Journal of Hydraulic Engineering

A physically based model for estimating the resistance coefficient for coniferous trees in open-channel flow is modified to account for variations in the flexibility between species. The new model is based on the assumption of a linear increase in foliage area with height and a dimensional analysis. It is supported by experiments in air and water. The advantage of the new model over existing methods for estimating resistance factors is its ability to account for the interaction between the vegetation and the flow, taking into account velocity, depth of flow, and vegetative conditions (including type, size, stage of maturity, and density of vegetation). Based on the mathematical model, a table is provided to estimate Manning's n value for flow through vegetation.

A numerical study of friction parameters associated with nearly flat tidal channels is reported. Such empirical parameters are often back-calculated using complex flow equations through a procedure referred to as “inverse problems.” However, estimates of friction parameters of tidal channels are liable to substantial uncertainties if water levels are used in their inverse problems. Even if the parameters are optimized by mathematically comparing gauged and simulated values, the inverse problem must satisfy the quality conditions of “uniqueness,” “identifiability,” and “stability.” To obtain an insight into the problem, this paper focuses on flows where these conditions may not hold. The study concludes that friction parameters can be unidentifiable if the inverse problem employs gauged high tide water levels, because the effect of storage on water level dominates over friction. Gauged discharge values render identifiable, stable, and unique estimates of friction parameters even at high tides, but this is not a practical proposition. Low tide levels should be used to determine friction parameters, as the use of high-tide water levels can make friction parameters, and subsequently simulated discharge values, anomalous.

This paper presents the results of a laboratory study of the velocity field in turbulent open-channel flow in a circular corrugated pipe of diameter D of 0.622 m for three slopes S of 0.55, 1.14, and 2.55% and a range of discharges from 30 to 200 L/s. The Manning n was found to be equal to 0.023. Velocities were relatively small in some portion of the flow near the boundary of the pipe, and these low velocity regions may be useful for fish passage upstream. In the region of fully developed flow, in the central vertical plane, the longitudinal velocity u was described by the Prandtl equation for rough turbulent flow, with a dip in the velocity profiles near the water surface. The velocity profiles in the noncentral planes were also described by the Prandtl equation for rough turbulent flow, but with a significant dip in the upper part of the flow. An empirical method was devised to describe the geometrical and kinematical properties of this velocity dip. The general findings of this study were also found to be valid for flow in a large corrugated pipe of diameter of 4.27 m with two slopes of 0.14 and 1.42%.

A 3D hydrodynamic and heat transport model was developed for Lake Okeechobee. Continuity, momentum, and temperature transport equations were solved. Dynamically coupled transport equations for turbulent kinetic energy and turbulent scale also were solved. The numerical scheme used spatial finite differencing and a three-time-level, external-internal mode splitting procedure. A 28-day calibration was conducted, using measured bathymetry, rainfall, relative humidity, total solar radiation, wind velocity, inflow, and outflow data. During the calibration period, little rainfall occurred, and lake water levels receded. Water surface elevation, horizontal velocities, and temperature were computed. Agreement between observed and simulated values was based on graphical comparisons, minimizing mean absolute and root-mean-square errors, and spectral analysis. Comparisons showed that the model reproduced general observed trends and short-term fluctuations. The model's heat transport and turbulence closure schemes behaved as expected with regard to water column stratification and mixing. Simulation accuracy may potentially be improved by adding wind-wave and vegetation resistance algorithms to the model.

Screening level analyses for risk-based corrective actions and preliminary remediation investigations and feasibility studies for contaminated sites require simple and conservative models for the transport of contaminants to potential receptor locations. A quasi-analytical method is presented to analyze the transport of contaminants originating at a source located near the ground surface separated from the water table by a relatively thick vadose zone. The method includes one segment to compute source decay rate, a second to simulate vertical transport through the vadose zone, and a third to simulate saturated zone transport to the receptor. Practical application of the method is demonstrated by an illustrative example. The method may be useful and convenient for situations where the objectives of the analysis do not warrant the use of sophisticated numerical models.

This note considers the evaluation of resistances in unsteady flow by means of a 1D unsteady friction model. The model is applied for the case of a water hammer, both in a single gravity pipeline and in a single pumped pipeline. Comparisons with experimental results show that the model does not predict the exact shape of the oscillation, but it gives, with high precision, the maximums and minimums of the pressure head oscillation if correct values of the parameter of the model are used. Because experimental evaluations can be made only for a few cases and can give rise to very different values depending on experimental conditions, the sensitivity of the model to physical and numerical parameters that influence the phenomenon is examined by comparison with the results of a quasi-2D model previously proposed.

The suggested practice of using single point test data to construct a “straight line” (i.e., hydraulically scaled) water supply plot is investigated herein. It is shown that this widely used practice may lead to large errors in determining the available pressure at a connection for a design flow condition. It is further shown that using a second test point to construct a quadratic water supply plot can produce far better accuracy. Inaccurate plots of the available pressures can lead to erroneous fire flow predictions and improperly designed fire protection sprinkler systems. This raises safety concerns in addition to poorly designed facilities.