117,333 research outputs found
Rio Quequén Grande basin (Argentina): impact of geological, environmental and human activities on water quality
No full textIn spite of the low urbanization and industrialization density of the Rio Quequén Grande basin, the socio-economical development of the last decades has produced a high environmental impact with a degradation of the water resources. This degradation is progressively increasing in intensity and expanding towards more internal zones of the basin. In the present research, we carried out a geochemical characterization of the superficial and underground water of Rio Quequén Grande basin. The Rio Quequén Grande drainage area is about 10.000 km2, located in the south-eastern sector of the Buenos Aires Province. It mainly consists of a flat environment of Quaternary aeolian
sediments and it flows into the Atlantic Ocean close to Necochea, the principal city within the area. The superficial waters of the principal fluvial branches and the groundwater of the Rio Quequén Grande basin have been sampled during the end of the 2001
and the beginning of the 2002. For the determination of the geochemical composition of the water resources samples from the superficial hydrographic network and wells
were collected and analysed in the laboratory. In particularly, a) electrical conductivity, temperature and pH have been measured in situ; b) Mg++, Ca++, Cl-, SO4- -and NO3-
anions and cations have been measured using spectrophotometer methods and c) Al, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Se, Mo, Ag, Cd, Pb, and U have been measured using a ICP-MS standard procedure. The integrated analysis of the obtained geochemical results allows us to infer the following: a) The geological setting has a strong influence on the water geochemical composition. b) The intense anthropogenic activity (predominantly
farming) heavily contribute to the environmental resource quality. c) The high-risk pollution zones have been recognised. In particular the water analyses show high variations of the physico-chemical characteristics. Also, near the river outlet, Cl
values of about 700 mg/l can be observed due to the intrusion of oceanic salty water.
d) In some of these locations a remarkably high concentration of toxic elements was found. Among those, the arsenic content reaches a concentration higher than 100 μg/l in the north-eastern sector of the hydrographic basin principally due to the lithological
composition of the Quaternary deposits locally rich in grains of volcanic origin
Caratterizzazione qualitativa dei sedimenti del Fiume Quequen Grande, Argentina
No full textIl più esteso deposito eolico dell’emisfero sud, che ricopre una superficie di circa 1.1x106 Km2, è la
regione dei loess argentini, compresi tra la latitudine 20° e 40° Sud, a cui appartiene l’area “pampeana
bonaerense” che riveste particolare interesse nello studio della genesi dei loess e degli eventi paleoclimatici
pleistocenici - olocenici. Particolarmente interessante è lo studio mineralogico-petrografico e
geochimico del bacino idrografico del Quequén Grande (Fig. 1), che, all’interno della regione “pampeana
bonaerense”, occupa circa 10.000 km2 del settore Sud-Est della provincia di Buenos Aires.
I loess argentini sono depositi quaternari che hanno registrato le variazioni paleoambientali tra i periodi
glaciali ed interglaciali in un territorio non soggetto ad importanti eventi deformativi e tettonici il cui
studio geologico, sedimentologico, petrografico e geochimico dei sedimenti e delle acque può contribuire
a chiarire gli effetti delle variazioni climatiche sul pianeta, e permettere l’identificazione di eventuali
marker paleoclimatici. Problematiche e metodi di approccio
Il presente studio del Fiume Quequén Grande è articolato nella caratterizzazione mineralogico-petrografica
di sedimenti fluviali e delle acque prelevati in corrispondenza di sezioni fluviali selezionate
per l’analisi e lo studio della dinamica fluviale (Teruggi et al., 2003). Tale indagine è finalizzata anche
alla definizione dell’impatto antropico e dello stato ambientale del bacino attraverso l’analisi dei sedimenti
fluviali e delle risorse idriche superficiali. Si ricorda che il bacino del Fiume Quequén Grande dal
punto di vista socioeconomico, fa parte di una delle pianure più produttive del mondo, soggetta ad attività
agricola intensiva. Inoltre l’analisi delle variazioni composizionali dei sedimenti può contribuire
alla formulazione dei fattori di rischio idrogeologico e sanitario in un’area costituita da sedimenti fortemente
erodibili coinvolti sempre di più frequentemente da eventi di inondazioni che spesso hanno
compromesso attività produttive e causato perdite di rilevanza economica. Vengono in più affrontati lo
studio dei processi di formazione del loess e delle relazioni fra le variazioni composizionali, tessiturali
e petrografiche dei sedimenti. Essendo un bacino di ambiente di pianura di origine eolica per apporti
extra bacinali costanti nel tempo (ad eccezione di piccoli apporti locali limitati a affluenti di piccola
estensione del settore settentrionale del bacino), eventuali differenze composizionali forniscono interessanti
informazioni sulla genesi del loess e di eventuali variazioni negli apporti, e quindi un contributo
ad un tema fin ad ora poco sviluppato nella letteratura scientifica
Sedimentology of a pseudomeandering river: the Cecina R. (central Italy)
No full textThe study reports about the result of a field investigation on the geomorphology and sedeimntology of a pseudomeandering river. A five phases model of bar evolution is proposed and discussed
Sedimentology of a pseudomeandering river (Cecina R., central Italy)
No full textPseudomeandering rivers (Wolman & Brush, 1961; Hickin, 1969) or wandering rivers (Church, 1983; Ferguson & Werrity, 1983; Desloges & Church, 1987) have not been studied in as much detail as other river morphologies and hence they are not well known. In recent decades, only a few studies have been carried out on them (Wolman & Brush, 1961; Church, 1983; Ferguson & Werrity, 1983; Desloges & Church, 1987). CANCELLARE LA FRASE 2 LASCIARE LA BIBLIOGRAFIA CHE SOSTIENE LA FRASE 3. Some authors considered pseudomeandering rivers as an unstable stage of transition between braided and meandering morphologies. By this assumption, even a very small variation in the hydraulics, sediment supply or structural setting would determine a change in the channel pattern. According to this hypothesis, pseudomeandering morphology should be just an exceptional, rare case. However, modern examples of pseudomeandering rivers are very common in the Northern Apennines (Orcia R., Ombrone R., Cornia R., Albegna R., Sieve R., Arno R., Cecina R.) as they were in the Pleistocene Valdarno basin (Billi et al., 1987)
Geomorphology and sediment transport in a very low relief catchment: R. Quequén Grande, Argentina
No full textThe aim of this work was to identify the geomorphological units
within the drainage network of the Rio Quequén Grande low relief basin,
situated in the southeast section of the province of Buenos Aires, and to
quantify the present sediment transport rate. For this purpose field surveys and
satellite images were analysed. The former included measurement of bed
material grain size and channel hydraulic geometry, in order to set up a bed
and a suspended load measurement programme. Six main geomorphic units
were identified: Ranges, Perirange Aeolian Hillocks, Hillocks with Lagoons,
Relic Hills, a Poor Drainage Alluvial Plain and an Alluvial Plain. Bed load
discharge and suspended sediment concentration measured during a bankfull
flood are very low, given the relatively high stream power of 287 W m-1. The
measured bed load discharge was three to five orders of magnitude lower than
six applied bed load equations, presumably due to low sediment availability
Geochemical characterization of the bed sediments of the Rio Quequen catchment, Argentina
No full textThe aim of this study was to conduct geochemical analyses of mud bed sediments and the superficial waters of the Rio Quequén Grande catchment, located in the southeast section of the province of Buenos
Aires. The Rio Quequén Grande outflow into the Atlantic Ocean, near the city of Necochea. The river has cut its
channel into aeolian deposits (loess and reworked loess). Most of the catchment consists of a flat plain.
Bed sediments and superficial water were sampled along the drainage network of the Rio Quequén Grande
catchment.
The mud bottom sediments were analyzed to determine the major and trace elements, using the Ray-X fluorescence (X RF) method and loss on ignition (LOI). Together with the analyzed samples, the composition of other
samples of Argentinian loess and the composition of the Upper Continental Crust (UCC) were also plotted. They
revealed considerable compositional variation.
The sample analysis also showed compositional differences as regards grain size. The samples from the Rio
Quequén Grande are of sedimentary origin, as are the majority of loess deposits in the world.
The main cations and anions of the superficial water were analyzed. In some samples a remarkably high concentration of toxic elements was found. Of these, the concentration of the arsenic content is higher than 100 μg/l
in the northeastern sector of the hydrographic basin, principally due to the lithological composition of the
Quaternary deposits, which are locally rich in grains of volcanic origin.
The integrated analysis of the geochemical results allows us to conclude that the geological setting has a strong
influence on the geochemical composition of the sediment and water. The major zones with a pollution risk were
identifie
RAPID AND LOW-COST PHOTOGRAMMETRIC SURVEY OF HAZARDOUS SITES, FROM MEASUREMENTS TO VR DISSEMINATION
No full textIn the field of geomatics, the development of 3D surveying techniques that can produce dense point clouds and high-resolution three-dimensional models has opened the possibility of using these techniques to generate digital replicas of a given asset to be used in contexts of cultural promotion or entertainment.These non-traditional applications have been made easier by the spreading of low-cost but fast surveying techniques, allowing them to be used in contexts or projects with fewer resources. Close-range photogrammetry is nowadays the cheapest, most flexible, and fastest technique that can be used to produce high-resolution and high-quality digital copies of reality. In this paper, we present an application of the Ant3D multi-camera system, a novel photogrammetric device designed for the rapid 3D surveying of sites characterized by poor accessibility and narrow spaces. The paper describes the three-dimensional acquisition of underground tunnels in a hazardous abandoned mining site. The digitalisation work aims to create 3D models to be experienced safely in a virtual- or augmented- reality immersive navigation of the site for cultural promotion. A workflow is proposed to turn raw reality-based 3D models into refined and efficient 3D assets that can be exploited in a game engine. Applications for mobile devices, desktop, and VR headsets, using the produced 3D assets are described.</p
Geochemical characterization of bed sediments of the Rio Quequén Grande catchment, Argentina
No full textThe aim of this study was to conduct geochemical analyses of mud bed sediments and the superficial waters of the Rio Quequén Grande catchment, located in the southeast section of the province of Buenos Aires. The Rio Quequén Grande outflow into the Atlantic Ocean, near the city of Necochea. The river has cut its channel into aeolian deposits (loess and reworked loess). Most of the catchment consists of a flat plain. Bed sediments and superficial water were sampled along the drainage network of the Rio Quequén Grande catchment. The mud bottom sediments were analyzed to determine the major and trace elements, using the Ray-X fluorescence (X RF) method and loss on ignition (LOI). Together with the analyzed samples, the composition of other samples of Argentinian loess and the composition of the Upper Continental Crust (UCC) were also plotted. They revealed considerable compositional variation. The sample analysis also showed compositional differences as regards grain size. The samples from the Rio Quequén Grande are of sedimentary origin, as are the majority of loess deposits in the world. The main cations and anions of the superficial water were analyzed. In some samples a remarkably high concentration of toxic elements was found. Of these, the concentration of the arsenic content is higher than 100 μg/l in the northeastern sector of the hydrographic basin, principally due to the lithological composition of the Quaternary deposits, which are locally rich in grains of volcanic origin. The integrated analysis of the geochemical results allows us to conclude that the geological setting has a strong influence on the geochemical composition of the sediment and water. The major zones with a pollution risk were identified
The Rio Quequen Grande basin (Argentina): geochemical characterization of the fluvial system (sediment and water).
No full textThe presentation reports about the geomorphological, hydrological and sediment characteristics of teh Rio Quequen in Argentina. This river is characterised by a very low relief ratio and a very low streambed gradient. Flow discharge and sedimeent transport measurement were made, the data obtained are anlysed and the results discussed
Monitoring and numerical modelling of riverbank erosion processes: a case study along the Cecina River (central Italy)
No full textRiverbank retreat along a bend of the Cecina River, Tuscany (central Italy) was monitored across a near annual cycle (autumn 2003 to summer 2004) with the aim of better understanding the factors influencing bank changes and processes at a seasonal scale. Seven flow events occurred during the period of investigation, with the largest having an estimated return period of about 1·5 years. Bank simulations were performed by linking hydrodynamic, fluvial erosion, groundwater flow and bank stability models, for the seven flow events, which are representative of the typical range of hydrographs that normally occur during an annual cycle. The simulations allowed identification of (i) the time of onset and cessation of mass failure and fluvial erosion episodes, (ii) the contributions to total bank retreat made by specific fluvial erosion and mass-wasting processes, and (iii) the causes of retreat. The results show that the occurrence of bank erosion processes (fluvial erosion, slide failure, cantilever failure) and their relative dominance differ significantly for each event, depending on seasonal hydrological conditions and initial bank geometry. Due to the specific planimetric configuration of the study bend, which steers the core of high velocity fluid away from the bank at higher flow discharges, fluvial erosion tends to occur during particular phases of the hydrograph. As a result fluvial erosion is ineffective at higher peak discharges, and depends more on the duration of more moderate discharges. Slide failures appear to be closely related to the magnitude of peak river stages, typically occurring in close proximity to the peak phase (preferentially during the falling limb, but in some cases even before the peak), while cantilever failures more typically occur in the late phase of the flow hydrograph, when they may be induced by the cumulative effects of any fluvial erosion
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