Donzère Dam – Assessment of the alluvium thickness in the riverbed of the Rhone l France

Project summary

Service provided:  Assessment of the alluvium thickness in the riverbed of the Rhone
Location:  Donzère, France
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Client:  Compagnie Nationale de Rhône (CNR)
Period of the service:  January 2013 - February 2013
Duration of service:  2 months
Sixense solutions used: 

Images of the project

Erosion of alluvium from the Rhône

The Donzère dam is a gravity dam on the Donzère-Mondragon canal in the Ardèche valley. This structure acts to control the river to enable electricity generation, navigation and irrigation of the neighbouring plains.

Following the appearance of an erosion of the Rhône alluvium immediately downstream of the Donzère dam, the National Company of the Rhône (CNR) sought the assistance of geophysical diagnostics to precisely locate the level of the bedrock.

To determine the thickness of alluvium and the bedrock after torrential flows, Sixense carried out a geophysical survey in order to provide the necessary information to the CNR.w


Investigation techniques

In this situation, Sixense used a combination of two investigative methods :

■ Electrical tomography,

■ Seismic refraction.

In analysing the results of soil resistivity and the velocitiy of wave propagation in the different layers, Sixense noticed a significant change in the bedrock levels from one bank to another.

The results enabled geotechnical drilling locations to be proposed in order to check for the presence of certain geological markers. These additional surveys allowed certain assumptions to be validated.

Project Key figures

3 electrical tomography profiles from 31 to 97 ml
9 seismic refraction profiles of 60 ml
1 electrical cable with 32 connections at 1m spacing