Artur Radecki-Pawlik

Hydromorphological complexity as a driver of the diversity of benthic invertebrate communities in the Czarny Dunajec River, Polish Carpathians

To verify whether the variability in benthic invertebrate communities along the mountainous Czarny Dunajec River is mainly driven by the variation in hydromorphological or water quality, diversity of the communities was determined for 18 cross-sections with 1–5 low-flow channels and compared with the complexity of physical habitat conditions and with physico-chemical water quality. An increase in the complexity of flow pattern in the river was associated with increasing cross-sectional variability in physical habitat parameters. Distinct hydromorphological characteristics of the cross-sections with a given number of low-flow channels were especially pronounced if the analysis was limited to the parameters measured directly, whereas calculated complex hydraulic and sedimentary variables represented information overload. Taxonomic richness of the invertebrate communities was unrelated to physico-chemical water parameters, which consistently pointed to the high water quality. Instead, the richness positively correlated with a degree of variation in physical habitat parameters and was best predicted by the number of low-flow channels in a river cross-section. This study indicates that physical habitat complexity in a mountain river can be considered a proxy to the diversity of its invertebrate communities and that restoration of such complexity will be necessary for future recovery of invertebrate communities in impacted river sections.

Interpretation of the invertebrate-based BMWP-PL index in a gravel-bed river: insight from the Polish Carpathians

Like its British prototype (Biological Monitoring Working Party score system), the Polish benthic invertebrate-based BMWP-PL index is commonly regarded as an indicator of river water quality. This interpretation of the index has been verified in a study of the gravel-bed Biała River. Benthic macroinvertebrates were sampled at 10 sites and compared in one channelized and one unmanaged cross-section per site. The resulting taxa richness and BMWP-PL index scores were compared with water quality and physical habitat characteristics in the cross-sections. Channelized and unmanaged cross-sections clearly differed in their physical habitat conditions, and water quality characteristics mostly varied in the downstream direction. Particular cross-sections hosted between 3 and 26 invertebrate taxa, with the respective BMWP-PL scores indicating the water in the surveyed cross-sections varied between high and poor quality. However, the BMWP-PL scores were unrelated to physicochemical characteristics of the river water, which consistently pointed to high water quality. Instead, the scores were significantly related to several physical habitat variables, with the number of low-flow channels in a cross-section explaining the largest proportion of the variance in the index values. The relationship of the scores with the complexity of flow pattern in the river and a lack of their dependence on physicochemical water characteristics show that the BMWP-PL index should not be regarded as an indicator of water quality but rather as an indicator of the ecological status of rivers, dependent both on their hydromorphological and water-quality characteristics.

On Using Artificial Rapid Hydraulic Structures (RHS) Within Mountain Stream Channels: Some Exploitation and Hydraulic Problems

The chapter describes rapid hydraulic structure (RHS) with increased roughness: one of the technical solutions intended to maintain river and stream beds in a good condition and at the same time ensure the development of a braided channel and contribute to the regeneration of channel bar structures, creating suitable living conditions for macrobenthos, and enabling unconstrained fish migration without additional fish passes. The chapter also discusses the problem of rebuilding the existing water straight drop structure in Brenna on the Brennica River (Polish Carpathians) which was changed into the rapid hydraulic structure. The technical project was set up in 1988 and finished in the same year. The structure was rebuilt in the field in early autumn 1990. The author of the chapter was a co-designer of the hydraulic structure.

Assessment of river hydromorphological quality for restoration purposes: an example of the application of RHQ method to a Polish Carpathian river

Planning and implementation of effective restoration projects require appropriate assessment of a river’s hydromorphological status. Two European standards on hydromorphological assessment of rivers and hydromorphological assessment methods used in Poland are reviewed in the context of their applicability for river restoration purposes. River Hydromorphological Quality assessment method is presented with a case study of the Biała River, Polish Carpathians, where this assessment was used as basis for a restoration project aimed to establish an erodible river corridor. The results of the assessment revealed significant differences in hydromorphological quality between unmanaged and channelized river cross-sections, indicating channel regulation as a major cause of the hydromorphological degradation of the Biała and confirming the choice of the erodible river corridor as an appropriate method of its restoration. The assessment indicated hydromorphological features of the river that were severely modified within the channelized reaches and which are likely to improve the most with the removal of bank protection and allowing free channel migration.

Flood Risk Management in the Upper Vistula Basin in Perspective: Traditional versus Alternative Measures

Flood-protection works carried out in the Upper Vistula basin since the late nineteenth century have been based on channel regulation and river embankment leading to fast evacuation of floodwater and a significant reduction in floodwater retention on the valley floors. Such a policy of flood-control management stemmed not only from the unfamiliarity with other methods and a generally technocratic approach to nature but also from the need to protect all arable land adjacent to rivers. This last motivation justified the approach in the early part of the period when farming provided for the existence of most of the society, but it progressively declined in significance with increasing urbanization of the region and economic development of the country. Flood-risk management based on the conventional methods has resulted in a severe degradation of the rivers’ ecological quality and increased peak discharges of flood waves recorded in the downstream parts of regulated and embanked river reaches. It is thus a priority to decelerate flood runoff and increase floodwater retention in less developed parts of the valleys in order to reduce flood hazard in spatially concentrated, urbanized areas along rivers. This paper presents alternative measures that either aim at reducing flood hazard at various stages of flood-wave passage through the region or serve to diminish flood risk by preventing development of river-adjacent areas, re-construction of bridges and cessation of the detrimental in-channel gravel mining.

Modelling Hydraulic Parameters of Flood Flows for a Polish Carpathian River Subjected to Variable Human Impacts

Channelization and channel incision have considerably modified channel morphology of the Czarny Dunajec River, and now it varies from a single-thread, incised or regulated channel to an unmanaged, multi-thread channel. Effects of these distinct channel morphologies on the conditions for flood flows were investigated in a study of 25 cross-sections from the middle river course. Cross-sectional morphology, channel slope and roughness were used as input data for the 1D steady-flow hydraulic modelling performed for discharges with recurrence interval between 1.5 and 50 years. Adjustment of roughness coefficients to obtain the agreement between simulated and observed peak levels of the 2014 flood allowed calibration of the model for particular cross-sections. As a result of differences in flow widths, cross-sectional flow areas and channel slope, flood flows in the three river reaches differ in unit stream power and bed shear stress, with the highest values of the parameters recorded in the incised reach, intermediate values in the channelized reach and the lowest values in the multi-thread reach. The recognised differences in the flow power and in tractive forces exerted on the flow boundary underlie and explain different evolutionary tendencies of particular river reaches during the past decades. Stabilization of river banks in channelized reaches induces a progressive increase in floodplain elevation; sedimentation in the analysed channelized cross-section of the Czarny Dunajec have reduced its initial flow conveyance by half and elevated water stages at given flood discharges by about 0.7 m during 30 years since the river channelization.

Ecological state of a mountain river before and after a large flood: Implications for river status assessment

Assessment of the ecological status of rivers is key to monitoring the achievement of the environmental goal of the EU Water Framework Directive and the success of restoration projects. In summer of 2009 and 2010, repeated assessments of physical habitat conditions and of fish and benthic invertebrate communities were performed at low-flow conditions in 10 unmanaged and 10 channelized cross-sections of the Biała River, Polish Carpathians. Between the two surveys, an 80-year flood occurred, significantly affecting habitat characteristics and river communities. In unmanaged cross-sections, active channel width increased, whereas the degree of cross-sectional variation of flow velocity decreased. In channelized cross-sections, the increase in active channel width and the cross-sectional variation of flow velocity was accompanied by a decrease in bed-material grain size. Before the flood, the unmanaged cross-sections hosted 2.3 times more benthic invertebrate taxa than the channelized ones, whereas after the flood, the number of taxa they supported was so reduced that the taxonomic richness of benthic invertebrate assemblages in both cross-section types became similar. In comparison to pre-flood conditions, the abundance of fish juveniles (YOY) in unmanaged cross-sections was reduced nearly by half; before the flood they hosted 5 times more juvenile individuals than channelized cross-sections and only twice as many after the flood. Finally, a differing assessment of flood impact on the ecological river quality was obtained with the invertebrate-based BMWP-PL index and the European Fish Index, with the former indicating a significant reduction of the quality in unmanaged cross-sections and the latter pointing to no such change. The results indicate that assessments performed before or after a major flood may yield significantly different results for the quality of abiotic and biotic elements of the river ecosystem. Final assessment should thus be based on repeated surveys to balance the effect of extreme hydrological events.

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.

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.