COMPARISON OF SOIL EROSION RILLS IDENTIFICATION BY MATHEMATICAL MODELS AND AERIAL PHOTOGRAPHS

References: 14th International Multidisciplinary Scientific GeoConference SGEM 2014, www.sgem.org, SGEM2014 Conference Proceedings, ISBN 978-619-7105-10-0 / ISSN 1314-2704, June 19-25, 2014, Book 2, Vol. 1, 521-528 pp

ABSTRACT
The importance of soil loss by water erosion becomes more eminent with the ongoing climate change, where more extreme precipitations in middle Europe are anticipated. The amount of soil transported from the field plot can substantially differ according to the intensity of rill erosion. The capability of mathematical models to predict appearance of extreme soil erosion spots on arable land (rills and gullies) are addressed in this paper. Three surface runoff\erosion models were tested by comparing their outcomes with rills identified from orthophoto maps. Empirical methods are represented by Universal soil loss eq. (USLE). The equation is a simple method of the long term modeling of the sediment yield. Limitations of this method are in estimating soil loss from rainfall episodes and application of this equation in areas with concentrated flow is debatable. Second tool used is physically based model SMODERP which is being developed on CTU Prague since 1990s. Soil characteristics are based on Czech soil taxonomy system. The model SMODERP is excellent tool for modeling of sheet and concentrated surface runoff. Hydrological part of the model includes the processes of infiltration (Phillips equation), sheet surface runoff (Kinematic wave based equation), rill runoff, surface retention. Third tested modeling approach is based on Erosion-3D simulation model, developed at TU Freiberg (Germany). Erosion-3D is physically based and fully distributed rainfallrunoff model allowing calculation of transported sediment. The model can be run for single event, repeated events or sequence of events and the outputs include characteristics of runoff and soil transported in three particle size fractions. The soil input parameters are based on German standard of soil classification KA4. The uncertainties in inputs strongly influence the absolute values of soil erosion, but spatial distribution of netto erosion can be useful in identification of rill erosion appearance. The paper describes validation and application of models at the experimental field plot near Benesov (Central Bohemia, Czech Republic) in 2010. Airborne photographs of the field plot with apparent consequences of a heavy rainstorm event were used to visually derive the pattern of erosion rills and ephemeral gullies which were used for the main comparison. Standardized plots (22.1 m in length, 9 % slope) for long term monitoring of erosion processes have been installed on this experimental field. Outflow from the plots and precipitation are automatically continuously measured during each natural rainfall event. The soil concentration in outflow and the volume of transported sediment is determined from samples in laboratory. Data from experimental plots can be used for validation of the model’s input parameters.

Keywords: SMODERP, Erosion-3D, erosion, modeling, USLE