Sediment production in large gullies of the Mediterranean area (NE Spain) from high-resolution digital elevation models and geographical information systems analysis

摘要

Recent studies in the Mediterranean area have shown gully erosion to have a very significant contribution to total soil loss. In the Penedes vineyard region (NE Spain), between 15 and 27% of the land is affected by large gullies and gully-wall retreat seems to be an ongoing process. Multi-date digital elevation model (DEM) analysis has allowed computation of sediment production by gully erosion, showing that the sediment production rates are very high by the, up-to-date, usual global standards. Here, we present a study carried out using large-scale multi-date (1975 and 1995) aerial photographs (1:5000 and 1:7000) to monitor sediment yield caused by large gullies in the Penedes region (NE Spain). High-resolution DEMs (1 m grid) were derived and analysed by means of geographical information systems techniques to determine the gully erosion rates. Rainfall characteristics within the same study period were also analysed in order to correlate with the soil loss produced. Mass movement was the main process contributing to total sediment production. This process could have been favoured by rainfalls recorded during the period: 58% of the events were of an erosive character and showed high kinetic energy and erosivity. A sediment production rate of 846 ± 40 Mg ha~(-1) year~(-1), a sediment deposition rate of 270 ± 18 Mg ha~(-1) year~(-1) and a sediment delivery ratio of 68.1% were computed for a gully area of 0.10 km~2. The average net erosion within the study period (1975-95) was 576 ± 58 Mg ha~(-1) year~(-1). In comparison with other methods, the proposed method also includes sediment produced by processes other than only overland flow, i.e. downcutting, headcutting, and mass movements and bank erosion.