Journal of Hydraulic Engineering

A study has been undertaken to determine the effect of walls in the modeling of flow through porous media. Two primary influences of the wall are identified: packing effects for an unconsolidated porous medium and viscous effects on the flow. The packing effect is considered through a series of experiments to arrive at an expression for the bulk porosity as a function of the ratio of particle diameter to pipe diameter. From this expression, and assuming that the region of greater haphazard packing occurs at a distance approximately one particle radius from the wall, a porosity of the wall region is determined. The viscous effects are accounted for by incorporating the Brinkman's extension term in the momentum equation. The combined effects are considered by employing a two region model for the fluid mechanics.

In combining open channel flow, the rise in the upstream flow depth due to the effect of lateral inflow from the branch channel can be significant. For right‐angled, sharp‐edged junctions of rectangular channels, a relation between the depth of flow at the junction and the ratio of the lateral discharge to the total discharge is derived on the basis of the momentum principle. Using this relationship, one can predict the rise in the flow depth when the undisturbed flow conditions in the channels are specified. In the proposed model, the contribution of the momentum transfer from the branch channel to the main channel is included, as this factor can be significant when the lateral discharge is relatively large. The proposed relationship is verified with the results of experiments related to combining flows for which the flow conditions downstream of the junction are both critical and unsubmerged. The study of combining flow at right angle junctions has a direct application in drainage network systems and river engineering.

Nonequilibrium analytical solutions are presented for fully penetrating wells by incorporating the concept of the existence of a non‐Darcy flow regime around the pumping well and a Darcian flow regime away from the well. For this purpose, an approximate procedure is proposed to find the distance to which the non‐Darcy flow extends. This distance is referred to as the critical well radius, which divides the whole flow domain into nonlinear and linear flow zones with distinctive hydraulic characteristics. The nonlinear flow law is characterized by the Forchheimer equation. Detailed expressions are derived separately for the specific discharge calculations for each zone. Depending on the observation well locations, drawdown distributions and subsequently relevant type curves are developed mathematically for each zone. Various limiting cases are discussed and their physical implications in the practical applications are exposed. In general, linear regime zone type curves converge asymptotically, for large times as well as distances, to the Theis type curve, whereas such a convergence is valid for the nonlinear flow regime, but for small times only.

The effect of swirl on air transport in a vertical drop shaft is described. Laboratory experiments on a vortex‐flow drop shaft showed that most of the air is entrained in the annular hydraulic jump that is formed when the annular jet flow changed to the pipe‐full flow. A significant portion of the air bubbles converged due to an inward pressure gradient toward the center of the drop shaft, coalesced to form large bubbles, and then rose toward the surface. A large number of air bubbles still were carried downstream for flow conditions where the jump occurred at the location of low circulation. The air transport rate down the drop shaft was virtually zero if the jump formed in the strong circulation flow‐region. The theoretical analysis indicates that the amount of air transported downstream depends upon the swirl number. The air concentration decreases with the increase in the swirl number.

Resistance to flow in unvegetated gravel‐bed rivers is basically dependent on the skin resistance, due to surface bed material, and bar form resistance, due to accelerations and decelerations in the flow between pools and riffles. Although flow is generally nonuniform, at riffle sections flow is locally uniform. It is these sections which principally control the velocity‐depth characteristics of the reach since hydraulic conditions in the pool result from the backwater effect of the riffle. Isolating the effect of bar forms on flow resistance is achieved by first establishing the roughness height of the surface bed material on the riffle. Overall resistance to flow, in terms of the total roughness height due to bed forms and grains for equivalent uniform flow, is determined from the riffle and reach average flow geometry and the grain roughness height. Differences between total and grain roughness heights define the bar form effect. Field data from 62 sites in the United Kingdom illustrate that at bankfull flow bar roughness heights are generally in the range 0‐0.5 m, although values as high as 1.5 m are also observed.

The influence of local evaporation and rainfall on the salinity of estuary water is generally neglected in salt intrusion models. In the Gambia estuary, it appears that the influence of rain and evaporation is important. A model is presented to simulate salt intrusion taking into account the effects of local rain and evaporation.

A laboratory experiment was performed to optimize the hydraulic efficiency of a portable net-type sediment trap, called the streamer trap, developed for use in the sandy coastal environment. Twenty-two trap nozzles were tested in bottom boundary flow and uniform flow water speeds in the range of 22 cm/s to 76 cm/s, and efficiencies were compared to chose of the conventional Helley-Smith trap. One design had a hydraulic efficiency close to unity for all test conditions and was selected for use in the field. The Helley-Smith trap had a variable efficiency in the range of 1.2 to 1.5.