Abstract
Fine sediments are important in the design and operation of hydropower plants (HPPs), in particular with respect to sediment management and hydro-abrasive erosion in hydraulic machines. Therefore, there is a need for reliable real-time measurements of suspended sediment mass concentration (SSC) and particle size distribution (PSD). The following instruments for SSC measurements were investigated in a field study during several years at the HPP Fieschertal in the Swiss Alps: (1) turbidimeters, (2) a Laser In-Situ Scattering and Trans- missometry instrument (LISST), (3) a Coriolis Flow and Density Meter (CFDM), (4) acoustic transducers, and (5) pressure sensors. LISST provided PSDs in addition to concentrations. Reference SSCs were obtained by gravimetrical analysis of automatically taken water samples. In contrast to widely used turbidimeters and the single-frequency acoustic method, SSCs obtained from LISST, the CFDM or the pressure sensors were less or not affected by particle size variations. The CFDM and the pressure sensors allowed measuring higher SSC than the optical or the acoustic techniques (without dilution). The CFDM and the pressure sensors were found to be suitable to measure SSC ≥ 2 g/l. In this paper, the measuring techniques, instruments, setup, methods for data treatment, and selected results are presented and discussed.
Highlights
In the design and operation of hydropower plants (HPPs), fine sediments are important with respect to reservoir sedimentation, hydro-abrasive erosion of hydraulic machines and related countermeasures
The following instruments for sediment mass concentration (SSC) measurements were investigated in a field study during several years at the HPP Fieschertal in the Swiss Alps: (1) turbidimeters, (2) a Laser In-Situ Scattering and Transmissometry instrument (LISST), (3) a Coriolis Flow and Density Meter (CFDM), (4) acoustic transducers, and (5) pressure sensors
This paper reports on the investigation of various measuring techniques for continuous suspended sediment monitoring (SSM) in a recent field study at the high-head HPP Fieschertal in the Canton of Valais, Switzerland
Summary
In the design and operation of hydropower plants (HPPs), fine sediments are important with respect to reservoir sedimentation, hydro-abrasive erosion of hydraulic machines (pumps and turbines) and related countermeasures. For a better understanding and management of sediment-related processes, in-situ measurements of suspended sediment mass concentration (SSC) and particle size distribution (PSD) with high temporal resolution are required. Many techniques for suspended sediment monitoring (SSM) in various application cases are available and described in literature [1] [2]. There are specific requirements for SSM systems at HPPs. For turbine erosion mitigation, reliable measurements of higher SSCs (up to e.g. 100 g/l), especially of coarser particles, are important – preferably with information in particle sizes
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