Karol Plesiński

Sediment Transport Processes Related to the Operation of a Rapid Hydraulic Structure (Boulder Ramp) in a Mountain Stream Channel: A Polish Carpathian Example

Rapid hydraulic structures—RHS—(called also boulder ramps) are modern, environment-friendly grade-control structures which mimic natural riffles and do not disturb longitudinal continuity of the stream for fish and benthic invertebrates. Due to the reduction of hydraulic gradient and backwater effect, such hydraulic structures change the pattern of sediment transport and deposition in the channel, facilitating persistence of alluvial streambed and the formation of gravel bars upstream and downstream of the structures. This is of key importance for preserving habitats for benthic invertebrates and the spawning ground of lithophilic fish if a stream has to be channelized. At the same time, properly designed rapid hydraulic structures must allow efficient transfer of sediment flux through their apron, helping to clean the structures of gravel and preventing their clogging. This study deals with observations and modeling of sediment transport in the vicinity of a rapid hydraulic structure in a mountainous gravel-bed channel. The study aims to: (i) show the effects of RHS on sediment transported along a stream channel, and (ii) to evaluate the performance of CCHE2D model in predicting sediment phenomena along the stream with rapid hydraulic structures. The studied structure is located in Porebianka Stream draining a flysch catchment in the Polish Carpathians. We measured and calculated hydraulic parameters characterizing the flow on and in the vicinity of the structure, such as velocity, dynamic velocity, shear stress, Froude number, Reynolds number and friction coefficient. The knowledge of those parameters allowed us, at the same time, to calculate sediment transport in the region of the structure using BAGS model for the Parker transport formula and parallel modeled the sediment transport with the CCHE2D model. The results show how the hydraulic structure (enabling the migration of fish and benthic invertebrates), operates in terms of sediment transport processes (basically, giving the answer to the question: what is the influence of RHS on sediment transport) which form the channel morphology in its vicinity. In that context the CCHE2D model is discussed with its advantages and impediments.

Plant basket hydraulic structures (PBHS) as a new river restoration measure

River restoration has become increasingly attractive worldwide as it provides considerable benefits to the environment as well as to the economy. This study focuses on changes of hydromorphological conditions in a small lowland river recorded during an experiment carried out in the Flinta River, central Poland. The proposed solution was a pilot project of the construction of vegetative sediment traps (plant basket hydraulic structures - PBHS). A set of three PBSH was installed in the riverbed in one row and a range of hydraulic parameters were recorded over a period of three years (six measurement sessions). Changes of sediment grain size were analysed, and the amount and size of plant debris in the plant barriers were recorded. Plant debris accumulation influencing flow hydrodynamics was detected as a result of the installation of vegetative sediment traps. Moreover, various hydromorphological processes in the river were initiated. Additional simulations based on the detected processes showed that the proposed plant basket hydraulic structures can improve the hydromorphological status of the river.

On bankfull methods determination again – why we care?

Abstract One more time we would like to pay attention of especially of the hydraulic engineer audience to bankfull stage and discharge. Along the paper we show commonly accepted definitions of it and ways of calculations. It is difficult to determine the size of the bankfull flow level, that is why the authors are presenting many selected methods. Some of the methods allow the determination of biotic bankfull flow through the occurrence of zones of vegetation characteristic and based on the observation of the occurrence of ground beetles (e.g. the Woodyer and the Radecki-Pawlik and Skalski methods). Some of the methods – most popular- are using morphometric parameters (e.g. the Williams, the Hey and Thorne, the Gauckler-Manning and finally the Lambor methods). We believe that the value of bankfull discharge would be accepted as a supporting tool for designers, hydraulics engineers and managers, especially those who care about river channel environment and cooperate with fluvial geomorphologists- and biologists as well as environmental agencies.

Dominant discharge in the Indus river from downstream of the Kotri barrage dam

Hydraulic data of the Indus River, downstream of Kotri Barrage dam are ana- lyzed. An attempt has been made to determine the dominant discharge, which is defined as that discharge which over a long time period transports the most sediments and could be used to predict the shape of river cross-section. For dominant discharge calculation Wolman and Millers approach has been applied. Since the transport of sediment concen- tration could be a more effective variable for forming the shape of the river cross-section, suspended sediment concentration has been introduced, because more than 85% of total load is in suspension. We show in the paper that water discharge Q = 1000 m 3 · s -1 of water is a frequent discharge and carries maximum sediment load. This discharge we call here the dominant discharge (Q dd ) for the Kotri dam cross section. Streszczenie. W pracy określono wartośc przeplywu korytotworczego dla rzeki Indus w przekroju zapory Kotri Barrage. Wykonano probe analizy przeplywu dominującego jako tego, ktory jest zdefiniowany jako trwający przez dlugi okres oraz transportujący najwiekszą ilośc rumowiska i moze byc stosowany do przewidywania ksztaltu przekroju poprzecznego

Impact of River Restoration on Hydromorphological Processes: The River Flinta as a Case Study

This paper deals with problems related to the improvement of the hydromorphological conditions of the river Flinta in its sections located in the Natura 2000 area. Based on a comprehensive study of the hydromorphological status of the river, four sections have been selected, where restoration measures can efficiently improve the river habitat conditions. For each of these sections we propose a set of technical and biological measures. One of the proposed solutions, investigated as a pilot project, was to construct plant barriers (sediment traps—vegetative baskets). Systematic measurements were carried out during one and a half year. These measurements provided information on the possible consequences of such actions in terms of hydromorphological changes.

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.

Possibilities of fish passage through the block ramp: Model-based estimation of permeability

Block ramps offer an opportunity to combine hydrotechnical structures with fish passages. The primary study objective was to evaluate the effectiveness of a block ramp for upstream fish movement in a mountain stream. Geodetic measurements of the bottom surface and water level were taken for three cross-sections. The description of the geometric and hydrodynamic parameters of the block ramp was supplemented with information on the width and length of crevices between boulders. Measurements of the geometric and hydrodynamic parameters of the block ramp were performed at 76 measurement sites, at three different types of discharge. Ichthyological data were collected in the analyzed stream. Measurements covered among others total length, width, and height of caught fish. Salmonid, cottid, balitorid, and cyprinid fish were studied. The determination of the main effects of the geometric and hydrodynamic parameters of the block ramp on the possibilities of use by target fish species employed generalized linear models (GLMs). The study shows that the block ramp cannot provide longitudinal connectivity and migration of fish occurring in the mountain stream. According to estimates, the block ramp did not meet the permeability expectations. The reason for low usefulness of the ramp for fish is particularly excessively strong water current. The stream concentration constituted an unsurmountable velocity barrier for fish moving upstream for each of the analyzed discharges. The developed model suggests that some crevices in the side zones of the ramp could be parts of the migration corridor, but only for small and medium-sized fish. At medium and high water stages, movement of fish in crevices was difficult due to fast water current, and at low and very low discharges, some crevices lost their permeability, and could become ecological traps for fish. The necessity of estimation of ramp permeability during pre-construction phase was emphasized.

Spatial Distribution of Dissolved Oxygen at Rapid Hydraulic Structures as an Indicator of Local-Scale Processes

This work aimed to examine the impact of rapid hydraulic structures on water temperature and dissolved oxygen concentration in the Porebianka mountain stream. This has been achieved by measurements of hydraulic characteristics and physiochemical properties of water such as water temperature and dissolved oxygen concentration. It has been shown that rapid hydraulic structures exhibit a large spatial diversity in morphology and flow paths, that manifests in the spatial heterogeneity of thermal conditions and oxygen concentrations at a single structure scale. The results have demonstrated that pools between the rapid have higher oxygen concentrations when compared to the rapid region. The highest concentrations of oxygen occured in pools located close to the upstream edge of the rapid ramp where the flow undergoes gradual acceleration. Elevated concentrations of dissolved oxygen were also observed in the dissipation basin. The lowest concentrations were observed at stream banks. The results emphasise the relative importance of site-specific characteristics on physiochemical properties of flow, which might help to understand multi-scale processes across rivers and improve future plans of restoration practices in mountain streams.

Dominant discharge – an outline of theory and a case study from the Raba river

Designing hydraulic structures engineers has only theoretical flows, calculated using formulas based on statistics. Knowledge of the dominant discharge could help determine designers who are interested in changes of the morphology of river channels, especially in terms of sediment transport. It was observed that the designing of a stable channel in the river is possible when defining characteristic of flow in the river which is the most frequently present in the river and in the same time it carries the sediment. That is the dominant discharge. It is this movement can represent both the hydraulic system and the geometry of the river cross-sections. The dominant discharge (also called river shaping channel discharge) is considered by many authors as a discharge that transports the largest amount of sediment, it takes a long time and has an impact on the formation of the shape of the river bed. Observations of Wolman and Miller showed that low but frequent flows of water might be responsible for new shape of the river channel, erosion of the riverbed, sediment deposition and consequently changes in river morphology. The paper presents Wolman method for dominant discharge use for the Raba River for chosen gauge cross section. Along in the paper we discuss the obtained results and the consequences of using dominant discharge for the practice. In six cross sections on the Raba River, Qdd was calculated values, which range from 31 m3 · s–1 (for the section in Rabka) to 395 m3 · s–1 (in Proszówki). These flows occur ISSN 1644-0765 DOI: http://dx.doi.org/10.15576/ASP.FC/2016.15.2.41 www.formatiocircumiectus.actapol.net/pl/