Journal of Hydraulic Engineering

The time‐marching approach (TMA) for determining steady‐state flows as the asymptotic limit of transient flows in pipelines has been improved. It is shown that the rate of convergence to steady state is increased by reducing the spectral radius of a coefficient matrix of a state‐vector equation, which is composed of the basic equations and boundary conditions linearized about the steady condition. A generalized TMA theory using the method of characteristics has been formulated and the spectral radius is minimized by changing system parameters to imaginary ones by using the energy and mass conservation equations. In addition, a practical method was designed to efficiently handle TMA in large pipelines without having to calculate eigenvalues. The TMA has been extended to accurately estimate friction factors using an explicit approximation to the Colebrook‐White formula.

The unique physiographic features of tidal inlets make it convenient to treat inlet hydraulics in two parts, one pertaining to the channel through the land barrier, and the other to the near‐field region characterized by ebb and flood circulations beyond the channel. Theoretical formulations for flow description in these regions lead to approximate but useful analytic solutions in simple cases. For detailed hydraulic description, physical and numerical modeling techniques are widely employed. Limitations in predictive capabilities seem to arise mainly from a lack of fuller understánding of hydromechanical processes. Such interactive phenomena as the propagation of the buoyant jet through ambient sea waters during the ebbing phase of tidal flow, and the influence of waves on the tidal flow regime, require considerable additional scrutiny via field investigations. The complex nature of inlet behavior necessitates the collection of site‐specific prototype information as an essential component of hydraulic analysis and interpretation.

A method is presented to predict water levels in tidal estuaries using Kalman filtering techniques. The method is illustrated by predicting the water levels in the Eastern Scheldt. This estuary appears to contain many of the features inherent in modeling flows in estuaries. It is seen that, although the geometry is very complicated due to numerous gullies and banks, a very simple schematization is sufficient. Furthermore, it is shown that nonlinear effects in the mouth due to the complicated geometry and the interaction between the tidal wave along the coast and the water movements in the estuary can be compensated by using stochastic dynamic methods applied to internal boundary conditions.

An experimental investigation of wind‐induced flow and mixing processes in a two‐layered system influenced by a thin film persisting on the water surface is reported in this study. Detailed documentation and description of the wind‐induced flow and mixing processes are given. The entrainment rates and flow pattern depend on two dimensionless numbers, one characterizing the influence of surface films, the other characterizing the response of stratified basins to wind stress in the absence of surface films. The differences between the flow and mixing processes of a two‐layered system influenced and not influenced by a surface film are pointed out and discussed.

The bank protection and grade controls of a river channel must be designed to contain the design flood and extend below the potential riverbed scour. Because of the convoluted relationships governing the flow and sediment processes, mathematical simulation becomes an effective means of evaluating channelbed scour under any flow pattern and design configuration. Channelization of the Santa Cruz River has been designed based upon the pattern of river channel responses simulated using a calibrated mathematical model. Scour and fill of the channel bed invoked by the longitudinal imbalance in sediment load are simulated; they are also tied in with the effects of the streamwise variation in spiral motion that induces an uneven bed topography, characterized by greater scour near the concave bank. Variable top and toe elevations for hydraulic structures have been determined and employed to make more efficient use of construction materials while providing effective protection against erosion. The study demonstrates the procedure with which the design configuration of a flood control channel may be determined.

Using a semiempirical approach, the discharge characteristics of standard spillways controlled by a plane vertical gate, mounted on the spillway crest, are investigated for free flow. It is shown that the proposed equation for discharge depends on the spillway geometry, the gate opening, and the actual head on the spillway. Several flow features are discussed. A diagram is presented for both gated and ungated standard spillway flow, which allows a simple application.

A series of experimental tests are carried out to aid in the optimal design of a jet‐mixer for a shallow circular basin. Mixing times for single and double jets with various orientations are investigated to determine the best arrangement. The best single jet is one directed along the diameter of the basin. A tangential jet near the basin perimeter has the longest mixing time. The best overall arrangement consists of tangential jet and 45° jet at a radius of 0.4 of the basin radius. An optimal design procedure is suggested.

An experimental study of open channel flow resistance in horseshoeshaped conduits is reported. The friction factor is shown to increase approximately 20 percent in comparison to values taken from the Moody diagram for depths larger than half‐full. For depths less than half‐full, the friction factor agrees with that determined directly from the Moody diagram with four times the hydraulic radius taken as the length scale. The resultant changes in the ratio of part‐full velocity to full‐flow velocity are investigated and compared with field results for circular pipes. For small relative depths of flow, the experimental results for relative velocity agree with those obtained using the Moody‐diagram friction factor for a houseshoe conduit with no shape correction, but they approach field results for circular conduits at higher relative depths of flow for which a shape correction is needed.