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Field Calibration of Bedload Monitoring System in a Sediment Bypass Tunnel: Swiss Plate Geophone

Author(s): Michelle Mueller-Hagmann, Ismail Albayrak, Robert Michael Boes

Linked Author(s): Ismail Albayrak

Keywords: Swiss plate geophone, bedload measurements, geophone calibration, sediment bypass tunnel, reservoir sedimentation

Abstract: Under the impact of climate change, sediment transport in melting water draining from glacier basins and reservoir sedimentation tend to increase worldwide. As a consequence, three main problems arise: (1) the loss of reservoir storage volume for energy production, flood retention, water supply and irrigation; (2) increased hydro-abrasion at turbines and hydraulic structures; and (3) negative environmental impacts due to downstream sediment deficit. An effective countermeasure against reservoir sedimentation in small to medium-sized mountainous reservoirs is to route sediment around the dam by using a sediment bypass tunnel (SBT). A major problem affecting nearly all SBTs is severe hydro-abrasion on the tunnel invert due to high bed load transport rates in combination with high flow velocities. Depending on site-specific operating conditions and sediment properties, i. e. size, hardness and shape, invert abrasion can cause considerable refurbishment costs. For optimized operation of SBTs with respect to sustainable sediment management and cost efficiency, continuous real-time monitoring of bed load transport is necessary. Bed load transport can be monitored indirectly by using passive sensors like geophones or hydrophones. However, these techniques require a site-specific calibration depending on hydraulic conditions, particle-size and shape. This study deals with the field calibration of a so-called Swiss plate geophone system implemented at the outlet of Solis SBT located in Grisons in the Swiss Alps. The geophones with a sampling rate of 10 kHz are placed across the whole tunnel width and have an inclination of 10� against the invert slope. Three different particle size classes were tested 16 32 mm, 32 63 mm and 0 400 mm. The results indicate that calibration is independent from flow velocity due to the counter inclination of the geophones. However, a certain degree of signal saturation due to high bed load transport rate occurred and hence a further investigation is needed

DOI:

Year: 2017

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