Mitigation

Some activities, such as infrastructure works, result in physical modifications of the river’s hydromorphology and habitats. These can have a negative impact for the river and its fauna and can be reduced through the implementation of mitigation measures such as:

 

Fish passage facilities

Fish passage facilities are structures that allow the upstream or downstream migration of aquatic organisms over obstruction to migration such as dams and weirs. This is achieved either by opening a waterway (fish pass), or else by trapping them in a tank and lifting them upstream (fish lift). The design of a fishway should take into account certain aspects of the behaviour of migratory species. Also, its effectiveness is closely linked to water velocities and to patterns of flow in the facility.

Publications providing general and technical information on fish passes are available:

 

EN - LIFE programme "Headwater streams and faunistic heritage associated" - 2009

This document presents the results of a specific study on the dimensioning of crossing structures suitable for the brook lamprey, conducted as part of the implementation of the LIFE programme "Headwater streams and faunistic heritage associated". A reminder of knowledge on the biology of species and a presentation of the experimental device are also proposed.

EN - FAO - 2002

This guidelines gives general and technical considerations as well as advice for the design and evaluation of fish passes, and proposals for choosing their hydraulic dimensions correctly and testing the functioning.

EN - Bulletin français de la pêche et de la pisciculture (now KMAE) - 2002

This book is a compilation of knowledge of all aspects concerning the planning and construction of fish passes as well as their monitoring for effectiveness

 

Management of hydraulic structures

This kind of management can also limit the impact on the environment and species. Examples are: stopping turbines during downstream migration to limit fish mortality; installing screens at inlets and fish-friendly turbines in order to reduce mortality of fish moving downstream or implementing an environmental minimum flow to sustain freshwater ecosystem.

You can find some documentation on this subject below:

 

EN - Onema - 2012

The symposium titled "Eels and ecological continuity. Optimising the design and management of installations" was organized by Onema and the steering committee of the Eels & Installations R&D programme on 28 and 29 November 2011 in Paris. In three sections, the document presents the results of the R&D programme to restore eel stocks.

 

Design of infrastructures compatible with aquatic ecosystems protection

It includes implementation of sustainable infrastructure projects which do not damage the physical, chemical and biological functions of aquatic ecosystems. Transport infrastructures are particularly concerned.

Some documents below propose more detailed information on how to consider aquatic ecosystems when designing and implementing infrastructures projects.

 

FR - Onema - 2014

This document recommends the steps to be taken to ensure that rivers and wetlands are considered when designing and implementing major rail projects.

FR - SETRA - 2013

This document presents the key principles and parameters to be taken into account when designing and installing small hydraulic structures adapted to environmental challenges.

 

Improvement of lateral continuity of waterways

Several types of measures can be implemented to improve lateral continuity of waterways: creation of riparian vegetated zones on river embankments, reconnection of side arms or ancient meanders or creation of artificial spawning grounds to encourage wildlife reproduction.

More information on the importance of lateral continuity and examples of lateral continuity improvement can be found below:

 

EN - Onema - 2013

On the Scarpe river, several techniques have been used to improve the lateral continuity of waterways: bio-engineering for bank-protection, work on the riparian vegetation, creation of an alluvial annex.

EN - Onema - 2013

This example deals with the removal of river embankment to improve lateral continuity of waterways without impacting the waterway.

EN - Onema - 2013

This fact sheet details the works done to reconnect the main channel with the side channels and to recreate diverse habitats in the Saône river

FR - Onema - 2013

These fact sheets provide knowledge on river dynamics and examples of improvments of lateral river continuity. Some of the examples were translated in english

EN - Onema - 2013

This example illustrates how bio-engineering techniques can help in maintaining waterways and lateral exchanges.