Authors:G. C. Efthimiou; S. Andronopoulos; I. Tolias; A. Venetsanos Pages: 899 - 921 Abstract: Abstract The peak values observed in a measured concentration time series of a dispersing gaseous pollutant released continuously from a point source in urban environments, and the hazard level associated with them, demonstrate the necessity of predicting the upper tail of concentration distributions. For the prediction of concentration distributions statistical models are preferably employed which provide information about the probability of occurrence. In this paper a concentration database pertaining to a field experiment is used for the selection of the statistical distribution. The inverses of the gamma cumulative distribution function (cdf) for 75th–99th percentiles of concentration are found to be more consistent with the experimental data than those of the log-normal distribution. The experimental values have been derived from measured high frequency time series by sorting first the concentrations and then finding the concentration which corresponds to each probability. Then the concentration mean and variance that are predicted with Computational Fluid Dynamics-Reynolds Averaged Navier–Stokes (RANS) methodology are used to construct the gamma distribution. The proposed model (“RANS-gamma”) is included in the framework of a computational code (ADREA-HF) suitable for simulating the dispersion of airborne pollutants over complex geometries. The methodology is validated by comparing the inverses of the model cdfs with the observed ones from two wind tunnel experiments. The evaluation is performed in the form of validation metrics such as the fractional bias, the normalized mean square error and the factor-of-two percentage. From the above comparisons it is concluded that the overall model performance for the present cases is satisfactory. PubDate: 2016-10-01 DOI: 10.1007/s10652-016-9455-2 Issue No:Vol. 16, No. 5 (2016)

Authors:Kabir Suara; Richard Brown; Michael Borgas Pages: 923 - 943 Abstract: Abstract In an estuary, mixing and dispersion resulting from turbulence and small scale fluctuation has strong spatio-temporal variability which cannot be resolved in conventional hydrodynamic models while some models employs parameterizations large water bodies. This paper presents small scale diffusivity estimates from high resolution drifters sampled at 10 Hz for periods of about 4 h to resolve turbulence and shear diffusivity within a tidal shallow estuary (depth <3 m). Taylor’s diffusion theorem forms the basis of a first order estimate for the diffusivity scale. Diffusivity varied between 0.001 and 0.02 m2/s during the flood tide experiment. The diffusivity showed strong dependence (R2 > 0.9) on the horizontal mean velocity within the channel. Enhanced diffusivity caused by shear dispersion resulting from the interaction of large scale flow with the boundary geometries was observed. Turbulence within the shallow channel showed some similarities with the boundary layer flow which include consistency with slope of 5/3 predicted by Kolmogorov’s similarity hypothesis within the inertial subrange. The diffusivities scale locally by 4/3 power law following Okubo’s scaling and the length scale scales as 3/2 power law of the time scale. The diffusivity scaling herein suggests that the modelling of small scale mixing within tidal shallow estuaries can be approached from classical turbulence scaling upon identifying pertinent parameters. PubDate: 2016-10-01 DOI: 10.1007/s10652-016-9458-z Issue No:Vol. 16, No. 5 (2016)

Authors:Gaurav Goel; Luqman K. Abidoye; Bhagu R. Chahar; Diganta B. Das Pages: 945 - 963 Abstract: Abstract Capillary pressure–saturation-relative permeability relationships (Pc–Sw–Kr) are functions of importance in modeling and simulations of the hydrodynamics of two-phase flow in porous media. These relationships are found to be affected by porous medium and fluid properties but the manner in which they are affected is a topic of intense discussion. For example, reported trends in fluid viscosity and boundary conditions effects have been found to be contrary to each other in different studies. In this work, we determine the dependency of dynamic Kr–Sw relationships (averaged data) on domain scale in addition to investigating the effects of fluid viscosity and boundary pressure using silicone oil (i.e. 200 and 1000 cSt) and water as the respective non-wetting and wetting fluids with a view to eliminating some of the uncertainties reported in the literature. Water relative permeability, Krw, was found to increase with increasing wetting phase saturation but decreases with the increase in viscosity ratio. On the other hand, the oil relative permeability, Krnw, was found to increase with the increasing non-wetting phase saturation in addition to the increase in viscosity ratio. Also, it was found that with the increasing boundary pressure Krw decreases while Krnw increases. The influence of scale on relative permeability was slightly indicated in the non-wetting phase with Krnw decreasing as domain size increases. Effect of measurement location on dynamic relative permeability was explored which is rarely found in the literature. Comparison was also made between Kr–Sw relationships obtained under static and dynamic condition. Finally, mobility ratio (m) and dynamic coefficient (τ) were plotted as a function of water saturation (Sw), which showed that m decreases as τ increases at a given saturation, or vice versa. PubDate: 2016-10-01 DOI: 10.1007/s10652-016-9459-y Issue No:Vol. 16, No. 5 (2016)

Authors:Mingliang Zhang; Huiting Qiao; Yuanyuan Xu; Yang Qiao; Kejun Yang Pages: 965 - 981 Abstract: Abstract Research on interactions among wave, current, and vegetation has received increasing attention. An explicit depth-averaged hydrodynamic model coupled with a wave spectral model (CMS-wave) was proposed in this study in order to simulate the wave and wave-induced current in coastal waters. The hydrodynamic model was based on the finite volume method while the intercell flux was computed by employing the Harten–Lax–van Leer approximate Riemann solver to investigate the dry-to-wet interface, and the drag force of vegetation was modeled as the sink terms in the momentum equations. The CMS-wave model was used to investigate the non-breaking and the breaking random waves propagation in vegetation fields. Afterwards, an empirical wave energy dissipation term with plant effect was derived to represent the resistance induced by aquatic vegetation in the wave-action balance equation. The established model was calibrated and validated with both the experimental and field data. The results showed that the wave height decreased significantly along the wave propagation direction in the presence of vegetations. The sensitivity analysis for the plant density, the wave height, and the water depth were performed by comparing the numerical results for the wave height attenuation. In addition, wave and wave-induced current through a finite patch of vegetation in the surf zone were investigated as well. The strong radiation stress gradient could be produced due to the variation of the energy dissipation by vegetation effect in the nearshore zone, which impacted the direction and amplitude of the longshore current. The calculated results showed that the coupling model had good performance in predicting wave propagation and the current over vegetated water regions. PubDate: 2016-10-01 DOI: 10.1007/s10652-016-9460-5 Issue No:Vol. 16, No. 5 (2016)

Authors:Duncan E. Farrow Pages: 983 - 995 Abstract: Abstract Numerical calculations for a model of the near-shore circulation in a lake subject to two diurnal forcing mechanisms are presented. The first mechanism is a heating/cooling term in the heat equation representing the daytime heating and nighttime cooling of the diurnal cycle. The second is a periodic surface stress modelling a sea-breeze/gully wind system typical of some coastal regions. The two forcing mechanisms can either act together or against each other depending on their relative phase. The numerical solutions are compared with previously published analytical solutions and used to explore the extra dynamics associated with non-linear effects (specifically advection). The latter dynamics include the formation of gravity currents and unstable density profiles leading to secondary circulation. PubDate: 2016-10-01 DOI: 10.1007/s10652-016-9461-4 Issue No:Vol. 16, No. 5 (2016)

Authors:Zakaraya Alhasan; Jan Jandora; Jaromir Riha Pages: 997 - 1019 Abstract: Abstract Sediment transport rate determination plays an essential role in mathematical models of embankment dam breaching. The sediment transport formulae commonly used today were mostly determined under considerably different conditions than those existing during the breaching of embankment dams, i.e. in connection with relatively mild longitudinal slopes. However, due to the scarceness of sediment transport relations for sediment transport rates on steep slopes, these traditional formulae are frequently used in dam breach modelling. This paper contains a description of a physical model of a 0.86 m high sandy dike constructed and breached at an outdoor laboratory operated by the Faculty of Civil Engineering, Brno University of Technology, Czech Republic. The dike shape and material were the same for all experiments. The used material was homogeneous non-cohesive medium-uniform sand. The results of the experimental breaching of the sandy dike were discussed and compared with sediment transport rates obtained from various empirical formulae. The comparison shows differences between experimental and calculated sediment transport rates which in all analysed cases indicate overestimation of the breaching rate calculated by empirical formulae. PubDate: 2016-10-01 DOI: 10.1007/s10652-016-9463-2 Issue No:Vol. 16, No. 5 (2016)

Authors:J. D. Qiao; S. K. Delavan; R. I. Nokes; D. R. Plew Pages: 1021 - 1041 Abstract: Abstract Laboratory experiments are conducted to quantify the mean flow structure and turbulence properties downstream of a spanwise suspended linear array in a uniform ambient water flow using Particle Tracking Velocimetry. Eighteen experimental scenarios, with four depth ratios (array depth to water column depth) of 0.35, 0.52, 0.78, and 0.95 and bulk Reynolds number (length scale is the array depth) from 11,600 to 68,170, are investigated. Three sub-layers form downstream of the array: (1) an internal wake zone, where the time-averaged velocity decreases with increasing distance downstream, (2) a shear layer which increases in vertical extent with increasing distance downstream of the array, and the rate of the increase is independent of the bulk Reynolds number or the depth ratio, and (3) an external wake layer with enhanced velocity under the array. The location of the shear layer is dependent on the depth ratio. The spatially averaged and normalized TKE of the wake has a short production region, followed by a decay region which is comparable to grid turbulence decay and is dependent on the depth ratio. The results suggest that the shear layer increases the transfer of horizontal momentum into the internal wake zone from the fluid outside of the array and that the turbulence in the internal wake zone can be modeled similarly to that of grid turbulence. PubDate: 2016-10-01 DOI: 10.1007/s10652-016-9465-0 Issue No:Vol. 16, No. 5 (2016)

Authors:Reza Parsa; Morteza Kolahdoozan; Mohammad Reza Alavi Moghaddam Pages: 833 - 844 Abstract: Abstract An experimental program was conducted to investigate vertical oil dispersion of surface oil spills under non-breaking regular waves. The variation in oil concentration caused by oil dispersion in a water column was studied to determine the vertical oil dispersion profile. The experiments were performed using different waves characteristics for different volumes of oil spill to evaluate the variation in oil concentration at three depths at two sampling stations. The correlations between oil concentration and the main parameters of wave characteristics, oil spill volume, sampling depth, and distance of sampling stations to spill location were assessed. The results revealed that the trend of variation in oil concentration versus wave steepness is linear. The results obtained from experimental measurements indicated that the oil concentrations at mid-depth were 44–77 % and the concentrations near the flume bed were 12–33 % of the concentration near the water surface. PubDate: 2016-08-01 DOI: 10.1007/s10652-016-9456-1 Issue No:Vol. 16, No. 4 (2016)

Authors:Peter Bacopoulos; Ethan J. Kubatko; Scott C. Hagen; Andrew T. Cox; Teddy Mulamba Abstract: Abstract Continuous data of vertical-profile salinity were analyzed for four stations located successively upriver in a macrotidal estuary, the lower St. Johns River (Northeast Florida, USA). The data analysis confirmed well-mixed salinity conditions in the river with at most 1.3 ppt of vertical variability at Dames Point (river km 20), where the main variations of salinity are along the longitudinal axis of the river. Given the well-mixed salinity conditions and dominant horizontal structure of salinity variations in the river, we present and apply a barotropic, two-dimensional modeling approach for hydrodynamic-salinity transport simulation in the lower St. Johns River. When properly forced by offshore surge, high-resolution wind fields and freshwater river inflows, the model replicated the salinity measurements remarkably well, including the separation into tidal and sub-tidal components. The data and model results show that, at times, offshore winds and surge can be more influential on longitudinal salinity variations than local winds over the river. We demonstrate the importance of using proper boundary conditions to force the model relative to the minimal sensitivity of the model to parameter adjustment of horizontal mixing and uncertainty-based perturbation of wind and inflow forcings. PubDate: 2016-10-14 DOI: 10.1007/s10652-016-9486-8

Abstract: Abstract This study implemented three analytical models to investigate the lateral distribution of depth-averaged streamwise velocity in a rectangular channel with lateral, unevenly-distributed, flexible submerged vegetation. Secondary flow, vegetation drag, and turbulent shear were introduced into the momentum equations to represent the interaction between vegetation and flow. Comparison of model results and experimental data indicated that predictions were improved with a mixing layer model, which considers the secondary flow term in the mixing region, particularly for channels with a high aspect ratio. The research established a relationship between the vegetation drag coefficient and the Reynolds number. A sensitivity analysis of the dimensionless eddy viscosity coefficient and bed friction factor indicated that the coefficient had as significant an impact as the second factor on the lateral velocity profile. A reasonable dimensionless eddy viscosity coefficient is essential to predict velocity accurately. PubDate: 2016-10-04 DOI: 10.1007/s10652-016-9485-9

Authors:Pedro Lopes; Jorge Leandro; Rita F. Carvalho; Daniel B. Bung Abstract: Abstract The study of stepped spillways in laboratory scales has been essentially focused on two separated sub-regimes within skimming flow. In this paper we investigate the appearance of an unclassified alternating skimming flow regime in a 0.5 m wide stepped spillway which does not fit on these earlier definitions, and which does not occur in a 0.3 m wide spillway. Our aim is to explain the genesis of this unclassified flow which is visualised in the physical stepped spillway, by using 3D numerical modelling. Flow depths and velocities are measured using an ultrasonic sensor and Bubble Image Velocimetry in the wider flume (0.5 m). The numerical model is validated with the experimental data from the 0.5 m wide spillway. After validation, the channel width of the same numerical model is reduced to 0.3 m wide spillway in order to characterise (compare) the case without (with) alternating skimming flow. Both cases are solved using Reynolds-Averaged Navier–Stokes equations together with the Volume-of-Fluid technique and SST k- \(\omega\) turbulence model. The experimental results reveal that the alternating skimming flow regime is characterised by an evident seesaw pattern of flow properties over consecutive steps. In turn, the numerical modelling clarified that this seesaw pattern is due to the presence of a complex system of cross waves along the spillway. These cross waves are also responsible for a mass and momentum exchange in the transversal direction and for the formation of the alternating skimming flow in the spillway. PubDate: 2016-10-01 DOI: 10.1007/s10652-016-9484-x

Authors:Liqun Lyu; Zhaoyin Wang; P. Cui Abstract: Abstract A typical two-phase debris flow exhibits a high and steep flow head consisting of rolling boulders and cobbles with intermittent or fluctuating velocity. The relative motion between the solid phase and the liquid phase is obvious. The motion of a two-phase debris flow depends not only on the rheological properties of the flow, but also on the energy transmission between the solid and liquid phases. Several models have been developed to study two-phase debris flows. An essential shortcoming of most of these models is the omission of the interaction between the two phases and identification of the different roles of the different materials in two-phase debris flows. The tracer particles were used for the velocity of solid phase and the velocity of liquid phase was calculated by the water velocity on the surface of the debris flow in the experiments. This paper analyzed the intermittent feature of two-phase debris flows based on videos of debris flows in the field and flume experiments. The experiments showed that the height of the head of the two-phase debris flow increased gradually in the initiation stage and reached equilibrium at a certain distance from the start of the debris flow. The height growth and the velocity of the flow head showed fluctuating characteristics. Model equations were established and the analyses proved that the average velocity of the two-phase debris flow head was proportional to the flood discharge and inversely proportional to the volume of the debris flow head. PubDate: 2016-09-20 DOI: 10.1007/s10652-016-9483-y

Authors:Moisés Brito; João Fernandes; João Bento Leal Abstract: Abstract The main goal of this study is the 3D numerical simulation of river flows with submerged vegetated floodplains. Since, vegetation layers are usually dense and present a large spatial heterogeneity they are here represented as a porous media. Standard semi-empirical relations drawn for porous beds packed with non-spherical particles are used to estimate the porous media parameters based on the averaged geometry of the vegetation elements. Thus, eliminating the uncertainty arising from a bulk drag coefficient approach and allowing the use of a coarser mesh. The free flow is described by Reynolds-averaged Navier–Stokes (RANS) equations, whereas the porous media flow is described by the volumetric-average of RANS equations. The volume-of-fluid method and an anisotropic explicit algebraic Reynolds stress model are used for free-surface and turbulence closure, respectively. The simulation approach is validated against results by other authors featuring vegetated flows in horizontal and rectangular open-channel. The computed results show that the time-averaged streamwise velocity and Reynolds shear stress vertical profiles are properly simulated. The validated approach was applied to simulate compound open-channel flows with submerged vegetated floodplains and compared with data obtained in an experimental facility. The results show that the proposed porous media approach is adequate to simulate flows with submerged vegetation on the floodplains. PubDate: 2016-09-09 DOI: 10.1007/s10652-016-9481-0

Authors:Nino Krvavica; Vanja Travaš; Nevenka Ožanić Abstract: Abstract The interfacial friction and entrainment were investigated in a microtidal salt-wedge estuary. A detailed sampling campaign was conducted in the Rječina River estuary in Croatia from January 2014 to June 2015. The observed vertical profiles of salinity s and temperature T confirmed the presence of a highly stratified estuary, represented by an upper layer of freshwater separated from a lower salt-wedge by a sharp density interface. The entrainment rate E across the interface was estimated by a two-layer box-model, based on the observed freshwater flow rate Q and layer-averaged salinity. Interfacial friction factor \(\lambda _i\) was estimated by fitting the results of a numerical model to the observed interface depths. For this purpose we applied a numerical two-layer shallow water model extended to account for irregular non-prismatic cross sections of the channel. We found that in microtidal conditions, the strength of the stratification is reduced with increasing Q. Furthermore, we found that as Q increases, so does the shear velocity, the interfacial friction factor and the vertical mixing across the interface. More detail analysis showed that E may be parametrized by bulk non-dimensional parameters, in particular, a combination of bulk Richardson number Ri and average friction factor \(\lambda\) , which accounts for the channel bed friction and the interfacial friction. On the other hand, \(\lambda _i\) can be linked to a combination of Reynolds number Re and bulk Richardson Ri. Contrary to previous studies, we showed that in field conditions, \(\lambda _i\) may increase with Re. PubDate: 2016-08-26 DOI: 10.1007/s10652-016-9480-1

Authors:Craig L. Strong; John F. Leys; Mike R. Raupach; Joanna E. Bullard; Hélène A. Aubault; Harry J. Butler; Grant H. McTainsh Abstract: Abstract Wind erosion processes affect soil surfaces across all land uses worldwide. Understanding the spatial and temporal scales of wind erosion is a challenging undertaking because these processes are diverse and highly variable. Wind tunnels provide a useful tool as they can be used to simulate erosion at small spatial scales. Portable wind tunnels are particularly valued because erosion can be simulated on undisturbed soil surfaces in the field. There has been a long history of use of large portable wind tunnels, with consensus that these wind erosion simulation tools can meet real world aerodynamic criteria. However, one consequence of striving to meet aerodynamic reality is that the size of the tunnels has increased, making them logistically difficult to work with in the field and resulting in a tendency to homogenise naturally complex soil surfaces. This homogenisation is at odds with an increasing awareness of the importance that small scale processes have in wind erosion. To address these logistical and surface homogenisation issues we present here the development and testing of a micro wind tunnel (MWT) designed to simulate wind erosion processes at high spatial resolution. The MWT is a duct-type design—0.05 m tall 0.1 m wide and with a 1.0 m working section. The tunnel uses a centrifugal motor to suck air through a flow‐conditioning section, over the working section and then through a sediment collection trap. Simulated wind velocities range from 5 to 18 m s−1, with high reproducibility. Wind speeds are laterally uniform and values of u * at the tunnel bed (calculated by measuring the pressure gradients within the MWT) are comparable with those of larger tunnels in which logarithmic profiles can be developed. Saltation sediment can be added. The tunnel can be deployed by a single person and operated on slopes ranging from 0 to 10°. Evidence is presented here that the MWT provides new and useful understanding of the erodibility of rangelands, claypans and ore stockpiles. PubDate: 2016-08-20 DOI: 10.1007/s10652-016-9478-8

Authors:Christian González; David H. Richter; Diogo Bolster; Samuel Bateman; Joseph Calantoni; Cristián Escauriaza Abstract: Abstract At the smallest scales of sediment transport in rivers, the coherent structures of the turbulent boundary layer constitute the fundamental mechanisms of bedload transport, locally increasing the instantaneous hydrodynamic forces acting on sediment particles, and mobilizing them downstream. Near the critical threshold for initiating sediment motion, the interactions of the particles with these unsteady coherent structures and with other sediment grains, produce localized transport events with brief episodes of collective motion occurring due to the near-bed velocity fluctuations. Simulations of these flows pose a significant challenge for numerical models aimed at capturing the physical processes and complex non-linear interactions that generate highly intermittent and self-similar bedload transport fluxes. In this investigation we carry out direct numerical simulations of the flow in a rectangular flat-bed channel, at a Reynolds number equal to Re = 3632, coupled with the discrete element method to simulate the dynamics of spherical particles near the bed. We perform two-way coupled Lagrangian simulations of 48,510 sediment particles, with 4851 fixed particles to account for bed roughness. Our simulations consider a total of eight different values of the non-dimensional Shields parameter to study the evolution of transport statistics. From the trajectory and velocity of each sediment particle, we compute the changes in the probability distribution functions of velocities, bed activity, and jump lengths as the Shields number increases. For the lower shear stresses, the intermittency of the global bedload transport flux is described by computing the singularity or multifr actal spectrum of transport, which also characterizes the widespread range of transport event magnitudes. These findings can help to identify the mechanisms of sediment transport at the particle scale. The statistical analysis can also be used as an ingredient to develop larger, upscaled models for predicting mean transport rates, considering the variability of entrainment and deposition that characterizes the transport near the threshold of motion. PubDate: 2016-08-05 DOI: 10.1007/s10652-016-9476-x

Authors:Juan Pablo Toro; Fabián A. Bombardelli; Joongcheol Paik; Inês Meireles; António Amador Abstract: Abstract In this work we address the mean flow and turbulence statistics in the non-aerated region of a stepped spillway by using two different numerical strategies in two dimensions. First, we present results regarding the flow in a large portion of the spillway, simulated with a volume of fluid (VoF) method to capture the position of the free surface (case A). Numerically-obtained data are in very good agreement with particle image velocimetry (PIV) data; further, results suggest that profiles of mean velocity, turbulent kinetic energy (TKE) and dissipation rate of TKE at the step edges are approximately self-similar. It was also found that values of TKE and dissipation rate of TKE in the boundary layer development region follow universal similarity laws which are valid for open-channel flows. In addition, the field of simulated dimensionless pressure and pressure distributions at the step edges are qualitatively similar to those reported in a recent experimental work. Second, additional simulations were developed as a pressure-driven flow for only a portion of the spillway (case B). This was possible due to prior knowledge of the water depths. We show that, despite the fact that the pressure field can not be interpreted as in case A, the numerical simulations closely reproduce the experimental data regarding averaged velocity, vorticity, and the turbulence statistics. It was also found that turbulence intensity profiles in the intermediate region are consistent with published experimental results for open-channel flows. These numerical results offer new avenues for the simulation of portions of stepped spillways to assess the physics at the inception point of air entrainment with more sophisticated turbulence closures. PubDate: 2016-08-04 DOI: 10.1007/s10652-016-9472-1

Authors:Mohamad M. Nasr-Azadani; Eckart Meiburg; Benjamin Kneller Abstract: Abstract Direct Numerical Simulations are employed to investigate the mixing dynamics of turbidity currents interacting with seamounts of various heights. The mixing properties are found to be governed by the competing effects of turbulence amplification and enhanced dissipation due to the three-dimensional topography. In addition, particle settling is seen to play an important role as well, as it affects the local density stratification, and hence the stability, of the current. The interplay of these different mechanisms results in the non-monotonic dependence of the mixing behavior on the height of the seamount. Regions of dilute lock fluid concentration generally mix more intensely as a result of the seafloor topography, while concentrated lock fluid remains relatively unaffected. For long times, the strongest mixing occurs for intermediate bump heights. Particle settling is seen to cause turbidity currents to mix more intensely with the ambient than gravity currents. PubDate: 2016-08-02 DOI: 10.1007/s10652-016-9477-9

Authors:Xiangyu Sun; Gustaaf Adriaan Kikkert; Chii Shang Abstract: Abstract To determine the feasibility of using a dam-break generated flow from the sea into a storm-drain to aid in the regeneration of iron particles that control the production of H2S in the storm-drain, a laboratory experimental investigation is carried out to measure the regeneration potential and the detailed hydrodynamics of the dam-break generated flow that causes the regeneration. The experiments are carried out using a reservoir of essentially infinite size, the sea, and a channel of limited width and adverse slope 1:20, the storm-drain. The regeneration experiments confirmed the ability of the dam-break generated flow to aid in the regeneration of the iron particles, however the regeneration potential varies from good to poor with distance away from the gate into the channel. The detailed measurements of the hydrodynamics highlighted that the dam-break generated flow from an infinite reservoir diverges little during the first uprush, has much smaller velocities during the first backwash and includes significant free surface waves. An initially wet channel bed reduces the flux into the channel. Close to the gate the flow depth increases more quickly but the velocity, and therefore the regeneration potential, is smaller. PubDate: 2016-07-27 DOI: 10.1007/s10652-016-9474-z