Check dams decrease the channel complexity of intermediate reaches in the Western Carpathians

Our new article published in Science of the Total Environment focuses on potential degradation of mountain channels affected by direct human interventions. We dealt with four channel complexity dimensions (longitudinal, cross-sectional, large wood and bed sediments) of foothill and steep streams treated by check dams. We observed that check dams altered the channel complexity of intermediate reaches (i.e., reaches between subsequent check dams) when compared with reaches of undisturbed streams. A higher degradation was typical for a foothill unconfined stream (S = 0.01-0.02 m/m), where this stream completely lost its vertical bed oscillations because of the transformation of pool-riffles to a uniform plane bed morphology. On the other hand, a steep stream (S = 0.06-0.12 m/m) indicated an increase in sediment homogeneity when compared to an untreated stream, but this management did not heavily affect longitudinal or cross-sectional heterogeneity. Due to the presence of managed riparian corridors, we did not observe differences in instream wood abundance between treated and untreated streams.

Galia, T., Škarpich, V. Ruman, S., Macurová, T. (2019): Check dams decrease the channel complexity of intermediate reaches in the Western Carpathians (Czech Republic). Science of the Total Environment 662, 881-894. doi: 10.1016/j.scitotenv.2019.01.305

Participation on the traditional conference of Czech Association of Geomorphologists

We participated on the traditional conference of Czech Association of Geomorphologists. 19th International Conference "State of geomorphological research in 2019", this year titled „Český ráj ´19” was held in the Bohemian Paradise in Parkhotel Skalní Město near Jičín from 3rd to 5th April 2019. It was organized by the Institute of Rock Structure and Mechanics of the CAS, in cooperation with Bohemian Paradise Geopark.

The conference venue was situated in the geomorphologically attractive area of Bohemian Paradise, near the famous Prachovské skály rock labyrinth. This unique area, formed by sandstone plateaus of Bohemian Cretaceous basin and dominant landmarks of Tertiary neovolcanic intrusions, offers some of the most spectacular landforms.

We participated with oral and poster presentations with focus on problematics of check dams in mountain streams and their effect on channel complexity, effect of instream wood on fluvial processes in the Odra River, perspectives of gravel bars in the sense of planned lock chamber construction in the lower Elbe River, a confluence hydrodynamic zone as integral part of fluvial system diversity and mapping geomorphic (dis)connectivity in the human modified landscape of the Slavíč River valley in the Moravskoslezské Beskydy Mts.

Proceedings were published (here).

Our research of instream wood in Mediterranean environment

This year, we continued with investigations of the abundance and geomorphic effect of instream wood in Mediterranean fluvial systems. In June, we again visited the Lefka Mts (the highest mountain range in Crete, Greece) to assess predictors of instream wood loads in intermittent and ephemeral streams draining this mountain range. We measured parameters of wood together with channel geometry and riparian forest characteristics in ca. 40 channel reaches. The preliminary results show that the frequency of instream wood has rather a random character, whereas the biomass in riparian forests is important for instream wood volumes in small Mediterranean channels. 

Wood deposited by a previous flood outside the bankfull channel.

Step consisted of instream wood acting as sediment retention element.

During late September, we also investigated characteristics of instream wood in larger intermittent river (the Evrotas) draining the Peloponnese peninsula. Together with colleagues from Hellenic Center of Marine Research (Dr. Vardakas, Prof. Kalogianni) we also tried to find connections between the occurrence of instream wood and local endemic fish species. The examined river is interesting by alterations of hydrologic (dry vs. wet channels) and geomorphic (single thread vs. wandering) patterns. These alterations are reflected in the abundance of instream wood together with the character of riparian trees and occasional removal of instream wood by local people.

Instream wood in a single-thread wet reach.

The stump transported by a previous flood into dry wandering channel.

Now we are processing field data from both studied areas and we are planning to prepare related scientific articles during the first moths of 2019.      

Field excursion about river restoration projects in Upper and Lower Austria

The field excursion trip took place for students of our Department of Physical Geography and Geoecology from 5 to 8th September 2018. The main idea was showing river restoration projects in Lower and Upper Austria, namely on the Danube River and its tributaries, e.g. on the Traun River or the Ybbs River.

On Tuesday 6th of September, the first day of field excursion trip was focused on river restoration projects in urban area of Linz City. Especially, on the restoration of gravel bars on the left-side bank of the Danube River and future vision of river restoration of Danube River, e.g. creating of islands and side-channels in Urfahr District.

The second day of excursion was focused on the river restoration projects in downstream part of the Ybbs River. We visited reaches between Greinsfurth and Winklarn villages where river restoration were realized, e.g. fishpass through Greinsfurth hydropower dam (or weir), distributary of the Ybbs River near Winklarn for increasing of biodiversity and heterogeneity of channel, or restoration of mouth of the Ybbs River to the Danube River.

The third day, we visited hydropower dam in Melk with lock chamber for river navigation on the Danube River. The last stop was close-to-natural fishpass through hydropower dam in Melk.

Restored gravel bars on the left-side bank of the Danube River in Linz.

Fishpass through Greinsfurth hydropower dam.

Greinsfurth hydropower dam.

Presentation of river restoration of distributary near Winklarn.

Crossing through the restored reach Ybbs River near Winklarn.

On the hydropower dam in Melk.

Field Excursion was supported by Moravian-Silesian Region  

Effect of hydraulics of regulated and re-naturalized channels on grain-size parameters

With co-operation with our colleague Assoc. Prof. Dr. Zdeněk Máčka from Masaryk University, we published article about effect of hydraulics of regulated and re-naturalized channels on grain-size parameters in Science of the Total Environment multidisciplinary journal.

The grain-size characteristics obtained on 68 gravel bars were confronted with modelled flow hydraulics and information obtained by fluvial-geomorphic mapping along 14.0-km river reach of the Bečva River (Outer Western Carpathian Mts., Czech Republic). 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.

The mapping of sediment (dis)connectivity brought important findings about the character of sediment flux in the studied reach, which were confronted with simulated cross-sectional hydraulics. We demonstrated that in the case of a high occurrence of lateral sediment inputs (tributaries, bank failures) and longitudinal sediment flux disconnectivities (weirs or boulder ramps), the assessment of the longitudinal distance, bar grain size and simulated hydraulics submerging bars did not produce any clear relationships. Although the sections with re-naturalized multi-thread patterns showed distinctive hydraulic variables (i.e., larger wetted width or lower unit stream power), we did not observe direct relationships with their bar sediment sizes. This implies that for complex fluvial systems of multi-thread rivers as the transition reaches connecting mountainous and lowland areas, even those in unconfined valley settings out of the primary sediment sources, additional factors (i.e., effect of bank failures and especially tributaries as sediment inputs, weirs or boulder ramps as sediment flux disconnectivities) beyond local flow hydraulics and distance from the main sediment sources contribute to better explanation of the downstream evolution of grain-size patterns.

View of the Bečva River channelized (managed) single channel sections (A, C, E) and retrogradually developed (re-naturalized) multi-thread channel sections (B, D).