Kerry A. Mazurek

Erosion of a polystyrene bed by obliquely impinging circular turbulent air jets

This paper presents the results of an experimental study of the erosion of a cohesionless bed by obliquely impinging circular turbulent jets. The jet of air, with velocity of 27.3 to 86.8 m/s and diameter at the nozzle of either 6.35 or 12.6 mm, was set to impinge on a bed of polystyrene particles at varying angles of impingement of 7.5 to 60°. Several characteristic dimensions of the scour hole were measured and analyzed and found to depend on the angle of impingement and the erosion parameter Fo(/(H/d), where Fo is the densimetric Froude number, H is the impingement distance, and d is the diameter of the jet at the nozzle. Correlations were developed for the main characteristics of erosion at asymptotic state. Observations of the growth of the scour hole are also presented.

Impingement of circular turbulent jets on rough boundaries

This paper presents the results of a laboratory study of the perpendicular impingement of circular turbulent jets on rough walls placed at large impingement distances. The jet of air, with velocity U 0 of 45-90 m/s and diameter d at the nozzle of either 6.4 or 12.7 mm, impinged on a wall with a roughness k s of 1.73, 8.23, or 15.18 mm. Measurements were taken of the boundary shear stresses created by the jet, as well as velocity profiles in the wall jet region. The maximum shear stress on the wall, expressed in the dimensionless parameter {τ0m(H/d)2/ρU 2 0, dépends on the relative roughness k s/H and is about 2.5-5 times as large as the value for smooth walls. The boundary shear stress increases to a maximum τ0m at a radial distance from the jet centerline r of about 0.12 H, where H is the height of the jet above the boundary, and decreases as r increases further. This is shifted slightly toward the jet centerline as compared to the jet impinging on a smooth wall. In the wall jet region, the boundary shear stress varies as 1 /r 2. The velocity distribution in the wall jet region was found to be similar.

Sediment Suspension by Burrowing Mayflies (Hexagenia spp., Ephemeroptera: Ephemeridae)

Burrowing and ventilation activities of benthic invertebrates can influence water column turbidity, nutrient concentrations, and possibly oxygen balance of lakewide ecosystems. In laboratory experiments, we determined rates of bioturbation-induced suspension of fine Lake Erie sediments caused by the burrowing mayfly Hexagenia of various sizes (lengths 13–28 mm) and multiple densities (70–1,111 larvae/m2) and water temperatures (10–25°C). Larvae were inoculated into 2-L jars containing Lake Erie sediment and water. Bioturbation and sediment settling rates were independently estimated from sediment concentrations in water, measured twice daily for 14–18 d. Nonlinear regression was used to estimate sediment suspension rate for each jar (flux, mg/L/h). Logarithmic transformations of size, density, and temperature best described sediment flux. Separate experiments demonstrated that flux was unaffected by sediment depth, but did vary by sediment type, which was related to location from which Lake Erie sediment had been collected. Sediment suspension rates increased as food became depleted. Sediment suspension by pre-emergent (25 mm long) larvae at densities and water temperature typical for late spring in western Lake Erie (400 larvae/m2 at 22°C) averaged 12 g/m2/h. Although this level of bioturbation by Hexagenia larvae in western Lake Erie likely contributes only a small fraction of the basinwide annual sediment load, sediment suspension is possibly an important epibenthic source of nutrients and sediment-associated contaminants during spring. Such concentrations would exceed the clearance capacity of dreissenid mussels and may partially explain why dreissenids have not become abundant in soft sediments of the western basin.

Effects of submergence and test startup conditions on local scour by plane

Experiments were carried out to study the scour of cohesionless soils by submerged plane turbulent wall jets. The Reynolds number based on the jet exit conditions was 32,500 and the densimetric Froude number was 6.2. Submergence, defined as the ratio of the tailwater depth (yt) to nozzle exit thickness (bo) was varied from 4 to 20. Detailed velocity measurements were conducted using a laser Doppler anemometer. The results confirm the presence of two distinct types of flow fields, one that occurs at lower submergences and the other at higher submergences (yt/bo = 8). At low submergences, velocity histograms indicate that the jet is initially close to the bed and then flicks towards the water surface, whereas at the higher submergences, no such flicking movement was observed. At higher submergences, the jet impingement point on the sand bed was highly unsteady. Low pass filtering of the velocity data give further details of these processes. For tailwater conditions corresponding to the high submergence range, the frequency of motion of the impingement point tends to increase as the tailwater depth is reduced. Furthermore, variations in scour and velocity profiles were noted in the mound region across the flume cross-section. The extent of these variations was found to be dependent on the level of submergence. In an effort to clarify some of the differences in the scour characteristics noted in earlier studies, three different test startup conditions were adopted. ”Startup“ is defined as the commencement of flow through the nozzle on to the sand bed. The conditions include an instantaneous attainment of final velocity, a gradual increase and a stepwise increase to final flow conditions. The velocity measurements indicate that the flow gradually evolves to a state that is independent of the startup condition. However, the scour profiles appear to be dependent on the startup conditions for a longer duration.

Turbulent sand jets in water

This Technical Note presents photographic observations of turbulent sand jets in water. Four sands, with mean diameters ranging from 0.17 to 1.47 mm. were used in combination with three nozzles of 8, 12.7 and 25.4 mm diameter. It was found that the linear growth rate of these sand jets increases with the parameter F0 which is proportional to the ratio of the momentum flux of the sand jet at the nozzle to buoyant force on the sand particles. For the largest value of F0 equal to about 15, the growth rate of the sand jet was 0.19 which is about 20% larger than that of turbulent water jets with Reynolds number larger than about 10,000.

Hybrid modelling approach to prairie hydrology: fusing data-driven and process-based hydrological models

Abstract Much of the prairie region in North America is characterized by relatively flat terrain with many depressions on the landscape. The hydrological response (runoff) is a combination of the conventional runoff from the contributing areas and the occasional overflow from the non-contributing areas (depressions). In this study, we promote the use of a hybrid modelling structure to predict runoff generation from prairie landscapes. More specifically, the Soil and Water Assessment Tool (SWAT) is fused with artificial neural networks (ANNs), so that SWAT and the ANN module deal with the contributing and non-contributing areas, respectively. A detailed experimental study is performed to select the best set of inputs, training algorithms and hidden neurons. The results obtained in this study suggest that the fusion of process-based and data-driven models can provide improved modelling capabilities for representing the highly nonlinear nature of the hydrological processes in prairie landscapes. Editor D. Koutsoyiannis; Associate editor L. See

An experimental study of sand deposition from sediment laden water jets

This paper presents the results of a laboratory investigation on the formation of sand mounds under circular sediment laden submerged turbulent water jets impinging on a horizontal bed, with the sand volume concentrations in the approximate range of 0.36–1.7%. After a small initial period, an axisymmetric mound was formed centrally under the jet. The profiles of the mounds were found to be approximately similar when plotted in a dimensionless form with the central height of the mound, ∣Δm and the radial distance, b where the height of the mound was equal to one half the central height, as scales. The normalized profile was described well by the cosine function. The length scale b in terms of a general scale L grew with the normalized time, to a power of 0.254. Using this relation and the volume of the sand discharged, a general equation was developed to predict the growth of Δm with time. The critical value of the parameter developed earlier for erosion by impinging clear water jets does not appear to apply to impinging jets carrying sediment.

Sediment Export Modeling in Cold-Climate Prairie Watersheds

AbstractNonpoint source pollution is a critical problem in Canadian prairie watersheds. However, sediment mobilization and export are poorly represented in existing models for these watersheds. The poor representation is partly because the hydrology of the region is highly influenced by the existence of numerous dynamically-connected landscape depressions that vary in storage capacity and because of the complex freeze-thaw cycles in the region. The objective of this research was to improve sediment export simulation modeling in these cold-climate prairie watersheds by incorporating a probability distribution function of depression storage capacity and a seasonally varying soil erodibility factor into the soil and water assessment tool (SWAT) model. The probability distribution function is used to represent the variation in storage capacity of the numerous depressions, whereas the seasonally varied soil erodibility factor is used to account for changes in erodibility as the soil freezes and thaws. Results ...

Erosion of sand beds by obliquely impinging plane turbulent air jets

This paper presents the results of an experimental study of the erosion of a cohesionless sand bed by obliquely impinging plane turbulent air jets. The jet, with velocity of 20.1-49.2 m/s and width at the nozzle, 2b o, of 4.7 mm, impinged on the bed at angles varying from 15 to 60°. The uniform sand bed had a mean particle size of 1.2 or 2.38 mm. Several characteristic dimensions of the scour hole were measured and found to depend mainly on the impingement angle and the erosion parameter F o/(H/2b o)0.5, where F o is the densimetric Froude number, and H is the impingement distance. Correlations were developed for the main characteristics of erosion at asymptotic state. As well, comparisons were made with the erosion of sand beds by obliquely impinging submerged plane water jets. The differences in the scour produced by the air and water jets were found to be significant.

Design Development and Field Application of RCC Jack Jetty and Trail Dykes for River Training

While river training structures are important tools to provide solutions to river engineering problems, conventional structures can be expensive and can create adverse environmental impacts. There is a need to develop affordable permeable river training structures. Jack jetties have been in use in the USA for various purposes, although there was no scientific methodology to support design of the structures when used for river training works. Therefore, laboratory studies have been carried out to develop this design methodology, which was verified by field-testing. Trail dykes were also tested in a similar fashion. Both types of structures show promise for use as inexpensive river engineering works.