Home - Themes - Restore ecological continuity - Toward integrated evaluations of lakes


    -Gaël Olivier \ Onema Auvergne-Limousin regional office
    "We have used the Alber and Charli protocols since the beginning of 2011, first on a few, fairly small lakes, notably those in the operational-monitoring network to validate the methods, then starting in 2012 on all the lakes in the surveillance-monitoring network..."

Toward integrated evaluations of lakes

The code names include Bavela, Corila, Charli and Alber. Thanks to the work of the Onema/Irstea research unit in Aix-en- Provence, scientists and water managers now have a set of standardised methods and protocols to describe lakes and their environment, and thus contribute to evaluating their ecological status. All the information will be available via new data bases now being set up.

What are the limits to the catchment basin of any given lake? What types of vegetation grow on or near its edges? What installations exist along the lake? What types of sediment line the lake bottom? The answers to these questions and many others will be available by 2014 for all French lakes listed in the Water framework directive (WFD), in the form of maps and standardised data formats. That is the result of the efforts since 2010 of the Onema/Irstea research unit in Aix-en-Provence to develop and validate the necessary tools that are now available for water managers throughout France.

By processing the available data (Alti®IGN database), the Bavela protocol determines the topographical catchment basin of lakes. A GIS (geographic information system) can then be used to extract the morphological characteristics (surface area, perimeter, average altitude, etc.), as well as other information such as land use, population density, surplus nitrogen, etc. Finally, a hydrological model provides for each basin the data series on monthly water resources from 1970 to 2008. In 2011, Bavela was used on the 473 WFD-listed lakes in continental France and the information has now been validated and is available to water managers in just a few clicks. The Corila protocol, also deployed in 2011, describes the riparian corridors of lakes, i.e. the land in the immediate vicinity of the lake edge. Using the TOPO® database, which describes landscape features divided into specific aspects, the protocol provides information on the one-metre scale concerning road and rail networks, vegetation, hydrography and orography. An upcoming version will include information on buildings.

Into the field to lake edges and bottoms

Two other, complementary protocols organise the gathering of information on lake edges. Charli deals with characterising habitats on lake edges and littoral zones, Alber with alterations to shorelines. Both are based on sets of orthophotographs drawn from IGN (French national geographic institute) databases, with additional data from on-site visits. For the visits, the technicians use a motorised boat equipped with a GPS system. For each section of the shoreline, for Charli they note the characteristics of habitats, e.g. the types of substrate (mud, sand, gravel, stones, etc.), vegetation, undercut banks, and for Alber, any observed anthropogenic alterations to lake edges, e.g. stone banking, addition or extraction of material, levees, line pipes and other equipment. The information is then stored in a database for spatialised data after GIS processing. Almost 150 lakes have already been analysed using Alber and Charli by teams from Onema regional offices and the Water agencies. Other campaigns will soon map the types of substrate on lake bottoms as well, using scientific echo-sounding equipment. After reviewing the available data on hydroacoustic techniques, INRA researchers at Thonon les Bains, in conjunction with the Onema/Irstea centre, identified the most suitable techniques for their purposes and determined how best to use them.

From the catchment basins to the lake bottoms, all the data produced by the various tools will be stored in databases by 2014 and available for defining WFD programmes of measures in 2015. There remains, however, an essential task for the Onema/Irstea centre, that is integrating all the information in a single diagnostic system. The teams have been working since the end of 2011 to model the links between biology and hydromorphology on the various interconnected scales ranging from catchment basins to riparian corridors, shorelines and lake bottoms. The goal is to develop a comprehensive and quantified method to assess the degree of lake alterations, the causes and the effects. That represents a scientific challenge and is eagerly awaited by water managers.

Managing solid transport in rivers

Rocks, stones, pebbles and sand travel down rivers in step with currents. Alluvium is a major factor in the hydromorphological and ecological balance of rivers and also plays an essential role for aquatic and riparian species. A deficit in sediment may cause numerous malfunctions that are currently observed in French rivers. That is why correct operation of sediment transport is now listed as a major objective in the legal texts governing water management and aquatic environments.

In 2011, Onema published the «Primer on managing solid transport in rivers», the second book in the «Knowledge for action» series. The book is both a summary of current knowledge on solid transport and a guide to assist in improving management.

A three-day technical workshop on managing sediment transport in rivers took place in Toulouse. About 50 people from universities, research organisations and State technical services met to discuss current knowledge on solid transport in rivers and priorities for R&D work. The workshop programme and summary documents are accessible on the Onema site.

* Authors: J.R. Malavoi, C.C. Garnier, N. Landon, A. Recking, Ph. Baranrposes and determined how best to use them.