Predicting soil erosion and sediment yield at the basin scale: Scale issues and semi-quantitative models

IAEG Commission No. 1—Engineering Geological Maps—is developing a guide to hazard maps. Scientists from 17 countries have participated. This paper is one of a series that presents the results of that work. It provides a general review of GIS landslide mapping techniques and basic concepts of landslide mapping. Three groups of maps are considered: maps of spatial incidence of landslides, maps of spatial–temporal incidence and forecasting of landslides and maps of assessment of the consequences of landslides. With the current era of powerful microcomputers and widespread use of GIS packages, large numbers of papers on the subject are becoming available, frequently founded on different basic concepts. In order to achieve a better understanding and comparison, the concepts proposed by Varnes (Landslide hazard zonation: a review of principles and practice, 1984) and Fell (Some landslide risk zoning schemes in use in Eastern Australua and their application 1992; Landslide risk assessment and acceptable risk. Can Geotech J 31:261–272, 1994) are taken as references. It is hoped this will also add to the international usefulness of these maps as tools for landslide prevention and mitigation. Six hundred and sixty one papers and books related to the topic are included in the references, many of which are reviewed in the text.

Engineering geology maps: landslides and geographical information systems

Relative contribution of rill/interrill and gully/channel erosion to small reservoir siltation in mediterranean environments [plus Supporting information]

Hydrological impact of water and soil conservation works in the Merguellil catchment of central Tunisia

Reservoir siltation because of water erosion is an important environmental issue in Mediterranean countries where storage of clear surface water is crucial for their economic and agricultural development. The high density of gully systems observed in Mediterranean regions raises the question of their contribution to reservoir siltation. In this context, this study quantified the absolute and relative contributions of rill/interrill and gully/channel erosion in sediment accumulation at the outlet of small Tunisian catchments (0·1–10 km2) during the last 15 years (1995–2010). To this end, a fingerprinting method based on measurements of caesium-137 and total organic carbon combined with long-term field monitoring of catchment sediment yield was applied to five catchments in order to cover the diversity of environmental conditions found along the Tunisian Ridge and in the Cape Bon region. Results showed the very large variability of erosion processes among the selected catchments, with rill/interrill erosion contributions to sediment accumulated in outlet reservoirs ranging from 20 to 80%. Overall, rill/interrill erosion was the dominant process controlling reservoir siltation in three catchments whereas gully/channel erosion dominated in the other two catchments. We identified the presence of marly gypsum substrates and the proportion of catchment surface covered by soil management/conservation measures as the main drivers of erosion process variability at the catchment scale. These results provided a sound basis to propose guidelines for erosion mitigation in these Mediterranean environments and suggested to apply models simulating both rill/interrill and gully/channel erosion in catchments of the region. Copyright © 2015 John Wiley & Sons, Ltd.

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Relative Contribution of Rill/Interrill and Gully/Channel Erosion to Small Reservoir Siltation in Mediterranean Environments

L'erosion ravinante reduit de plus en plus les terres cultivables en Tunisie Centrale en les transformant en badland. Le developpement des ravins est variable dans l'espace et dans le temps suite a la variabilite des parametres physiques et naturels qui regissent l'accroissement des ravins. Nous nous sommes proposes dans cette recherche d'etudier l'effet des formations lithologiques sur le developpement des ravins dans le bassin versant de 1500 ha d'Oued Maiez situe en Tunisie Centrale. Les cartes du reseau hydrographique de 1963 et 1989 ont eteetablies a partir des photographies aeriennes au 1/12,500 non redressees. La prospection du terrain nous a permis de constater que la nature lithologique des differentes unites geologiques et superficielles identifiees comme relativement homogenes dans le bassin versant est un facteur determinant dans le developpement des ravins. Ainsi, les argiles gypseuses de la formation Cherichera (Lutetien-Priabonien) presentent un chevelu de ravins dense alors que les sables fins de l'Oligocene inferieur sont incises par des ravins en forme de gorges etroites dont la profondeur depasse souvent les 5 m (Fig. 7). Nous avons alors etabli un leve cartographique detaille au 1/12,500 de ces differentes unites qui sont au nombre de 8.

Importance du facteur lithologique sur le développement des ravins du bassin versant d'Oued Maiez en Tunisie Centrale

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Intégration de certains facteurs biophysiques dans l'espace pour l'étude du ravinement dans le sous bassin versant d'Oued Maiz dans la région de Haffouz (Tunisie centrale)

M. F. Megdiche

Papers

Importance du facteur lithologique sur le développement des ravins du bassin versant d'Oued Maiez en Tunisie Centrale

Intégration de certains facteurs biophysiques dans l'espace pour l'étude du ravinement dans le sous bassin versant d'Oued Maiz dans la région de Haffouz (Tunisie centrale)