Large eddy simulation (LES) is used to investigate the evolution of Boussinesq gravity currents propagating through a channel of height H containing a staggered array of identical cylinders of square cross-section and edge length D. The cylinders are positioned with their axes horizontal and perpendicular to the (streamwise) direction along which the lock-exchange flow develops. The effects of the volume fraction of solids, φ, the Reynolds number and geometrical parameters describing the array of obstacles on the structure of the lock-exchange flow, total drag force acting on the gravity current, front velocity and global energy budget are analysed. Simulation results show that the currents rapidly transition to a state in which the extra resistance provided by the cylinders strongly retards the motion and dominates the dissipative processes. A shallow layer model is also formulated and similarity solutions for the motion are found in the regime where the driving buoyancy forces are balanced by the drag arising from the interaction with the cylinders. The numerical simulations and this shallow layer model show that low-Reynolds-number currents transition to a drag-dominated regime in which the resistance is linearly proportional to the flow speed and, consequently, the front velocity, U f , is proportional to t −1/2 , where t is the time measured starting at the gate release time. By contrast, high-Reynolds-number currents, for which the cylinder Reynolds number is sufficiently high that the drag coefficient for most of the cylinders can be considered constant, transition first to a quadratic drag-dominated regime in which the front speed determined from the simulations is given by U f ∼ t −0.25 , before undergoing a subsequent transition to the aforementioned linear drag regime in which U f ∼ t −1/2 . Meanwhile, away from the front, the depth-averaged gravity current velocity is proportional to t −1/3 , a result that is in agreement with the shallow water model. It is suggested that the difference between these two is due to mixing processes, which are shown to be significant in the numerical simulations, especially close to the front of the motion. Direct estimation of the drag coefficient C D from the numerical simulations shows that the combined drag parameter for the porous medium, Γ D = C D φ(H/D)/(1 − φ), is the key dimensionless grouping of variables that determines the speed of propagation of the current within arrays with different C D , φ and D/H.

Aquatic vegetation in rivers and coastal regions controls the flow structure in terms of mean velocity and turbulence. The vegetation in the flow affects the transportation of nutrients, microbes, dissolved oxygen, sediment, and contaminants; therefore, the flow characteristics of different types of vegetation layers should be examined in order to understand the effects of vegetation on the flow structure. In this paper, the effect of the submergence ratio and SVF (Solid Volume of Fraction) of a vegetation patch, which was present across half of the channel in a spanwise direction, on the flow structure at the wake region was examined. For this purpose, different submergence ratios with different SVFs were considered in the experiments, and velocity measurements were performed in the wake region of the vegetation layer with an Acoustic Doppler Velocimeter (ADV). According to the results, the effect of different vegetation heights and SVFs on the velocity distribution was obtained. Moreover, inflectional velocity distribution over the cross-section in the wake region of the vegetation layer was obtained, and it was concluded that jet flow occurred in the non-vegetated half of the channel due to the vegetation layer.

2 3The problem of propeller jet-induced erosion has significantly risen during the past three decades due to an increase in the manoeuvrability of ships. Therefore, propeller-induced scours need to be considered in the design of quay structures. In this study, the effect of slope angle on propeller jet erosion was examined. Three different slope angles of m 5 2?5, 2?0 and 1?5 were considered. Additionally, three different cases were considered, including an armoured layer with and without a toe apron and pile on an armoured layer with a toe apron. Flow velocity and scour measurements were performed in the experiments. For each slope angle, armour layer damage on the slope was defined by use of a damage level parameter. In addition, critical densimetric Froude numbers (Fr d,cr ) were defined for the start of damage at different slope angles.

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Urban stormwater is an important environmental problem, especially for metropolitans worldwide. The most important issue behind this problem is the need to find green infrastructure solutions, which provide water treatment and retention. Floating treatment wetlands, which are porous patches that continue down from the free-surface with a gap between the patch and bed, are innovative instruments for nutrient management in lakes, ponds, and slow-flowing waters. Suspended cylindrical vegetation patches in open channels affect the flow dramatically, which causes a deviation from the logarithmic law. This study considered the velocity measurements along the flow depth, at the axis of the patch, and at the near-wake region of the canopy, for different submerged ratios with different patch porosities. The results of this experimental study provide a comprehensive picture of the effects of different submergence ratios and different porosities on the flow field at the near-wake region of the suspended vegetation patch. The flow field was described with velocity and turbulence distributions along the axis of the patch, both upstream and downstream of the vegetation patch. Mainly, it was found that suspended porous canopy patches with a certain range of densities (SVF20 and SVF36 corresponded to a high density of patches in this study) have considerable impacts on the flow structure, and to a lesser extent, individual patch elements also have a crucial role.

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It has become increasingly important in recent years to study the effects of vegetation fields on the fluvial areas which are very important for the ecosystem. The water plant fields can be classified as submerged, emergent and suspended vegetation. The major difference of the suspended vegetation is the effect of the bottom boundary layer under the plant. Suspended vegetation is obstacle and will cause a decrease in speed of the flow and the vertical velocity distribution will deviate from the classical logarithmic distribution. Contrary the decrease in speed in the upper layer due to the plant, the speed increase will ocur in the gap beneath the plant. In this research, 181 rigid cylinders with a diameter of 1.0cm were fixed to a 30cm diameter wooden head and mounted on the upper side of the channel. The plant was allowed to enter into 15cm of water and there is a 15cm gap beneath the plant, between the channel bed and the plant end. An ADV (Acoustic Doppler Velocitymeter) was used to collect data from 11 different points (4 points before the plant and 7 points after the plant) and 8 different depths. Experimental results have shown that the suspended vegetation is a barrier to flow and affects the the velocity of the flow.