ANALYSIS OF THE EVOLUTION OF GULLY EROSION IN OLIVE GROVES USING PHOTOGRAMMETRY TECHNIQUES. RELATIONSHIPS WITH RAINFALL REGIME

Abstract. Gully erosion is one of the main processes of soil degradation, reaching 50%–90% of total erosion in basins. As erosion processes are related to rainfall regime, the depletion and deposition rates can be increasing in a climate change scenario. This paper deals with the quantification of erosion processes in an active gully affecting olive groves of the province of Jaén (southern Spain), using geomatics techniques (photogrammetry and LiDAR). Eight historical aerial flights from 1980 to 2016, a LiDAR dataset (2014) and 2 recent UAS surveys (2019–2020) were used and processed in a common reference system with the support of field GNSS ground control points. Then, DSMs and orthophotographs were obtained and DSMs of differences (DoDs) calculated, from which we can identify gullies, calculate the depletion and deposition areas, and estimate height differences and volumes involved. These analyses result in an average depletion of about −1.6 m (incision) and a waste volume up to 30000 m³ (soil losses), which lead to a rates of −0.05 m/year and −44 t/ha*year, respectively. These rates are very different along the considered periods, reaching the maximum values (near −300–450 t/ha*year) in 2009–2011 and 2011–2013, coinciding with the periods of higher rainfall in the last fifty years, that probably have underwent an increase of 10–30% in the last decades. Thus, the evolution of the gully area for 40 years has been analysed in relation to the rainfall regime that has been established from the daily rainfall data.