Maciej Wyrębek

Cross-Section Changes in the Lower Part of a Mountain River After the Flood in Spring 2010, as Presented by Means of CCHE2D Program

The Bialka River flows in the Tatra Mountains region in South Poland. The turn of spring and summer 2010 in Poland was characterized by extremely heavy rainfall which led to two major floods affecting the territory of the whole country. Geodetic measurements of the bankfull channel and measurements of bed material granulation were carried out. Measurements of morphological changes in a mountain river Bialka performed on 12–14 May 2010 turned out to be made immediately before the flood. Inventory measurements conducted afterwards, i.e., on 1–2 July 2010, illustrated the river activity during the flood. The measurements were compared to the results of modeling performed with the use of the two-dimensional CCHE2D computer model. It makes it possible to compute water flows in open channels as well as the transportations. The model of bedload movement for the Bialka River was based on the Wu, Wang, and Jia equation. The amount of transported bedload in the model was compared to the MPM formula, calibrated for mountain rivers.

Flume Experiments on Gravel Bed Load Transport in Unsteady Flow—Preliminary Results

This chapter presents settings and results of laboratory experiments on bed load transport. Experiments were performed for unsteady hydrographs and for steady flow conditions. Continuous measurements of transported mass and flow rate reveal a clockwise hysteresis of bed load rate versus flow rate. A comparison between bed load rate in unsteady and steady flow shows that it depends to a large extent on sediment supply. The results are discussed in the light of variable sediment supply, and suggestions for procedure of further experiments are presented.

Wetlands in River Valleys as an Effect of Fluvial Processes and Anthropopression

The aim of the article is to show how the fluvial processes in rivers and their valleys can support wetland restoration activities. The exemplary objects were localized in the Upper Vistula Basin (Poland) and dealt with riverbed stability, channel capacity as well as revitalization of rivers with their valleys regarding wetland restoration. All of the mentioned parameters depend on the intensity of fluvial processes in rivers, especially meandering, anastomozing or braided. Rivers always tend to reach the state of hydrodynamical balance reflecting the actual river dynamics. The nature of channel transformation is quite complex. For example, the curvature of natural river increases proportionally to the transported load alimentation and inversely to the slope of the river. The human-modified rivers also tend to increase the curvature of their channels. Interestingly, all rivers create wetlands in the areas naturally connected to the main channel. Those wetlands are regularly watered by flood events. As a result, the areas with wetlands are a perfect natural environment for fauna and flora. River channels which are situated close to such an environment are also rich in fish and invertebrates. Wetlands in mountainous areas are rare or unique unlike in lowlands where they are more likely to be found. The channel incision reduce a possibility of wetland formation in the river valley, especially after bank enforcement. The presented case studies are the effect of different projects running by the Department of Water Engineering and Geotechnics, the University of Agriculture in Krakow on the rivers and streams: Vistula, Nida, Porebianka, Czarny Dunajec. These rivers differ in many aspects; however, each of the them is located in an area where wetlands or wetted areas are likely to appear. Among the described rivers are lowland and mountain rivers. Some of them are managed according to the European Water Framework Directive, i.e., in a close-to-nature manner.

Numerical Modeling of Water Flow Conditions with Spatial Distribution of Boulders in Main Channel

The article presents a study on the influence of spatial distribution of boulders placed in the main channel on parameters of flow conditions. Restoration guidelines recommend boulders structures but engineering solutions must be individually adapted to local situation. The depth-averaged 2D numerical model of unsteady, free-surface flow in open channels was used to calculate spatial distribution of velocity magnitude, slope of water surface level and water depth. The impact of individual boulder on the flow conditions in river channels increases through the group arrangement. Model of the Wisloka River section was changed by implementation of boulders in various configurations: a group of three or four placed in triangles or rhomboids, openwork deflectors, groups located by the banks, groups located alternately to form a curvilinear thalweg. The effect of boulders structure on velocity spatial distribution along the channel was calculated for discharge Q 10-day = 15 m3 s−1. Impact of single boulder structures on flow velocity is visible up to 20–30 m and increases for multiple single boulders structures up to 30–60 m. In addition, stability of individual boulder for discharge Q 1% and influence the flood hazard were tested.

Numerical Modeling of Flow Dynamics on a Gravel Bar During High Discharge in a Mountain River

Numerical modeling of changing parameters on a gravel bar during different discharges in a small mountain river is presented here. The study bar is one of the best developed bars of the upper Wisloka. Within its reach, the river may erode its banks and transport bed material. Flowing out from the Magurski National Park, the Wisloka may be assumed as being close to a natural river. As fluvial processes are very dynamic there, the bar and channel transformations occur every year. Granulometry measurements demonstrated high variation of bed material composition in different parts of the bar and the channel. The bed material was classified as fine gravel, coarse gravel, cobbles, and coarse sand. This simulation was performed based on a 2015 measurement campaign; however, in situ measurements were started in 2008. From among a wide spectrum of parameters yielded by numerical simulations, the study focused on average vertical velocity and bed shear stresses. They were compared to critical parameters of the bed material movement. The simulations were performed for different flows, from low discharges to bankfull ones, and they indicated potential dynamic changes in the bed activity.

Laboratory studies on bedload transport under unsteady flow conditions

Abstract Two sets of triangular hydrographs were generated in a 12-m-long laboratory flume for two sets of initial bed conditions: intact and water-worked gravel bed. Flowrate ranging from 0.0013 m3 s-1 to 0.0456 m3 s-1, water level ranging from 0.02 m to 0.11 m, and cumulative mass of transported sediment ranging from 4.5 kg to 14.2 kg were measured. Then, bedload transport rate, water surface slope, bed shear stress, and stream power were evaluated. The results indicated the impact of initial bed conditions and flow unsteadiness on bedload transport rate and total sediment yield. Difference in ratio between the amount of supplied sediment and total sediment yield for tests with different initial conditions was observed. Bedload rate, bed shear stress, and stream power demonstrated clock-wise hysteretic relation with flowrate. The study revealed practical aspects of experimental design, performance, and data analysis. Water surface slope evaluation based on spatial water depth data was discussed. It was shown that for certain conditions stream power was more adequate for the analysis of sediment transport dynamics than the bed shear stress. The relations between bedload transport dynamics, and flow and sediment parameters obtained by dimensional and multiple regression analysis were presented.