Gotowa bibliografia na temat „Nerang River estuary (Queensland)”

Knowledge of the vertical migration behaviour of postlarval penaeid prawns is important in understanding postlarval migration from offshore spawning grounds to estuarine nursery areas. We sampled throughout several 24-h periods in two estuaries in Australia to assess the distribution of postlarvae in the water column. We used four trawl nets: one net in the top 0.5 m of the water column and three nets one above the other, from the seabed to 0.72 m above the seabed. Penaeus plebejus was abundant in catches in the Nerang River, southern Queensland, while Penaeus semisulcatus, Penaeus esculentus and Penaeus merguiensis were caught in the Embley River, northern Queensland. For all species, the highest catches at the surface were on night flood tides. Many postlarvae in the Embley River were caught in nets above the seabed on ebb tides, suggesting that net migration patterns cannot be determined simply by sampling surface waters. The vertical distribution of penaeid postlarvae is determined primarily by tide and day/night; however, water turbidity and cloud cover, factors that reduce light at the seabed, are also likely to be important. All these aspects of postlarval behaviour should be included in hydrodynamic models of larval advection from spawning grounds to inshore nursery areas.

Environmental Context. The Fitzroy River Basin constitutes a major source of suspended sediment and nutrient fluxes to the southern Great Barrier Reef. Improved land management practices to ameliorate these catchment loads require an understanding of the sediment sources and dynamics. This multidisciplinary geochemical and modelling study provides for the first time a quantitative estimate of sediment sources delivered to, and their degree of retention in, the Fitzroy River Estuary. Abstract. Sources of sediment deposited in the Fitzroy River Estuary (FRE) have been identified and quantified using an integrated geochemical, modelling and reconnaissance soil sampling approach. A companion paper (this volume) identifies the major sources of sediments in impoundments on the major river systems and sediment sampled from flood events in the Fitzroy River Basin (FRB). Sediment within the FRE may display distinct longitudinal variation with little basaltic material retained. Sediments derived from the Bowen Basin, which occupies the greatest portion of the FRB, and from the Surat Basin display the greatest longitudinal variation. All FRB soils have a similar total phosphorus (P) concentration. Thus, in considering P export from the catchment it is the total sediment flux which is of major importance, rather than the relative proportions of individual catchment soils. This research provides crucial new regional scale information on the sediment sources deposited within the FRE.

A laboratory-based study of the behaviour of phosphorus (P) was carried out on the soils of the lower Herbert River catchment, Queensland, Australia. The aim was to explore the potential for P sorption or desorption by Herbert soils in associated river and estuary waters, so that the extent of problems associated with sugarcane production and soil-derived inputs to streamwater could be defined. Anion exchange resin was used as a sink for P. The equilibrium phosphate concentration (EPC) measured in simulated soil pore water (0.01M CaCl2), and the EPC in the simulated river and estuary waters were strongly correlated. Based on this, and the close relationship between P sorption and selected soil properties, it was possible to estimate P desorption using commonly measured properties. Much less desorption of P took place in simulated estuary waters than in simulated river water of much lower ionic strength. This suggests that environmental degradation arising from the downstream export of soil-borne P from Herbert cane lands is likely to be concentrated in freshwater areas. Sorption properties of P in soils of the lower Herbert appear to be closely associated with aluminium-rich minerals, rather than with iron (hydr)oxides.

Above- and below-ground biomass of five species of mangroves was estimated for the Mary River, south-eastern Queensland. Below-ground : above-ground biomass ratios of species in the upstream reaches (Avicennia marina, Aegiceras corniculatum and Excoecaria agallocha) averaged <0.5, and those of species in the saline conditions of the mouth (Avicennia marina, Rhizophora stylosa) ranged between 0.9 and 1.5. Within the estuary mouth, above-ground biomass of Avicennia marina and Ceriops tagal decreased between frontal saline and upper-intertidal hypersaline environments, and this was reflected in the below-ground : above-ground biomass ratios, which increased to approximately 3.5 for both species.

Environmental context. The Fitzroy River Basin is a major source of suspended sediment and nutrients to the southern Great Barrier Reef lagoon. A reduction in sediment and nutrient loads is necessary to protect coastal reefs and this requires an understanding of the sediment sources. The present geochemical and modelling study provides a quantitative estimate of the spatial and temporal variations in the sources of sediment deposited in the Fitzroy River coastal zone. Abstract. Sediment sources to the Fitzroy River coastal zone have been identified and quantified using an integrated geochemical and modelling approach. The coastal sediments display little geochemical variation as a result of substantial homogenisation during hydrodynamic processes and indicate a sediment composition consistent with derivation from mixed catchment sources. A lack of substantial temporal geochemical variation in the sediment records indicates weathering regimes and hydrodynamic transport have been relatively consistent throughout the Holocene. Despite this apparent geochemical homogeneity, a modelling approach using a Bayesian statistical model revealed changes in catchment sediment sources over time. Variations in the occurrence and intensity of rainfall events in different parts of the catchment as well as land-use changes following European settlement are likely to have had a substantial effect on the relative contributions of the catchment sources delivered to and deposited in the coastal zone. Additionally, large variations in flow events and variable estuary hydrodynamics result in different catchment soil types being delivered and deposited under different conditions. The present study found that basaltic material is the dominant catchment source in the coastal surface sediments with an estimated enrichment of ~3 relative to catchment and estuary abundances. Basaltic soils present as a more recent and extensive, weathered surficial cover are more readily mobilised than other catchment soils and will be transported further within freshwater flood plumes. It is likely that in large flood events, this basaltic material may reach the coral-dominated outer shelf. Improved land management practices to reduce sediment loads can be targeted to the areas supplying the majority of sediment to the coastal zone.

Hydraulic lock structures have been used for hundreds of years to control and maintain water levels in waterways. The most common are gated water regulation structures used to catch and divert water, and form an essential and critical part of many flood control and agricultural schemes. Although there are clear economic advantages to building the structures, they can contribute to major water quality problems for the waterways they influence (i.e. increased residence times and a change in mixing ability). Further, in most cases, the methods previously used to assess how the structures and their operations influence the flow regimes between the two connected systems were limited, thus hydraulic designers rely on simple formulations, existing literature and experience. Consequently, the objectives of this thesis were to undertake a detailed field study and develop a methodology and computer simulation tool to calculate the flow through a hydraulic structure connecting two water bodies so that future designs can be undertaken based upon sound knowledge. To demonstrate the outcomes of this thesis, the methodology and model were applied to an existing hydraulic structure (referred to as Structure C). Structure C is used to connect and exchange water between the tidally dominated section of the Nerang River estuary and an artificial lake system (Burleigh Lakes) on the Gold Coast, Australia. The gates of this structure open four times each day (once during each semi-diurnal tidal phase) and remain open for a period of 2 hours, allowing alternative and partial exchange between the two water bodies. To gain a better understanding of the dynamics of each waterbody under the influence of the structure, a series of detailed field experiments were initially undertaken to understand and quantify the exchange of water and its mixing ability. Tide gauges deployed within the lake indicated a water level change during each opening of up to 22 cm, equating to 413,600 m3 of water entering the lake over the 2 hour discharge period. Salinity profiles showed that the structure permitted the exchange of saline and freshwater between the two systems, during each tidal cycle, in turn maintaining the lake system as a saline (brackish environment). However, the field study also revealed that the controlled exchange of water between the systems perpetuated a permanently stratified environment on both sides of the structure. To simulate the flow dynamics influenced by Structure C, new routines were incorporated into an existing hydrodynamic model (BFHYDRO) within the model's grid and computational code, as part of this thesis. To achieve this, the flow in and out of the hydraulic structure cell (used to represent the hydraulic structure's location within the model grid) was calculated entirely from the local water level gradients on either side of the structure at each time-step, and not prescribed. This was found to be essential for complex tidally-dominated systems, such as the Nerang River. Routines were also developed to replicate the opening and closing times of the gates. Following the development of the methodology, the hydraulic structure cells were tested and applied to simulate the flow through Structure C and the complex exchange between the estuary and lake, in 2 and 3-dimensions. Tests indicated that the opening and closing times of the gates and the calibration of the discharge coefficient (which forms part of the broad-crested weir formula) were the most sensitive parameters to ensure the correct volume of water exchange between the two systems. Statistically, the model-predicted results compared very well with available surface elevation data within the estuary and lake, and thus, quantified the ability of the hydraulic structure cells to simulate the flux between the estuary and lake for each opening. Following the model validation process, results from the existing configuration were compared with hypothetical design alternatives and are documented herein. Further, part of the thesis also explored a practical and effective computer based learning strategy to introduce and teach hydrodynamic and water quality modelling, to the next generation of undergraduate engineering students. To enhance technology transfer a computer based instructional (CBI) aid was specifically developed to assist with the setup, execution and the analysis of models' output, in small easy steps. The CBI aid comprised of a HTML module with links to recorded Lotus Screen cam movie clips. The strategy proved to be a useful and effective approach in assisting the students to complete the project with minimum supervision, and acquire a basic understanding of water quality modelling. Finally, it is anticipated that this new modelling capability and the findings detailed herein will provide managers with a valuable tool to assess the influence of these structures on water circulation for present and future operations within the region. This model can also be set up at other sites to pre-assess various design configurations by predicting changes in current flows, mixing and flushing dynamics that a particular design might achieve, and assist with the selection process before the final selection and construction.

Hydraulic lock structures have been used for hundreds of years to control and maintain water levels in waterways. The most common are gated water regulation structures used to catch and divert water, and form an essential and critical part of many flood control and agricultural schemes. Although there are clear economic advantages to building the structures, they can contribute to major water quality problems for the waterways they influence (i.e. increased residence times and a change in mixing ability). Further, in most cases, the methods previously used to assess how the structures and their operations influence the flow regimes between the two connected systems were limited, thus hydraulic designers rely on simple formulations, existing literature and experience. Consequently, the objectives of this thesis were to undertake a detailed field study and develop a methodology and computer simulation tool to calculate the flow through a hydraulic structure connecting two water bodies so that future designs can be undertaken based upon sound knowledge. To demonstrate the outcomes of this thesis, the methodology and model were applied to an existing hydraulic structure (referred to as Structure C). Structure C is used to connect and exchange water between the tidally dominated section of the Nerang River estuary and an artificial lake system (Burleigh Lakes) on the Gold Coast, Australia. The gates of this structure open four times each day (once during each semi-diurnal tidal phase) and remain open for a period of 2 hours, allowing alternative and partial exchange between the two water bodies. To gain a better understanding of the dynamics of each waterbody under the influence of the structure, a series of detailed field experiments were initially undertaken to understand and quantify the exchange of water and its mixing ability. Tide gauges deployed within the lake indicated a water level change during each opening of up to 22 cm, equating to 413,600 m3 of water entering the lake over the 2 hour discharge period. Salinity profiles showed that the structure permitted the exchange of saline and freshwater between the two systems, during each tidal cycle, in turn maintaining the lake system as a saline (brackish environment). However, the field study also revealed that the controlled exchange of water between the systems perpetuated a permanently stratified environment on both sides of the structure. To simulate the flow dynamics influenced by Structure C, new routines were incorporated into an existing hydrodynamic model (BFHYDRO) within the model's grid and computational code, as part of this thesis. To achieve this, the flow in and out of the hydraulic structure cell (used to represent the hydraulic structure's location within the model grid) was calculated entirely from the local water level gradients on either side of the structure at each time-step, and not prescribed. This was found to be essential for complex tidally-dominated systems, such as the Nerang River. Routines were also developed to replicate the opening and closing times of the gates. Following the development of the methodology, the hydraulic structure cells were tested and applied to simulate the flow through Structure C and the complex exchange between the estuary and lake, in 2 and 3-dimensions. Tests indicated that the opening and closing times of the gates and the calibration of the discharge coefficient (which forms part of the broad-crested weir formula) were the most sensitive parameters to ensure the correct volume of water exchange between the two systems. Statistically, the model-predicted results compared very well with available surface elevation data within the estuary and lake, and thus, quantified the ability of the hydraulic structure cells to simulate the flux between the estuary and lake for each opening. Following the model validation process, results from the existing configuration were compared with hypothetical design alternatives and are documented herein. Further, part of the thesis also explored a practical and effective computer based learning strategy to introduce and teach hydrodynamic and water quality modelling, to the next generation of undergraduate engineering students. To enhance technology transfer a computer based instructional (CBI) aid was specifically developed to assist with the setup, execution and the analysis of models' output, in small easy steps. The CBI aid comprised of a HTML module with links to recorded Lotus Screen cam movie clips. The strategy proved to be a useful and effective approach in assisting the students to complete the project with minimum supervision, and acquire a basic understanding of water quality modelling. Finally, it is anticipated that this new modelling capability and the findings detailed herein will provide managers with a valuable tool to assess the influence of these structures on water circulation for present and future operations within the region. This model can also be set up at other sites to pre-assess various design configurations by predicting changes in current flows, mixing and flushing dynamics that a particular design might achieve, and assist with the selection process before the final selection and construction.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Engineering
Full Text

Southern Moreton Bay and the adjacent continental shelf have provided a natural laboratory in which to describe the sedimentology, sequence stratigraphy and coastal evolutionary processes of a wave dominated coastline. Sequence stratigraphy has become a routine tool for Earth Scientists in the exploration of hydrocarbons and as such detailed studies in Quaternary depositional environments are required to provide analogues for ancient environments. The Quaternary has a well documented sea level curve which when used in combination with high resolution seismic, drill core and age dating provides the opportunity to derive accurate and detailed depositional scenarios for various stages of sea level. This study has established that the southeast Queensland coastal prism is an example of a relatively sediment deficient margin as a result of the low gradient of the regional topography and the low flow rate of the fluvial systems. This differs dramatically from the regions from which most of the generic sequence stratigraphic models have been derived (ie. North America and Europe) where major fluvial systems have high flow rates and generally greater topographic relief Consequently the system described herein provides an important variation on generic sequence stratigraphic models, particularly in the way a fluvial system responds to periods of low sea level. The incision of the Logan/ Albert fluvial system has been mapped across the coastal plain, through the lagoon and under the inner to mid-continental shelf The valley system is not apparent on the outer shelf. This may primarily be a function of stream gradient. The gradient of the incised valley is approximately 0.002 in the coastal prism, the outer continental however is 10 km wide with a relief of 2-3m giving a gradient of 0.00025. This essentially flat shelf area coincides with the lack of incision on the shelf. As a result of the extremely low gradient of the outer shelf area in combination with potentially hard substrate and a reduced stream power during glacial periods, it is unlikely that the Logan/ Albert Pluvial system incised to the shelf edge. The low gradient of the exposed shelf during glacial lowstands therefore resulted in the over extension and loss of stream power (reduced transport efficiency) of the Logan/ Albert flu vial system. The area that is now the outer shelf was most likely occupied by single channel thick shelf bypass channels (c.f. Posamentier & Allen, 1999) or became a low-lying fluvial shallow braid plain. The earliest deposition in the study took place on the continental shelf where three sequences are dominated by transgressive and lowstand systems tracts with highstand systems tracts not being readily recognised. On the coastal plain, three sequences have been cored and described in the Logan River incised valley. These sequences have been dated in this study at 40,000 yBP and 25,000 yBP and <18,000 yBP. This indicates that the Logan River incised valley can be classified as a compound valley fill (Zaitlin et al., 1994) characteristic of a relatively long lived fluvial system. Seismic mapping indicates the first sediment deposited in southern Moreton Bay was related to late lowstand conditions (the first onset of sea level rise and the creation of sufficient accommodation to allow for vertical aggradation), and was confined to the thalwegs of incised valleys. Seismic geometries suggest that deposition took place in fluvial point bars and therefore is most likely gravel and sand dominated. A transgressive surface separates these late lowstand fluvial sediments from an early to mid transgressive unit. The early to mid transgressive sediments are characterised by h high amplitude continuous reflectors and are generally confined within the wider valley walls, and are interpreted to have been deposited in a quiet estuarine setting. After the peak at 1OOkyBP, sea level began to fall into the next glacial maximum at 18 kyBP. This sea level fall was not smooth and was punctuated by a number of transgressive-regressive cycles. As a consequence three force regressive shelf perched early lowstand wedges are recognised on the continental shelf adjacent to the southern Moreton Bay area. These wedges have been grouped as sequence set C and represent subsequences within the overall early lowstand or falling stage systems tract associated with this punctuated falling sea level. Each of these sequences represent coastal plain deposits forming at a stage of sediment by-pass in the upper reaches of the fluvial valleys creating minor but significant sequence boundaries. The main sequence boundary GL is related to incision associated with the major sea level fall that peaked at 18 kyBP. This surface is heavily incised in places and formed at stages associated with each of the falls on the overall falling sea level limb. In the southern area incision related to the paleo-Logan Albert system is up to 60m on the coastal plain. The Logan system has re-inherited its main valley, and its position is structurally controlled. The Logan River valley was reincised as a result of the low sea level associated with the last glacial maximum. The first sediments to be deposited within this reincised valley were fluvial point-bar polymictic gravels and quartz-lithic sands these are interbedded with overbank deposits of mud and silt. These deposits are confined to the valley thalwegs. The earliest dateable material sampled by drilling in this study was 13,650 ±60 yBP (Beta-104824), indicating late·lowstand to early transgressive conditions based on the sea level curve of Chappell, et al., (1996). The transgressive surface, which overlies these deposits, is contained within the valleys and is recognised by the input of estuarine fauna! assemblages although the quartz-lithic and poorly sorted character of the sediments does not change. This in turn is overlain by high amplitude, concordant reflectors that are generally confined to the greater valley walls and shown to be laminated estuarine mud by drilling. The thickness and fine grained nature of these sediments in conjunction with a rapid sediment accumulation rate (approximately 11mm/year) indicates extensive creation of accommodation space consistent with the rapid transgression experienced on the east Australian coast at this time (up to 2.5rn/100years. A major tidal ravinement surface overlies the laminated muds of the early to mid transgressive phase of sedimentation. This surface is highly erosive and recognised as an abrupt change from laminated mud to clean well-sorted fine grained quartzose sand in conjunction with a shelly lag. The tidal ravinement surface is often coincident with the GL sequence boundary in areas. The last glacial transgression reached its peak at 6.5kyBP at approximately - 1.5 m higher than present. Age dating shells from a depth of 3m near the +2.5m contour on the coastal plain gave an Amino Acid Ratio consistent with an age of approximately 6.5kyBP. The Pimpama Coastal Plain was inundated at the peak of the transgression. Sediments form a depth of 6.lm were dated at 4780±60 yBP (WK-7663) in LR#3. Given the thickness of the overlying section it is apparent that the area was still part of an active flood tidal delta setting well beyond the peak of sea level at 6.5 kyBP. This is in keeping with a relatively rapid drop in sea level after 3000 yBP as is proposed by Flood, (1983), and explains the virtual absence of regressive bayhead delta sands on the coastal plain. The H4 seismic unit represents the current highstand since the peak of the late transgression. It is generally confined to the immediate vicinity of the Logan River bayhead delta and constrained geographically to the Redland Bay area. Where seen the unit downlaps onto the maximum flooding surface. This maximum flooding surface is coincident with the bay floor in most places of the northern area as a result of insufficient sediment supply to the area either from the Logan River or the tidal delta. When sea level fell by 1-l.5m approximately 3000 yBP, the tidal prism of the southern Moreton Bay area was dramatically decreased. As a result the efficient ancestral tidal inlet which had developed between the newly developed South Stradbroke barrier Island and North Stradbroke Island had to narrow and become shallower until it eventually closed. This period of closure allowed for the tidal circulation to decrease in the vicinity of southern Moreton Bay to virtually nil as that area became a tidal null point for tides now entering the area from South Passage (to the north) and the Nerang Inlet (to the south). Consequently the only sediment input was mud, silt and quartz-lithic sand supplied by the Logan and Pimpama Rivers. As a result, the sand shoals of the previous flood tide delta became relict and colonised by mangroves forming intra-to supra tidal · islands. This situation remained until 1898 when the sea broke through at Jumpinpin. Once this had occurred the regional tidal null point was shifted to become coincident with an area closer to the mouth of the present Logan River and the northern end of Canaipa Passage. The main effect was the scouring of previously inactive abandoned tidal channels to become the deep channels of present day. Quartzose marine sand has entered into the lagoon by a distance of nearly 9krn since 1898.

The coastal region influences many aspects of our lives, including our economy, our quality of life and our safety and security. Many large cities in Australia are located along estuaries and coasts. As a consequence of the growing human population, most coastal areas throughout Australia are now facing threats of over urbanisation, and industrialisation, resulting in significant impacts on the coastal aquatic environments. Additional challenges may also come from more frequent severe flooding resulting to climate changes, which could degrade the environment even further and more rapidly. Sediment accumulation and transport in estuaries and coastal bays is one of major issues, not only impacting on the maintenance of navigation channel but also resulting in ecological problems. For several decades, a large number of investigations of sediment transport have been conducted in Australia, which them mostly addressing conditions of the sediment delivered to the estuary within the dry season. However, a limited number of researches have been done in great detail, focusing on the hydrodynamic and sediment transport in the wet season. In recent years, with the development of computing and satellite technologies, the study on the hydrodynamic and sediment transport has allowed studies to be conducted on large spatial and temporal scales. Additionally, this has meant it is now easier to investigate the event-driven behaviour severe flooding events.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Griffith School of Engineering
Science, Environment, Engineering and Technology
Full Text

The knowledge and understanding of sediment transport is essential for the development of effective management strategies for nutrient and sediment loading in estuarine systems. Estuarine suspended sediment (in high concentrations), has the ability to adversely impact upon surrounding ecosystems, such as the Great Barrier Reef, Australia. Due to a recent decline in water and sediment quality, it has recently been mandated that a number of tropical, coastal estuarine systems in Queensland, such as the Fitzroy River estuary, have their sediment loading reduced. In order to meet these requirements, a greater understanding of the sediment transport dynamics and driving processes (such as flocculation and settling velocity) needs to be achieved, and the accuracy of estimation improved. This research project was motivated by the need to improve the general accuracy of field measurements for estuarine suspended sediment transport and dynamics. Field-based measurements (especially settling velocity) are necessary for the parameterisation of sediment transport models. The difficulty in obtaining accurate, in situ data is well documented and is generally limited to methods that isolate a water sample from its natural environment, removing all influences of estuarine turbulence. Furthermore, the water samples are often extracted from points (Eulerian) where the history of the suspended particles is generally unknown. These sampling methods typically contain intrinsic errors as suspended sediment transport is essentially Lagrangian (i.e., flows with the net motion of flow-field) in nature. An investigation into different drogue systems conducted in parallel with a study into the tidal states of the Fitzroy River estuary led to the development of a novel Lagrangian drogue device, the LAD. Additionally, the water-tracking ability of the LAD was tested and found to accurately follow a parcel of estuarine water over a slack water period. Therefore the LAD was deployed in the Fitzroy River to assist in the further understanding of complex sediment transport processes such as flocculation and settling velocity in a natural estuarine flow field. The final device (the LAD - Lagrangian Acoustic Drogue) was developed, utilizing the principals of acoustic backscatter intensity-derived SSC measurements. The investigation of a series LAD deployments (during slack water) in the Fitzroy River estuary, revealed the dominant suspended sediment processes and also gave an insight into the prevailing flow-patterns. Results showed the presence of a settling lag mechanism between low and high tide, which can initiate a net sediment flow upstream with each flood tide. The bulk settling velocity showed comparable results at both low and high water. The LAD derived bulk settling velocity as a function of concentration (SSC), yielding a strong positive correlation (r2 = 0.73). Also the importance of flocculation in the bulk settling and clear up of the water column during periods of still water (high and low tide) was demonstrated as all in situ settling velocities (0.33 - 1.75 mm s-1) exceeded single grain approximations (0.47 mm s-1). This research demonstrates the potential for Lagrangian drogue studies as an effective measuring platform for the accurate quantification of estuarine suspended sediment dynamics. The application of the LAD in the Fitzroy River has lead to a significant improvement in the understanding of the system's real sediment transport processes. This research has provided an effective and accurate technique for measuring real settling velocities for input into numerical models or for the validation of existing model outputs. Furthermore, this technique shows great potential for application in other estuarine systems.

The knowledge and understanding of sediment transport is essential for the development of effective management strategies for nutrient and sediment loading in estuarine systems. Estuarine suspended sediment (in high concentrations), has the ability to adversely impact upon surrounding ecosystems, such as the Great Barrier Reef, Australia. Due to a recent decline in water and sediment quality, it has recently been mandated that a number of tropical, coastal estuarine systems in Queensland, such as the Fitzroy River estuary, have their sediment loading reduced. In order to meet these requirements, a greater understanding of the sediment transport dynamics and driving processes (such as flocculation and settling velocity) needs to be achieved, and the accuracy of estimation improved. This research project was motivated by the need to improve the general accuracy of field measurements for estuarine suspended sediment transport and dynamics. Field-based measurements (especially settling velocity) are necessary for the parameterisation of sediment transport models. The difficulty in obtaining accurate, in situ data is well documented and is generally limited to methods that isolate a water sample from its natural environment, removing all influences of estuarine turbulence. Furthermore, the water samples are often extracted from points (Eulerian) where the history of the suspended particles is generally unknown. These sampling methods typically contain intrinsic errors as suspended sediment transport is essentially Lagrangian (i.e., flows with the net motion of flow-field) in nature. An investigation into different drogue systems conducted in parallel with a study into the tidal states of the Fitzroy River estuary led to the development of a novel Lagrangian drogue device, the LAD. Additionally, the water-tracking ability of the LAD was tested and found to accurately follow a parcel of estuarine water over a slack water period. Therefore the LAD was deployed in the Fitzroy River to assist in the further understanding of complex sediment transport processes such as flocculation and settling velocity in a natural estuarine flow field. The final device (the LAD - Lagrangian Acoustic Drogue) was developed, utilizing the principals of acoustic backscatter intensity-derived SSC measurements. The investigation of a series LAD deployments (during slack water) in the Fitzroy River estuary, revealed the dominant suspended sediment processes and also gave an insight into the prevailing flow-patterns. Results showed the presence of a settling lag mechanism between low and high tide, which can initiate a net sediment flow upstream with each flood tide. The bulk settling velocity showed comparable results at both low and high water. The LAD derived bulk settling velocity as a function of concentration (SSC), yielding a strong positive correlation (r2 = 0.73). Also the importance of flocculation in the bulk settling and clear up of the water column during periods of still water (high and low tide) was demonstrated as all in situ settling velocities (0.33 - 1.75 mm s-1) exceeded single grain approximations (0.47 mm s-1). This research demonstrates the potential for Lagrangian drogue studies as an effective measuring platform for the accurate quantification of estuarine suspended sediment dynamics. The application of the LAD in the Fitzroy River has lead to a significant improvement in the understanding of the system's real sediment transport processes. This research has provided an effective and accurate technique for measuring real settling velocities for input into numerical models or for the validation of existing model outputs. Furthermore, this technique shows great potential for application in other estuarine systems.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Engineering
Full Text

This research contributed to the rather limited knowledge on the transport of organic contaminants in estuarine environments from South-East Queensland. Modelling studies were conducted to assess the fate of some current-use pesticides and pharmaceuticals in the Brisbane River estuary. The vertical transport of per- and polyfluoroalkyl substances (PFASs) in soils from a previous firefighting training ground was also assessed. The outcomes of this study contribute to the global stock taking of organic contaminants in the environments and are expected to be useful in designing effective containment or remediation strategies for organic contamination.