| Titre | Occupation des sols et régimes hydrologiques : les enseignements des bassins versants guyanais | |
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| Auteur | J.-M. Fritsch | |
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Revue | Annales de géographie |
| Numéro | no 581-582, 1995 | |
| Rubrique / Thématique | Articles |
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| Page | 26-63 | |
| Résumé |
L'influence du couvert végétal sur les écoulements est un thème souvent invoqué lorsqu'il est question des effets anthropiques sur le cycle hydrologique. En présentant les méthodes et les procédés habituellement utilisés (telle que la méthode des bassins jumelés), on montre pourquoi il est très difficile en pratique de mettre en évidence et de quantifier ces effets. En s'appuyant sur des études de cas tirées du programme Ecérex en Guyane française, on montre que selon le bassin versant et selon le paramètre hydrologique considéré (écoulement annuel, pointe de crue), les effets hydrologiques des manipulations du couvert végétal (déboisement, reboisement, conversion de forêt en prairie, etc.), peuvent dans certains cas être évalués avec précision et avec un risque statistique très faible, mais que dans d'autres cas l'incertitude est beaucoup plus grande et qu'il y a présomption hydrologique plutôt que preuve scientifique. La sensibilité de cette étude d'impact sur un bassin traité dépend pour l'essentiel de la capacité à reconstituer le comportement hydrologique du bassin en l'absence du traitement. Source : Éditeur (via Persée) |
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| Résumé anglais |
The effect of land use and vegetal cover changes on runoff regimes is taken as one of the most typical effects of mon activity on the hydrological cycle. A presentation of the available methods and tools used by the hydrologist to assess these effects (such as the paired watershed approach), shows that even if these impacts do exist, it might be very difficult to quantify them. The data collected on ten small watersheds during the Ecerex experiment in French Guyana is taken as a case study. According to the watershed and to the hydrological parameter considered (annual runoff, peak flow), the hydrological effects of land use changes were assessed with high accuracy and quantified with a very low statistical risk, but for some of the experiments, the uncertainty was much wider and the outcome is more a presumption than a scientific proof. The major issue for evaluating the effects of any treatment is the capacity of the hydrologist to predict the hydrological behaviour which would have been observed on a specifie treated watershed under the same climatic conditions, if the treatment would not have been applied. The Ecerex experiment started with a 2-year calibration period, which has shown a wide range of runoff under natural forest : for a similar amount of rainfall, the variation of runoff within the set of the ten watershed was in a range of 1 to 5, Le. stormflow volumes varied from 7 % to 54 % of the rainfall, according to soil characteristics. The initial treatment (logging followed by mechanised land clearing) has created bare soil conditions for seven of the watersheds. The increase of stormflow during the first year after the treatment was very high (+ 228 mm to + 714 mm, or + 66 % to + 199 % in relative terms). The highest relative increases were observed for the watersheds having the lowest flows in natural conditions. The treatments applied include natural regrowth of the forest, fast-growing tree plantation (pine, eucalyptus), fruit trees plantation, grazing, traditional slash-and-burn agriculture. The effects on annual stormflow and on peak discharges were quantified for the first years after the application of the treatments. Source : Éditeur (via Persée) |
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| Article en ligne | http://www.persee.fr/doc/geo_0003-4010_1995_num_104_581_13867 |
