Soil water erosion on road embankments in eastern Spain

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Abstract

Road embankments erosion is a serious problem in Spain. By means of simulated rainfall experiments (45 mm h 1 during one hour on 0.41 m2 plots) soil and water losses were measured on five road embankments located on the SW of the Valencia province, Spain. The bare road embankments, still under construction, contributed with 30 times more soil erosion than the vegetated ones. The measurements here presented demonstrate that road embankments are an important source of sediments, especially during the construction works, and it is recommended that restoration works should be undertaken after the road construction to reduce sediment removal, protect the road and avoid traffic accidents.

Introduction

Road construction and improvement has been one of the most significant features of the Spanish economical development since the 60s, but especially since the 80s. In fact, the fast economical development of Spain is related to the improvement of the roads. Other economical activities that are being seeing as icons of the Spanish development are the AVE (Alta Velocidad Española, High Speed Train), the new industrial areas surrounding the cities and the intense building activities, especially near the coast and in the large cities. However those economical activities results in many environmental disturbances such as the removal of vegetation, the disturbance of the soil, the exposure of soil to erosion agents, the soil sealing and the general landscape degradation. Roads and road embankments induce high erosion rates (Luce and Black, 1999, MacDonald et al., 2001, Megahan et al., 2001, Ramos-Scharrón and MacDonald, 2005).

This paper is focussed on the effect of road embankments on soil erosion. In eastern Spain, embankments are usually bare after the road construction and gullies and rills are usually found. Those high erosion rates can result in river and reservoir siltation, the degradation of the road and even in traffic accidents as has been shown by Navarro Hevia (2002). Although the environmental problem of road embankments is increasing due to the road network development, the awareness of the problem is still very poor. In fact, the economical investment on soil erosion control on road and railway embankments is almost negligible, and even the research carried out in Spain is still very scarce (Estalrich et al., 1997, Albaladejo et al., 2000, Larrea and Arnáez, 1994, Navarro Hevia, 2002). Due to the high rainfall inter-annual variability and the recurrent droughts; plots, collectors, erosion pins will take long to measure the erosion rates. Simulated rainfall is very efficient under semiarid lands, and provides useful data as the rainfall characteristics are designed by the author (Meyer, 1965). The aim of this paper is therefore to show soil loss assessment by means of simulated rainfall on road embankments in eastern Spain where environmental conditions favours high erosion rates (Thornes, 1985). This paper assesses the soil erosion rates on road embankments in eastern Spain, and also the effect of vegetation recovery on soil erosion is studied by comparing vegetated and non-vegetated slopes. Experiments were carried out under summer-dry and winter-wet conditions which also will shed light on the effect of soil moisture on soil erosion, and his seasonal changes.

Section snippets

Materials and methods

Measurements were carried out on ten different locations in south-western part of the Valencia province in the eastern Spain. The road embankments selected were carried out on vegetation covered slopes and under construction, where vegetation was nil and soil erodibility very high. The sites comprised:

  • 1.

    Two road embankments on the N-340 road embankments near the towns of Alberic and Carlet, south-facing, and constructed ten years prior to the experiments when they where seeded by ray-grass and

Results

Vegetation at the studied road embankments is very low, especially those ones under construction, where vegetation cover is always lower than 7% during winter and 2% during summer for average values. At Carlet and Alberic the vegetation cover values were respectively 37 and 42% (summer and winter) and 46.4 and 54.8% which demonstrate the slow vegetation recovery after ten years and the lowest vegetation cover during summer. The very low organic matter content (always lower than 1%) and the very

Discussion

The rainfall simulation approach shows that soil losses are very high on road embankments after construction as vegetation cover is very low. After natural vegetation recovery the erosion losses are much lower but still exist. Other studies in Spain such as Estalrich et al. (1997) by means of 28 m2 plots confirm that the erosion rates on road embankments reach values of 25 Mg ha 1 year 1, which is a non-tolerable erosion rate. The research carried out by Albaladejo et al. (2000) at the Cabril

Conclusions

The rainfall simulation experiments carried out demonstrate that soil losses on road embankments are extremely high, especially on those recently built and constructed and without vegetation. Seasonal measurements show that soil losses are greater in winter when the soil is wet. Vegetation recovery is recommended to avoid soil losses, river and reservoir siltation and traffic accidents.

Acknowledgements

The Masia d'Agricultura i Ramaderia Ecològica (El Teularet), Dirección General de la Biodiversidad del Ministerio de Medio Ambiente (RESEL, Red de Estaciones Experimentales de Seguimiento y Evaluación de la Erosión y la Desertificación), the Leader-II (Macizo del Caroig), the Obra Social (CAM) and the GV-2005–02 projects supported the research. Tom Fowke kindly reviewed the manuscript.

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