Zdeněk Máčka

Floods and floodplain changes of the River Morava, the Strážnické Pomoraví region (Czech Republic) over the past 130 years

Abstract The development of the River Morava floodplain has been influenced by several natural and anthropogenic factors. This paper focuses on variations in flood activity and channel changes of the River Morava in the region of Strážnické Pomoraví (southeastern Czech Republic). Floods are analysed in terms of measured peak water stages, Hk (Rohatec, 1886–1920) and peak discharges Qk (Rohatec/Strážnice, 1921–2010) evaluated with respect to their N-year return period (H N or QN ). The frequency of floods with Qk ≥ Q 2 reaches a significant maximum in March, followed by July. According to flood series compiled from 1881 onwards, their frequency peaked in the 1961–1970 decade with the most severe events occurring in July 1997 (Q 100), March 2006 and June 2010 (Q 50). During the study period the natural dynamics of the original anabranching channel patterns were significantly modified by human intervention, such as the abandonment of some anabranching channels, channel straightening, enlargement of the main channel, flood-dike construction, and the creation of the Baťa shipping channel. These changes resulted in decreased frequency and a reduction in the extent of floodplain inundations compared to the period prior to channel modifications in the 1930s. Citation Brázdil, R., Máčka, Z., Řezníčková, L., Soukalová, E., Dobrovolný, P. & Matys Grygar, T. (2011) Floods and floodplain changes of the River Morava, the Strážnické Pomoraví region (Czech Republic) over the past 130 years. Hydrol. Sci. J. 56(7), 1166–1185.

A critical review of field techniques employed in the survey of large woody debris in river corridors: a central European perspective

In forested watersheds, large woody debris (LWD) is an integral component of river channels and floodplains. Fallen trees have a significant impact on physical and ecological processes in fluvial ecosystems. An enormous body of literature concerning LWD in river corridors is currently available. However, synthesis and statistical treatment of the published data are hampered by the heterogeneity of methodological approaches. Likewise, the precision and accuracy of data arising out of published surveys have yet to be assessed. For this review, a literature scrutiny of 100 randomly selected research papers was made to examine the most frequently surveyed LWD variables and field procedures. Some 29 variables arose for individual LWD pieces, and 15 variables for wood accumulations. The literature survey revealed a large variability in field procedures for LWD surveys. In many studies (32), description of field procedure proved less than adequate, rendering the results impossible to reproduce in comparable fashion by other researchers. This contribution identifies the main methodological problems and sources of error associated with the mapping and measurement of the most frequently surveyed variables of LWD, both as individual pieces and in accumulations. The discussion stems from our own field experience with LWD survey in river systems of various geomorphic styles and types of riparian vegetation in the Czech Republic in the 2004–10 period. We modelled variability in terms of LWD number, volume, and biomass for three geomorphologically contrasting river systems. The results appeared to be sensitive, in the main, to sampling strategy and prevailing field conditions; less variability was produced by errors of measurement. Finally, we propose a comprehensive standard field procedure for LWD surveyors, including a total of 20 variables describing spatial position, structural characteristics and the functions and dynamics of LWD. However, resources are only rarely available for highly time-demanding surveys. We therefore include a set of core LWD metrics for routine baseline surveys of individual LWD pieces (diameter, length, rootwad size, preservation of branches and rootwad, geomorphological/ecological function, stability/mobility) and wood accumulations (number of LWD pieces, geometrical dimensions, channel blockage, wood/air ratio), which may provide useful background information for river management, hydromorphological assessment, habitat evaluation, and inter-regional comparisons.

Litovelské Pomoraví—Landscape Around Anastomosing River Pattern of Morava

The Morava River, rising on the slopes of the Kralický Sněžnik Mts. at the border with Poland, enters the vast tectonic depression of Hornomoravský uval after ca. 80 km of its course. Here it begins to deposit much of the sediments that were eroded in the mountainous part of the catchment. On the flat bottom of the Hornomoravský uval Basin, the Morava is branching to numerous wide as well as narrow channels creating the dense network of “arteries” similar to branches of a river in delta at the seashore. Modern fluvial geomorphology recognises this unusual river style to be an anastomosed channel pattern . The present-day channel network consists of the dominant Morava channel, from which numerous side channels are branching fed with water raised in the main channel by weirs. This basic pattern of channels is supplemented by a dense network of smaller, ephemeral channels that are filled with water only during the floods . Anastomosed channels, in many cases intensively meandering , are surrounded by large areas of natural floodplain forests . The landscape interwoven with numerous river arms and covered with fertile soils was ideal for construction of mills and establishing permanent settlements. Medieval economical activities stand at the beginning of change of the natural anastomosed fluvial system to the present-day harmonic cultural riverscape.

Variations in bar material grain-size and hydraulic conditions of managed and re-naturalized reaches of the gravel-bed Bečva River (Czech Republic)

European multi-thread rivers have undergone rapid morphological changes during past centuries due to the extensive direct and indirect human impacts on fluvial systems. As a consequence, we can identify altered patterns of bed sediment calibre reflecting disturbed sediment connectivity and modified flow hydraulics. Changes in the grain-sizes of samples collected on 68 gravel bars in August 2015 were studied along 14.0-km river reach of the Bečva River (Outer Western Carpathian Mts., Czech Republic). The grain-size characteristics obtained were confronted with modeled flow hydraulics and the present stage of the channel. The studied channel reach is presently characterized by several distinctive sections: for a long time (ca. 100 years) regulated single channel sections with artificial bank stabilizations incised several meters in the floodplain and by contrast, multi-thread channel patterns of two sections, which have witnessed retrograde development after large floods in 1997 and 2010 with 100- and 50-year recurrence intervals, respectively. The present channel behaviour of managed (regulated) and re-naturalized (multi-thread) river sections corresponded well with the modeled hydraulic variables for one-year discharge recurrence interval. Especially, re-naturalized river sections showed lower values of flow competence which facilitated the deposition of sediment material in the form of gravel bars. The high occurrence of lateral sediment sources (e.g., tributaries, bank failures) together with sediment disconnectivities (e.g., boulder ramps) in the longitudinal river reach were observed, and grain-size parameters did not particularly reflect the hydraulic conditions. Especially tributaries as sediment inputs had significant effect on bar grain size and increase of channel diversity, although, in general results indicate a gradual downstream fining.

Response of channel dynamics to recent meander neck cut-off in a lowland meandering river with artificial training history: the Morava River, Czech Republic

ABSTRACT One-decade-long observations of post-cut-off channel development and oxbow lake formation are presented to offer insight into the morphological response of the Morava River to neck cut-off. The main objectives were: calculation of the amount of sediment released to the channel by collapse of the meander neck; comparison of floodplain erosion and deposition rates before and after cut-off; and description of the rate and pattern of oxbow lake sedimentation. The amount of sediment released due to cut-off (~35 000 m3) equalled 2–5 years of sediment input by lateral erosion averaged for the past six decades. Bank erosion rates substantially exceeded long-term averages (0.63–6.21 m year−1, post cut-off). Despite a low entrance angle, alluvial plugs in a newly formed oxbow lake were established within a few months. Between 2006 and 2016, sedimentation of the alluvial plugs proceeded at an average rate of 0.55 m year−1, reflecting the time since cut-off and the frequency of overbank flows.

Strážnické Pomoraví—Holocene Evolution of a Unique Floodplain and Aeolian Landforms

The Morava River drainage basin is the largest fluvial system of the eastern part of the Czech Republic. The Morava enters the Dolnomoravský uval Basin (northern tip of the Vienna Basin) at its lower course, where a 3.5 km wide floodplain is developed. The most interesting section of floodplain may be found between the towns Veseli nad Moravou and Hodonin, where Pleistocene and Holocene sediments of the Morava River are accompanied by the unique complex of lacustrine sediments remodelled by the wind action to the shape of up to 10 m high sand dunes . The Morava river was branching into many large as well as small arms in its floodplain, creating an anastomosed channel pattern . Diverse mosaic of aquatic and (semi)terrestrial habitats were present as it is displayed on old maps of the floodplain. The majority of small anastomosed channels vanished due to the river regulation works started in the nineteenth century and most of the river flow was concentrated into one dominant channel. This channel was affected by substantial deepening, widening and lateral migration in the second half of the twentieth century triggered by river regulation in 1930s. The aerial extent of floodplain inundation was reduced to approximately one-fourth of its original extent due to the construction of flood defence dykes. The Stražnicke Pomoravi region is one of last remaining examples of a lowland meandering river with more or less preserved natural dynamics of fluvial processes in the Czech Republic.

Response of lateral channel dynamics of a lowland meanderingriver to engineering-derived adjustments - an example of theMorava River (Czech Republic)

Abstract Freely meandering (quasi)natural reaches of lowland rivers represent a rare phenomenon in Central Europe. Increasing attention is currently being paid to the dynamics of quasi-natural (artificially influenced) meandering rivers as this attention represents the basic prerequisite for the development of appropriate restoration strategies on regulated rivers. This study focused on a 5.5 km long reach of the Morava River in the Strážnické Pomoraví region, Czech Republic that is characterised by quasi-natural evolution after substantial engineering adjustments were made in the first decades of the twentieth century. Based on Geographic Information Systems (GIS) analysis of aerial photographs, the spatio-temporal dynamics of bank erosion and accretion rates were quantitatively described and variables that control channel migration rates were identified. High rates of lateral shifts were localised in high sinuosity segments (sinuosity 1.17-2.37), whereas segments with very low rates were straight or formed into slightly curved bends (sinuosity 1.05-1.18). As a key factor, engineering works that influenced local river bed slope and induced a dramatic increase in bank erosion rates were identified. River engineering works induced a dramatic increase in bank erosion rate (2.19 m/year for 1938-53 and 1.47 m/year for 1953-63). An interval of approximately 25 years was needed before the erosion rates dropped back to values documented before river regulation (0.35-1.09 m/year for 1841-1938). Other important controlling variables included radius of curvature, frequency and magnitude of floods and, locally, river bank material properties and floodplain land cover.