Environmental Reliability for Sustainable Dredging

Environmental Reliability for Sustainable Dredging

1. Introduction

Dredging is process of digging under water for purpose to maintain the depth in navigation channels. Dredging is required to develop and maintain navigation infrastructure, reclamation, maintenance of river flow, beach nourishment, and environmental remediation of contaminated sediments. Study on environmental impact of dredging is not new and recently there is concerned about balance between the need to dredge, economic viability, social technical approval and adequate environmental protection can be challenge. Various methods has been implemented for management of dredging activities, but choose in the best practice approach is also a bog challenge that require high level of understanding of the technical and economical aspects of the dredging process. input from ecological experts and dredging specialists. Community participation from port authorities, regulatory agencies, the dredging industry and non-governmental organisations such as environmentalists and private sector consultancies.

.2. The Need for and dredging requirement

Dredging is the excavation, lifting and transport of underwater sediments and soils for the construction and maintenance of ports and waterways, dikes and other infrastructures, for reclamation, maintenance of river flow, beach nourishment, to extract mineral resources, particularly sand and gravel, for use for example in the construction industry, and for the environmental remediation of contaminated sediments.

Globally, many hundreds of millions of cubic meters (m3) of sediments are dredged annually, with most of this volume being handled in coastal areas. A portion of this total represents capital dredging which involves the excavation of sediments to create ports, harbors, and navigable waterways. Maintenance dredging sustains sufficient water depths for safe navigation by periodic removal of sediment accumulated due to natural and human-induced sedimentation. Maintenance dredging may vary from an almost continuous activity throughout the year to an infrequent activity occurring only once every few years. Dredging activities offer social, economic and environmental benefits to the whole community. Hydrography chart and bathymetric map are used as guidance to vision of discrete bottom of water. Vigilant is requiring for the bottom as the, they are proned to sudden change leading to shoaling due to flood or drought. Survey of a navigation channel to locate dredging area done through drawing of isolines, or lines connecting points of equal depth, on the map so that captains and ships' pilots can get an idea of the "hills and valleys" underwater [1,3].

Dredge material:Dredging is necessary to maintain waterways channel. Nearly 400 million cubic yards of material is dredged each year. Consequently, about 400 million cubic yards of material must be placed in approved disposal sites or else used for another environmentally acceptable purpose. Sustainable disposal of dredge material is very imperative as it ends up saving a lot of money and maintains reliability and efficiency use of resources advantage of sustainable beneficial disposal are [2,3]:

Cost saving on money spent on finding and managing disposal sites.

It avoids habitat and ecological impacts that disposal may cause.

It saves capacity in existing disposal sites.

It can be a low-cost alternative to purchasing expensive fill for construction projects.

It can be used to enhance or restore habitat.

3. Environmental requirement of dredging project

The tendering of a dredging contract typically occurs after a full engineering design has been completed (i.e. after the planning and design phase). However, for other types of contracting mechanisms (e.g., design-build), the tendering of contract may occur early in the overall project process, thus requiring the Contractor to perform much of the evaluation and design work himself. Table 1 shows phases of dredging project and the risk control components.

The planning and design phase begins with defining overall functional requirements to meet the project objectives. This involves evaluating potential environmental impacts and any regulatory constraints, and concludes with preparing projects specifications. The planning and design phase is used to identify risk areas and risk control option in advance to help protect the environment during dredging, transport, and disposal activities and subsequent monitoring and possible remedial actions. Elements of project formulation include:

Functional Requirements

Conceptual Design

Regulatory Framework

Baseline Environment

Stakeholder Input

Potential impact Review the baseline condition as a consequence of construction and post-project activities.

Environmental Impact Assessment (EIA)

Risk control option

Prepare Final Project Design and Specifications

Afinal design addresses all major elements of the project: engineering design, environmental management, construction sequencing, and construction management. The specification's level of detail will depend on the type of contract, thecomplexity of the project, and the experience with dredging of both the project proponent and contractor(s). Additional environmental review may be required to establish that any residual risk, or actual impact, is acceptable Risk control option must be based on a clear definition of the project's technical and regulatory requirements. Studies conducted during the EIA or project planning, as well as information from regulators and stakeholders can contribute technical information for informed risk control option including [3,4] :

Sediment characterization (e.g., grain size distribution, level of contamination, etc.)

Bathymetric/topographic surveys with design profiles, which establishes the volume of sediment to be dredged;

An understanding of hydraulic/hydrodynamic/oceanographic conditions that may restrict operations;

The destination or final use of the dredged material, including placement options and locations;

The environmental functions and value of the area to be dredged, establishing environmental boundary conditions;

The environmental value of dredged material management areas (e.g., placement in confined or unconfined areas, or beneficial use options);

Existing site uses (e.g., navigation, recreational use, commercial fishing, quality of life impacts [air, noise, light]) to establish reasonable operational measures;

Legal conditions.

Environmental aspects related to future use and maintenance of the project's post construction condition should consider the areas of facility operations, future maintenance, long-term monitoring. During the construction phase, the contractor assumes primary responsibility for meeting the requirements of the project specifications, including meeting permit and contractual environmental conditions and implementation of risk control options. Major steps in the construction phase include:

Tendering and Contract Award

Contractor Defines Construction-Methods and Selects Equipment

Project Execution: Risk control option should based on best practice

Figure 2a shows example of post dredging impact in Kuala Terengganu

Figure 2a Post dredging impact in Kuala Terengganu

5.0 Environmental risk requirements of dredging project

Risk analysis in a dredging project, including taking into account adherence to the Precautionary Principle. It involves methods for assessing the significance of the likely impacts and essential environmental characteristics that require consideration during both the planning and implementation phases and the mechanisms whereby impacts can occur.

5.1 Qualitative based environmental impact assessment

Understanding the environments in which dredging and dredged material placement occur is a prerequisite of prudent decision making for environmental protection. A thorough knowledge of baseline conditions is needed so that a dredging project's environmental effects can be assessed properly and monitored against an agreed baseline. The baseline data must address natural variations, seasonal patterns and longer term trends to provide a context for determining whether a change is the result of dredging or not. As a minimum, characterization of the potentially affected environment should consist of recent surveys (performed within the last three years) and studies of the relevant environmental attributes.

For reliability the studies must be conducted by qualified scientific and engineering personnel using accepted methods. The boundary includes the physiographic, hydrologic, ecologic, social, and political boundaries of the project areas. In general, the following types of data are required for characterization of the dredging and placement sites, the transport corridor, and the areas around these sites, which could be indirectly affected, to adequately address the range of management options [5, 6]:

Bathymetric and adjacent topographic data;

Habitat and species distribution;

Resources such as fish populations, shellfish beds, oil and gas fields, aggregate mining and spawning grounds;

Physical and chemical nature of sediments;

Water quality;

Hydrodynamic data;

Cultural resources, including archaeological and anthropological conditions;

Human demography and land use characteristics;

Users of the environmental resources, such as commercial, recreational, and subsistence fisheries;

Navigation routes; and

Services in the project area, such as pipelines and cables.

In addition, it is necessary to take into account any cumulative impacts. Certain ongoing activities, such as fisheries and navigation, could have impacts that in combination with the proposed dredging result in more significant effects than would result from the project activities alone. This information is generally included in the impact assessment.

5.2 Between environmental risk assessment and environmental impact assessment

In practice, different approach is used to evaluate and "measure" the environmental impacts of a dredging project. ERA is defined as the examination of risks resulting from the technology that threaten ecosystems, animals and people (EEA, 1998). There are three main types of ERA: human health, ecological, and applied industrial risk assessment. The origin of ERA is the assessment of risks in the industry. Then, the same approach was applied in a broader scale for assessing the risks of the release of chemicals posed to human health. The more recently developed ecological risk assessment follows the same approach as human health ERA, but extending the assessed "end-points" to species other than human beings.

A conventional approach of an environmental risk assessment begins with the problem formulation and the identification of the hazard (or hazards). Then, the possible ways of release of the hazard are estimated, and the exposure of those chosen target species is assessed. The final steps are the consequence assessment and the estimation of the risk. Some of the steps require the use of models (e.g. the assessment of the release and the exposure), and the outcome is usually a quantitative assessment. It should be noted that many choices have to be done in the design of the risk assessment, and thus the definition and method used in each of them will be of importance to the final outcome [7].

The difference between ERA and EIA is that the later do not treat risks as probabilities. Generally the potential impacts are predicted, and assessed quantitatively or qualitatively. However, it also uses models requires for making many decisions in the design of the assessment, which could influence the final result. Any evaluation of the impacts of a certain project has to face difficulties and uncertainties, in part due to the scientific uncertainties involved, but in part due to the decisions to be made for framing and defining the problem. The impact assessment will have to specify the range of species to include and thus get entangled in nontrivial normative (ethical, ecological and economic) issues.

5.3 Risk based design and precautionary principle

n the context of dredging projects it can be stated that because of great natural variability there will often be a lack of full scientific certainty about the scales of potential impacts. In accordance with the Precautionary Principle decision to forego a project should be a last resort following exhaustive consideration of all reasonable RCO and reaching a conclusion that adequate environmental protection could not be achieved. Prohibiting dredging may ensure that no impacts occur, but may also generate high risk to human safety (e.g., lack of removal of shoals that pose navigation hazards) or result in lost commerce and harm to the economy. The RCO should be selected such that clear, defined, and ideally quantitative thresholds of protection can be achieved (e.g. to control measures of suspended sediment within a specified concentration / duration range). Work on environmental issue has always involved dispute because of impacts analysis. Global climate Change might be regarded as a primary example where this strong interlinkage between science and policy making is broadly acknowledged, Social science studies have shown how the production of scientific knowledge played a crucial part in the rise of climate change as a topic of worldwide interest and to the political arena while, on the other hand, knowledge and research on climate change issues is influenced by social factors

In most countries, the majority of dredged material is placed at sea. Land disposal options are normally much more expensive therefore, they are applied only when either transport costs to sea are inhibitory, or beneficial use is not an option, or the material is too contaminated (Burt et al., 1997a). In order to meet sustainability requirement the following describe 3 case studies where beneficial work in dredging are translated to cost [10,11].

On environmental sustainability According to US green port project, 2001, case study on Boston port navigation improvement project done in the US dredging and construction project use mitigation like Surface sediments contaminated with metals, PAHs, PCB, and other organics, Channels were over-dredged by 20 ft. Contaminated material was placed on barge and deposited into over-dredged in-channel disposal cells and covered with 3 ft. clean material, All clean material deposited in Mass Bay Disposal Site.

Another case done in port of los Angelis use copper treatment by developing onsite system to treat copper contaminated marine sediments, Pilot study dredged, treated, and disposed of 100 tons of contaminated sediment, Full-scale project cleaned up 21,000 cubic yards of contaminated sediment, Saved $1.5 million in cleanup costs over alternative.

Studies done in Europe also confirm use of processing plant for dredge material. Also regional sediment management program done by (USACE, 2003) compiled various methodologies to reduce shoaling.

5.4 Reliability and decision support framework

Various studies have been carried out to find the best hybrid supply for given areas. Results from specific studies cannot be easily applied to other situations due to area-specific resources and energy-use profiles and environmental differences. Energy supply system, with a large percentage of renewable resources varies with the size and type of area, climate, location, typical demand profiles, and available renewable resource. A decision support framework is required in order to aid the design of future renewable energy supply systems, effectively manage transitional periods, and encourages and advance state-of-the-art deployment as systems become more economically desirable. The DSS could involve the technical feasibility of possible renewable energy supply systems, economic and political issues.

Reliability based DSS can facilitate possible supply scenarios to be quickly and easily tried, to see how well the demands for electricity, heat and transport for any given area can be matched with the outputs of a wide variety of possible generation methods. This includes the generation of electricity from intermittent hybrid sources. DSS framework provide the appropriate type and sizing of spinning reserve, fuel production and energy storage to be ascertained, and support the analysis of supplies and demands for an area of any type and geographical location, to allow potential renewable energy provision on the small to medium scale to be analyzed. DSS can provide energy provision for port and help guide the transition towards higher percentage sustainable energy provision in larger areas. The hybrid configuration of how the total energy needs of an area may be met in a sustainable manner, the problems and benefits associated with these, and the ways in which they may be used together to form reliable and efficient energy supply systems. The applicability and relevance of the decision support framework are shown through the use of a can simulate case study of the complex nature of sustainable energy supply system design.

5.5 Regulatory requirement and assessment

The current legal requirements have been developed based on reactive approach which leads to system failure. Reactive approach is not suitable for introduction of new technology of modern power generation systems. This call for alternative philosophy to the assessment of new power generation technologies together with associated equipment and systems from safety and reliability considerations, such system required analysis of system capability and regulatory capability. System based approaches for regulatory assessment is detailed under goal based design as shown in figure.

IMO has embraced the use of goal based standards for ship construction and this process can be equally well applied to machinery power plants.

Legal framework for dredging

The most important international agreements regarding dredging are the London Convention 10, issued in 1972 and reviewed in the 1996 Protocol 11; and the OSPAR Convention 12 from 1992. IMO also unveil Formal safety assessment for marine system. These international agreements establish frameworks within which the contracting countries are obliged to operate with respect to their handling of materials destined for placement in the sea. However, these Conventions do not include regulations of the dredging operations per se, which are mainly established at the national level, nor for the conditions of disposal of in land. Convention for the prevention of marine pollution by dumping of wastes and other matter (www.londonconvention.org).

A review of the Convention began in 1993 and was completed in 1996 with the acceptance of The 1996 Protocol to the London Convention. The 1996 Protocol has not yet come into force as it has not yet been ratified by a sufficient number of countries (19 out of 26). Conventions for the Protection of the Marine Environment of the North-East Atlantic (www.ospar.org).On the other hand, dredging activities are subject to national regulations, which can vary very much among the countries. In some cases there is a specific directive regarding dredging in Malaysia the royal Malaysia navy regulate the dredging. Thus the are other agencies but there is not integration for effectiveness of the system.(personal communication .

5.2 Quantitative and formal system engineering based risk analysis

"Risk" is generally understood as an expression of the quantified link between an environmental hazard or "stressor" and the potential negative consequences it may have on targets or "receptors". When discussing risk the types of stressors as well as the targets of interest must be specified. Thus project risk can be distinguished from engineering risk, and environmental risk. But, in practice it may be very difficult to establish a quantifiable relationship between hazard and target response because of the many uncertainties in the cause-effect chain and the dynamic nature of aquatic ecosystems. Risk analysis provides a means to accommodate these uncertainties. Formal risk assessment procedures have not been adopted by many regulatory agencies or they have been applied mainly to dredging of contaminated sediments. Typically risk assessment takes the form of "professional judgment" based on the experience and expertise of parties engaged in project co-ordination [12].

Risk analysis provides an opportunity to focus on the real concerns of a project, instead of relying on fixed and inflexible standards such as threshold levels for contaminants or fixed percentages of allowable overflow of a dredger. For the purpose of this report, risk assessment is mainly captured in the EIA, whereas risk management takes the form of best management practice determination. Risk evaluation is the path from the scientific system based quantitative risk analysis is the internationally recognized best practice and modest concept of risk analysis. Table shows components of risk analysis.

The design concept needs to address the marine environment in terms of those imposed on the power plant and those that are internally controlled. It is also necessary to address the effects of fire, flooding, equipment failure and the capability of personnel required to operate the system. In carrying out a hazard assessment it is vital that there are clearly defined objectives in terms of what is to be demonstrated. The assessment should address the consequence of a hazard and possible effect on the system, its subsystems, personnel and the environment. An assessment for reliability and availability of a hybrid power generation system and its installation in a ship could use a FMEA tool. An effective FMEA needs a structured approach with clearly defined objectives

The assessment analysis processes for safety and reliability need to identify defined objectives under system functionality and capability matching. These two issues are concerned with system performance rather than compliance with a prescriptive requirement in a standard. The importance of performance and integration of systems that are related to safety and reliability is now recognized and the assessment tools now available offer such means. Formal Safety Assessment (FSA) is recognized by the IMO as being an important part of a process for developing requirements for marine regulations. IMO has approved Guidelines for Formal Safety Assessment (FSA) for use in the IMO rule-making process (MSC/Circ.1023/MEPC/ Circ.392). Further reliability and optimization can be done by using stochastic and simulation tools [8, 13].

5.4 Uncertainties and risk in dredging projects

The physical and biological characteristics of aquatic environments vary both spatially and temporally. Therefore characterizing these environments and assessing impacts and risk will always involve some uncertainty. This requires the need for basic understanding of how marine and the ecosystems function and how natural events and anthropogenic activities affect these functions. In the ideal situation, all environmental risks associated with a dredging project would be quantifiable, making the need for specific management practices clear. In reality, dredging can potentially affect diverse assemblages of organisms or their habitats on both spatial and temporal scales. Because the scales of the interactions between organisms and the dredging process are difficult to determine, often the consequences of a project are largely speculative. Some degree of uncertainty will therefore always be present indecisions regarding the need for special management practices to protect the environment.

5.4.1 Potential Physical Changes and Environmental Impacts from Dredging and Disposal of Dredged Material

Below water, the sound from the dredge vessel could have environmental effects such as interfering with fish behavior, possibly leading to disturbed migratory routes, although fish might easily avoid temporarily disturbed areas without consequence. Other potential environmental effects not directly related to dredging but associated with the presence of the dredger include spills of oil and fuel, exhaust emissions, and the possible introduction of invasive species via the release of ballast water.One of the less understood areas of concern is the impact of sediment released into the aquatic environment that may occur at any of the stages from excavation to placement. A high concentration of sand in suspension will have very low turbidity while a relatively low concentration of fine silt or clay in suspension will have a high turbidity. ALlso sediment effect on the flora and fauna, concentration, the turbidity, the total amount of loss of sediments or the spatial distribution of a sediment plume are other impacts.

5.4.2 Spatial and Temporal Scales of Effects: The environmental effects vary spatially and temporally from project to project. When the effects are considered to have a significant adverse impact it is necessary to investigate means to reduce or mitigate them. The significance of the environmental effects depends on site-specific factors that govern the vulnerability and sensitivity of environmental resources in the project area. When the sediment being moved is chemically contaminated, the need for environmental protection is generally recognized by all stakeholders.

Complexity with respect to uncertainty has made necessity for several efforts to find tools for the assessment and management of different types of uncertainty. As mentioned before, the word uncertainty is used in many different situations for expressing a lack of certain, clear knowledge for taking a decision. Uncertainty is any departure from the unachievable ideal of complete determinism. In the case presented here, uncertainty signifies that is not possible to provide a unique, undisputable, objective assessment of a certain action (for example an environmental risk assessment of the dredging). However, depending on the actor (e.g. the modeller, the policy-maker, or stakeholders), the perception of the nature, kind, object and meaning of uncertainty can be very different. This will be clear when presenting the perception of uncertainty of the stakeholders involved in the case. Nevertheless, the simple definition presented above gets more complicated when trying to describe the sources, or the sorts or dimensions of uncertainty.

Typology approaches adopted for characterization and assessment of uncertainty by this group focus on uncertainties encountered from the point of view of the modeler that assesses policy-makers (which they call model based decision support). Therefore, their proposal aims to be useful for expressing the uncertainty involved in the use of models, perhaps rather than expressing uncertainty from the point of view of the policy-makers or stakeholders. The typology is based in the distinction of three dimensions of uncertainty:

i the location of uncertainty (where within the model);

ii the level of uncertainty (from deterministic knowledge to total ignorance); and,

iii the nature of uncertainty (whether the uncertainty is due to the imperfection of our knowledge or is due to the inherent variability of the phenomena being described).

5.5 Risk communication and management

Parties involved in a dredging project view the process differently depending on their individual perceptions of these risks and rewards, as well as their individual tolerance of the perceived risk. In this sense there may be several types of risk in a project. For the proponent the consequences of failure of the whole project may be very severe and will usually be measured in economical terms. For an environmentalist the potential effects on the environment may be recognized as the highest priority risk. Communication is an essential component of sharing concerns and identifying means to mitigate them to the fullest extent reasonably possible. During the risk analysis, it is important to balance the identified environmental effects and risks against the economic and social consequences of the project. Complete and transparent communications are therefore essential throughout the process from beginning to end. This refers to all parties involved. Communication should address uncertainties and natural variability in the environment. Seldom does an actual project present a clear choice between unbiased, neutral, and generally accepted options. Rather, the choice among options is frequently driven by values and perceptions. This tension can best be reduced through open lines of communication that include:

A transparent process;

Outreach that begins during the earliest possible stage of the project and continues throughout all phases;

An open and honest process; and

Proactive engagement of local and/or regional media, because their influence on public opinion can be large.

5.6 Selecting evaluation and risk control option for dredging project

Action might be taken to adjust the monitoring program itself or as a direct response to the monitoring results. Based on the monitoring data, adjustments to the monitoring program could include:

Reducing the level of monitoring because no effect was observed;

Continuing with the existing monitoring program to gain further clarification of the response; or

Expanding the monitoring program to include additional parameters or sites.

So that responding can be quick and effective, it is necessary to establish hierarchy of options to adverse monitoring results. The level of response can be targeted to the receptor and its sensitivity. Options could include:

Continuing with dredging under the existing regime;

Modifying the dredging regime to reduce the actual effect on a sensitive parameter;

Ceasing dredging within an area until further information is gathered;

Ceasing dredging within an area altogether; or

Ceasing dredging and implementing recovery measures.

For a monitoring program to be fully effective, it must include a timely communication of results and related actions. Stakeholders should be involved to help build overall program credibility.

Risk control options are meant to improve the environmental performance of a dredging project. Some form of environmental evaluation or Environmental Impact Assessment (EIA) is normally required by international conventions. One example is the London Convention, which establishes a framework for the evaluation of placement of dredged material at sea. The "Specific Guidelines for Assessment of Dredged Material" (International Maritime Organization, 2000) comprises the following steps:

Dredged material characterization;

Waste prevention audit and evaluation of disposal options;

Is the material acceptable for marine placement?;

Identify and characterize the placement site;

Determine potential impacts and prepare impact hypothesis(ies);

Issue permit;

Implement project and monitor compliance; and

Field monitoring and assessment.

Within the LC-DMAF guidance it is stated that

All dredging and placement projects will cause some changes to the environment. It is therefore necessary to determine whether these can be considered serious and or irreversible. Because adequate information is rarely available to answer these questions with absolute certainty, an evaluation of the relative risk of permanent detriment to the environment is required. Many factors affect this assessment of the general environmental risk including the scale of the project, the natural variability of all of the elements of the system likely to be affected, possible contamination levels, and the timing of the project. Preparation of an EIA involves collaboration among environmental scientists and engineers in consultation with port authorities, dredging companies, and often a diverse assemblage of stakeholders. The amount of technical information available will be important, but should be used in tandem with the perceptions and knowledge held by the engaged stakeholders. Risk evaluation is a value judgment reached by consideration of the total body of evidence offered by all interested parties.

These constrains are very important to bear in mind when we think of environmental management at the local or regional level with projects with are used limited time and budget of money. Therefore the lack of knowledge that can be experienced by both managers and citizens in assessing a concrete project may have more to do with limited resources than general scientific ignorance. Benefit-Cost Analysis (BCA) is a tool for organizing information on the relative value of alternative public investments like environmental restoration projects. When the value of all significant benefits and costs can be expressed in monetary terms, the net value (benefits minus costs) of the alternatives under consideration can be computed and used to identify the alternative that yields the greatest increase in public welfare. However, since environmental goods and services are not commonly bought or sold in the marketplace, it can be difficult to express the outputs of an environmental restoration project in monetary terms.

Risk monitoring

It is acknowledged that monitoring can take many forms and fulfill various objectives before, during, and after any dredging and placement project. This document does not provide an exhaustive description of monitoring technology but rather focuses on the role of monitoring as a necessary element in the context of BMP application. In particular, monitoring can be proposed as a management practice in itself or used to assess the effect of other management practices. Monitoring is the first step-in determining whether corrective actions will be necessary to ensure the required outcomes [13,14].

One of the key issues related to any environmental monitoring program is the scope for combining broad monitoring objectives for separate parameters into a single survey. Monitoring programmes can be categorized into three types:

Surveillance monitoring

Feedback monitoring

Compliance monitoring

Formulating a suitable monitoring strategy requires the following elements:

Targeted objective

Beeline condition

Monitoring criteria

Methodology for measuring change

Threshold values

Timely review procedure

Requirements for monitoring are site-specific and based on the findings of the baseline surveys. For example, surveys could be necessary to record:

The abundance and distribution of species, which is needed to determine

the rate of species and community recovery within the study area;

The effect of dredging on seabed morphology;

The effect of dredging on the concentration of suspended sediments in the water column;

The type of substrate remaining following dredging;

Use of the area by fish; and

Actual effects on any sensitive species or communities within the study area.

Sometimes, model studies can be used to determine the appropriate locations for monitoring. Monitoring involves many uncertainties and difficulties that need to be considered. Models are generally not well validated or calibrated and so it is not easy to quantify the results with certainty though they are continually improving. After the monitoring criteria have been selected, the methodology for measuring change against those criteria needs to be determined.

The monitoring could be in the water column, on the seabed, on land or in the air. It could be physical, chemical, or biological or a combination. Key considerations in establishing the monitoring methodology are summarized below:

The methodology used to monitor environmental effects should be the same as that used to determine the characteristics of the relevant parameter during the baseline survey, to ensure comparability.

The sampling stations should be the same, although there are likely to be fewer stations (e.g., the feature of interest may require a more targeted approach than was adopted for the baseline survey).

For parameters where timing is critical (e.g., benthic and fish sampling), repeat surveys should be undertaken at the same time of year as the baseline survey to ensure that seasonal changes in abundance and distribution do not affect the results.

The frequency of sampling is determined based on the monitoring objectives and criteria. The expected impact is also a factor to consider when determining frequency of sampling. For some parameters (e.g., impacts on geology), changes occur over a long time scale and therefore require less frequent monitoring, possibly post project.

It is important to identify a level above or below which an effect is considered unacceptable, referred to as an environmental threshold. If the monitoring shows that the threshold level is close to being reached then remedial action is required to reduce the level of effect. In the absence of a threshold value, monitoring of many parameters is justified to improve the knowledge base of the particular effect. Timely review of monitoring results is essential to ensure the success of the program. It is recommended that the results of monitoring should be reviewed at times that will allow for meaningful adjustments to the dredging and placement activities.

Conclusions

Dredging provides economic and social benefits for the whole community. However dredging can and often will have an impact on the environment outside of the desired change, of say deepening a channel. To assess the significance of these effects an environmental impact study often needs to be undertaken. During such a study, cumulative and in-combination effects should be considered as it is important to place the dredging activity into context with other activities, e.g., fisheries, navigation, etc. Previous regulatory work for system design has been prescriptive by nature. Performance based standards that make use of alternative methods of assessment for safety and reliability of component design, manufacture and testing is recommended for hybrid alternative energy system installation.

System failure and carefree of environment in past project poised all field of human endeavor to adopt precautionary principle by providing tools to conduct dredging projects in an environmentally sound manner and design based on comprehensive system based scientific method discussed in this paper. Properly applied the precautionary principle provides incentives to develop better solutions. The paper present structured approach and strives for an objective means of selecting the most appropriate Risk control option for that lead to the best protection of the environment and meet sustainable development requirement. Absolute Reliability of the dredge work can be realize by using predictive statistical tools and the data collected.

Reference

[1] Erftemeijer PLA and Lewis III RRL (2006): Environmental impacts of dredging on seagrasses: A review. Marine Pollution Bulletin 52, pp. 1553-1512

[2] Herbich JB (2000): Handbook of Dredging Engineering, 2nd Edition. McGraw-Hill Professional, 992 pages

[3] International Maritime Organization (IMO) 2000): Specific guidelines for assessment of dredged material

[4] John SA, Challinor SL, Simpson M, BurtTN and Spearman J (2000). Scoping the assessment of sediment plumes from dredging. CIRIA Report C547, London,190 pages

[5] Keevin TM, (1998): A review of Natural Resource Agency Recommendations for Mitigating the Impacts of Underwater Blasting. Reviews in Fishery Science, pp. 281-313

[6] New Delta Project (2007): Final report of Theme 6 Sustainable Dredging Strategies'. Framework for a sustainable dredging strategy. 2007, 48 pages www.newDelta.org

[7] OSPAR (2007): Draft literature review on the impacts of dredged sediment disposal at sea. Document Nr. EIHA 07/2/2-E

[8] International Maritime Organization (IMO). Amendments to the Guidelines for Formal Safety Assessment (FSA) for Use in the IMO Rule Making Process. MSC MEPC.2/Circ 5 (MSC/Circ.1023 MEPC/Cir. 2006 [9] PIANC (2006): Working Group Envicom 10: Environmental risk assessment of dredging and disposal operations.

10] PIANC (2008): Working Group Envicom14: Dredged material as a resource options and constraints

[11] PIANC Working Group Envicom 16:Dredging and port construction around Coral Reefs t.b.p.

12] Rees HL, Murray LA, Waldock R, BolamSG, Limpenny DS and Mason CE (2002): Dredged material from port developments: A case study of options for effective environmental management.

[13] EPA (2001): Guidelines for dredging. Best practice environmental management. Environment Protection Authority, Victoria, Australia. Publication 691. 116pages.

[14] PIANC (1998) Working Group PTC I-17: Handling and treatment of contaminated dredged material from ports and inland waterways "CDM"

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