Journal of Hydraulic Engineering

Fusegates are the mechanical equivalent of a fuse plug. A typical installation consists of multiple gates placed on a spillway crest. When installed, the gates approximate the shape of a labyrinth weir in which each gate represents one cycle of the labyrinth. The gates are held in place by gravity. For a moderate range of reservoir levels, the water flows over the fusegates as it would over a labyrinth weir. If the reservoir level exceeds some predetermined value, the fusegate overturns by rotating about its downstream edge. Each gate is set to overturn at a progressively higher reservoir elevation. For the maximum design discharge, usually equivalent to the probable maximum flood, all of the fusegates tip and the entire crest length is available to pass the flow. Fusegates are supplied by the manufacturer in three standard configurations. The empirically derived discharge coefficients for these configurations are presented. General stability equations of fusegates are derived, and the tipping moments for one configuration is shown. A procedure to design a fusegate installation is outlined and is illustrated with an example. The advantages of a fusegate over a fuse-plug installation are that operation of the system can be controlled to within a few centimeters, it acts like a labyrinth spillway for flows that are less than some critical discharge, and that the entire installation is not lost for floods less than the probable maximum flood.

A design procedure for sizing gabion mattresses is presented that is based on depth-averaged velocity in the same manner as the Corps of Engineers' 1991 riprap-design guidance. This allows variation of gabion-mattress rock size and thickness with cross-section shape, channel alignment, and side slope. Stability is based on size of rock in the gabion rather than thickness, and stability coefficients are determined from flume-test results. Recommended mattress thickness and rock gradation are also presented.

A feed-forward back-propagation-type neural network was used to predict the flow conditions when interfacial mixing in stratified estuaries commences. This was achieved by training the network to extrapolate data from laboratory experiments performed over many years by several researchers. Before this training could be carried out, however, many decisions concerning the size of the network required and its training parameters had to be made. These decisions were made on the basis of successfully training a similar stratified flow condition, that of thermal wedges downstream of a power plant's outlet, where the theoretical solution is known. Finally, these results were compared with an approximate stability equation utilizing results from inviscid flow theory, rough turbulent flow theory, and laboratory experiments on interfacial friction. Although the agreement was not exact, it was close enough to predict what the stability conditions in real estuaries should be. This prediction was verified with the only prototype data available, that from three fjords, which agreed with both the neural network and theoretical results.

The water-surface profiles over the wavy bed and along the wavy side wall are analytically investigated using a Laplace equation. The nonlinear dynamic and kinematic conditions on the free surface are treated by the perturbation method and analytic solutions are obtained. As a result, the shapes of the crest of the water-surface profile are flatter in length than that of the trough over and along the wavy boundary in subcritical flow. In supercritical flow, the shapes of the crest are more peaked and shorter than that of the trough over and along the wavy boundary. The theoretical result of the water-surface profile of the open-channel flow over the wavy boundary is in good agreement with the experiments. The theoretical result for the flow along the wavy side wall in subcritical flow is also good agreement with experiment, but it in supercritical flow is not.

Surface bed-material sampling by grid methods produces particle frequency distributions that are not directly applicable to sediment-transport models. Appropriate conversion models are required to turn these distributions into volumetric frequency distributions. A conversion model has been widely applied in the past, in which grid-by-number particle distributions coincide with volume-by-weight distributions. This model was derived from oversimplified assumptions on particle shapes and sizes. In this paper the validity of that model is considered. A conversion model based on the statistical properties of homogeneous mixtures is presented, in which limitation is not introduced on the number of size fractions and on particle dimensions. The derivation of the new model allows for the application of the old one only in those circumstances, where an operational bias in sample collection is necessarily introduced. Results from the model proposed here are in good agreement with experimental results from other authors and with an extensive set of new experimental results obtained from the photographic analysis of bimodal and trimodal mixtures.

Bed roughness and rainfall impact affect hydraulic friction in overland flow. The relationship between friction, velocity, discharge, and channel slope was examined for the case of shallow, spatially varied flow on rough surfaces. Rainfall was simulated on artificially roughened surfaces in a laboratory. Measured flow velocities were compared to theoretical velocities computed from a dynamic equation for spatially varied flow and from the Darcy-Weisbach uniform flow equation. The measurements showed that the constant that relates the Darcy-Weisbach friction coefficient to Reynolds number can become larger than the theoretical value for smooth laminar flow. An analysis of the dynamic equation showed that frictional forces were much larger than forces resulting from changes in hydrostatic pressure and momentum. Water-surface profiles based on the Darcy-Weisbach friction equation nearly matched those from the dynamic equation for spatially varied flow. A regression was developed from the Darcy-Weisbach equation. The regression accurately predicted flow velocity when absolute roughness, rainfall rate, channel discharge, slope, slope length, and viscosity were known.

The eddy viscosity function, proposed in this note, is characterized by a damping coefficient, Γ_o, the asymptotic value for a large Reynolds number. It is related to the Reynolds stress in the near-wall region. As the Reynolds number decreases in pipes and subcritical open-channel flow, the velocity profile is progressively displaced from the universal log-linear relation, which is accounted for by increasing values of the damping coefficient. The inverse relation between the Reynolds number and the damping coefficient follows from an analytical solution of the velocity profile, which is composed of both a viscous and a turbulent component. The inverse relation, derived from the logarithmic gradient of the viscous component, also yields the minimum Reynolds number for completely turbulent flow. Furthermore, it provides the basis for the correlation of various characteristics in the laminar-turbulent transition and of heat and mass transfer coef-ficients. All of these relations, which are singular functions of the asymptotic value of the damping coefficient, Γ_o, support the cubic, rather than the quartic, variation of Reynolds stress and eddy viscosity in the near-wall region.