Journal of Hydraulic Engineering

Experiments have been carried out in a fixed-bed flume for a schematized straight river reach with groynes on one side to study the dynamics of the flow near groynes. The flume had a geometrical scale of $1:40$, based on typical dimensions of the Dutch River Waal. Both emergent and submerged groynes were studied. The measurements demonstrate the differences in the nature of the turbulence between submerged and emerged groynes stages; and provide insight into the flow pattern in the vicinity of groynes, the shape and the extent of the mixing layer at different flow stages, and the dynamic behavior of the velocity along the mixing layer between the main channel and the groyne fields. A parameterization of the turbulence characteristics of the flow near groynes is presented. Large-scale velocity fluctuations are found in all test cases, with timescales that vary with the flow stage. The large-scale $u$ and $v$ velocity fluctuations are in phase in the center of the mixing layer and out of phase for the points on the boundaries of the mixing layer.

This study presents field observations and numerical modeling of surface seiche formations on a shallow reservoir in a complex terrain (Rules Reservoir, Spain). The influence of the surrounding topography on the atmospheric loading (barometric pressure and wind speed) is investigated, with the associated atmospheric-hydrodynamic coupling. During a 13-day field study, maximum free surface oscillations of 4 cm were recorded after the passing of a short duration storm ($<5\min$), which included a peak wind gust of $22\mathrm{m}/\mathrm{s}$. Observations also present evidence of resonant excitation of the free surface caused by high-frequency microscale harmonics ($<10\min$) in the atmospheric forcing. Resonant excitation caused by harmonics in the atmospheric forcing is significant for small reservoirs situated in regions of complex terrain where topographical obstacles modify the flow patterns in the near-surface boundary layer, generating eddies with harmonics in the microscale range of the atmospheric forcing spectrum. Harmonics in the atmospheric forcing are observed for a range of periods (200–700 s) during the survey. Surface oscillations of 2 cm are generated when the frequency of the forcing matches the fundamental reservoir modal frequency, even for low wind speeds. A two-dimensional depth-integrated numerical model predicted the observed surface seiche formation in both cases.

Most theoretical and numerical studies employ diffusion theory to investigate suspended sediment distributions in fluvial rivers, yet diffusion-theory-based descriptions are strictly valid only in the limit of small particle inertia and low concentrations. This paper presents a transport equation for sediment in suspension based on a two-fluid model of solid/liquid two-phase flows. The transport equation is derived from the consideration of mass conservation for solid particles. The velocity of the solid phase is obtained from an asymptotic solution of the momentum conservation equation for solid phase. Moreover, this transport equation is a typical convection-diffusion equation that includes the conventional diffusion equation as a special case when particle inertia is small and concentrations are low. Retaining the essential features of two-fluid models, the transport equation is applicable to sediment-laden flows with a wide range of particle inertia and sediment concentrations. Comparisons of the results with available experimental observations are presented, and fairly good agreement is obtained.

One potential problem affecting below-grade storm-water storage tunnels is the occurrence of geysering, which is defined as the return of conveyed water to grade. Most investigations to date have linked this occurrence with inertial oscillation of the water within vertical shafts. Another mechanism that can lead to geysering is the release of air and water through ventilation towers. This study presents a systematic investigation on geysering caused by the release of large air pockets through partially water-filled ventilation towers. Parameters considered in the study included the water level in the ventilation tower, air-phase pressure head, and ventilation tower diameter. An important parameter in geysering was the diameter of the ventilation tower. A simplified numerical model was developed to simulate the experiments; it was able to reproduce the essential features of the experiments.

Applications of frequency-domain analysis in pipelines and pipe networks include resonance analysis, time-domain simulation, and fault detection. Current frequency-domain analysis methods are restricted to series pipelines, single-branching pipelines, and single-loop networks and are not suited to complex networks. This paper presents a number of formulations for the frequency-domain solution in pipe networks of arbitrary topology and size. The formulations focus on the topology of arbitrary networks and do not consider any complex network devices or boundary conditions other than head and flow boundaries. The frequency-domain equations are presented for node elements and pipe elements, which correspond to the continuity of flow at a node and the unsteady flow in a pipe, respectively. Additionally, a pipe-node-pipe and reservoir-pipe pair set of equations are derived. A matrix-based approach is used to display the solution to entire networks in a systematic and powerful way. Three different formulations are derived based on the unknown variables of interest that are to be solved: head-formulation, flow-formulation, and head-flow-formulation. These hold significant analogies to different steady-state network solutions. The frequency-domain models are tested against the method of characteristics (a commonly used time-domain model) with good result. The computational efficiency of each formulation is discussed with the most efficient formulation being the head-formulation.

A sediment plug is defined as aggradation in a river that completely blocks the main channel. Information from documented cases of sediment plug development in alluvial rivers was used to develop criteria for plug formation and to identify the setup conditions for sites that are prone to plug formation. Site characteristics, processes, and associated parameters were evaluated based on a comprehensive literature review and evaluation of data. A plug formation theory was developed and tested using a unique sediment transport/movable bed numerical model that simulates the key processes considered to affect plug formation. The theory and model were calibrated and validated against field data, and then used to develop simplified criteria that can be used to predict plug formation. Findings from this study can be used to identify sites that may be prone to plug formation, and the criteria can be used to evaluate the potential for plug formation based upon field site conditions when data are not available to complete a more detailed study.

This paper investigates the well-known model for unsteady friction developed by Zielke in 1968. The model is based on weights of past local bulk accelerations and is analytically correct for laminar flow, but computationally demanding. Different models have been proposed using dynamic properties, typically based on instantaneous accelerations (IAB) that are more rapid in computational schemes. Unfortunately, they are not as accurate as Zielke’s model and fail to model certain types of transients. This paper points out that the water hammer transient is dominated by a periodicity varying along the pipe. Because of this, the unsteady friction calculated by the Zielke model is distributed nonuniformly along the pipe, and changes in the pipe length change the local unsteady friction. This phenomenon may explain why IAB models using calibrated coefficients to match experimental results have a large span in value for the reported coefficients. This paper will hopefully contribute to further work to find highly accurate and rapid models. The subject deserves to be brought up for discussion as a part of a total understanding of the problem.

The one-dimensional unsteady-state hydraulic model (UNET) was developed by the U.S. Army Corps of Engineers and has been used for flood protection in some large rivers. In its use for the real-time management of levee and drainage districts for flood protection, such as on the Mississippi River Basin, the required number of simulations for combinations of scenarios would present a great challenge for modelers to provide data for operational-mode decision making. The goal of this paper is to identify the most sensitive parameters for the spillway, simple levee failure, and complicated levee failure options in UNET so that simulations for real-time operation can focus on the most sensitive parameters without sacrificing much modeling accuracy. The sensitivity analysis was performed for the 50-year frequency flood in the lower Illinois River during which the Thompson Lake Levee and Drainage District or the Emiquon Area were used as temporary flood storage by using a state-of-the-art variance-based sensitivity analysis method—extended Fourier amplitude sensitivity test (FAST). The first-order and total-effect sensitivity indexes computed from the FAST method were used to evaluate the affect of the parameters to flood-peak reduction. As a result, the least and most sensitive variables for the spillway, simple levee failure, and complicated levee failure options in UNET were identified, and this knowledge helps significantly reduce the number of simulations for management scenarios by focusing on only the most sensitive parameters.

The two-dimensional (2D) depth-averaged river model Finite-Element Surface-Water Modeling System (FESWMS) was used to predict flow distribution at the bend of a compound channel. The site studied was the Highway 13 bridge over the Big Sioux River in Flandreau, South Dakota. The Flandreau site has complex channel and floodplain geometry that produces unique flow conditions at the bridge crossing. The 2D model was calibrated using flow measurements obtained during two floods in 1993. The calibrated model was used to examine the hydraulic and geomorphic factors that affect the main channel and floodplain flows and the flow interactions between the two portions. A one-dimensional (1D) flow model of the bridge site was also created in Hydrologic Engineering Centers River Analysis System (HEC-RAS) for comparison. Soil samples were collected from the bridge site and tested in an erosion function apparatus (EFA) to determine the critical shear stress and erosion rate constant. The results of EFA testing and 2D flow modeling were used as inputs to the Scour Rate in Cohesive Soils (SRICOS) method to predict local scour at the northern and southernmost piers. The sensitivity of predicted scour depth to the hydraulic and soil parameters was examined. The predicted scour depth was very sensitive to the approach-flow velocity and critical shear stress. Overall, this study has provided a better understanding of 2D flow effects in compound channels and an overall assessment of the SRICOS method for prediction of bridge pier scour.

Conventionally, wall shear stress in an unsteady turbulent pipe flow is decomposed into a quasi-steady component and an “unsteady wall shear stress” component. Whereas the former is evaluated by using “standard” steady flow correlations, extensive research has been carried out to develop methods to predict the latter leading to various unsteady friction models. A different approach of decomposition is used in the present paper whereby the wall shear in an unsteady flow is split into the initial steady value and perturbations from it. It is shown that in the early stages of an unsteady turbulent pipe flow, these perturbations are well described by a laminar-flow formulation. This allows simple expressions to be derived for unsteady friction predictions, which are in good agreement with experimental and computational results.

A lake tap is the submerged piercing of a tunnel at the intake to connect the reservoir to the tunnel system. It is referred to as a dry lake tap if the tunnel is dry before the blasting of the last rock plug at the tunnel entrance. Transient state conditions in the tunnel following a dry lake tap are modeled using the lumped and distributed-system approaches. Fourth-order Runge-Kutta method and the method of characteristics are used in the lumped-system model and distributed-system models, respectively. The results computed by the lumped and distributed-system approaches agree with one another. Pressures computed by using distributed-system and lumped-system models are compared with the experimental results available in literature for rapid filling of a pipeline with closed end. The rate of dissipation of pressure oscillations in the measured air pressure during prototype lake tap at Crater Lake Snettisham project in Alaska, and in the experiments reported in the literature is higher than that computed by the mathematical models using steady state friction and constant wave velocity.

This paper presents a protection structure built for a bridge pier consisting of six narrow piles. Accumulation of large woody debris upstream of the pile group during high-flow terms might have induced much larger scour depths compared with those expected for the single pile. A phenomenological sketch of the system suggested that accumulation of debris material during peak flows and subsequent descent of the same material during the tail of the events represented a very dangerous two-stage process owing to the high expected scour. Consequently, a countermeasure was designed, consisting of a plate preventing the descent of debris below its elevation. The performance of the plate in reducing local scour was subjected to some preliminary laboratory tests, and satisfactory results were obtained. This paper reports some tentative performance observations for the real structure built on the river, based on the amount of debris trapped during a recent event with moderate flow.