Runoff generation on abandoned fields in the Central Ebro Basin. Results from rainfall simulation experiments

Abstract

In the semi-arid Central Ebro basin experimental rainfall simulations with a small mobile jet rainfall simulator according to Calvo et al. (1988), Lasanta et al. (1994 and 2000) were carried out on abandoned fields near María de Huerva to investigate the conditions of runoff generation and local erodibility. On the silty soils, susceptible to soil sealing and crusting very divergent rates of runoff and erosion rates caused by water are found. On the crusted young fallow land runoff coefficients range between 20 and 95%, erosion rates range between 9 and 460 gm-2 in the experiments. The start of runoff was recorded between the second and fifth minute. Soil surface sealing leads to a decrease in infiltration rates and a consequent increase in runoff in comparison to freshly tilled agricultural fields. On the old fallow land, values range from 0 to 76% and 0 to 78 gm-2 depending on other parameters such as slope and the activity of the edaphon. The start of runoff was recorded between the third and the fifteenth minute. A remarkable fact is that material delivery does not significantly decrease with increasing vegetation cover. Only with a vegetation cover of over 60% does material output decrease obviously. The runoff rates show the same order of magnitude than those recorded by Lasanta et al. (2000) in abandoned fields near Peñaflor, but the erosion rates in María de Huerva are significantly lower.