Modeling the spatial distribution of water erosion within a Spanish olive orchard microcatchment using the SEDD model

Olive orchards located in mountainous or hilly landscapes in Southern Spain have been identified as one of the major sources of sediments for streams in the region. This paper presents a modeling study of the magnitude and spatial distribution of sources of sediment within a small 6.1 ha olive orchard forming a microcatchment in a mountainous area. The model used was SEDD, which was calibrated using rainfall, runoff and soil erosion patterns monitored over a 3-year period. Although the data series are incomplete, 46 events were observed. SEDD permitted an analysis of the erosive behavior and the sediment delivery ratio (SDR) in the catchment on an event scale. High variability in catchment responses was observed, due to differences in the characteristics of storms and the seasonal ground cover. A small group of two or three erosive events, occurring mainly in autumn, were responsible for most annual runoff and sediment loads, while the impact of spontaneous grass cover was apparent in events occurring in spring, where, despite high runoff depth, the sediment loss was low. This bimodal tendency justified the calibration of the SEDD model through the medians of β-values in both the periods September–January and February–June. The results of the calibration (E = 0.97 and RMSE = 0.03 t ha− 1) confirmed the applicability of SEDD to predict soil loss in the microcatchment and to allow us to complete the data series. Although the annual mean of SDR in the catchment for the study period was 3.8%, high spatial variability was found in the geomorphological units identified, with SDR values between 0.3% and 21.7%. On the event scale, probabilities of 50% for surpassing an SDR value of 10% were calculated for only 6% of the catchment area. The location of these most significant sources of sediment will permit the design of more efficient management plans in order to reduce sediment discharge into streams.

► We apply SEDD model to explain erosion spatial pattern in an olive tree catchment.
► We explore the impact of the model factors C-USLE, erosivity and β -parameter.
► We identified a bimodal β-distribution allowing to obtain a fine calibration.
► Rainfall seasonal pattern and cover protection justified the model adjusting.
► Empirical studies should explore the heavy deposition calculated in the catchment.