Aquatic vegetation can influence hydraulic performance in channels, rivers, and floodplains. Most previous studies used cylindrical stems to simulate vegetation, while few studies used shrub-like or sedge structures that exhibited a maximum width near the top of the vegetation. In contrast, this research focuses on shrub-like structures that show a maximum width near the bottom of the vegetation. To understand the effects of aquatic vegetation on velocity distribution, water surface profile, and energy loss, experiments have been conducted in an open channel with a rectangular cross-section. The results indicated that the streamwise velocity within the lower layer remains nearly constant with depth where z/y is less than 0.20. However, once z/y exceeds 0.20, the streamwise velocity increases rapidly as the depth increases toward the water surface. Additionally, the shape of the vegetation influences the position of the inflection point. Moreover, the water level rises upstream of the vegetated area, decreases within it, and gradually returns to the normal depth downstream. The bed slope has little effect on relative energy loss, with maximum values reaching 6.61%, while the presence of vegetation leads to a significant increase, reaching up to 22.51%. The relative energy loss increases with a higher submerged ratio. A new empirical equation is proposed to estimate the relative energy loss in vegetated channels.

The Manning Equation is widely used in hydraulic engineering to estimate mean velocity and discharge in open channels. This equation is based on various parameters, with the roughness coefficient being the most crucial factor. The nature of the channel is the primary factor in estimating this roughness coefficient. In vegetated channels, several factors affect the roughness coefficient, including water depth, velocity, friction slope, type, height, and density of the vegetation. In this research, an experimental investigation is conducted to analyze the roughness coefficient caused by submerged and floating vegetation. Artificial flexible elements made of perspex are used to simulate submerged vegetation, while foam integrated with aluminum wires is utilized to represent floating vegetation. The roughness coefficient values are estimated for various discharges (25.0, 30.0, 35.0, and 40.0 l/sec), flow depths (0.25, 0.30, and 0.35 m), and friction slopes in both non-vegetated and vegetated channels with various bed slopes (0.0010, 0.0020, 0.0023, 0.0049, and 0.0062). An analysis of the relationship between the roughness coefficient and the Froude number reveals that this coefficient exhibits a power function relationship with the Froude number. The roughness coefficient increases with higher friction slopes and decreases as the Froude number rises. Additionally, the presence of vegetation significantly increases the roughness coefficient from 0.032 to 0.098 when the submerged ratio is 0.94, the bed slope is 0.0062, and the Froude number is 0.19. The roughness coefficient further escalates with higher submerged ratios. New empirical equations have been developed to estimate the roughness coefficient.

Piano key weirs (PKWs) increase the effective crest length and provide high discharge capacity within limited spillway widths; however, their hydraulic efficiency depends on key geometry. Addressing the limited understanding of key-curvature effects, this study systematically investigates the influence of inlet- and outlet-key curvature on the discharge coefficient (C_d) and crest-wise discharge distribution of type-A PKWs. Nine configurations are examined experimentally in a flume at the Hydraulics Research Institute, Egypt. These include a reference model with linear inlet and outlet keys and modified geometries incorporating C- and S-shaped keys in both normal and inverted forms. Experiments are conducted under free-flow conditions for total-head ratios H_T/P up to 0.23, where H_T is the total upstream head above the crest and P is the PKW height. A three-dimensional numerical model using FLOW-3D HYDRO is validated against these experimental data and subsequently extended to H_T/P ≈ 0.50–0.60. All reported results and conclusions are based on the numerical simulations over the full investigated range. Results show that C_d increases to a peak near H_T/P ≈ 0.08 and then decreases gradually for all configurations. Both inlet- and outlet-key curvature influence hydraulic performance by modifying flow guidance and redistribution along the crest. However, only the inverted C-shaped inlet configuration (M2) improves efficiency, increasing C_d by about 5.46% on average over the investigated head range and enhancing the total discharge by approximately 4.36% at H_T/P ≈ 0.12 relative to the reference case. Discharge-distribution analysis indicates that this improvement results from inlet feeding and efficient flow conveyance along the sidewall crest. A predictive relation is developed for the optimal configuration to support hydraulic design.

Local scour due to free hydraulic jump downstream hydraulic structures may cause damage or complete failure of these structures, so controlling of this phenomenon is very important. The main goal of this study is to reduce the characteristics of a scour hole downstream sudden expansion stilling basin. An experimental study was conducted to study the effect of expansion ratio and position of the sill. Ninety experimental runs were carried out considering the wide range of Froude numbers ranging from 3.42 to 8.67. Five values of the expansion ratio (e = 2.73, 1.92, 1.76, 1.50 and 1.25) and four values of the relative position of lateral single sill (Lx/LB = 0.20, 0.30, 0.40 and 0.50) were investigated. The dimensional analysis was employed to drive expressions correlating the different variables affecting the scour phenomena. It was found that, the flow patterns in most of the cases were a symmetrical and the resulting scour and deposition were also a symmetrical. The relative scour depth, the relative scour length and the relative energy loss, increase by increasing the initial Froude number and vice versa. The expansion ratio (e = 1.50) gives the minimum values of scour dimensions. The best location of the sill for reducing the scour dimensions at 0.30LB from the gate opening. Prediction equations were developed using the multiple linear regression (MLR) to model the relative scour depth Ds/y1 and the relative scour length Ls/y1.