Abstract
The results from several rainfall simulations performed on two abandoned fields of different ages in the Central Ebro Depression have been analysed by application of the physically based hydraulic model HILLFLOW 1D. The data gained by the simulations was used to parameterise the model. Afterwards, the runoff generation characteristics were determined by simulation of different rainfall intensities and different macroporosities of the soil. The young fallow land shows a minimum intensity for runoff generation of 6 mm h-1. An increase of the rainfall intensity leads rapidly to a growing runoff coefficient, being the value modelled for 30 mm h-1 nearly the same as the simulated one (40 mm h-1). Another con - clusion of the simulations and their modelling is the homogeneity of the soils on the young fallow land, with no macroporosity all over the profile. On the other hand, the rainfall simulations and the modelling on the old fallow land show a high variability of rainfall-runoff response patterns, strongly conditioned by the presence of macropores. They are distributed very irregularly throughout the soil of the old fallow land. In both cases, water infiltrates only little into the soil matrix, for that measures for enhancing soil hydraulic properties are needed.
Highlights
The use of rainfall simulations to understand processes of runoff-generation and erosion has found a widespread use during the last decades
The rainfall simulations in Maria de Huerva are described in detail by Ries & Langer
The application of the soil data gained in laboratory (Table 2), assuming no macropores in the soil, led to a total runoff coefficient substantially lower than the one measured in the field experiments
Summary
The use of rainfall simulations to understand processes of runoff-generation and erosion has found a widespread use during the last decades. Possibilities and limitations are resumed by Cerdà (1999). In areas where soil water is the limiting factor to plant growth and vegetation succession to recolonise abandoned farmland, there is a need to understand the infiltration processes and the water movement during rainfall events into the soil. The experimental design for this purpose is complicated and would reduce considerably the possible number of experiment repetitions, introducing systematic errors, especially at low rainfall intensities. Saline and gypsiferous soils show some complications for accurate soil-water measurements with gravimetric methods or Time-Domain-Reflectometry (TDR) (NSSC, 1996; Soilmoisture Inc., 1990). The present combination of a large number of rainfall simulations
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