Development of a large wood jam in medium-high mountains :an example of the Mazák Stream, Moravskoslezské Beskydy Mts., Czechia

Abstract

Wood jams represent an important ecological and morphological element in fluvial systems influencing sediment / instream wood transport and storage. ,erefore, the knowledge of jam ages is important in evaluating a jam’s development and stability. ,is study presents a reconstruction of the chronological development of the largest wood jam in the wider area of the culmination peak of the Moravskoslezské Beskydy Mts. (Western Carpathians). ,e studied jam was composed of more than 60 logs whose morphometric parameters and orientations were recorded. Dendrochronological dating of 11 logs revealed the ages at which tree death occurred. ,e jam development was probably initiated in the end of 1930s via an occurrence of debris flow that caused the channel to narrow and the wood material to start accumulating. Frequently occurring floods, together with extreme wind flow velocities, seem to be the most important factors controlling tree death and log movement from the upstream channel-reach to the jam