Assessing patterns of spatial distribution of large wood in semi-natural, single-thread channels of Central Europe

Abstract

Spatial distribution of large wood (LW) is frequently assessed in a simplified form as a degree to which wood is clustered into jams usually as the consequence of previous wood mobility in the stream. In this study, longitudinal patterns of LW distribution in ten semi-natural, single-thread reaches (catchment area 0.10–1479 km2, channel width 2.5–34 m, bed slope 0.0009–0.23 m m−1) of watercourses of the temperate climatic zone in Central Europe were quantitatively evaluated using a one-dimensional Ripley’s K statistic and the parameter of concavity. Although these metrics could not indicate clear differences in distribution patterns between the mountain confined and the lowland unconfined reaches, they helped reveal some specific features of LW spatial organisation. Ripley’s K statistic indicated a higher degree of LW aggregation in the reach recently disturbed by a high-magnitude debris flow/debris flood event and the reaches with suggested intensive LW transport. A regular pattern of LW distribution with respect to the recurrent LW retention features was suggested by a reversal of the trend in calculated concavity values, as channel bins with the lowest values of the parameter roughly equalled the spacing of meanders. Moreover, the used metrics indicated somewhat contradictory distribution patterns in some of the study reaches, with Ripley’s K demonstrating the occurrence of LW aggregation along the whole longitudinal profile and concavity values indicating downstream variation in LW counts and volumes between short subsequent channel sections. Both quantitative metrics can provide valuable information about longitudinal patterns of LW storage and they have a potential to be used in geomorphic research focused on any features distributed along line structures.