In this thesis, the theory of three dimensional numerical modeling of transport and re-suspension of fine sediments is studied and a computer program is develped for simulation of the three dimensional suspended sediment transport. The computer program solves the three dimensional advection-diffusion equation simultaneously with a computer program prepared earlier for the simulation of three dimensional current systems. This computer program computes the velocity vectors, eddy viscosities and water surface elavations which are used as inputs by the program of fine sediment transport. The model is applied to Bay of Izmir for different wind conditions.

Graduation date: 1999

Graduation date: 1982

Samples collected from 5 bridge sites from around the state of Georgia are analyzed to determine their erosion and rheologic behavior. Most sites were subject to large amounts of local scour due to flood events resulting from Tropical Storm Alberto in 1994. According to the Federal Highway Administration's Hydraulic Engineering Circular No. 18 by Richardson and Davis (2001), scouring of bridge foundations is the most common cause of bridge failure resulting from floods. The erosion rates of the soils are measured in a rectangular tilting flume capable of applying up to 21 Pa of shear stress at the bed. Samples from Shelby tubes are extruded into the flow from below the bed using a hydraulic piston. The displacement is measured as a function of time using a cable-pull potentiometer. The soils are also subject to extensive geotechnical analysis. Sieve and hydrometer analyses are performed to obtain the particle size distribution for each sample. Atterberg Limits and other standard geotechnical measures are also found. Additionally, insight into the shear strength and cohesive nature of the fine (<0.75 micrometers) particles is gained using a stress controlled rheometer to measure the rheological characteristics of the slurry. These results are used to improve and extend a relationship for the critical shear stress of soils developed in previous research that can be used in bridge scour prediction formulae as affected by soil parameters. In addition, the rheologic properties of the soil in terms of a dimensionless yield stress are related to the critical value of the Shields parameter for estimating critical shear stress for erosion.

The development and testing of a shear cell for the purpose of measuring swash zone bed shear stress is presented. Direct measurements of bed shear stress were subsequently obtained using the shear plate in small, medium, and large-scale laboratory facilities. Measurements from both dam- break and bore-driven swash experiments are considered, covering a wide range of hydrodynamics and bed roughness. The dam-break problem is of interest here due to the theoretical analogy with the run-up of a solitary bore on a beach. Estimates of the flow velocities through the full swash cycle were obtained through numerical modelling and verified against measured velocity data. In conjunction, these data are used to calculate skin friction coefficients. The measurements indicate strong temporal and spatial variation in bed shear stress throughout the swash cycle, and a clear distinction between the uprush and backwash phase. For a single swash event, the maximum uprush bed shear stresses occur in the lower swash zone, within the range 0<x/Rx<0.3. The maximum backwash bed shear stresses also occur in the lower swash zone, and extend seaward of the initial bore collapse location. For a given cross-shore location the peak uprush bed shear stress is typically greater than the peak backwash bed shear stress by at least a factor two and up to a factor four. Local skin friction coefficients also indicate strong temporal and spatial variation. Furthermore, the behaviour of the local skin friction coefficient (back calculated from the measured bed shear stress using predicted, depth-averaged, flow velocities) over the swash cycle is inconsistent with the classical behaviour that is expected on the basis of the low Reynolds number flow. Smooth bed dam break and swash uprush friction coefficients appear to follow the general behaviour observed for smooth, turbulent open channel flow for an increasing Reynolds number. However, for a decreasing Reynolds number the behaviour of Cf differs from the steady flow relation. This is attributed the unsteady swash flow regime and flow history effects. It is expected that differences in flow history between the uprush and backwash have implications in terms of swash boundary layer growth and the resulting bed shear stress. A Lagrangian model for the swash boundary layer development is presented to consider these flow history effects. The model is based on the momentum integral approach for steady, turbulent, flat-plate boundary layers, with appropriate modifications to account for the unsteady flow regime. Fluid particle trajectories and velocity are computed and the boundary layer growth across the entire swash zone is estimated. Predictions of the bed shear stress agree well with the direct bed shear stress measurements and show a bias toward uprush sediment transport which has consistently been observed in measurements.

Thesis (PhD)--Macquarie University, School of Earth Sciences, 1981. / Bibliography: leaves 218-233. / Introduction -- Methods -- Boulder size -- Boulder morphology -- Boulder roundness -- Beach form -- Boulder movement -- Process inference from studies of coastal protection structures -- Summary and conculsion. / Five boulder beaches along the central New South Wales coast were selected for the study of their sedimentary properties, form, and sediment transport. Each beach is aligned obliquely to the approaching waves and is composed of local sediment. One beach, which appears to have little or no recent sediment input, is considered to be a closed sediment system and the other four beaches, which appear to have recent sediment supply, are considered to be open sediment systems. -- On the open system beaches, boulder size fines towards the embayment in the direction of transport, and on all beaches size fines up-beach (contrasting with the up-beach coarsening of pebble and cobble beaches). During transport, breakage and chipping diminish boulder size, and the products of these forms of abrasion constitute a subordinate fine population causing the distribution of size to be positively skewed, contrasting with most fine-sediment beaches which exhibit negative size skewness. -- More boulders are oblate than prolate, but this may reflect geology rather than coastal weathering processes. In contrast to pebble beaches, no longshore or up-beach shape zoning exists, and boulder shapes are believed to be largely determined by geology. Boulder shape is not related to boulder size. Sphericity varies little within each beach and nowhere does it increase seaward as is common for pebble and cobble beaches. -- Boulder roundness tends to increase longshore towards the embayment, and decrease up-beach. The relationships between boulder roundness and size may be influenced by sediment supply. Roundness and shape of boulders do not appear to be related. -- Overall beach form is consistent and no rhythmic features could be identified. Surface packing or armouring occurs on all beaches and may contribute to beach stability. Foreshore slopes tend to be concave upward and range between 7° and 12°, significantly lower than the slopes of >= 24° predicted in the literature for boulder-sized sediment. This anomaly may be explained by the fact that only very high-energy waves, which produce low beach slopes, are competent to transport boulders. -- Boulder mobility is evident on all beaches and was monitored on one beach. Wave competency appears to determine the maximum size of transported boulders, and a competency model is proposed in which it is predicted that there exists a power relationship between transported particle diameter and significant wave height. Since boulder beaches and rubble coastal protection structures have environmental and compositional similarities, beach-boulder movement is examined in the light of engineering studies of protection-structure stability. Two no-damage design formulae were found to over-predict the movement of the smaller-sized beach sediment and underpredict the movement of the larger-sized sediment. This effect may be due to the packing of beach boulders. -- Up-beach fining, positive size skewness, the absence of shape zoning, much particle breakage, the absence of sphericity grading, and low foreshore slope are all characteristics of the five studied boulder beaches which contrast markedly with the characteristics of pebble and cobble beaches. These findings, combined with the development of a reasonable predictive transport model, suggest that the studied boulder assemblages are organized and distinct coastal deposits, which may properly be termed beaches. / Mode of access: World Wide Web. / 309 leaves ill. (some col.), maps

The adverse impacts on vegetation and soils due to livestock grazing have been extensively studied for many years. The extent to which native wildlife may also be causing change to their environment, as a result of local increases in population density, has been the subject of debate in a number of countries. In Australia there has been a growing awareness in recent years that native herbivores, particularly kangaroos and wallabies, may also be causing changes to ecosystem dynamics. Environmmental changes, produced firstly by the aboriginal people and then by Europeans, have favoured the larger macropods, resulting in increased population levels. These impacts can also be seen in areas around cities, where pressure from urbanisation has restricted populations to smaller and smaller patches of remnant vegetation and reserves, increasing the pressure on diminishing food resources within these patches. This study focuses on one of the areas that supplies drinking water to Melbourne, the Yan Yean Reservoir catchment, which is situated 37 km north east of Melbourne. This study adds to our understanding of the impacts of native wildlife populations by investigating the extent of some of these possible changes to ecosystem dynamics.

New laboratory data are presented on the influence of long waves on sediment transport in the surf zone. Due to the very significant difficulties in isolating the morphodynamic processes induced by long waves in field conditions, the laboratory study was designed practically to measure the net sediment transport rates, and gradients in sediment transport, arising from the interaction between long waves and short waves in the surf zone. The bathymetric evolution of model sand beaches, with dB50B = 0.2 mm, was observed under monochromatic short waves, long-wave short-wave combinations (free long waves), and bichromatic wave groups (forced long waves). The beach profile change and net cross-shore transport rates, Q(x), were extracted and compared for conditions with and without long waves. The experiments include a range of wave conditions, e.g. high-energy, moderate-energy, low-energy waves, and the beaches evolve to form accretionary, erosive, and intermediate beach states. Hydrodynamic measurements were made to identify the influence of long waves on short waves and to determine the correlation between surf zone bars and standing long waves. A shallow water wave model was modified for this application to surf zone morphodynamics and compared to both hydrodynamics and measured sediment transport. This data clearly demonstrate that free large-amplitude long waves influence surf zone morphodynamics not only under accretive conditions, by promoting onshore sediment transport, but also under erosive conditions, by decreasing offshore transport. For the dominant berm-bar feature, the strong surf beat induces offshore transport in the inner surf zone and onshore transport around the outer surf zone and throughout the shoaling zone. In contrast, forced (bound) long waves and wave groups correlated with bichromatic short wave groups play a pronounced role under erosive conditions, increasing offshore sediment transport across the whole beach profile. For accretionary conditions, only a very narrowbanded wave group promotes onshore sediment transport across the whole beach profile, while broader banded wave groups again promote offshore transport. The modified numerical model of Li et al. (2002) provides good predictions of the standing long wave pattern for the long-wave short-wave combinations, but generally poor agreement for the bichromatic wave groups. Similarly, this model performs poorly in terms of predicting the net sediment transport for all waves, even after optimising the sediment transport coefficients. This is because the model cannot predict the correct hydrodynamics around the breakpoint position and does not correctly represent net sediment transport mechanics. Overall, the model does not correctly predict the trends in beach profile evolution induced by the long waves and wave groups. Further, there is little evidence that the long wave nodal structure plays a dominant role. The influence of the free long waves and wave groups is consistent with the concept of the Gourlay parameter, H/wBsBT, as a dominant parameter controlling net erosion or accretion. Free long waves tend to reduce H/wBsBT, promoting accretion, while wave groups tend to increase H/wBsBT, promoting erosion.

Wave-formed rippled sediment beds are extremely important to the processes that act on or across the sediment-water interface. Ripples increase the exchange of materials between the sediment and the water column, enhance sediment transport rates, and act to increase the dissipation of waves by increasing the hydraulic roughness of the seafloor. Previous research has, however, failed to take into account the substantial spatial and temporal variation rippled beds display when formed under real sea conditions. Based on a set of laboratory experiments a spectral method to predict and model rippled beds has been developed. Through the use of the rippled surface's spectral density function the spatial and temporal variability of the rippled surface can be taken into account with greater efficiency. A prediction method for the equilibrium ripple spectrum was developed based on a nondimensional spectral form, which utilised the peak orbital excursion diameter and the 50th percentile grain size diameter of the sediment bed. The method provided an effective technique to predict ripple parameters with the same degree of accuracy achievable at small scale as more accepted ripple prediction methods. A new method was derived to model the changes a rippled bed undergoes as it actively evolves between two given equilibrium states due to a change in surface wave conditions. The evolution of a rippled bed can be described mathematically in exactly the same way as a rippled bed growing from a flat bed condition. The method allows any bed to be modelled through time if the flow conditions and sediment properties are known. There is little advantage in using the spectral method to predict rippled beds when they are in equilibrium with the flow conditions. The main benefit of the spectral method comes when attempting to model rippled beds evolving under changed flow conditions. In the same way as the parameterisation of surface waves in terms of their spectral density function has increased the ability to model wind generated wave fields, studies of rippled beds would benefit from the increased detail and ease the spectral method brings. / Thesis (Ph.D.)--School of Civil and Environmental Engineering, 2005.

This thesis examines the processes of longshore sediment transport in the swash zone of a mixed sand and gravel shoreline, Lake Coleridge, New Zealand. It focuses on the interactions between waves and currents in the swash zone and the resulting sediment transport. No previous study has attempted to concurrently measure wave and current data and longshore sediment transport rates on a mixed sand and gravel lakeshore beach in New Zealand. Many of these beaches, in both the oceanic and lacustrine environments, are in net long-term erosion. It is recognised that longshore sediment transport is a part of this process, but very little knowledge has existed regarding rates of sediment movement and the relationships between waves, currents and swash activity in the foreshore of these beach types. A field programme was designed to measure a comprehensive range of wind, wave, current and morphological variables concurrently with longshore transport. Four electronic instruments were used to measure both waves and currents simultaneously in the offshore, nearshore and swash zone. In the offshore area, an InterOcean S4ADW wave and current meter was installed to record wave height, period, direction and velocity. A WG-30 capacitance wave gauge measured the total water surface variation. A pair of Marsh-McBirney electromagnetic current meters, measuring current directions and velocities were installed in the nearshore and swash zone. Data were sampled for 18 minutes every hour with a Campbell Scientific CR23x data-logger. The wave gauge data was sampled at a rate of 10 Hz (0.1 s) and the two current meters at a rate of 2 Hz (0.5 s). Longshore sediment transport rates were investigated with the use of two traps placed in the nearshore and swash zone to collect sediment transported under wave and swash action. This occurred concurrently with the wave measurements and together yielded over 500 individual hours of high quality time series data. Important new insights were made into lake wave processes in New Zealand's alpine lakes. Measured wave heights averaged 0.20-0.35 m and ranged up to 0.85 m. Wave height was found to be strongly linked to the wind and grew rapidly to increasing wind strength in an exponential fashion. Wave period responded more slowly and required time and distance for the wave length to develop. Overall, there was a narrow band of wave periods with means ranging from 1.43 to 2.33 s. The wave spectrum was found to be more mixed and complicated than had previously been assumed for lake environments. Spectral band width parameters were large, with 95% of the values between 0.75 and 0.90. The wave regime attained the characteristics of a storm wave spectrum. The waves were characteristically steep and capable of obtaining far greater steepness than oceanic wind-waves. Values ranged from 0.010 to 0.074, with an average of 0.051. Waves were able to progress very close to shore without modification and broke in water less than 0.5 m deep. Wave refraction from deep to shallow water only caused wave angles to be altered in the order of 10%. The two main breaker types were spilling and plunging. However, rapid increases in beach slope near the shoreline often caused the waves to plunge immediately landward of the swash zone, leading to a greater proportion of plunging waves. Wave energy attenuation was found to be severe. Measured velocities were some 10 times less at two thirds the water depth beneath the wave. Mean orbital velocities were 0.30 m s⁻¹ in deep water and 0.15 m s⁻¹ in shallow water. The ratio difference between the measured deep water orbital velocities and the nearshore orbital velocities was just under one half (us/uo = 0.58), almost identical to the predicted phase velocity difference by Linear wave theory. In general Linear wave theory was found to provide good approximations of the wave conditions in a small lake environment. The swash zone is an important area of wave dissipation and it defines the limits of sediment transport. The width of the swash zone was found to be controlled by the wave height, which in turn determined the quantity of sediment transported through the swash zone. It ranged in width from 0.05 m to 6.0 m and widened landward in response to increased wave height and lakeward in response the wave length. Slope was found to be an important secondary control on swash zone width. In low energy conditions, swash zone slopes were typically steep. At the onset of wave activity the swash zone becomes scoured by swash activity and the beach slope grades down. An equation was developed, using the wave height and beach slope that provides close estimates of the swash zone width under a wide range of conditions. Run-up heights were calculated using the swash zone width and slope angle. Run-up elevations ranged from 0.01 m to 0.73 m and were strongly related to the wave height and the beach slope. On average, run-up exceeds the deep water wave height by a factor of 1.16H. The highest run-up elevations were found to occur at intermediate slope angles of between 6-8°. Above 8°, the run-up declined in response to beach porosity and lower wave energy conditions. A generalised run-up equation for lake environments has been developed, that takes into account the negative relationship between beach slope and run-up. Swash velocities averaged 0.30 m s⁻¹ but maximum velocities averaged 0.98 m s⁻¹. After wave breaking, swash velocities quickly reduced through dissipation by approximately one half. Swash velocity was strongly linked to wave height and beach slope. Maximum velocities occurred at beach slopes of 5°, where incident swash dominated. At slopes between 6° and 10°, swash velocities were hindered by turbulence, but the relative differences between the swash and backswash flows were negligible. At slope angles above 10° there was a slight asymmetry to the swash/backswash flow velocities due to beach porosity absorbing water at the limits of the swash zone. Three equations were developed for estimating the mean and maximum swash velocity flows. From an analysis of these interactions, a process-response model was developed that formalises the morphodynamic response of the swash zone to wave activity. Longshore sediment transport occurred exclusively in the swash zone, landward of the breaking wave in bedload. The sediments collected in transit were a heterogeneous mix of coarse sands and fine-large gravels. Hourly trapped rates ranged from 0.02 to 214.88 kg hr⁻¹. Numerical methods were developed to convert trapped mass rates in to volumetric rates that use the density and porosity of the sediment. A sediment transport flux curve was developed from measuring the distribution of longshore sediment transport across the swash zone. Using numerical integration, the area under this curve was calculated and an equation written to accurately estimate the total integrated transport rates in the swash zone. The total transport rates ranged from a minimum of 1.10 x 10-5 m³ hr⁻¹ to a maximum of 1.15 m³ hr⁻¹. The mean rate was 7.36 x 10⁻² m³ hr⁻¹. Sediment transport was found to be most strongly controlled by the wave height, period, wave steepness and mean swash velocity. Transport is initiated when waves break at an oblique angle to the shoreline. No relationships could be found between the grain size and transport rates. Instead, the critical threshold velocities of the sediment sizes were almost always exceed in the turbulent conditions under the breaking wave. The highest transport rates were associated with the lowest beach slopes. It was found that this was linked to swash high velocities and wave heights associated with foreshore scouring. An expression was developed to estimate the longshore sediment transport, termed the LEXSED formula, that divides the cube of the wave height and the wave length and multiplies this by the mean swash velocity and the wave approach angle. The expression performs well across a wide range of conditions and the estimates show very good correlations to the empirical data. LEXSED was used to calculate an accurate annual sediment transport budget for the fieldsite beaches. LEXSED was compared to 16 other longshore sediment transport formulas and performed best overall. The underlying principles of the model make its application to other mixed sand and gravel beaches promising.