Aplicação da Micromorfologia de Solos ao Estudo de Sedimentos Alúvio-Coluviais em Cabeceiras de Vale

Previous work on the role played by valley head areas in humid regions brought to light geomorphological units of the drainage net in which erosion and sedimentation would tend to be recurrent in time and space. Valley heads studied in Brazil had already proved to be very sensible to gully erosion processes, which, besides its importance to land degradation, also is a common process of hillslope evolution on humid regions. Gully erosion carries out from slopes important amounts of sediments, which may either, accumulate as proximal colluvium and alluvium or be conveyed through the drainage net. When colluvium and alluvium accumulate in proximal areas sedimentary structures may be preserved allowing the study of evolutionary processes. This paper is an attempt to apply micromorphological analysis to the study of the sedimentary structures preserved in gullied hillslopes of some southern Brazilian areas. The deposits are dated either in accordance to the supposed age of the gully incision, as estimated by aerial photographs, or by the record, in the field, of the depositional event. As a result, the age of the study deposits ranges from about 200 to 30 years, including fresh sediments just deposited one day before sampling. The paper stresses the relationship between macroscopic structures and micromorphological parametrical description, emphasizing interpretation of sedimentary structures as the result of variable overland flow rates on the gullied hillslopes.

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Reconstructing long-term gully dynamics in Mediterranean agricultural areas

Hydrology and Earth System Sciences ◽

10.5194/hess-21-235-2017 ◽

2017 ◽

Vol 21 (1) ◽

pp. 235-249 ◽

Cited By ~ 9

Author(s):

Antonio Hayas ◽

Tom Vanwalleghem ◽

Ana Laguna ◽

Adolfo Peña ◽

Juan V. Giráldez

Keyword(s):

Land Use ◽

Temporal Resolution ◽

Land Use Changes ◽

Mediterranean Area ◽

Gully Erosion ◽

Aerial Photographs ◽

High Temporal Resolution ◽

Erosion Rates ◽

Erosion Processes

Abstract. Gully erosion is an important erosive process in Mediterranean basins. However, the long-term dynamics of gully networks and the variations in sediment production in gullies are not well known. Available studies are often conducted only over a few years, while many gully networks form, grow, and change in response to environmental and land use or management changes over a long period. In order to clarify the effect of these changes, it is important to analyse the evolution of the gully network with a high temporal resolution. This study aims at analysing gully morphodynamics over a long timescale (1956–2013) in a large Mediterranean area in order to quantify gully erosion processes and their contribution to overall sediment dynamics. A gully network of 20 km2 located in southwestern Spain has been analysed using a sequence of 10 aerial photographs in the period 1956–2013. The extension of the gully network both increased and decreased in the study period. Gully drainage density varied between 1.93 km km−2 in 1956, a minimum of 1.37 km km−2 in 1980, and a maximum of 5.40 km km−2 in 2013. The main controlling factor of gully activity appeared to be rainfall. Land use changes were found to have only a secondary effect. A new Monte Carlo-based approach was proposed to reconstruct gully erosion rates from orthophotos. Gully erosion rates were found to be relatively stable between 1956 and 2009, with a mean value of 11.2 t ha−1 yr−1. In the period 2009–2011, characterized by severe winter rainfalls, this value increased significantly to 591 t ha−1 yr−1. These results show that gully erosion rates are highly variable and that a simple interpolation between the starting and ending dates greatly underestimates gully contribution during certain years, such as, for example, between 2009 and 2011. This illustrates the importance of the methodology applied using a high temporal resolution of orthophotos.

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Reconstructing long-term gully dynamics in Mediterranean agricultural areas

10.5194/hess-2016-239 ◽

2016 ◽

Cited By ~ 1

Author(s):

Antonio Hayas ◽

Tom Vanwalleghem ◽

Ana Laguna ◽

Adolfo Peña ◽

Juan V. Giráldez

Keyword(s):

Land Use ◽

Temporal Resolution ◽

Land Use Changes ◽

Mediterranean Area ◽

Drainage Density ◽

Gully Erosion ◽

Aerial Photographs ◽

High Temporal Resolution ◽

Erosion Rates ◽

Erosion Processes

Abstract. Gully erosion is an important erosive process, especially in Mediterranean basins. However, the longterm dynamics of gully networks and the variation of sediment production in gullies is not well known. Available studies are often done over a few years only, while many gully networks form, grow, and change in response to environmental and land use or management changes over a long period. In order to clarify the effect of these changes, it is important to analyze the evolution of the gully network with a high temporal resolution. This study aims at analyzing gully morphodynamics over a long time scale (1956–2013) in a large Mediterranean area in order to quantify gully erosion processes and its contribution to overall sediment dynamics. A gully network of 20 km2 located in SW Spain, has been analyzed using a sequence of 10 aerial photographs in the period 1956–2013. The extension of the gully network both increased and decreased in the study period. Gully drainage density varied between 1.93 km km−2 in 1956, with a minimum of 1.37 km km−2 in 1980 and a maximum of 5.40 km km−2 in 2013. The main controlling factor of gully activity appeared to be rainfall, while land use changes were found to have only an indirect effect. A new Monte Carlo-based approach was proposed to reconstruct gully erosion rates from orthophotos. Gully erosion rates were found to be relatively stable between 1956–2009, with a mean value of 11.2 ton ha−1 yr−1, while in the period 2009–2011, characterized by extreme winter rainfalls, this value increased significantly, to 591 ton ha−1 yr−1. These results show that gully erosion rates are highly variable and that a simple interpolation between the start and end date would highly underestimate gully contribution during certain years, such as for example between 2009–2011. This illustrates the importance of the applied methodology using a high temporal resolution of orthophotos.

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The role of the geometry and frequency of rectangular rills in the relationship between sediment concentration and stream power

Soil Research ◽

10.1071/s97019 ◽

1997 ◽

Vol 35 (6) ◽

pp. 1359 ◽

Cited By ~ 2

Author(s):

B. Fentie ◽

C. W. Rose ◽

K. J. Coughlan ◽

C. A. A. Ciesiolka

Keyword(s):

Soil Erosion ◽

Overland Flow ◽

Sediment Concentration ◽

Stream Power ◽

Flume Experiments ◽

Erosion Processes ◽

Physically Based ◽

The Relationship ◽

Raindrop Impact

We examined, both experimentally and theoretically, whether rilling results in higher soil erosion than would have occurred without rilling. The possibility of rilling occurs when overland flow-driven erosion processes are dominant over erosion due to raindrop impact, and that is the situation assumed in this paper. Stream power (or a quantity related to stream power such as shear stress) is commonly used to describe the driving variable in flow-driven erosion. Five flume experiments were designed to investigate the relationship between stream power and sediment concentration and how this relationship is affected by the ratio of width to depth of flow (r), and the frequency or number of rills per metre width (N) of rectangular rills. This paper presents the results of these experiments and uses a physically based soil erosion theory to show that the results of the 5 flume experiments are in accord with this theory. This theory is used to investigate the effect of all possible rectangular rill geometries and frequencies on the maximum possible sediment concentration, i.e. the sediment concentration at the transport limit, by developing general relationships for the influence of r and N on sediment concentration. It is shown that increased stream power, which can be due to rilling, does not necessarily result in higher sediment concentration.

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Hydrogeomorphic processes affecting dryland gully erosion: Implications for modelling

Progress in Physical Geography Earth and Environment ◽

10.1177/0309133318819403 ◽

2018 ◽

Vol 43 (1) ◽

pp. 46-64 ◽

Cited By ~ 3

Author(s):

Roy C. Sidle ◽

Ben Jarihani ◽

SanLinn Ismail Kaka ◽

Jack Koci ◽

Abdulaziz Al-Shaibani

Keyword(s):

Land Management ◽

Management Practices ◽

Overland Flow ◽

Ground Cover ◽

Gully Erosion ◽

Annual Rainfall ◽

Surface Erosion ◽

Distributed Data ◽

Erosion Processes ◽

Sediment Loads

Gullies contribute high sediment loads to receiving waters and significantly degrade landscapes. In drylands, low annual rainfall and resultant poor ground cover, coupled with high-intensity storms and dispersive soils, predispose these landscapes to gully erosion. Land management, such as grazing, exacerbates gully-forming processes by degrading ground cover and compacting soils, thereby increasing and concentrating overland flow. Current surface erosion models do not adequately represent sediment export from gullied terrain due to lack of distributed data and complex hydrogeomorphic processes, such as overland flow concentration, waterfall erosion, soil pipe collapse, and mass wasting. Here, we outline the strengths and weaknesses of past modelling approaches in erodible terrain and focus on how gully erosion processes can be better simulated at appropriate scales using newly available remote-sensing techniques and databases, coupled with improved understanding of relevant hydrogeomorphic processes. We also discuss and present examples of challenges related to assessing land management practices in drylands that affect gully erosion.

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Monitoring Geomorphic Change and Catchment Sediment Production to Understand the Erosive Dynamics in a Gullied Channel by Means of High-Resolution DEMs

Proceedings ◽

10.3390/proceedings2019030056 ◽

2020 ◽

Vol 30 (1) ◽

pp. 56

Author(s):

Alberto Alfonso-Torreño ◽

Álvaro Gómez-Gutiérrez ◽

Susanne Schnabel ◽

J. Francisco Lavado Contador ◽

Manuel Pulido Fernández ◽

...

Keyword(s):

High Resolution ◽

Soil Loss ◽

Sediment Load ◽

Gully Erosion ◽

Negative Consequences ◽

Inference System ◽

Erosion Processes ◽

Agrosilvopastoral Systems ◽

Positive Balance ◽

The Relationship

Gully erosion in valley bottoms is a frequent process with negative consequences in the dehesa environment. Soil loss, decrease of soil and descend in biomass are among the negative aftereffect of gully erosion processes. Studies conducted in agrosilvopastoral systems described the dynamics of gullied channels by means of fixed topographic cross sections or with low spatial resolution Digital Elevation Models (DEMs). Currently, high spatial and temporal resolution DEMs can be produced with spatially distributed information due to the development of new systems, platforms and sensors. Additionally, the rainfall and sediment discharge could also be monitored. This control allows us to relate gully erosion with catchment hydrology. The goals are (1) to quantify the sediment budgets by the spatio-temporal distribution of erosion and/or deposition in the gullied channel, (2) to interpret the geomorphic processes driving erosion and deposition and (3) to analyze the relationship between the morphological change and the catchment runoff and the sediment load. The studied area is a gullied channel located in the SW Iberian Peninsula and developed over a recent sedimentary deposit. The channel reaches an extension of 1 km in length and 2 m in depth. The methodology included the following steps: (1) flying the same study area with different time periods using a fixed-wing small Unmanned Aerial System (sUAS) to capture high-resolution aerial images and surveying Ground Control Points (GCPs) using a GNSS, (2) Structure-from-Motion photogrammetry processing using the acquired images and the GCPs to produce high-resolution DEMs for each date, (3) Applying the DEMs of difference approach to estimate topographic changes and to quantify the sediment budget and finally (4) analyzing the relationship between rainfall events, discharge, sediment load and changes in the channel previously estimated. Resulting DEMs and orthophotographs showed a Ground Sampling Distance of 0.02 m with a georeferencing Root Mean Square Error of 0.03 m. A spatially variable threshold (to differentiate actual geomorphic change from noise or errors) was produced using a Fuzzy Inference System and considering photogrammetric errors, slope and vegetation as factors. The applied method proved to be suitable to interpret the geomorphic changes for the gullied channel. For the 2016–2018 period, the gully showed a positive balance indicating accumulation of sediments coming from the hillslopes of the catchment. It is the period with the highest rainfall when numerous events generated runoff. On the contrary, for the period 2018–2019 a total soil loss of −119 m3 was estimated.

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Overland Flow Resistance Law under Sparse Stem Vegetation Coverage

Water ◽

10.3390/w13121657 ◽

2021 ◽

Vol 13 (12) ◽

pp. 1657

Author(s):

Jingzhou Zhang ◽

Shengtang Zhang ◽

Si Chen ◽

Ming Liu ◽

Xuefeng Xu ◽

...

Keyword(s):

Flow Resistance ◽

Overland Flow ◽

Vegetation Coverage ◽

Dominant Factor ◽

Roughness Coefficient ◽

Hydraulic Parameters ◽

Slope Condition ◽

Manning Roughness ◽

The Relationship ◽

Manning Roughness Coefficient

To explore the characteristics of overland flow resistance under the condition of sparse vegetative stem coverage and improve the basic theoretical research of overland flow, the resistance characteristics of overland flow were systematically investigated under four slope gradients (S), seven flow discharges (Q), and six degrees of vegetation coverage (Cr). The results show that the Manning roughness coefficient (n) changes with the ratio of water depth to vegetation height (h/hv) while the Reynolds number (Re), Froude number (Fr), and slope (S) are closely related to vegetation coverage. Meanwhile, h/hv, Re, and Cr have strong positive correlations with n, while Fr and S have strong negative correlations with n. Through data regression analysis, a power function relationship between n and hydraulic parameters was observed and sensitivity analysis was performed. It was concluded that the relationship between n and h/hv, Re, Cr, Q, and S shows the same law; in particular, for sparse stem vegetation coverage, Cr is the dominant factor affecting overland flow resistance under zero slope condition, while Cr is no longer the first dominant factor affecting overland flow resistance under non-zero slope condition. In the relationship between n and Fr, Cr has the least effect on overland flow resistance. This indicates that when Manning roughness coefficient is correlated with different hydraulic parameters, the same vegetation coverage has different effects on overland flow resistance. Therefore, it is necessary to study overland flow resistance under the condition of sparse stalk vegetation coverage.

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