Dredging Operations Research Articles

Primary Productivity in the Golden Horn

The shores of the Golden Horn--once most important seaport of the region--represented throughout history a romantic and recreational venue. This tributary to the Bosphorus, however, became seriously polluted with the extensive industrialization and rapid population growth in Istanbul over the past century. Two main tributaries, the Alibeykoy and the Kagithane, dumped both liquid and solid waste from residential areas and industry (small and large-scale) into the Golden Horn. As a result of this pollution, the landward three to four kilometers of the estuary became swamped with sediment. The dominance of anaerobic activity resulted in a highly unpleasant smell, and the shallow depth as one progressed up the bay restricted navigation. In early 1997 The Istanbul Metropolitan Municipality began a dredging operation and gradually diverted all domestic and industrial wastewater discharge from the Golden Horn. Since then there have been remarkable improvements in water quality. This paper presents the state of eutrophication through the water body of the Golden Horn; parameters such as DO, TKN, NH(3)-N, NO(3)-N, the total phosphorus (TP) and dissolved phosphorus (PO(4)-P), phytoplankton and chlorophyll-a have been were analyzed in samples of water taken from various points in the Golden Horn. The presence of DO and the phytoplankton, both indicators of primary productivity in an aquatic body, has been evaluated in relation to former conditions.

Historical and ecological analysis of coral communities in Castle Harbour (Bermuda) after more than a century of environmental perturbation

The coral reefs in Bermuda’s Castle Harbour basin have been subjected to varying anthropogenic stressors for over 100 years. These include restriction of water flow through the construction of a causeway in the late 19th century and an extensive dredging and land reclamation operation during World War II. In the 1970s, disposal of bulk waste commenced at a foreshore reclamation site in Castle Harbour. Since 1996 the waste stream has included blocks of cement-stabilized municipal incinerator ash. This study provides a historical and quantitative ecological review of the Castle Habour reef ecosystem as a case study, assessing the responses of the reef to more than a century of anthropogenic disturbance. Measures of the coral community, flow rates, turbidity and sedimentary regimes suggest the present structure of the coral community largely reflects the impacts of the historic dredge and fill operations prior to the establishment of the foreshore dump site. Recent increases in the abundance of some sediment tolerant, massive reef-building coral species ( Diploria strigosa and Montastraea cavernosa) suggest adaptation to chronic sediment stress.

NATIONAL WATER GRID—ITS OBJECTIVE AND CHALLENGE

ABSTRACT In countries like India, having a large variation of water resources with space and time, inter-basin water transfer projects seem to be the ultimate solution to ease the water crisis and achieve a stable economic growth of the nation. But the projects of such huge magnitudes are always prone to large controversies, due to their numerous advantages and disadvantages. The water crisis in India may be stated as due to its vast expanse, huge population and a large variation of annual precipitation, both spatially and temporally. The substitute to the interlinking of rivers can be considered as adopting some techniques like extensive water harvesting, massive dredging operations to improve upon the water carrying capacity of the river systems, extensive soil conservation, tank rehabilitation schemes in the south and linking up all the existing coastal navigational canals for economical transport. This paper presents the scenario of inter-basin water transfers in India, its objectives, scope and the challenges to be met in the investigation, planning, design, execution and maintenance of the project.

Development of A Two-Dimensional Analytical Model for Predicting Toxic Sediment Plumes Due to Environmental Dredging Operations

A two-dimensional analytical transport model is developed to predict the dredge induced plume concentration in the horizontal plane under steady-state for simple hydraulic conditions. The derivation of the analytical solution is based on the solution to the advection-diffusion equation. The application of this analytical model is limited to mechanical dredge operations, bucket dredge, which has continuous point source in the water column. The analytical model developed herein is used to simulate sediment concentration distributions from a hypothetical dredging site and compared to results from a similar model using Stokes’ settling. The result shows that Stokes’ settling underestimates settling in the near-field and overestimates settling in the far-field plume. In summary, the model provides the ability to account for the rapid settling of larger particles in the suspended sediment near the dredging operations while simulating the slower settling and diffusive transport of smaller particles moving away from the dredging sites.

The potential of screening for agents of toxicity using gene expression fingerprinting in Chironomus tentans

Stress responses of sediment dwelling organisms offer novel opportunities to study the toxicity of compounds within that environment. Current analytical methods are limited and do not assess exposure or bioavailability. Restriction fragment differential display-polymerase chain reaction is a gene expression profiling technique that allows comparison of the effects of different chemicals on an organism. We used the restriction reaction to assess the potential of using stress responses of invertebrates to discriminate between different contaminants. Larvae of an infaunal invertebrate, Chironomus tentans, were exposed to polyaromatics (fluoranthrene, phenanthrene, and DDT), and metals (copper, zinc and lead) in 16 hr aqueous exposures. Distinctly different restriction reaction gene expression patterns were observed in response to these exposures. These results suggest that gene expression fingerprinting could complement current procedures for detecting contaminants or classes of contaminants. Application of this approach could result in significant cost savings to sediment dredging and remediation operations.

Bioavailability of hydrophobic organic contaminants and quality of organic carbon

U.S. laws require that contaminant bioaccumulation potential be evaluated before dredged material can be recycled. Simple fugacity models, e.g. organic contaminant aqueous partition coefficient (Koc)-derived theoretical bioaccumulation potential, are commonly used to estimate the partitioning of hydrophobic organic contaminants between sediment organic matter and organism lipid. Koc-derived models, with or without the addition of a soot carbon term, did not accurately or consistently predict total polycyclic aromatic hydrocarbons (PAHs) and polychlorobiphenyls partitioning of eight sediments from ongoing dredging operations onto C18-coated filter paper. These models also failed to predict the partitioning of individual PAHs from these eight sediments. These data underscore the trade-offs between the ease of using simple models and the uncertainty of predicted partitioning values.

The U.S. Minerals Management Service Outer Continental Shelf Sand and Gravel Program: Environmental Studies to Assess the Potential Effects of Offshore Dredging Operations in Federal Waters

Abstract The U.S. Department of the Interior, Minerals Management Service, provides policy direction relative to the development of all marine mineral resources located beneath Federal waters of the United States. Over the last ten years or so, geological studies encompassing the collection and analysis of seismic, vibracore, and grain size data have been conducted in partnership with coastal States in the Atlantic and Gulf of Mexico to locate suitable sources of compatible sand for beach and coastal restoration. Environmental studies have been initiated to provide biological, physical, and other pertinent information for decisions regarding leasing and use of this resource. Aggregate dredging studies also have been conducted in the event that an offshore aggregate mining operation is proposed in the future. A symposium was held in New Orleans in January 2002 to report results from several studies completed over the past 2 years. The papers prepared for this Special Issue summarize the findings of recentl...

Progress in Management of Sediment Bypassing at Coastal Inlets: Natural Bypassing, Weir Jetties, Jetty Spurs, and Engineering Aids in Design

Maintenance of navigable channels at coastal inlets typically requires sediment bypassing to preserve integrity of the adjacent beaches. Artificial bypassing mimics or preserves the pathways of sediment in the littoral zone and harmonizes the requirement for deepening navigation channels within the context of the natural sediment-sharing system of inlets and beaches. A range of techniques can be applied to perform bypassing. Customary on-demand channel dredging is not always the best solution because sediment shoaling does not necessarily follow a predictable schedule, potentially compromising navigation reliability between allowable dredging windows. If sediment can be directed to a location other than the channel, planning of dredge operations may be optimized and less expensive equipment feasible. A weir jetty system is one such solution. This paper presents progress in understanding of sediment bypassing through analytical prediction and takes a lessons-learned approach to design and modification of weir jetty bypassing systems. Results from recent physical model studies of spur jetties are also discussed with regard to their control on the nearshore current at coastal inlets and how spurs can be designed to alter sediment bypassing.

Influence of aeration on hydrophobic organic contaminant distribution and diffusive flux in estuarine sediments.

Dredging operations, resuspension events during storms, and bioturbation alter the oxic state of estuarine sediments and induce changes in the composition of dissolved and particle-associated natural organic matter. These changes may alter the distribution of hydrophobic organic chemicals (HOCs) in sediments and their diffusive flux across the sediment-water interface. In this study, the impact of aerating anoxic sediments on the distribution and diffusive flux of a model HOC, 2,2',4,4'-tetrachlorobiphenyl (TeCB), was investigated. Anoxic estuarine sediments collected from three sites along a salinity gradient were used to determine site-specific apparent sorption coefficients for porewater dissolved organic carbon (Kpwdoc) and sediment organic carbon (Koc) under anoxic and oxic conditions. A two-compartment sediment flux model was employed to examine the diffusive flux of TeCB under both oxic states. Aeration of anoxic porewaters resulted in significant decreases in porewater dissolved organic matter (DOMpw) aromaticity as indicated by declines in molar absorptivity at 254 nm (p < 0.005). Aeration also resulted in a 9-13% decrease in DOMpw concentration (p < 0.005) at the two sites exhibiting lower ionic strengths; the high ionic strength site did not exhibit a significant change in DOMpw concentration (p > 0.10). The impact of aeration on TeCB distribution and diffusive flux appeared to be site-specific. Aeration of anoxic sediments induced a significant 1.4 log unit reduction in Kpwdoc at the lowest ionic strength site (p < 0.0005), while sediments from the intermediate ionic strength site exhibited a significant 0.6 log unit increase (p < 0.005). No significant change in sorption to DOMpw was observed for the high ionic strength site (p > 0.10). The sediment displaying the drop in Kpwdoc also exhibited a significant 0.4 log unit drop in Koc (p < 0.01), while the other two sites did not exhibit significant aeration-induced changes in sorption to particle-associated organic matter (p > 0.10). No significant change in diffusive flux was observed for two sites (p > 0.10), while a significant 89-110 mg m(-2) yr(-1) increase in diffusive flux was observed at the low ionic strength site (p < 0.10). This latter result represented approximately a doubling in diffusive flux. In the systems studied, facilitation of TeCB transport across the sediment-water interface by organic colloids did not appear important.

Temporal-spatial trends in heavy metal contents in sediment-derived soils along the Sea Scheldt river (Belgium)

The aim of this study was to survey the alluvial plains of the Sea Scheldt river in Belgium for the presence of old sediment-derived soils, and to appraise the heavy metal contamination at these sites. Historically, sediments of periodical dredging operations have been disposed in the alluvial plain without concern for the potential presence of contaminants. Up to 96% of the areas that were affected by sediment disposal (ca. 120 ha) was found to be polluted by at least one of the metals Cd, Cr, Zn or Pb. Concentrations of Cd, Cr and Zn were, in 10% of the cases, higher than 14, 1400 and 2200 mg/kg DM, respectively. Based on the Flemish decree on soil sanitation, Cu and Ni concentrations were of less environmental concern on any site. The pollution in the Sea Scheldt alluvial plain nevertheless is lower than for the Upper Scheldt alluvial plain. The sediment-derived soils in the most upstream part near Ghent were used for disposal of sediments from dredging operations elsewhere. Metal concentrations were explored and both spatial and temporal trend were analysed. The pollution levels encountered warrant caution as most of the soils affected by historical dredged sediment disposal are currently in use for pasture.

Arthur Earland (1866–1958) and his links with Ireland

Abstract. INTRODUCTIONIn a recent paper, Robinson &amp;amp; Austin (2001) document the foraminiferal slide collection of Arthur Earland, and the correspondence between him and D’Arcy Wentworth Thompson, held at the University of St Andrews, Scotland. A number of slides are of material collected in Irish waters, and an interesting photograph is reproduced showing Earland standing on the Irish Fisheries cruiser Helga in the company of two men. This brief note examines Earland’s links with Ireland, discusses the provenance of some of Earland’s Irish material, confirms the date the photograph was taken, suggests who the photographer was, and provides biographical information on the two additional men portrayed in it – G. P. Farran and R. Southern.EARLAND IN IRELAND IN 1911Figure 1 (of Robinson &amp;amp; Austin, 2001) shows Earland, Farran and Southern on the deck of the cruiser Helga. This cruiser was used for a large number of research cruises carried out by the Irish Fisheries board between the early 1900 s and 1914. The photograph dates from the middle of August 1911 when the ship was used during the celebrated Clare Island Survey off the west coast of County Mayo, Ireland (Praeger, 1949). This ambitious project brought together over 200 European naturalists and experts (including Earland), in order to carry out a comprehensive survey of all aspects of the natural history in and around Clare Island (Collins, 1985). Southern directed the dredging operations from the Helga.Edward Heron-Allen and Arthur Earland were asked to work up the Foraminifera and arrived at . . .

Optimization of Mechanical Dredging Operations for Sediment Remediation

Sediment remediation involves restricted activities in the dredging process in order to minimize environmental risk. Operational constraints add significant capital cost to the overall project. This paper presents an example of the special conditions for a typical environmental dredging operation. REMSIM software, which simulates the sediment remediation processes, aids in planning for environmental dredging by reducing uncertainties in cost and performance estimations. The scow and bucket capacities, number of scows, and effective working time are parameters that improve productivity significantly as they are increased. The purpose of this paper is to help dredging contractors use their navigational dredging knowledge base to estimate costs, performance, and equipment selection for future environmental dredging projects where contaminant dispersion is a concern. REMSIM is used to obtain cost and productivity comparisons between environmental dredging and typical navigational dredging situations. Equipment and performance parameters can be adjusted in order to compensate for environmental dredging limitations while improving productivity and minimizing costs.

Surfis: a tool for designing and optimizing dredging schemes

Digital Terrain Models (DTM) can be useful tools for the design and evaluation of dredging operations. Nevertheless, DTM's based on linear interpolation of data from a rectangular grid do not provide confidence intervals for unsampled locations. SURFIS is a computer program to develop DTM's that include mapped random errors for complete study areas. Contrary to other geostatistical methods it can easily be applied by non-specialists. Application of SURFIS in the Biesbosch led to significant reduction in the amounts of material that needed to be dredged. We conclude that application of SURFIS may lead to more accurate dredging operations, resulting in lower costs for removal and storage of contaminated sediments.

SURFIS: A tool for designing and optimizing dredging schemes

Digital Terrain Models (DTM) can be useful tools for the design and evaluation of dredging operations. Nevertheless, DTM's based on linear interpolation of data from a rectangular grid do not provide confidence intervals for unsampled locations. SURFIS is a computer program to develop DTM's that include mapped random errors for complete study areas. Contrary to other geostatistical methods it can easily be applied by non-specialists. Application of SURFIS in the Biesbosch led to significant reduction in the amounts of material that needed to be dredged. We conclude that application of SURFIS may lead to more accurate dredging operations, resulting in lower costs for removal and storage of contaminated sediments.

The point load test for weak rock in dredging applications

The point load test is shown useful for weak/saturated rocks which are commonly encountered in mechanical dredging operation. To support the dredging use of the point load test, orginally intended to obtain a field strenth index for hard rock materials, a comparative, testing program was initiated, which included more than four hundred rock tests. The resulting data base system provides test a summary of test data and comparison calculations. The data base contains point load and unconfined compressive strength tests and some wet versus dry strength comparison tests. Applicability of the point load test was shown for the weak rock materials typical of many coastal deposits. A correlation with unconfined compressive strength was demonstrated for several dredge sites, and for a low-strength rock simulant. However, correlation factors were consistently much lower than the generalized, or target average, values cited in testing standards, which are consistent with results in hard rock tunneling and mining applications.

Management of marine construction works using ecological modelling

A system of bridges and tunnels between Denmark and Sweden is being constructed. The environmental management of the dredging and reclamation work includes planning using a mathematical model which can forecast the effect of different spill scenarios in order to minimize adverse effects on eelgrass beds. To develop the model, plots of eelgrass beds (4 m 2 ) were covered with nets excluding 30, 60 and 90% of the light. Shoot density, leaf and root/rhizome biomass, and soluble carbohydrates in roots and rhizomes were observed in order to determine the response of the plants to shading. In selected plots, all aboveground biomass was harvested to assess the re-growth potential. The minimum level of soluble carbohydrates necessary for securing re-growth was 60-90 mg g -1 . The inclusion of the subsediment parts of the eelgrass permits model runs beyond one growth season, and the prediction of re-growth after subsequent shading and winter dormancy. The model has been satisfyingly calibrated and validated. A feedback monitoring system has been developed based on field studies of eelgrass variables, a set of pre-fixed environmental criteria and forecasting of the effects of the construction works. The system facilitates planning and management of the dredging and reclamation operations, and mitigating actions during the progression of the work.

Determination of the performance of a dredge operating on water and soil-water mixture

1. The head, power, efficiency, and vacuum-gauge suction head during operation of floating suction dredges change depending on the depth of submergence of the suction pipe underwater and do not depend of soil size. 2. The output of dredges varies with underwater depth of the suction pipe. The greater the depth of submergence of the suction pipe, the more the output of the dredge decreases. 3. The performance curves of the soil pumps recorded during operation on water and soil-water mixture under test-bed (laboratory) and field conditions on soils of various sizes and density correspond to those calculated by formulas (8–11).

Sediment toxicity in Savannah Harbor

Savannah Harbor, located near the mouth of the Savannah River, Georgia and South Carolina, is impacted by industrial and municipal effluents. Potential release of contaminants stored in harbor sediments through dredging and shipping operations requires that contaminated areas be identified for proper management of the system and protection of wildlife resources. During 1991, Hyalella azteca were exposed in 10-d static-renewal toxicity tests to pore-water and solid-phase sediment samples collected from 26 sites within Savannah Harbor. Pore-water toxicity was more pronounced than that for solidphase sediment. Toxicity and reduced leaf consumption demonstrated impaired sediment quality at specific sites within Savannah Harbor and Back River. Factors responsible for the decreased sediment quality were ammonia, alkalinity, and metal concentrations (cadmium, chromium, lead, molybdenum, and nickel). Elevated concentrations of metals and toxicities in Back River sediments indicated impacts from adjacent dredge-spoil areas.

Predicting Water Quality during Dredging and Disposal of Contaminated Sediments from the Sitcum Waterway in Commencement Bay, Washington, USA

The Sitcum Waterway is a heavily trafficked industrial and commercial waterway located in the Port of Tacoma off Commencement Bay, Washington. Vessel traffic within the waterway, which is a cornerstone of Port of Tacoma operations, consists of large cargo ships and associated tug, barge, and service boat traffic. The waterway is about 3,000 feet long and about 700 feet wide. Large pier structures exist on both sides of the waterway. The waterway's bottom sediments have become contaminated with metals and organic compounds (primarily polycyclic aromatic hydrocarbons). The source of these contaminants is believed to be related to historical ore unloading activity and various industrial wastewater and stormwater outfalls. The Commencement Bay Nearshore/Tideflats (CB/NT) area is a Superfund site. Within the Superfund site, the Sitcum Waterway is considered one of several problem areas. The EPA has identified various options for sediment remedial action in their overall Record of Decision for the entire CB/NT Superfund site. The available options include dredging of contaminated sediment and subsequent confinement in either a capped aquatic, nearshore, or upland disposal facility. Ultimately, hydraulic dredging and confined nearshore disposal were selected as the preferred remedial option. As part of the technical support studies required for formal selection of a remedial option, we performed tests to predict water quality during dredging and disposal operations associated with nearshore filling of the contaminated sediment. Modified elutriate tests were performed on two composite sediment samples. Each sediment composite was used to perform triplicate elutriate tests. The test procedure employed was based on the modified elutriate test as described by the U.S. Army Corps of Engineers. Four metals (antimony, arsenic, lead, and zinc) were detected. Ammonia and cyanide also were detected. Receiving water composite results had similar concentrations as the seawater composite samples except for lower concentrations of cyanide, lead, and zinc. These results were used in the water quality computer models EFQUAL and PLUMES to aid in remedial design activities. EFQUAL computed dilution requirements using the total effluent discharge concentrations for two discharge locations; within the Sitcum Waterway and at the mouth of the Sitcum Waterway. The only chemical that required dilution, as determined by EFQUAL, was cyanide. Because the ambient concentration for total cyanide exceeds the marine water quality criteria, the receiving water quality standard was adjusted to 10, 20, and 30 percent above ambient concentration to evaluate the required dilution factors at each of these levels. PLUMES, developed to predict plume dilution from effluent discharge to marine and fresh water bodies, incorporated ambient water body characteristics, physical properties of the effluent, and the hydrodynamics of the outfall pipe or diffuser. PLUMES computed both volumetric dilutions and chemical concentrations as a function of distance from the diffuser port. EFQUAL was used in conjunction with PLUMES to predict the required dilution zone distances. Dilution zone distances for discharge at the mouth of Sitcum Waterway ranged from 330 to 130 feet and in the Sitcum Waterway from 27 to 4.3 feet. These results indicate dredging and nearshore confined disposal of Sitcum Waterway sediments can be accomplished without significant water quality impact.

Instruments for measuring the operating parameters of a dredge

1. Devices for measuring all dredge operating parameters were developed and tested. 2. The devices developed are distinguished by simplicity of design, accessibility for manufacture in workshops, their installation and adjustment can be performed by the dredge crew according to the available instruments. 3. The technical manuals can be sent by the authors by agreement with customers. For concluding an agreement, contact the article's coauthor N. N. Kozhevikov at the address: 105568, Moscow, Chechulin Street, house 22, apartment 22, telephone 308-80-96.