Landscape control on channel adjustment in response to flooding

This PhD thesis examines how landscape characteristics shape the geomorphic effectiveness of flood events in postglacial landscapes. First, pre- and post-flood DEMs of the Nicola River in British Columbia, Canada, were used to quantify erosion and deposition by landform type. The Nicola River experienced a >100-year return period flood in 2021. The analysis shows that the active channel and floodplains function almost equally as sediment sources and sinks, resulting in a relatively balanced sediment budget. In contrast, glaciofluvial terraces, alluvial fans, and colluvium act primarily as sediment sources, contributing to flood-driven sediment export. These landforms appear to serve a dual role by buffering sediment during typical flows but releasing sediment during rare extreme events. This indicates that flood-related sediment export is largely governed by access to this stored material. Building up on previous findings a historical context to the geomorphic response of the Nicola River to the 2021 flood is provided. A geomorphically effective flood was defined as one that leads to at least a 50% increase in initial channel width. Spatial and temporal patterns show that highly confined reaches lacked geomorphically effective events until the 2021 flood. However, many unconfined reaches exhibited a 50% increase in channel width across each observation period. Confined reaches, characterized by low sediment storage, act as transport zones, whereas unconfined reaches, with high sediment storage, function as depositional zones. This suggests that geomorphic effectiveness in unconfined, sediment-rich areas is driven by decadal floods and results in high channel width variability, while in confined, sediment-starved reaches, it is controlled by centennial events capable of overcoming landscape constraints. Finally, we test a conceptual model by Hassan et al. (2023) that links postglacial landscape characteristics to lateral sediment connectivity. Although the model identifies key controls, it lacks quantitative support and does not account for differences in flood magnitude. To address this, findings from the Nicola River are compared with three other post-glaciated basins that experienced flooding. This comparison adds a temporal dimension to understanding how landscape controls influence fluvial behavior and flood response in postglacial settings.