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Dollar spot is caused by the fungus Clarireedia spp. and is the most economically important disease of golf course turfgrass in temperate regions of the United States. Previous research has demonstrated that nitrogen (N) fertilization may reduce dollar spot severity, but the results have been inconsistent, and the impact of N as part of repeated foliar fertilization applications to golf course putting greens remains unclear. Two independent trials were replicated in Madison, Wisconsin and Glenview, Illinois in the 2015, 2016, and 2017 growing seasons. The objective of the first trial was to evaluate the effect of four different N rates applied as urea (4.9, 9.8, 19.4, and 29.3 kg N/ha applied every 2 weeks) on dollar spot severity, and the objective of the second trial was to evaluate the effect of three N sources (calcium nitrate, ammonium sulfate, and ammonium nitrate applied every 2 weeks) on dollar spot severity. Results from the N rate trial at both locations indicated that only the highest (29.3 kg N/ha) rate consistently reduced dollar spot severity relative to the nontreated control. Nitrogen source had minimal and inconsistent impacts on dollar spot severity based on location and year. Although these results show that meaningful reductions in dollar spot severity can be achieved by manipulating N fertilizer application rates, the rate of N needed for disease suppression may be impractical for most superintendents to apply and result in undesirable nontarget impacts.

Recently, major tsunami events have resulted in considerable damage to low-lying coastal developments as well as significant loss of life. This is owing to the fact that coastal communities and associated infrastructure are not able to withstand the extreme hydrodynamic forces induced by the overland progression of large tsunami waves. This paper reports the findings of a study, which is part of an ongoing comprehensive (hydraulic-structural engineering) research program initiated at the University of Ottawa in Canada. The goals of the latter are to contribute to the understanding and quantification of extreme hydrodynamic impacts on structural elements, and to the development of design guidelines for structures located in tsunami-prone areas. In this study, a single-phase three-dimensional (3D) weakly compressible smoothed-particle hydrodynamics (WCSPH) model is used to investigate the hydrodynamic forces, induced by the impact of rapidly advancing tsunami-like hydraulic bores, on a freestanding ...

[1] Most rivers exhibit regions of strong channel curvature that are characterized by more complex and variable flow and erosion patterns, compared to regions of lower curvature. Studies investigating high-curvature bends using eddy-resolving techniques have been limited, and the effect of bend angle on flow and erosion has rarely been investigated. This study investigates flow in a 135° nonerodible bank open channel bend of high curvature: ratio of radius of curvature, R, to channel width, B, is 1.5. The bathymetry is obtained during the final stages of a clear water scour experiment. Large Eddy Simulation is used to investigate the effect of secondary flow on the redistribution of streamwise momentum, the details of coherent structures, and mechanisms leading to erosion within the bend. Results are compared with those from a similar numerical study of a 193° sharply curved open channel bend with R/B = 1.35. The angle of the 135° bend is representative of typical regular meander geometry, while the larger angle of the 193° bend is representative of a tortuous meander geometry. The different bathymetries induced important quantitative and qualitative differences in the vortical and turbulence structure within the open channel for the two cases. Inner bank streamwise-oriented vortical (SOV) cells formed in both cases, but the position and extent of shear layers forming between regions of fast and slow moving fluid differed, and flow did not separate at the inner bank in the 135° bend. An outer-bank cell was observed in the 135° bend, but not in the 193° bend. Distributions of predicted boundary shear stresses indicated the capacity of the flow to erode the outer bank of a sharply curved bend under two representative regimes found in the field.

A series of seven stream barbs were installed in two consecutive channel bends of Sawmill Creek (Ottawa, Canada), a semi-alluvial stream with bed and banks composed of consolidated clay. Stream barbs (also known as submerged groynes) are low-profile linear rock structures that project out from the bank (in an upstream direction) to redirect flow and prevent erosion of the bank. As well as providing bank protection, barbs promote vegetated stream banks, create scour hole resting pools for fish habitat and can increase aquatic species diversity. Flow conditions (discharge and water levels), water velocity distribution using acoustic Doppler velocimeters and an acoustic Doppler current profiler, and bathymetry using a Total Station have been measured over a period of 5 years, both before (2 years) and after (2 years) the construction of the barbs, providing valuable data for understanding stream barb performance in a semi-alluvial channel. Pre-barb velocity measurements indicate that the flow field in the first bend is dominated by strong secondary circulation and high cross-stream bed stresses that comprise a substantial proportion of the total near-bed Reynolds stress. Post-barb results indicate that velocity magnitude along the outer bank was reduced. Scour occurred in the channel centre near barb tips, but in general, little to no bathymetry changes were measured between seasonal surveys, suggesting that the barbs had limited impact on bed topography and/or that semi-alluvial channel bends are resistant to change. Recommendations for future design and implementation of stream barbs are also included. Copyright © 2013 John Wiley & Sons, Ltd.

A series of laboratory flume experiments were performed to study the effect of stream barbs on flow field dynamics and sediment erosion in a 135° mobile-bed channel bend. Stream barbs (also known as spur dikes or submerged groynes) are low-profile linear rock features that redirect high velocity flow away from the outer bank of channel bends. Unlike emergent groynes, the submerged nature of these structures creates a unique combination of horizontal shear (plunging type flow) and vertical shear (at the groyne tip). Spatially dense, high frequency velocity data were collected and analyzed to describe the pattern and magnitude of three-dimensional (3D) velocity throughout the bend and in the vicinity of the stream barbs. This paper demonstrates that the outer bank region (particularly between barbs) may still be at risk of erosion (or even increased erosion greater than the same case without barbs) if stream barbs generate excessive secondary velocities (because of their size and layout) that are op...

Flow within an alluvial channel bend is significantly affected by channel geometry, including curvature ratio (bend radius/channel width, R/B) and aspect ratio (channel width/flow depth, B/H). High curvature bends (R/B≤3) can experience substantially more erosion than milder curvature bends. This study employs a three-dimensional Reynolds-Averaged Navier-Stokes (RANS) model to investigate the effects of curvature ratio and aspect ratio on bend flow with respect to a high curvature (R/B=1.5) base case in a 135° bend. Experimental data are used to validate the RANS model predictions for the high curvature base case with a flat bed (FB) and an equilibrium deformed bed (DB). Five curvature ratios (1.5, 3, 5, 8, and 10) and four aspect ratios (5.00, 6.67, 9.09, and 12.50) are investigated. Results show that a decrease in R/B or B/H for the FB cases results in a strong increase in total circulation of the regions associated with the primary cell of cross-stream circulation (Γ+), an increase in maximum b...

In this paper, the simulation of the impact with structures of tsunami-like bores rapidly advancing on dry and wet beds is performed using a three-dimensional numerical model based on the Smoothed Particle Hydrodynamics (SPH) method. Firstly, to validate the numerical model, physical experiments are simulated and a quantitative comparison between experimental and numerical results is presented. Secondly, numerical results of the propagation of bores on dry and wet beds are compared to the analytical solution of the shallow water equations. Furthermore, the resulting time-histories of the pressures and net force acting on a square column and a vertical wall due to the impact of these bores are compared qualitatively. To better understand the development of the hydrodynamic forces, a detailed analysis of the velocity field and of the water surface elevation is also incorporated. This study is part of a comprehensive interdisciplinary research program whose purpose is to help develop design guidelines for tsunami-prone structures.

A new flume bed-sediment hardening method employing a surficial layer of plaster of Paris coated by spar urethane has been developed and tested for sand beds. Unlike existing bed-hardening techniques, this method is gentle enough to be used in and subsequently removed from a laboratory flume made of Plexiglas, yet is durable enough to last several days under flowing water. Tests showed that artificially fixed beds withstand an estimated bed shear stress of up to 0.251 N/m2 for 52 h. The effects of the hardening technique on bed roughness were evaluated. A mean absolute difference in the bed roughness estimate between fixed and loose beds of 0.166 mm was found when tested on a sand bed. Although roughness estimates seemed reasonable, standard deviations were high. Further testing under a wider range of flow conditions and sediment sizes is required to assess the effect of the hardening technique on roughness.

This paper presents the results of an experimental investigation into the hydraulic efficiency of a vertically oriented water intake. Under low submergence conditions, the operation of such an intake is affected significantly by the formation of surface vortices, which result in significant flow reduction and the downstream entrainment of air and swirl. The experimental work considered the fact that vortex formation is governed by the geometrical characteristics of the intake, including the diameter, local shape, submergence, surrounding boundary, etc, and the velocity distribution in the approaching flow. Therefore, an experimental study was conducted to investigate the influence that the local shape and the proximity to nearby boundaries have on the hydraulic performance of a vertical water intake. The results of this experimental investigation will hopefully lead to a better understanding of the phenomena governing the flow in such structures and to the elaboration of improved engineering design guidelines.

The development of a fully three-dimensional finite volume morphodynamic model, for simulating fluid and sediment transport in curved open channels with rigid walls, is described. For flow field simulation, the Reynolds-averaged Navier–Stokes equations are solved numerically, without reliance on the assumption of hydrostatic pressure distribution, in a curvilinear nonorthogonal coordinate system. Turbulence closure is provided by either a low-Reynolds number k−ω turbulence model or the standard k−e turbulence model, both of which apply a Boussinesq eddy viscosity. The sediment concentration distribution is obtained using the convection-diffusion equation and the sediment continuity equation is applied to calculate channel bed evolution, based on consideration of both bed load and suspended sediment load. The governing equations are solved in a collocated grid system. Experimental data obtained from a laboratory study of flow in an S-shaped channel are utilized to check the accuracy of the model’s hydrodyn...

A three-dimensional numerical model was used to examine the turbulent flow field and associated sediment transport due to a series of barbs (submerged groynes) in a channel bend. Model results were in good agreement with measured laboratory data and adequately simulated the important features of sediment transport. Statistical comparison of the predicted and measured equilibrium bed geometry found average regression coefficients of determination of 0.77 and 0.72 for the 90° and 135° channels, respectively. The predicted velocity data followed expected trends. The capability of a three-dimensional numerical model to simulate sediment transport through bend sections of a channel containing barbs was verified. This included the simulation of the effects of different arrangements of barb groups and an analysis of the data to determine the relation of the flow field to associated scour and deposition in a complex fluvial environment. These novel results are useful for improved analyses of the bank-protection capabilities of these structures and for the development and improvement of design guidelines.Key words: three-dimensional models, numerical models, movable bed models, channel bends, turbulence, secondary flow, scour, barbs, groynes.

Phase 1 of an ongoing laboratory study of a novel form of stream-bank protection structure is described. "Barbs" are dike-like stone structures designed to protect the (usually unstable) outside-bank regions of channel bends. These low-profile structures point upstream into the flow and typically extend to about 1/4-way across the channel. By disrupting near-bank velocity gradients they promote sediment deposition along the eroding outside-bank region. Their presence also modifies the "helicoidal"-type flow pattern of the bend such that secondary currents, which would otherwise attack the outside-bank, are redirected towards the center of the channel. This novel form of bank protection structure is currently undergoing field tests on selected bends on a number of shallow "wide" streams in Illinois, USA. While initial results are encouraging, additional studies are necessary to develop design criteria for their wider application. In phase 1 of this study, the effectiveness of different arrangements of barb groups, in both 90° and 135° moveable-bed bend sections of a hydraulically "narrow" rectangular channel, are investigated. For each hydraulic condition considered, the channel-bed scour profiles generated by the different barb groups are compared to corresponding "reference" profiles generated in the absence of barbs. Judging the effectiveness of the different barb groups in promoting long-term stability of the outside-bank region is based on two criteria: (i) percent reduction achieved in scouring in the vicinity of the outside-bank and (ii) degree to which the channel thalweg (deepest portion) is moved from the outside-bank region towards the center of the channel.Key words: barb, channel bends, local scouring, bank erosion, bank protection, secondary currents.

In view of the selfcalibrating feature, the brink depth generated at the entrance to a freelydischarging drop structure in a prismatic open channel is widely used for estimating channel discharge. ...

In this paper we describe the development and validation of a 2-D finite-difference mathematical model for simulating inert pollutant transport in compound channels. In its formulation the model couples depth-averaged (depth-integrated) versions of the classical 3-D Navier-Stokes equations and the advection-diffusion equation with constant eddy-viscosity model. The numerical solution scheme is Platzman’s space-staggered scheme, and a double time step operation is employed in the analysis. The model is initially validated using laboratory data of continuous-injection dye tracer experiments performed in a large asymmetrical compound-shaped channel at the Hydraulics Laboratory, University of Ottawa. Comparison between predicted and observed dye concentration curves indicates generally good agreement in the overall shapes of the curves, as well as in the peak concentrations and the times to peak.

Most previous laboratory studies of local scour at bridge abutments were performed in rectangular channels in which the distributions of flow velocity and bed shear stress were considered uniform in the transverse direction. In reality, however, bridge abutments usually terminate in the flood plain zone of rivers where velocity and shear stress are not uniformly distributed. This paper presents the results of a laboratory study performed to investigate the impact of lateral momentum of flow intercepted by abutment and flow related to a specific channel width at the abutment end, is a significant parameter to account for lateral momentum transfer and should be incorporated in the scour prediction formulation. Also, based on the discharge ratio, Froude number, and critical Froude number associated with the sediment size, a relationship for predicting maximum local scour depth at bridge abutments was proposed. (A)

L'objectif principal de cette etude etait d'optimiser l'horaire de pompage et de relâchement du reservoir d'approvisionnement d'eau dans la Municipalite regionale d'Ottawa-Carleton (MROC), dans le but de reduire les couts d'operation relies. Les demandes horaires doivent etre satisfaites avec un cout minimum de pompage. L'article precedent (partie 1) decrit le systeme de la MROC et le modele numerique utilise dans l'analyse d'optimisation. Le present article (partie 2) presente les principaux resultats obtenus de l'optimisation, et rapporte sur l'objectif de la seconde etude, qui etait d'examiner l'impact sur les couts d'operation d'augmenter : (i) la capacite d'emmagasinage du reservoir, (ii) la capacite de la station de traitement ; et (ii) la demande d'eau des consommateurs. En general, la programmation lineaire s'est averee une bonne option pour generer des horaires optimises de pompage et de relâchement de service du reservoir. Les analyses des alternatives de gestion d'eau ont confirme que le systeme d'approvisionnement d'eau de la MROC etait dimensionne pour des demandes journalieres maximales, cependant, les operations jours-a-jours seraient simplifiees si les amenagements actuels d'emmagasinage et de traitement seraient elargies. Il serait economiquement difficile de justifier les couts de construction a partir des economies potentielles d'energie obtenues de cette etude. Il semble ainsi qu'il est important de commencer la gestion de la demande.

The principal objective of this study was to optimize pump scheduling and reservoir releases in the Regional Municipality of Ottawa-Carleton's (RMOC) water supply system with a view to reducing electricity-related operating costs. Pump schedules and reservoir releases for enhanced operation were obtained using a linear programming optimization model that incorporated Ottawa Hydro's electricity tariff structure for "large" users. A second objective was to investigate the impact on system operating costs of increasing (i) reservoir storage capacity, (ii) treatment plant capacity, and (iii) water demand by consumers. This paper (part I) describes the RMOC distribution system and reviews the model development. The next paper (part II) presents the analyses performed for the two study objectives, and important results. Key words: water supply system, pump scheduling, pumping costs, optimization, modelling.

This study evaluates various alternatives to account for flood plain conveyance in steady compound channel flows. Evaluations are based on applying several traditional discharge estimation methods to a steady, uniform flow laboratory data set. Many of the applied techniques overestimate compound channel discharge. Six interface and two other standard methods for computing discharge in open channels were compared. Each interface method uses a particular arrangement of imaginary interface planes to artificially sub-divide the compound flow field into homogeneous zones. These methods are named for the particular interface plane arrangement adopted. The two standard methods do not involve interface planes. In general, among the methods tested, the outward-facing diagonal interface plane method and the vertical interface plane method produced the most accurate simulations.

Floodplain conveyance in compound channel flows is examined through applications of the dynamic flow routing model DWOPER to both laboratory and field data sets. Three different approaches regarding the modelling of off-channel storage are considered, namely, the single-channel approach and two interface-plane methods, which artificially separate main channel flows from floodplain flows, using (i) vertical and (ii) diagonal interface planes. The single-channel method, which views composite flow fields as single units without storage, produced significant differences between simulated and observed stage and discharge hydrographs. The vertical interface method gave generally good results in the case of the laboratory data, but was less successful when applied to the field data. The diagonal interface method, which in this instance applied outward-facing diagonal interface planes at the junctions of the main channel and floodplain zones, produced superior results overall. Key words: floodplain, conveyance, unsteady flow, compound channels, off-channel storage, interface planes.

A mathematical model for routing unsteady flows through compound channels is described. The new model, RUFICC, accounts for flood plain contributions to system conveyance and also for lateral momentum transfer between adjacent deep and shallow zones of compound flow fields. In the modeling approach composite channel sections are divided into representative deep (main channel) and shallow (flood plain) zones. Continuity and momentum equations are written separately for the different sub-sections and summed to yield the composite section equations. The one-dimensional model equations, which are a modified form of the St. Venant equations, are solved using a four-point implicit finite-difference scheme. The initial model validation tests reported herein used laboratory data from a European study on unsteady flow in open channels. For the various model flood events simulated a good agreement was obtained between predicted and observed stage and discharge hydrographs. RUFICC's performance was compared to those...

The seasonal and annual global distributions of diabatic heating during the First GARP Global Experiment (FGGE) are estimated using the isentropic mass continuity equation. The data used are from the FGGE Level IIIa analyses generated by the United States National Meteorological Center. Spatially and temporally coherent diabatic heating distributions are obtained from the isentropic planetary scale mass circulation that is forced by large-scale heat sources and sinks. The diabatic heating in the Northern Hemisphere is closely associated with the distribution of land and ocean. While cooling prevails over Eurasia and North America and heating occurs along the east coasts of these two continents during northern winter, a contrasting situation exists during northern summer with heating over most of the continents and cooling over the oceans where subtropical anticyclonic circulations prevail. Heating in the tropics, mostly from moist convection, has considerable longitudinal variations which change seasonally. Of particular importance is the seasonal progression of the primary centre of heating within the planetary scale Asiatic monsoon which is located over the western equatorial Pacific during northern winter and near the Philippines and Southeast China during northern summer. DOI: 10.1111/j.1600-0870.1983.tb00201.x

[1] Detailed mapping of bathymetry and three-dimensional water velocities using a boat-mounted single-beam sonar and acoustic Doppler current profiler (ADCP) was carried out in the vicinity of two submerged wing dikes located in the Lower Missouri River near Columbia, Missouri. During high spring flows the wing dikes become submerged, creating a unique combination of vertical flow separation and overtopping (plunging) flow conditions, causing large-scale three-dimensional turbulent flow structures to form. On three different days and for a range of discharges, sampling transects at 5 and 20 m spacing were completed, covering the area adjacent to and upstream and downstream from two different wing dikes. The objectives of this research are to evaluate whether an ADCP can identify and measure large-scale flow features such as recirculating flow and vortex shedding that develop in the vicinity of a submerged wing dike; and whether or not moving-boat (single-transect) data are sufficient for resolving complex three-dimensional flow fields. Results indicate that spatial averaging from multiple nearby single transects may be more representative of an inherently complex (temporally and spatially variable) three-dimensional flow field than repeated single transects. Results also indicate a correspondence between the location of calculated vortex cores (resolved from the interpolated three-dimensional flow field) and the nearby scour holes, providing new insight into the connections between vertically oriented coherent structures and local scour, with the unique perspective of flow and morphology in a large river.

A series of seven stream barbs were installed at two consecutive channel bends in Sawmill Creek, a semi-alluvial stream located in Ottawa, Canada. Stream barbs (also known as submerged groynes) are low-profile linear rock structures that extend from the outside bank regions of channel bends in an upstream direction, to redirect the attacking currents and prevent erosion of the bank. As well as providing bank protection, these structures promote vegetated stream banks, create resting pools and scour holes for fish habitat, and increase biodiversity for aquatic species. Despite these benefits, because of their relative novelty as river training structures, stream barbs are not a common means of stream bank protection in Canada and are possibly non-existent for semi-alluvial or clay channels. Three years of monitoring and measurement of flow conditions (discharge, water velocity and depth) and bathymetry, before (2 years) and after (1 year) the construction of the barbs, have been collected at the Sawmill Creek study site, providing valuable data for understanding their performance in a semi-alluvial channel. Sawmill Creek has a predominately clay bed and banks, presenting a rare opportunity to study the unique dynamics between flow and sediment transport within a clay channel. This paper reports on (i) the unique site conditions and monitoring methodology; (ii) preliminary results of the 3 year monitoring program; and (iii) recommendations for future design and implementation of these structures.

Des methodes d'optimisation sont utilisees pour estimer les donnies de propagation des crues par des canaux ouverts mixtes (canaux principaux avec pkrimtttres d'inondation). Ces donnees incluent la geometrie des sections de canal irregulittres et la rugosite limitrophe. Les icarts entre les debits et les niveaux simulis et ceux observes sont reduits en utilisant trois algorithmes d'optimisation : la methode de Powell, I'algorithme de Rosenbrock et la methode Simplex de Nelder et Meade. La methode de Powell a produit des resultats mediocres alors que les methodes de Rosenbrock et Simplex ont permis d'obtenir de bons resultats. Les donnies estimies a I'aide des mithodes de Rosenbrock et Simplex ont Cte utilisees pour calculer differentes propagations des crues observies dans un canal en laboratoire. On a constate une bonne concordance entre les debits et les niveaux de pointe simulis et ceux estimes a I'aide de donnkes reelles.

A three-dimensional numerical model Simulation in Intakes with Multiblock option (SSIIM) was used to model the effects of placing a series of barbs along an unstable section of Sawmill Creek, a small urban stream in the city of Ottawa, Canada. Stream barbs (a type of submerged groyne) are low-profile linear rock structures that prevent the erosion of stream banks by redirecting high velocity flow away from the bank. As they can be built at a relatively low cost and also provide significant ecological benefit, these structures are an important and relatively new method of stream bank protection. The numerical model was used to assess various design alternatives for a series of seven stream barbs at two consecutive channel bends requiring stabilization measures along their outer banks. Design criteria were principally based on the goals of reducing local velocities, shear stress and subsequent erosion at the outside bank of each bend, and on moving the thalweg away from the (existing) outside bank regions towards the centre of the channel. This paper reports on (i) the unique site conditions and environmental protection requirements, (ii) the results of the numerical simulation, and (iii) the design methodology.

The subject of flow through rockfill is of increasing interest in Canada. Rockfill drains are presently used by mining companies in order to permit existing creeks to flow through the base of mine waste dumps. There is potential for the use of flow through rockfill dams for mini-hydro schemes because the adoption of a costly concrete spillway may be unnecessary in some cases. An important issue in the design of flow through rockfill structures is the pore pressure distribution and the associated hydraulic gradients, neither of which are associated with Darcy's law. For such determinations the finite difference scheme of Curtis and Lawson, which is based on the partial differential equation presented by Parkin et al., was investigated. However, expressions for edge nodes under this non-Darcy finite difference scheme do no exist. This paper presents the effect on the results of using more direct expressions for the edge nodes. Analytical results are compared with observed piezometric heads in the case of two model flow through rockfill dams. Further, it is shown that through the use of a standard electronic spreadsheet, piezometric heads for non-Darcy flow in porous media and the associated hydraulic gradients can be modelled directly without the need of complex computer programming. Key words: flow through rockfill embankment, piezometric head, finite difference method, non-Darcy flow.

Approximately two years after promulgation of the Energy Employees Occupational Illness Compensation Program Act, the National Institute for Occupational Safety and Health Office of Compensation and Analysis Support selected a contractor team to perform many aspects of the radiation dose reconstruction process. The project scope and schedule necessitated the development of an organization involving a comparatively large number of health physicists. From the initial stages, there were many technical and managerial challenges that required continuous planning, integration, and conflict resolution. This paper identifies those challenges and describes the resolutions and lessons learned. These insights are hopefully useful to managers of similar scientific projects, especially those requiring significant data, technical methods, and calculations. The most complex challenge has been to complete defensible, individualized dose reconstructions that support timely compensation decisions at an acceptable production level. Adherence to applying claimant-favorable and transparent science consistent with the requirements of the Act has been the key to establishing credibility, which is essential to this large and complex project involving tens of thousands of individual stakeholders. The initial challenges included garnering sufficient and capable scientific staff, developing an effective infrastructure, establishing necessary methods and procedures, and integrating activities to ensure consistent, quality products. The continuing challenges include maintaining the project focus on recommending a compensation determination (rather than generating an accurate dose reconstruction), managing the associated very large data and information management challenges, and ensuring quality control and assurance in the presence of an evolving infrastructure. The lessons learned concern project credibility, claimant favorability, project priorities, quality and consistency, and critical path project activities.

Barbs (or submerged groynes) are low-profile linear rock structures that are primarily used to prevent the erosion of stream banks. They are a variation of a groyne, similar to spur dikes and bendway weirs. Barbs are typically anchored, in series, to the outside bank in stream bends and extend in an upstream direction from the bank into the flow. This configuration redirects flow away from the outer stream bank and disrupts the velocity gradient close to the outer bank, encouraging sediment deposition adjacent to the barb. These interactions between the flow pattern and the sediment transport around the barb prevent erosion of the bank. Furthermore, vortices generated by the barb create local scour holes that can enhance aquatic habitat. A three-dimensional numerical model, Sediment Simulation in Intakes with Multiblock option (SSIIM), was used to examine the turbulent flow field and associated scour and depositional patterns due to a series of barbs in a mobile-bed channel bend. Previous physical model observations were used for model calibration and verification. Barb design was optimized to minimize scour. The parameters considered in the optimization were channel bend angle, barb alignment angle, and barb spacing. In this paper the spatial distribution of the three-dimensional flow field through a series of barbs in a 90o channel bend are mapped and the impact on the flow field of subtle differences in barb geometry are examined. Special emphasis is placed on the influence of barb design on secondary currents in the meander bend and the generation of three-dimensional vortices, and the consequent impact on scour.

In this paper, the simulation of the violent impact of tsunami-like bores with a square column is performed using a single-phase, weakly compressible three-dimensional Smoothed Particle Hydrodynamics (SPH) model. In order to avoid large fluctuations in the pressure field and to obtain accurate simulations of the hydrodynamic forces, a Riemann solver-based formulation of the SPH method is utilized. Large-scale physical experiments conducted by the authors are reproduced using the numerical model. Time-histories of the water surface elevation as well as time-histories of the pressure distribution and net total force acting on the column are successfully compared. As observed in previous breaking wave impact studies, results show that the magnitude and duration of the impulsive force at initial bore impact depend on the degree of entrapped air in the bore-front. Although ensuring a stable pressure field, the Riemann solver-based SPH scheme is believed to induce excessive numerical diffusion, as sudden and large water surface deformations, such as splashing at initial bore impact, are marginally reproduced. To investigate this particular issue, the small-scale physical experiment of Kleefsman et al. (2005) is also considered and modeled.

Potential errors in calculated vertical suspended sediment concentration profiles in river flows carrying mixed sediments are investigated. These profiles are usually obtained through application of a standard ‘diffusion‐dispersion’ model; however, such models are normally formulated on the basis of a unique grain size for the sediment. Accordingly, in the case of sediment mixtures, the grain size distribution is usually divided into several size ranges (‘fractions’), which are then characterized by their respective geometric means. Numerical errors induced through this procedure are quantified in a parametric study. While depthaveraged concentrations can be over‐esimated by a factor of 1.2 when the concentration gradient is weak, they can be under‐estimated by a factor of 15 when the gradient is large. Estimates are found to be particularly sensitive when the chosen reference level is small and the fraction width is large. Fall velocity coefficients are introduced to correct the discrepancy between the a...

A Comprehensive laboratory study, employing an appropriate range of flow Froude Number and contraction ratio, was undertaken for curvilinear and accelerating flow occuring against the advancing face and through the gap at end-dumped channel constrictions. Pertinent results on flow pattern, velocity distribution and boundary shear distribution, are reported and discussed. The locus of the shear maxima, which attains its highest point value on the advancing face of the constriction is observed to essentially overlap the path of the high velocity filament; a pattern that is similar to that found in a channel bend. Results show that which an increase in the contraction ratio, the corresponding increase in boundary shear over that in the uncontracted channel is exponential, although the increase in velocity is only nominal. A followup laboratory study on shear distribution at over-bank channel constrictions shows an identical trend.

Experiments were performed in turbulent air flow in a trapezoidal duct with a mean aspect ratio of 3.5, corner angles of 64 and 116 degrees, and with both hydraulically smooth and partly roughened walls. Measurements in the fully developed flow region include wall shear stress and isocontours of the axial mean velocity, the normal and shearing turbulent stresses, and the turbulent kinetic energy. The formation of possibly symmetric secondary flows near smooth-wall corners, and their suppression near smooth and rough-wall corners, are documented. Finally, the inadequacy of gradient transport as a model of this flow is demonstrated.

The design of an effective storm water junction structure requires calculation of the energy losses, and associated backwater effects, in the vicinity of the junction under anticipated maximum flows in the incoming sewers. In the case of hydraulically inefficient junctions, energy losses due to stream mixing and from drag can lead to surcharged conditions in the conduits. Under these conditions Sangster suggests appropriate energy loss coefficients based on extensive tests on small-scale junction structures in which the inflow and outflow pipes were surcharged. However, efficient storm sewer systems normally operate under free surface conditions. Consequently the experimental program, described in this note, had the following main objectives: 1. To provide data on the relative efficiency of different-shaped junction structures operating under free surface conditions; 2. to investigate junctions having large inlet pipe diameters and small incoming pipe slopes; and 3. determination of suitable modifications to junction geometry in light of recent attempts to improve the performance of some inefficient junctions in an existing sewer system.

A theoretical and experimental investigation is made concerning the relationships between secondary flow phenomena in alluvial channel bends and boundary shear-stress distribution and related stable bed topography generated in the vicinity of same. The physical model, a wide rectangular channel system in which two-dimensional flow conditions were reproduced, incorporated an adjustable bend test section and bends having central angles of 45—, 60—, and 70? were adopted in the study. Particular emphasis was placed on an examination of the secondary circulation decay process along that portion of the straight channel reach immediately following the bend section. Observed stable bed topography within the bend and along the downstream decay zone related favorably to the steady-state boundary shear-stress distributions obtained from a numerical model of the flow field therein.

Field studies on a 4.9-km reach of the Ottawa River confirmed that mercury in the system is almost completely (approx 97%) associated with the bed sediments. However, mercury concentration varies widely in the study section and is a function of particle size and type of sediments. A laboratory study, in which the distribution of radioactive mercury among various sediment components was monitored under dynamic conditions, does lead to predictions of mercury concentrations that closely match observed field values. Sediments with high organic content, in particular the wood chips and fiber deposits common in the Ottawa River, have associated with them 50 times the amounts of mercury associated with sand particles on a weight per weight basis. The results emphasize the importance of performing material classification and binding affinity analysis.

The mass circulation of the zonally averaged global circulation is investigated in isobaric and isentropic coordinates through the use of a FGGE Level IIIa data set. The isobaric mass circulation during the First GARP Global Experiment is consistent with previous results, i.e., direct Hadley cells in low latitudes and indirect Ferrel cells in midlatitudes of both hemispheres. Within the isentropic framework, the combination of a geostrophic mean mode of mass transport within the baroclinic wave structure of extratropical latitudes, and an ageostrophic mean mode in tropical latitudes, yields an isentropic mass circulation spanning the hemisphere. The asymmetric structure of midlatitude baroclinic waves provides the degree of freedom for a geostrophic mode of mass transport that is fundamental to the direct Hadley-type circulation in isentropic coordinates. This direct Hadley-type circulation is explicitly linked to heat sources and sinks on a planetary scale. The diabatic heating estimated from th...

The structure of turbulence in compound channel flows is examined in a laboratory study. Shear stresses and turbulence intensities are measured in a channel comprised of a deep central section flanked on either side by wide shallow berms (flood plains). The study concerns the nature of turbulence in the mixing regions separating the deep and shallow zones. Also studied is the mixing region’s effect on the compound flow field for both “wide” and “narrow” channel conditions. Under “narrow” channel conditions the mixing process extends to the center of the main channel flow field; however, under “wide” channel conditions, the central region is not affected and observed turbulence levels at the center of the main channel are in close agreement with theoretical values for a two-dimensional flow field. Apparent shear stress at the vertical main channel-flood plain interface was measured directly and compared favorably with estimated values based on momentum considerations.

The temperature of a heated effluent stream, discharging from a thermoelectric power station, can be reduced by introducing a tempering water flow in the discharge channel upstream from the receiving body. This laboratory model study investigates the possibility of increasing the rate of temperature reduction by optimizing the mixing process between two different temperature streams. The hydraulic jump is used as the mixing agent and results obtained are compared with the corresponding standard dilution method of entrainment of the coolant by jet-induced turbulence. With regard to location of the jump the standard prediction techniques proved inadequate in the study configuration. Temperature distributions were observed throughout the flow field in order to investigate mixing efficiency. Records indicated that the tempering and effluent flows were completely mixed by the jumps. Comparison of the standard and study dilution methods showed that the latter required a much shorter length of channel for complete mixing of the two streams.

The time-averaged structure of global monsoonal circulations and planetary scale transport processes are determined from the FGGE Level IIIa operational data set generated by the US National Meteorological Center. Through isentropic diagnostics, rotational and irrotational components of the horizontal mass transport and the distribution of heating for the planetary scale are analyzed for the months of January. April, July and October of 1979. The global monsoonal circulations coupled with the planetary scale of differential heating occur in the form of large scale Hadley-type and Walker-type circulations. Net heating within a given region and net cooling in another region in association with latent heat release and differences in boundary flux of energy through the earth's surface and the top of the atmosphere result in forcing of isentropic mass circulations that link energy source with energy sink regions, a result basic to thermally forced circulations. The primary planetary source of energy in the region of Indonesia-Philippines-Southeast Asia is linked through isentropic mass transport with sinks of energy in the regions of the two circumpolar vortices, the Sahara and subtropical anticyclonic circulations. This primary center of the source of energy in the Indonesia-Southeast Asia area moves seasonally from one hemisphere to the other. Other source regions of energy occur over Brazil in January and Central America and Africa in July. Through horizontal transport of mass and energy, the winter Asiatic monsoonal circulation links radiative cooling over Asia to sensible and latent heat release within mid-latitude baroclinic waves and also to latent heat release in the Indonesia, Philippine and New Guinea regions. The role of mid-latitude baroclinic waves in providing for mass and energy exchange between polar and subtropical regions within the time-averaged isentropic structure is briefly discussed. DOI: 10.1111/j.1600-0870.1985.tb00274.x