Journal of Hydraulic Engineering

The stepped spillway design is associated with significant flow resistance and associated energy dissipation on the steps, yielding smaller, more economical downstream dissipation structures. A number of design guidelines were developed for steep stepped spillways typical of concrete gravity dams. The focus of this study is on embankment stepped spillways. A large set of air-water flow data is compared with reanalyzed data sets to provide a simple unifying design approach for the residual energy at the stepped chute’s downstream end and to highlight the uncertainties involved. The results provided some simple design criteria in terms of the dimensionless residual energy of stepped chutes with flat steps. It is believed that a stepped design with a $1V:2.5H$ slope ($\theta =21.8°$) might be optimum in terms of energy dissipation performances. The Darcy-Weisbach friction factors were close for all stepped data ranging between $0.1\le f_e\le 0.4$.

The aim of this research is to measure the clear-water scouring produced by supercritical flow around a rectangular-shaped obstacle. The initial uniform flow condition without the obstacle is such that the Shields parameter remains slightly lower than critical so that the sediment constituting the mobile bed is not transported. The sediment begins to move after the obstacle is suddenly inserted; the two-dimensional (2D) water surface and the 2D bed topography fields around the obstacle are then measured at specific times after this. The initial flow pattern exhibits a typical bow-wave like hydraulic jump detached upstream from the obstacle that occurs over the rough plane bed. For the more widely studied subcritical regime configuration, the scour initiates on the sides of the obstacle and migrates towards its upstream face where the scour depth continues to increase over time. This causes the hydraulic jump to migrate downstream, approaching the obstacle with negligible effect on the bed topography. Downstream from the obstacle, the sediment deposits and forms a specific deposition zone whose maximum elevation also increases with time before reaching a plateau. The flow pattern downstream of the obstacle is strongly influenced by this deposition and exhibits two consecutive bow-waves aligned in the streamwise direction with the hydraulic jump located upstream. The experiment runs for two hours and even though all evolution rates decrease with time, this duration is not sufficient to obtain a stable situation of the flow pattern and bed topography. This paper ends with a similarity analysis of the typical field conditions for which this clear-water scouring process could occur.

When subjected to a strong swirling jet flow induced by a rotating ship’s propeller, the bed of a waterway may undergo significant changes. These changes will not only cause instability to quay structures and damage the protection work of the beds/banks of rivers and canals, but also resuspend the bed sediment. The latter likely will pollute the water column and affect the aquatic life. In this study, the propeller-jet velocity and sediment-concentration profiles downstream of a propeller are measured using an acoustic Doppler velocity profiler and a suction device, respectively. The estimates obtained by using formulas for the axial velocity and four published methods for calculating the reference near-bed concentration of suspended sediment are compared with the experimental data. Moreover, the behavior underlying the temporal and spatial variations in seabed scour and sediment suspension is also investigated. A new set of equations for estimating the sediment concentration profiles is developed. The new equations generally yield reasonably good estimates of the reference concentration and Rouse number at the measurement locations within the scour hole and on the deposition mound. The proposed modified Rouse equation produces reasonable predictions that are consistent with the experimental data.

River ice complicates river hydraulics and morphodynamics by adding a new boundary layer to the top of the flow. This boundary layer affects the velocity distribution throughout the depth due to increased flow resistance, and varies the local boundary shear stress on the bed (lower boundary) by adding new shear stress on the upper boundary (under surface of the ice). Variation of shear stress plays an important role in incipient motion of upper and lower boundary materials: sediment motion and transport are directly affected by local boundary shear stress, as are ice cover thickness, condition, and progression. This paper provides estimates of upper and lower boundary shear stress during stable ice cover and the important stage of ice cover breakup using available methods based on continuous field measurements of velocity profiles obtained with a bottom-mounted acoustic Doppler current profiler in the Nelson River, Canada. Boundary shear stresses varied dynamically with transformation of the ice cover, including the presence and removal of slush ice and formation of the ice jams. Estimated upper boundary shear stress varied between 0.52 and $23.87\mathrm{N}/{\mathrm{m}}^2$, whereas lower boundary shear stress varied between 1.51 and $2.40\mathrm{N}/{\mathrm{m}}^2$, with the highest values observed during breakup. These values are compared with estimates from previous laboratory experiments.

Since the construction of the Tamiami Trail in the 1920s, overland flow to the Florida Everglades has decreased significantly, affecting ecosystems from the wetlands to the estuary. As part of the effort to return flows to historical levels, several changes to the existing water management infrastructure have been implemented or are in the design phase. These changes include the construction of two bridges [a 1.6-km (1-mi) and a 4.2-km (2.6-mi) bridge] and the removal of the Tamiami Trail roadway, as well as increasing canal water levels to increase head elevations north of Everglades National Park (ENP). A numerical model of ENP hydrology was developed using MIKE SHE/MIKE 11 software to review the effects of these structure changes and evaluate the potential impact of bridge construction. Model simulations show that the newly constructed 1.6-km bridge along the Tamiami Trail could increase water delivery to the Northeast Shark Slough (NESS) by about 6%. The 1.6-km bridge, plus the proposed 4.2-km bridge, could increase flows by about 10% from the baseline. These simulations also show an increase of flow to the eastern canals by less than 1% for each scenario, demonstrating that bridge implementation along the Tamiami Trail will have a minimal impact on eastern canal operations and flood management. The percent probability of water levels exceeding baseline conditions was determined for the simulation period. This analysis showed that the length of time of inundation, or the hydroperiod, would increase for large areas of the park with the introduction of each bridge. Additional simulations were conducted to demonstrate the effect of proposed water-level increases for canals north of the park. Raising water levels in the canal by up to 0.3 m (1 ft) increased overland water levels up to 21 cm in some areas within ENP. These simulations demonstrate that a general increase in water levels and hydroperiods within ENP will be achieved by adding bridges to the Tamiami Trail roadway and by increasing water levels in the canal.

Run-of-the-river hydropower is a typical form of power generation in mountainous regions. This study investigates the velocity field upstream of Aberfeldie dam, a run-of-the river facility on the Bull River near Wardner, British Columbia, Canada. As is typical for these types of run-of-the river facilities, the headpond of this dam is very shallow (approximately 1 m deep) because of long term sediment deposition. Near the facility’s power intakes, a large scour hole has been created because of increased velocities induced by the intakes. This study conducted field measurements and developed a computational fluid dynamic (CFD) model to investigate the velocity field under various flow conditions. The CFD solver shows in a simplistic way that flow-induced bed shear stress likely causes a fluctuating, dynamic bed form that varies by season and the distance upstream, so that a consistent velocity pattern is seen across the entire headpond. The velocity field generated by the CFD solver is used to evaluate the entrainment risk of mountain whitefish and westslope cutthroat trout based on swimming mechanics and life stage. The unique habitat conditions generated by the scour hole act as an attractant to the high risk zone, greatly increasing fish density adjacent to the intakes at this facility.

The Vajont disaster was caused in 1963 by a landslide of about 270 million cubic meters that fell into a hydroelectric reservoir and generated a wave about 200 m high which overtopped the dam and caused 1917 casualties. With the aim of assessing why the real wave height was underestimated, a series of two-dimensional experiments were performed at the University of Padua in 1968 considering a scale characteristic cross section of the Vajont basin near the dam: the landslide was pushed into the stored water by a moving plate over the sliding surface and the maximum wave run-up along the opposite mountain side was measured as a function of the landslide falling time. Some of these results have been compared to smoothed particle hydrodynamics numerical simulations in which both water and noncohesive sediment are simulated as weakly compressible fluid; water is treated as Newtonian fluid while a proper rheological model is adopted for the landslide to mimic its non-Newtonian behavior. The computed falling time and maximum wave run-up are in good agreement with the results from the 2D laboratory experiment which is closer to the real event.

Free surface, axially symmetric shallow flow is analyzed in both the centrifugal and centripetal directions. Referring to the inviscid steady flow over a flat plate characterized by a unique value of specific energy, the analytical sub- and supercritical solutions are determined. Furthermore, the sub- and supercritical steady solutions for the flow with friction over a flat plate are determined, provided that inertial terms are important compared with frictional terms. In the inviscid case, the sub- and supercritical solutions over a bottom topography are determined, provided that the bottom unevenness is compatible with a continuous solution. In the fundamental case of inviscid flow over a flat plate, the discontinuous solution also is analyzed for a direct hydraulic jump imposed by proper boundary conditions. In the simple scheme of an inviscid shock of zero length, the jump position and the sequent depths are analytically derived, thus indicating that all results are uniquely functions of one dimensionless number, i. e., the specific energy ratio between the sub- and supercritical flows.