The impact of road and railway embankments on runoff and soil erosion in eastern Spain

Abstract. Road and railway infrastructure increased in the Mediterranean region during the last three decades. This included the building of embankments, which are assumed to be a~large source of sediments and runoff. However, little is known about soil erosion rates, the factors that control them, and the processes that contribute to detachment, transport and deposition of sediments from road and railway embankments. The objective of this study was therefore to assess the impacts of road and railway embankments as a source of sediment and water, and compare them to other land use types (citrus plantations and shrublands) representative of the Cànyoles watershed to evaluate the importance of road embankments as a~source of water and sediment under high magnitude low frequency rainfall events. Sixty rainfall experiments (1 m² plots; 60 min duration; 78 mm h⁻¹ rainfall intensity) were carried out on these land use types: 20 on two railway embankments (10 + 10), 20 on two road embankments (10 + 10), and 10 on citrus and 10 on shrubland. Road and railway embankments were characterized by bare soils with low organic matter and high bulk density. Erosion processes were more active in road, railway and citrus plots, and null in the shrublands. The non-sustainable soil erosion rates of 3 Mg ha⁻¹ y⁻¹ measured on the road embankments were due to the efficient runoff connectivity plus low infiltration rates within the plot as the runoff took less than one minute to reach the runoff outlet. Road and railway embankments are both an active source of sediments and runoff, and soil erosion control strategies must be applied. The citrus plantations also act as a~source of water and sediments (1.5 Mg ha⁻¹ y⁻¹), while shrublands are sediment sinks, as no overland flow was observed due to the high infiltration rates.