Os escorregamentos são processos naturais que podem trazer diversos impactos ambientais, sociais e econômicos.A identificação e mapeamento de áreas suscetíveis a escorregamentos são procedimentos importantes no gerenciamento de bacias hidrográficas. O uso de modelos de estabilidade de encostas auxilia na gestão da problemática envolvendo os escorregamentos, mas frequentemente negligenciam o efeito da vegetação. Este trabalho apresenta uma metodologia para analisar o efeito da vegetação em modelos de estabilidade de encostas. Em primeiro lugar, parâmetros relacionados a vegetação foram inseridos no equacionamento do Fator de Segurança (FS). A partir de análise de sensibilidade, verificou-se quais parâmetros possuem maior influência na estabilidade. Posteriormente, o modelo SHALSTAB foi modificado, inserindo os parâmetros mais relevantes, e aplicado na Bacia do rio Cunha. Os efeitos mecânicos, gerados pela presença da vegetação, inseridos na equação do FS são: coesão das raízes (cr); sobrecarga gerada pelo peso da vegetação (Sw); tensão cisalhante oriunda da ação do vento nas copas das árvores (Ve). Observou-se que cratua no sentido de aumentar a estabilidade da encosta e sua influência é a mais significativa dentre os parâmetros analisados e é maior em solos rasos, diminuindo com o aumento da profundidade. O parâmetro Sw atua na redução da estabilidade da encosta e exerce maior influência em solos
A conectividade de sedimentos pode ser entendida como a transferência de sedimentos entre diferentes compartimentos da paisagem através das relações entre seus componentes. Isso ocorre, principalmente, por meio da interação entre processos hidrológicos e sedimentológicos, os quais, por sua vez, são controlados por características geomorfológicas. O tema vem se tornando fundamental para o entendimento da dinâmica dos sedimentos em uma bacia hidrográfica, pois avalia a transferência dos sedimentos de maneira integrada e inovadora, considerando diferentes processos e características, diferindo das demais metodologias de estudo da dinâmica da paisagem. Consequentemente, muitas metodologias diferentes foram desenvolvidas em todo o mundo para avaliar a conectividade de maneira quantitativa e qualitativa. No entanto, entre esses estudos, diferentes terminologias foram adotadas. Grande parte das metodologias avalia a conectividade dos sedimentos a partir de aspectos estruturais (geomorfológicos) que distribuem no espaço as relações entre os componentes do sistema. Atualmente, são sugeridas abordagens utilizando aspectos funcionais (hidrológicos), que trazem dependência temporal para a conectividade. Entretanto, poucas metodologias inseriram as características do próprio sedimento nesta avaliação. Em relação aos estudos brasileiros, poucas investigações sobre conectividade foram realizadas, surgindo a necessidade de trabalhos considerando as características físicas das bacias brasileiras. A partir disso, a presente revisão discute, inicialmente, os diferentes conceitos de conectividade utilizados atualmente. Em seguida, resume e discute as metodologias desenvolvidas para avaliar a conectividade dos sedimentos, destacando as propriedades estruturais e funcionais relevantes para o estudo da conectividade. Adicionalmente, estudos de conectividade desenvolvidos em território brasileiro são apresentados. Conclui-se que, somente a partir de estudos que levem em conta a interação entre geomorfologia, hidrologia e sedimentologia, será possível uma avaliação integral da conectividade dos sedimentos. Ademais, a conectividade se apresenta como uma potencial ferramenta para o gerenciamento de bacias hidrográficas, trazendo avanços no entendimento da dinâmica dos sedimentos e, consequentemente, na evolução da paisagem.
<p>The hillslope-channel coupling has a fundamental role in sediment control of a catchment, especially when the catchment is prone to mass movements. Debris flow is a type of mass movements that provides an important sediment contribution to a channel, which is influenced by hillslope-channel coupling degree. This coupling can be represented by the connectivity, a concept utilized as an approach to many queries regarding water and/or sediment transport through methodologies which relates a river with its drainage area. In this regard, this study addresses the representation of debris flow in terms of connectivity. We applied a debris flow computational modelling (DFM) and an index of connectivity (IC) in Mascarada catchment, south Brazil, where hundreds of mass movements were triggered in 2017, to evaluate the potential, limitations and capacity of IC to represent patterns of mass movements&#8217; connectivity. The IC is calculated for each cell of the catchment&#8217;s digital elevation model (DEM) (horizontal resolution of 1 m) in relation to the drainage network. Therefore, the IC represents the lateral connectivity (hillslope-channel) and its capacity to mobilize sediment to the channel. The DFM utilizes the Multiple Flow Direction to distribute volumes of a fluid with a determined kinematic viscosity through a slope, originated from initiation areas with a depth pre-determined by the user. The model utilizes uniform and steady flow solutions for Newtonian fluid, considering a rectangular channel. The DFM simulated the observed debris flow reasonably well, with an accuracy of 68%. However, since the simulation reached the channel and carried the volumes beyond the observed debris flow scar, it presented an overestimation area of 65%. When relation the simulated debris flow paths with the IC, we observed a superposition between those paths and high IC values. Also, the results showed a pixel-by-pixel positive linear correlation between high flow depths (representing convergence of flow) and IC, with values varying from 0,1 and 0,5. Only one of the nine simulated debris flow did not reach the channel and it had the lowest mean IC value along its flow path. Simulated debris flow that reached the channel showed high hillslope-channel connectivity, denoting the important role of high magnitude sediment transport events in sediment connectivity. Therefore, the IC was capable to represent and indicate patterns of debris flow that reached the channel. Though, the results also indicated that IC must be carefully interpreted when employed to understand debris flow and related processes &#8211; some areas have high fluid depth due to low connectivity, but others have high depth in response of convergence of flow due to highly connected areas. In this regard, an integration of connectivity and debris flow modelling tools can by an important step to understand sediment connectivity and to represent patterns of high magnitude mass movements events.</p>
Hydrological and sedimentological dynamics are controlled by hillslope‐channel (de)coupling, which is influenced by several natural and anthropogenic factors. However, studies on sediment connectivity are recent and present numerous challenges to be overcome. Furthermore, there is a need to explore and identify sediment connectivity governing processes and phenomena. In this study, hydrological monitoring and indices application were used to access aspects of sediment connectivity in a small catchment (0.89 km2), located on a plateau in southern Brazil. The indices are a combination of variables conceptually known as controllers of the spatial and temporal organization of sediment flows in the system. The application of these tools proved to be relevant for the characterization of structural and functional connectivity of the study area. The tools applied were structural index of connectivity (IC); index of hydrosedimentological connectivity (IHC), based on observed events; field connectivity index (FIC). The characterization of structural connectivity highlighted natural sinks and blankets zones as the main elements of disconnection in the catchment. The functional connectivity was evaluated for five distinct magnitude events, the results showed a higher influence of sediment availability and antecedent moisture conditions than the other structural factors. The FIC validated the theoretical indices in the study area and highlighted the importance of coupling thresholds between the numerous sediment sources in a known event.
<p>Debris flows are major geophysical processes which are able to modify the landscape. Structural sediment connectivity describes the physical coupling of landscape units, and it may be affected by the occurrence of single large-magnitude debris flows and/or by the cumulative changes determined by frequent, small-magnitude events. Understanding the coupling of hillslopes to the main channel during and after debris flows is essential for comprehending catchments sediment transfer at different timescales. Debris flows might provoke sudden changes in the landscape through processes such as bed and bank erosion, overbank deposition and natural dam formation. While debris flows may modify the landscape, their characteristics (e.g., path, runout) are strongly affected by the geomorphological settings. Indeed, there is an interplay between landscape morphology and debris flows, one conditioning the other and vice versa. In this regard, determining how much structural connectivity influences the coupling of debris flow with the channel network remains a challenge. An evaluation of the structural connectivity before and after storm events that triggered debris flow has been carried out on multi-temporal DTMs available for the Stolla basin (Autonomous Province of Bozen-Bolzano, Italian Alps) utilizing the Index of Connectivity (IC) and on a pre-event DTM for the Revolver basin (Santa Catarina state, Southern Brazil). To understand whether the morphological changes caused by the debris flows had an impact on flow routing during the event, some of the debris flow events were simulated by a physically based model. The topographic changes caused by the simulated scenarios have been used to compare pre- vs post-event sediment connectivity.</p><p>&#160;</p><p>&#160;</p>
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