The purpose of the research is application of empirical formulae for determination of bankfull discharge in the Powa river. The chosen river is lowland stream. In the research the values of the bankfull discharge obtained for condition before and after regulation are compared. For this purpose the measurements of cross-sections done in 2007 and 2014 are used. The measured cross-sections are located upstream of the Stare Miasto reservoir. The chosen river reach is ungauged, because the nearest and only gauge station in the Powa river is located downstream of the reservoir. The computations are done in three stages. In the first step the bankfull discharge is determined by the empirical formulae (Wolman and Williams formulae). In the second step the HEC-RAS program is used to determine separately the bankfull discharge and comparisons are done for verification of previous values. The third step includes combination of HEC-RAS simulations with empirical formulae. The results are compared for five selected cross-sections. On the basis of computations it may be noticed that the differences between applied methods are large. Although, the determination of the bankfull discharge is important, the results presented in the paper does not provide unique answer to the question which method is suitable.