Nelson Ferreira Fernandes

Hillslope evolution by diffusive processes: The timescale for equilibrium adjustments

Diffusive processes such as creep, rain splash, and biogenic transport play a major role in controlling the development of convex hilltops on soil-mantled landscapes. Although many diffusion-based models have been proposed, little attention has been given to the effects of changing transport rates and boundary conditions. We use numerical and analytical solutions of the one-dimensional diffusion equation to explore whether hilltop convexities can be in equilibrium with contemporary climate and local channel incision rates. The results show that the timescale of such morphological adjustments varies substantially depending on whether the hillslope is tending to increase or decrease its convexity through time. By comparing the relaxation times estimated here with the frequency of the climatic oscillations observed in the last few million years, we argue that most of the convex hilltops observed in the field today are likely to be far from time-independent morphological features.

Topographic controls of landslides in Rio de Janeiro: field evidence and modeling

Landslides are common features in the Serra do Mar, located along the southeastern Brazilian coast, most of them associated with intense summer storms, specially on the soil-mantled steep hillslopes around Rio de Janeiro city, where the favelas (slums) proliferated during the last few decades. On February 1996, hundreds of landslides took place in city of Rio de Janeiro triggered by intense rainstorms. Since then, many studies have been carried out in two experimental river basins in order to investigate the role played by the topographic attributes in controlling the spatial distribution of landslides inside them. Landslide scars and vegetation cover were mapped using aerial photographs and field observations. A detailed digital terrain model (4 m 2 resolution) of the basins was generated from which the main topographic attributes were analyzed, producing maps for slope, hillslope form, contributing area and hillslope orientation. By comparing these maps with the spatial distribution of the landslide scars for the 1996 event, a landslide potential index (LPI) for the many classes of the different topographic attributes was defined. At the same time, field experiments with the Guelph permeameter were carried out and a variety of scenarios were simulated with the SHALSTAB model, a process-based mathematical model for the topographic control on shallow landslides. The results suggest that most of the landslides triggered in the studied basins were strongly influenced by topography, while vegetation cover did affect landslide distribution. Between the topographic attributes, hillslope form and contributing area played a major role in controlling the spatial distribution of landslides. Therefore, any procedure to be used in this environment towards the definition of landslide hazards need to incorporate these topographic attributes. D 2003 Elsevier B.V. All rights reserved.

Parameterization of soil properties for a model of topographic controls on shallow landsliding: application to Rio de Janeiro

A key problem in the use of physically based models of landslide hazards is how to parameterize the representation of soil properties. We applied a physically based model for the topographic control on shallow landsliding (SHALSTAB) to two catchments in Rio de Janeiro to investigate the accuracy of model results in relation to parameterization of soil properties. In so doing, we address the relevance of values derived from laboratory tests to the field problem, as well as the trade-offs inherent in model parameterization. We ran the model for all combinations of reasonable cohesion, bulk density, and friction angle values and compared model predictions to mapped landslides scars. We rank sorted model performance through the proportion of the total area of landslide scars correctly predicted as potentially unstable. Application of the model to an area where soil properties are not well known can be based on either a standard parameterization that emphasizes topographic controls, or on local calibration of soil parameters against a map of known landslide locations. Our analysis suggests that, in general, acquisition of high-quality digital elevation models (DEMs) is more important than generation of spatially detailed soil property values for reconnaissance level assessment of shallow landslide hazards.

Combining Spatial Models for Shallow Landslides and Debris-Flows Prediction

Abstract: Mass movements in Brazil are common phenomena, especially during strong rainfall events that occur frequently in the summer season. These phenomena cause losses of lives and serious damage to roads, bridges, and properties. Moreover, the illegal occupation by slums on the slopes around the cities intensifies the effect of the mass movement. This study aimed to develop a methodology that combines models of shallow landslides and debris-flows in order to create a map with landslides initiation and debris-flows volume and runout distance. The study area comprised of two catchments in Rio de Janeiro city: Quitite and Papagaio that drained side by side the west flank of the Macico da Tijuca, with an area of 5 km 2 . The method included the following steps: (a) location of the susceptible areas to landslides using SHALSTAB model; (b) determination of rheological parameters of debris-flow from the back-analysis technique; and (c) combination of SHALSTAB and FLO-2D models to delineate the areas more susceptible to mass movements. These scenarios were compared with the landslide and debris-flow event of February 1996. Many FLO-2D simulations were exhaustively

Rio de Janeiro: A Metropolis Between Granite-Gneiss Massifs

The city of Rio de Janeiro is well-known for its outstanding landscape, particularly the several steep rocky domes that emerge close to the coast. Such a wonderful scene results from a combination of differential weathering controlled by the presence of a variety of Neoproterozoic gneisses and Cambrian granites and strong valley incision along subvertical faults and fractures. In this chapter we present the geological and geomorphological aspects that influence the daily life of more than 12 million inhabitants of the Rio de Janeiro metropolitan region, in two areas around Guanabara Bay: Coastal Massifs and the Serra dos Orgaos escarpment. The combination of such topographic constraints, intense summer rainstorms, and dense occupation frequently creates a scenario with a high potential for landslide-derived hazards.

The Guanabara Bay, a Giant Body of Water Surrounded by Mountains in the Rio de Janeiro Metropolitan Area

The Guanabara Bay in Rio de Janeiro is one of the most important Brazilian morphological features, both in terms of its geological and geomorphological evolution as well as considering its historical importance to the development of Brazil. The existing morphological contrast, varying from mountain escarpments , hills, fluvial, and marine coastal plain s, beaches, and lagoons, results from a complex evolution that imprinted in the landscape an intriguing diverse morphology which constitutes a highly attractive touristic natural scenario that is well known internationally. Its geological and geomorphological history is related to the Paleogene extensional faults and alkaline magmatism within the Guanabara Graben that was filled by Cenozoic continental and/or fluviomarine sediments. In this landscape, the use of natural resources has constrained human occupation for more than 500 years. It was only in the 2000s that improved environmental consciousness promoted measures toward minimizing environmental degradation processes.

Aplicação do Código Florestal Brasileiro como subsídio para o planejamento ambiental: um estudo de caso na região noroeste do estado do Rio de Janeiro

This studied verified the application of the Brazilian Forest Code (CFB) in the Santa Maria creek basin, in northwestern Rio de Janeiro, as a support to environmental planning. This basin is fully located in the county of Sao Jose de Uba, and it has been subject to different processes of soil use and occupation, resulting in water and erosion problems. In order to perform the study, a map of current soil use and occupation was designed through automatic supervised classification, using air photos of Companhia de Energia do Rio de Janeiro -CERJ (Rio de Janeiro Power Company) and Mineral Resources Department -DRM/RJ. In order to design the map of soil use and occupation in compliance with the scenario established in article 2 of the CFB, a surrounding belt (buffer zone) was created. The results show that there would be conflicts between the CFB application and the current use of areas for agriculture, animal husbandry, exposed soil and urban area. In agriculture and animal husbandry, the conflicting use could be softened with adequate handling and conservation practices. Applying the CFB would significantly contribute to increasing APP (forest), promoting increased water seepage in soil and water system recharge, and decreasing overland runoff and soil erosion.

RADAR Images Supporting Rescue and Recovery Actions for Landslide and Flood Disasters: A Rio de Janeiro State Case Study

The use of RADAR images for monitoring natural disasters has two advantages compared to optical satellite images: RADAR images can be collected day or night, and regardless of weather. In major disasters related to landslides or floods, weather conditions are adverse and generally includes dense cloud cover that prevents use of optical satellite images. In a project approved between the Japan Aerospace Exploration Agency and the University of Rio de Janeiro State, there was an agreement to transfer up to twenty PALSAR2 images (with up to one meter spatial resolution) for monitoring natural disasters related to landslides or floods in Rio de Janeiro State. The procedure for monitoring is to collect ten images before the Brazilian rainy season (which in Rio de Janeiro starts in November-December and finishes around March-April. This is the opposite of Asia, which is in the dry season, so the satellite can be provided quickly in this period) to be used to obtain reference images for the follow methods: Coherent Change Detection (CCD) and Differential/Polarimetric Interferometry (DInSAR/Pol-InSAR). When a disaster with landslides or floods happens, it will be possible, to quickly and without any weather problems, detect if some land has slipped (mapping potential areas to slip), and if some areas are flooded. The main objective of this project is to subsidize the creation of maps for government agencies to use in planning strategies to minimize the hazard impacts and to assist governmental agencies at two stages: (1) during the disaster: helping rescuers and rescue efforts, indicating priority areas to be worked on and the numbers of people affected; and (2) after the disaster: mapping the extent of the affected areas, to assist in planning the recovery of these areas.

Identification of the affected areas by mass movement through a physically based model of landslide hazard combined with a two-dimensional flood routing model for simulating debris flow

Natural disasters are one of the worlds greatest socioeconomic problems and one of the most notable of which is that of mass movements, which are natural phenomena that change the relief and cause great damage to mankind. Mass movements can be classified by: type of material involved, velocity and mechanism of movement, type of deformation, geometry of the displaced mass and water content. Among them, the shallow landslides stand out. These movements are triggered during intense rainfall, frequently in the summer. Shallow landslides transform into debris flow mainly due to water infiltration. They reach long distances, velocity and high transport capacity, including large boulders. It is essential not only to predict shallow translational landslides but also to predict debris flow occurrence and runout as a secondary effect. The aim of this study is to develop a methodology which combines a model to predict landslides with another one that determines debris flows pathways and depositions. The study area is located in the west slope of Macico da Tijuca, involving the Quitite and Papagaio river basins, in the Jacarepagua neighbourhood of Rio de Janeiro, Brazil.

Identification of areas prone to shallow landslide in Parque Nacional da Serra dos Órgãos (Brazil) considering seasonal rainfall

Mathematical modeling is being increasingly used to predict events occurring in nature. Within the diverse existing models, one which stands out is the SHALSTAB. This model of prediction of shallow landslide occurrence was applied in Parque Nacional da Serra dos Órgãos (PARNASO) by using data for average monthly pluviosity, aiming to identify, within the landscape, the spatial variability at places prone to shallow landslide throughout the year. The methodology is sectioned into the following stages: a) elaboration of the digital elevation model (DEM) and its derived maps, such as slope and contribution area, b) application of the SHALSTAB model, considering the various events of rainfall throughout the year, and c) quantification of areas prone to landslide for each rainfall event occurred. The model results indicate the dynamics of the locations which present instability due to the seasonality of rainfall intensity.