Summary:

The results of investigations carried out in the stream Bukowiński are pre-sented in this paper. The aim of investigation was definition of influence of wood jam on change of dimensionless coefficient of resistance and coefficient of rough-ness. The performed measurements included cross-section leveling and longitudinal leveling of the stream channel, bed sediment sampling, and hydrometric meas-urements. Cross-section leveling included five cross-sections in the 47-m long stream sector; these were located upstream and downstream the wood jam and in its region. Differentiation of water flow velocity in the region of wood log was shown. The dimensionless coefficient of resistance was calculated taking into ac-count the equivalent bottom roughness determined by use of Gladki`s formulae [van Rijn 1984]. In the aim of the qualification of the equivalent bottom roughness three samples of bottoms sediment were taken in the cross-section with the log. It was found that the wood log in the Bukowiński stream caused a change of hydraulic conditions of water flow and, in consequence, the dimensionless coefficient of resistance in the wood jam section increased by about 71%. The coefficient of channel roughness was also determined and it was shown that the coefficient of roughness in the section of wood jam, which 60% of channel cross-section cover by water flow carrying out 0,141 m3s-1, caused increasing of this coefficient by over 17,5%.