The composition and distribution of fish assemblages was examined in a floodplain lake system in the Amazon basin. Quantitative samples were collected during the 1992-1993 flooding season at Marchantaria Island, Solimoes River. A total of 25,819 specimens representing 8 orders, 30 families, 101 genera and 139 species of fish were collected. Analysis of species richness distribution among 7 vegetation strata showed that vegetated sites had higher species richness than unvegetated sites. Stands of Paspalum repens had the most diverse fish fauna. Canonical correspondence analysis (CCA) was used to investigate relationship between fish assemblages and 16 environmental variables. CCA revealed that dissolved oxygen, water transparency, water depth and aquatic vegetation structure were significantly related to fish assemblage organization. The results suggest that physiological adaptations to hypoxia and habitat complexity play a major role in the organization of these assemblages. The morphology, ontogenetic development, shape variability and deposition of otolith microincrements are described for floodplain serrasalmin fishes. Serrasalmin otoliths were similar to other ostariophysan, nevertheless their shape was species-specific. Elliptical Fourier analysis showed that Mylossoma aureum lapilli were highly variable in shape when compared to closely related species. PCA and discriminant function analysis indicated that two distinct forms of lapillus can be recognized for M. aureum, and intra-species variation was higher than inter-species variation. Otolith microincrement analysis was tested for these fishes, and microincrement deposition validation showed that Piaractus brachipomus deposits otolith increments on a daily basis. Patterns of spatial distribution, growth and mortality characteristics of larvae and juvenile were examined for M. aureum inhabiting the Marchantaria Island floodplain. Otolith-derived birth date reconstruction showed that M. aureum spawning season extended from late November to March, and peak larvae recruitment to the island occurred in mid-December. Larvae and juveniles had different spatial distributions in relation to habitat usage. Instantaneous growth coefficients (g) varied from 0.0197(d�����) to 0.265(d�����) among cohorts. Early-season cohorts had wider otolith microincrements and higher instantaneous growth coefficients than late-season cohorts. Mortality estimated by the decline of loge (abundance) regressed on age indicated that cohort-specific instantaneous mortality varied significantly among cohorts, ranging from 0.027(d�����) (2.6%/d) to 0.103(d�����) (9.7%/d). / Graduation date: 2001

Flow modelling in a compound channel is a complex matter. Indeed, due to the smaller velocities in the floodplains than in the main channel, shear layers develop at the interfaces between these subsections, and the channel conveyance is affected by a momentum transfer corresponding to this shear layer, but also to possible geometrical changes in a non-prismatic reach. In this work, a one-dimensional approach, the Exchange Discharge Model (EDM), is proposed for such flows. The EDM accounts for the momentum transfer between channel subsections, estimated as proportional to the velocity gradient and to the discharges exchanged through the interface; where two main processes are identified : (1) the turbulent exchange, due to the shear-layer development; and (2) the geometrical transfer, due to cross-sectional changes. The EDM is successfully validated for discharge prediction, but also for water-profile computation, through comparison with existing laboratory and field measurements. The momentum transfer due to turbulent exchanges is then studied experimentally, theoretically and numerically. At first, new experimental data, obtained by using Particle Tracking Velocimetry techniques, are presented : the periodical vortex structures that develop in the shear layer are clearly identified and characterised. Secondly, a hydrodynamic linear stability analysis enables to predict quite successfully the wave length of some observed vortices. Lastly, an Unsteady-RANS numerical method is used to simulate the perturbation development. The estimated vortex wave lengths agree again with the measurements and the theoretical predictions, although vortices merging occurs in the simulation results, which was actually not observed experimentally. The velocity-profile prediction is found improved when the effect of vortices is considered, thanks to the corresponding additional shearing. The geometrical transfer is also investigated experimentally and numerically. Novel experiments are designed, with the measurements of the flow in a compound channel with symmetrically narrowing floodplains. The mass transfer and the evolution of the flow distribution along the channel length are clearly observed. A significant additional head loss due to this transfer is measured, in accordance with the EDM hypothesis. Measured water profiles are finally compared successfully with the EDM predictions. In addition to the EDM development and validation, the so-called Lateral Distribution Method (LDM) is also investigated and the significance of the secondary-currents models proposed by previous authors for this method is discussed. When considering the velocity-profile prediction, the effect of these helical secondary currents is again clearly highlighted, by using dispersion terms in the Saint-Venant equations. However, the actual physical meaning of the related dispersion coefficients remains uncertain. In addition, an extended LDM is also proposed and discussed for non-prismatic flow modelling, using the new narrowing-channel data set./La modélisation des écoulements dans les rivières à plaines inondables est particulièrement complexe. En effet, la vitesse de l'eau étant plus faible sur la plaine d'inondation que dans le lit mineur, une couche de cisaillement se développe à l'interface entre ces sous-sections. La débitance totale de la rivière est dés lors réduite, à cause du transfert de quantité de mouvement qu'occasionne la présence de la couche de cisaillement, mais aussi de part les changements de géométrie qui peuvent se produire dans un lit non-prismatique. La présente thèse propose, pour la représentation de tels écoulements, une nouvelle approche uni-dimensionnelle dénommée Modèle des Débits d'Echange ("Exchange Discharge Model" – EDM). Le transfert de quantité de mouvement entre les soussections de la rivière est pris en compte par l'EDM comme étant proportionnel au gradient de vitesse entre celles-ci et aux débits échangés à travers leur interface. A cette interface, deux phénomènes sont essentiellement présents : (1) un échange turbulent, dû au développement de la couche de cisaillement; et (2) un transfert géométrique, correspondant aux changements de section. L'EDM est validé avec succès pour la prédiction du débit et pour le calcul de lignes d'eau, par comparaison avec des données existantes de laboratoire et de terrain. Le transfert de quantité de mouvement dû à l'échange turbulent est ensuite étudié expérimentalement, théoriquement et numériquement. De nouvelles mesures sont obtenues, au moyen d'une technique de vélocimétrie par suivi de particules. Les structures périodiques qui se développent dans la couche de cisaillement sont clairement identifiées et caractérisées. Deuxièmement, une analyse linéaire de stabilité hydrodynamique permet de prédire théoriquement les longueurs d'onde de quelques tourbillons qui ont été observés expérimentalement, et ce avec succès. Enfin, un modèle numérique, de type "Unsteady-RANS", est utilisé pour simuler la croissance des tourbillons dans la couche de cisaillement. Encore une fois, les longueurs d'onde obtenues correspondent relativement bien avec les valeurs mesurées et prédites théoriquement; bien que les coalescences de tourbillons qui se produisent numériquement n'aient pas été observées expérimentalement. La prédiction des profils de vitesse est améliorée, lorsque l'effet des tourbillons est considéré, grâce à la contrainte de cisaillement additionnelle que ceux-ci génèrent. Les transferts géométriques sont également explorés expérimentalement et numériquement. Une nouvelle campagne expérimentale a été réalisée, en considérant l'écoulement dans un lit composé symétrique, dont les plaines d'inondation se rétrécissent progressivement. Le transfert de masse entre sous-sections et la redistribution des débits qui lui est associée sont clairement observés au long du canal. Une importante perte de charge additionnelle due à ce transfert est mesurée, en concordance avec les hypothèses de l'EDM. Finalement, les lignes d'eau mesurées sont reproduites avec succès par un calcul utilisant l'EDM. En complément au développement et à la validation de l'EDM, la "Lateral Distribution Method" (LDM) est également utilisée, avec pour objectif la clarification du rôle des termes de courants secondaires proposés par différents auteurs. Par rapport à la prédiction du profil de vitesse, l'effet de ces courants secondaires est très marqué. Il est ici reproduit en utilisant des termes de dispersion dans les équations de Saint-Venant. Cependant, le sens physique des valeurs des coefficients de dispersion qui doivent être utilisés est discutable. Par ailleurs, une LDM étendue, pour les écoulement en lits nonprismatiques, est proposée et commentée, en utilisant le nouveau jeu de données pour le canal convergent.

No description available.

Spatial and temporal information on catchment sediment sources and sinks can provide an improved understanding of catchment response to human-induced disturbances. This is essential for the implementation of well-targeted catchment-management decisions. This thesis investigates the nature and timing of catchment response to human activities by examining changes in sediment sources and sinks in a dry-tropical subcatchment of the Great Barrier Reef (GBR) catchment area, in northeastern Australia. Changes in catchment sediment sources, both in terms of spatial provenance and erosion type, are determined using sediment tracing techniques. Results indicate that changes in sediment source contributions over the last 250 years can be linked directly to changes in catchment land use. Sheetwash and rill erosion from cultivated land (40???60%) and channel erosion from grazed areas (30-80%) currently contribute most sediment to the river system. Channel erosion, on a basin-wide scale, appears to be more important than previously considered in this region of Australia. Optically stimulated luminescence and 137Cs dating are used to determine pre-and post- European settlement (ca. 1850) alluvial sedimentation rates. The limitations of using 137Cs as a floodplain sediment dating tool in a low fallout environment, dominated by sediment derived from channel and cultivation sources, are identified. Low magnitude increases in post-disturbance floodplain sedimentation rates (3 to 4 times) are attributed to the naturally high sediment loads in the dry-tropics. These low increases suggest that previous predictions which reflect order of magnitude increases in post-disturbance sediment yields are likely to be overestimates. In-channel bench deposits, formed since European settlement, are common features that appear to be important stores of recently eroded material. The spatially distributed erosion/sediment yield model SedNet is applied, both with generic input parameters and locally-derived data. Outputs are evaluated against available empirically-derived data. The results suggest that previous model estimates using generic input parameters overestimate post-disturbance and underestimate pre-disturbance sediment yields, exaggerating the impact of European catchment disturbance. This is likely to have important implications for both local-scale and catchment-wide management scenarios in the GBR region. Suggestions for future study and the collection of important empirical data to enable more accurate model performance are made.

This study presents a new Lagrangian model for predicting dynamics and transport in rivers and shallow water flows. A hydrostatic model is developed for the prediction of rivers and floodplain flow and lateral interactions between them. The model is extended to the Boussinesq weakly non-linear, non-hydrostatic model for the simulation of solitary waves and undular bores. A model for advection-diffusion transport of tracers in open channel flow is also presented. The simulation results are compared against an analytical solution and published laboratory data, field data and theoretical results. It is demonstrated that the Lagrangian moving grid eliminates numerical diffusion and oscillations; the model is dynamically adaptive, providing higher resolution under the wave by compressing the parcels (grid). It also allows flow over dry beds and moving boundaries to be handled efficiently. The hydrostatic model results have shown that the model accurately simulates wave propagation and non-linear steepening until wave breaking. The model is successfully applied to simulate flow and lateral interactions in a compound channel and flood wave movement in a natural river. The non-hydrostatic model has successfully reproduced the general features of solitary waves such as the balance between non-linearity and wave dispersion and non-linear interactions of two solitary waves by phase-shift. Also, the model successfully reproduced undular bores (high frequency short waves) from a long wave and the predicted maximum height of the leading wave agreed very well with the published results. It is shown that the simple second order accurate Lagrangian scheme efficiently simulates dispersive waves without any numerical diffusion. Lagrangian modeling of advection-diffusion transport of Gaussian tracer distributions, top hat tracer distributions and steep fronts (step function) in steady, uniform flow has provided exact results and has shown that the scheme allows the use of a large time step without any numerical diffusion and oscillations, including for the advection of steep fronts. The scheme can handle large Courant numbers (results are presented for Cr = 0 to 20) and the entire range of grid Peclet numbers from zero to infinity. The model is successfully applied to tracer transport due to flow induced by simple waves, solitary waves and undular bores

Made available in DSpace on 2014-06-11T19:30:31Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-04-20Bitstream added on 2014-06-13T20:21:13Z : No. of bitstreams: 1 sartori_lr_dr_prud.pdf: 4148637 bytes, checksum: 5616600e595cbbe65fef21b03cd5309c (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O propósito deste trabalho foi avaliar o potencial dos dados PALSAR polarimétricos para discriminar e mapear espécies de macrófitas (vegetação aquática) de uma área alagável da Amazônia, a planície de inundação do Lago Grande de Monte Alegre, no estado do Pará. A coleta de dados foi realizada quase simultaneamente à aquisição dos dados de radar. Três principais espécies de macrófitas foram encontradas na área: Paspalum repens (PR), Hymenachne amplexicaulis (HA) e Paspalum elephantipes (PE). Variáveis morfológicas foram medidas em campo e usadas para derivar outras variáveis tais como a biomassa. Atributos foram gerados a partir da matriz de covariância [C] extraída da imagem ALOS/PALSAR em modo SLC (single look complex). Os atributos polarimétricos foram analisados para as três espécies e identificados aqueles capazes de discriminar as espécies. Foram aplicadas as seguintes abordagens de classificação: baseada em regras, baseada em modelos de decomposição (Decomposições de Freeman-Durden e Cloude-Pottier), baseada em estatística (Classificação supervisionada baseada na distância Wishart) e híbrida (Classificador Wishart com classes de entrada baseadas na decomposição de Cloude-Pottier). Finalmente, a variável morfológica “volume da haste” foi modelada por regressão múltipla em função de alguns atributos polarimétricos. Os resultados sugerem que a imagem polarimétrica banda L possui potencial para discriminar as espécies de macrófitas, sendo os principais atributos para isso sigma zero HH ( ), sigma zero HV ( ) e sigma zero VV ( ), índice de estrutura da copa... / The purpose of this work was to evaluate the potential of fully polarimetric PALSAR data to discriminate and map macrophyte species in the Amazon floodplain, more specifically in the Monte Alegre Lake, in the state of Pará, Brazil. Fieldwork was carried out almost simultaneously to the radar acquisition. Three main species were found in the study area: Paspalum repens (PR), Hymenachne amplexicaulis (HA) and Paspalum elephantipes (PE). Macrophyte morphological variables were measured on the field and used to derive others variables, like the biomass. Attributes were calculated from the covariance matrix [C] derived from the SLC (single look complex) data. The polarimetric attributes were analyzed for the three species and it was identified that ones capable of discriminating them. The following classification approaches were applied: a rule-based classification, model-based classifications (Freeman-Durden and Cloude-Pottier), a statistical-based classification (supervised classification using Wishart distance measure) and a hybrid classification (Wishart classifier with the input classes based on the H/a plane). Finally, the morphological variable “stem volume” was modeled using multiple regression. The findings suggest that the fully polarimetric image has potential for discriminating plant species, being the main attributes sigma-nought HH ( ), sigma-nought HV ( ) and sigma-nought VV ( ), canopy structure index ( ), HH-VV polarimetric coherence ( ), helicity of the third scattering mechanism (τ ), orientation angle of the first scattering mechanism ( ) and scattering type phase of the first mechanism ( ); among the different classifications, only the supervised (Wishart) and the rule-based discriminated the species, with overall accuracy of 75,04% and 87,18%, respectively; the stem volume was modeled using the following attributes: biomass index ( ), volumetric scattering ... (Complete abstract click electronic access below)

Resumo: O propósito deste trabalho foi avaliar o potencial dos dados PALSAR polarimétricos para discriminar e mapear espécies de macrófitas (vegetação aquática) de uma área alagável da Amazônia, a planície de inundação do Lago Grande de Monte Alegre, no estado do Pará. A coleta de dados foi realizada quase simultaneamente à aquisição dos dados de radar. Três principais espécies de macrófitas foram encontradas na área: Paspalum repens (PR), Hymenachne amplexicaulis (HA) e Paspalum elephantipes (PE). Variáveis morfológicas foram medidas em campo e usadas para derivar outras variáveis tais como a biomassa. Atributos foram gerados a partir da matriz de covariância [C] extraída da imagem ALOS/PALSAR em modo SLC (single look complex). Os atributos polarimétricos foram analisados para as três espécies e identificados aqueles capazes de discriminar as espécies. Foram aplicadas as seguintes abordagens de classificação: baseada em regras, baseada em modelos de decomposição (Decomposições de Freeman-Durden e Cloude-Pottier), baseada em estatística (Classificação supervisionada baseada na distância Wishart) e híbrida (Classificador Wishart com classes de entrada baseadas na decomposição de Cloude-Pottier). Finalmente, a variável morfológica "volume da haste" foi modelada por regressão múltipla em função de alguns atributos polarimétricos. Os resultados sugerem que a imagem polarimétrica banda L possui potencial para discriminar as espécies de macrófitas, sendo os principais atributos para isso sigma zero HH ( ), sigma zero HV ( ) e sigma zero VV ( ), índice de estrutura da copa ... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The purpose of this work was to evaluate the potential of fully polarimetric PALSAR data to discriminate and map macrophyte species in the Amazon floodplain, more specifically in the Monte Alegre Lake, in the state of Pará, Brazil. Fieldwork was carried out almost simultaneously to the radar acquisition. Three main species were found in the study area: Paspalum repens (PR), Hymenachne amplexicaulis (HA) and Paspalum elephantipes (PE). Macrophyte morphological variables were measured on the field and used to derive others variables, like the biomass. Attributes were calculated from the covariance matrix [C] derived from the SLC (single look complex) data. The polarimetric attributes were analyzed for the three species and it was identified that ones capable of discriminating them. The following classification approaches were applied: a rule-based classification, model-based classifications (Freeman-Durden and Cloude-Pottier), a statistical-based classification (supervised classification using Wishart distance measure) and a hybrid classification (Wishart classifier with the input classes based on the H/a plane). Finally, the morphological variable "stem volume" was modeled using multiple regression. The findings suggest that the fully polarimetric image has potential for discriminating plant species, being the main attributes sigma-nought HH ( ), sigma-nought HV ( ) and sigma-nought VV ( ), canopy structure index ( ), HH-VV polarimetric coherence ( ), helicity of the third scattering mechanism (τ ), orientation angle of the first scattering mechanism ( ) and scattering type phase of the first mechanism ( ); among the different classifications, only the supervised (Wishart) and the rule-based discriminated the species, with overall accuracy of 75,04% and 87,18%, respectively; the stem volume was modeled using the following attributes: biomass index ( ), volumetric scattering ... (Complete abstract click electronic access below) / Orientador: Nilton Nobuhiro Imai / Coorientador: José Cláudio Mura / Banca: Evlyn Marcia Leão de Moraes Novo / Banca: Thiago Sanna Freire Silva / Banca: João Roberto dos Santos / Banca: Vilma Mayumi Tachibana / Doutor

Submitted by Diego Fernandes de Biagi (biagidiego@gmail.com) on 2017-09-26T22:38:48Z No. of bitstreams: 1 Dissertação_def.pdf: 1007536 bytes, checksum: 6e4b98e74276cfce2b86ad5b2672a227 (MD5) / Approved for entry into archive by Kelly Ayala (kelly.ayala@fgv.br) on 2018-04-02T19:18:03Z (GMT) No. of bitstreams: 1 Dissertação_def.pdf: 1007536 bytes, checksum: 6e4b98e74276cfce2b86ad5b2672a227 (MD5) / Made available in DSpace on 2018-04-02T19:18:03Z (GMT). No. of bitstreams: 1 Dissertação_def.pdf: 1007536 bytes, checksum: 6e4b98e74276cfce2b86ad5b2672a227 (MD5) Previous issue date: 2017-03-31 / The objective of the essay is to identify and map the processes that defined the practice of the “floodplain football” in São Paulo, more specifically at the public equipments called “Clubes da Comunidade” (Community Clubs). It intends to reconstitute the trajectory and stablishment of football as an institutionalized and encoded sport in Brazil and São Paulo, its different forms of practice and how it was exploited and treated by several groups through time, concerning the elite, the popular classes and the political class. Therefore, the uses of the terms “professional”, “amateur” and “varzeano” (term used to refer to the players of floodplain football) will be studied and the impact they had on the location and spatial distribution of the terrains destined to the informal and popular football, what was the influence of the urban policies in São Paulo and which role do the Community Clubs play on the preservation of floodpain football nowadays. / O trabalho tem como objetivo mapear e identificar os processos que instituíram a prática do futebol de várzea em São Paulo, mais especificamente nos equipamentos públicos chamados “Clubes da Comunidade”. Pretende reconstituir a trajetória de estabelecimento do futebol como esporte institucionalizado e codificado no Brasil e na cidade de São Paulo, suas diferentes formas de prática e como foi apropriado e tratado por diversos grupos ao longo do tempo, desde a elite até as classes populares, passando pela classe política. Para tanto, serão estudados os usos feitos dos termos “profissional”, “amador” e “varzeano” e qual impacto estes tiveram na localização e distribuição espacial dos terrenos destinados ao futebol informal e popular, qual a influência das políticas urbanas paulistanas nisso e qual o papel dos “Clubes da Comunidade” na preservação da prática nos dias atuais.

xvi, 150 p. : ill. (some col.), maps (some col.) A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number. / Floodplain roads and railroads are common features in river landscapes, but their distribution and impacts have not been explicitly studied. This dissertation discusses the impacts of floodplain roads and railroads on channel and floodplain processes in river landscapes at the continental, regional, and local scales. At the continental scale, I documented the spatial patterns of roads and railroads in the floodplains of the continental United States and the regional variability of their potential impacts. Based on these results, I developed a conceptual model based on topography and the interaction of transportation and stream networks that suggests that the area of lateral disconnection caused by transportation infrastructure should be most extensive in mid-sized alluvial valleys in relatively rugged settings, such as those located in the western United States. I used pre-existing digital geologic, hydrologic, and transportation data with Geographic Information Systems software to map floodplain areas and lateral disconnection along the floodplains of two river systems in Washington State. I developed methods to quickly and inexpensively delineate potential or historic floodplain surfaces, to analyze lateral floodplain disconnection caused by different types of structure, and to rank floodplain reaches in terms of salmon habitat potential. Although all floodplains exhibited disconnection, the floodplain maps and habitat rankings helped identify opportunities for habitat preservation and restoration. At the local scale, I mapped and measured the impacts of lateral disconnection, showing that channel and riparian habitat was degraded in locations with floodplain transportation infrastructure confining the channel compared with similar nearby sites lacking such confinement. Railroad grades and road beds function as confining structures in the riparian zone, disrupting flood pulses and the exchange of water, sediment, and biota between channels and their floodplains and within the floodplain. Over longer time periods, these structures can also impede the natural meandering and migration of channels across their floodplains, disrupting the erosional and depositional processes that drive the high habitat and biological diversity characteristic of floodplains. My results show that human-caused disconnections need to be further incorporated into river science and management. This dissertation includes previously published and unpublished co-authored material. / Committee in charge: W. Andrew Marcus, Chairperson, Geography; Daniel Gavin, Member, Geography; Patricia McDowell, Member, Geography; Joshua Roering, Outside Member, Geological Sciences

Der geschichtliche Prozess der Bodenbesetzung und – nutzung auf der Grundlage von Entwaldung und ungeordneter Bodenbewirtschaftung verursachte Konflikte zwischen der Zielsetzung der Umweltsanierung und der sozialwirtschaftlichen Reproduktion der auf Flächen mit hohen Umwelteinschränkungen siedelnden Landwirte. Diese Dichotomie zeigt sich derzeit in der Anwendung des Umweltrechts, insbesondere im neuen brasilianischen Waldschutzgesetz, das 1965 durch das Bundesgesetz Nr. 4.771 erlassen wurde, wenn es sich um Naturschutzgebiete (APPs) handelt, also um Landstriche entlang der Gewässer, die entsprechend geschützt und deren natürliche Vegetationsbedingungen erhalten werden müssen. Ausgehend von Elementen der Flussgeomorphologie gründet sich die von der vorliegenden Untersuchung verfolgte Diskussion auf die Hinterfragung der geometrischen Maβnahmen der Naturschutzbestimmungen durch die Vorlage einer Methodik zur Bestimmung dieser Flächen. Um zum Ergebnis zu gelangen, wird eine geschichtliche Rückbesinnung auf den Bodenbesetzungsprozess in Nordwest Rio Grande do Sul, zu der die Proben der Untersuchung gehören, sowie eine theoretische Interpretation des weltweiten Naturschutzes vorgenommen und werden die Naturschutzgebiete für Brasilien auf drei Untersuchungsebenen diskutiert: der gegebene gesetzliche Rahmen, die Verwendung dieser Flächen und der Zustand, in dem diese sich im Nordwesten von Rio Grande do Sul befinden. Die soziale Funktion des landwirtschaftlichen Betriebs wird als wichtiger Punkt dieser Diskussion betrachtet, denn von ihr ausgehend geschieht der ganze Prozess der Verantwortungsüberweisung für den Schutz oder Nichtschutz von Naturschutzgebieten. In diesem Sinne untersuchen wir auch, wie IBAMA, FEPAM und Staatsanwaltschaft sich positionieren und angesichts der gesetzten Thematik handeln. Für die vorgeschlagene Methodik bestimmten wir drei Bereiche des Flusses Santo Cristo zu Pilotflächen, für die wir die Längsdeiche und Auen als Parameter für die Bestimmungen der Naturschutzgebiete definierten. Ebenso beurteilten wir die Bodenstruktur der Region, um eine der Art der lokalen Betriebshöfe unmittelbar verbundene Deutung zu ermöglichen. Von diesen Vorzeichen ausgehend wurde eine kritische Lesart des Verhaltens dieser Flächen möglich, indem ihre derzeitige Verwendung derjenigen der gesetzlichen Anforderungen entgegengestellt wurde. Aus der vorliegenden Untersuchung ergeben sich als wesentliche Schlüsse: Eine vertiefte Untersuchung über die Naturschutzgebiete ist dringend und erforderlich, um einen neuen Gesetzesvorschlag zu erarbeiten, der effektive Fachparameter zur Bestimmung der Naturschutzgebiete festlegt und der gleichzeitig die Entwicklung von Untersuchungen anstrebt, die darauf zielen, alternative nachhaltige Nutzungsalternativen für diese Flächen vorzulegen; Beurteilung der Schutz- und Erhaltungskonzeptionen in der Absicht, dass letztere eine breite Palette von Vorteilen für die kleinen landwirtschaftlichen Betriebshöfe in dem Maβe mit sich bringen, wie die Bodenschutzmaβnahmen zum Ausgleich der Natur beitragen und in der Erzeugung dieser Betriebshöfe einen reellen Gewinn erbringen. Schlieβlich legen wir eine Reihe von Studien vor, die in der Absicht einer Vertiefung der von uns erforschten thematischen Diskussion verfolgt werden können. / O processo histórico de uso e ocupação da terra, baseado no desflorestamento e no manejo desordenado do solo, tem gerado conflitos entre os objetivos de recuperação ambiental e de reprodução socioeconômica dos agricultores assentados sobre áreas de elevadas restrições ambientais. Esta dicotomia reflete-se na atualidade através da aplicação mais efetiva da legislação ambiental, principalmente, do Código Florestal brasileiro, instituído pela Lei Federal n. 4.771 de 1965, que trata das Áreas de Preservação Permanente, APPs, que são as faixas marginais aos corpos hídricos que devem ser devidamente preservadas e mantidas com vegetação nativa. A discussão apresentada pelo presente estudo está pautada no questionamento das medidas geométricas contidas na definição das APPs nesse instrumento legal, buscando apresentar uma metodologia para a definição destas áreas a partir de elementos da geomorfologia fluvial, além daqueles relacionados com a cobertura vegetal de entorno. Para chegar aos resultados desse estudo se apresenta uma retomada histórica do processo de ocupação da Região Noroeste do Rio Grande do Sul, na qual se inserem as áreas amostrais, faz-se uma leitura teórica sobre conservação da natureza em nível mundial e discute-se as APPs em três níveis de análise para o Brasil: a) o arcabouço jurídico que está posto; b) o uso destas áreas e c) o estado da arte em que elas se apresentam no noroeste do Rio Grande do Sul. A discussão da função social da propriedade rural é vista como ponto importante desta discussão, por ser a partir dela que se dá todo o processo de responsabilização pela preservação ou não das APPs. Neste sentido, buscamos também compreender como o Ibama, a Fepam e o Ministério Público Estadual se posicionam e desenvolvem as suas atividades frente à temática colocada. Definimos como áreas piloto para a aplicação da metodologia proposta, três setores do Rio Santo Cristo, para os quais definimos os diques marginais e as planícies de inundação como parâmetros para a definição das APPs. Da mesma forma, avaliamos a estrutura fundiária da região para possibilitar uma leitura diretamente relacionada com o tipo de propriedade existente no local. A partir destas definições foi possível estabelecer uma leitura crítica das características dessas propriedades, comparando o seu uso atual com as exigências legais. Ficam como principais conclusões do presente estudo: a) que é urgente e necessário um estudo mais aprofundado sobre a questão das APPs para que seja possível apresentar uma proposta de alteração da legislação que busque parâmetros técnicos efetivos para a definição das APPs; b) que se busque igualmente o desenvolvimento de estudos que objetivem apresentar alternativas de uso sustentado para estas áreas; c) que se avaliem os conceitos de preservação e conservação com o intuito de compreender que o último traz uma grande gama de benefícios para as pequenas propriedades rurais, na medida em que as práticas conservacionistas auxiliam no equilíbrio da natureza e trazem um ganho real na produção destas propriedades. Por fim, apresentamos um conjunto de estudos que podem ser realizados com o intuito de aprofundar as discussões da temática por nós pesquisada. / The historic land grab and land usage process based on deforestation and disorderly land management caused conflicts between environmental cleanup and socioeconomic reproduction of the farmers settled on areas that underlie strict environment restrictions. This dichotomy at present gets evident in the application of the environmental legislation, particularly the new Brazilian Forest Code entitled by the federal Law No. 4.771 of 1965, when it involves permanent nature reserve (APPs), that is, marginal stripes along water corps that must be preserved with the associated original vegetation. The discussion herewith stated is based on the closer examination of the geometrical measures of the definition of the permanent nature reserves trying to present a method for the definition of theses areas out of the elements of the fluvial geomorphology. To reach the result, we make recourse to the historical land grab process in the northwestern region of Rio Grande do Sul, to which belong the areas herein studied. We make a theoretical interpretation of nature conservation at international level and discuss nature reserves at three study levels for Brazil: the given legal framework; the usage of these areas; and their conditions in northwest Rio Grande do Sul. The discussion of the social function of the farms is seen as an important aspect of this discussion because thereof happens the responsibleness for the conservation or not conservation of the preservation areas. We also study the positioning of Ibama, Fepam and prosecution in this question. We determinate three segments of the Santo Cristo river as pilot areas for the application of the proposed methodology, wherefore we defined natural levee and floodplains as patterns for the definition of nature preservation areas. We did also evaluate region’s estate to allow an understanding directly related to the kind of local property. These definitions allowed us establishing a critical understanding based on the behaviour of these areas comparing their current usage to the legal demands. The most important conclusions of this study are: 1) a deeper study of nature preservation areas urges and is necessary to allow the presentation of a new legal proposal that looks for effective technical patterns for the definition of nature reservation areas; 2) that one also tries to develop studies that try to show alternatives of sustainable usage of these areas; 3) that preservation and conservation concepts get evaluated with the intend to understand that this brings a wide scope of benefits to the small farms thus far as the conservation practices help to stabilize nature and to carry a real gain in the production of these farms. Finally we present a scope of studies that can be done with the aim of deepening the discussions of the question here studied.