Dredging Project Research Articles

Using a modified dredging elutriate testing approach to evaluate potential aquatic impacts associated with dredging a large freshwater industrial harbor.

Potential adverse impacts to the aquatic environment should be minimized whenever possible during an environmental dredging project by selecting realistic and technically feasible environmental targets. These targets need to balance short term impacts with the longer term benefit of removing contaminated sediments from the environment. Environmental dredging is part of the planned remediation of Randle Reef (a 60 hectare zone of mostly PAH-contaminated sediments) in Hamilton, Ontario, Canada. In this study, we describe the results of dredging elutriate toxicity testing (DETE) to assess the potential risks from dredging this PAH contaminated site. A modified elutriate preparation method intended as an alternative measure of conditions within the dredging plume was assessed with both standard water column species (Daphnia magna and fathead minnow [Pimephales promelas]) and alternative benthic and epibenthic test organisms (Chironomus dilutus and Hyalella azteca). The standard DETE test was also conducted with H. azteca to compare with the modified DETE results. The greatest toxic response was seen in the alternative test species; however, the modified DETE method resulted in less toxicity than the standard protocol. The relationship between toxicity results and chemical and/or physical characteristics of the samples was examined, but differences in toxicity could only be explained by differences in the total suspended solids concentrations in the elutriate samples. Challenges associated with DETE assessment of PAH-contaminated sediments and the implications for establishing dredging benchmarks are discussed. Integr Environ Assess Manag 2017;13:155-166. © 2016 SETAC.

4D ANIMATION RECONSTRUCTION FROM MULTI-CAMERA COORDINATES TRANSFORMATION

Reservoir dredging issues are important to extend the life of reservoir. The most effective and cost reduction way is to construct a tunnel to desilt the bottom sediment. Conventional technique is to construct a cofferdam to separate the water, construct the intake of tunnel inside and remove the cofferdam afterwards. In Taiwan, the ZengWen reservoir dredging project will install an Elephant-trunk Steel Pipe (ETSP) in the water to connect the desilting tunnel without building the cofferdam. Since the installation is critical to the whole project, a 1:20 model was built to simulate the installation steps in a towing tank, i.e. launching, dragging, water injection, and sinking. To increase the construction safety, photogrammetry technic is adopted to record images during the simulation, compute its transformation parameters for dynamic analysis and reconstruct the 4D animations. In this study, several Australis© coded targets are fixed on the surface of ETSP for auto-recognition and measurement. The cameras orientations are computed by space resection where the 3D coordinates of coded targets are measured. Two approaches for motion parameters computation are proposed, i.e. performing 3D conformal transformation from the coordinates of cameras and relative orientation computation by the orientation of single camera. Experimental results show the 3D conformal transformation can achieve sub-mm simulation results, and relative orientation computation shows the flexibility for dynamic motion analysis which is easier and more efficiency.

4D ANIMATION RECONSTRUCTION FROM MULTI-CAMERA COORDINATES TRANSFORMATION

Abstract. Reservoir dredging issues are important to extend the life of reservoir. The most effective and cost reduction way is to construct a tunnel to desilt the bottom sediment. Conventional technique is to construct a cofferdam to separate the water, construct the intake of tunnel inside and remove the cofferdam afterwards. In Taiwan, the ZengWen reservoir dredging project will install an Elephant-trunk Steel Pipe (ETSP) in the water to connect the desilting tunnel without building the cofferdam. Since the installation is critical to the whole project, a 1:20 model was built to simulate the installation steps in a towing tank, i.e. launching, dragging, water injection, and sinking. To increase the construction safety, photogrammetry technic is adopted to record images during the simulation, compute its transformation parameters for dynamic analysis and reconstruct the 4D animations. In this study, several Australis© coded targets are fixed on the surface of ETSP for auto-recognition and measurement. The cameras orientations are computed by space resection where the 3D coordinates of coded targets are measured. Two approaches for motion parameters computation are proposed, i.e. performing 3D conformal transformation from the coordinates of cameras and relative orientation computation by the orientation of single camera. Experimental results show the 3D conformal transformation can achieve sub-mm simulation results, and relative orientation computation shows the flexibility for dynamic motion analysis which is easier and more efficiency.

Great Lakes Water Levels: Decomposing Time Series for Attribution

Great Lakes water levels have been trending downwards throughout the 20th and into the 21st centuries. Potential causes are numerous. There have been dredging and water diversion projects over the last 110 years, increasing demand for fresh water consumption from a rising population, and considerable variations in environmental factors (rainfall, snowfall, air temperature, and wind), all causal in nature. A thorough assessment of the National Ocean and Atmospheric Administration (NOAA) National Center for Environmental Information (NCEI) and the NOAA National Centers for Environmental Prediction and the National Center for Atmospheric Research (NCEP/NCAR) — Reanalysis Project (RP) archives of time series of winds, air temperatures, rainfall and snowfall, and water level data, reveals that falling lake levels can be linked to rising air temperatures. Nonuniform, post-glacial, isostatic adjustments of the entire Great Lakes region has further complicated the system as land mass tilting causes localized uplift or subsidence that has also altered relative water levels. A mathematical decomposition of the various data sets and accessory calculations strongly indicate regional atmospheric temperature increases over the entire 20th century and the early 21st century resulting in increased evaporation, appears to be the dominant driving factor in the continued downward trend of water levels in the Great Lakes. Moreover, a high degree of correlation was discovered in comparing water level in the Great Lakes with the comparable temporal variability and record length trends evident both the Global (Land and Ocean) Surface Temperature Anomaly (GSTA) time series and the Atlantic Multidecadal Oscillation (the AMO). It is of note that there have been several water level events since 2013 from which the long term losses of fresh water have undergone a change and the lakes have gained fresh water. This presents an apparent quandary to our nearly 120 year, record length study which revealed downward trends in water levels. To wit, this recent upward movement begs the question: Is the two-year change a precursor to increases in water levels or is it just a local blip? We will focus on data up to 2013, but comment upon recently reported increases as part of our analyses.

Development of Optimization Model for River Dredging Management Using MCDA

The main purpose of this study is to develop an optimal river dredging management model by applying MCDA (Multi-Criteria Decision Analysis) technique specifically in Korea where river dredging research are scarce. This model supports the decision making by providing weight factors covering dredging cost, and social and environmental impacts. This model requires various input data which are dredging points, dredging machines, dewatering machines, disposal sites. Furthermore, for the model development, the researcher applied imaginary dredging project area for model assessment and analysis. We used a total of 5 cases of weight factors combination. It can classify weight factors combination in 2 categories. The first category is weight factors combination for single-objective optimization and another category is weight factors combination for multi-objective optimization. The single-objective optimization is same that one weight factor is 1.0 and other weight factor is 0.0. The multi-objective optimization is used equality weight factors combination or weight factors from previous study. According to model simulation, it shows that cost of dredging is different approximately 18% due to weight factors. Besides, the maximum cost is obtained when weight factor of social impact is 1.0. In contrast, minimum cost of dredging projects is discovered when weight factor of cost is 1.0. From the weight factors in previous study, it illustrates that there are about 2% beyond the minimum cost of dredging projects, and approximately 18% less than maximum cost. Next study will be used real river dredging areas or simulation results of bed changes. The results of this study can be efficiently applied to 4 major rivers in Korea where periodical river dredging is necessary.

Great Lakes Water Levels: Decomposing Time Series for Attribution

Great Lakes water levels have been trending downwards throughout the 20th and into the 21st Centuries. Potential causes are numerous. There have been dredging and water diversion projects over the last 110 years, increasing demand for fresh water consumption from a rising population, and considerable variations in environmental factors (rainfall, snowfall, air temperature and wind), all causal in nature. A thorough assessment of United States federal agency and laboratory data archives of time series of winds, air temperatures, rainfall and snowfall, and water level data, reveals that falling lake levels can be linked to rising air temperatures. Non-uniform, post-glacial, isostatic adjustments of the entire Great Lakes region has further complicated the system as land mass tilting causes localized uplift or subsidence that has also altered relative water levels. A mathematical decomposition of the various data sets and accessory calculations strongly indicate regional atmospheric temperature increases over the entire 20th century and the early 21st century resulting in increased evaporation, is the dominant driving factor in the continued downward trend of water levels in the Great Lakes. Moreover, a high degree of correlation was discovered in comparing water level in the Great Lakes with the comparable temporal variability and record length trends evident both the Global (Land and Ocean) Surface Temperature Anomaly time series and the Atlantic Multi-Decadal Oscillation. It is of note that there have been several water level events since 2013 from which the long term losses of fresh water have undergone a change and the lakes have gained fresh water. This received a great deal of attention in both the public press and a scientific newsletter and shows that there is a danger in only dealing with a small portion, 2 years, of a 120 year climate record.

Platform of integrated tools to support environmental studies and management of dredging activities

Dredging activities can cause environmental impacts due to, among other, the increase of the Suspended Solid Concentration (SSC) and their subsequent dispersion and deposition (DEP) far from the dredging point. The dynamics of the resulting dredging plume can strongly differ in spatial and temporal evolution. This evolution, for both conventional mechanical and hydraulic dredges, depends on the different mechanisms of sediment release in water column and the site-specific environmental conditions. Several numerical models are currently in use to simulate the dredging plume dynamics. Model results can be analysed to study dispersion and advection processes at different depths and distances from the dredging source. Usually, scenarios with frequent and extreme meteomarine conditions are chosen and extreme values of parameters (i.e. maximum intensity or total duration) are evaluated for environmental assessment. This paper presents a flexible, consistent and integrated methodological approach. Statistical parameters and indexes are derived from the analysis of SSC and DEP simulated time-series to numerically estimate their spatial (vertical and horizontal) and seasonal variability, thereby allowing a comparison of the effects of hydraulic and mechanical dredges. Events that exceed defined thresholds are described in term of magnitude, duration and frequency. A new integrated index combining these parameters, SSCnum, is proposed for environmental assessment. Maps representing the proposed parameters allow direct comparison of effects due to different (mechanical and hydraulic) dredges at progressive distances from the dredging zone. Results can contribute towards identification and assessment of the potential environmental effects of a proposed dredging project. A suitable evaluation of alternative technical choices, appropriate mitigation, management and monitoring measure is allowed in this framework. Environmental Risk Assessment and Decision Support Systems (DSS) may take advantage of the proposed tool. The approach is applied to a hypothetical dredging project in the Augusta Harbour (Eastern coast of Sicily Island–Italy).

Ecosystem-based carbon footprinting of marine engineering projects

Dredging projects use large amounts of fuel, which leads to substantial carbon dioxide (CO2) emissions. Until now, reducing the carbon footprint of dredging projects has mainly involved investigating the possibilities of dredging schemes and vessels that are more fuel efficient. A reduction in the order of 10–20% may be within reach, most of it is a win–win situation since fuel reduction will also reduce costs. A further reduction in carbon dioxide emissions may be possible on a project-by-project basis but will involve a trade-off between dredging costs and carbon dioxide emissions. Marine engineering projects also have an impact on primary production and formation of organic carbon and on sedimentation processes and burial of organic carbon in sediments. Both impacts influence carbon sequestration and can be a substantial or even overriding factor in the ‘carbon footprint’ of a project. The carbon footprint of a marine engineering project is often larger and more complex than previously anticipated. However, a more comprehensive carbon footprint also shows that a significant reduction in carbon dioxide emissions is possible when the designs and dredging and maintenance schemes stimulate sequestration of organic carbon in the wider environment.

Dynamics of a deep-water seagrass population on the Great Barrier Reef: annual occurrence and response to a major dredging program.

Global seagrass research efforts have focused on shallow coastal and estuarine seagrass populations where alarming declines have been recorded. Comparatively little is known about the dynamics of deep-water seagrasses despite evidence that they form extensive meadows in some parts of the world. Deep-water seagrasses are subject to similar anthropogenic threats as shallow meadows, particularly along the Great Barrier Reef lagoon where they occur close to major population centres. We examine the dynamics of a deep-water seagrass population in the GBR over an 8 year period during which time a major capital dredging project occurred. Seasonal and inter-annual changes in seagrasses were assessed as well as the impact of dredging. The seagrass population was found to occur annually, generally present between July and December each year. Extensive and persistent turbid plumes from a large dredging program over an 8 month period resulted in a failure of the seagrasses to establish in 2006, however recruitment occurred the following year and the regular annual cycle was re-established. Results show that despite considerable inter annual variability, deep-water seagrasses had a regular annual pattern of occurrence, low resistance to reduced water quality but a capacity for rapid recolonisation on the cessation of impacts.

Hydraulic Theory and Hydraulic Engineering Projects of the Wusong River (吳淞江) Basin Between the Sixteenth and Nineteenth Centuries

이 ë ¼ë¬¸ì€ ëª Â·ì²­ì‹œëŒ€ 강남 지역의 ì „ë°˜ì ì¸ 수리 체계와 당시 활발하게 ì „ê°œ 된 수리 공사가 지닌 의의를 ê³ ì°°í•˜ê¸° 위한 것이다. ëª Â·ì²­ 두 왕조는 대규모 준 설 공사의 ì§€ì†ì ì¸ 시행을 통해, 국가 세수의 확보와 농민의 생산 활동 보장이 라는 ëª©ì ì„ ë‹¬ì„±í•˜ë ¤ 했다. 그러나 수리 체계 자체의 ì• í™”, 과다한 비용, 여러 계층의 이해관계 때문에 대형 수리 공사는 본래 ëª©ì ì„ 달성하지 못했으며, 이미 16세기부터 ë‹¨íŽ¸ì ì´ë©° 현실성이 있는 소규모 수리 공사에 대한 관심이 등장했 다.<br/>한편 ì‚¬íšŒê²½ì œì  변화가 한층 더 ì§„ì „ëœ 청대에는 강남 지역에서 폭넓게 ì „ê°œ 된 ìƒì— ìž‘ë¬¼ì˜ 확대로 수리 ë¬¸ì œì— 대한 새로운 인식이 등장하게 되었다. 이는 수리 시설에 의지한 단순한 곡물생산이 아닌 다양한 경작을 통해, ê°œì„ ì˜ 여지가 희박했던 수리시설의 압박으로부터 ë²—ì–´ë‚˜ë ¤ 했기 때문이다. 그러므로 16세기 이후 강남 지역의 다양한 ìƒì— ìž‘ë¬¼ 재배나 ìˆ˜ê³µì— ë°œì „ì€ ë¹„íš¨ìœ¨ì ì´ì—ˆë˜ 수리 시설에서 비롯된 또 다른 양상이기도 하다. 그러나 이런 í˜„ì‹¤ì ì¸ ì œì•½ê³¼ 실패에 도 ë¶ˆêµ¬í•˜ê³ , 대형 수리 공사가 ë°˜ë³µì ìœ¼ë¡œ 진행된 ì´ìœ ëŠ” ë¶„ëª æ±Ÿå— 지역이 지 닌 ê²½ì œì  중요성과 함께 治水가 지닌 본래의 理想을 달성하기 위한 ê²ƒì´ë¼ê³ í• ìˆ˜ 있다. ì£¼ì œì–´: 강남 지역, 蘇州府와 松江府, 吳淞江, 治水, 治田, 수리비용, ìƒì— ìž‘ë¬¼, 水利志, 明經世文編, 皇朝經世文編

The role of environmental impact assessment in protecting coastal and marine environments in rapidly developing islands: The case of Bahrain, Arabian Gulf

Bahrain, a group of islands, is facing several environmental challenges, including degradation of coastal and marine environments due to intensive dredging and reclamation activities. Presently, reclamation activities have resulted in adding around 110 km2 representing an increase of 14% of the total land area of Bahrain. Recognizing the role of Environmental Impact Assessment (EIA) in protecting environment from degradation and pollution associated with coastal developments, Bahrain formally adopted EIA in its environmental system in 1998. The present study investigated the practice and effectiveness of EIA in protecting coastal and marine environments in Bahrain by reviewing selected EIA reports and soliciting views of EIA experts, consultants, academics and other relevant bodies. Shortcomings in environmental and ecological assessment practices related to coastal and marine developments were recognized and constrains that restrict the effectiveness of EIA in protecting coastal and marine environments in Bahrain were identified. Maintaining a sustainable use of coastal and marine natural resources in Bahrain requires measures to holistically address the interactions among the several dredging and reclamation projects and their additive and cumulative impacts. This could be achieved through enhancing the current practice of EIA process and adopting Strategic Environmental Assessment (SEA) for dredging and reclamation activities.

Estimating source terms for far field dredge plume modelling

Far field modelling of dredging induced suspended sediment plumes is important while assessing the environmental aspects of dredging. Realistic estimation of source terms, that define the suspended sediment input for far field dredge plume modelling, is key to any assessment. This paper describes a generic method for source term estimation as it is used in practice in the dredging industry. It is based on soil characteristics and dredge production figures, combined with empirically derived, equipment and condition specific ‘source term fractions’. A source term fraction relates the suspended fine sediment that is available for dispersion, to the amount of fine sediment that is present in the soil and the way it is dredged. The use of source term fractions helps to circumvent modelling of complicated near field processes, at least initially, enabling quick assessments. When further detail is required and extra information is available, the applicability of the source term fractions can/should be evaluated by characterisation monitoring and/or near field modelling. An example of a fictitious yet realistic dredging project demonstrates how two different work methods can trigger two distinctly different types of stress to the environmental system in terms of sediment concentration and duration.

Investigating the Effects of Hydrographic Survey Uncertainty on Dredge Quantity Estimation

Quantity estimation is a critical issue in dredging projects since it has a direct impact on the project process and cost. Hydrographic surveying is the main tool for measuring the horizontal coordinates and elevation of the sea bed and subsequently quantity estimation. In the present work, data from different dredging projects in Egypt have been utilized with Monte Carlo simulation to investigate the effects of the hydrographic survey uncertainty on the estimated dredge quantities. Results showed that the horizontal position uncertainty significantly affects the estimated dredged volume uncertainty especially in irregular bed's areas. Consequently, the conventional low-cost, low accuracy positioning devices (e.g., DGPS) may increase the cost of dredging. Therefore, more accurate high-cost devices (e.g., RTK GPS) could be recommended to reduce the costs of the dredging projects. The results showed also that uncertainty of measured bed levels have a direct impact on the estimated volume. Hence, the effect of tide correction techniques is studied and an alternative approach for dredged volume estimation is proposed to avoid the uncertainty in measuring the tide. In this approach, the measured depths are referenced to the ellipsoidal geodetic datum rather than the chart datum.

Water management in a city of southwest China before the 17th century

Kunming City is the capital of Yunnan Province, China. From the 12th century, it has developed from a remote rural town to become a large city. Successful water management was one of the key dynamic factors in the city's development. As a result of the location of Kunming City, in its early age it was in a narrow area between the north bank of Dian Chi lake and the mountains, therefore the water management in the history of Kunming City mainly focused on two key projects, one being the Song Hua Ba Dam with the function to control flooding from Pang Long Jiang river, and the other the Hai Kou He river dredging project to control the drainage from Dian Chi lake, therefore shaping a water supply system for the city in the upper basin of the Yangtze River. Pang Long Jiang river is only one large river from the mountains flowing across the city into Dian Chi lake. Therefore the city's development from its early age (11th century) mainly depended on irrigation and flood control of Pan Long Jiang river basin and the basic water system for the city was formed before the 17th century (Ming Dynasty), the most important period of the city's water history.

연안준설 사업에 따른 해양 수질 및 퇴적물 영향평가 개선 방안

2000년대 초반부터 연안준설 사업의 수요가 크게 증가하였고, 기타 연안개발 사업과도 중첩되어 준설토의 발생량은 지속적으로 증가하고 있다. 이로 인해 주변해역에 대한 환경 영향이 심화될 수밖에 없는 상황에서, 2011년 제출된 해역이용협의서 중 준설이 포함된 사업의 해수 및 해저 퇴적물에 대한 해양환경영향평가 현황을 파악하였다. 해양환경영향평가 항목 중 일반 항목들의 조사 비율은 대체로 높은 반면, 중금속 등 유해 물질의 경우에는 세부항목들 간 조사 비율 편차가 크게 나타났다. 한편 중금속 분석 시 협의서 작성 지침에 따른 전처리 과정(완전 분해)과 분석 방법이 제대로 수행되지 않았다. 또한 작성 지침에 명시되어 있지는 않지만, 결과값에 대해 신뢰도 확보를 위한 검증(회수율 및 검출한계 산정) 수행 현황도 매우 미흡한 것으로 파악되었다. 이로 인해 연안 준설 및 개발에 따른 주변 해양환경영향평가가 부실하게 진행되고 있는 것으로 나타났다. 향후 해양 수질 및 퇴적물 환경에 대해 보다 엄정한 평가와 진단을 위해서는 협의서 작성에 관한 세부 지침의 보완이 요구되며, 해역이용협의 제도의 개선을 통해 정확한 해양환경영향평가가 수행되도록 협의서 작성지침의 준수 의무를 강화할 필요가 있는 것으로 판단되었다. Since the early 2000s, demand for coastal dredging projects have been significantly increased, and the dredged sediments have showed the continuing marked increases through the multiple projects with other coastal development and constructions. As significant or potential degradation of marine environment has been mounting, we checked the current situation of marine environmental impact assessment through marine water and sediment qualities in relation with dredging projects of the sea area utilization consultation statements submitted in 2011. While analysis percentages of the general items were usually higher, harmful components such as metals revealed wide variation of analysis percentages. In the event of analysis of metals, the pre-treatment process (full digestion) and analysis method were not properly implemented in accordance with the guidelines for preparation of consultation statements. Although not specified in the guidelines, verification procedures (tests of recovery efficiency and detection limit) to secure the reliability were almost ignored. As a result, most of developers did conduct poor marine environmental impact assessment on coastal dredging and related projects. We suggested that the responsible government authority should establish new detailed guidelines on the sea area utilization consultation for more strict evaluation and diagnosis of marine environment and distinctly request the developer to obey the guidelines by complementing the system of the sea area utilization consultation.

MODELLING OF A NEARSHORE PLACED SAND MOUND

Nearshore placement of sand is becoming a more popular option in two related types of coastal engineering projects: beach nourishment and inlet dredging. Placing the sand in the nearshore instead of directly on the beach can reduce the costs of a beach nourishment project (Douglass 1995); furthermore, the environmental impact to the beach and dune ecosystem may be perceived to be less for open-water disposal with subsequent migration than for direct placement on the beach. Nearshore placement of sand is also an option in navigation dredging projects for similar reasons. Several design and planning questions relate to the fate of dredged sand placed in the nearshore. Can we economically use profile nourishment, and what is the certainty that a constructed submerged feature will move onshore or remain in place? And if it will move, what is the rate of its movement? Another question concerns how deep material should be placed. In order to answer these questions, together with physical model experiments, several empirical/numerical models have been developed in the past in the United States as a part of the Corps of Engineers 'Dredging Research Program' (DRP) (Hands 1991, Larson and Kraus 1992). &#x0D; Hydrodynamic modelling of the nearshore environment has reached a verifiable level of maturity in the last decades as a result of well-defined equations, established numerical solutions and quality laboratory and field data. On the contrary, modelling of sediment transport and beach profile evolution has not yet approached a similar level of accuracy. Most commonly applied models to predict beach profile modifications and to estimate the migration rate of nearshore constructed sand mounds rely on empirical relationships (Douglass 1995). More recently, the numerical model C-SHORE (Kobayashi et al. 2007; Figlus et al. 2011) was developed resulting in simple, practical and accurate code that predicts beach-dune profile evolution over the near-shore region in response to waves, currents and water levels. In the present work, a calibration and verification procedure is considered for the numerical model C-SHORE (Kobayashi et al. 2007) and the empirical model (Douglass 1995).

Availability of Professional Construction Management for the Administration of Public Business

The short length and rapid flow of rivers in Taiwan lead to vast differences between river reservations and silting. River dredging is a necessary measure to reduce flood damage and prevent secondary disasters from striking residents along riverbanks during flood seasons[1]. The government of Ilan County in Taiwan was the first to perform river dredging projects using public administration (PBA). This approach resulted in strong performance in disaster prevention and increased local sources of income[1]. However, operational mode was adopted by government departments, the efficiency of which is lower than that of government-owned but privately-run organizations. In other words, the PBA method increased governmental revenue; however, it remains unknown whether overall effectiveness was enhanced. A river dredging project commissioned by Hsinchu County incorporated professional construction management (PCM) in addition to PBA to increase operational performance[2]. This study analyzed and compared the two projects. From the aspect of management, river dredging conducted under the PBA method complicates operational management. Commissioning PCM for operations enables the coordination of various interfaces and enhances the progress of construction. PCM teams also serve as the connecting link between owners and contractors through the implementation of multi-layer structures, hierarchical responsibilities, centralized management, mutual supervision, and reduced abuses, enhancing overall project quality.

Local and regional effects of reopening a tidal inlet on estuarine water quality, seagrass habitat, and fish assemblages

Blind Pass is an inlet that separates Sanibel and Captiva Islands in southwest Florida but has historically closed and opened by both anthropogenic and natural processes. In July 2010, a dredging project to open the small inlet between the two barrier islands was completed. The objective of this study was to use and supplement ongoing estuary-monitoring programs to examine the responses of water quality, seagrass habitat metrics, and fish assemblages both in the immediate vicinity of the inlet and at broader scales (up to 40km2). As far as we are aware, there are no previous studies with this intensity of sampling, both before and after an inlet opening. Significant increases in salinity and turbidity were observed inside Blind Pass, with significant decreases in CDOM and chlorophyll a, however, the effects were not far-reaching and limited to less than 1.7km from the inlet within Pine Island Sound. Seagrass habitat metrics were expected to respond rapidly after the inlet was opened given the reduced light attenuation. However, there were no changes in shoot densities, species composition, and epiphytic algae within the approximately one-year duration of the study. The reopening of the pass did not substantially change fish assemblage structure, except for those from deeper habitats. Although immediate increases in the abundances of estuarine-dependent species were predicted in shallow habitats post opening, this did not occur. In conclusion, the effects of reopening a relatively small ocean inlet on water quality were apparent in the immediate vicinity of the inlet (within 1.7km), but far-reaching effects on water quality, seagrass metrics, and fish assemblages were not immediately apparent in this well-flushed estuary. If subtle changes in tidal exchange and circulation affect productivity of seagrasses or its fish assemblages at broad scales, it may take several years to reach a steady state.

Settlement and Consolidation Mechanism of Cohesive Sedimentation in Estuarine Environment

Estuarine area is the intersection zone of river estuary, coastal and land-phase. Cohesive sediment deposition for mutation affects estuary channel transport and brings great challenges to dredging project. Consolidation indicators are closely related to sedimentation and dredging, and there are apparent errors in application of Terzaghi theory in cohesive sediment consolidation evaluation for large stain characteristics. Then it is necessary to modify some consolidation parameters to extend Terzaghi theory in cohesive sediment consolidation. Considering a whole process of sedimentation and consolidation, a unified equation can be established based on sediment deposition and consolidation theory. Equation parameters can be determined by the simulation test (settlement column experiment). According to the settlement curves and volume fraction distribution curves by simulation experiment, modified consolidation coefficient and the trends can be determined, and modified consolidation coefficient can apply in dredging and deposition project.

Study on Incentive Mechanism of Large-Scale Dredging Project Based on Fairness Preference

This paper establishes fair incentive model of large-scale dredging project using principal-agent theory and fairness preference theory and analyzes the influence of technical parameters of ships and bid price of the dredging project on principal, agent incentives and profits. Study shows that the principal-agent model must be corrected, so this paper puts forward correction methods and calculation methods.