Large wood retention in a large meandering river: Insights from a 5-year monitoring in the Odra River (Czechia)

Abstract

Large wood (LW) is an integral component of watercourses. However, we still need to gain more knowledge of the geomorphic processes related to LW in large lower-energy, meandering rivers due to the limited number of field studies dealing with LW transport and retention in these widespread fluvial systems. This study aims to detect the predictors of the interannual variability of LW during a period of five years in a meandering river wider than the height of riparian trees. We employed four LW inventories between 2016 and 2021 in a 3.65 km long active meandering reach of the Odra (Oder) River, Czechia. We found a negligible interannual variation in LW volumes (8.3–9.2 m3/ha), but much higher in frequencies (4.4–7.0 LW/100 m). However, the variations of LW volumes in individual meander bends did not allow us to develop any robust model predicting LW volumes. We found a higher number of significant models with two independent variables that included variables from the at-site meander and from the first upstream meander in comparison to the second upstream meander. This suggests a higher importance of local “retention” and “recruitment” variables at the expense of variables of “recruitment” related to the more distant meanders. Variables derived from riparian stands were recognised as important predictors entering into 7 of 13 models with two independent variables. This points to the complex recruitment-retention function of riparian stands for LW. We found evidence that the presence of stable LW pieces can drive local channel morphodynamics, and the observed spatiotemporal variation in jams was not only a product of the suggested frequent transport of LW and instability of jams but also of the possible burial of jams in sediments. Our results documented the complex links between the morphodynamics of meandering rivers and the biogeomorphic impact of living or dead vegetation.