Drau River Research Articles

Северокавказцы – жертвы трагедии на Драве [North Caucasians as Victims of the Tragedy on the Drava River

This article discusses the tragedy that stroke North Caucasian refugees in late May-early June of 1945 on the Drava / Drau river valley near the Austrian city of Lienz. In line with the Yalta Agreement between President Roosevelt, Prime Minister Churchill and Generalissimo Stalin, the refugees, along with a large number of Cossacks, were extradited by the British authorities to the Soviet military command. However, in Russian historiography, there is barely any information on the presence of the highlanders in the Lientsev tragedy of the Cossacks. The article attempts to reconstruct the composition, living conditions of refugees in the national communities and provide details of the dramatic events that took place in the camp on May 28 - June 1, 1945. In doing so, the paper discusses some historical documents and testimonies of eyewitnesses, including representatives of the North Caucasus, who managed to avoid deportation. During the extradition, a number of highlanders, including many civilians, resisted the authorities, committing suicide and fleeing, but many were shot. The North Caucasian colony was led by a white emigrant, Major General Sultan Klych-Girei (1880-1947), who shared the fate of the officers of the Cossack Camp. Representatives of the North Caucasian diaspora in Turkey annually meet to remember “the tragedy on the Drava”, which marks 75th anniversary this year

Workflow for hydrologic modelling with sUAS-acquired aerial imagery

Operating with a conceptual workflow for the appropriate processing of high-spatial resolution small unmanned aircraft system (sUAS) data for hydrologic modelling of floodplains during flood events, this research investigated the effects of input data fidelity on hydrologic model generation. A digital surface model (DSM) and co-registered orthophoto mosaic of a stretch of the Drau River in southern Austria was generated. A digital terrain model (DTM) was then approximated from the generated DSM to within a vertical root-mean-square error (RMSE) of 4.65 cm. Horizontal and random metrics of roughness were calculated based on the DSM and then used to determine spatially-varying values of Manning’s n coefficient across an observed floodplain. A distributed two-dimensional hydrologic model of a river channel and simulated floodplain was performed using open source hydraulic modelling software. The effectiveness of each roughness metric at multiple pixel resolutions to model significant variations in reported velocity, water surface elevation and depth during a flood event was tested in a controlled sensitivity analysis. Results indicated that accuracy in hydrologic modelling is impacted by image spatial resolution. Research results conclude by emphasizing the importance of context in hydrologic modelling scenarios to effectively meet the needs of end users.

Passive acoustic monitoring of bed load discharge in a large gravel bed river

AbstractSurrogate technologies to monitor bed load discharge have been developed to supplement and ultimately take over traditional direct methods. Our research deals with passive acoustic monitoring of bed load flux using a hydrophone continuously deployed near a river bed. This passive acoustic technology senses any acoustic waves propagated in the river environment and particularly the sound due to interparticle collisions emitted during bed load movement. A data set has been acquired in the large Alpine gravel‐bedded Drau River. Analysis of the short‐term frequency response of acoustic signals allows us to determine the origin of recorded noises and to consider their frequency variations. Results are compared with ancillary field data of water depth and bed load transport inferred from the signals of a geophone array. Hydrophone and geophone signals are well correlated. Thanks to the large network of deployed geophones, analysis of the spatial resolution of hydrophone measurements shows that the sensor is sensitive to bed load motion not only locally but over distances of 5–10 m (10–20% of river width). Our results are promising in terms of the potential use of hydrophones for monitoring bed load transport in large gravel bed rivers: acoustic signals represent a large river bed area, rather than being local; hydrophones can be installed in large floods; they can be deployed at a low cost and provide continuous monitoring at high temporal resolution.

Integrated automatic and continuous bedload monitoring in gravel bed rivers

Bedload monitoring techniques have been developed and applied for many years in rivers ranging from steep mountain torrents to the large gravel-bed Danube River in Austria. Most monitoring stations use a combination of direct (mobile bag samplers, slot samplers) and indirect (geophones, hydrophones) measurement methods. Each individual technique is adequate, yet features particular boundary conditions and limitations related to hydraulic and sampling efficiency, functionality during floods, sampling duration or grain size. We show the capabilities and limitations of the different monitoring devices with respect to technical, operational and economic criteria, evaluating their suitability for determining bedload transport parameters. Bedload monitoring results of a measuring site at the Drau River in Carinthia/Austria are used to illustrate the specific range of the device application. We present an integrated automatic and continuous bedload monitoring system. It complements the specific limitations of single monitoring methods by additional measurement devices, enabling comprehensive monitoring of the bedload transport process. We then derive the Bedload Discharge Integrated Calculation Approach and the Bedload Rating Curve Approach and discuss their application for determining bedload discharge Qb and total bedload mass Vb. Whereas the integrated approach combines data from direct monitoring methods with indirect techniques, the rating curve approach uses only data from direct bedload monitoring devices. We demonstrate that applying an integrated automatic and continuous bedload monitoring system and combining the Bedload Discharge Integrated Calculation Approach and Bedload Rating Curve Approach yields accurate bedload discharge results.

The Hydromorphological Evaluation Tool (HYMET)

River engineering structures, such as bank protection or bed sills, act as constraints on the hydromorphology of rivers and limit morphodynamic processes. Accordingly, the deviations of a river's morphology from a natural reference condition have been attributed to the degree of artificiality in the observed river section and river restoration works mainly aimed at reducing artificial constraints within the river reach. Less attention has been drawn to alterations of the sediment continuum between sediment production in the river's catchment and downstream river reaches. However, the sediment supply from upstream is strongly reflected in the morphodynamics such as bar formation or the reworking of the riverbed. Any alteration of sediment supply may affect the morphological appearance of a reach and determine its deviation from an undisturbed condition.We introduce the Hydromorphological Evaluation Tool (HYMET), which accounts in a hierarchical procedure for sediment supply and sediment transfer as catchment and river network based preconditions for sustainable morphodynamics in river reaches. At the reach scale, artificiality and the sediment budget are assessed. In contrast to existing evaluation methods for assessing hydromorphological state, no reference condition is needed for determining hydro-morphological alterations. Here, with re-established sediment supply and reduced artificiality, a river reach is expected to develop morphodynamics that approach a morphodynamically and ecologically sustainable condition.Application to the Drau River showed that the alteration of sediment supply strongly affects the hydromorphological condition and thus the evaluation result of a restored reach, indicating the remaining potential for the re-initiation/re-establishment of morphodynamics through catchment-wide restoration plans.

Bedload pulses in a hydropower affected alpine gravel bed river

This study investigated the sediment resupply and transport dynamics at the Upper Drau River upstream of Lienz (Eastern Tyrol, Austria). Due to a hydropower plant, a 24km long river reach of this alpine gravel bed river is under residual flow conditions, although sediment is still resupplied into the reach through many active torrents and tributaries. As a result, sediment deposition in the residual flow reach intensified, hence increasing maintenance efforts to stabilize this river section and ensure flood protection. In combination with a new sediment management program, a continuous bedload monitoring system was installed 2km downstream of the residual reach in 2001 to support the development of adapted sediment management strategies. The surrogate bedload monitoring system consists of 16 impact plate geophones, installed over a 17m wide cross section. The unprecedented 15-year dataset of high-resolution bedload intensity revealed a complex process of gravel storage and intermittent resupply from the residual reach, allowing the authors a detailed analysis of frequently occurring bedload pulses.These transport features are triggered by increased discharges during floods in the residual reach and created pronounced anticlockwise bedload hysteresis or, with a temporal shift to the event peak, caused distinct shifts in the bedload activity downstream. Bedload pulses produce very high bedload fluxes while in transit, tend to increase bedload flux in the post-event phase, and can alter and reduce the upstream sediment storage leading to a lowering of bedload availability for future pulses. The observed time lags between main discharge events and the arrival of the macro-pulses are correlated with mean water discharge during pulse propagation, thus enabling a prediction of the pulse arrival at the monitoring station solely based on the hydrograph. In combination with the hydrological setup of the reach, the observed bedload pulse time lags allowed an estimation of pulse velocities in the range 0.002−0.05ms−1.

Intra‐event scale bar–bank interactions and their role in channel widening

AbstractChannel bars and banks strongly affect the morphology of both braided and meandering rivers. Accordingly, bar formation and bank erosion processes have been greatly explored. There is, however, a lack of investigations addressing the interactions between bed and bank morphodynamics, especially over short timescales. One major implication of this gap is that the processes leading to the repeated accretion of mid‐channel bars and associated widenings remain unsolved. In a restored section of the Drau River, a gravel‐bed river in Austria, mid‐channel bars have developed in a widening channel. During mean flow conditions, the bars divert the flow towards the banks. One channel section exhibited both an actively retreating bank and an expanding mid‐channel bar, and was selected to investigate the morphodynamic processes involved in bar accretion and channel widening at the intra‐event timescale. We repeatedly surveyed riverbed and riverbank topography, monitored riverbank hydrology and mounted a time‐lapse camera for continuous observation of riverbank erosion processes during four flow events. The mid‐channel bar was shown to accrete when it was submerged during flood events, which at the subsequent flow diversion during lower discharges narrowed the branch along the bank and increased the water surface elevation upstream from the riffle, which constituted the inlet into the branch. These changes of bed topography accelerated the flow along the bank and triggered bank failures up to 20 days after the flood events. Four analysed flow events exhibited a total bar expansion from initially 126 m2 to 295 m2, while bank retreat was 6 m at the apex of the branch. The results revealed the forcing role of bar accretion in channel widening and highlighted the importance of intra‐event scale bed morphodynamics for bank erosion, which were summarized in a conceptual model of the observed bar–bank interactions. Copyright © 2015 John Wiley & Sons, Ltd.

Evaluating climate change impacts on Alpine floodplain vegetation

This study aims to evaluate the long-term impacts of climate change on Alpine riparian vegetation. Special attention is given to the hydrological factors influencing the establishment, development, and retrogression of riparian vegetation. The study has been carried out in a reach of the upper course of the Drau River (Austria). Long-term effects of climate change on the local riparian vegetation were simulated using a dynamic vegetation model. The model simulates annual time steps, and provides the spatial and quantitative vegetation distribution changes over time. Climate change impacts have been estimated by performing five simulations, spanning 31 years. The first simulation was based on the reference period 1960–1990 while the remaining four were based on the sub-scenarios of the IPCC storyline A1B. Simulation results show consistent variations in both the distributions of quantitative and spatio-temporal vegetation type, primarily due to peak discharges alterations rather than to the mean spring discharges which typically influence the recruitment. Climate change scenarios forecasting an overall increase of peak discharge lead to prevailing retrogression as opposed to successional processes. Conversely, in the climate change scenarios with peak flow reduction, successional processes are dominant and vegetation is predicted to expand into the active channel.

Implementing a dynamic riparian vegetation model in three European river systems

ABSTRACTRiparian ecosystems are required to be preserved to achieve a good ecological status. The Water Framework Directive (2000/60/EC) specifically supports the assessment of new management tools that allow the European Member States to achieve good ecological status of river‐related ecosystems. Within several approaches, a dynamic riparian vegetation distributed model (CASiMiR‐vegetation), with a time step of 1 year, has been selected as a useful first‐step tool to achieve the Water Framework Directive requirements. The model has been implemented into three river reaches with different climatic and hydrologic settings, located in three European countries. Common bases were established in the model setup. The model was calibrated independently in the Kleblach reach (Drau River, Austria), the Ribeira reach (Odelouca River, Portugal), and the Terde reach (Mijares River, Spain) with simulation periods of 8, 11 and 41 years, respectively. The parameter values and the results were comparable between the different countries. The calibration performance achieved high correctly classified instances (60%). Additionally, weighted kappa values ranged from 0·52 to 0·66 in distinguishing riparian succession phases. The model behaved similarly in the validation, even offering better results in most cases. This work demonstrates the applicability of this model in the simulation of the riparian vegetation dynamic distribution over a wide range of environments. As it performs in a robust manner and with good results in reaches with different hydrological characteristics, the model could be also applied to analyse different hydrological scenarios or to predict changes after restoration measures within a reach. Copyright © 2012 John Wiley & Sons, Ltd.

Spatio-temporal variability of bedload transport rate: analysis and 2D modelling approach

Field measurements to calibrate numerical bedload formulae are largely missing. Measurements using a Large Helley-Smith sampler were performed over a period of five years in the large Alpine Drau River, Austria. Our results reveal the high spatio-temporal variability of bedload transport rates. Commonly used bedload predictors poorly describe measured transport rates. Temporal and localised cross-sectional variation in bedload transport rates are observed in short time frames. To obtain significant mean values, the measurement period has to be extended to cover the existing bedload transport periodicity. The discrepancy between bedload transport measurements and simulation is partially explained by local hydraulic variations. The results can be improved, particularly for verticals where most of the bedload occurs, by relating measured transport rates to local hydraulic parameters. The incorporation of local cross-sectional parameters demonstrates the utility of 2D bedload models and their greater predictive power over similar 1D models.

Evaluation and Improvement of Bed Load Discharge Formulas based on Helley–Smith Sampling in an Alpine Gravel Bed River

Bed load discharge formulas have been evaluated by analyzing them in relation to measured Helley-Smith data for the gravel-bedded armored Drau River, Austria. Comparison of calculations with measurements leads to ranking of the formulas that depends on the evaluation parameters. The choice of formula is made with respect to our specific aims: the investigation of individual floods requires a different approach from that of long-term budgets. Formula performance is consistently improved when conditions for the threshold of motion are modified according to data measured up on the initiation of motion. Formulas such as those reported by Parker in 1990, Zanke in 1999, and Sun and Donahue in 2000 are capable of coping with partial transport, which is commonly found in Alpine rivers. These formulas therefore provide encouraging results, particularly after the introduction of modifications. The augmentation of field measurements, even if limited in scope, considerably improves the performance of bed load discharge formulas.

Re‐establishing and assessing ecological integrity in riverine landscapes

1. River–floodplain systems are among the most diverse and complex ecosystems. The lack of detailed information about functional relationships and processes at the landscape and catchment scale currently hampers assessment of their ecological status.2. Intensive use and alteration of riverine landscapes by humans have led to severe degradation of river–floodplain systems, especially in highly industrialised countries. Recent water‐related regulations and legislation focussing on high standards of ecological integrity back efforts to restore or rehabilitate these systems.3. Most restoration projects in the past have suffered from a range of deficits, which pertain to project design, the planning process, the integration of associated disciplines, scaling issues and monitoring.4. The so‐called `Leitbild' (i.e. a target vision) assumes a key role in river restoration and the assessment of ecological integrity in general. The development of such a Leitbild requires a multistep approach. Including explicitly the first step that defines the natural, type‐specific reference condition (i.e. a visionary as opposed to an operational Leitbild), has great practical advantages for restoration efforts, primarily because it provides an objective benchmark, as is required by the European Water Framework Directive and other legal documents.5. Clearly defined assessment criteria are crucial for evaluating ecological integrity, especially in the pre‐ and postrestoration monitoring phases. Criteria that reflect processes and functions should play a primary role in future assessments, so as to preserve and restore functional integrity as a fundamental component of ecological integrity.6. Case studies on the Kissimmee River (U.S.A.), the Rhine River (Netherlands and Germany), and the Drau River (Austria) are used to illustrate the fundamental principles underlying successful restoration projects of river–floodplain systems.