Journal of Hydraulic Engineering

While the application of uncertainty propagation methods to hydrometry is still challenging, in situ collaborative interlaboratory experiments are a valuable tool for empirically estimating the uncertainty of stream gauging techniques in given measurement conditions. The authors propose a simple procedure for organizing such experiments and processing the results according to the authoritative ISO standards related to interlaboratory experiments, which are of common practice in many metrological fields. Beyond the computation and interpretation of the results, some issues are discussed regarding the estimation of the stream gauging technique bias in the absence of accurate enough discharge references in rivers; the uncertainty of the uncertainty estimates, according to the number of participants and repeated measurements; the criteria related to error sources that are possibly meaningful for categorizing measurement conditions. The interest and limitations of the in situ collaborative interlaboratory experiments are exemplified by an application to the hydro-acoustic profiler (ADCP) stream gauging technique conducted in 2010 at two different sites downstream of Génissiat hydropower plant in the Rhône river, France. Typically, the expanded uncertainty (with a probability level of 95%) of the average discharge over six successive transects varied from $\pm 5\%$ at one site with favorable conditions to $\pm 9\%$ at the other site due to unstable flow conditions.

One-dimensional (1D) models can be applied, for engineering purposes, to long-term and large-scale morphodynamic simulations of entire river systems only if appropriate simplifications are introduced. This paper proposes an improvement of an existing simplified 1D model based on the local uniform flow hypothesis, coupled with a synthetic description of the transverse profile, which provides the active river width by analyzing the total and the vegetated widths of a watercourse, with assumed variables of the water flow. The overall density of the riparian vegetation, expressed in terms of biological carrying capacity, is predicted as a function of the local climate and some stresses due to interaction between hydrology, morphology, and biology. The constitutive equations have been deduced and the relevant parameters have been calibrated and validated against various hydrological and geometrical data, taken by satellite imagery covering two large watercourses located in tropical and subtropical areas (Parana and Zambezi rivers) and small streams located in temperate zones. The work confirms the opportunity to deal with hydro-morpho-biodynamic river modeling at large spatial and temporal scale through a mixed 1D + quasi-2D approach. The 1D submodel permits long-term computations at watershed scale of the river longitudinal evolution, while the quasi-2D submodel provides the transversal description of the watercourse in terms of vegetated and nonvegetated widths and vegetation density, which in its turn reflects on the 1D computations.

Two regimes can be distinguished for the pickup flux of sand. At a Shields parameter of less than about 0.5 (corresponding with flow velocities of $0.5–1\mathrm{m}/\mathrm{s}$), the erosion process is dominated by the size and density of the grains (grain by grain pickup). At higher flow velocities, the bulk properties of the sand bed start to influence the erosion process. Dilative behavior results in the inflow of water to the sand bed, which reduces the pickup flux (dilatancy-reduced pickup) because of the shearing of layers of sand. A pickup function was recently developed for this regime, incorporating the effect of bulk properties, such as permeability and porosity, on the pickup. This function agrees well with data of previous erosion experiments in which the permeability and porosity of the sand bed were varied. However, these experiments just met the condition for dilatancy-reduced pickup. The flow velocity during these previous experiments was between 1 and $1.5\mathrm{m}/\mathrm{s}$, while the Shields parameter varied between 1 and 2. In order to validate this pickup function for dike breaching and jetting of sand, during which the flow velocity ranges within $5–50\mathrm{m}/\mathrm{s}$, erosion experiments were executed at higher flow velocities. These experiments were executed in an adapted closed flume of the slurry circuit of the Dredging Research Laboratory at the Delft University of Technology (DUT) at flow velocities of $2–6\mathrm{m}/\mathrm{s}$ (Shields parameter is between 50 and 1,000). The results of these experiments are consistent with the theory of dilatancy-reduced pickup. The porosity of the sand bed influences the erosion process, especially at flow velocities of more than $4\mathrm{m}/\mathrm{s}$ bulk property.

Natural bedrock rivers exhibit diverse erosional morphologies. Although the formation of alternate bars on bedrock has been noted in previous studies, the influence of these alternate bars on bedrock erosion has not been clarified. In this study, the authors propose a model for bedrock-alluvial channels that reproduces both bar formation and erosional morphology. In addition, the authors report on numerical simulations to evaluate the influence of sediment supply on the state of the bed at and over the bedrock surface. The numerical results illustrate the formation of different morphologies for different supply rates. When the sediment supply rate is close to transport capacity, mixed alluvial-bedrock alternate bars form. These bars are analogous to purely alluvial alternate bars. A meandering thread of alluvial material migrates downstream over a uniformly eroding bedrock surface. When the sediment supply rate is well below capacity, however, multiple incisional troughs (grooves) form on the bedrock surface, and alluvial cover tends to concentrate in the troughs.

On a stepped spillway, the steps act as macroroughness elements, contributing to enhanced energy dissipation and significant aeration. In a skimming flow, the upstream flow motion is nonaerated, and the free surface appears smooth and glossy up to the inception point of free-surface aeration. In this developing flow region, a turbulent boundary layer grows until the outer edge of the boundary layer interacts with the free surface and air entrainment takes place. The flow properties in the developing flow region were documented carefully in a large stepped spillway model (1V:1H; $h=0.10\mathrm{m}$). The upstream flow was controlled by a broad-crested weir and critical flow conditions were observed along most of the weir crest, although the pressure distributions were not hydrostatic at the upstream and downstream ends. Downstream of the broad crest and upstream of the inception point, the free surface was smooth, although some significant free-surface curvature was observed for all discharges. The boundary layer growth was faster than on a smooth chute for identical flow conditions. The inception point of free-surface aeration was observed when the boundary layer thickness reached 80% of the flow depth: $\delta /d_i\approx 0.8$. The location of the inception point of free-surface aeration and the flow depth at inception were compared successfully to previous laboratory and prototype results.

In skimming flow on a stepped spillway, the upstream flow motion is nonaerated and a turbulent boundary layer develops until the outer edge of the boundary layer interacts with the free surface; that is, at the inception point of air entrainment. Herein, new experiments were performed in the developing flow region on a large $1\mathrm{V}:1\mathrm{H}$ stepped spillway model with step height $h=0.10\mathrm{m}$. The flow properties in the developing flow region were carefully documented. In the developing boundary layer, the velocity distributions followed a $1/4.5$th power law at the step edges. Detailed velocity and pressure measurements showed some rapid flow redistribution between step edges and above step cavities. The application of the momentum integral equation indicated an average friction factor of 0.18, which is close to the observed air-water-flow friction factor of 0.23, suggesting that the spatially averaged dimensionless shear stress was comparable in the developing flow and fully aerated flow regions.

High-speed diffuse flow is a commonly complex process in tunnels with full-section aerators and lateral expansion walls. The transformation of pressure is prone to produce cavitation on the lateral expansion walls downstream of an aerator. The expansion threatens the stability of the structure and can cause damage. In this paper, the diffuse flows downstream of a radial sluice and full-section aerator were studied by combining a realizable $k-\epsilon$ turbulent model with a mixture multiphase model. Hydraulic characteristics such as pressure distribution and cavitation were investigated. The relationship among pressure, cavitation index, lateral divergence angle $\alpha$, and Froude number $\mathsf{F}$ were proposed. Empirical formulas were presented to calculate and evaluate the pressure and cavitation index on side walls. The calculated results agree well with the physical model. With decrease in divergence angle, pressure increases gradually so that the flow cavitation index increases as well. Profiles of gate openings demonstrated gradual improvement in pressure and cavitation index with an increase in the magnitude of the gate opening. The studies showed that the degree of gate opening has a great effect on the pressure and flow cavitation index of side walls. The lateral expansion and partial gate-opening increased the risk of cavitation erosion on side walls downstream of the radial sluice. Research results provided a reference for optimizing the design of similar engineering.

This study aims to assess the reliability of hydraulic performance of concrete pipes at the design stage. The reliability assessment is on the basis of the use of Markov chain theory for modeling pipe deterioration during service life and coefficient of variation (COV) for representing uncertainty in design, installation, and operational parameters. The results of a case study in this study show that increasing pipe diameter from 600 mm (as per current design) to 750 mm (as per reliability assessment) can significantly reduce the risk of hydraulic failure during service life and delay inspection and hydraulic rehabilitation by 10 years.

This paper develops an analytical model to predict the stage-discharge relationship for flow in rectangular ice-covered channels. The flow cross section are divided into three subsections on the basis of hydraulic radius separation theory. Based on the determination of flow characteristics, such as hydraulic radius, subsection area, and mean velocity within each flow subsection, an analytical model for discharge assessment in a rectangular ice-covered channel is presented. Comparisons between the predicted results of the proposed model and the collected data from literature show that the proposed method does well in predicting the stage-discharge relationship in rectangular ice-covered channels. The effects of the main influencing parameters on the stage-discharge relationship are discussed and a simplified model is presented for stage-discharge prediction in wide ice-covered channels.