Journal of Hydraulic Engineering

To investigate the complex hydrological, morphodynamic, and environmental processes in watersheds, a physically-based integrated two-dimensional (2D) surface and three-dimensional (3D) subsurface model for flow, soil erosion and transport, and contaminant transport in the surface-subsurface system is presented in this paper. The model simulates the rainfall-induced surface flow by solving the depth-averaged 2D diffusion wave equation and the variably-saturated subsurface flow by solving the 3D mixed-form Richards equation. The surface and subsurface flow equations are coupled using the continuity conditions of pressure and exchange flux at the ground surface. The model uses the concept of nonequilibrium in the depth-averaged 2D simulation of nonuniform total-load sediment transport in upland fields, considering detachments by rainsplash and hydraulic erosion driven by surface flow. The integrated 2D surface and 3D subsurface contaminant transport model takes into account the contaminant changes due to sediment sorption and desorption, as well as exchanges between surface and subsurface domains due to infiltration, diffusion, and bed change. The model applies the same set of surface equations of flow, sediment, and contaminant transport for describing both upland areas and streams, so that no special treatments are required at their interface. The established model has been evaluated by comparisons with published experimental, numerical, and analytical data and then applied in an agricultural watershed. The model is suitable for wetland areas and agricultural watersheds in which streams are not very narrow and deep, and meanwhile a relatively fine mesh that can distinguish the streams is preferred.

A phenomenological kinetic energy theory of buoyant axisymmetric multiphase plumes is constructed, with particular attention to the modeling of the dispersed phase. The dissolution is treated by means of the Ranz-Marshall equation involving a mass-transfer coefficient dependent on the plume properties. The model is compared with various experiments, yielding satisfactory agreement. A central ingredient in the model is the turbulent correlation parameter $I$ , playing a role analogous to the conventional entrainment coefficient $\alpha$ . We use experimental data to suggest a relationship between $I$ , the initial gas flux at the source, and the depth of the gas release.

The critical submergence for a group of multiple pipe intakes is predicted using a “superposition method” based on a potential flow solution. Experiments on groups of two, three, and four intakes were conducted. Experimental and theoretical results indicate that intakes in a group mutually influence the discharge into an individual intake. Therefore, the critical submergence for an intake in a group becomes larger than that for an isolated intake under identical flow conditions. The agreement between the theoretical and experimental results is found to be satisfactory.

In the present paper, we investigate the effectiveness of a flood defense project based on storage reservoirs, presently under study for the Magra River and Vara River (Italy). We have focused the analysis on two detention reservoirs and studied their response to different hydrological scenarios mostly in terms of flood mitigation efficiency, leaving aside sediment transport issues. The analysis has been carried out with the aid of a physical model and one-dimensional numerical simulations. Experimental and numerical simulations have been performed spanning a wide range of hydrological conditions. Some of the results can be generalized for different applications where similar flood control systems are employed.

Rain gardens are infiltration systems that provide volume and water quality control, recharge enhancement, as well as landscape, ecological, and economic benefits. A model for application to rain gardens based on Richards equation coupled to a surface water balance was developed, using a two-dimensional finite-volume code. It allows for alternating upper boundary conditions, including ponding and overflow, and can simulate heterogeneous soil-layering or more complex geometries to estimate infiltration and recharge. The algorithm is conservative, and exhibits good performance compared to standard models for several test cases (less than 0.1% absolute mass balance error); simulations were also performed for an experimental rain garden and comparisons to collected data are presented. The model accurately simulated the matrix flow, soil water distribution, as well as deep percolation (potential recharge) for a natural rainfall event in the controlled experimental setup.

This technical note presents a critical analysis flow over weirs of finite crest length, with square-edged or rounded entrance, for free-flow conditions. Using the flow equation for the broad-crested weir with parallel flow in the critical state as the basis, we have defined the discharge coefficient $C_d$ , with the head on the weir as the length scale. Based on an extensive analysis of the experimental observations in the literature, we have confirmed the classification of finite crest length weirs into four classes of long-crested, broad-crested, short-crested, and sharp-crested weirs. For the square-edged entrance, we have developed robust correlations for $C_d$ when the Weber number is greater than 1. For weirs with a rounded entrance, for which the data set is not that extensive compared to the square-edged case, we have developed good correlations for $C_d$ .

The contraction coefficient under sluice gates on flat beds is studied for both free flow and submerged conditions based on the principle of momentum conservation, relying on an analytical determination of the pressure force exerted on the upstream face of the gate together with the energy equation. The contraction coefficient varies with the relative gate opening and the relative submergence, especially at large gate openings. The contraction coefficient may be similar in submerged flow and free flow at small openings but not at large openings, as shown by some experimental results. An application to discharge measurement is also presented.

The hydrodynamic pressure field is important for the design and safety of steeply sloping stepped spillways, which are typically designed for considerably lower maximum specific discharges than smooth spillways. The hydraulic performance of stepped spillways at high velocities may compromise its use due to major concern with safety against cavitation damage. Hydraulic model investigations were conducted in different large-size stepped chutes to characterize the nonaerated flow region which is potentially prone to cavitation damage and the pressure field acting on the step faces. The clear water depths and energy dissipation in the developing flow region are described in terms of integral measures of the turbulent boundary layer. Expressions for the location of and the flow depth at the inception point of air entrainment are derived. Pressure distributions on the horizontal and vertical faces of the step along the spillway are presented. Measurements indicated a different behavior of the pressure field in the aerated and nonaerated flow region. The mean and fluctuating pressure coefficients along the spillway are approximated by a regression function. The vertical face near the outer step edge close to the inception point of air entrainment is identified as a critical region for predicting cavitation inception in flow over stepped spillways. From the analysis of the pressure fluctuations in that region a maximum velocity of 15 m/s is proposed as a criterion to avoid extreme negative pressures in typical prototype steeply sloping stepped spillways, eventually leading to the occurrence of cavitation in the nonaerated flow.

Concentration profiles and overall flow parameters were measured in a 0.37-mm-sand-mixture flow above a plane stationary deposit in a pressurized circular pipe of the inner diameter of 150 mm. The new data and additional data from the literature are used to propose a tentative transport formula of the Meyer-Peter and Müller type, and a slip-ratio formula, for flows at high shear stress in enclosed conduits.