Six years of spatiotemporal variations of large wood at the meander scale

Meander bends are perceived as sites with high large wood (LW) retention potential by trapping transported LW at their concave banks or on point bars. We employed five field inventories between 2016 and 2022 (2016, 2019, 2020, 2021 and 2022) in 13 subsequent meander bends of the Odra (Oder) R., Czechia, to assess spatiotemporal variations of LW in the period characterised by ordinary flow events including a flood of 5-year recurrence interval (10/2020, 308 m³/s). We found an increasing trend in LW volume (121.1 m³ in 2016 and 138.1 m³ in 2022, respectively) in a 3.65 km long study reach. We observed a high disproportion in the longitudinal LW distribution during individual surveys along the study reach. Furthermore, four upstream meander bends had stable LW volumes during the study period, whereas the bends located in the middle and downstream part of the study reach indicated large fluctuations of LW loads without any regular trend. These fluctuations are likely related to (i) chronic recruitment of LW from outer meander banks, (ii) burial of LW during floodplain accretion, and (iii) LW mobility during high flows. Independent variables representing the characteristics of the riparian trees (tree basal area and the length of the riparian forest at the bend) were detected as significant predictors of the LW volume at the meander scale. Future research will focus on the complex links among the migration rates of individual meanders, the characteristics of riparian stands, and the dynamics of LW in the channel and floodplain.