Controlling the Environmental Impact of Dredging Activities

Nantes − Saint Nazaire Port’s dredging policy is based on delivering optimal maintenance of channel depth according to expected traffic levels, while also limiting the impact of such operations on the estuarine environment. This strategy relies on making due allowance for the hydrology of the River Loire, since the River’s flow has a significant effect on inputs of sediments and the conditions for their removal.



The fleet of dredgers operating on the Loire Estuary comprises the Milouin, the Samuel de Champlain and the André Gendre, which are deployed alongside three hydrographical survey craft.

 

A Comprehensive Environmental Monitoring Programme

The operations involving the dredging and disposal at sea of dredged materials are subject to authorization under the provisions of the French Environmental Code, in the form of Inter-Prefectoral Authority approval (from Loire Atlantique and Vendée), following a public inquiry. Nantes − Saint Nazaire Port develops a comprehensive environmental monitoring programme in order to survey the impact of its dredging activities on the estuarine and marine environments: monitoring of the quantities of materials that are dredged and disposed of, and of the bathymetry of the disposal zone; inventories of the benthic fauna in the dredging and disposal zones, and of the macroalgae of the rocky plateau of La Banche; monitoring of the dissolved oxygen and turbidity levels, and of the physico-chemical quality of the materials that are dredged and disposed of, etc. The findings are then reported to the Monitoring Committee, the administrative body charged with validating the level of impact of the dredging and disposal operations in line with the Inter-Prefectoral Authority approval.

Innovative Studies

Prior to approval being obtained, wide-ranging measurement campaigns at sea and innovative studies in the area of hydrosedimentary modelling notably led Nantes − Saint Nazaire Port to focus on depositing the dredged materials in deeper waters. This provision considerably reduces the sediment dispersion effects and therefore the impact on natural environments. The proposed measure resulted in the extension of the La Lambarde disposal zone further out to sea, approved by a Prefectoral Authority Order dated 24th April 2013 authorizing maintenance dredging of the channel and the disposal of sediments for a period of ten years.

What becomes of the sediments deposited at the La Lambarde site is a subject of ongoing interest for Nantes − Saint Nazaire Port. New, long-term turbidity measurements and modelling are soon to be undertaken. This is a way for Nantes − Saint Nazaire Port to better appreciate the effects of the disposal operations in the context of the outer limits of the Estuary, which are influenced by various fluvial inputs.

A Next Step in 2018

An intermediate authorization application will be submitted by April 2018 to the dredging and Disposal Operations Monitoring Committee and to the Departmental Council for the Environment and for Health and Technological Risks. It will present the results of the monitoring operations conducted since 2013 and will make it possible to extend or to reorientate dredging practices and monitoring provisions. 

Retrofit of the Dredger Samuel de Champlain

In order to help to reduce its environmental impact, Nantes − Saint Nazaire Port has joined twelve other partners in supporting the S/F SamuelLNG for a Blue Atlantic Arch Progamme, which is coordinated by the GIE Dragages Ports Port dredging Group and co-financed by the European Union as part of the Connecting Europe Facility Programme. One of the principal actions of this project, which was officially launched in December 2016, consists in fitting the dredger Samuel de Champlain with a dual-source, gas oil / liquefied natural gas engine system. This change will make it possible to obtain a significant reduction in pollutant emissions on the Loire Estuary, and notably:

- the virtual elimination of sulphur oxide and fine particulate emissions;
- a 65 % reduction in nitrogen oxide emissions;
- a 15 to 20 % reduction in greenhouse gas emissions.