Sediment transport monitoring

Aigner J., Habersack H., Rindler R., Blamauer B., Wagner B., Schober B., Comiti F., Dell'Agnese A., Engel M., Liebault F., Bel C., Bellot H., Fontaine F., Piegay H., Benacchio V., Lemaire P., Ruiz-Villanueva V., Vaudor L., Cavalli M., Marchi L., Crema S., Brardinoni, F., Bezak N., Rusjan S., Miko? M., Abel J., Becht M., Heckmann T., Rimböck A., Schwaller G., Höhne R., Cesca M., Vianello A., Krivograd Klemen?i? A., Pape? J., Lenzi M.A., Picco L., Moretto J., Ravazzolo D., Jäger G., Moser M., Hübl J., Chiari M., 2015, Sediment transport monitoring, 2015,

The SedAlp project contributes to an integrated management of sediment transport in Alpine basins. It is directed to an effective reduction of sediment-related risk while promoting the enhancement of riverine ecosystems and reducing the impacts of hydropower plants (balancing the implementation of EU Directives and national law e.g. RES, WFD, NGP etc.). SedAlp includes pilot actions in various representative Alpine river basins of five countries and contributes in particular to monitor sediment and wood transfer in a large set of Alpine catchments. A major goal of the project was to understand spatial and temporal variability of processes and to provide planning, warning and predictive tools but also sediment and wood management recommendations for protecting people. Furthermore the project includes strategy policy development and implementation actions for the improvement of sediment continuity in Alpine river basins. SedAlp regards the geological and climatic variability across the Alps that generate complex patterns of sediment transfer, whereas management conflicts are similar. To reach the ambitious goals of the project, it is essential to understand the key processes of sediment and wood transport. Workpackage 5 with the title "sediment transport monitoring" was focused to enhance the knowledge about these transport processes by conducting the first standardized transnational monitoring of sediment and wood transport in Alpine basins. WP5 concentrated on monitoring and assessing fluxes of sediment and wood at the local scale. Measured fluxes are strongly depending on the supply from the catchment and on the connectivity to source areas, analysed in WP4. The output of WP5 feeds WP6 which studied the interferences between structures and sediment/wood fluxes and forms the basis for WP7 which linked the catchment with channel processes. Finally, the results of WP5 contribute to policy recommendations in WP8. Within WP5, monitoring activities on 28 different pilot sites in Austria, Germany, France, Italy and Slovenia have been conducted between 2012 and 2015. The monitored transport processes covered woody debris, debris flow, bedload and suspended load. The different pilot sites showed a great diversity in catchment size, channel slope and hydraulic parameters and covered the whole bandwidth from small, high alpine catchments (e.g. Strimm_ 5 km² catchment size, 2427 m elevation a.s.l) to large catchments in the alpine valleys (e.g. Drau/Dellach: 2131 km² catchment size, 600 m elevation a.s.l). With the results of the monitoring activities, a database using different parameters regarding the transport process has been established and reflects the big diversity of the different pilot sites. The coordinated sediment transport monitoring outlined the links between the various processes responsible for sediment delivery at catchment scale and stresses out the need for a closer integration between the monitoring of various sediment transport processes in Alpine headwaters. Due to the wide range of different measurement methods used within the project, one focus of this work package was to standardize the measurement procedures and harmonize data analysis. This led to the 1st milestone "Protocol on standardized data collection methods in sediment transport monitoring for transboundary exchange". These protocols were intended to describe the used monitoring techniques and data processing methods for debris flows, wood transport and bedload transport. Furthermore, the protocols work also as guidelines to assist in choosing the appropriate monitoring method for supporting prospective monitoring efforts. 4 An important aspect of the project was to understand spatial and temporal variability of the monitored processes. The observed appearance of clockwise and counter clockwise hysteresis effects between sediment and discharge, showed the significant role of the location of the active sediment source in the temporal variability of sediment transport. Analysis of the spatial distribution showed an evolvement of the bedload transport width with increasing discharge which provides vital information for an improved planning of river related measures. To determine these process related variability, the use of appropriate monitoring methods as well as their right application is of great importance. Indirect monitoring methods (e.g. geophone devices) pointed out their potential in the automatic and continuous detection of these transport processes. The presented data reflect a high spatial and temporal variability in the occurrence of bedload, suspended load debris flow and wood transport and reveal significant consequences for the practical usage of monitoring methods, data and application. Many river engineering tasks require detailed information about the extent of sediment transport and wood mobility, which are provided by sediment and wood transport relations and equations. The 3rd milestone "First set of practically applicable bedload/wood transport relations and models" gives an overview about the most common transport relations and formulas. Furthermore it presents the difficulties and challenges in the application of these relations and shows the last developments in improving transport equations. The comparison between measured and calculated specific bedload transport rates showed substantial differences in the derived results. For the practical use of these relations it is strongly recommended to select, calibrate and validate the sediment and wood transport equations using monitored field data. The evaluation of river restoration projects showed the need of an improved process understanding between sediment transport an engineering measures. The functionality and sustainability of river restoration measures are, beside the hydrologic and hydraulic conditions, mainly depending on the superior sediment regime and thus the sediment input into the reach. By increase or decrease of the mean sediment input, the hydraulic and thus morphological conditions of the reach need to rearrange to the given input by e.g. lateral and vertical adjustments of the river bed or by changing the river type.

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