Made available in DSpace on 2015-03-13T17:08:29Z (GMT). No. of bitstreams: 1 JesimaelAS.pdf: 2490132 bytes, checksum: 0f657a274eca483047a74fdbb2b8e032 (MD5) Previous issue date: 2000-04-13 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / Geological and geophysical studies (resistivity, self potential and VLF) were undertaken in the Tararaca and Santa Rita farms, respectively close to the Santo Ant?nio and Santa Cruz villages, eastern Rio Grande do Norte State, NE Brazil. Their aim was to characterize water acummulation structures in crystalline rocks. Based on geological and geophysical data, two models were characterized, the fracture-stream and the eluvio-alluvial through, in part already described in the literature. In the Tararaca Farm, a water well was located in a NW-trending streamlet; surrounding outcrops display fractures with the same orientation. Apparent resistivity sections, accross the stream channel, confirm fracturing at depth. The VLF profiles systematically display an alignment of equivalent current density anomalies, coinciding with the stream. Based on such data, the classical fracture-stream model seems to be well characterized at this place. In the Santa Rita Farm, a NE-trending stream display a metric-thick eluvioregolith-alluvial cover. The outcropping bedrock do not present fractures paralell to the stream direction, although the latter coincides with the trend of the gneiss foliation, which dips to the south. Geophysical data confirm the absence of a fracture zone at this place, but delineate the borders of a through-shaped structure filled with sediments (alluvium and regolith). The southern border of this structure dips steeper compared to the northern one. This water acummulation structure corresponds to an alternative model as regards to the classical fracture-stream, being named as the eluvio-alluvial trough. Its local controls are the drainage and relief, coupled with the bedrock weathering preferentially following foliation planes, generating the asymmetry of the through / O Estado do Rio Grande do Norte apresenta extensas ?reas onde se sobrep?em clima semi-?rido e terrenos cristalinos. Algumas destas ?reas apresentam cobertura relativamente espessa de solo, o que dificulta ainda mais os trabalhos de loca??o de po?os (para extra??o de ?gua subterr?nea) pelo m?todo tradicional que ? baseado na an?lise de fotografias a?reas e geologia de superf?cie. Esse conjunto de fatos faz com que o ?ndice de insucesso das loca??es seja da ordem de 30%. Este trabalho descreve os resultados de estudos estruturais e geof?sicos, realizados em tr?s localidades do estado, com o objetivo de caracterizar as estruturas acumuladoras de ?gua subterr?nea no cristalino, de modo a compor uma base interpretativa que permita aumentar o ?ndice de sucesso das loca??es de po?os. Os trabalhos estruturais envolveram a coleta de dados de fraturas e folia??es e os trabalhos de geof?sica est?o baseados em dados de eletro-resistividade, potencial espont?neo e VLF(Very Low Frequency). A interpreta??o integrada dos dados estruturais e geof?sicos evidenciou que o modelo riacho-fenda n?o se constitui no modelo ?nico de acumula??o de ?gua no cristalino. Constatou-se a exist?ncia de outra estrutura, muito promissora ao ac?mulo de ?gua nestes terrenos, a qual foi denominada de calha el?vio-aluvionar. As estruturas riacho-fenda e calha apresentam caracter?sticas bem distintas e, portanto, os crit?rios de loca??o em cada estrutura s?o bastante diferentes. Na estrutura do tipo riacho-fenda ocorre a coincid?ncia do riacho com a zona de fratura ou com as suas bordas. As dire??es das fraturas coletadas em afloramentos s?o consistentes com a dire??o do riacho. Al?m disso, ocorre a correla??o de anomalias geof?sicas de um perfil a outro, delimitando a zona fraturada e a sua dire??o. Por outro lado, o modelo calha, proposto neste trabalho, representa uma estrutura de acumula??o de aluvi?o e/ou regolito. Os perfis geof?sicos, principalmente as se??es de resistividade aparente, delimitam muito bem as bordas da estrutura e fornecem uma boa indica??o da topografia do topo do cristalino sobre o qual est?o acumulados os sedimentos. As anomalias geof?sicas detetadas no centro da estrutura calha n?o apresentam continuidade de um perfil para o outro, mas ocorre boa correla??o das anomalias provocadas pela borda da estrutura. A implanta??o da estrutura calha ? fortemente condicionada pela folia??o da rocha: a maior dimens?o da estrutura calha ? paralela ? dire??o da folia??o e a forma e mergulho das bordas da calha s?o controladas pelo mergulho da folia??o. No caso das loca??es em que seja v?lido o modelo riacho-fenda, a utiliza??o do VLF oferece excelente resposta tanto em rela??o ? localiza??o da zona fraturada quanto na determina??o da dire??o do seu eixo de prolongamento. Por outro lado, no caso de loca??es em que seja v?lido o modelo calha, o m?todo de eletro-resistividade, em especial a t?cnica da se??o de resistividade aparente, proporciona a delimita??o das bordas da estrutura, bem como revela os locais da calha que apresentam maior espessura de aluvi?o e/ou regolito

The need to consider groundwater and surface water as a single resource has fostered the interest of the scientific community on the interactions between surface water and groundwater. The region below and alongside rivers where surface hydrology and subsurface hydrology concur is the hyporheic zone. This is the region where water exchange determines many biogeochemical and ecological processes of great impact on the functioning of rivers. However, the complex processes taking place in the hyporheic zone require a multidisciplinary approach. The combination of innovative point and distributed techniques originally developed in separated disciplines is of great advantage for the indirect identification of water exchange in the hyporheic zone. Distributed techniques using temperature as a tracer such as fiber-optic distributed temperature sensing can identify the different components of groundwater-surface water interactions based on their spatial and temporal thermal patterns at the sediment-water interface. In particular, groundwater, interflow discharge and local hyporheic exchange flows can be differentiated based on the distinct size, duration and sign of the temperature anomalies. The scale range and resolution of fiber-optic distributed temperature sensing are well complemented by geophysics providing subsurface structures with a similar resolution and scale. Thus, the use of fiber-optic distributed temperature sensing to trace flux patterns supported by the exploration of subsurface structures with geophysics enables spatial and temporal investigation of groundwater-surface water interactions with an unprecedented level of accuracy and resolution. In contrast to the aforementioned methods that can be used for pattern identification at the interface, other methods such as point techniques are required to quantify hyporheic exchange fluxes. In the present PhD thesis, point methods based on hydraulic gradients and thermal profiles are used to quantify hyporheic exchange flows. However, both methods are one-dimensional methods and assume that only vertical flow occurs while the reality is much more complex. The study evaluates the accuracy of the available methods and the factors that impact their reliability. The applied methods allow not only to quantify hyporheic exchange flows but they are also the basis for an interpretation of the sediment layering in the hyporheic zone. For upscaling of the previous results three-dimensional modelling of flow and heat transport in the hyporheic zone combines pattern identification and quantification of fluxes into a single framework. Modelling can evaluate the influence of factors governing groundwater-surface water interactions as well as assess the impact of multiple aspects of model design and calibration of high impact on the reliability of the simulations. But more importantly, this modelling approach enables accurate estimation of water exchange at any location of the domain with unparalleled resolution. Despite the challenges in 3D modelling of the hyporheic zone and in the integration of point and distributed data in models, the benefits should encourage the hyporheic community to adopt an integrative approach comprising from the measurement to the upscaling of hyporheic processes.