Soil erosion caused by extreme rainfall events:: mapping and quantification in agricultural plots from very detailed digital elevation models

This paper presents a method that can be used to quantify and map soil losses at field scale produced by extreme rainfall events. The amounts of sediment produced by overland flow and concentrated overland flow (inter-rill, rill and gully erosion) at the agricultural plot scale are evaluated from elevation differences computed from very high resolution digital elevation models (DEMs), from before and just after an extreme rainfall event. Geographical Information Systems (GIS) techniques are used to analyse the multi-temporal spatial data. The research case study presented makes reference to a mechanised vineyard plot located in the Alt Penedes-Anoia region (Catalonia, Spain). The rainfall event, which occurred in June 2000, registered 215 mm, 205 min of which fell in 2 h 15 min. The average intensity of the downpour was 91.8 mm h(-1) with a maximum intensity in 30-min periods of up to 170 mm h(-1). The erosivity index R reached a value of 11,756 MJ ha(-2) mm h(-1), 10 times greater than the annual value for this area. The volume of soil detached by the rainfall, as measured by the proposed method, was 828 +/- 19 m(3). About 57% of those materials were deposited in other parts within the same plot. The balance was negative, with a total 352 +/- 36 in 3 of soil loss from the plot, which represented a rate of 207 +/- 21 Mg ha(-1). The paper analyses the characteristics of the rainfall event in relation to historical data and discusses the proposed method for soil erosion mapping at plot scales in relation to other measurement methods. (C) 2002 Elsevier Science B.V. All rights reserved.