Author(s): Gabriel Spreitzer; Isabella Schalko; Robert M. Boes; Volker Weitbrecht

Linked Author(s): Gabriel Spreitzer, Isabella Schalko, Volker Weitbrecht

Keywords: SmartWood; Floods; Impact forces; Large wood dynamics; Wood in rivers

Abstract: While wood in rivers constitutes an essential element for the regulation of stream power and habitat creation, large wood (LW) carried during floods poses a high risk for interactions with in-stream structures such as bridges, dams or weirs. Although significant damage or total failure of impacted structures is frequently reported, there are no field-scale data of LW impacts available to date. Thus, acceleration data from innovative inertial measurement units (IMUs), which are deployed in the course of the SmartWood_3D research project at the Laboratory of Hydraulics, Hydrology and Glaciology (VAW) of ETH Zurich, were used to measure field-scale impact forces of transported LW during floods. The field experiments considered the release of up to four sensor-tagged prototype logs – SmartWood – at a time into flooded channels (approximately HQ₁) in Switzerland. Each SmartWood-log is fully debranched and measures 4.40 m in length at a mean diameter of 0.33 m. During the preparation of SmartWood in the laboratory, wood density decreased from 680 kg/m³ for the freshly cut and wet logs directly from the forest to 450 kg/m³ for the completed SmartWood logs at dry condition. The wetted density of SmartWood during the field experiments was roughly 500 kg/m³, yielding an impacting mass of roughly 188 kg. After SmartWood had been released into the channel, the logs were instantly mobilised by the high flow. On their journey downwards, complex LW dynamics were observed and successfully measured with high temporal resolution for the first time to the authors’ knowledge. Of particular interest were interactions of SmartWood with channel boundaries and in-stream obstacles (e.g., boulders). Deceleration of impacting logs were found to be significant, reaching the maximum measurable acceleration range (± 16 g) of the applied smart-sensors. The gained results contribute to a better understanding of LW dynamics in rivers and will help engineers to assess the vulnerability of existing structures as well as to improve the design of future flood-resilient structures in fluvial environments.

DOI: https://doi.org/10.3850/IAHR-39WC2521711920221245

Year: 2022