Abstract
Abstract. Gully erosion is an important erosive process in Mediterranean basins. However, the long-term dynamics of gully networks and the variations in sediment production in gullies are not well known. Available studies are often conducted only over a few years, while many gully networks form, grow, and change in response to environmental and land use or management changes over a long period. In order to clarify the effect of these changes, it is important to analyse the evolution of the gully network with a high temporal resolution. This study aims at analysing gully morphodynamics over a long timescale (1956–2013) in a large Mediterranean area in order to quantify gully erosion processes and their contribution to overall sediment dynamics. A gully network of 20 km2 located in southwestern Spain has been analysed using a sequence of 10 aerial photographs in the period 1956–2013. The extension of the gully network both increased and decreased in the study period. Gully drainage density varied between 1.93 km km−2 in 1956, a minimum of 1.37 km km−2 in 1980, and a maximum of 5.40 km km−2 in 2013. The main controlling factor of gully activity appeared to be rainfall. Land use changes were found to have only a secondary effect. A new Monte Carlo-based approach was proposed to reconstruct gully erosion rates from orthophotos. Gully erosion rates were found to be relatively stable between 1956 and 2009, with a mean value of 11.2 t ha−1 yr−1. In the period 2009–2011, characterized by severe winter rainfalls, this value increased significantly to 591 t ha−1 yr−1. These results show that gully erosion rates are highly variable and that a simple interpolation between the starting and ending dates greatly underestimates gully contribution during certain years, such as, for example, between 2009 and 2011. This illustrates the importance of the methodology applied using a high temporal resolution of orthophotos.
Highlights
Understanding gully erosion dynamics under changing land use and climate conditions is essential for soil and water conservation
This study aims at analysing gully morphodynamics over a long timescale (1956–2013) in a large Mediterranean area in order to quantify gully erosion processes and their contribution to overall sediment dynamics
The average gully erosion rate of 39.7 t ha−1 yr−1 for the total catchment area obtained in this study, by means of photointerpretation techniques combined with stochastic methwww.hydrol-earth-syst-sci.net/21/235/2017/
Summary
Understanding gully erosion dynamics under changing land use and climate conditions is essential for soil and water conservation. Much research effort has gone into characterizing and modelling erosion rates in order to identify key problem areas and propose management solutions. A European-wide effort was conducted to improve the quantification of water erosion either with RUSLE (Panagos et al, 2015) or with similar models (Quinton et al, 2010; Van Oost et al, 2007). Such models represent a minor part of the water erosion processes by not considering the contribution of gullies.
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