Journal of Hydraulic Engineering

Failure to purge seawater from the diffuser section of ocean outfalls can cause seawater to circulate through the diffuser section of the outfall. Tunneled outfalls with their long risers are particularly susceptible to this problem. Seawater circulation reduces the hydraulic efficiency of an outfall and there is a possibility that the diffuser may ultimately be blocked by accumulated sediments and marine growth. Purging capability is therefore a fundamental design consideration for ocean outfalls with long risers. While theoretical models can provide upper bounds to the purging flow, the details of the purging process are complex and not amenable to theoretical analysis. Consequently, hydraulic models are a valuable aid to the design process for these types of outfall. The paper develops the model scaling laws appropriate to high riser outfalls. These are based on the various physical interactions involved in the purging process and it is shown that fluid inertia, buoyancy, friction and entrainment all play a role in defining the scaling laws.

A 1:16‐scale hydraulic model of the actuator cover‐plate assembly of the Dwight D. Eisenhower Lock ice‐flushing system in the St. Lawrence River, operated by St. Lawrence Seaway Development Corporation, U.S. Department of Transportation, Massena, New York, is used to obtain basic design loads for a new assembly design. The ice‐flushing bypass system was originally installed in 1981 in the existing filling and emptying culvert. The model investigation includes tests of two basic layouts of the cover‐plate assembly that failed in the prototype and the determination of preferable configurations based on the measured live‐load pressures. The investigation reveals potential for cavitation damage due to extremely high velocities in the main culvert of the lock. The investigation also provides useful engineering data for redesigning the actuator cover‐plate assembly. The new prototype assembly has not experienced any problems in the past seven years.

A theoretical investigation of local scour downstream of grade‐control structures based on two‐dimensional jet diffusion and particle stability is experimentally verified. Turbulent jet diffusion reduces fluid velocity near the bed particles and equilibrium scour is obtained when noncohesive bed particles cannot be removed from the scour hole. Equilibrium scour depth is written as a function of velocity, flow depth and particle size. The theoretically derived equation is remarkably similar to the regression equations reported in the literature. The experimental investigation uses a large‐scale physical model with unit discharge up to $2.5m^2/s$ (27 sq ft/sec) and scour depths exceeding 1.4 m (4.6 ft). When combined with previous data sets at smaller scales, a total of 231 scour‐depth measurements cover a wide variety of conditions: wall to vertical jets, small to large flow submergence, and various face angle slopes. The agreement between calculated scour depths and laboratory measurements is satisfactory considering the wide variety of configurations analyzed.

Reliability and flexibility in the face of failure conditions are implied aspects of redundancy in water‐distribution networks. Explicit and comprehensive ways to measure either the reliability or the redundancy of water‐distribution networks have not yet been developed. In this paper a measurement of the redundancy inherent in the layout of water distribution networks is developed using an axiomatic approach based upon the desired properties of such a measurement. The local redundancy at a node and the redundancy imposed by redundancies at adjacent nodes (global redundancy) are addressed by the measurement. The measurement is examined in an application to candidate layouts obtained from the solutions of a distribution layout design model. A comparison between redundancy measurements and network performance, as indicated by percentage of flow supplied under a range of link failures, demonstrates that an increase in the value of redundancy, as measured by the entropic parameter, increases the ability of the water‐distribution network to respond to failure problems in the network. The value of the measurement in design is demonstrated by its use in the least‐cost design of an example network.

The use of the variational principle to maximize the entropy is illustrated for possible applications in open‐channel flow study. The illustrations include those in: (1) Modeling of velocity distribution by probabilistic formulation and entropy maximization; (2) relating the entropy to the parameters of velocity distribution models; (3) relating the entropy to the energy and momentum coefficients; (4) relating the mean velocity given by the Manning's equation to the velocity distribution and the entropy; and (5) relating the entropy to the locations of the mean and maximum velocities in a channel cross section. The “entropy parameter” M and the maximum velocity $u_{\max }$ are emphasized as important new parameters. Many flow properties can be expressed in terms of M. Knowledge of $u_{\max }$ is equivalent to knowing the range of flow velocity in a channel cross section, an important statistical parameter, which along with the mean velocity can completely describe the probability‐density function of flow velocity and, hence, the velocity distribution and other related flow properties. Such a concept is new to open‐channel hydraulics.

An efficient channel‐flow routing scheme for large drainage networks with compound sections and for continuous long‐term simulation is often needed for sediment and water‐quality investigations. A Muskingum‐Cunge channel‐flow routing scheme is adopted for this purpose. Main channel and overbank flow in compound cross sections are decoupled and routed separately to quantify the different flow characteristics in each channel portion. A variable time step is introduced to increase the efficiency of the numerical scheme. The adaptations of the channel‐flow routing scheme are tested against hydraulic channel‐flow routing using the DAMBRK model. Test conditions consist of several hypothetical flood hydrographs in long prismatic channels with significant overbank storage. For the tested cases, hydrograph peak and time to peak are, on the average, within 4% of the results from hydraulic routing. Simulated hydrograph shapes are consistent with expectations, and hydrograph distortions, resulting from overbank flood plains, are well reproduced. Furthermore, execution time of the numerical scheme is generally more than one order of magnitude faster than the benchmark hydraulic routing.

Dye‐concentration measurements are conducted in the recirculating region of a sudden open‐channel‐flow expansion, where the water depth is shallow compared with the horizontal length scale of the channel expansion. The turbulent motion is anisotropic, and is subjected to a stabilizing bed‐friction influence, in the confinement between the free surface and the channel bed. Two opposing mechanisms affect the transverse mixing processes in the shallow recirculating flow. On the one hand, the transverse mixing is reduced by the stabilizing bed‐friction effect. On the other hand, it is enhanced by a confinement effect, which becomes effective when the width‐to‐depth ratio of the channel expansion exceeds a value of about $9\sim 12\text{.}$ These opposing influences are equally significant in the range of the bed‐friction number from 0.08–0.10. The concentration data of the present investigation are complementary to the published velocity data obtained in the same recirculating flows. Both sets of data are useful for model calibration of shallow open‐channel flows.

The most commonly encountered particles in the areas of sediment transport, fluidization, sedimentation, etc. are nonspherical. The role of these particles can be ascertained only through the knowledge of drag coefficient and fall velocity. Graphical relationships for the determination of drag coefficient and fall velocity are available in the literature. The graphical relationships are less accurate because they are subject to errors of judgment. Furthermore, these relationships cannot be used for any analytical purposes. In 1954, Schulz et al. collected extensive data for the drag coefficient and fall velocity of nonspherical particles. Based on these data, empirical equations for the drag coefficient and fall velocity of nonspherical particles of natural and mechanical origin are derived from curve fittings and presented. It is hoped that these equations will find use in the analytical modeling of various engineering problems involving fluid‐nonspherical particles interaction.

Flume studies were conducted in which riprap-protected embankments were subjected to overtopping flows to determine the average interstitial velocity of the through-flow. Velocity measurements were made in riprap having median stone sizes $D_{50}$ ranging from 1.02 in. (2.6 cm) to 6.2 in. (15.8 cm) on embankment slopes of 1–20%. A tracer solution injection and recording system was developed to estimate the through-flow velocities. The average interstitial velocities for 19 flume tests were measured and reported. A predictive relationship was developed in which the average interstitial velocity was a function of the embankment slope and rock size $D_{10}$. Flow measurements varied ±40% about the average velocity.

An experimental investigation of the influence of cross-sectional geometry on the discharge capacity of rectangular and compound channels is presented. It is found that a wide rectangular channel carries as much as 80% less than a narrow rectangular shape, and as much as 25% less than a compound shape of the same overall width, for the same cross-sectional area, and bed slope. Comparison of friction factors reveals that values in a wide rectangular channel could be as much as 45% greater than in a narrow rectangular section, and as much as 25% greater than in a compound section of the same overall width. The findings show the danger of ignoring shape effects in open channels, and underline the need for a systematic investigation of their influence on discharge capacity.

The aim of this technical note is to evaluate the effect of the maximum precipitation of synthetical hyetograph on rainfall hydrograph generation. Fourteen intense storms of long duration are analyzed. The results show an important variation of the coefficient r in relation to the rainfall duration. While the choice of a constant value of coefficient r makes it, in fact, easier to apply the method of synthetic hyetographs, in certain cases the optimization of a storm sewer network requires a variable value of r in time. The application of this approach to an urban basin in the Moncton area results in two hydrographs with practically the same peak discharge, but displaced in time.