Assessment of sediment connectivity using modelling and field-based approaches in the Slavíč River catchment (Moravskoslezské Beskydy Mts, Czech Republic)

Mountain streams act as conveyors of sediments within the river continuum, where the physical transport of sediments between river reaches through the catchment or between individual parts (e.g., between hillslopes and channels) of the catchment is assumed. This study focused on sediment connectivity analysis in the Slavíč River catchment in the Moravskoslezské Beskydy Mts in the eastern part of the Czech Republic. The connectivity index and connectivity index target modelling were combined with an analysis of anthropogenic interventions. Additionally, field mapping, grain size of bed sediments and stream power analysis were used to obtain information about connectivity in the catchment. Based on the analysis and obtained results, terrain topography is the current main driving factor affecting the connectivity of sediment movement in the Slavíč River catchment. However, the modelling provided valuable information about high sediment connectivity despite different recent land use conditions (highly forested area of the catchment) than those in historical times from the 16th to 19th centuries when the Slavíč River catchment was highly deforested and sediment connectivity was probably higher. The analysis of anthropogenic interventions, field mapping, grain size of bed sediments and stream power analysis revealed more deceleration of sediment movement through the catchment, decreased sediment connectivity with bed erosion, and gradual river channel process transformation in some reaches. Field mapping has identified various natural formations and human-induced changes impacting the longitudinal and lateral connectivity in the Slavíč River. For instance, embankments along 48% of the river's length, both on the right and left banks, significantly hinder lateral sediment supply to the channel. Stream power index analysis indicates increased energy levels in the flowing water in the river's upper reaches (up to 404.8 W m^-2). This high energy is also observed in certain downstream sections (up to 337.6 W m^-2), where it is influenced by human activities. These conditions lead to intensified erosion processes, playing a crucial role in sediment connectivity. Similar observations were described in recent studies that pointed out the long-term human interventions on many streams draining European mountains, where a decrease in sediment connectivity in these streams is linked with sediment deficits and the transformation of processes forming channels.