Abstract The volcanic Trindade Island is a remote Brazilian offshore territory in the South Atlantic, located ca. 1.140 kilometers east of the southeast coast of Brazil. The island’s permanent exposure to geological hazards requires assessment. However, the lack of erosion and landslides temporal data impedes predictive geohazard analyses. Therefore, we compiled pre-existing data from nautical charts and surveyed the surface terrain on Trindade Island to generate Digital Terrain Models (DTMs) and comparative accuracy analyses. The DTM based on pre-existing data shows the lowest accuracy (root mean square error - RMSE: 12.3 m) yet is adequate for regional studies. In contrast, the DTM developed from real-time kinematic global navigation satellite systems (RTK-GNSS) has the highest vertical accuracy (RMSE: 0.48 m), but spatial variability of ground elements was underestimated and limited to meter-sized (and larger) elements. The DTM obtained using the unmanned aerial vehicle (UAV) with ground control points (GCP), on the other hand, presented lower accuracy (RMSE: 2.37 m) than the RTK-GNSS model but still allowed observation of centimetric (and larger) ground features. For geohazard assessment on Trindade Island, models that allow fine-scale studies are needed. A UAV with GCP provides such standards and proved to be the most viable option in remote and complex sites as well. Hence, this study, the first to allow multi-temporal analysis of geohazard assessment on Trindade Island, offers a viable solution for similar analyses in other remote locations.

RESUMO O objetivo deste trabalho foi avaliar a eficiência de diferentes modelos para estimar as taxas de infiltração de água nos tipos de solo Ferralic Arenosols e Rhodic Ferralsols localizados na região sudeste do Brasil, assim como a influência de nove tipos de uso do solo e práticas de manejo na modelagem da infiltração. A parametrização dos modelos foi realizada ajustando-se 42 curvas experimentais de infiltração obtidas em campo por meio do infiltrômetro tipo duplo anel. As propriedades básicas do solo das condições de infiltração foram determinadas por meio de ensaios laboratoriais. Os resultados foram avaliados usando estatística descritiva e indicadores de acurácia (coeficiente de eficiência de Nash e Sutcliffe e erro quadrático médio). Os modelos investigados simularam satisfatoriamente as taxas de infiltração e o modelo mais acurado foi o de Kostiakov modificado, seguido do Horton; Singh e Yu; Holtan modificado; Holtan; Philip; Green e Ampt/Mein e Larson e Kostiakov. Os diferentes tipos de usos da terra e práticas de manejo do solo afetam significativamente as taxas de infiltração, principalmente nas combinações que apresentam macroporosidade, que resultou em um comportamento errático da infiltração e afetou a acurácia dos modelos de infiltração.

ABSTRACT The efficiency and suitability of different models to estimate infiltration rates in Ferralic Arenosols and Rhodic Ferralsols in southern Brazil are evaluated in this paper. The influence of nine types of land use and soil management practices on infiltration modeling is also assessed. Model parameterization was performed fitting 42 experimental infiltration curves obtained by in situ tests with a double-ring infiltrometer. Soil characterization was also performed in laboratory. The results were assessed using basic statistical descriptors and model accuracy indicators (Nash and Sutcliffe efficiency coefficient and root mean square error). The investigated models satisfactorily simulated the infiltration rates and the most accurate model was modified Kostiakov, followed by the Horton; Singh and Yu; modified Holtan; Holtan; Philip; Green and Ampt/Mein and Larson and Kostiakov. Different types of land uses and soil management practices significantly affect the infiltration rates, mainly those combination with great presence of macroporosity that resulted in an erratic infiltration behavior and affected the infiltration model accuracy.

RESUMEN El factor de retardo (Rd) es uno de los principales parámetros para el transporte de solutos. Su valor puede variar significativamente dependiendo del método utilizado para su determinación. En este artículo, el Rd del sodio se determina experimentalmente utilizando columnas de suelo arenoso no perturbado, para comparar cuatro métodos de determinación de Rd y evaluar el impacto del método elegido en la predicción del movimiento de sodio. Se realizaron experimentos en muestras de suelo no perturbado y análisis analítico. Los resultados mostraron que el suelo tiene doble porosidad y caminos preferenciales. Las curvas de llegada estaban de acuerdo con las características físicas del suelo. Los valores de Rd variaron de 1.7 a 7.77 dependiendo de la concentración inicial y del método utilizado. Estas diferencias surgen del modelo conceptual de cada método de determinación de Rd. El análisis experimental y analítico indicó que cuanto mayor es la Rd, más lento es el movimiento. Los métodos que mejor reprodujeron el movimiento de sodio obtenido en el laboratorio fueron las isotermas de Ogata y Banks (1961), Langmuir y Freundlich. Los modelos de predicción presentaron errores más pequeños con el aumento de la concentración inicial. En estos casos, las concentraciones pronosticadas pueden sobreestimarse hasta un 22,5% cuando se utiliza un método no adecuado. Estos resultados sugieren que el método de determinación de Rd puede afectar fuertemente la predicción del movimiento de sodio. Debido a eso, al determinar Rd, es de vital importancia evaluar cada método y cómo pueden ser adecuados para el suelo bajo investigación.

ABSTRACT The retardation factor (Rd) is one of the main important solute transport parameters. Its value can vary significantly depending on the method used for its determination. In this paper, the sodium Rd is experimentally determined using undisturbed sandy soil columns to compare four methods of Rd determination and assess the impact of the chosen method on the prediction of sodium movement. Column experiments in undisturbed soil samples and analytical analysis were performed. The results showed that the soil has dual-porosity and preferential pathways. The breakthrough curves were in accordance with the soil’s physical characteristics. The Rd values ranged from 1.7 to 7.77 depending on the initial concentration and on the method used. These differences arise from the conceptual model of each Rd determination method. The experimental and analytical analysis indicated that the higher the Rd, the slower the movement. The methods that best reproduced the laboratory sodium movement were Ogata and Banks’ (1961), Langmuir and Freundlich’s isotherms. The prediction models presented smaller errors with the increase of the initial concentration. In these cases, the predicted concentrations can be overestimated up to 22.5 % when using a not suitable method. These results suggest that the Rd determination method can strongly affect the prediction of the sodium movement. Because of that, it is of vital importance to evaluate each method and how they can be adequate for the soil under investigation when determining Rd.

Apresentam-se, nesse artigo, os resultados da avaliação da alteração de diferentes litotipos basálticos (basaltos densos, basaltos vesículo-amigdaloidais e brecha basáltica). As amostras analisadas são oriundas de quatro derrames basálticos da Formação Serra Geral, da região das obras da barragem de Itaipu. Nesse trabalho, são apresentados a classificação do grau de alteração, análises em microscópio digital 200X e ensaios de pH, de condutividade elétrica e de compressão pontual. Os resultados mostraram que os valores de pH e de condutividade elétrica são significativos na avaliação do grau de alteração, especialmente quando as classificações tátil-visuais e de resistência não refletem com tanta precisão esse parâmetro.

This paper presents the results of an evaluation of the weathering of different basaltic lithotypes (dense basalts, vesicular-amygdaloidal basalts, and basaltic breccias) from four basaltic flows of the Serra Geral Formation of the Itaipu Dam region. Samples were classified according to their degree of weathering based on analysis with a 200X digital microscope and were subjected to pH, electrical conductivity, and point-load strength tests. The results show that pH and electrical conductivity values are effective for the evaluation of weathering, especially when tactile-visual classification does not provide an accurate evaluation of the rock's different degrees of weathering.

O transporte de poluentes líquidos e gasosos, em meios geológicos porosos, depende das características físicas e químicas dos materiais inconsolidados, rochas, águas, assim como das características dos poluentes. Entre essas características, os aspectos da sorção têm importância fundamental e são função da mineralogia e respectivas proporções, pH, Eh e das características dos vazios. Na região de São Carlos, centro leste do Estado de São Paulo, Brasil, ocorrem 2 tipos de materiais inconsolidados, sendo um residual dos arenitos com cimento constituído de finos e, secundariamente, argilitos, siltitos e conglomerados da Formação Itaqueri, de idade cretácea, e outro sedimento arenoso de idade terciária. Esses materiais geológicos constituem as bases de muitos locais onde são lançados produtos químicos, caracterizados como fontes de poluição difusa ou pontual, e, por este motivo, foi desenvolvido um estudo para avaliá-los quanto aos aspectos de sorção para alguns cátions inorgânicos que são freqüentes nessas fontes, em concentrações variadas. Para tal, foram caracterizados ainda quanto ao peso específico dos sólidos, granulometria, mineralogia e índices físico-químicos. Para avaliar os aspectos de sorção, foram desenvolvidos ensaios de equilíbrio em lote (Batch Test), utilizando soluções químicas de KCl, ZnCl2 e CuCl.H2O, considerando três valores de pH para as soluções constituídas pelos materiais inconsolidados e as espécies químicas, assim como a mistura das três soluções.

The transport of liquid and gaseous pollutants through porous geological media depends on the physical and chemical characteristics of the unconsolidated material, rocks and water, associated with the characteristics of the pollutants. Of these characteristics, the sorption aspect is of fundamental importance and is a function of the mineral proportions, pH, Eh and void aspects encountered in the porous media. In the São Carlos region, located in the eastern-central part of the State of São Paulo, Brazil, there are basically two types of unconsolidated materials: the first is a residual from sandstones cemented with fines and the secondarily composed of claystones, siltstones and conglomerates from the Cretaceous Period that constitute the Itaqueri Formation; the second is a sandy sediment of the Tertiary Period. These geological conditions are found in areas where chemical products are disposed of, characterized as either diffuse or point pollutions sources. Because of this situation, a study was developed to evaluate the sorption aspects of some inorganic cations that are frequently found in these sources, in varied concentrations. Taken into consideration were their physical/chemical properties, such as: specific weight, grain size, mineralogy, cationic exchange capacity, pH, hydraulic conductivity. Batch tests were run using solutions of KCl, ZnCl2 and CuCl.H2O at three different pH values, and then with a combined solution (KCl + ZnCl2 + CuCl.H2O), also at three different pH values.