An assessment of stream morphological conditions of channel changes at the regional scale: the case of andalusian river systems (Southern Spain).

A regional-scale geomorphic analysis of Andalusian rivers was carried out with the objective of characterizing river conditions and morphological changes. For this aim, an assessment of the morphological conditions by the Hydro-Morphological Quality Index (HMQI) was initially performed. The HMQI has been applied to 356 river reaches, allowing to characterise the geomorphic conditions of the rivers and better evaluate the causes of alterations. Overall, approximately 54% of the river reaches are in moderate condition, 22% are in good condition, 16% are in poor condition, and few cases are classified as high or very poor (approximately 4.5% and 4%, respectively). The assessment of river conditions was followed by an analysis of changes in channel morphology and width from 1956–present carried out for most alluvial, unconfined or partly confined river segments. The analysis revealed that most segments have undergone moderate to intense channel narrowing, with only a few segments experiencing widening. The morphological channel pattern changed in approximately 37% of the cases. For the overall geomorphic conditions, the causes of these changes are associated with socioeconomic development, specifically the decline in bedload caused by dams, increasing agricultural activities adjacent to rivers, and the fixation of some reaches crossing urbanised areas.