Linking sediment connectivity with sediment transport risk assessment in small forested catchments in the Czech Republic

Steep mountain environments are typically characterized by high sediment production. In the case of high hillslope–channel connectivity, high production and intensive transport of sediments are problematic and can cause damage in inhabited areas. At the end of the 19th century, due to flood events, large‐scale torrent control measures were inappropriately applied, disrupting the natural processes, and riparian and water ecosystems in watersheds. Connectivity in watersheds affects the course and magnitude of hazards that threaten human society. This is also why the topic of connectivity should be considered in the management of watercourses. Our study links the issue of sediment connectivity (lateral/longitudinal) and the sediment transport‐related risk in unmeasured forested watersheds Hučivá Desná and Upper Moravice. We applied a methodology for sediment transport‐related risk assessment and the well‐established effective catchment area (ECA) approach and connectivity index (IC) to two headwater streams. The results showed the parts of the streams with the highest degree of hazard related to sediment transport and sediment contribution areas connected to them. Based on the field survey, it was found that the best suitable threshold for ECA delineation for Hučivá Desná catchments is 8° and for Upper Moravice is 10°. Area of sediment contribution areas for Hučivá Desná is four times bigger than for Upper Moravice. The Hučiva Desná, therefore, has a higher potential sediment supply from the slopes, which also increases the possibility of occurrence of hazards associated with the sediment transport regime. All three applied methods confirmed that the parallel roads along channels decrease slope–channel connectivity, especially in the Upper Moravice catchment. The combination of methodologies created a suitable tool to identify the most problematic stretches of streams in terms of sediment connectivity and risk related to sediment transport, which can be useful for water and sediment management in unmeasured forested watersheds.