This paper deals with the bed-load transport of river sediments moving by saltation. The movement of spherical solid particles in an open channel flow is determined by numerical calculations based on Lagrangian approach. This approach reflects the balance of the drag force, lift force, added mass force, Magnus and Basset forces. The particle behaviours for different boundary conditions as well as for different particle sizes are discussed in detail. Solving the Lagrange equation makes it possible to compute the sequences of trajectories of individual saltating grains and to receive the vertical profile of sediment concentration. To verify these calculations, comparisons with measurements are presented. The comparisons are made for a few sediment sizes in the range from 0.00053 to 0.015 m and for the Peter-Meyer and Mueller, and Fernandez Luque and Beek formulae. The results of comparisons show that the model can be used for estimating the bed-load transport.

A stretch of the Odra river between km 20.7 (Chałupki gauging section) and km 27.7 (Olza river mouth) is subject to natural morphological processes and has 7 natural meanders. Some of the factors causing the morphological changes in this meandering river stretch include the transport and sedimentation of bed-load and suspended load. The extent and rate of those changes depend on the intensity and scale of hydrological events. The course of such changes could be easily observed after extreme floods when mass transport of sediment occurs. For example, the sediment mass transport as a consequence of the 1997 flood resulted in a change of the Odra river channel in the area of meander I (break of the meander and shortening of the river course) and the development of sediment islands in the cut-off old arm. The substructure of the islands consist of bed-load (stones, boulders, gravel and coarse sand), and the superstructure is built of fine-grained sediments (silt, clay) containing organic matter. Using the available hydrological data, the authors tentatively estimated the suspended load transport in the Chałupki gauging section and determined the amount of suspended load settled in the upper layer of the island in the area of the broken meander. The settled fine-grained organic mud has cohesive properties which are important for stabilisation of new islands and for development of pioneering vegetation.

Investigations of the time and spatial macro-scale of the present paper are based on the measurements of instantaneous velocities in a two-stage trapezoidal channel under five various tests in the channel. The results of calculations of macro-scale of turbulence were showed for the main channel and floodplains with trees and without. These investigations have shown the following: the values of time macro-scale have changed in range since 0.1 to 1.2 s; in all five tests the distributions of the sizes of the eddies reveal stable regularity; the relative length of eddies are bigger on the floodplains and achieve value of 0.1 to 2.5 of the flow depths on the flood plains, whereas in the main channel the sizes of largest eddies do not exceed the value of 1.2 of the total water depth. The largest lengths of eddies were affirmed on the floodplains in vicinity of the main channel in zone of interaction. The smallest eddies are over the bottom of the main channel.

The recording of low flows, including base flow, has particular importance in the case of intensive draw-offs of water from a water-course. It provides a basis for the proper water management of a water intake and ensures that the flows creating the right conditions for the survival of water organisms and vegetation are maintained. The paper presents the results of the geodetic and hydrometric surveys conducted on the Uszwica river during three years of the building of a water gauge. The latter was built with the aim of recording the base flow, in accordance with the permit required by the Water Law Act and issued for the damming-up and draw-off of water by the Okocim Brewery. At the water levels lower than the base flow, the brewery has no right to take water from the Uszwica river. The measurements and the developed rating curves showed that the geometrical changes in the river’s cross-section caused by the passing flood waves have a significant influence on establishing the water level at the base flow. The change in water depths and the ordinates of average low and base flows in the gauging section were determined.

Special structures called fishways or fishpasses serve a purpose of allowing fish to pass through the step slope of a river formed as a result of artificial river damming by way of dams, weirs, steps and other structures or natural damming caused by waterfalls. There are three types of fishways: technical, natural and special. Prior to creating a design for a fishway, it is necessary to understand the hydraulic and hydrological conditions of the river and the technical characteristics of the water structure as well as to gather data on the existing species of fish, especially migratory fish, and the expected restitution. On the basis of these data, the design concept is prepared taking into consideration a number of determinants such as the size of the fishway, the location of the entrances and the water level, flow and velocity. The calculation procedure depends on the type and form of the fishway and the water flow conditions. For technical fishways (chamber, verical slot and Denila types), classical hydraulic formulae of outflow or overflow are generally applied. For natural fishways, the calculation process is more complicated. For example, in designing a stone slipway-type fishway it is necessary to determine the roughness coefficient, the medium and maximum velocities, as well as the maximum flow at a given water level. Besides, stream distributions, attracting currents, and sediment movement should be considered, which necessitates using mathematical models. The paper presents the procedures of hydraulic calculations for various fishway constructions.

The paper presents the results of experimental investigations aimed to evaluate the efficiency of energy dissipation devices. The experiments were conducted on a weir model with a gate regulating the outflow of water, a stilling basin and a horizontal stiff bed protection downstream of the basin. The channel bed downstream of the protection had a filling of sand (d₅₀ = 1.1 mm, (d₈₄/d₁₆)^0,5 = 1.77), where the stream of flowing water formed a scour. The energy dissipators were modified during the experiments by placing baffle blocks in two arrangements in the stilling basin. To assess the effectiveness of their operation according to two criteria: (i) the reduction in the values of the basic characteristics of stream turbulence downstream of the stilling basin and (ii) the intensity of bed scouring with time and the final size of the local scour, vertical measurements of water velocity were made along the bed protection and the depths of the local scour formed during the flow were measured. It was found that baffle blocks reduced water velocity at the bed downstream of the stilling basin and had a limiting effect on the size of scour.