Contraction of the fluvial territory in the Jarama River (Spain)

Abstract

Rivers are dynamic systems, with mobility due to their changing flows. Variations in flow give rise to floods, forming floodplains, whose human occupation depends on the probability of flooding; the reduction of floods favours human occupation. This study analyses the modification of the fluvial territory of the lower stretch of the Jarama River between 1956 and 2020, through orthophotographic analysis. The regulation of the basin by dams has led to the disappearance of floods, favouring human occupation of the fluvial territory. Concurrently, the length of the river channel has increased by 2.3% due to the excavation of some meanders, favoured by the modification of flows due to the discharge of wastewater treatment plants. As a consequence, the fluvial territory has increased by 0.88 km2 due to erosion, but at the same time has lost 14.36 km2 due to human occupation, with a net loss of 58.3% of the area. Most of the occupied fluvial territory has been used for agriculture, followed by grassland and mining, although much of the grasslands are former mining areas. The current public river domain is very narrow, and is defined as a fixed space, incompatible with fluvial dynamics. Floodplains are a strategic resource, as a defence against floods and to preserve river dynamics, sediment transport and biodiversity. It is necessary to preserve the fluvial territory and expand it by recovering lost land, and to maintain a space of freedom for the river, allowing its natural dynamics.