Channel adjustments in the lower Guadalquivir River (southern Spain) over the last 250 years

Abstract

The lower Guadalquivir River has been subjected to a series of channel adjustments over the last 250 years, mainly in response to human factors and disturbances. From 1778 to 1918, the results show an oscillation in the sinuosity along the upstream segment and a reduction along the downstream segment in response to artificial cut-offs. The first phase of incision started in approximately the 1840s–1850s, following a previous phase of predominant aggradation probably related to abundant sediment supply caused by deforestation in the catchment. During approximately the last 100 years, notable incision and progressive channel narrowing occurred in both segments, although secondary aggradation (upstream of the dams) and widening (in a portion of the downstream segment) were also observed. The first phase of bed incision migrating upstream is interpreted as a consequence of artificial meander cut-offs, whereas most of the adjustments that occurred during the last 100 years are interpreted as a consequence of the large number of dams in the catchment and along the studied area, which caused a notable deficit in bedload.