Land drainage functioning and hydrological impacts in rural catchments: model development and field experiments

International audienceThe development of an integrated theory of subsurface drainage based on hydrology and hydrogeology concepts is presented. The historical context, the main hypothesis derived from the Boussinesq equation and the validation of the model predictions are discussed. Theoretical developments of this equation demonstrate that a single parameter (σ)-a combination of soil and drainage system properties-is sufficient for predicting the dynamics of subsurface drain flow rates. We also demonstrate that these drain flow rates are a function of the level of water replenishment in the system (classically the water table elevation), of the recharge intensity of the aquifer and of a buffer function related to the swelling or deflation of the water table shape during recharge events. For values of σ > 1, the buffer role of the water table is negligible. In that case approx. 13% of the water table recharge contributes to the flow rate, which is shown to explain the observed disconnection between water table elevations and peak flow rates at the outlet of classic agricultural drainage systems and to predict these peak flow rates accurately. A modelling approach based on this theory and validated experimentally (SIDRA model) allowed us to test the quality of the peak flow prediction. The SIDRA model also includes a surface runoff module and has been coupled to different modelling tools and used to analyse the impacts of subsurface drainage on water quality. The approach contributed towards the development of tools that helped to connect better the drainage systems to the hydrological functioning of watersheds

Restauration de la nature : vers de nouvelles références et pratiques. Aperçu de cinq années de recherche du programme «recréer la nature»

The interdisciplinary research programme “Recreating Nature : rehabilitation, restoration, and creation of ecosystems” was launched by the Ministry in charge of the Environment (Directory of Research) in 1995, in response to needs identified by practitioners and scientists. Four research questions were addressed : i) motivating factors of those involved, ii ) identification of reference systems, iii) relevant spatio-temporal scales, iv) ways of monitoring and assessing restoration projects. Twenty projects have been selected, some concerned with spe¬ cific degraded ecosystems (coral reefs, islands, grasslands, scrub, forest, wetlands, freshwater), others concerned with more specific mitigation measures assisting in the development of large infrastructures (railway lines, ski runs, gravel pits). The programme included sites from continental France, overseas Departments and Territories, and a transboundary site. Successful ecosystem restoration depended on rigorous control of ecological dynamics under various constraints, and included a landscape approach, consideration of the past, and the participation of stakeholder groups. Both social and political will is required, as well as ecological knowledge. As in the medical sciences, there is an art to nature restoration, with a need for ethical as well as scientific foundations.Le Programme national de recherche «Recréer la Nature : réhabilitation, restauration et création d’écosystèmes» a été lancé par le Ministère chargé de l’environnement en 1995. Il est centré autour de quatre questions. Quels sont les déterminants des choix et les motivations des intervenants ? Comment sont choisis les systèmes de références ? Quelles sont les échelles spatio-temporelles pertinentes d’action ? Quelles sont les modalités de suivi et d’évaluation de ces interventions ? Les 20 projets sélectionnés sont géographiquement distribués sur l’ensemble du territoire français (métropole et Dom-Tom) et concernent les systèmes humides ou aquatiques, arbustifs ou arborés, herbacés, coralliens ou insulaires, les zones modifiées par l’extraction de granulats ainsi que les différents corridors végétaux bordant les réseaux ferroviaire et autoroutier. Le succès de la restauration des écosystèmes dépend du contrôle rigoureux des dynamiques écologiques sous diverses contraintes. Il exige en outre une approche paysagère, prenant en compte la dimension historique et impliquant l’ensemble des groupes sociaux intéressés. La restauration des écosystèmes relève aussi bien de questions écologiques que sociales et politiques. A l’instar de la démarche médicale, la restauration des écosystèmes doit s’appuyer sur un corpus de connaissances scientifiques, mais aussi sur une éthique.Décamps Henri, Lesaffre Benoît. Restauration de la nature : vers de nouvelles références et pratiques. Aperçu de cinq années de recherche du programme «recréer la nature» . In: Revue d'Écologie. Supplément n°9, 2002. pp. 9-16