Meander Dynamics

In the area of the Mesolithic-Neolithic Friesack bog site
in the Lower Rhinluch, archaeological excavations have
recovered a sequence of 昀氀uviatile and telmatic sedimentary layers from the Younger Dryas to the Atlantic. The
primary and secondary sedimentary structures and the
granulometry of the layer sequence were analysed on the
basis of soil lacquer peels in order to narrow down the depositional environment more closely. The outcrop pro昀椀les
are dominated by medium sandy 昀椀ne sands with tabular
cross-bedding layers. Based on the depositional features
the sediment bodies are interpretated as 昀氀uvial point bars.
In the digital terrain models, it can be seen that the archaeological site is located on the sliding slope of a paleo meander arc with a wavelength of approx. 600 - 700 m. This
was subsequently cut back erosively by smaller river meanders. The Friesacker Rhin, which has since disappeared,
belongs to the youngest generation of meanders. Its residual structure consists of sand bars 350 to 450 m long.
Their east-dipping beds wedge out at 28 m above sea level
and mark the 昀氀ood level for the middle Preboreal. For the
younger Preboreal, as well as the Boreal, omission phases and a sinking of the water level are recorded, while in
the Atlantic the 昀氀ood level rose again. The 昀氀uvial system
is based on large-cycle changes in climatic conditions, in
which changes to the river courses and their catchment areas took place. The deformation structures observed in the
soft sediments of Friesack 4 are interpreted as secondary
structures that arose in the course of diagenesis through
the drainage and compaction of the mud and peat layers.
The found load marks, 昀氀ame and cushion structures are
interpreted as soil physical designed.

River meandering and anabranching have become major problems in many large rivers that carry significant amounts of sediment worldwide. The morphodynamics of these rivers are complex due to the temporal variation of flows. However, the availability of remote sensing data and geographic information systems (GISs) provides the opportunity to analyze the morphological changes in river systems both quantitatively and qualitatively. The present study investigated the temporal changes in the river morphology of the Deduru Oya (river) in Sri Lanka, which is a meandering river. The study covered a period of 32 years (1989 to 2021), using Landsat satellite data and the QGIS platform. Cloud-free Landsat 5 and Landsat 8 satellite images were extracted and processed to extract the river mask. The centerline of the river was generated using the extracted river mask, with the support of semi-automated digitizing software (WebPlotDigitizer). Freely available QGIS was used to investigate the tempor...

Meandering rivers are among the most dynamic Earth-surface systems, which generally appear in fertile valleys, the most valuable lands for agriculture and human settlement. Landsat time series and morphological parameters are complementary tools for exploring river dynamics. Karun River is the most effluent and largest meandering river in Iran, which keeps the Karun’s basin economy, agriculture, and industrial sections alive; hence, investigating morphological changes in this river is essential. The morphological characteristics of Karun have undergone considerable changes over time due to several tectonic, hydrological, hydraulic, and anthropogenic factors. This study has identified and analyzed morphological changes in Karun River using a time series of Landsat imagery from 1985–2015. On that basis, morphological dynamics, including the river’s active channel width, meander’s neck length, water flow length, sinuosity index, and Cornice central angle, were quantitatively investigat...

A common phenomenon associated with alluvial rivers is their meander evolution, eventually forming cutoffs. Point bar deposits and ox-bow lakes are the products of lateral bend migration and meander cutoff. The present study focuses on identifying the meanders of River Manu and their cutoffs. Moreover, this study compares the temporal evolution and predicts the progress of selected meanders of River Manu. In the present research, the Survey of India topographical map, satellite imagery, and geographic information system (GIS) technique were used to examine the evolution of the Manu River meander. Subsequently, a field visit was done to the selected cutoffs and meanders of River Manu to ascertain the present status and collect data. It has been observed that many cutoffs have undergone temporal changes, and their sizes have decreased. Some have become dried or converted to agricultural fields. The width of River Manu has decreased in all the selected bends from 1932 to 2017. The sinu...

This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

River meandering and anabranching have become major problems in many large rivers that carry significant amounts of sediment worldwide. The morphodynamics of these rivers are complex due to the temporal variation of flows. However, the availability of remote sensing data and geographic information systems (GISs) provides the opportunity to analyze the morphological changes in river systems both quantitatively and qualitatively. The present study investigated the temporal changes in the river morphology of the Deduru Oya (river) in Sri Lanka, which is a meandering river. The study covered a period of 32 years (1989 to 2021), using Landsat satellite data and the QGIS platform. Cloud-free Landsat 5 and Landsat 8 satellite images were extracted and processed to extract the river mask. The centerline of the river was generated using the extracted river mask, with the support of semi-automated digitizing software (WebPlotDigitizer). Freely available QGIS was used to investigate the tempor...

A common phenomenon associated with alluvial rivers is their meander evolution, eventually forming cutoffs. Point bar deposits and ox-bow lakes are the products of lateral bend migration and meander cutoff. The present study focuses on identifying the meanders of River Manu and their cutoffs. Moreover, this study compares the temporal evolution and predicts the progress of selected meanders of River Manu. In the present research, the Survey of India topographical map, satellite imagery, and geographic information system (GIS) technique were used to examine the evolution of the Manu River meander. Subsequently, a field visit was done to the selected cutoffs and meanders of River Manu to ascertain the present status and collect data. It has been observed that many cutoffs have undergone temporal changes, and their sizes have decreased. Some have become dried or converted to agricultural fields. The width of River Manu has decreased in all the selected bends from 1932 to 2017. The sinu...

A common phenomenon associated with alluvial rivers is their meander evolution, eventually forming cutoffs. Point bar deposits and ox-bow lakes are the products of lateral bend migration and meander cutoff. The present study focuses on identifying the meanders of River Manu and their cutoffs. Moreover, this study compares the temporal evolution and predicts the progress of selected meanders of River Manu. In the present research, the Survey of India topographical map, satellite imagery, and geographic information system (GIS) technique were used to examine the evolution of the Manu River meander. Subsequently, a field visit was done to the selected cutoffs and meanders of River Manu to ascertain the present status and collect data. It has been observed that many cutoffs have undergone temporal changes, and their sizes have decreased. Some have become dried or converted to agricultural fields. The width of River Manu has decreased in all the selected bends from 1932 to 2017. The sinu...

A common phenomenon associated with alluvial rivers is their meander evolution, eventually forming cutoffs. Point bar deposits and ox-bow lakes are the products of lateral bend migration and meander cutoff. The present study focuses on identifying the meanders of River Manu and their cutoffs. Moreover, this study compares the temporal evolution and predicts the progress of selected meanders of River Manu. In the present research, the Survey of India topographical map, satellite imagery, and geographic information system (GIS) technique were used to examine the evolution of the Manu River meander. Subsequently, a field visit was done to the selected cutoffs and meanders of River Manu to ascertain the present status and collect data. It has been observed that many cutoffs have undergone temporal changes, and their sizes have decreased. Some have become dried or converted to agricultural fields. The width of River Manu has decreased in all the selected bends from 1932 to 2017. The sinuosity index has changed from 2.04 (1932) to 1.90 (2017), and the length of the river has decreased by 7 km in 85 years . The decrease in length is evident from lowering the number of meanders. Uniformity coefficient and coefficient of curvature of the bank soil samples were calculated, indicating that the soil is poorly graded and falls under the cohesionless category. Based on cross-section analysis, sediment discharge, grain-size analysis of the bank material, channel planform change, and radius of curvature, it can be stated that almost all the selected bends have the probability of future cutoff. The highest probabilities were observed in bend 3 (Jalai) and bend 4 (Chhontail).

Rivers in mountain areas have alluvial beds largely consisting of coarse alluvia (blocks, cobble, gravel) mobilized and transported downstream only during exceptional hydrological phenomena. Their distribution influences river-bed stability, sediment transport rates and high-water levels, because alluvial deposits define bed roughness. As a rule, especially in large rivers, the size of alluvia deposited on river-beds gradually decreases downstream (downstream fining), as the river transport capacity is reduced. This tendency can be interrupted by discontinuities, caused by the lateral input of alluvia or by anthropogenic interventions. The aim of this paper is to analyze the spatial distribution of the size of bed material along two small rivers, Gemenea and Slătioara, located in the northeastern part of the Eastern Carpathians, Romania. The phenomena of grain-size fining or coarsening of the material deposited along these river-beds are of low intensity. The high degree of connecti...

One of the most common actions in river research and rehabilitation is to divide stream networks into more manageable spatial scales; such as zones, segments, and reaches. The segment is a popular unit for stream management, being the scale over which geomorphic characteristics considered to be relatively consistent and comparable. Stream confluences are the typical criteria for differentiating these segments, as the input of discharge at a confluence is assumed to impart a predictable and significant step-change in morphology. This research examines this assumption. We explore the nature, magnitude and significance of morphologic adjustment at a set of confluences in Victoria, Australia. Symmetry ratio (relative size of merging streams) is shown to be a key indicator for predicting the magnitude and significance of adjustment at any given confluence over the scale of the study region. We recommend using symmetry ratio and an improved understanding of confluence dynamics to assist in defining geomorphic thresholds and spatial-scale boundaries within stream systems. This has direct implications for how stream networks are described for both research and management.

The boost in the national and international research on the centennial and multicentennial-scale changes in the configuration of river channels has led to a need for standardization of database acquisition methods, so that the final results may be accurately compared regardless of the size of the analyzed river and its physical environment. This paper introduces: the working materials needed for such studies (sources available in Romania and their preparation); landmarks necessary for the delimitation of the study area, typological classification of the channels, delineation of the representative channel sectors; methods for acquiring morphometric data (planform). The literature (with illustrative case studies cited in this paper) provides examples on how the results can be processed and interpreted in order to obtain valuable indicators of the trends in channel changes and the stages in the evolution of their configuration. Moreover, they may also indirectly deliver information on the historical changes in the controlling factors (i.e. climate variation or anthropogenic interventions) which generate changes in the morphology and morphometry of river channels.

Researchers have proposed several thresholds to predict the transition from unstable to stable states in incised channels. One of the most frequently applied is the 35Wm -2 threshold of specific stream power. However this threshold has not formally been tested in environments distinct from its origin. An approach integrating GIS and hydrologic relationships was developed to calculate specific stream power and shear stress at over 1000 sites in Fairfax County, Virginia, USA. Analysis indicated that specific stream power did not discriminate between stable and unstable sites, even when the dominant substrate material was incorporated into the analysis. Substrate type provided a greater influence statistically on channel stability than values of specific stream power, but substrate type alone did not discriminate between stable and unstable sites. Although the research methods failed to provide any practical evidence to support the notion of a stability threshold of specific stream pow...

This paper analyses the magnitude and frequency of floods in Bucegi Mountains (in Romanian Carpathians) in order to highlight their particularities and identify possible trends in flood occurrence. It is focused on the Valea Cerbului River’s catchment, a small basin (approx. 26 km2) situated on the eastern slope of Bucegi Mountains. The importance of this area is given by its economic value (mainly tourism) and by the presence of major communication axes in its lower part. The analysis is carried out for a period of 50 years (1961 – 2010), based on flow data (mean daily and maximum annual discharge) recorded at Buşteni gauging station, on Valea Cerbului River, and using mostly statistical methods (frequency analysis, linear trends analysis based on Mann-Kendall test). The results show that the magnitude of the annual floods has an upward trend, statistically significant, for α = 0.1 level of significance. After 1990, there was observed an increase in the frequency of floods with sig...

Despite numerous researches on river channel incision, there are fewer studies on the impact of channel adjustments on floods. This paper aims to investigate channel adjustments and to analyse their impact on the frequency of floods by estimating the return period of the bankfull discharge of the Prahova River in the South-Eastern Subcarpathians (Romania). The study is based on the analysis of the maximum annual discharges and cross-section profiles of the Prahova River at Câmpina gauging station (1976–2015). To estimate the return period of the bankfull discharge, the log Pearson III distribution was used. Overall, the maximum depth and the cross-section area at the bankfull stage increased during the analysed period, indicating channel incision and lateral stability. The bankfull discharge of 1976 could be reached every year and the one of 2015 could occur almost every 5 years. Therefore, due to channel incision and increased channel capacity, overflowing the bankfull stage is a l...

Geomorphologic Vulnerability of Slopes in the Urban Planning of Târgu Mureș Municipality. The identification of the geomorphologic vulnerability of a territory is a very important stage in the process of urban planning. Târgu Mureș municipality has extended its built-up area in the last few years independently of the restrictions which should be imposed in order to avoid the situation of building in areas with a high probability of landslide occurrence. As a consequence, the present study classified the built-up area of Târgu Mureș in probability classes for landslide occurrence according to the Governmental Order 447/2003 and using GIS technology which facilitates such complex analyses. Specialised data was collected using geomorphologic mapping which captured the active slope processes. These were eventually used for validating the final results.

La planicie aluvial del río Portoviejo es parte de un sistema geomorfológico fluvial dinámico que, ha experimentado cambios espaciales en el tiempo y sobre ellos, la acción humana ha sido cada vez más influyente y determinante. Uno de los aspectos necesarios para comprender este complejo esquema evolutivo, además de conocer el comportamiento hidrológico de la cuenca y de sus aspectos geomorfológicos, es el análisis de la dinámica espacio-temporal del canal principal del río en diferentes períodos y, a lo largo de su recorrido en la llanura aluvial, pues ello guarda relación con la movilidad de los escenarios de inundaciones. Los parámetros geométricos del canal principal de un río son muy sensibles a experimentar cambios, como consecuencia de intervenciones antrópicas o de la intensificación de las mismas así, como también, cambios en los patrones de meandros, debido a la carga de sedimentos y a las afectaciones en la geometría del canal. Debido a ello, es propósito de este trabajo, analizar los cambios espacio-temporales de los patrones de meandros del canal principal del río Portoviejo en su planicie aluvial, mediante el análisis de los parámetros morfométricos de sus patrones de meandros. La metodología de trabajo consistió en la revisión y análisis de informes técnicos, imágenes de satélite de Google Earth, cartografía base de la temática existente y observaciones de campo, a partir de las cuales se realizaron fotointerpretaciones de los patrones de meandro y, una matriz de información detallada. Se realizó un muestreo en cada patrón de meandros, para los distintos períodos considerados en el estudio, sobre los cuales se cuantificaron los siguientes parámetros geométricos: longitud del cuello de meandro (L), longitud del eje (A), ancho del meandro del río (W), radio de la curvatura (R), longitud de la curvatura (S) y sinuosidad (C). Los resultados muestran de manera preliminar que, la variabilidad espacio-temporal más significativa de los meandros se observa en el tramo entre las localidades de Colón y Ciudadela Nuevo Portoviejo, correspondiente a áreas con asentamientos poblacionales no planificados y, con intensificación de actividades antrópicas. En este segmento del río se aprecian cambios importantes en la posición de los meandros, determinados por procesos de migración, estrangulamiento o acortamiento, los cuales se expresan considerablemente en la variabilidad de los valores del R. Por el contrario, en el tramo del río, correspondiente al área consolidada de la ciudad de Portoviejo, no se perciben variaciones considerables, lo que define un patrón meandriforme.

In this section, we will discuss the spatial pattern of bed material distribution along the river network as the link between sediment sources and sediment delivery. The variety of controls (i.e., drainage basin size and features, sediment source distribution and effectiveness, longitudinal profile shape, major anthropogenic interventions, etc.) will be related to the characteristics of riverbed deposits. In this context of sediment dynamics along the two rivers, we propose a spatial analysis of channel material grain size and grain size distribution form, by addressing downstream fining and downstream coarsening, as well as riverbed material distribution bimodality, form variability and grain petrography of fluvial sediments. Finally, sediment budgets are discussed for two major rivers representative for Romania (Siret and Prut) which highlight the role of sediment sources and human impact.

The study highlights the relevance of integrating hydro-geomorphological typologies in pluri-disciplinary ecological researches on ecosystem functioning, in two contrasted hydrosystems: the Rhine alluvial plain and the Yzeron basin. Two hydro-geomorphological typologies of reference status in rivers, elaborated from the same conceptual scheme, are compared with two bio-typologies of ecosystem functioning characterization, one based on communities of aquatic macrophytes (Rhine plain) and the second on oligochaete assemblages (Yzeron basin). The two bio-typologies mainly reflect water exchanges between surface water and groundwater. In the Rhine plain, morphodynamics of the D3 geomorpho-type modify the tendency of increasing in the trophic level from upstream to downstream areas, this increasing being only verified for the D4 geomorpho-type. Indeed, morphodynamics of the D3 geomorpho-type prevents channel clogging and activates the limnocrene groundwater springs, inducing water oligotrophication and increase of biodiversity. In the Yzeron basin, which is impacted by polluted urban water runoffs, the B3 and A1 geomorpho-types present the highest values of Ecological Potentials (EPs) due to greater slopes and active surface water/groundwater exchanges. Results suggest that some biological characteristics and ecological functions could be spatialized on larger spatial scales through appropriate geomorphic river typologies.

River morphological quality assessment, derived from quantification of human pressures as well as river channel alteration, is a demand of the Water Framework Directive (WFD) in terms of integrating hydromorphological elements in defining ecological status. Our study's aim is to contribute to the hydromorphological evaluation by proposing indicators and separating classes, based on a revisited Morphological Quality Index (rMQI) protocol. The rMQI is based on 12 indicators of human pressures, 10 indicators of channel form adjustments, and 11 indicators of functionality. The rMQI scoring system allows for the quantification of changes when compared to reference conditions, be they undisturbed or nearly undisturbed by human interventions, with absent channel adjustments and a functioning natural river style. We used the lower, meandering sector of the Prahova River to demonstrate our assessment methodology. The Lower Prahova River suffers from a minor local intervention and a diminishing intensity of fluvial processes specific to a meandering style. Meanders geometry was affected by significant changes that included a decrease in the radius of curvature, width and width-to-mean-depth ratio. We concluded that the Lower Prahova River has a good morphological quality, which is rated as second class on a scale of five levels, from natural to severely modified. We recommend an improvement in the

The concept of dominant discharge is used in geomorphologic studies concerned with stability of riverbeds and riverbed management. The results of our study involves the specific energetic conditions on the Niraj River during maximum river flow (by analysing the bankfull discharge and the stream power during peak flow) and during normal flow (by analysing the stream power at average flow). The bankfull discharge value is considered fundamental for the present riverbed formation, for Niraj river beeing situated between 20.8 m 3 /s and 928 m 3 /s, depending on local morphometrical riverbed condition. Therefore using the Manning-Strickler formula, the bankfull discharge was calculated due to the fact that it is considered to be the main estimative parameter of the riverbed hydraulic geometry. The values of stream power varied between 3.51 (W/m 2 ) and 289 (W/m 2 ) and It was determined by means of data gathered on seven cross sections, taking into consideration the upstream riverbed typology. In two sectors, considered to be representative for the riverbed typology, the return periods were calculated, probability of exceedance (66%) and non-exceedance as well (1.5 year) as the influence of bankfull discharge on the Niraj riverbed dynamics in the 1970-2012 interval. The case study was performed on two different sectors taking into account the evolution of the sinuosity index, which is dependent on the influence of natural and anthropic factors. The analysis enabled the comparison of meandering rates for 100 year interval, both in the sectors with a natural evolution of the riverbed and in the sectors with high anthropic impact as a resuls of constraints of the dams. The high lateral dynamics is mainly caused by the decrease of slope gradient and the decrease of bank resistance due to extreme events with high energetic values (varying between 30.2 and 105.3 W/m 2 in the upper and middle sectors of the Niraj river). The obteined bankfull discharge values with 1.5 year probability (41.6 m 3 /s for Cinta and 28.9 m 3 /s for Bereni) were validated by comparing the calculated data within the cross sections located near the Gălești and Cinta hydrometric stations and the data obtained by hidrometrical measurements in the two stations mentioned above. The results are included in the confidence interval of 5%.

One of the most important hydraulic mega structures in Romania, classified as the third largest in Europe, its Stânca Costești reservoir, on Prut River. After Stânca Costești reservoir construction, hydrological parameters of Prut river (for example liquid and solid discharges) were severely modified. This study quantifies some of the geomorphic effects on the river’s active channel and plan form, in the context of the overall changes occurring in the last century (1915-2005 period ) The analysis was based on the different editions of the available topographic maps and aerial photos, which have recorded historical configurations of the Prut river channel. For each time period, several morphometric indices, such as minor riverbed width, major riverbed width, sinuosity index and meander curvature, were measured using GIS and further interpreted.. The preliminary conclusion, indicate’s that once Stânca Costești reservoir was constructed, the morphometric indices, evolved in different mode, downstream to Stânca Costești reservoir.

Natural rivers are subjected to continuous adjustments in response to any change in the environment. These environmental changes may occur naturally, as in the case of climatic variation or changes in vegetative cover, or may be related to human activities including channelization, damming, bank protection, and bridge construction. Identifying the value of that discharge ('dominant' or 'effective' discharge, Q D ) considered responsible for the main changes operated by a river has been a subject of great challenge to scientists and engineers during the last decades. In fact, this threshold value is largely adopted for stream-management decisions, for predicting the stable slope upstream of grade-control structures, and for designing moderateto large-sized hydraulic structures. In this paper, a simple concept of dominant discharge, corresponding to that value of Q D that accounts for at least 50% of the total suspended sediment load transported by the river, is introduced and discussed. The work is based on a long-term data set that includes measurements of monthly discharge and suspended sediment load in 27 stream gauge stations located in three different regions of southern Italy. The analysis showed that Q D corresponds to values of the return time, T, ranging from 1 to 5 years, confirming previous findings by other authors in similar analyses. Also, as the values of Q D were well correlated with the 1.5-year peak discharges of the same investigated rivers, an empirical approach is suggested in order to estimate Q D in rivers with no sediment load measurements.

Abstract: The concept of dominant discharge is used in geomorphologic studies concerned with stability of riverbeds and riverbed management. The purpose of this research is to determine the specific energetic conditions on the Niraj River during maximum river flow (by analysing the bankfull discharge and the stream power during peak flow) and during normal flow (by analysing the stream power at average flow). Using the Manning – Strickler formula, the bankfull discharge was calculated due to the fact that it is considered to be the main estimative parameter of the riverbed hydraulic geometry. The bankfull discharge value should be considered fundamental for the present riverbed formation. The stream power was determined by means of data gathered on seven cross sections, taking into consideration the upstream riverbed typology. In two sectors, considered to be representative for the riverbed typology, the return priods were calculated, probability of exceedance and non-exceedance as well as the influence of bankfull discharge on the Niraj riverbed dynamics in the 1970-2012 interval. The case study was performed on two different sectors in respect to the evolution of the sinuosity index, which is dependent  on the influence of natural and anthropic factors. The analysis enabled the comparison of meandering rates for 100 year interval, both in the sectors with a natural evolution of the riverbed and in the sectors with high anthropic impact. The results were validated by comparing the calculated data within the cross sections located near the Gălești and Cinta hydrometric stations and the data obtained by measurements in the two stations mentioned above. The results are included in the confidence interval of 5%.

Vulnerability to channel migration of the Niraj river. The aim of this paper is to analyze the changes in the geometrical characteristics of the Niraj river. In order to determinate the zone exposed to the migration of the river we tried to identify the channel migration zone and we study the historic migration zone base on a composite area defined by the channel location in 1910, 1960, 2008, so we obtained the zone of channel occupation for a 100 years' timeframe. Therefore, for delineating the channel migration we digitized polygons for the bank full channel for each time series, and merge them in the same polygon. For anticipated future migration beyond the historic corridor boundary, we added to the channel migration zone an erosion polygon, based on the geological, and land-use characteristics. As a result we obtain a complex set of data which will allow for practitioners to use it in different contexts like: to predict the rate and extend of meander migration, evaluating the risk to existing facilities -necessaries for design countermeasures against the negative effects.