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The Paraguay River Basin has been intensively occupied since the 1970 years and its channel dynamic has been changing. The dynamics of the fluvial corridor’s margins was studied, tends as objective evaluating the erosion for a period of nineteen years, using the crossing of images of satellite TM Landsat 5 of the year of 1984 and ETM Landsat 7 de 20...
The Paraguay River Basin has been intensively occupied since the 1970 years and its channel dynamic has been changing. The dynamics of the fuvial corridor's margins was studied, tends as objective evaluating the erosion for a period of nineteen years, using the crossing of images of satellite TM Landsat 5 of the year of 1984 and ETM Landsat 7 de 20...
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... Wolman was the first to conduct such studies in Montgomery county in the eastern United States [20]. In Australia, they were used in measurements of the rates of bank retreat on rivers Ngaradj [48] and Daintree [26], and on Gowrie Creek [49]. In Italy, they were used in studies on bank erosion on the Cecina River [50]; in Denmark, on the Odense shores [51]; in England, on the banks of the Swale, Ouse, and Ure [2], rivers in Devon [9]; and in the United States, on the shores of Lake Michigan [33,34]. ...
The rate of bank retreat was measured using erosion pins on the alluvial banks of the rivers in the Podhale region (the boundary zone between Central and Outer Carpathians) during the hydrological year 2013/2014. During the winter half-year (November–April), the bank retreat was mainly caused by processes related to the freezing and thawing of the ground (swelling, creep, downfall). During the summer half-year (May–October), fluvial processes and mass movements such as lateral erosion, washing out, and sliding predominated. The share of fluvial processes in the total annual amount of bank retreat (71 cm on average) was 4 times greater than that of the frost phenomena. Erosion on bank surfaces by frost phenomena during the cold half-year was greatest (up to 38 cm) on the upper parts of banks composed of fine-grained alluvium, while fluvial erosion during the summer half-year (exceeding 80 cm) mostly affected the lower parts of the banks, composed of gravel. The precise calculation of the relative role of frost phenomena in the annual balance of bank erosion was precluded at some stations by the loss of erosion pins in the summer flood.
... 1-2 times longer = 100-200 m (Table 1). Streambank profile and stability measurements were based on categories of eroded streambank profiles described by (Saynor et al. 2003). Tree and shrub cover was estimated using the visual methods of Specht described by (Walker and Hopkins 1984). ...
Agricultural riparian zones are often vulnerable to weed invasion and degradation of the physical streambank character through the trampling of livestock. Riparian zone restoration seeks to improve habitat biodiversity, minimise streambank erosion and improve water quality. In order for this to be effective land managers need to broadly understand the connections between riparian systems and adjoining agricultural ecosystems and to understand the habitat requirements of wildlife species adapted to the evolving riparian landscape. Common wombats ( Vombatus ursinus) are abundant in the riparian agricultural landscapes of south-eastern Australia, but there is concern about their persistence in other landscapes. To understand the importance of riparian characteristics for wombats, we examined five physical and five vegetative characteristics associated with abundance of wombat burrows in the riparian zone of an agricultural landscape in south-eastern New South Wales, using two independent datasets. The abundance of wombat burrows increased substantially with increasing shrub cover in both datasets. There was weaker but consistent support for an association between wombat burrows and stream order and vegetation width. There were more burrows per metre by high than low order streams and burrows were most abundant at an intermediate vegetation width. In one of the two datasets, burrow abundance declined as the proportion of native shrubs in the shrub layer increased. As wombats are generally limited to riparian buffers in agricultural landscapes, these results are important as a first step toward managing and restoring the riparian zone. Restoration strategies, for example, may need to consider retaining patches of shrubs, even if they are weeds, whereas native shrubs are established in interspersed patches along larger rivers, in order to maintain suitable wombat habitat.
This dissertation has investigated soil erosion caused by water on the slopes, by
conducting field and laboratory experiments on an active gully and some of the
surrounding slopes. As objectives, two types of gully monitoring were adopted and
some soil analyses were carried out to assess land degradation and could start the
recovery of a little area, testing in it the effectiveness of geotextiles made from
banana´s fibers. Bibliographic references about the theme were searched all over the
course period, to give the research bases needed. Some important maps were used
to compose the study area characterization as a whole, the São Pedro´s river basin,
at the north State of Rio de Janeiro. A lot of field trips were conducted, firstly to find a
compatible area and then to make the monitoring procedures and the recovery tests.
Laboratory analysis allowed verifying soil erodibility of the study area, and most of
the results pointed out sandy loam soils to deeper layers and sandy clay loam soils to
more superficial layers. It demonstrates that silt contents are greatest in subsurface,
especially added to high fine sand contents, which gives this materials a high
erodibility level and turns greater its erosion susceptibility, when exposed to erosive
agents. Monitoring with erosion pegs and pins showed to have a complementary
potential. Through these procedures it was achieved an erosion rate of 2.49 tons of
soil mass loss during approximately a year of investigations. Considering only the
little gully of the area, the erosion could reach 100 t.ha-1. Integrating these factors to
the lower contents of organic matter and organic carbon, commonly below of 3.5%
and 2.0%, respectively; the acidity of the soils, although not in critical rates; soil
compaction, always close to 1.50 g/cm³ or higher, and porosity below 45%; the
diagnosis showed alarming levels of land degradation on the study area, clearly
noticed by the marked presence of cattle trampling terracetes and rapidly expanding
gullies. The recuperation was successful with the unpublished use of banana´s fibers
to manufacture biological geotextiles. The vegetation cover has developed and
established in a few months with geotextiles help, exposing the aptitude of the
geotextiles made from Banana´s materials to recover this degraded land. In addition
to these conclusions, it is claimed the need for more important elements to be
considered, in order to increase the diagnosis results, so the techniques could be
improved and help with sustainability.
Esta dissertação estudou a erosão dos solos causada pela ação da água
sobre as encostas, através da condução de experimentos de campo e laboratório
sobre uma voçoroca em atividade e algumas encostas de seu entorno. Como
objetivos, foram realizados dois tipos de monitoramento dessa feição erosiva e
análises do solo da área, para diagnosticar a degradação e dar início à recuperação
de parte da área degradada, testando a eficiência de geotêxteis de fibras de
bananeira. Para a realização da pesquisa foi levantada a bibliografia referente ao
tema, durante todo o período de realização do curso. Os devidos mapas foram
utilizados para compor a caracterização da área de estudos como um todo, a bacia
hidrográfica do rio São Pedro, norte fluminense. Foram realizados diversos trabalhos
de campo, desde a procura por uma área compatível, até os monitoramentos e
recuperação realizados. As análises laboratoriais permitiram verificar a erodibilidade
dos solos. A maioria dos resultados apontou solos de textura franco arenosos para
camadas mais profundas, e franco argilo arenosos, para camadas mais superficiais.
Isso demonstrou que os teores de silte são mais elevados em subsuperfície,
principalmente somados aos altos teores de areia fina, conferindo alta erodibilidade
a esses materiais, e maior suscetibilidade em caso de serem expostos aos agentes
erosivos. Os monitoramentos das bordas e dos pinos de erosão se mostraram
potencialmente complementares. Por estes, chegou-se a taxas de erosão de 2,49
toneladas de massa de solo, algo em torno de um ano de estudos. Considerando o
tamanho da área a que se referem tais taxas, que foram mensuradas na menor
voçoroca da área, a erosão poderia chegar a 100 toneladas por hectare. Integrando
estes fatores, aos baixos teores de matéria orgânica e carbono orgânico,
comumente abaixo de 3,5% e 2,0%, respectivamente; à acidez apresentada pelos
solos, embora não crítica; à compactação apresentada pelos solos, sempre com
valores próximos a 1,50 g/cm³, ou mais elevados e à porosidade abaixo de 45%; o
diagnóstico aponta níveis preocupantes de degradação da área estudada,
visivelmente percebida pela presença marcante de terracetes de pisoteio do gado e
de voçorocas em expansão rápida. O início de recuperação foi bem sucedido com a
utilização inédita das fibras de bananeira para a confecção de geotêxteis
biodegradáveis. A cobertura vegetal se desenvolveu e estabeleceu em poucos
meses, com o auxílio dos geotêxteis, expondo a aptidão das telas feitas com
materiais da bananeira para a recuperação da área. Além dessas conclusões,
afirma-se a necessidade de melhorar o diagnóstico, agregando elementos não
considerados aqui, para o melhor aproveitamento das técnicas empregadas e a sua
sustentabilidade.
Data on rates of sedimentation are essential in studies of sedimentation systems. These data are obtained in three main study contexts: (1) the study of sedimentation systems that are active today, (2) the source-to-sink study of sedimentation systems that no longer are active, and (3) the study of the relationship between accumulation rate and measurement timespan. The aim of this paper is to question the meaning of measured rates of sedimentation, and their interpretability, particularly in these three contexts.
Individual measurements of rate of sedimentation must always be interpreted with care. Firstly, there are different definitions, for instance with different statistical support or measurement dimension; values that are defined differently cannot be compared directly. Secondly, appropriate sampling schemes must have been used for the measurement; this minimises sampling bias. Thirdly, the inherent limitations of the data sources must be taken into account. Rates of sedimentation can usually be measured successfully in active sedimentation systems. The same is not true for systems that are no longer active; these can only be studied using the stratigraphic successions left behind. Rates of erosion can never be measured successfully in stratigraphic successions.
Rate of sedimentation is essentially a ratio – an amount of sedimentation per length of time – therefore the obvious strategy to use in determining it is first to measure the amount and the time independently, then to combine the values. The amount can be measured in terms of thickness or volume or mass per unit area. The duration of the time interval can be preset using quasi-continuous measurement techniques or site reoccupation, or it can be identified from interval-specific sedimentary structures, or it can be measured using dated horizons. An alternative strategy is to use a surrogate measurement variable. Rates of erosion in ancient systems are usually measured in this way, using cosmogenic radionuclide concentrations. These two strategies are reviewed in this paper.
Sets of measurements made in systems that are active today can certainly be used to estimate the rate of sedimentation for the system as a whole. This estimation is best carried out using geostatistical estimation techniques. The alternative is simply to average the measured rate values. This latter approach should not be used, however, because the mean sedimentation rate in a system gives information only about the net sediment movement at the system boundaries. It says nothing at all about how the system is operating or about its spatial and temporal variability.
Measurements of rates of sedimentation made for source-to-sink studies are necessarily made in stratigraphic successions. The measurements are used to estimate quantities in the sediment mass budget equation. The amount of decumulation is inherently incapable of being measured in stratigraphic successions, therefore there are always unknowns in the mass budget equation whenever the lithic surface at the start of the time interval considered cannot be recognised everywhere. This means that the mass budget equation is applicable in practice only when all the systems involved in the study are entirely non-erosional for that entire time interval — a highly unrealistic situation.
The consistently inverse relationship documented between accumulation rates and measurement timespan is taken usually to indicate that this relationship is substantially scale-invariant. This in turn is often taken as indicating that the stratigraphic record is fractal in nature. There are nevertheless grounds for doubt, all of which relate to the ways that the data are collected and used for estimation. The relationship is in fact the natural mathematical result of last-in-first-out (LIFO) operation and is produced in any type of system in which addition and removal processes both operate. It says nothing particular about sedimentation processes. The future analysis of accumulation rate data collected from stratigraphic successions will sensibly be framed in the context of estimating the parameters of a LIFO model.
The catchment of Ngarradj Creek is located in the wet dry tropics of the Northern Territory, Australia, and is a major right-bank tributary of the Ramsar-listed Magela Creek wetlands. It contains the Energy Resources of Australia Jabiluka project area which is currently in a long-term care and maintenance phase. As part of a long-term study of rates of geomorphic processes within the catchment, a series of research projects were initiated in 1998 by the Environmental Research Institute of the Supervising Scientist (eriss). One of the projects involved determining baseline graphic grain size statistics of the bed material and other sediment stores within the catchment and evaluating any impacts of the Jabiluka project area on these statistics. The graphic grain size statistics investigated included graphic mean size, inclusive graphic standard deviation, inclusive graphic skewness, graphic kurtosis and normalised kurtosis.
Bulk sampling was used to collect mainly bed material but also bar, bench, floodout, splay and distributary channel sediments on the tributaries draining the Jabiluka project area as well as Ngarradj Creek at the Swift Creek gauge downstream of the junction with the Jabiluka project area tributaries. The gauging reaches on Ngarradj Creek at upper Swift Creek and on East Tributary, upstream of the Jabiluka project area, were also sampled at the same time and served as multiple reference sites that were not impacted by the Jabiluka project area. Bed-material was systematically sampled every dry season between 1998 and 2003 but other sediment storages were usually sampled only once between 1998 and 2000. The 56 permanently monumented cross sections used to assess channel changes served as the bed-material sample sites because they ensured that the sample sites could be accurately relocated each year. All samples were sieved and graphic grain statistics were calculated from the cumulative percentage grain size distributions.
The grain size statistics for the period 1998 to 2003 indicated that:
Tributary Central had the coarsest graphic mean size and the greatest range in grain size statistics because three different types of river reaches were sampled. There was no change in graphic grain size statistics between 1998 and 2003.
Tributary North main gully and Tributary North tributary gully have similar grain size statistics which are different from those for the Tributary Central and gauging station river reaches. There was no change in graphic grain size statistics between 1998 and 2003 on Tributary North main gully but inclusive graphic skewness and graphic and transformed kurtosis increased after 1998, most probably due to the effects of dry season fires.
The East Tributary, upper Swift Creek and Swift Creek gauging station reaches have similar graphic grain size statistics. Graphic mean size increased at all three sites between 1998 and 1999 and the data analysis indicated that this increase was statistically significant at ρ = 0.05 level for East Tributary (ρ = 0.01) and Swift Creek (ρ = 0.014), although the increase was not significant (ρ = 0.053) at upper Swift Creek. Graphic and transformed kurtosis also changed significantly after 1998 at upper Swift Creek and inclusive graphic skewness changed significantly after 1998 at the Swift Creek gauge. After the increase between 1998 and 1999, graphic mean size remained relatively constant at all three main channel sites until 2003. The trend in graphic mean size recorded at the downstream Swift Creek gauge was also observed at the upstream East Tributary and upper Swift Creek sites indicating that it was an upper catchment-driven and not a project area-driven change. A coarse-grained phase of sand transport in the main channel network commenced after 1998 but was not generated by the Jabiluka project area tributaries, despite the construction of the Jabiluka project area during the 1998 dry season. The multiple upstream reference sites that were not impacted by the Jabiluka project area were important to determine that this increase was caused by a similar change at both upstream reference sites. A longer record (greater sample size) is still required before the change is significant at ρ = 0.05 in the upper Swift Creek gauge reach.
The grain size statistics constitute thorough baseline information for the Ngarradj catchment and can now be used to determine any subsequent changes due to future activities on the Jabiluka project area. Box plots for each site, when combined with appropriate statistical tests, can be used to assess future departures from these baseline data. This will be important if the Jabiluka project area is reopened in the future as well as to assess the efficacy of the Jabiluka project area rehabilitation.
Bank erosion rates and processes across a range of spatial scales are poorly understood in most environments, especially in the seasonally wet tropics of northern Australia where sediment yields are among global minima. A total of 177 erosion pins was installed at 45 sites on four sand-bed streams (Tributaries North and Central, East Tributary and Ngarradj) in the Ngarradj catchment in the Alligator Rivers Region. Bank erosion was measured for up to 3·5 years (start of 1998/99 wet season to end of 2001/02 wet season) at three spatial scales, namely a discontinuous gully (0·6 km2) that was initiated by erosion of a grass swale between 1975 and 1981, a small continuous channel (2·5 km2) on an alluvial fan that was formed by incision of a formerly discontinuous channel between 1964 and 1978, and three medium-sized, continuous channels (8·5–43·6 km2) with riparian vegetation. The bank erosion measurements during a period of average to above-average rainfall established that substantial bank erosion occurred during the wet season on the two smaller channels by rapid lateral migration (Tributary Central) and by erosion of gully sidewalls due to a combination of within-gully flows and overland flow plunging over the sidewalls (Tributary North). Minor bank erosion also occurred during the dry season by faunal activity, by desiccation and loss of cohesion of the sandy bank sediments and by dry flow processes. The larger channels with riparian vegetation (East Tributary and Ngarradj) did not generate significant amounts of sediment by bank erosion. Deposition (i.e. negative pin values) was locally significant at all scales. Bank profile form and channel planform exert a strong control on erosion rates during the wet season but not during the dry season. Copyright © 2006 Commonwealth Government of Australia.
Even though soil loss in the lowlands imposes not as much a restriction on land use and agricultural productivity as in erosion affected mountainous areas, the input of fine sediment into the rivers and streams is a concern due to water quality issues and substrate siltation. Drains, river banks and agricultural fields are the three main sources of fine sediment in lowland regions. For a successful implementation of measures to decrease sediment input a well-founded knowledge of the individual entry pathways is essential. To assess the importance of possible entry pathways, a GIS based methodology (SEPAL) has been established combining the ABAG, a river bank erosion formula and a regression approach to include the contributions of drains. SEPAL has been applied on a study catchment in Northern Germany. The results show that 15% of the sediment input into the river comes from agricultural drains, 71% from river banks and 14% from adjacent fields. A comparison of the results with field-mapping and -sampling shows that the approach is plausible. The calculated total annual sediment input is 616 t yr−1, while the measured suspended sediment load is 636 t yr−1. It can be concluded that the methodology is suitable for estimating sediment entry pathways and annual sediment loads in lowland catchments as a base for modelling projects and further investigations. However, further work is necessary for gaining sound knowledge about uncertainties and especially about the processes forcing sediment input from drains.
