Abstract
The implementation of the Water Framework Directive has driven the assessment of European rivers toward process-based evaluation of hydromorphological conditions. However, detecting short-term channel adjustments in restored systems remains a key challenge. This study investigates the post-restoration channel trajectory of the Mareta River (NE Italian Alps), historically channelised and incised due to intensive gravel mining and check-dams construction (Scorpio et al., 2020). Building upon previous datasets over more than a decade, new high-resolution UAV-derived DEMs and orthophotos significantly increase the temporal resolution of available topographic data, shifting from sparse observations (2012-2016-2018) to a higher-frequency monitoring framework (2024-2025-2026). This improvement enables the detection of short-term channel adjustments at the reach scale that are typically overlooked in restored Alpine rivers. DEMs of Difference (DoD) are used to quantify spatial patterns and volumes of erosion and deposition (Williams et al., 2020), while Geomorphic Unit Survey (GUS) mapping and related indices (GUSI-R and GUSI-D) are analysed to track temporal changes in geomorphic unit richness and density (Belletti et al., 2017). This study explicitly tests the hypothesis that early-stage recovery is expressed by (I) increasing geomorphic unit diversity, (II) a shift in the erosion/deposition balance, and (III) spatial correspondence between depositional areas and the expansion of active geomorphic units. Results indicate a progressive transition from incision-dominated conditions toward enhanced lateral activity and sediment storage. Increases in GUS indices are observed in reaches where DoD analyses highlight net deposition and bar development, suggesting that sediment accumulation is directly linked to the reactivation of channel processes at the reach level. The higher temporal resolution of UAV surveys proves critical in capturing these localised and transient dynamics. The integration of volumetric (DoD) and process-based (GUS) metrics, combined with increased survey frequency, provides a robust framework for detecting subtle geomorphic changes over short timescales. This approach supports a more process-oriented evaluation of restoration trajectories and offers practical implications for adaptive river management in Alpine environments.