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Surrogate bedload transport measurements with acoustic sensors

English title Surrogate bedload transport measurements with acoustic sensors
Applicant Rickenmann Dieter
Number 172606
Funding scheme Project funding (Div. I-III)
Research institution Swiss Federal Research Inst. WSL Direktion
Institution of higher education Swiss Federal Institute for Forest, Snow and Landscape Research - WSL
Main discipline Geomorphology
Start/End 01.03.2018 - 28.02.2021
Approved amount 281'307.00
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All Disciplines (4)

Discipline
Geomorphology
Hydrology, Limnology, Glaciology
Civil Engineering
Fluid Dynamics

Keywords (9)

bedload transport measurement; sediment transport; gravel-bed river; mountain stream; torrent; fluvial geomorphology; river engineering; surrogate bedload measurements with impact plates; acoustic bedload monitoring

Lay Summary (German)

Lead
Die Messung des Geschiebetransportes in Flüssen und Wildbächen ist wichtig für die Gefahrenbeurteilung und für die Verbesserung der Kenntnisse der Faktoren, welche den Geschiebetransport beeinflussen. Die direkte Messung des Geschiebetransportes ist schwierig, aufwändig oder unmöglich, zum Beispiel bei Hochwasserabfluss. Daher entwickeln wir eine indirekte, akustische Messmethode.
Lay summary

Inhalt und Ziel des Forschungsprojekts

Das übergeordnete Ziel ist eine Verbesserung der Beobachtungen zum Geschiebetransport in Kiesflüssen. Im Projekt werden akustische Messungen des Geschiebetransportes sowohl in einer grossen Versuchsanlage in Südbayern als auch in verschiedenen Bächen und Flüssen in der Schweiz durgeführt. Mit diesen Untersuchungen soll die indirekte, akustische Messmethode so gut verstanden werden, dass quantitative Informationen zum Geschiebetransport auch in solchen Gerinnen abgeleitet werden können, wo parallel dazu keine direkten Messungen des Transportes, zum Beispiel durch Fangkörbe, gemacht werden können.

Wissenschaftlicher und gesellschaftlicher Kontext des Forschungsprojekts

Die Arbeit wird es erlauben, zukünftig vermehrt kontinuierliche Messungen zum Geschiebetransport in Flüssen und Wildbächen durchzuführen, was bisher nur in Einzelfällen möglich war. Die entwickelte Messmethode wird zum besseren Verständnis des Geschiebetransport beitragen und die Grundlagen für die Gefahrenbeurteilung bei Hochwassern in Gebirgsgebieten verbessern.

Direct link to Lay Summary Last update: 26.06.2017

Responsible applicant and co-applicants

Employees

Name Institute

Project partner

Associated projects

Number Title Start Funding scheme
137681 Sediment transport measurements with geophone sensors 01.04.2012 Project funding (Div. I-III)
124634 Sediment transport in steep streams 01.05.2009 Project funding (Div. I-III)

Abstract

In the recent decade or so, an increasing number of studies using bedload surrogate acoustic measuring techniques were performed both with flume experiments and in field settings. The Swiss plate geophone system is one of the techniques for which considerable experience has been accumulated over the last 15 years; it has been installed at more than 20 field sites, and direct bedload samples have been collected at many of these sites. This measuring technique has been successfully calibrated for total bedload flux at several field sites. In addition, a method has been developed to determine bedload transport by grain size classes, based on a detailed analysis of the field measurements at the Swiss Erlenbach stream including records of the full raw geophone signal. Recent flume experiments with the Swiss plate geophone system (performed in the context of a preceding SNSF project) allowed to better study in a controlled way factors influencing the signal response, for varying conditions of flow hydraulics, particle size and shape, and bed roughness. A robust method to identify particle size was developed, based on the maximum amplitude and the centroid frequency of that part of the raw signal which is due to a single particle impact on the steel plate. Flume-based relations between impulses and particle diameter were validated with direct bedload samples from field measurements at four sites in mountain gravel-bed streams. The flume-based estimations of impulses were within a factor of about two of the field measurements on average. A procedure was developed to estimate bedload transport mass using the flume-based relations and a stream-dependent calibration function. The estimated masses were on average in the range of +/-90 % of measured bedload masses in the field. The main limitations of this first set of systematic flume experiments were that the flow conditions were not sufficiently close to prototype conditions, i.e. discharges and flow depths were generally too small, and bed roughness was only replicated in a simplified way.In the proposed project we intend to overcome these limitations. We plan to perform a new set of controlled experiments, using an outdoor flume facility with a maximum water discharge of up to 5 m3/s, allowing to much better replicate field conditions both regarding flow hydraulics and bed roughness, than in the previous SNSF project. One important goal of this study is to explore whether such flume experiments can eventually completely replace time consuming and costly field calibration measurements. More specifically, the objectives of the planned project are:- to collect new field calibration measurements for the Swiss plate geophone (SPG) system and the Miniplate accelerometer (MPA) system, including sampling of the raw signal and measuring flow velocity profiles- to further develop the SPG system and to test the MPA system by performing systematic prototype flume experiments- to test and quantify the signal response for a defined impact onto the sensor plates at different field sites and among neighboring sensor plates at a given field site- to determine to what degree the prototype flume experiments can be used to develop a generally valid signal analysis procedure that can be applied to un-calibrated field sites- to test the applicability of an alternative, cheaper surrogate measuring system using a more compact construction with accelerometer sensors (MPA system)One of the main tasks is to perform new field calibration measurements (Task A), and it will include:- four Swiss field sites with existing SPG systems (Erlenbach, Albula, Navisence, Avancon de Nant) - additional installation of the new MPA system at these field sites- collecting bedload samples for calibration measurements, measuring flow velocity profiles for a range of flow conditions, and measuring the variability of signal response from different plates and the degree of pick-up of signal from neighboring plates with strong impactsThe second main task is to perform new prototype flume experiments at an outdoor flume facility allowing to use prototype discharges and realistic bed roughness configurations (Task B), and it will include:- replicating field conditions (bed roughness/material, flow conditions) for the same four streams with field calibration measurements to be made in Task A (Erlenbach, Albula, Navisence, Avancon de Nant) - installing both a SPG system and a new MPA system- feeding uniform particles in different size (weight) classes, taken from the four streams- repeating experiments for a range of typical flow conditions in the field The third task (Task C) consists in a detailed analysis of both the field and flume measurements. In particular it will involve analyzing the full raw signal from both types of measurements (i.e. from both Tasks). This will allow to refine existing approaches to interpret the geophone signal, to develop new approaches if necessary, and to also examine the performance of the MPA system, a slightly alternative acoustic measuring system (compared to the SPG system) but with considerably lower installation costs.
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