Hydrological connectivity of alluvial Andean valleys: a groundwater/surface-water interaction case study in Ecuador

The Andean region is characterized by important intramontane alluvial and glacial valleys; a typical example is the Tarqui alluvial plain, Ecuador. Such valley plains are densely populated and/or very attractive for urban and infrastructural development. Their aquifers offer opportunities for the required water resources. Groundwater/surface-water (GW–SW) interaction generally entails recharge to or discharge from the aquifer, dependent on the hydraulic connection between surface water and groundwater. Since GW–SW interaction in Andean catchments has hardly been addressed, the objectives of this study are to investigate GW–SW interaction in the Tarqui alluvial plain and to understand the role of the morphology of the alluvial valley in the hydrological response and in the hydrological connection between hillslopes and the aquifers in the valley floor. This study is based on extensive field measurements, groundwater-flow modelling and the application of temperature as a groundwater tracer. Results show that the morphological conditions of a valley influence GW–SW interaction. Gaining and losing river sections are observed in narrow and wide alluvial valley sections, respectively. Modelling shows a strong hydrological connectivity between the hillslopes and the alluvial valley; up to 92 % of recharge of the alluvial deposits originates from lateral flow from the hillslopes. The alluvial plain forms a buffer or transition zone for the river as it sustains a gradual flow from the hills to the river. Future land-use planning and development should include concepts discussed in this study, such as hydrological connectivity, in order to better evaluate impact assessments on water resources and aquatic ecosystems.     

Kinematic significance of mingling-rolling structures in lava flows: a case study from Porri Volcano (Salina, Southern Tyrrhenian Sea)

 A basaltic andesite lava flow from Porri Volcano (Salina, Southern Tyrrhenian Sea) is composed of two different magmas. Magma A (51 vol.% of crystals) has a dacitic glass composition, and magma B (18 vol.% of crystals), a basaltic glass composition. Magma B is hosted in A and consists of sub-spherical enclaves and boudin-like, banding and rolling structures (RS). Four types of RS have been recognized: σ–type;δ–type; complex σ-δ–types and transitional structures between sub-spherical enclaves and rolling structures. An analysis of the RS has been performed in order to reconstruct the flow kinematics and the mechanism of flow emplacement. Rolling structures have been selected in three sites located at different distances from the vent. In all sites most RS show the same sense of shear. Kinematic analysis of RS allows the degree of flow non-coaxiality to be determined. The non-coaxiality is expressed by the kinematic vorticity number Wk, a measure of the ratio Sr between pure shear strain rate and simple shear strain rate. The values of Wk calculated from the measured shapes of microscopic RS increase with increasing distance from the vent, from approximately 0.5 to 0.9. Results of the structural analysis reveal that the RS formed during the early–intermediate stage of flow emplacement. They represent originally sub-spherical enclaves deformed at low shear strain. At higher strain, RS deformed to give boudin-like and stretched banding structures. Results of the kinematic analysis suggest that high viscosity lava flows are heterogeneous non-ideal shear flows in which the degree of non-coaxiality increases with the distance from the vent. In the vent area, deformation is intermediate between simple shear and pure shear. Farther from the vent, deformation approaches ideal simple shear. Lateral extension processes occur only in the near-vent zone, where they develop in response to the lateral push of magma extruded from the vent. Lateral shortening processes develop in the distal zone and record the gravity-driven movement of the lava. The lava flow advanced by two main mechanisms, lateral translation and rolling motion. Lateral translation equals rolling near the vent, while rolling motion prevailed in the distal zones. Received: 6 November 1997 / Accepted: 29 November 1997     

Mechanisms for ground-surface fracturing and incipient slope failure associated with the 2001 eruption of Mt. Etna, Italy: analysis of ephemeral field data

During the July–August 2001 eruption of Mt. Etna development of extensional fractures/faults and grabens accompanied magma intrusion and subsequent volcanic activity. During the first days of the eruption, we performed an analysis of attitude, displacement and propagation of fractures and faults exposed on the ground surface in two sites, Torre del Filosofo and Valle del Leone, located along the same fracture system in the region surrounding the Valle del Bove depression on the eastern flank of Mt. Etna. Fractures and faults formed as the consequence of a shallow intruding dyke system that fed the several volcanic centres developed along the fracture system. The investigated sites differ in slope attitude and in geometrical relationships between fractures and slopes. In particular, the fracture system propagated parallel to the gentle slope (<7° dip) in the Torre del Filosofo area, and perpendicular to the steep slope (25° dip) in the Valle del Leone area. In the Torre del Filosofo area, slight graben subsidence and horizontal extension of the ground surface by about 3 m were recorded. In the Valle del Leone area, extensional faulting forming a larger and deeper graben with horizontal extension of the ground surface by about 10 m was recorded. For the Valle del Leone area, we assessed a downhill dip of 14° for the graben master fault at the structural level beneath the graben where the fault dip shallows. These results suggest that dyke intrusion at Mount Etna, and particularly in the region surrounding the Valle del Bove depression, may be at the origin of slope failure and subsequent slumps where boundary conditions, i.e. geometry of dyke, slope dip and initial shear stress, amongst others, favour incipient failures.     

Simulating Oxygen Intrusion into Highly Heterogeneous Fractured Media Using High Performance Computing

Fractured crystalline rocks are under consideration by several countries as host formations for high-level nuclear waste repositories. The redox evolution in these host rock formations is an important issue for the stability and safety of these disposal sites. If, for example, during a glaciation/deglaciation event, oxygen-rich glacial meltwater penetrates to the depth of the planned repository, some of the engineered barriers would be adversely affected. Moreover, oxidizing conditions would increase the solubility and mobility of many radionuclides. Reactive transport simulations, which are typically used to assess the redox buffering capacity of these host rock formations, are computationally demanding, and thus, calculations for the evaluation of oxygen penetration are usually carried out over simplified geometries and the heterogeneity of the site, both physical (e.g., variability in the groundwater flow field and the kinematic porosity) and mineralogical (e.g., variability in the abundance of Fe(II)-bearing minerals), is usually represented in a simplified fashion. Here, it is shown how a recently developed numerical framework, combined with high performance computing technologies, allows the full geometrical, physical and mineralogical complexity of the site under study to be efficiently included in these types of reactive transport calculations. A synthetically generated realistic three-dimensional fractured medium is used to assess oxygen penetration patterns and their dependence on both the hydrogeological conditions and the availability of Fe(II)-bearing minerals. The results of the calculations point out the significant influence of both physical and mineralogical heterogeneity on the oxygen penetration patterns, thus highlighting the importance of a model parameterisation consistent with the site complexity.     

Benchmarking the software packages to model and assess the seismic response of unreinforced masonry existing buildings through nonlinear static analyses

Bulletin of Earthquake Engineering - Seismic modelling of unreinforced masonry (URM) buildings is addressed worldwide according to different approaches, not only at research level, but also in the...     

Nonlinear modeling of the seismic response of masonry structures: critical review and open issues towards engineering practice

Bulletin of Earthquake Engineering - This paper provides a comphrensive review of the critical aspects of nonlinear modeling for evaluating the seismic response of masonry structures, emphasizing...     

Cost–benefit analysis of flood mitigation measures: a case study employing high-performance hydraulic and damage modelling

Natural Hazards - This paper shows a detailed, advanced procedure to implement cost–benefit analyses (CBAs) in order to assess the effectiveness of flood mitigation measures. The town of Lodi...