Flood, dissolution subsidence and landslide hazards, damages and mitigation structures in Cadrete village (Ebro Depression, NE Spain)

Abstract

The present work suggests that preventive planning based on the avoidance of hazardous areas recognizable through detailed geomorphological studies may contribute significantly to reduce the risk in urban areas. Subsidence, floods and slope movements cause significant damage in numerous buildings of Cadrete village, located in the Huerva River valley (NE Spain). This multihazard village is built on a terrace surface placed between the floodplain and a scarp made up of horizontally lying gypsum and argillaceous Tertiary sediments. The low recurrence floods that affect the floodplain of the Huerva River have caused severe damage in recently built houses and industrial states. Regardless of the application of the projected structural correction measures, the mitigation of the flood risk requires a preventive planning based on the avoidance of the flood-prone areas. A detailed geomorphological map shows that the scarp is affected by a large density of slope movements (translational and rotational slides, rock-falls, topples, lateral spreading). The majority of the movements are restricted to the lower litostratigraphic unit made up of shales and gypsum. The damage in buildings derived from slope movements is always related to the reactivation of old rotational landslides caused by anthropogenic alterations in the slopes (excavation, loading, additional water supply). This fact indicates the inadequateness of the old landslides for the construction of structures in spite of their apparent favourable topography. On the other hand, a large number of buildings are affected by cracking and tilting due to ground subsidence. The most severely damaged areas include the foot of the scarp. The subsidence damage is attributed to the karstification of gypsum and possibly halite in the bedrock and to the hydrocompaction of gypsiferous silts. A reversible hydraulic connection controlled by the precipitation regime between the Tertiary karstic aquifer and the Quaternary alluvium is proposed.