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- Title
Numerical Modeling of Potential Large Wood Entrainment in Rivers: Application of Hybrid Modeling in the Inter‐Dam Reach of the Dyje River, Czechia.
- Authors
Hlavňa, M.; Máčka, Z.; Záthurecký, J.
- Abstract
Mobilization of large wood in river channels during floods represents a hazardous factor, augmenting flood risk and endangering infrastructures such as bridges, weirs, and reservoir dams. A hybrid modeling approach combining numerical models with field‐based surveys has been recently used to elucidate the processes of LW entrainment and deposition in rivers. We used two‐dimensional hydraulic modeling performed in HEC‐RAS to simulate LW entrainment in two valley bottom segments of the Dyje River, Czechia, where LW deposition is a significant hazard to the dam of the downstream Znojmo reservoir. We surveyed all LW pieces in the inundation area of the 2002 extreme (>Q100) flood and simulated their entrainment for eight flood scenarios (1–100‐year recurrence interval). We used the equations of Braudrick and Grant (2000, https://doi.org/10.1029/1999WR900290) to calculate the LW entrainment threshold; we introduced coefficient k accounting for the incomplete submersion of LW pieces resting on an inclined surface into the original equations. Four entrainment categories — stable, wetted stable, wetted buoyant, and wetted entrained — were defined, and the proportion of LW pieces in each category was calculated for the flood scenarios. We found marked differences in entrainment categories for respective flood scenarios between the two valley segments. These were attributed to the differences in pieces' dimensions, their spatial distribution within the inundation area, and valley‐bottom topography, which affects the hydraulic conditions for a given discharge. The presented approach enables the calculation of the LW quantity potentially mobilized by the flood of a certain magnitude indicating the degree of potential risk for the infrastructures located downstream. Plain Language Summary: Fallen trees (large wood) in rivers that are transported downstream during floods may be trapped on infrastructures such as bridges, weirs, and reservoir dams with their potential damage. Transported wood may also be deposited in the channel narrowings, raising water upstream, diverting flow, and enhancing scour of channel bed and banks. Hydraulic modeling combined with field surveys may be used as a tool for an assessment of the risk resulting from entrainment, transport, and deposition of large wood in rivers with vulnerable infrastructures. We used two‐dimensional hydraulic modeling to calculate the amount of entrained large wood in two valley segments of the central European Dyje River for eight flood scenarios ranging from low flow conditions to a 100‐year flood. The modeling results show large differences in the modes and quantity of entrained wood between the two surveyed valley segments. Topography of the inundation area in the confined valley setting of the Dyje River showed to be an important factor influencing hydraulic conditions and, therefore, wood entrainment during modeled flood events. Key Points: 2‐D hydraulic modeling of LW entrainment for eight flood scenarios showed significant between‐site variability in entrainment modesThe model results are sensitive to the precision of the digital terrain model and the correct localization of LW in the inundation areaThe valley‐bottom topography affecting flow hydraulics was an important variable affecting the onset of LW transport during model flood scenarios
- Subjects
CZECH Republic; WOOD; FLOOD risk; FLOOD warning systems; FLOODS; DIGITAL elevation models; RIVER channels; HYDRAULIC models; FIELD research
- Publication
Water Resources Research, 2024, Vol 60, Issue 4, p1
- ISSN
0043-1397
- Publication type
Article
- DOI
10.1029/2023WR035145