Author(s): Philipp Gmeiner; Marcel Liedermann; Michael Tritthart; Helmut Habersack
Keywords: No Keywords
Abstract: The forces occuurring in a riveer bed are subbject to tempooral andd spatial flucctuations, which are closeely linked to the chaaracteristics of turbulent floows. In fact thhe random natture of turbulent floows suggests that statisticcal methods are reqquired when dealing withh sediment transport, heence measurements of the instantanneous bed sheear stress seemm to be inevitable. Beed shear stresss represents aan important llink bettween turbuleent flow conditions and seddiment transpport, andd is thus a funndamental parrameter to desscribe and preddict moorphodynamicc processes. Though indirrect methodss to evaaluate bed sshear stress are widely applied, thhese techniques are only capable of estimatingg mean valuess of bedd shear stresss. In contrast the advaantage of dirrect measurement tecchniques is thhe acquisitionof temporal bed sheear stress variaations. Therefore a ddevice for direct measurrements of the fluctuating bed shear stress in a gravel bbedded river wwas dessigned and tested. In labboratory flumme tests a static calibration wass performed to determinne the inherren fricctional losses of the measuurement system, resulting in a lineear relationshhip between applied and measured forcces The functioningg of the streaamlined shapee was confirmmed andd the comparison of directtly measured bed shear strress waas in good agreement wwith calculated and modeeled inddependent data sets. Besidde that a resoonance frequency anaalysis as well as statisticcal analyses of the direcctly measured bed shhear stress werre performed. Afftter design, coonstruction annd laboratory measurementts a proototype device is availablee for direct measurementss of bedd shear stresss in gravel beed rivers. Futuure work aims a testing the funcctional capabbility of the device for ffiield measurements.