Home - Themes - Restore ecological continuity - Evaluating the ecological impact of obstacles


    -Thierry Clauss \ Onema Bas-Rhin regional office
    "Between April and June, we tested the ICE protocol while collecting measurements on installations in order to assess their impact on ecological continuity..."

    -Michaël Ovidio \ University of Liège
    "My team is specialised in the study of the behavioural ecology of river fish using radio-telemetry techniques..."

Evaluating the ecological impact of obstacles

After leading the project to draw up an inventory obstacles to river flow, by pulling together all national data on all rivers in continental France, which resulted in the national database on river obstacles (ROE), Onema then managed efforts to develop a national method to evaluate ecological continuity. The goal was to assess the impact of obstacles on the passage of aquatic species and sediment. This vast project, a part of the national plan to restore ecological continuity, will identify the installations causing the greatest problems and set priorities for corrective action.

What are the risks that an installation will block the passage of aquatic species and sediment? To find out, Onema coordinated the creation of a standardised national protocol for data collection intended for Onema personnel and other environmental and territorial-development actors in charge of listing the obstacles. The protocol, called ICE (Information on ecological continuity), was developed with a group of national and international scientists.

A major investment in time and effort by Onema territorial personnel made it possible to test and improve the protocol. In each department, they applied the same method to 20 installations, which consisted of determining the geometric characteristics of the obstacle (height, shape, building material, site map), its functional characteristics (moving elements, dimensions, functions and types of flow) and the physical structure of the river (granulometry, reservoir sedimentation, incision rates, etc.), both upstream and downstream of the obstacle.

Optimising the protocol and formulating indicators of discontinuity risks for fish

Following the test carried out in 2010, a work group was set up, comprising experts from the ecohydraulic centre in Toulouse, University of Liège, University of Paris 1 and Onema. The group succeeded in significantly simplifying the data-collection process in the field and thus reducing the time required by personnel for each installation to less than one hour on average. It also developed indicators of discontinuity risks for continental fish, which were grouped into different categories according to their physical capability to overcome obstacles.

This work required in-depth analysis of current scientific knowledge, processing of the results of scientific-fishing campaigns carried out in the monitoring networks and advanced ecohydraulic modelling.

Discontinuity indicators could then be formulated by comparing the characteristics of the analysed obstacle and the physical capabilities of the given categories of species. The indicators then served to rank obstacles in four categories, 1) insurmountable barriers, 2) high-impact partial barriers, 3) medium-impact partial barriers and 4) limited-impact surmountable barriers.

A project to design a data-input and analysis tool was launched to enable personnel collecting data in the field to immediately calculate the risks for a species or group of species.

The ICE protocol will be used initially on rivers with major regulatory issues and for the water bodies in the surveillance-monitoring network. Starting in 2012, it will be deployed on a wider basis, notably in the Water agencies, State technical services, for stakeholders active in sub-basin management plans (SBMP) or local environmental contracts, design offices, etc., in conjunction with information sessions and training.