Saturday, 30 June 2018

Ongoing research of instream wood in Carpathian headwater streams

Two our scientific papers were recently published, which deals with instream wood in the headwaters draining the highest peak of the Moravskoslezské Beskydy Mts, Czech part of Western Carpathians. The main aim of the article in Forest Ecology and Management was to find controlling factors of occurrence of large and small wood under mixed forest canopy. Deciduous trees significantly contribute to increasing number of observed small wood due to the recruitment of individual branches from these trees. However, higher frequencies of small wood did not turn into its larger active-channel volumes. On the other hand, conifers were important for the observed frequency of large wood pieces because of (i) recruitment of the whole trees and (ii) longer residence time of local conifers. Additionally, less-confined valley floor also led to increasing frequency of large wood, whereas highly confined valleys are prone to formation of large wood 'bridges' above the zone of bankfull flows. This paper was prepared under cooperation with colleagues from University of Geneve.

Conceptual model of LW and SW abundance and stability based on conifer/deciduous tree species and valley confinement. 

The second paper dealing with steps created by single wood pieces was published by Ecological Engineering. Detailed characteristics of 73 log steps in managed temperate Carpathian forests were assessed together with channel- and wood-based thresholds for log step development. The upstream threshold of log step occurrence can be assigned to those locations in stream longitudinal profiles, where transport capacity during ordinary high flows exceeds the critical value for the initiation of bedload movement (suspended-mode transport is usually not able to form sedimentary wedge upstream individual spanning logs). Downstream thresholds are controlled by stream transport capacity and wood dimensions, which also correspond to the limited recruitment of large wood pieces in local managed forests. The development of a log step at a particular channel width or basin area was controlled by the wood length, but the resultant step parameters (step height and width, length of upstream sedimentary wedge and volume of stored sediments) were better correlated with wood diameter. Nevertheless, the average sediment storage generated by a log step was only 0.51 cubic meters.      
Step created by a single wood piece. 

Empirical model of the potential development of log steps in the studied channels without debris flow or hyperconcentrated flow occurrence. 

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