Measuring rill erosion at Sparacia experimental area (Sicily, South Italy)

Abstract:

Soil loss data at plot scale are needed to test the applicability of the provisional soil erosion models and to evaluate the variables and main factors affecting the physical phenomena of erosion. The soil-erosion process (rill, interrill, etc.) examined affects the choice of the measurement technique and the experimental scheme used.

The experimental station for soil erosion measurement, ‘Sparacia’, of the Department of Agricultural, Food and Forestry Sciences, University of Palermo is located in western Sicily, Southern Italy. The area has a typical Mediterranean semi-arid climate, with an average annual rainfall of 700 mm. The soil is a Vertic Xerocrept (according to USDA classification) with a clay texture and a negligible gravel content.

Plots having different length (11, 22, 33 and 44 m) and width (2, 4 and 8 m) and several microplots (0.25 × 0.25 m², 0.4 × 0.4 m², 1 × 1 m², 1 × 2 m² and 1 × 5 m²) are operating on a hillslope having a slope steepness of 14.9%. Two unit plots (22 m long and 9% steep) were also realized in 2014. Other 22-m-long plots were installed on an hillslope having a slope steepness of 26% (two plots) and of 22% (two plots).

In the measurement period September 2004–March 2010, the direct relief of the rills was carried out for nine events. Each rill was measured by a metric ruler and a rillmeter.

For the erosion event of October 3, 2011 a direct relief of 19 rills occurred on a 8 x 44 m plot was also surveyed by a quadricopter Microdrones MD4-200. This survey resulted preferable because it does not change the surface of the rilled area, allows a fast execution and the Digital Elevation Model (DEM) can be generated.

The rill network was also surveyed using the three-dimensional photoreconstruction (3D-PR) technique which allows to obtain a digital terrain model (DTM) by a large series of oblique images of the channel from consumer un-calibrated and non-metric cameras. For an erosion event (October 2016) both terrestrial and low‐altitude aerial surveys were carried out by consumer grade camera and quadcopter (low‐cost unmanned aerial vehicle) to measure rill erosion on two plots with steepness of 22% and 26%. The 3D digital terrain models were obtained applying the structure from motion (SfM) technique. For both plots, SfM always provided reliable soil loss measurements, which were affected by errors ranging from −8% to 13%.