Journal of Hydraulic Engineering

With the increased emphasis on developing integrated models capable of simulating runoff through hydrologic systems that include hillslopes and wetlands, analytical solutions have become useful in analyzing and testing numerical models applied to both. An analytical solution in algebraic form is developed in this paper to describe a sinusoidal moisture profile migrating through a wetland or a hillslope, the magnitude of the peak runoff, and the phase lag. The solution is obtained for an instantaneous sinusoidal recharge signal, and results are expressed in terms of the basin geometry and flow resistance parameters. The analytical solution is used to verify the accuracy of a numerical model based on the implicit total variation diminishing Lax-Friedrichs (TVDLF) method. This method is used in the Regional Simulation Model (RSM) developed at the South Florida Water Management District (SFWMD) to simulate the complex hydrologic system of south Florida. The runoff peak, phase lag, propagation speed, and decay rate over a range of Péclet numbers are used in the comparison of analytical and numerical solutions. The numerical model using the TVDLF method is tested by applying to the Boggy Creek watershed in central Florida, and the wetland stormwater treatment area (STA)-3/4 in south Florida to simulate storm runoffs and water levels. Results show that the model using a general power-law equation to represent flow resistance, and a conceptual model consisting of a canallike drainage feature to represent rapid drainage can be used to simulate the hydrology in both the watershed and the wetland.

Dams are civil structures essential to modern civilization. However, they can be a threat if not properly designed and operated. A particular risk that potentially can lead to dam failure is the blocking of the spillway inlet with driftwood or debris. This study investigated, on the basis of physical modeling, this blocking as well as the related backwater rise and discharge-capacity reduction. Considerable quantities of driftwood were supplied upstream of an ogee weir with piers, and the subsequent reservoir level rise was measured. Particular focus was placed on extreme events in terms of driftwood occurrence (volume) and discharges (design value). It was found that a gated ogee blocked with driftwood performs with a reduced discharge coefficient as long as no countermeasures are taken, such as pier overhang, the removal of piers, or the installation of a rack. The performance of these countermeasures was studied, and criteria were developed to control the perturbing effect of driftwood.

This paper presents a new method that is able to define the hydraulic jump peculiarities in rough-bed conditions. The findings of this paper improve the literature and guidelines on the design of a stilling basin over a rough bed, taking into account both the Froude number and bottom roughness. It starts with experimental evidence on the flow field and considers the characteristic length scale of the phenomenon as drawn from velocity measurements in the hydraulic jump region. The assumption in the length scale leads to different results compared with the known formulas in the literature related to the hydraulic jump on a rough bed. The formulas in the literature consider the effects of gravel roughness only, neglecting the effects due to the incident Froude number in the evaluation of integrated bottom shear stress. The comparison of the presented results with experimental measurements in the literature highlights the reliability and accuracy of this novel method. This method is theoretically based, but because it needs experimental data in application, it can be considered semiempirical. The results presented here allow for the design of hydraulic jump stilling basins over rough beds.

The effect of a turbulent coflow on a turbulent round jet is investigated experimentally. The primary objective of this work is to study the evolution of the turbulent jet as the level of the coflow turbulence is varied. Velocity measurements of the jet were conducted at three Reynolds numbers, with the jet issuing into two different levels of coflow turbulence. It is observed that the decay rate of the centerline mean velocity, spreading rate, and mass flow rate of the jet increase as the level of the coflow turbulence increases. Similarly, both the inward mean radial velocity close to the edges of the jet, which can be related to the entrainment velocity, and the velocity variances increase when the turbulence level of coflow increases. Given the increased spreading rate, mass flow rate, and inward mean radial velocities, it can be inferred that the entrainment into the jet also increases as the coflow turbulence intensifies. Lastly, for the range of parameters studied, self-similarity of mean velocity profiles occurs at a downstream position for which the ratio of the coflow to jet integral lengthscales is of order one.

Engineered log jams (ELJs) are used widely in practice as a river restoration measure. One desired feature of an ELJ is its porous nature, which plays an important role in hydrodynamics and sediment response. Currently there are very limited studies of porous hydraulic structures such as ELJs, and ELJs often are treated as solid obstructions for the purpose of flow and scour predictions. In this study, laboratory experiments were conducted to examine flow and bathymetric response near porous versus nonporous ELJ structures emplaced in an experimental flume. Time-averaged velocity, turbulent fluctuations, and the initial and final bathymetry were measured for four cases of porous and nonporous structures. Alterations in the flow field near the porous structure resulted in reduced maximum scour depths and lower total transport of bed material. It was found that existing predictive equations for scour geometry fail to match experimental data for the porous structures due to the lack of consideration of porosity’s role in altering the flow conditions. Conceptual models of the flow zones and the stages of erosion were presented and discussed. A simple predictive model for scour depth around ELJs was developed.

This study presents scientific methods for risk assessment of levee seepage failure. First, the levee seepage failure probability, $P_f$, was calculated by reliability analysis considering muddying and slope sliding due to the development of the seepage line and uncertainty in the soil index. $P_f$ is useful for estimating levee sites with a high seepage risk. Next, the seepage flow number, SFn, which is a dynamic dimensionless number governing general seepage flow, was derived by nondimensionalizing Richards’ equation. Then, the levee vulnerability index, $t^{*}$, was obtained by applying SFn to the phenomena of levee seepage and failure. Values of $t^{*}$ were determined by applying it to damage results of model levees and field levees. Because $t^{*}$ and $P_f$ corresponded well in the field levees in which considerable damage such as levee breaching and slope sliding or collapse have occurred, the risk of levee seepage failure can be estimated by $t^{*}$. Finally, $t^{*}$ can provide a dynamic similarity condition to describe the phenomenon of levee seepage and failure and can be a useful tool for understanding levee seepage failure.

Actively generated pressure waves are studied widely and applied in transient-based leak detection for pipe systems. High-frequency (HF) waves, the wavelength of which is on the order of the pipe diameter or smaller, provide higher resolution to pinpoint defects. However, the mechanism of how HF waves interact with a leak is not yet well understood. This paper investigated the effect of a leak on the HF waves in a water-filled pipe using computational fluid dynamics (CFD) simulations. To facilitate the analysis, only the plane wave and the first high-order radial modes were considered. The interaction between the leak and the two modes was analyzed. The group velocity of the first high mode was analyzed to investigate the effect of the leak on the cut-off frequency. However, the shift in cut-off frequency was not observed for the moderate leak size investigated in this paper. Therefore, it was concluded that the shift of the cut-off frequency is very small and should not be used as a signature for leak detection. On the other hand, the results showed that the leak induces very significant scattering of the excited modes. Such scattering provides clear information that may be utilized for leak detection.