Summary:

The formation of an armouring layer can be observed on the base of morphological changs by direct measurements of granulometry (grain diameter generally grows after flood) or by computer simulation of changes of the grain sieve curve. This procedure is based on the Gessler’s analysis of the probability of grain movement, on the basis of the shear stress of the acting water. The critical shear stress is calculated using the Wang function developed for Carpathian streams. The armouring layer is formed by that part of non-cohesive bed material, which is not washed away during the flow. The increase in critical shear stress is due to the increase of the mean diameter dm as small fractions are washed out from the bed. The thickness of the armouring layer is approximately equal to the size of the largest stones of the layer. This process in rivers with natural flow is different from this one below reservoirs; in the former case it takes place at a significant distance below dams. In this case, the armouring layer formation causes bed scouring, linked with a change in the water slope and depth. This scouring may be assumed to be a stochastic process. According to Gessler, the probability that a grain will not be moved from the bottom depends on relative critical shear stress. We can observed hydrodynamic evaluation of a mountain river and stream by calculation: – grain-size hiding factor relating the limit between movement and immobility to clogging effect in material of various grain-size, – beginning of the bedload movement determining the limit between movement and immobility for fine- and coarse-grained material based on dimensionless stresses, – grain shape relating dimensionless stresses to grain shape coefficient, – bedload transport as total dragged bedload transport, as a sum of partial fraction transports – at changing critical stresses, as a function of sieve curve standard deviation, – prediction of armoring process, probability of grain immobility related to drag force surplus as a function of critical stresses to normal stresses relation, – analysis of flow with hydrodynamic balance in which the armour layer is destroyed, Directives of EU do not impose methods of habitat and species conservation. The only criterion is the maintenance of favorable conservation status for them. That means that the area of habit must be stable in long term or increasing, and its quality must be maintained. The restoration processes are welcomed. One of the most important aims when preparing river training and renaturalization is the correct calculating of hydrodynamics balance of the bed with respect to the analysis of critical shear stress for bed material fractions and of capacity of bed load transport. The correct determination of critical shear stress, of critical depth of water, of critical velocity in non-uniform materials is strictly connected with the incipient motion of bed load. This paper presents investigations and measurement which are important to describe the condition of renaturalization. According to hydrodynamic balance under natural conditions new parameters of river renatulization parameters were created.