Gabriel Spreitzer

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Spreitzer

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Gabriel

ORCID

0000-0003-4074-0225

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Publications 1 - 6 of 6

Quantification of large wood (LW) impact forces at field-scale using SmartWood
Spreitzer, Gabriel; Schalko, Isabella; Boes, Robert; et al. (2022)
Proceedings of the 39th IAHR World Congress
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.
SmartWood: field-based analysis of large wood movement dynamics using inertial measurement units (IMUs)
Spreitzer, Gabriel; Schalko, Isabella; Boes, Robert; et al. (2024)
Environmental Sciences Europe
Wood plays an important ecological role in rivers. Yet challenges arise when large wood (LW) is mobilised and transported during floods. Due to a lack of quantitative data, movement behaviour of LW during floods is still not well understood to date. A proof-of-concept study was conducted at three Swiss rivers to test state-of-the-art sensor-tagged logs, so-called “SmartWood” and collect quantitative field-scale data about LW movement behaviour. The experiments utilised innovative inertial measurement units (IMUs), which have been developed at the Laboratory of Hydraulics, Hydrology and Glaciology (VAW) at ETH Zurich and implanted into wood logs (SmartWood) at prototype scale. Each IMU comprised three individual sensors (gyroscope, accelerometer, and magnetometer) and was equipped with an on-board processor, an AA battery (4.35 V), a memory (8 MB), and a Wi-Fi transmitter (100 m) for data transfer. After successful initial verification tests of the sensors, the IMUs were installed into debranched wood logs, measuring 4.35 m in length and 0.33 m in diameter. At the time of the field experiments, each SmartWood-log weighted between 170 and 220 kg, yielding a density of roughly 500 kg∙m⁻³. At the Limmat, Thur, and Grosse Melchaa Rivers in Switzerland, innovative yet discontinuous data were obtained. Results revealed consistent movement dynamics across all field sites. Specifically, we observed positive yaw movement during transport of SmartWood along the left river bank and negative yaw movement along the right river bank. Furthermore, interactions of SmartWood with channel boundaries, riparian vegetation, and objects (e.g., ferry dock) were registered and quantified, even when the SmartWood-log was transported out of sight of traditional sensing methods. The conducted field experiments enabled the initial testing of SmartWood in the field and exposed critical limitations of the IMUs and software algorithms for the reconstruction and analysis of floating LW dynamics. The gained knowledge and introduced sensing method will benefit the quantitative assessment of LW dynamics in rivers to maintain safety and functionality for instream structures (e.g., considering LW movement dynamics for the robust design of LW retention and guiding structures), but also river restoration projects and numerical models that rely on quantitative field-scale data.
Towards a non-intrusive method employing digital twin models for the assessment of complex large wood accumulations in fluvial environments
Spreitzer, Gabriel; Schalko, Isabella; Boes, Robert; et al. (2022)
Journal of Hydrology
Quantification and assessment of large wood (LW) accumulations in fluvial systems is still considered difficult due to the complex nature of wooden deposits. Although knowledge about volumetric measures and porosity parameters of LW accumulations is crucial for the prediction of hydraulic and geomorphic effects, it has not yet been possible to obtain accurate measurements. These limitations are mainly based on a lack of applicable sensing technologies available in the past. In the present study, a close-range aerial surveying technique (Structure from Motion (SfM) photogrammetry) is applied for generating 3D replicates (digital twin models) of wooden deposits, enabling their volumetric assessment. In addition, manually conducted volumetric measure-ments of corresponding prototype LW accumulations help to improve and calibrate the SfM-derived estimates. For the first time, precise porosity parameters for LW accumulations, ranging from 52.5 to 83.2%, are provided. In addition, a novel parameter - the packing arrangement - is used, which describes the structural alignment of individual elements in the LW accumulation and benefits porosity estimates based on the applied 2.5D and 3D photogrammetric approach. Accordingly, randomly and loosely organised LW accumulations allow for a high penetration depth of the 3D approach, resulting in a more accurate estimate of the actual porosity, as the 3D volumetric estimate approaches the solid wood volume of the corresponding LW accumulation. An empirical approach has been developed for future approximation of LW accumulation porosity, without the need of knowing the solid wood volume. With the present work a significant improvement of our understanding in employing a non-intrusive sensing technique is provided, linked with manually conducted field measurements of the solid wood volume of LW accumulations. Our study contributes to an improved data acquisition and pro-cessing plan, which represents a further important step towards a systematic assessment framework that is ur-gently needed by river managers and engineers to better evaluate and manage LW in fluvial systems.
Physical modelling of large wood (LW) processes relevant for river management: Perspectives from New Zealand and Switzerland
Friedrich, Heide; Ravazzolo, Diego; Ruiz-Villanueva, Virginia; et al. (2022)
Earth Surface Processes and Landforms
In the last 30 years, work on large wood (LW) has expanded and matured considerably, and river scientists, managers and practitioners now have a better appreciation of the role of LW in maintaining ecosystems, forming or stabilizing riverine landforms, and interacting with river morphodynamics. We have gained a better understanding of the hazards posed by the recruitment and transport of LW in the river channel and associated infrastructure. While LW dynamics have traditionally been studied in the natural river environment, innovations in laboratory techniques have enabled important advances in understanding LW process dynamics, using physical scale models, new sensors, scanners and sophisticated model boundary conditions. Current trends in LW laboratory research focus on (1) mobilization and transport of logs, (2) trapping and deposition of sediment in the presence of LW and (3) LW contribution to hydraulic flow resistance. Ultimately, a combined process understanding is needed to assess impacts upon infrastructure with erodible boundaries, such as bridge piers and LW retention racks. In this review, we present a critical analysis of emerging experimental work on LW obtained through physical modelling studies. We put recent experimental work in context with global LW management challenges. In particular, we set our work in context with the present environmental and engineering issues that confront catchment and natural resource managers in Switzerland and New Zealand. We show how improved physical models incorporating LW transport, accumulation and scouring processes are needed to contribute to more reliable hazard and risk assessment and improved river management in LW-prone systems. © 2021 John Wiley & Sons Ltd.
The effect of large wood accumulations with rootwads on local geomorphic changes
Ravazzolo, Diego; Spreitzer, Gabriel; Tunicliffe, Jon; et al. (2022)
Water Resources Research
Large wood (LW) can be transported along a river during floods, increasing flood-associated hazards, particularly when it accumulates at river-spanning infrastructures such as bridges and weirs. While most flume studies have explored LW movement with simple wooden elements (dowels), only a few studies have used elements with more complex LW geometries, such as rootwads, under unsteady flow conditions. Quantitative assessment of interactions amongst more complex wood elements and river flow has rarely been attempted the effect of this additional complication has even been ignored, in both field and laboratory studies. In this study, flume experiments were conducted to assess the effect of rootwads on local scour and deposition in a flume with a mobile gravel-bed. The experiment was conducted under unsteady flow conditions, with a constricted segment of the reach, recreating conditions to wood accumulations and blockage. Results revealed that LW with rootwads tends to generate more stable accumulations than LW without rootwads, leading to the formation of more porous loosely packed accumulations. In this initial set of flume experiments, the patterns of scour were quite variable, but on average, the porous and stable LW accumulations with rootwads showed more spatially extensive disturbance of the bed. LW accumulations without rootwads led to the development of scour pits that reached the bottom of the flume more quickly than in the LW accumulations without rootwads. The mean accumulated bedload volumes were of similar magnitude overall, however, highlighting the many contingencies in the chain of processes between dam formation and resultant bed scour.
Measuring the impact: new insights into flood-borne large wood collisions with river structures using an isolated sensor-unit
Spreitzer, Gabriel; Ravazzolo, Diego; Tunnicliffe, Jon; et al. (2022)
Natural Hazards
Large Wood (LW) transported during floods or channelized mass flows poses a high risk for engineered structures, often leading to significant damage or total failure of the impacted structure. To date little is known about impact magnitudes caused by LW collisions. To better control for such interactions, a better understanding of transport dynamics and impact forces is required. The present laboratory study employs state-of-the-art sensor units installed in scaled logs to capture acceleration data from collisions of waterborne LW with 2 in-stream structures-bridge pier and retention structure-each providing different examples of rigid engineered systems. Through precise measurements of acceleration and impact duration (stopping time), the resultant impact forces of LW collisions can be calculated. Here, for the first time, impact forces were quantified in a scaled stream environment based on the inertial frame of the object causing the impact, rather than the more commonly used instrumented structure approach. High-resolution accelerometer measurements were compared to conventional analytical (force balance) approaches. They revealed the need for accurate inertia measurements to appropriately account for prevailing hydraulic flow conditions and the effects of LW interactions in fluvial environments. Although log velocity and stopping time are crucial parameters for assessing LW impact forces, accurate measurements are still elusive due to limitations in available sensing techniques. By presenting proof-of-concept results, this study contributes to an improved understanding of LW impact forces during floods. Based on these encouraging results, we recommend more sensor-based field studies in future, needed for the design of resilient structures.

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Gabriel Spreitzer

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