Spatiotemporal variations of large wood and river channel morphology in a rapidly degraded reach of an intermittent river

The links between rapid channel degradation and related large wood (LW) recruitment and storage are still not precisely understood, especially in aquatic systems with high human and natural pressures such as intermittent rivers in the peri-Mediterranean region. In this study, by using multidisciplinary research (analysis of satellite images time series, detailed field inventory, and simulated hydrological data), we focused on rapid upstream propagation of channel degradation (i.e., incision and consequent channel widening) in an intermittent Mediterranean river (Evrotas River, southern Greece) as a response to short-term intensive gravel extraction from the active channel and removal of riparian vegetation in the 2013-2016 period. Subsequently, our objective was to link this channel transformation with the spatiotemporal changes of LW storage in the active channel. We found that short-term and spatially limited human impact, coupled with high flows, allowed rapid upstream progression (similar to 2 km) of erosion processes (approximately twofold widening of the active channel) during the relatively short 2-year period (2017-2019). This morphological response accelerated LW recruitment through bank erosion and its subsequent storage in the active channel. Incision and channel widening processes were interrupted in the 2019-2021 period due to the prevalence of relatively low, geomorphologically non-effective flows. However, the storage of LW in the channel continued to increase as a result of the higher trapping efficiency of the widened channel, a delay between tree death and its final uprooting, or by LW recruitment processes not directly related to flood events. We suggest that freshly recruited LW has the potential to accelerate the establishment of a new channel equilibrium and increase channel heterogeneity through its interaction with flows and sediments.

Automated summary

This study investigates the rapid upstream propagation of channel degradation and its connection to spatial and temporal changes in large wood (LW) storage in an intermittent Mediterranean river. The results show that short-term human impacts and high flows led to the rapid progression of erosion processes and an increase in LW recruitment and storage. Although the incision and channel widening processes were interrupted in the later period, LW storage continued to increase due to various factors.