The quantity and attributes of woody accumulations in the Moravskoslezské Beskydy Mountains streams

Wood accumulations are important morphological agents forming the character of high-gradient streams in the Moravskoslezske Beskydy Mts. The aim of the research is to define both the extent and character of the impact of wood accumulations on the streams. A total of 126 accumulations have been identified of the total wood volume of 503 m3 that is unevenly distributed within the studied streambeds. The wood volume in the studied streambeds is particularly dependent on the age and species composition of vegetation, channel morphology, and the geological bedrock resistance to the action of the stream, especially in forced alluvial reaches. The research revealed the deposition of fine-grained material immediately upstream of the wood accumulations, creating gravel bars and capturing fine organic debris. On the other hand, immediately downstream of the accumulations fine-grained fractions are carried away and coarser material is deposited, creating pools and plunge pools, evorsion potholes and bank scours. The research further showed a low intensity of the transport of woody material through the streambeds. The accumulations usually occur in the place where the stream has been dammed by a fallen tree member or in structurally predisposed streambed segments. As a result, discontinuities in energy and material flow occur that help to increase the streambed heterogeneity.