Journal Article

Evaluation of Different Numerical Approaches to Modeling Flood Flows Over Groynes

Mosselman, Erik, Yossef, Mohamed F. M., Ambagts, Lindert, Yildiz, Burhan

2024

Overview

The hydraulic resistance of groynes is an important factor in the determination of design flood water levels on rivers and the assessment of how much these levels are lowered by modifying the groynes. In standard one‐ or two‐dimensional numerical hydrodynamic models for flood risk management, groynes are commonly represented as subgrid features with a local energy loss according to a weir formula. We tested this representation by using a two‐dimensional horizontal mesh at various groyne submergence degrees by comparing the results with those of flume experiments. We also compared the results with simulations using different 2D and 3D approaches on finer grids that incorporate groynes in the bed topography. In one of the two tested 3D models, complete Reynolds‐averaged Navier‐Stokes equations were solved. The second tested 3D model was constructed simpler by assuming hydrostatic pressure distribution in the vertical direction. We employed Delft3D software in construction and execution of all models. One of the 3D models did predict the hydraulic resistance at low submergence better than the standard model, but it slightly underestimated the resistance at higher submergences. Despite differences in flow characteristics, weirs and groynes were found to produce similar flow resistances for the same height and boundary conditions. Simulations of groyne modifications showed that hydraulic resistance decreased nonlinearly with groyne lowering and streamlining. Plain Language Summary Groynes are used for river training. Their positive effects include riverbank stabilization, improvement of navigability and prevention of ice jams. However, during floods they become submerged and increase the flood water depths by blocking the flow and increasing turbulence. This may lead to severe outcomes. Floods are among the most fatal disasters that affect the globe. Even an increase of flood water depths by some centimeters may cause disastrous outcomes. Engineers generally resort to approximate solutions for adding the effects of groynes into hydraulic flood models for long river reaches. In this paper, we assess the capabilities of these approximate models as well as those of more simplified and more advanced models. Insights were sought to help flood modelers for better prediction of flood water levels. Our study shows that the most widely used groyne resistance model leaves room for further development, despite demonstrated capabilities. Key Points Characterizing the effect of groynes on river flow in two‐dimensional hydrodynamic models by using weir formulas was evaluated Alternative methods to implement groynes into two‐ and three‐dimensional river models were proposed, and their reliability was tested The performances of two of the available modeling options in simulating the groyne modifications were assessed

• Publisher: John Wiley & Sons, Inc,Wiley
• Subject: 2DH model / 3D model / Boundary conditions / computer software / Disasters / energy / Energy loss / Energy losses / Environmental risk / Flood forecasting / Flood management / Flood models / Flood predictions / Flood risk / Floods / Floodwater / Flow characteristics / Flumes / groyne modifications / Groynes / hydraulic flumes / hydraulic resistance / Hydraulics / Hydrodynamic models / hydrodynamics / Hydrostatic pressure / Ice jams / numerical model / Pressure distribution / Risk management / River banks / Riverbanks / Rivers / subgrid representation / Submergence / Three dimensional models / topography / Turbulence / Vertical distribution / water / Water depth / Water levels / Weirs