JCJC SIMI 6 - JCJC - SIMI 6 - Système Terre, environnement, risques

A novel System for the Characterisation of Agregates and Flocs in highly concentrated rivers (SCAF) – SCAF

SCAF: System for the characterisation of agregates and flocs in highly concentrated rivers

No instrument can measure fine sediment settling fluxes during flood events. While this variable is of upmost importance for numerical modelling we will develop and apply a System for the Characterisation of Agregates and Flocs (SCAF) in various natural environments and in the laboratory.

Instrumental development for a better understanding of sediment dynamics

The overarching goal of this project is to develop new capability of observation of suspended sediment properties (settling velocity, particle size, and flocculation factor) and to better predict suspended sediment dynamics in natural or man-regulated turbid rivers.

The project consists in three main objectives:
O1) An instrumental development with a first step dedicated to application by scientits in the laboratory or under controlled field conditions, and a second step dedicated to end users such as water agencies, hydroelectricity operators or river managers.
O2) Sediment in transit from hillslopes.
Results of laboratory and field experiments will help us to evaluate the mechanisms which transform soil aggregates, freshly eroded, into
suspended sediments.
O3) Revisiting hydrodynamic laws. Data assimilation with scaf instrument will be done to assess the robustness of the model to simulate SS dynamics.
during flushing operation

SCAF alpha system is now available

Laboratory experiments have been conducted with an international pannel composed of H.Michallet (LEGI, Grenoble), Ian Droppo (Environment Canada) and A.Manning (Univ Plymouth, HR Wallingford, UK).

Development of SCAF alpha 1 for semi automatic measurements under natural conditions

under progressSome publications

Wendling, V. Legout, C., Gratiot, N., Grangeon, T. and Michallet, H. 2016. Dynamics of soil aggregates in turbulent ?ow : respective e?ect of soil type and suspended concentration. Catena, 141, 66-72.

Wendling, V., Gratiot, N., Legout, C., Droppo, I.G., Coulaud, C. and Mercier, B. 2015. Using an optical settling column to assess suspension characteristics within the free, flocculation and hindered settling regimes. J. of Soils and Sediment, (15) 1991-2003.

Jodeau, M., Antoine, G., Cormier, M., Monnoyer, Q. and Gratiot, N., 2016. Settling velocity of sediment from reservoirs, laboratory measurements and modeling. 2016. River flow 2016. Ed Constantinescu, Garcia and Hanes, CRC Press. pp 937-943.

Jodeau, M., Cazilhac, M., Poirel, A., Negrello, P., Pinte, K., Bouchard, J-P. and Bertier, C. 2014. Innovative in-situ measurements, analysis and modeling of sediment dynamics in Chambon reservoir, France. Reservoirs Sedimentation. Ed. Schleiss, de Cesare, Franco and Pfister, CRC Press. 300pp. ISBN 9781315736914.

Mercier, B., Wendling, V., Coulaud, C., Legout, C., Gratiot, N., 2016. Développement d’un Système de Caractérisation des Agrégats et des Flocs (SCAF). Instrumentation, Mesures, Métrologie. Ed. E.Vourch, édition Lavoisier.

Gratiot, N., Coulaud, C., Legout, C., Mercier, B., Mora, H.Wendling, V., 2015. Unit for measuring the falling speed of particles in suspension in a fluid and device comprising at least one measuring unit and one automatic sampler. Patent-Publication number WO2015055963 A1.

During the 21th century, the management of water resource is in the way of becoming a main issue because of the increasing growth of population. Water constitutes a major resource for three main concerns: first, it is an essential resource for basic human needs (drinking, irrigation) and for many industrial activities; secondly, it transports and disperses pollutants in the aquatic ecosystem with direct environmental consequences. Finally, it constitutes a renewable source of energy through hydro-electricity. From an operational point of view, a good management of water resources is closely linked to a good management of suspended sediments (SS). The SS add real costs to the treatment of drinking water since the turbidity must be virtually eliminated for effective disinfection to occur. The SS also provide attachment sites for heavy metals, pesticides or other toxic organic contaminants such as PCBs and PAHs. Apart from this water quality issues, settling of SS and their accumulation in reservoirs reduce the storage capacity and is one of the main obstacles to the recognition of the hydroelectricity as a compatible energy with sustainable development.
The SCAF project puts SS toward the heart of its scientific approach. The physical characteristics describing SS transfer put in balance sediment settling flux on a hand and turbulent diffusive flow of the river on the other hand. Yet no instrument is capable of measuring in-situ settling fluxes for the high concentrations (10-300 g l-1) frequently reached during floods in mountainous environments (PIE 2010 ). To fill this deficit, the project gather a team of scientists (LTHE) and an industrial end-user (EDF) with the objective of 1) designing and developing an original System for the Characterization of Aggregates and Flocs in intermittent and highly concentrated flows (SCAF), 2) exploiting these new observations to improve the formulation and modelling of sediment conveyance in natural or regulated rivers. The SCAF project is organized into three tasks. Task 1 focuses on the development and validation of SCAF instrument. Following the encouraging evaluation to the proposal FingerStreams (coord. Evrard, ANR Edition 2011, see Annex 8.2) and the funding by the EC2C0 CYTRIX (coord. Legout, INSU 2011, 10k€), the development of a prototype SCAF alpha.0 has been launched. It is based on the coupling of an automated sampler with an optical sounding method. The SS properties (settling velocity, particles size) are deduced from turbidity, by using a method previously validated (You, 2004 ; Gratiot, 2010 ; Sottolichio et al. 2011). The calibration and validation of the SCAF prototype will be done in close collaboration with two international experts (A.Manning, Univ of Plymouth, UK and I.Droppo, Environmental Canada) through joint experiments conducted in France and Canada. The scaling up to the industrial SCAF beta demonstrator will benefit from the support and the experience of EDF, the leader company of hydropower in Europe. Thanks to the SCAF, the ultimate goal of the project is to measure original SS properties during flushing or concentrated flood events (Task 2). This, in order to revisit SS transport laws (Task 3), and provide a better numerical modelling of highly concentrated flows. The perspectives of applications of SCAF system are various. The monitoring of fine sediment properties with SCAF could help in the planning of river restoration, monitoring of aquatic pollution fluxes (adsorption of contaminants and nutrients on particles) and the optimisation of the hydropower capacity generation. These topics are gaining interest in Europe, where the European Water Framework Directive has been launched to guarantee a sustainable use and management of rivers with quantified objectives to be reached in 2015.

Project coordinator

Monsieur Nicolas Gratiot (INSTITUT DE RECHERCHE POUR LE DEVELOPPEMENT) – nicolas.gratiot@ird.fr

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

IRD - LTHE INSTITUT DE RECHERCHE POUR LE DEVELOPPEMENT

Help of the ANR 168,399 euros
Beginning and duration of the scientific project: September 2012 - 36 Months

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