Journal of Hydraulic Engineering

The most common bedload transport calculation methods use an equation for the vector direction that is a linear function of the transverse slope. Existing theoretical formulations that account for nonlinear effects when transverse slopes are steep (such as noncohesive stream banks) are not widely used in practice, due largely to the complexity of their implementation. In this analysis, a single equation for the bedload transport rate direction is derived that accounts for the nonlinearity. The equation is cast in the same form as most linear formulations, but with the constant replaced by a function that requires the equation to be solved numerically. Negligible streamwise slopes are assumed, which allows the simplified expression; otherwise, the derivation follows past rigorous theoretical treatments that are valid for transverse slopes up to the angle of repose. A direct comparison is made between linear and nonlinear derivations that highlights the approximations inherent in the linear form. Application of the equation to two different types of past experiments illustrates the degree of error associated with evaluating bedload data involving steep transverse slopes using a traditional linear form for the vector direction.

Piano key weirs (PKWs) are a weir type characterized by an effective rating curve. Accordingly, this control structure is primarily applied at dams to increase the spillway capacity. In recent years, PKWs also have been implemented in rivers combined with low-head hydropower or to regulate waterways. For the latter application, a weir type without gates may be favorable, but the issue of the passage of sediments arises. Such sediments are either deposited in the backwater or transported to the weir during intense floods. An efficient sediment passage is necessary to avoid inundations upstream of the weir and to maintain a navigable waterway. Two options arise: (1) to flush the sediments (e.g., through a gate in the weir), or (2) to carry them over the weir crest. The second option is favorable, if upstream riverbed aggradation can be avoided, because no mechanical devices (i.e., gates) are used. This study analyzed the sediment passage over a PKW driven uniquely by the flow. Systematic physical model tests were conducted to study the upstream riverbed behavior as well as the passage of sediments over the PKW. Three PKW configurations, two sediment granulometries, and six discharges were considered. Key results refer to the modified rating curve under high riverbed levels and to the upstream scour process of sediment deposits. Finally, the sediment passage capacity was linked to the equilibrium sediment transport conditions upstream of a PKW. Pragmatically formulated, this relation indicates—at least for the tested configurations—that sediments arriving at the PKW also pass over it.

Turbidity currents are generated when denser river water plunges and flows along the bottom of a lake, reservoir, or ocean. The plunging and downstream movement are driven by density differences due to temperature and/or suspended sediment, and currents have been observed to move slowly over long distances. This study presents observations of multiple turbidity currents in a large reservoir in California, United States, during runoff events following a major wildfire in the upstream watershed. Several aspects of the currents are documented and discussed, including the conditions leading to plunging, the vertical and longitudinal structure of turbidity within the currents, the velocity of the currents, and the development of a muddy lake upstream from an old submerged dam in the reservoir.