Hillside destabilization factor analysis in two basins of the atlantic side: Sollube-Mape (Bizkaia) and Aramaio (Álava)

Abstract

Slope processes are recurrent phenomena of the atlantic side of the Basque Country albeit they show different behaviours in its distinct geographical settings. In this paper an analysis of the triggering and determining factors in two basins, one coastal and another in an inner site, characterized by middle mountainous landscape, is presented. Rainfall, fieldwork and thematic cartography data have been employed in order to get a susceptibility assessment and an analysis of vulnerable areas. The location of different constructive elements and their exposition have been added to the susceptibility analysis. A relationship between rainfall events and slope processes has been verified. It differs from one basin to the other. In the coastal one, high daily rainfall intensity data (rainfall average of 46 mm)link to landslide processes generation, by contrast in the inner one, these processes are triggered by rainfall persistence (until 12 days with a total amount of 298 mm)and the succession of events of daily rainfall over 30 mm (4 in 2009 with 363,9 mm). Other elements have resulted determining factors like slope (≥10 y ≥50%, respectively), the presence of subsuperficial water between a waterproof substrate and a regolith (>0,5 m thick) modified by the forest activity. Finally the assessment of landslide susceptibility done by GIS tools concludes that the 28% of the coastal basin has a high-very high values, meanwhile the inner one has the 60% of its area.