Modeling flow in a coral reef requires a closure model that links the local drag force to the local mean velocity. However, the spatial flow variations make it difficult to predict the distribution of the local drag. Here we report on vertical profiles of measured drag and velocity in a laboratory reef that was made of 81 Pocillopora Meandrina colony skeletons, densely arranged along a tilted flume. Two corals were CT‐scanned, sliced horizontally, and printed using a 3‐D printer. Drag was measured as a function of height above the bottom by connecting the slices to drag sensors. Profiles of velocity were measured in‐between the coral branches and above the reef. Measured drag of whole colonies shows an excellent agreement with previous field and laboratory studies; however, these studies never showed how drag varies vertically. The vertical distribution of drag is reported as a function of flow rate and water level. When the water level is the same as the reef height, Reynolds stresses are negligible and the drag force per unit fluid mass is nearly constant. However, when the water depth is larger, Reynolds stress gradients become significant and drag increases with height. An excellent agreement was found between the drag calculated by a momentum budget and the measured drag of the individual printed slices. Finally, we propose a modified formulation of the drag coefficient that includes the normal dispersive stress term and results in reduced variations of the drag coefficient at the cost of introducing an additional coefficient.

The hydrodynamics of freshwater macrophytes can be affected by the conditions in the field and storage procedure used prior to experiments • This impact is quantified as up to 30% of the drag coefficient, similar to the impact associated with using different macrophyte species • Higher levels of plant stress are associated with lower drag forces

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This paper describes the application of the two-dimensional (2D) modelling approach implemented in the open-source code Delft3D for the simulation of morphological development of a natural meandering river. A specific reach of the Dhaleshwari River (Bangladesh) for which field data has been available served as case study. The bed morphology and meander planform adjustment in the study area were simulated over a 10-year period considering a time-varying discharge scenario. The results showed that the 2D model was able to reproduce morphological characteristics such as scour depth, bank erosion and pool-riffle morphology, even though the model showed some deficiencies to reproduce bankfull channel width and transverse bed slopes. Regarding the planimetric evolution, the planform parameters (i.e., meander belt width, meander wavelength and radius of curvature) confirmed that the model results are realistic and are in agreement with results reported in the literature.

<p>The entrainment and transport of sediment by hydrodynamic mechanisms is strongly related to bed shear stress exerted by flow. Therefore, to quantify sediment transport and to determine sediment incipient motion conditions, accurate estimations of bed shear stress are required. Most of the existing methods used in hydraulics and river engineering to determine bed shear stress are indirect, and are mostly restricted to limited flow conditions or contain a large degree of uncertainty. Although devices to perform direct measurements of boundary shear stress exist, they are normally based on expensive technology. We developed a shear plate for direct shear stress measurements, using relatively low cost components. In this work we present preliminary results of measurements performed with the new shear plate, to characterize the bottom shear stress generated by a ship propeller. The data result in the expected quadratic relation between bed shear stress and jet velocities, and also give evidence of a good reproducibility. We show that the new shear plate appears to be a promising device for reliable measurements of submerged boundary shear stress under a wide range of environments and flow conditions.</p>