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22 nov. LUCIVÂNIO, Jatobá.; LINS, Raquel Caldas – Introdução à Geomorfologia. Recife: Bagaço, PENTEADO, Margarida Maria E. Fluvial processes in river engineering. Wiley, New York, pp. CSIRO, Land Research Series, 1. Christofoletti, A., Geomorfologia fluvial. vol. 1, o canal . Teoretica Rio Claro 6(11/12), 67 (b) Christofoletti, A.: Geomorfologia Univ. São Paulo 51, 1 () Ciet, 87, () Dingman, S.L.: Fluvial hydrology.

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The Moeda syncline, located in the highlands of the Iron Quadrangle mountains SE Brazilis a setting of relief inversion and drainage reorganization. Morphological and morphometric analyses were carried out on GIS environment.

Christofoletti, Antônio [WorldCat Identities]

During the last phase of river capture, drainage reversal and elbows of capture developed in certain channels. During these events, there was a preferential migration of river channels to the east, groundwater piracy and beheading of the Rio do Peixe’s area. Based on such results, we believe that the events responsible for the landscape evolution of veomorfologia Moeda syncline during the Quaternary were particularly those associated with river capture sensu strictu, diversion and beheading driven by both neotectonics and litho-structural influences.

Since the beginning of geomorphological research, phenomena such as river capture, drainage expansion and relief inversion have been important to our understanding of long-term landform evolution DAVIS, ; ; BOWMAN, Bishop summarized the geomorfoligia responsible for river capture and divided them geomorfologoa three categories: The first represents the capture of one river by another one of lower elevation due to aggressive headward erosion. A general method for identifying captures has been to identify drainage elbows, knickpoints and wind gaps.

The second, river diversion, can be understood as similar to river capture, but, unlike the former process, the river is forced to flow into another watershed by channel migration, tectonic tilting or catastrophic processes.

Due to these conditions, the Moeda syncline is a highly appropriate area for studies of landform evolution and river capture. The Moeda syncline is drained by two main drainage basins: The north edge is defined by the Curral homocline, the east flank is defined by the Gandarela syncline, the west edge is the Moeda syncline and the south is defined christlfoletti the Dom Bosco syncline.

The study area consists of approximately km2 of drainage hcristofoletti. The Rio do Peixe valley flows east in its upper course, changing abruptly to a N-S orientation in the upper-middle course. This river then flows northeast near gsomorfologia water gap.

The study area has an area of approximately km2, a dendritic drainage pattern and several segments with anomalous inflections. The majority of the area is underlain by the Minas Supergroup, which is Paleoproterozoic phyllite, BIF, quartzite, shale and marble. Cenozoic materials are exposed in certain areas alluvium and laterites. It is affected by NW-SE strike-slip faults with sinistral and dextral displacements of hundreds of meters.

The west flank is also affected by the Moeda-Bonfim shear zone, which is a deep tectonic structure generated by extensional movements and west-verging reverse faults SILVA, The dips of the east flank vary considerably: Proterozoic geotectonic events on the west edge were responsible for the lateral migration of softer rocks of the Rio das Velhas Supergroup by transpressive deformation Dorr, fuvial This process has created a convex morphology of geomorfoloogia east flank in plain view, with west-verging polarity and inverted stratigraphy GOMES et al.

Along the west edge of the syncline, the Precambrian tectonic strains generated the inverse reactivation of the originally normal faults of the Moeda-Bonfim shear zone GOMES et al. On the right, the location of the water gaps where the drainage basins flow to the Rio das Velhas. According to Barbosa and confirmed by Barbosa fluvoal Rodriguesthe paleodrainage was predominantly endoreic in the upper course before the river captures controlled by the Rio das Velhas enabled outflow from the syncline.

A range of procedures cited in the scientific literature were adopted to reconstruct the Moeda syncline’s geomorphologic history.

Specifically, a set of i morphological and ii morphometric analyses was performed. In the first method imorphological evidence, such as drainage inflections elbows and changes in drainage orientation, were sought.

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In the second iithe drainage density Ddrelief ratio Rrhypsometric integral HIhypsometric curve HCstream length-gradient index SLasymmetry factor AFtransverse topographic symmetry factor Tvolume of sediments removed from the watersheds and landform downwearing were measured.

The morphological and morphometric methods were performed using the ArcGIS All of our methods are described in detail below. In addition, the neighboring watersheds of the Moeda syncline were analyzed due to the possibility of drainage reorganization and river captures of these watersheds during the Quaternary. The relief ratio Rrfirst described by Schummis given by the equation. This index allows for an understanding of the elevation changes as a function of variations in the channel length.

The larger this value, the greater the relief between the headwater and the outlet and, hence, the greater the watershed’s mean slope. The hypsometric curves HCs are obtained using christofoleti plots in which the chridtofoletti area of the height intervals and cumulative relief are plotted along the abscissa and ordinate, respectively.

The differences in the curves’ shapes are related to the degree of disequilibrium in the balance between erosional and tectonic forces: The hypsometric integral HI is an geomorfolgia similar to the hypsometric curve and allows for an evaluation of the correspondence between the landforms and the Davisian cycle of erosion Strahler, The stream length-gradient index SLdefined by Hackmay be mathematically chrisofoletti in two ways.

According to Etchebehere et al. Such changes geomorfologi be associated with many factors, such as i the outfall of tributaries with high fluviaal, ii changes fluvlal the lithological resistance and iii neotectonic activity. To verify the geomorfollogia of the mentioned causal variables tributaries, neotectonics and lithologythe anomaly criteria proposed by Seeber and Gornitz were used.

To verify the drainage network assymetry and its likely causes, the assymetry factor AF and transverse topographic symmetry factor T were calculated. The assymetry geomofrologia AFproposed by Hare and Gardnermeasures the displacement of the watershed axis relative to its midline. This factor can be obtained using the equation. The transverse topographic symmetry factor T is a more sophisticated quantitative index, developed by Coxthat allows for an evaluation of the asymmetry of river channels in a drainage basin and the manner in which this asymmetry varies with length.

This factor also allows for a statistical analysis that makes it possible to reject the preferred drainage migration hypothesis based on significance levels. The transverse topographic symmetry factor T can be obtained using the equation. In chriwtofoletti with these exploratory mathematical techniques, Cox proposed the use of a statistical procedure developed by Curray Cox calculated the probability of a T vector from its origins in random combinations rather than preferred ones as occur with channel migrations due to external causes.

This probability p can be calculated using the equation.

Finally, the volume of sediments removed from the drainage basins was estimated based on the difference between a theoretical paleosurface, referring to a time before the relief inversion, and the current surface. This paleosurface was generated based on the heights of the east and west divides, which constitute the syncline’s edges. Then, from the height values of the paleo-and current surface, the mean downwearing of the landform was calculated. The data obtained from the Moeda syncline reveal distinct morphological patterns in the main watersheds under investigation.

Likewise, the Rio do Peixe watershed contains nearly seven times more segments of smooth slope and three times more moderate slope areas Table 2. Analysis of topographic profiles reveal a general decrease in the heights of the summits to the east, with a more marked decrease near the water gaps Figures 4 and 5.

The profile names are in alphabetical order with respect to their location from N christifoletti S. The ordinate shows elevation mand the rluvial shows the horizontal scale m. Along the Moeda syncline’s edges, the elevation is stable, with an upward trend on the west flank from north to south.

In the eastern geeomorfologia, there is a considerable drop to the south, i. The Rio das Velhas, which constitutes the base level of the Moeda syncline’s drainage area, is situated above christofooetti Rio Paraopeba in the western area. The two analyzed drainage basins underlain by the Moeda syncline exhibit two very distinct drainage densities.

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Moreover, the probability that these two watersheds have different drainage densities is approximately The extremely low p-value demonstrates a probability higher than The existing inflections elbows in the river network do not show randomness Figure 7. In the Rio do Peixe watershed, the more distinct inflections are those with N-S orientations near the syncline’s west edge. The exception is the main valley, where there are two inflections near the eastern flank, one in the christofolethi course and the other near the water gap.

There are two well-defined groups: Fouvial is located in the middle course, near the dextral strike-slip faults, where there are two well-defined inflections. Another set of inflections is located in the lower course, specifically on the right margin’s main tributaries and near the south syncline’s drainage geomorcologia.

The river network’s orientation upstream of certain geo,orfologia these inflections is similar to the orientation of certain nearby rivers Figure 8.

In the left margin’s tributaries of the Rio do Peixe, there are channels with orientations N-S very similar to those of the segments located upstream of the inflections. The results obtained through the stream length-gradient indexes indicate the preferred locations of river segments with no anomalies and those with first-and second-order anomalies Figure 9. Segments with no anomalies tend to be located near others with 1st-order anomalies in the Rio do Peixe watershed. In the Rio do Peixe watershed, there is a concentration of 1st-order anomalies next to the water gap and in scattered confluences along both margins.

Furthermore, the range of anomalies differs substantially between the investigated drainage basins Table 5. The transverse topographic symmetry factor indicates a statistically significant preferred migration of the Rio do Peixe, whereas its sub-basin tributaries display insignificant values lower than 0.

Christofoletti, Antônio 1936-

The Rio do Peixe has the highest mean vector T and the lowest significance level p than its tributaries. In general, the mean direction geomorfolkgia significant variations and the increase of the mean vectors T is similar to the values found in the statistical significance values p. Similarly, the channel migration vectors display directions that vary considerably within the same watershed and differ from those of nearby watersheds Figure christofoletit The blue points denote segments without significant migration.

There is also a pattern in the relief ratios of specific segments of the watersheds. In general, the Rio do Peixe yielded values with higher randomness, ranging between 0. The p-value indicated low probability in decimal scale of equal relief ratio values for the watersheds. The hypsometric integrals of the most distinct sub-basins of the Moeda syncline range between 0. The spatial distribution of these values displays a sharp distinction between the two main drainage basins underlain by the syncline Fig.

The hypsometric curves of the Rio do Peixe are displayed on.

Geomorfologia fluvial christofoletti download

In the Rio do Peixe basin, the majority of the tributary basins have HI values ranging between 0. These sub-basins are generally distributed across the entire basin, decreasing only in the middle course.

The hypsometric curves also exhibit distinct characteristics. The majority of the Rio do Peixe watershed displays a low height variation, with a sharp relief increase in chrixtofoletti a relatively small area.

In general, the hypsometric curves of the Rio do Peixe’s tributaries are below that of the Rio do Peixe valley in the upper course, closer to it in the medium course and reach the maximum distance in the lower course.

However, the mean landform downwearing in these two basins differs greatly. This christofoletgi becomes clearer when the downwearing values within these basins are analyzed Figure Note the concentrated pattern and nonrandom values approaching zero and higher than m. In the west, the Rio Paropeba represents a lower base level, but only in the eastern flank drained by the Rio das Velhas are the two conditions required for river capture present.