Along the paper the problems connected with fine and coarse woody debris in rovers are described. Especially last years many papers appear in Polish and international literature covering that subject. Thus, the paper aims in getting acquainted the reader with the woody debris problems in mountain and lowland rivers. Parallel in the paper two case studies are presented, respectively from mountain and lowland river when some hydrodynamical parameters were measured and analyzed. The obtained results show that woody debris has the influence on changes of the values of hydrodynamics parameters within river channel. Case studies were run on the Warta River (lowland river) and the Raba River (mountain river).

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