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Challenges for the Establishment of Sediment Budgets – Comparison of Three Sediment Budgets in Austria

Author(s): Sabrina Schwarz; Rolf Rindler; Helmut Habersack

Linked Author(s): Sabrina Schwarz, Rolf Rindler, Helmut Habersack

Keywords: Sediment budget; Challenges; Sediment transport; Time period; Basic dat

Abstract: The establishment of sediment budgets is a major challenge, that many institutions and scientists have already dealt with. Reasons to establish sediment budgets include sediment continuity, climate change, land use changes, changes in morphology, the investigation of suitable river engineering measures or flood events. Sediment balancing is also used as management concepts to counteract the problems of a river in the long term (e.g. sediment discontinuity, erosion, sedimentation). The present study comprises three sediment budgets. All three project regions are located in the south of Austria, Carinthia. However, these sediment budgets differ in the fundamental question, basic data and the time scale, which varies from two weeks to 27 years. The first balance is a long-term sediment budget and includes the morphological changes of a river. To develop a suitable river engineering measure setting for the Gail River - within a time period of 27 years - we used historical data, sediment input data, grain size distributions, surveys of riverbed changes, a tracer study and bedload measurements as data basis. The challenge of this balance lies in the many sediment-input and -output variables that have to be considered over a 27-year period. The second balance is a medium-term balance. Data of tributaries (grain size, slope, profile, discharge), a tracer study and bed load of the river were used to evaluate the plausibility of a unique, existing monitoring system at the Drava River. From the generated balance there is a difference of 15.900 tons (sediments >22,4 mm) between the calculated and measured loads during an investigation period of two years. This balance was drawn up for 2015/2016 and it was difficult to gather data for exactly these two years. For the short-term third case study balance, a flood event has been considered. With grain size distributions, suspended sediment data and river bed as well as floodplain level surveys the input and output of bed load and suspended load was balanced for a flood event at the Gail River. The balance shows that 1,4 million m³ of sediment was in motion during the flood event. The challenge in this balance lies in some balance variables, such as sediment deposition in the surrounding area, bank erosion or soil erosion. Not all data could be measured or determined in the required level of detail. Due to numerous factors involved, such as time scale, morphological changes or the level of detail of data bases, drawing up an overall and representative sediment balance is highly challenging. However, with the use of the presented three case studies, this paper aims to demonstrate how a sediment balance can be established under different restrictions.

DOI: https://doi.org/10.3850/IAHR-39WC252171192022858

Year: 2022

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