Thursday, 29 September 2016

Geomorphic impact of historical slate mining activity on gravel-bed streams

Our present research concerned on the geomorphic effect of historical mining of slate slabs on small stream channels. The mining activity in the Nízký Jeseník Mts (Eastern Sudetes) took place mainly in 19th century and almost all mines and quarries were closed until 1950s. Unusable rocks were usually deposited on dumps in front of the mine entrances and quarries. Dumps located on the hillslopes adjacent to the channels and former floodplains were studied as important inputs of coarse material for local streams and the alterations in bed grain-sizes and channel morphologies were evaluated.  The sediment supply from investigated dumps in low-order (I-III.) channels often transformed channel-reach morphologies (pool-riffles to plane beds), significantly altered adjacent and downstream caliber of bed sediments, and decreased the bankfull width near the points of active sediment inputs. This supply of larger grains into channels also increased potential stability of channel beds. By increased transport capacity of a stream, the significance of slate dumps as sediment inputs for evaluated supply limited or transport-balanced streams decreased as expressed obtained results for larger IV-order gravel-bed stream.
The paper has been recently published in Zeitschrift für Geomorphologie

Large slate dump in Deštná
Slate dump coupled with the channel - the case of the Lobník Stream.

Increased bed grain-sizes near the positions of active sediment inputs. Supplied slate slabs
significantly exceed  stream transport capacity calculated for bankfull flows.

Sunday, 4 September 2016

Inventory of large wood in the Odra River

The upper Odra River upstream Ostrava City represents unique geomorphic meandering pattern on the boundary between the Western Carpathians and Bohemian Massif. During the first week of September, the inventory of instream wood in the protected area of the Odra River took place, where the removal of large wood due to flood risk is prohibited since 2015. In total, 146 individual pieces of large wood were measured and positions of additional large wood jams (several including up to 20 logs) were mapped in ca. 4 km long reach. In addition, 32 large wood pieces were tagged in order to observe their future movement during high water stages. We assume extensive lateral supply of instream wood particularly in active meanders, which was also documented during field mapping.