River Planform Research Articles

Feeding the hungry river: Fluvial morphodynamics and the entrainment of artificially inserted sediment at the dammed river Isar, Eastern Alps, Germany

Dams interrupt the sediment continuum in rivers by retaining the bedload; combined with flow diversion, bedload retention in tributaries and river engineering measures, this causes a bedload deficit leading to changes in river planform and morphodynamics, with potentially detrimental downstream effects. As part of the SedAlp joint project (Sediment management in Alpine basins: integrating sediment continuum, risk mitigation and hydropower), this study investigates changes within a section of the dammed river Isar between the Sylvenstein reservoir and the city of Bad Tölz.We use a multi-method approach on a range of spatial and temporal scales. First, we analysed historical maps and aerial photos to analyse river planform and landcover changes within the river corridor of the whole study area on a temporal scale of over 100years. Results show that major changes occurred before the construction of the Sylvenstein reservoir, suggesting that present morphodynamics represent the reaction to different disturbances on different time scales. Second, changes in mean bed elevation of cross profiles regularly surveyed by the water authorities are analysed in light of artificial sediment insertion and floods; they are also used to estimate the sediment budget of river reaches between consecutive cross profiles. Results suggest stability and a slight tendency towards incision, especially near the Sylvenstein reservoir; further downstream, the sediment balance was positive. Third, we acquired multitemporal aerial photos using an unmanned aerial vehicle and generated high-resolution digital elevation models to show how sediment artificially inserted in the river corridor is entrained. Depending on the position of the artificial deposits in relation to the channel, the deposits are entrained during floods of different return periods.

A Combinatorial Reasoning Mechanism with Topological and Metric Relations for Change Detection in River Planforms: An Application to GlobeLand30’s Water Bodies

Changes in river plane shapes are called river planform changes (RPCs). Such changes can impact sustainable human development (e.g., human habitations, industrial and agricultural development, and national border security). RPCs can be identified through field surveys—a method that is highly precise but time-consuming, or through remote sensing (RS) and geographic information system (GIS), which are less precise but more efficient. Previous studies that have addressed RPCs often used RS, GIS, or digital elevation models (DEMs) and focused on only one or a few rivers in specific areas with the goal of identifying the reasons underlying these changes. In contrast, in this paper, we developed a combinatorial reasoning mechanism based on topological and metric relations that can be used to classify RPCs. This approach does not require DEMs and can eliminate most false-change information caused by varying river water levels. First, we present GIS models of river planforms based on their natural properties and, then, modify these models into simple GIS river planform models (SGRPMs) using straight lines rather than common lines to facilitate computational and human understanding. Second, we used double straight line 4-intersection models (DSL4IMs) and intersection and difference models (IDMs) of the regions to represent the topological relations between the SGRPMs and used double-start-point 8-distance models (DS8DMs) to express the metric relations between the SGRPMs. Then, we combined topological and metric relations to analyse the changes in the SGRPMs. Finally, to compensate for the complexity of common river planforms in nature, we proposed three segmentation rules to turn common river planforms into SGRPMs and used combinatorial reasoning mechanism tables (CRMTs) to describe the spatial relations among different river planforms. Based on our method, users can describe common river planforms and their changes in detail and confidently reject false changes. Future work should develop a method to automatically or semi-automatically adjust the segmentation rules and the combinatorial reasoning mechanism.

Modelling sediment clasts transport during landscape evolution

Abstract. Over thousands to millions of years, the landscape evolution is predicted by models based on fluxes of eroded, transported and deposited material. The laws describing these fluxes, corresponding to averages over many years, are difficult to prove with the available data. On the other hand, sediment dynamics are often tackled by studying the distribution of certain grain properties in the field (e.g. heavy metals, detrital zircons, 10Be in gravel, magnetic tracers). There is a gap between landscape evolution models based on fluxes and these field data on individual clasts, which prevent the latter from being used to calibrate the former. Here we propose an algorithm coupling the landscape evolution with mobile clasts. Our landscape evolution model predicts local erosion, deposition and transfer fluxes resulting from hillslope and river processes. Clasts of any size are initially spread in the basement and are detached, moved and deposited according to probabilities using these fluxes. Several river and hillslope laws are studied. Although the resulting mean transport rate of the clasts does not depend on the time step or the model cell size, our approach is limited by the fact that their scattering rate is cell-size-dependent. Nevertheless, both their mean transport rate and the shape of the scattering-time curves fit the predictions. Different erosion–transport laws generate different clast movements. These differences show that studying the tracers in the field may provide a way to establish these laws on the hillslopes and in the rivers. Possible applications include the interpretation of cosmogenic nuclides in individual gravel deposits, provenance analyses, placers, sediment coarsening or fining, the relationship between magnetic tracers in rivers and the river planform, and the tracing of weathered sediment.

Spatial Scaling of Environmental Variables Improves Species-Habitat Models of Fishes in a Small, Sand-Bed Lowland River.

Habitat suitability and the distinct mobility of species depict fundamental keys for explaining and understanding the distribution of river fishes. In recent years, comprehensive data on river hydromorphology has been mapped at spatial scales down to 100 m, potentially serving high resolution species-habitat models, e.g., for fish. However, the relative importance of specific hydromorphological and in-stream habitat variables and their spatial scales of influence is poorly understood. Applying boosted regression trees, we developed species-habitat models for 13 fish species in a sand-bed lowland river based on river morphological and in-stream habitat data. First, we calculated mean values for the predictor variables in five distance classes (from the sampling site up to 4000 m up- and downstream) to identify the spatial scale that best predicts the presence of fish species. Second, we compared the suitability of measured variables and assessment scores related to natural reference conditions. Third, we identified variables which best explained the presence of fish species. The mean model quality (AUC = 0.78, area under the receiver operating characteristic curve) significantly increased when information on the habitat conditions up- and downstream of a sampling site (maximum AUC at 2500 m distance class, +0.049) and topological variables (e.g., stream order) were included (AUC = +0.014). Both measured and assessed variables were similarly well suited to predict species’ presence. Stream order variables and measured cross section features (e.g., width, depth, velocity) were best-suited predictors. In addition, measured channel-bed characteristics (e.g., substrate types) and assessed longitudinal channel features (e.g., naturalness of river planform) were also good predictors. These findings demonstrate (i) the applicability of high resolution river morphological and instream-habitat data (measured and assessed variables) to predict fish presence, (ii) the importance of considering habitat at spatial scales larger than the sampling site, and (iii) that the importance of (river morphological) habitat characteristics differs depending on the spatial scale.

The effect of lateral confinement on gravel bed river morphology

In this paper, we use a physical modeling approach to explore the effect of lateral confinement on gravel bed river planform style, bed morphology, and sediment transport processes. A set of 27 runs was performed in a large flume (25 m long, 2.9 m wide), with constant longitudinal slope (0.01) and uniform grain size (1 mm), changing the water discharge (1.5–2.5 L/s) and the channel width (0.15–1.5 m) to model a wide range of channel configurations, from narrow, straight, embanked channels to wide braided networks. The outcomes of each run were characterized by a detailed digital elevation model describing channel morphology, a map of dry areas and areas actively transporting sediment within the channel, and continuous monitoring of the amount of sediment transported through the flume outlet. Analysis reveals strong relationships between unit stream power and parameters describing the channel morphology. In particular, a smooth transition is observed between narrow channels with an almost rectangular cross-section profile (with sediment transport occurring across the entire channel width) and complex braided networks where only a limited proportion (30%) of the bed is active. This transition is captured by descriptors of the bed elevation frequency distribution, e.g., standard deviation, skewness, and kurtosis. These summary statistics represent potentially useful indicators of bed morphology that are compared with other commonly used summary indicators such as the braiding index and the type and number of bars.

Braiding of submarine channels controlled by aspect ratio similar to rivers

Braided channels are rare in submarine environments, yet common in fluvial systems. Laboratory experiments suggest that the formation mechanisms are the same, but submarine channels are typically not wide enough to promote braiding. The great majority of submarine channels formed by turbidity and density currents are meandering in planform; they consist of a single, sinuous channel that transports a turbid, dense flow of sediment from submarine canyons to ocean floor environments1,2. Braided turbidite systems consisting of multiple, interconnected channel threads are conspicuously rare1. Furthermore, such systems may not represent the spontaneous planform instability of true braiding, but instead result from erosive processes or bathymetric variability3,4,5. In marked contrast to submarine environments, both meandering and braided planforms are common in fluvial systems6,7. Here we present experiments of subaqueous channel formation conducted at two laboratory facilities. We find that density currents readily produce a braided planform for flow aspect ratios of depth to width that are similar to those that produce river braiding. Moreover, we find that stability model theory for river planform morphology8 successfully describes submarine channels in both experiments and the field. On the basis of these observations, we propose that the rarity of braided submarine channels is explained by the generally greater flow depths in submarine systems, which necessitate commensurately greater widths to achieve the required aspect ratio, along with feedbacks9,10 among flow thickness, suspended sediment concentration and channel relief that induce greater levee deposition rates and limit channel widening.

A Conceptual Model of Vegetation–hydrogeomorphology Interactions Within River Corridors

AbstractWe propose a conceptual model of vegetation–hydrogeomorphology interactions and feedbacks within river corridors (i.e. river channels and their floodplains) that builds on previous similar hydrogeomorphologically centred models by incorporating hydrogeomorphological constraints on river corridor vegetation from region to reach scales; defining five dynamic river corridor zones within which different hydrogeomorphological processes are dominant so that plants and physical processes interact in different ways, and considering the potential distribution of these zones longitudinally from river headwaters to mouth, laterally across the river corridor, and in relation to different river planform styles; considering the way in which vegetation‐related landforms within each zone may reflect processes of self‐organization and the role of particular plant species as physical ecosystem engineers within the context of the dominant hydrogeomorphological processes; focussing, in particular, upon a ‘critical zone’ at the leading edge of plant–hydrogeomorphological process interactions that is located somewhere within the area of the river corridor perennially inundated by flowing water (zone 1) and the area that is frequently inundated and subject to both sediment erosion and deposition processes (zone 2). Within the critical zone some plant species strongly influence the position and character of the margin between the river channel and floodplain, affecting channel width, channel margin form and dynamics, and the transition from one river planform type to another; and considering the vegetated pioneer landforms that develop within the critical zone and how their morphological impact needs to be scaled to the river size. The model is illustrated using three example reaches from rivers within different biogeographical zones of Europe, and its potential application in the context of river management and restoration/rehabilitation is discussed. Copyright © 2015 John Wiley & Sons, Ltd.

Is history of rivers important in restoration projects? The example of human impact on a lowland river valley (the Obra River, Poland)

Palaeoenvironmental and palaeohydrological reconstructions can provide important guidance for river restoration projects. This paper reconstructs the trajectory of river pattern changes of a lowland river (the Obra River, western Poland) as a basis to inform realistic restoration activities. The history of river changes is reconstructed for the last 12,700radiocarbonyearsBP. The sequence and timing of change differ from widely recognized, conventional assessments of transitions from braided to meandering planforms in the Polish Lowlands. Traces of a laterally migrating anabranching system were found in the middle Obra valley. In its lower course, a transition from a braided to meandering planform took place later than in other rivers of the Polish Lowlands. Sediment delivery from parts of the catchment situated downstream of lakes in the river course could have been the main reason for maintenance of the braided pattern. Restoration scenarios that take into account the trajectory of river planform changes are hypothesized in relation to variations of sediment supply and degree of anthropogenic impact.

The response of a gravel‐bed river planform configuration to flow variations and bed reworking: a modelling study

AbstractA 2D depth‐averaged model has been developed for simulating water flow, sediment transport and morphological changes in gravel‐bed rivers. The model was validated with a series of laboratory experiments and then applied to the Nove reach of the Brenta River (Northern Italy) to assess its bed material transport, interpret channel response to a series of intensive flood events (R.I. ≈ 10 years) and provide a possible evolutionary scenario for the medium term. The study reach is 1400 m long with a mean slope of 0.0039 m m−1. High‐resolution digital terrain models were produced combining LiDAR data with colour bathymetry techniques. Extensive field sedimentological surveys were also conducted for surface and subsurface material. Data were uploaded in the model and the passage of two consecutive high intensity floods was simulated. The model was run under several hypotheses of sediment supply: one considering substantial equilibrium between sediment input and transport capacity, and the others reducing the sediment supply. The sediment supply was then calibrated comparing channel morphological changes as observed in the field and calculated by the model. Annual bed material transport was assessed and compared with other techniques. Low‐frequency floods (R.I. ≈ 1.5 years) are expected to produce negligible changes in the channel while high floods may erode banks rather than further incising the channel bed. Location and distribution of erosion and deposition areas within the Nove reach were predicted with acceptable biases stemming from imperfections of the model and the specified initial, boundary and forcing conditions. A medium‐term evolutionary scenario simulation underlined the different response to and impact of a consecutive sequence of floods. Copyright © 2015 John Wiley & Sons, Ltd.

Application of remote sensing and GIS for evaluation of the recent morphological characteristics of the lower Brahmaputra-Jamuna River, Bangladesh

This paper deals with the morphological changes of the lower Brahmaputra-Jamuna River (BJR) in Bangladesh. Within few decades, the planform of the river has been changed abruptly by the combined effect of natural process and human interventions. Morphological features observing in this study were river planform, channel width, bankline migration and channel bed elevation. Eighteen sets of remote sensing data series from 1973 to 2011were analyzed using ERDAS/Imagine and GIS to document the variation of geomorphic elements of the lower BJR. GIS analysis of remote sensing data showed that the changes of channel planform were quite significant over the past 40 years, occurring two major phases of channel development. The changing patterns in the first phase (i.e., between 1973 and 1992) were quite irregular. However, the second phase ranging between 1992 and 2011 was unidirectional (mostly eastward). In general, the studied river reach was widened and the average rate of migration was 225 m y–1 that was three–folds the values of the first phase. The height and slope of sand bars were gradually increasing, showing the highest value around the Jamuna Multipurpose Bridge (JMB) section. The planform characteristics of BJR at the downstream of JMB showed that the river reach was gradually widening and shifting eastwards. However, the reach at the upstream of the JMB showed westward migration. The recent trends of channel changes suggest that the river planform has lost it’s naturally condition and it may, therefore, be predicted that increasing nature of channel width likely to continue in the immediate future.

Development of meander cutoffs—a multi-temporal satellite-based observation in parts of Sindh River, Madhya Pradesh, India

Identification of fluvial landforms is of paramount importance in river planform change studies. Satellite remote sensing is a proven technology to identify fluvial landforms and map the associated changes over a period of time because of its synopticity and repetivity. Sindh River, which is the lifeline in central India, changes its course in the alluvial plain, mainly due to meander cutoffs. In this study, multi-temporal satellite data over a period of 23 years were used to find out the behaviour of a meander loop in parts of the Sindh River. It was found that the meander cut off in this loop is a typical neck cutoff unlike chute cutoff in general. The river shows a decreasing trend of sinuosity index during the observation period.

3-D Numerical Simulation of Flow Structures in a Sharp Bend of the Lower Yangtze River

The three-dimensional (3-D) flow structures in the Taiziji Waterway of the Lower Yangtze River were simulated by a 3-D numerical model, where the river plan form is a sharp bend and island-braided. The verification results of the 3-D model indicated that the simulated results agree with the measured data. The patterns of 3-D flow structures in this sharp bend with different discharge were analyzed based on the calculated results.The simulated results demostrated that strong 3-D features of flow structures can be found in the sharp bend of Taiziji Waterway, the bottom velocity vectors point to the convex bank while the surface vectors point to the concave bank. The velocity distribution alone the lateral direction in the sharp bend depends mostly on the flow discharge. The discharge ratio of the left branch increases as flow discharge increases.

Vegetative impacts on hydraulics and sediment processes across the fluvial system

Summary Vegetation creates a complicated system of feedbacks and linkages across the fluvial system that is realized through river planform shape. Interactions occur among flow hydraulics, sediment deposition and erosion, and plant morphology, density, and biomechanics. Interest in the interactions and feedback loops between vegetation and the fluvial system has grown extensively in the past few years. This interest is partially driven by the popularity of stream restoration activities worldwide that include re-vegetation of stream banks and formation of an ecosystem that is intended to encourage the growth of aquatic macrophytes. We present a review of the research into the interactions and dependencies between vegetation and the fluvial system to identify hydraulic and sediment dynamics that are consistent around vegetation located in the channel, on channel banks, and over the floodplain. We illustrate process commonalities operating across spatial locations within the fluvial system and highlight some of the current research opportunities and challenges to encourage research collaborations between those working in areas of the fluvial system traditionally viewed as disparate.

Plants as river system engineers

ABSTRACTPlants growing within river corridors both affect and respond to fluvial processes. Their above‐ground biomass modifies the flow field and retains sediment, whereas their below‐ground biomass affects the hydraulic and mechanical properties of the substrate and consequently the moisture regime and erosion susceptibility of the land surface.This paper reviews research that dates back to the 1950s on the geomorphological influence of vegetation within fluvial systems. During the late twentieth century this research was largely pursued through field observations, but during the early years of the twenty‐first century, complementary field, flume and theoretical/modelling investigations have contributed to major advances in understanding the influence of plants on fluvial systems. Flume experiments have demonstrated the fundamental role of vegetation in determining river planform, particularly transitions from multi‐ to single‐thread forms, and have provided insights into flow–vegetation–sediment feedbacks and landform building, including processes such as channel blockage and avulsion. At the same time, modellers have incorporated factors such as moisture‐dependent plant growth, canopy and root architecture and their influence on flow resistance and sediment/bank reinforcement into morphodynamic models. Meanwhile, field investigations have revealed that vegetation has a far more important and complex influence on fluvial systems than previously realized.It is now apparent that the influence of plants on river systems is significant across space scales from individual plants to entire forested river corridors. Small plant‐scale phenomena structure patch‐scale geomorphological forms and processes, and interactions between patches are almost certainly crucial to larger‐scale and longer‐term geomorphological phenomena. The influence of plants also varies continuously through time as above‐ and below‐ground biomass change within the annual growth cycle, over longer‐term growth trajectories, and in response to external drivers of change such as climatic, hydrological and fluvial fluctuations and extremes. Copyright © 2013 John Wiley & Sons, Ltd.

River sinuosity in a humid tropical river basin, south west coast of India

The variability in ground water potential at different regions of the Meenachil River basin and the remarkable distribution of palaeodeposit of sand at its middle to lower reaches have led to interpret the sinuosity indexes of the main channel as well as the tributaries of the River for elucidating the relationship between mathematical expressions and filed observations. The measurement of digital elevation model-derived river sinuosity was carried out for 846 km2 of the basin area of Meenachil River. The drainage networks of 10 major sub-watersheds and four mini-watersheds were delineated using remote sensing data—geocoded false colour composite of Indian Remote Sensing satellite (IRS)-1D (LISS III) data with a spatial resolution of 23.5 m—coupled with the Survey of India toposheets (1:50,000). The calculation of the sinuosity indexes were carried out using Arc GIS (8.3 version) software. Hydraulic sinuosity indexes, topographic sinuosity index and standard sinuosity index were calculated. The study depicts the remarkable correlation between theoretical data sets with field observations and the influence of tectonic control on river planforms. Three structurally controlled regions of Meenachil River basin were established using Remote Sensing and Geographical Information System.

Predicting the Planform Configuration of the Braided Toklat River, Alaska, With a Suite of Rule‐Based Models1

Abstract: An ensemble of rule‐based models was constructed to assess possible future braided river planform configurations for the Toklat River in Denali National Park and Preserve, Alaska. This approach combined an analysis of large‐scale influences on stability with several reduced‐complexity models to produce the predictions at a practical level for managers concerned about the persistence of bank erosion while acknowledging the great uncertainty in any landscape prediction. First, a model of confluence angles reproduced observed angles of a major confluence, but showed limited susceptibility to a major rearrangement of the channel planform downstream. Second, a probabilistic map of channel locations was created with a two‐parameter channel avulsion model. The predicted channel belt location was concentrated in the same area as the current channel belt. Finally, a suite of valley‐scale channel and braid plain characteristics were extracted from a light detection and ranging (LiDAR)‐derived surface. The characteristics demonstrated large‐scale stabilizing topographic influences on channel planform. The combination of independent analyses increased confidence in the conclusion that the Toklat River braided planform is a dynamically stable system due to large and persistent valley‐scale influences, and that a range of avulsive perturbations are likely to result in a relatively unchanged planform configuration in the short term.

Decadal length changes in the fluvial planform of the River Ganga: bringing a mega-river to life with Landsat archives

The Landsat programme, which was started in 1972, initiated an era of space-based Earth observation relevant to the study of large river systems through the provision of spatially continuous, synoptic and temporally repetitive multispectral data. Free access to the Landsat archive via the Internet from mid-2008 has enabled the scientific community to reconstruct the Earth's changing surface and, in particular, to reconstruct the planform dynamics of the world's largest rivers. The present research reconstructed the planform changes occurring in the lower reaches of one of the Asian mega-rivers, the River Ganga (Ganges), from 1972 to 2010 using the Landsat archive. Sequential river planform maps generated from the time-series revealed the pattern of evolution of the river system over the study period. Specifically, within the observed sequence, the river started as a single-thread channel that then began meandering at four locations. The meander bends increased in sinuosity until chute cut-offs were triggered, returning the river to a state similar to that at the beginning of the sequence. This periodic pattern is constrained by several hard points in the geology, and by the Farakka Barrage, meaning that the observed cyclic pulsing is likely to continue into the future. This constrained pattern has significant implications for local planners who may currently fear that the river is migrating laterally.

Numerical modelling of two-dimensional morphodynamics with applications to river bars and bifurcations

We study the numerical approximation of the two-dimensional morphodynamic model governed by the shallow water and Exner equations to simulate reach-scale two-dimensional morphodynamics of bedload-dominated alluvial rivers. The solution strategy relies on a full coupling of the governing equations within each time step. The resulting system of governing equations contains nonconservative products related to the longitudinal and lateral bed slopes and source terms related to friction. The full problem is solved numerically on unstructured triangular grids, simultaneously updating the principal part and adding the source terms (friction) using a splitting technique.The principal part is solved by means of a novel second-order accurate upwind-biased centred scheme of the finite volume type, while the source terms are added to the problem by solving a system of ordinary differential equations. A new algorithm for treating the wetting-and-drying is also proposed.The model is applied to well-established test problems in order to verify the accuracy of the proposed method, the robustness of the wetting-and-drying algorithm and the ability of the model in dealing with transcritical flows. Finally we test the model ability to reproduce two dimensional morphodynamic processes occurring at the scale of tens of channel widths in bedload dominated alluvial rivers with homogeneous grain size. This is achieved by comparing model outcomes with those of analytical theories and flume experiments on the same morphodynamic processes. These selected “benchmarks” include migrating free bars spontaneously developing in straight reaches, steady bars forced by abrupt river planform changes and the dynamics of channel bifurcations.

A systematic overview of the coincidences of river sinuosity changes and tectonically active structures in the Pannonian Basin

As tectonic movements change the valley slope (low-gradient reaches of valleys, in sedimentary basins), the alluvial rivers, as sensitive indicators, respond to these changes, by varying their courses to accommodate this forcing. In our study sinuosity values, a commonly used characteristic parameter to detect river pattern changes, were studied for the major rivers in the Pannonian Basin in order to reveal neotectonic influence on their planform shape.Our study area comprises the entire Pannonian Basin (330,000km2) located in eastern Central-Europe, bounded by the Alps, Carpathians and Dinarides. The studied rivers were mostly in their natural meandering state before the main river regulations of the 19th century. The last quasi-natural, non-regulated river planforms were surveyed somewhat earlier, during the Second Military Survey of the Habsburg Empire. Using the digitized river sections of that survey, the sinuosities of the rivers were calculated with different sample section sizes ranging from 5km to 80km. Depending on the bank-full discharge, also a ‘most representative’ section size is given, which can be connected to the neotectonic activity.In total, the meandering reaches of 28 rivers were studied; their combined length is 7406km. The places where the river sinuosity changed were compared to the structural lines of the “Atlas of the present-day geodynamics of the Pannonian Basin” (Horváth et al., 2006). 36 junctions along 26 structural lines were identified where the fault lines of this neotectonic map crossed the rivers. Across these points the mean sinuosity changed. Depending on the direction of the relative vertical movements, the sinuosity values increased or decreased. There were some points, where the sinuosity changed in an opposite way. Along these sections, the rivers belong to the range of unorganized meandering or there are lithological margins.Assuming that the rivers indicate on-going faulting accurately, some places were found, where positioning of the faults of the neotectonic map could be improved according to the sinuosity jumps. However, some significant sinuosity changes cannot be correlated to known faults. In these cases other factors may play a role (e.g., hydrological changes, increase of sediment discharge also can modify sinuosity). In order to clarify the origin of these changes seismic sections and other geodynamical information should be analyzed to prove or disprove tectonic relationship if hydrological reasons can be excluded.

The role of historical sources in the functional representation of a river in the new world. The case of the Argentinian Paraná

How can we understand and construct a New World with European benchmarks that do not necessarily apply in this environment? In order to discover and appropriate a territory, its nature must be touched. Therefore, the body of the Paranà river has changed, with the scars of territorial colonisation remaining today. We can then ask how different cartographies represent the fluvial dynamics of a New World river and how the maps lead to the identification of this change. By adopting a global framework across the Argentinian Paraná, we seek to identify changes in the river dynamics. The geohistorical approach using old maps gives a new representation of the Paraná river. Our archive research allowed us to collect 60 maps depicting a period covering the fifteenth to the twentieth century. The scales of analysis also vary: the maps show the Paraná from its regional integration (1/100,000) up to a continental scale (1/18,500,000). The validation of the cartography is performed by comparing the representations with descriptions of the river found in texts dating from the same period. The methodology used is a map-to-map comparison, following the theory of river systems (Schumm 1977), in which sandbanks, islands and river planforms are considered to be markers of the river dynamics. The maps thus provide an answer: it is possible to trace the causes from the results. The causes are themselves related to spatial and climatic phenomena. Early maps show a braided planform in the upper reach of the Paraná and a Paraguay channel free of deposits. The current dynamics indicate an inversion in sedimentary transportation and deposit. The deforestation mechanisms in the Misiones territory and their abandonment could lead to a shift in the sediment load. This hypothesis will be demonstrated through analysis of the maps, its validation by texts and the results of a field studies.