Runoff generation, sediment movement and soil water behaviour on calcareous (limestone) slopes of some mediterranean environment s in southeast Spain s

Abstract An interpretation of soil hydrology and erosion data obtained from limestone areas in southeast Spain is presented in the framework of recent hypotheses on runoff generation mechanisms in Mediterranean environments. The main objective is to synthesise and harmonise the data in theoretical concepts or behavioural models of hydrological functioning of Mediterranean limestone slopes. For this purpose, data were collected in a typical limestone area, with climatic characteristics ranging from subhumid to semiarid. Several sites were chosen with comparable slopes, vegetation and soils along a transect of 20 km to carry out several research projects. The data discussed in this paper consist of information on water redistribution within the soil profiles obtained from long duration (up to 5 h) rainfall simulation experiments with continuous monitoring of soil moisture at different depths. Runoff and sediment concentration data were obtained (i) from rainfall simulation experiments with different antecedent soil moisture conditions and (ii) as natural results from open Gerlach plots on runoff and sediment movement over 4 years. Three conceptual models of water redistribution during the infiltration process could be observed, two of them imply nonuniform water redistribution within the soil profile due mainly to macropore flow caused by specific soil surface characteristics. At the plot scale, runoff generated in bare patches is mainly Hortonian. In plots with previously wetted soils or soils with high infiltration capacities, the generated runoff implies the saturation of the upper soil. Both types of runoff are discontinuous through time and space. The runoff generation mechanisms at the slope scale have been synthesised into two conceptual models: a Hortonian discontinuous runoff model that takes place in the most degraded slopes or during high intensity rain events and, a mixed runoff generation model in less degraded slopes or in previously wet soils, where infiltration excess runoff as well as saturation excess runoff can happen on the same slope. In both cases, slopes behave as a patchwork of runoff and runon areas, the size of the runoff or runon patches is dependent on the climatological conditions. These control the hydrological disconnection between different parts of the slopes. Hortonian and saturation runoff can both be generated and infiltrated downslope.

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