Resumo

TAGUAS, Encarnación; YUAN, Yongping; PENA, Adolfo  e  AYUSO, J. Luis. Prediction of ephemeral gullies by using the combined topographical index in a micro-catchment of olive groves in Andalucía, Spain. Agrociencia [online]. 2010, vol.44, n.4, pp.409-426. ISSN 2521-9766.

Most studies of erosion in olive groves to examine the effect of sheet and rill erosion have been conducted at plot scale. However, work done on other land uses and at minor scales in the Mediterranean area have justified that the loss of soil resulting from concentrated flow can be decisive in the total balance. The compound topographic index (CTI) is a parameter to locate and describe the initiation of ephemeral gullies for a type of soil, use and management that could complement information from other indices, such as the universal equation of soil loss from sheet and rill erosion. The CTI was applied in an olive micro-catchment under minimum tillage with spontaneous cover, located in the western central area of Andalucía (Spain). After the digitization of ephemeral gullies on a high-resolution orthophoto, the degree of success of each of the observed and predicted pixels was compared to one another and values between 3 and 5 were estimated as the characteristic thresholds for the resolutions of 1.5 m and 3.0 m. These critical values are useful for the localization of gullies in other catchments, regardless of the scale, where the rainfall pattern is comparable, as well as the type of soil (Cambisol) and management (no-till with spontaneous grass cover in spring). Despite the suitability of the index to locate most of the gullies, different mechanisms of gully development were identified in field over the worst-represented gullies. Despite the low values of the drainage areas at the headwaters of them, their presence is explained by the role of the surface calcium material and high saturated hydraulic conductivity values, favoring the accumulation of flow and reducing the resistance of soil to the removal of sediments.

Palavras-chave : ephemeral gully; compound topographic index (CTI); olive; micro-catchment; soil properties.

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