristic length scale of the power-law model, the flow structure appears to contain three length scales at the very maximum: the connecting scale, the channelling scale, and the homogenization scale, above which the equivalent permeability tends to a constant value. These scales, including their existence, depend on the fracture length distribution and on the transmissivity distribution per fracture. They are basic in defining the flow properties of fracture networks.
3 citations