The Role of Human Activities in the Development of Alluvial Fans

Abstract In a study carried out in the Iberian Range, Spain, the characteristics of 293 basins were studied, 165 having developed alluvial fans and 128 without alluvial fans. Different statistical analyses demonstrate that the main factors explaining the presence of alluvial fans are the drainage density and the coefficient of torrentiality. Other important factors are the proportion of abandoned fields and reforestation, that is, the areas most affected by human activities in the past. The basins where the presence of alluvial fans is highest have a large proportion of medium and low gradients, favouring the use of the territory as cultivated fields and pastureland. In contrast, basins without alluvial fans at their mouth are characterized by very steep slopes, generally covered by forest, where agricultural activity was impossible.