Morphological Changes and Alterations in Erosion–Accretion Patterns in a Semiarid Brazilian River

ABSTRACT Rivers in semiarid environments are highly sensitive to morphodynamic adjustments induced by hydrological variability and anthropogenic regulation, with direct implications for sediment transport, channel stability and river management. This study analyses the morphodynamic evolution and erosion–deposition patterns of the Jaguaribe River, located downstream of the Castanhão Dam (operational since 2002) in northeastern Brazil. A spatiotemporal investigation was carried out for the period 1958–2025 using historical aerial photographs, satellite imagery and multitemporal geomorphological mapping. Field‐based cross‐sectional surveys and hydrosedimentological data collected mainly between 2007 and 2010 were used to support the interpretation of post‐dam channel adjustment. Four reaches were defined based on geomorphological attributes, tributary confluences and channel configuration. The results indicate that the Castanhão Dam altered the downstream hydrosedimentological regime by attenuating peak discharges and contributing to an estimated reduction in sediment transport exceeding 50%. However, the spatial distribution of erosion, deposition, bar stabilisation and bank retreat was not controlled by dam regulation alone, but was also modulated by tributary inputs, low‐water crossings, riparian vegetation, land‐use disturbance and inherited geomorphic conditions. Enhanced bank erosion was observed in sectors with limited riparian vegetation, with lateral retreat rates reaching up to 7 m year −1 , whereas margins with more vegetated margins showed lower susceptibility to erosion. Morphological responses included the persistent bar stabilisation, vegetation encroachment, localised channel migration and partial stabilisation of the active channel belt. A notable downstream trend was identified in the middle and lower reaches, which display characteristics of a wandering gravel‐bed river, including coarse bed material, sandy and gravelly bars, thalweg migration and fewer active channels than typical braided systems. These findings show that dam‐induced adjustments in semiarid rivers should be interpreted as multi‐driver responses, combining basin‐scale flow regulation with reach‐scale geomorphic and anthropogenic controls.