Effect of grade-control structures on bed sediments and local channel parameters

Grade-control structures (GCSs) including check-dams and bed sills represent the typical management of torrential streams, preventing massive bed erosion and bedload transport. On the other hand, they strongly affect connectivity of aquatic biota and sediments. A lot of papers have been published about the effect of large dams on discontinuity of bed sediments and channel incision so far, but the clear relationship between check-dams and channel processes in dynamic mountain channels remains less understood. Our last paper published in Geomorphology deals with issues of downstream grain-size trends and development of scours in the longitudinal profile of the Mohelnice River (A = 40 km^2, S = 1-2 %, W = 15-20 m) with 18 GCSs in various stage of their destruction. These GCSs were (re)constructed in 1970s and since that, they were damaged by high-magnitude floods in 1996, 1997 and 2010. We measured present grain-sizes by Wolman method in sedimentary wedges of these GCSs and also scour geometry related to GCSs. In addition, present geometry of GCSs was measured and compared to their original stage in 1970s to determine their stage of destruction.

Partly destructed check-dam in the Mohelnice River

Besides other things, obtained results demonstrated that downstream coarsening especially of higher grain-size percentiles occurs throughout the sequence of GCSs. Present grain sizes do not correlate with the present channel slope or the present height of GCSs. However, the sequence of 18 GCSs at 2.6 km longitudinal distance is still passable for grain sizes up to 200 mm (at least during floods close to 20 R.I. intervals) as documented development of gravel bar downstream this sequence. The geometry of scour holes (maximum depth, lenght) relatively well corresponded to the present height of GCSs, showing dynamic adjustments of scours to changed geometry of damaged GCSs and thus, the present water drop heights. It is also evident, that these damaged GCSs still stabilise channel bed against erosion and their lowered height increases connectivity for sediments and some aquatic species.

Grain sizes of sedimentary wedges in the Mohelnice River: D16 - green, D50 - red, D84 - blue, D95 - yellow. Grain sizes of downstream channel-bar (black squares) and present height of check-dams (present water drops) are also displayed.  

Our research dealing with GCSs continues on the nearby Bystrý Torrent. There we obtained grain-size characteristics of ca. 50 small gravel bars in the heavy channelized stream with ca. 35 GCSs on 2 km longitudinal distance (A < 10 km^2, S = 2-3 %, W = 5 m). Preliminary results show a good relationship between the equilibrium channel slope upstream individual check-dams and grain-sizes, but some other variables need to be tested. So, the article is still in preparation to be submitted during the first months of next year. However, both studied will provide insight into the effect of GCSs management on downstream calibre of bed sediments via the artificial adjustment of transport capacity of the stream.

START – Danube Region Project Fund - new project was received

Within the program „START – Danube Region Project Fund“ (see link), Quantification of morphological changes in river channels and its impact on flood risk (MORCHFLOOD - PA 05 Environmental Risks) project was received. Members of Czech-Rivers research group, namely assistant professors Mgr. Stanislav Ruman, RNDr. Václav Škarpich, Ph.D. and RNDr. Tomáš Galia, Ph.D. from Department of Physical Geography and Geoecology are lead partners of project.

Other project partners (i) Department of Physical geography and Geoecology (Commenius University in Bratislava, Slovakia) and (ii) Department of Physical Geography, Geomorphology and Natural Hazards (Slovak Academy of Science) are involved in this project.

The main aim of the project will be focused to quantification of changes in river morphology and its connection with flood risk in detail. This target will be implemented through field works (surveys) which will take place in selected parts of Bečva and Topl'a Rivers, where morphological changes and flood risk is present. Final outputs will be summarised in the Study. Target of second activity is to bring the outputs to practice, when two workshops will be organized. Target groups for both workshops are Water Authorities and Municipalities occurring in selected river basins and all persons concerned in this phenomena.

Project is part-financed by the European Union.

 

Prof. Wyżga, Dr. Ruiz-Villanueva and Dr. Plesiński visited us

Bartlomiej Wyżga (Polish Academy of Sciences), Virginia Ruiz-Villanueva (University of Bern) and Karol Plesiński (Agrocultural university of Krakow) visited our department and some field locations in order to discuss possibilities of any further collaboration and to start some field measurements. Václav Škarpich presented an incised part of the Morávka River to our Polish colleagues and together they started to evaluate the role of large boulders on flow hydraulics and erosional processes in the channel. A pilot measurement of cross-sectional geometry and flow velocity were done during low water stage, but also under low water temperature conditions. 

Karol Plesinski a Bartlomiej Wyzga during flow velocity measurements

At the same time, Tomáš Galia, Radek Tichavský and Karel Šilhán showed to Virginia high-gradient tributaries of the Mazák Stream and the Velký potok Stream, when they focused especially on the woody debris in the view of their transport dynamics and influence on channel processes. Next sunny day, large woody debris were inspected on the meandering Odra River and the gravel bed Bečva River.  

Karel Šilhán, Virginia Ruiz-Villanueva and Tomáš Galia discussing in the Mazák Stream

We all together visited some additional interesting locations during the third day (the high-gradient Bučací Stream, grade-control structures in the Mohelnice River, and the Morávka local channel widening).  We found a lot of interesting topics of the joint research in the friendly atmosphere and we also sincerely hope, that most of them will be realized during next years.  

Collective photo from the Bučací Stream

Financial support of the Moravian-Silesian Region for students and academic researchers of Department of Physical Geography and Geoecology

Within the program „Podpora vědy a výzkumu v Moravskoslezském kraji 2014 (RRC/07/2014)“ (see link in Czech), financial support for two PhD students and three assistant professors was received. Namely PhD students Mgr. Radek Tichavský, Mgr. et Mgr. Ondřej Turský and assistant professor RNDr. Tomáš Galia, Ph.D. (member of Czech-Rivers research group), RNDr. Jan Lenart, Ph.D. and RNDr. Václav Škarpich, Ph.D. (member of Czech-Rivers research group) were involved in financial support. The main aim of the program was support of starting community of talented students and young researchers at universities in the Moravian-Silesian Region from 1st of January 2014 to 31st of August 2015. 

Financial support of PhD students and assistant professors of Department of Physical Geography and Geoecology resulted in publishing of several peer-reviewed articles with impact factor and home and international conference participations with oral/poster presentation of research topics.

V rámci programu „Podpora vědy a výzkumu v Moravskoslezském kraji 2014 (RRC/07/2014)“ (odkaz na web) získali finanční podporu dva studenti doktorského studia Environmentální geografie Mgr. Radek Tichavský a Mgr. et Mgr. Ondřej Turský a také odborní asistenti RNDr. Tomáš Galia, Ph.D. (člen výzkumné skupiny Czech-Rivers), RNDr. Jan Lenart, Ph.D. a RNDr. Václav Škarpich, Ph.D. (člen výzkumné skupiny Czech-Rivers). Cílem finanční dotace v období 1. 1. 2014 – 31. 8. 2015 bylo podpořit začínající vědeckou kariéru talentovaných studentů a mladých vědeckých pracovníků univerzit v moravskoslezském regionu.

Finanční podpora studentů a absolventů Katedry fyzické geografie a geoekologie PřF Ostravské univerzity přispěla k publikování několika prestižních vědeckých publikací v impaktovaných časopisech a k prezentaci vědeckých výsledků na řadě zahraničních i domácích konferencí.

REFORM: International Conference, 2015 (Wageningen, Netherlands)

We were involved in 'Novel Approaches to Assess and Rehabilitate Modified Rivers' an international conference on river and stream restoration. Conference followed REFORM - Summer School (see report - link). Main scope and objectives of the conference was to enlarge awareness of the need and appreciation for the benefits of river rehabilitation.

Members of CZECH-RIVERS, Dr. Tomáš Galia and Dr. Václav Škarpich presented information about river restoration projects and monitoring in Czech part of the flysch Carpathians. Namely about: (i) Morávka River channel widening and (ii) Kněhyně torrent restoration project where we involved in the research monitoring.

Time schedule and basic description of presented contributions:

Anti-erosive construction in the Morávka River – problematic approach to management of flysch Carpathian rivers, Czech Republic 

Authors: Václav Škarpich, Tomáš Galia, Jan Hradecký, Radek Dušek

June 30, 2015 (17:45 p.m to 19:15 p.m.) - poster presentation

During the last century the Morávka River channel has been transformed from anabranching to single channel river pattern that incised as deep as into the bedrock. These changes have been caused by a strong and inappropriate management (as a bank stabilising, weir and valley dam constructing). Contemporary channel changes have not been evident at reach r. km 7.0 to 10.5 which has partly preserved the original anabranching river pattern with lateral erosion. In order to preserve this anabranching channel reach and the prevention of proceeding backward erosion and protection against destruction Vyšní Lhoty weir at r. km 11.3 anti-erosion construction of local channel widening was constructed at r. km 10.7. However, spring flood in year 2010 accelerated present erosive processes and channel incision to the bedrock and showed that the antierosive construction was not well designed. In some parts, the original river bed has lowered by as many as 2.5 m. The anti-erosion construction itself has also been affected by massive incision. This paper summarizes results of monitoring, processes and function of anti-erosion construction of local channel widening with connection to bad management of Water Authorities in Czech Part of the flysch Carpathian Mts and discuss the problematic management solution of destabilized channel reach and gives proposition of the future management.

Torrent restorations in the flysch mid-mountain environment: The case study of the Kněhyně Torrent, Czech Republic 

Authors: Tomáš Galia, Václav Škarpich, Jan Hradecký

July 1, 2015 (11:30 a.m. to 11:45 a.m.) - oral presentation

The occurrence of channel-reach morphologies (e.g., bedrock channels, step-pools, anabranching channels) in mountainous landscape is driven by several internal and external time- and space-variable factors. Especially, the identification of the sediment supply potential related to transport capacity is crucial for later stream management in torrential mountain channels. The contribution deals with theoretical aspects of stream restorations of this part of fluvial net with emphasis on the flysch Western Carpathians on the example of restored anabranching channel-reach of the Kněhyně Torrent. This channel-reach was partly renaturalized by the 100y flood event in 1997, when the single riprap-regulated channel was transformed into anabranching pattern with relatively large gravel deposits. Stabilization elements were added into the channel to preserve that morphology during the restoration project realized in 2003-2004. The field geomorphological mapping shows, that longitudinal disconnectivity in the form of checkdams exists in the stream longitudinal profile and recent potential sediment sources are limited at the watershed scale. These facts make difficult the sustainable preservation of the transport-limited conditions in the Kněhyně. We suppose, that the original anabranching pattern noticed by the 2nd Military survey (half of the 19th century) was resulted from the higher sediment supply caused by different land-use of mountain region and the important role was played by the sediment delivery driven by debris flows under suitable climatic conditions during the LIA. The role of potential sediment supply estimations, bedload transport modelling and dendrogeomorphological approach is discussed in order to better asses relationship between the sediment supply, transport capacity and resulted channel-reach morphology.