Summary:

Using rivers and mountain streams for economic purposes led to the loss of ecological balance and to the intensification of morphological processes, which in most cases caused erosion as well as the lowering of riverbed. Such changes have made stabilising the river bed and its banks necessary. In our work, on the basis of the analysis of project documentation and the simulations of flood events on several mountain streams, we made an attempt to answer the question: are the river training works enough to let the catastrophic floods pass safely and do they take into account the morphological processes which have a formative influence on the riverbeds? It has been proved that as far as hydraulic structures are concerned, the adjustments that are being planned comply with the requirement of ensuring the required capacity of the river channel. Maintaining the required capacity of the river channel creates the need for constant remedial works. When dimensioning cross-sections with stable bottoms, the width of the river valley is a serious limitation which, in urban environment, does not allow the engineers to design a crosssection of a river channel whose shape would be most efficient one. In case of river channels with moveable bottoms, the size of the river cross-section should be chosen so as not to entrain to the transport the armouring layer for normal flow. Simplified calculations of the initial conditions of bedload transport lead to overdimensioning of the river channel. This, in turn, leads to local accumulation of the bed material and the condition of hydrodynamic balance is not fulfilled. Moreover, the size and shape of individual grains influence the incipient motion of bedload transport. What follows is that the empirical formulae used for estimating the granulometric composition of the deposit should be replaced with direct measurements.