ALBERT

Description:    Prediction of mixing intensity of water masses in riverine Lake Tegel (Berlin, Germany) can be used to trace the fate of pollutants that enter the lake through several inflows. Because the contributions of each inflow have not yet been quantified and because the lake features complex bathymetry and numerous islands, a hydrodynamic circulation model with high spatial resolution and dynamic wind forcing is useful. We applied the two-dimensional version of the Princeton Ocean Model to separate the influences of wind and river discharge on the currents and mass transport in Lake Tegel. For model validation, we compared the simulation results with 1 year of electrical conductivity data, which was used as a conservative tracer to distinguish between water from the River Havel and water supplied by a smaller second inflow. Calculation of currents alone is insufficient to investigate water exchanges between rivers and lakes, especially when several islands create multiple pathways for river intrusion. Therefore, mass transport simulations are applied. Our calculations based on archetypical scenarios indicate that the proportion of (polluted) water from the River Havel in the main basin of Lake Tegel fluctuates with river discharge and wind, which either amplify or neutralize each other. Content Type Journal Article Category Original Article Pages 1-19 DOI 10.1007/s10652-012-9236-5 Authors Sebastian Schimmelpfennig, Department of Ecohydrology, Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Müggelseedamm 310, 12587 Berlin, Germany Georgiy Kirillin, Department of Ecohydrology, Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Müggelseedamm 310, 12587 Berlin, Germany Christof Engelhardt, Department of Ecohydrology, Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Müggelseedamm 310, 12587 Berlin, Germany Gunnar Nützmann, Department of Ecohydrology, Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Müggelseedamm 310, 12587 Berlin, Germany Journal Environmental Fluid Mechanics Online ISSN 1573-1510 Print ISSN 1567-7419

Description:    This paper describes a σ -coordinate scalar transport model coupled with a Boussinesq-type hydrodynamic model. The Boussinesq model has the ability to calculate both three-dimensional velocity distributions and the water surface motion. To capture ‘dispersion’ processes in open channel flow, horizontal vorticity effects induced by a bottom shear stress are included in the Boussinesq model. Thus, a reasonable representation of vertical flow structure can be captured in shallow and wavy flow fields. To solve the coupled Boussinesq and scalar transport system, a finite-volume method, based on a Godunov-type scheme with the HLL Riemann solver, is employed. Basic advection and advection–diffusion numerical tests in a non-rectangular domain were carried out and the computed results show good agreement with analytic solutions. With quantitative comparisons of dispersion experiments in an open channel, it is verified that the proposed coupled model is appropriate for both near and far field scalar transport predictions. From numerical simulations in the surf zone, physically reasonable results showing expected vertical variation are obtained. Content Type Journal Article Category Original Article Pages 1-22 DOI 10.1007/s10652-012-9256-1 Authors Dae-Hong Kim, Department of Civil Engineering, University of Seoul, Seoul, Republic of Korea Patrick J. Lynett, Sonny Astani Department of Civil and Environmental Engineering, University of Southern California, Los Angeles, CA, USA Journal Environmental Fluid Mechanics Online ISSN 1573-1510 Print ISSN 1567-7419

Description:    This work proposes an approach to simulate wind flow fields around an urban environment with the aim of evaluating the potential impact of buildings on the general wind patterns and power production using the current generation of commercial wind turbines. The simulation process was performed with the aid of accessible computational tools that can potentially render the proposed procedure applicable in other cases of interest. The roughness of the urban environment was defined as the association of roughness map, topography, and an alternative process for obtaining the volumetry of buildings. A case study was conducted in a region located at the district of Boa Viagem (Recife-PE) for assessing the applicability of the approach. Scenarios were designed in order to simulate wind flow patterns and pre-identify sites that have suitable wind energy potential for electric power production by investigating the combination of wind speed magnitude and turbulence intensity. From the results obtained, it was possible to identify zones of potential wind sources that are not detected in classical wind atlas probably due to the influence of the built environment on local wind flow patterns. Content Type Journal Article Category Original Article Pages 1-18 DOI 10.1007/s10652-012-9258-z Authors Alex Maurício Araújo, Universidade Federal de Pernambuco, Recife, PE, Brazil Daniel Arraes de Alencar Valença, Universidade Federal de Pernambuco, Recife, PE, Brazil Aigbokhan Isaiah Asibor, Universidade Federal de Pernambuco, Recife, PE, Brazil Pedro André Carvalho Rosas, Universidade Federal de Pernambuco, Recife, PE, Brazil Journal Environmental Fluid Mechanics Online ISSN 1573-1510 Print ISSN 1567-7419

Description:    In an open channel, a change from a supercritical to subcritical flow is a strong dissipative process called a hydraulic jump. Herein some new measurements of free-surface fluctuations of the impingement perimeter and integral turbulent time and length scales in the roller are presented with a focus on turbulence in hydraulic jumps with a marked roller. The observations highlighted the fluctuating nature of the impingement perimeter in terms of both longitudinal and transverse locations. The results showed further the close link between the production and detachment of large eddies in jump shear layer, and the longitudinal fluctuations of the jump toe. They highlighted the importance of the impingement perimeter as the origin of the developing shear layer and a source of vorticity. The air–water flow measurements emphasised the intense flow aeration. The turbulent velocity distributions presented a shape similar to a wall jet solution with a marked shear layer downstream of the impingement point. The integral turbulent length scale distributions exhibited a monotonic increase with increasing vertical elevation within 0.2 〈 L z /d 1 〈 0.8 in the shear layer, where L z is the integral turbulent length scale and d 1 the inflow depth, while the integral turbulent time scales were about two orders of magnitude smaller than the period of impingement position longitudinal oscillations. Content Type Journal Article Category Original Article Pages 1-16 DOI 10.1007/s10652-012-9254-3 Authors Gangfu Zhang, School of Civil Engineering, The University of Queensland, Brisbane, QLD 4072, Australia Hang Wang, School of Civil Engineering, The University of Queensland, Brisbane, QLD 4072, Australia Hubert Chanson, School of Civil Engineering, The University of Queensland, Brisbane, QLD 4072, Australia Journal Environmental Fluid Mechanics Online ISSN 1573-1510 Print ISSN 1567-7419

Description:    Air–water flows at hydraulic structures are commonly observed and called white waters. The free-surface aeration is characterised by some intense exchanges of air and water leading to complex air–water structures including some clustering. The number and properties of clusters may provide some measure of the level of particle-turbulence and particle–particle interactions in the high-velocity air–water flows. Herein a re-analysis of air–water clusters was applied to a highly aerated free-surface flow data set (Chanson and Carosi, Exp Fluids 42:385–401, 2007 ). A two-dimensional cluster analysis was introduced combining a longitudinal clustering criterion based on near-wake effect and a side-by-side particle detection method. The results highlighted a significant number of clustered particles in the high-velocity free-surface flows. The number of bubble/droplet clusters per second and the percentage of clustered particles were significantly larger using the two-dimensional cluster analysis than those derived from earlier longitudinal detection techniques only. A number of large cluster structures were further detected. The results illustrated the complex interactions between entrained air and turbulent structures in skimming flow on a stepped spillway, and the cluster detection method may apply to other highly aerated free-surface flows. Content Type Journal Article Category Original Article Pages 1-15 DOI 10.1007/s10652-012-9255-2 Authors Simin Sun, School of Civil Engineering, The University of Queensland, Brisbane, QLD 4072, Australia Hubert Chanson, School of Civil Engineering, The University of Queensland, Brisbane, QLD 4072, Australia Journal Environmental Fluid Mechanics Online ISSN 1573-1510 Print ISSN 1567-7419

Description:    A positive surge is a unsteady open channel flow resulting from the rapid rise of the free-surface. The phenomenon may be observed in water supply canals and channels as well as in some estuaries during spring tidal conditions. The formation and development of positive surges can be predicted using the method of characteristics and shallow water equations. The paper is the second part of a study presenting the results from new experimental investigations conducted in a large rectangular channel. Detailed unsteady velocity measurements were performed with a high temporal resolution using acoustic Doppler velocimetry and non-intrusive free-surface measurement devices. Several experiments were conducted with the same initial discharge ( Q = 0.060 m 3 /s) and six different gate openings after closure resulting in both non-breaking undular and breaking bores. A comparison between main features of the undular surges with literature theories demonstrated that the experimental data were mostly in agreement with Andersen’s theory. The analysis of unsteady flow field including Reynolds stresses confirmed and extended previous findings about positive surge hydrodynamics. Content Type Journal Article Category Original Article Pages 641-651 DOI 10.1007/s10652-011-9222-3 Authors Carlo Gualtieri, Department of Hydraulic, Geotechnical and Environmental Engineering (DIGA), University of Napoli “Federico II”, Via Claudio 21, 80125 Napoli, Italy Hubert Chanson, School of Civil Engineering, The University of Queensland, Brisbane, QLD 4072, Australia Journal Environmental Fluid Mechanics Online ISSN 1573-1510 Print ISSN 1567-7419 Journal Volume Volume 11 Journal Issue Volume 11, Number 6

Description:    Marine aquaculture is expanding rapidly without reliable quantification of effluents. The present study focuses on understanding the transport of dissolved wastes from aquaculture pens in near-coastal environments using the hydrodynamics code SUNTANS (Stanford Unstructured Nonhydrostatic Terrain-following Adaptive Navier–Stokes Simulator), which employs unstructured grids to compute flows in the coastal ocean at very high resolution. Simulations of a pollutant concentration field (in time and space) as a function of the local environment (bathymetry), flow conditions (tides and wind-induced currents), and the location of the pens were performed to study their effects on the evolution of the waste plume. The presence of the fish farm pens cause partial blockage of the flow, leading to the deceleration of the approaching flow and formation of downstream wakes. Results of both the near-field area (area within 10 to 20 pen diameters of the fish-pen site) as well as far-field behavior of the pollutant field are presented. These detailed results highlight for the first time the importance of the wake vortex dynamics on the evolution of the near-field plume as well as the rotation of the earth on the far-field plume. The results provide an understanding of the impact of aquaculture fish-pens on coastal water quality. Content Type Journal Article Category Original Article Pages 329-352 DOI 10.1007/s10652-011-9209-0 Authors Subhas K. Venayagamoorthy, Department of Civil and Environmental Engineering, Colorado State University, Fort Collins, CO 80523-1372, USA Hyeyun Ku, Department of Civil and Environmental Engineering, Colorado State University, Fort Collins, CO 80523-1372, USA Oliver B. Fringer, Environmental Fluid Mechanics Laboratory, Department of Civil and Environmental Engineering, Stanford University, Stanford, CA 94305, USA Alice Chiu, Program on Food Security and the Environment, Stanford University, Stanford, CA 94305, USA Rosamond L. Naylor, Program on Food Security and the Environment, Stanford University, Stanford, CA 94305, USA Jeffrey R. Koseff, Environmental Fluid Mechanics Laboratory, Department of Civil and Environmental Engineering, Stanford University, Stanford, CA 94305, USA Journal Environmental Fluid Mechanics Online ISSN 1573-1510 Print ISSN 1567-7419 Journal Volume Volume 11 Journal Issue Volume 11, Number 4

Description:    Experimental results on tracer gas diffusion within the near wake of a simplified model car (Ahmed model with a rear slant angle of 25°) are presented. Pollutant emission is simulated using heated air injected through a small pipe at one side of the model base. Fine cold wire thermometry is used to measure instantaneous temperature excess and variance of temperature gradient in the near wake. Measurements of the three mean velocity components were made using a laser Doppler anemometers system. Characteristics of the mean and fluctuating temperature fields, time-averaged flow streamlines and scalar dissipation measurements are presented and discussed. The local mixing time scale is determined from the measured mean dissipation rate of temperature variance. Its value shows that micromixing is not a limiting phenomenon for chemical reactions in the near wake. Content Type Journal Article Category Original Article Pages 573-589 DOI 10.1007/s10652-011-9219-y Authors K. Gosse, C.N.R.S. UMR 6614, CORIA Université de Rouen, Site Universitaire du Madrillet, BP 12, 76801 Saint Etienne du Rouvray Cedex, France M. Gonzalez, C.N.R.S. UMR 6614, CORIA Université de Rouen, Site Universitaire du Madrillet, BP 12, 76801 Saint Etienne du Rouvray Cedex, France P. Paranthoën, C.N.R.S. UMR 6614, CORIA Université de Rouen, Site Universitaire du Madrillet, BP 12, 76801 Saint Etienne du Rouvray Cedex, France Journal Environmental Fluid Mechanics Online ISSN 1573-1510 Print ISSN 1567-7419 Journal Volume Volume 11 Journal Issue Volume 11, Number 6

Description:    An idealised two-dimensional laboratory model of tsunamis generated by submarine landslides is described. The experimental configuration corresponds to the benchmark configuration suggested by other researchers in the international tsunami community. It comprises a semi-elliptical rigid landslide with a height to length ratio of 0.052 sliding down a 15° slope. The initial landslide submergence and specific gravity are varied, the second of which primarily determines the initial landslide acceleration. In these experiments the landslide motion is generally well approximated as consisting of two periods of constant acceleration. The first phase of positive acceleration finishes as the landslide reaches the base of the slope, while the second period of a slower deceleration continues until the landslide comes to rest along the horizontal base of the tank. A novel experimental technique, which utilises laser-induced fluorescence (LIF), is employed to measure the free surface displacement over the entire space and time domains. This enables the wave potential energy field to be computed directly and provides a vivid picture of the wave generation and development process. Particle tracking velocimetry provides detailed information on the landslide motion and also some data on the sub-surface velocity field. Experimental runs require multiple repeats (typically 35–50) of the same setup in order to capture the entire wave field with the desired resolution. Thus high level experimental repeatability is required, and this is demonstrated. A range of parameters relevant to hazard management are presented and discussed. Maximum crest and trough amplitudes of the offshore propagating waves are shown to be approximately proportional to the initial landslide acceleration and somewhat less strongly dependent on the initial landslide submergence. The maximum wave run-up experienced at the shoreline is shown to depend almost linearly on the magnitude of a high deceleration that occurs for a short period when the landslide nears the toe of the slope. The initial submergence and initial acceleration do not directly determine the maximum wave run-up, although for these experiments they impact indirectly on the magnitude of the deceleration. The efficiency of the energy transfer from the landslide potential energy to the wave field potential energy reaches values of up to 6% and is found to be strongly dependent on the initial submergence. However because of the link between the landslide mass and its acceleration, this efficiency is almost completely independent of the initial acceleration. The results from a numerical model based on linear, inviscid and irrotational wave theory, and solved with the boundary element method, are compared with the data from the experimental program. The numerical model accurately produces the generated sequence of wave crests and troughs, but slightly overpredicts their phase speed by between 2 and 4%. For all other parameters the numerical model predictions are within 25% of the experimental values, although this includes both under- and overprediction for the range of independent parameters covered. Content Type Journal Article Category Original Article Pages 133-165 DOI 10.1007/s10652-010-9205-9 Authors L. P. Sue, Beca Pty Ltd., Melbourne, Australia R. I. Nokes, Department of Civil and Natural Resources Engineering, University of Canterbury, Christchurch, New Zealand M. J. Davidson, Department of Civil and Natural Resources Engineering, University of Canterbury, Christchurch, New Zealand Journal Environmental Fluid Mechanics Online ISSN 1573-1510 Print ISSN 1567-7419 Journal Volume Volume 11 Journal Issue Volume 11, Number 2

Description:    An analysis of concentration time series measured in a boundary-layer wind tunnel at the University of Hamburg is presented. The measurements were conducted with a detailed aerodynamic model of the Oklahoma City (OKC) central business district (CBD) at the scale of 1:300 and were part of the Joint Urban 2003 (JU2003) project. Concentration statistics, as well as concentration probability density (PDF) and exceedance probability (EDF) functions were computed for street- and roof-level sites for three different wind directions. Taking into account the different length scales and wind speeds in the wind-tunnel (WT) and full-scale experiments, dimensionless concentrations and a dimensionless time scale are computed for the comparison with data from the JU2003 full-scale tracer experiments, conducted in OKC in 2003. Using such dimensionless time, the WT time series cover a ~20 times longer time span than the JU2003 full-scale time series, which are analysed in detail in an accompanying, first part of this paper. The WT time series are thus divided into 20 consecutive blocks of equal length and the statistical significance of parameters based on relatively short records is assessed by studying the variability of the concentration statistics and probability functions for the different blocks. In particular at sites closer to the plume edge, the results for the individual blocks vary significantly and at such sites statistics from short records are not very representative. While the location of three sampling sites in the WT closely matched the sites during the full-scale experiments, the prevailing wind directions during the JU2003 releases were not exactly matched. The comparison between full-scale and WT concentration parameters should thus primarily be interpreted in a qualitative rather than direct quantitative sense. Given the differences in mean wind directions and concerns about the representativeness of full-scale concentration statistics, the WT and full-scale results compared well. The 98 percentile concentrations for almost all full-scale releases analyzed are within the scatter of the percentiles observed in the block analysis of the WT time series. Furthermore, the concentration percentiles appear linearly correlated with the fluctuation intensities and the linear relationships determined in the wind tunnel agree well with full-scale results. Content Type Journal Article Category Original Article Pages 43-60 DOI 10.1007/s10652-010-9195-7 Authors P. Klein, School of Meteorology, University of Oklahoma, 120 David L. Boren Blvd., Norman, OK 73072, USA B. Leitl, Meteorological Institute, EWTL, University of Hamburg, Hamburg, Germany M. Schatzmann, Meteorological Institute, EWTL, University of Hamburg, Hamburg, Germany Journal Environmental Fluid Mechanics Online ISSN 1573-1510 Print ISSN 1567-7419 Journal Volume Volume 11 Journal Issue Volume 11, Number 1