Unlike the contiguous windthrows, the scattered windthrows occurring as a result of wind gusts of lower speed (100-140 km/h) than in the first case (>140 km/h) are much more difficult to detect due to their much smaller areas and due to their very large number (several hundred in the wooded Vosges Mountains). The objective of this research is to present a rapid procedure for the detection of the scattered windthrows based on low cost, Landsat type images, knowing that certain sensors cannot be accessed without significant investments. Our application is based on the study of effects caused by the Storm Xynthia in the Vosges Mountains in the North-East of France, on 28 February 2010. Thus, based on two sets of Landsat satellite images, we used the “dark object” approach and the Disturbance Index, as well as the image classification before and after the storm, resulting in a map of changes. Following the detection process, 257 scattered polygons were detected, totalling 229 ha. For validation purposes, high-resolution images and orthophotoplans taken before and after storm were used. The error matrix was calculated, achieving an overall accuracy of 86%, which confirmed the quality of our analysis and supported this procedure for detecting scattered windthrow based on low cost resources.

Unlike the contiguous windthrows, the diffuse windthrows occurred as a result of wind 12 gusts of lower speed (100-140 km/h) than in the first case (>140 km/h) are much more difficult to

The OumErRbiabasin is one of the watersheds with the largest number of hydraulic infrastructures in Morocco. These hydraulic structuressupply water for drinking, industrial and agricultural uses. The Ahmed El Hansali dam is a 740 Mm³ reservoir located near Zaouyat Cheikh andhave an active storage of473 Mm³. The succession of dry years in the OumErRbiabasin has had a negative impact on the water resource and has caused a remarkable decrease in the reservoir of the Ahmed el Hansali dam. In this paper, the MNDWI (Modified Normalized Difference Water Index) from Landsat 5-TM, Landsat 7-ETM, and Landsat 8-OLI satellite images was used to estimate the spatial and temporal fluctuations of the volumes of water stored in the reservoir between hydrological years 2002-03 and 2018-19. Results show that the volumes estimated by remote sensing reasonably match the volumes estimated by the OumErRbia Hydraulic Basin Agency (OERHBA)using recorded water levels and reservoir storage curve for years 2002-03 and 2013-14; the determination coefficient R² exceeds 0.90. The mapping of the extent of the dam’s impoundment has shown a very significant decreasein the flooded area level during dry years.

No abstract

Dans la partie française du bassin de la Moselle, les plus longues chroniques de débits dépassent rarement 50 ans. Il est donc parfois difficile d'évaluer le caractère exceptionnel de certains événements hydrologiques, notamment les étiages de ces dernières années. Ce travail vise à mettre en œuvre trois méthodes de reconstitution des débits mensuels (un modèle pluie-débit, un modèle statistique et un modèle débit-débit) appliquées à trois stations hydrométriques situées sur la Moselle. Des trois méthodes, l'approche statistique semble la plus efficace pour estimer les étiages. Les reconstitutions qui en découlent montrent que les étiages récents (1976, 2003 et 2018) sont certainement les plus bas de ces 150 dernières années. Des données limnimétriques anciennes peuvent être utilisées pour valider les débits reconstitués.