The catastrophic failure of the spillway chute at Oroville Dam in February 2017 raised concerns throughout the water resources industry regarding design, construction, and maintenance practices for concrete spillway chutes, especially joints and cracks that could allow penetration of high-pressure water into a chute foundation. The independent forensic team investigation found that hydraulic jacking was the most likely cause of the initial chute slab failure, highlighting a need for better analysis of the hydraulic jacking potential of existing spillways and more resilient designs for spillways that operate under high-velocity flow conditions. This paper reviews the Oroville Dam event and findings and previous laboratory testing performed to evaluate uplift pressures and flow transmitted through spillway joints. A reanalysis of previous studies was used to develop relations between chute velocity, joint geometry, and uplift pressure transmitted into a joint. Uplift pressure head in these relations is expressed in a dimensionless manner, either as a percentage of the velocity head in the boundary layer at midheight of the offset into the flow, or as a percentage of the channel-average velocity head. The first approach is potentially more useful for prototype applications, but the second method provides the best fit to the available experimental data. Additional research is still needed to quantify rates of flow through open joints, confirm relations between uplift pressure and boundary layer velocities, and evaluate the effects of aerated flow.

Spillways of large and small dams experience flow conditions that exceed the capabilities of common water surface profile computer programs. Unique channel geometries, steep slopes, and streamline curvature demand rigorous mathematics, while phenomena associated with aerated flow and potential cavitation require special analyses, especially for stepped chutes. SpillwayPro is a generalized, energy-based, water surface profile calculation tool for both smooth and stepped chutes that integrates cavitation analysis and aerated flow effects, with separate modules supporting aerator design and the development of optimized structure profiles that meet cavitation parameter objectives. Simultaneous calculation of smooth and stepped-chute flow profiles enables the rapid assessment of the energy dissipation benefits of steps, as well as their unique aerated flow and cavitation issues. SpillwayPro’s technical basis is presented, and its results are compared to the data from prototype case studies and empirical methods developed from large-scale laboratory studies. SpillwayPro’s fundamental energy-based methods are useful for cases that differ from idealized empirical approaches and would benefit from a more rapid analysis than can be accomplished with physical or computational fluid dynamics (CFD) modeling.

New construction practices for roller compacted concrete (RCC) overlays and stepped chutes are changing the step geometry from a traditional square-edge, vertical face to a 45° beveled face. A large-scale 3(H):1(V) (i.e., θ = 18.4°) stepped chute model was tested with a 45° beveled face step with a height (h) of 152 mm. Results were compared to data on square-edge, vertical face steps previously obtained. The distance to the inception point of free-surface aeration normalized by the surface roughness was reduced approximately 25% for the same Froude number defined in terms of roughness height. An existing inception point relationship for vertical face steps was adjusted with a best fit correction factor to predict the free-surface inception point for this chute slope and beveled face angle. Relative flow depths, mean air concentration, and energy loss data showed similar general trends for vertical face and beveled face steps, but the depths and air concentrations for beveled face steps were slightly higher for equal values of relative free-surface inception point, L_i/L, and relative step height (e.g., h/d_c). Energy loss at the free-surface inception point ranged from approximately 20 to 40% of total head for both step types. Additional research is needed to determine the generalized effects of the bevel angle and the chute slope on flow properties. This research is expected to be used by field engineers for the design of stepped chutes with beveled face steps.

New laboratory experiments were conducted on a radial gate to evaluate the energymomentum procedure for calibration. Prior work had used an artificial energy correction, E_corr, to match observed conditions. In the current work, non-hydrostatic pressures, velocity, and momentum distribution coefficients were used instead. This avoids the quirky behavior associated with E_corr. Non-hydrostatic pressure distributions were found in the jet, but they had an insignificant influence on the head-discharge calibration. Velocity-distribution coefficients were added to both the energy and momentum equations. The value of the momentum coefficient was related to the relative submergence; roughly 1.08 for low submergence, increasing to 1.3 at high submergence. For this data set, the energy equation was able to predict free-flow discharge within ± 2%. The energy-momentum equations were able to predict the discharge for submerged flow to ± 5% when the downstream channel width was equal to the gate chamber width, and within ±8% for a wider downstream channel. No improvement was found for estimating the wall force exerted downstream when the tailwater channel is wider than the gate. These new calibrations have been implemented in the new WinGate software.

Coanda-effect screens exclude coarse and fine debris from a variety of water intakes. Water overflows an inclined wedge-wire screen with tilted wires that shear high velocity flow from the bottom of the water column. The screens hydraulically self-clean, making them ideal for remote, nonpowered sites. Flow conditions vary widely over the length of most screens. Previous testing related flow capacity to gravitational, surface tension, and viscous forces, but the range of flow conditions was limited versus potential applications. This study tested small sections of prototype-scale screens at varying slopes, and discharge coefficients were related to Froude and Weber numbers. Tests with variable water temperatures proved that screen performance is independent of Reynolds number and viscosity, but depends strongly on surface tension. Several screen geometries (i.e., wire size, shape, and slot size) were tested, and the performance of all screens could be modeled with power curve functions of the Weber number modified by the Froude number. Individual screens exhibited some unique performance characteristics, but 10 of the 13 screens could be modeled effectively as a group.