PIANC report #100

Dredging Management Practices for the Environment

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Axel Netzband (Chairman of WG 13)

Working Group PIANC Envicom 13

Best Management Practices Applied to Dredging and Dredged Material Disposal Projects for the Protection of the Environment

PIANC Report 100

Dredging Management Practices for the Environment – A structured selection approach

Navigating the Environment –Managing Risks and Sustaining BenefitsNew Orleans, October 28, 2009

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Starting point

• A wide variety of environmental management practices exists with the intention of reducing or eliminating perceived environmental risks.

• Restrictions and constraints may have significant logistical, execution schedule and cost implications.

• Balance the benefits of constructing and maintaining navigation infrastructure in a cost efficient manner and the recognised need to care for the environment.

• Make knowledgeable choices among existing BMPs, and identify promising alternatives to routinely applied practices.

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Definition of Management Practice

“A Management Practice is a practice intended to improve the environmental performance of a dredging project, inclusive of excavation, transport, and placement of dredged material.”

PIANC Envicom 13

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Description of Management PracticesE 18 Modify available equipment

Title Apply Green valve or Environmental Valve Description By using Green valve (or environmental valve) in overflow, air entrainment can be reduced, concentrating overflow-outflow, reducing

susceptibility for dispersal of fines. This results in decreased turbidity as the overflow material is transported vertically down more rapidly due to density effects.

Applicability Fits on most modern TSHD.

Can also be installed on barges, when being hydraulically loaded.

Limitations Most effective when relatively large portion of fines in dredged mixture.

Modern equipment required. Not all TSHD can be equipped with green valve systems.

Involves more complicated process control.

Not to be used where agitation losses are desirable part of the process.

Advantages Concentrated overflow reduces extent and content of turbidity plume.

Disadvantages Slightly reduced loading capacity might marginally extend project duration.

Some cost increase.

Predictability Yes by modelling.

Plume development might be predicted. Biological consequences are often not very clear, only qualitative assessment possible.

Monitoring Yes

Examples References

M. van Parys et al. ”Environmental Monitoring of the dredging and relocation operations in the coastal harbours in Belgium: MOBAG 2000”, WODCON XVI, Kuala Lumpur, Malaysia, May 2001

G.H.van Raalte ” The effect of an ‘environmental’ or so called ‘green’ valve on the behaviour of turbidity plumes”, Boskalis, June 2005

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Environmental Windows (U.S.)

A temporal constraint placed upon a dredging or dredged material disposal operation to protect biological resources or habitat. The window is the period during which dredging may occur. A seasonal restriction represents the period during which the operation is prohibited.

… are a temporary moratorium on dredging, which equates to zero tolerance of risk… are institutionalized by default… have no predetermined performance standards

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The Precautionary Principle

“Where there are threats of serious or irreversible damage, lack of full scientific certainty shall not be used as a reason for postponing cost-effective measures to prevent environmental degradation”.

Principle 15 of the UN Rio Declaration on Environment and Development (1992)

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Is dredging clean sediment a risky business?

• With the exception of responses to exposure to contaminated sediments, many other forms of impact remain hypothetical and exceedingly few have been shown to be biologically meaningful at the population level

• Proving the negative (no impact) is essentially impossible

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Turbidity, Nature, and Human Activities

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Dredging impacts

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EU Communications

“Where there is scientific uncertainty, implement evaluation procedures and take appropriate preventive action in order to avoid damage to human health or to the environment.”

Renewed Sustainable Development Strategy, European Council (2006)

“The precautionary principle should be considered within a structured approach to the analysis of risk which comprises three elements: risk assessment, risk management, risk communication. The precautionary principle is particularly relevant to the management of risk.”

EU Communication on the precautionary principle (2000)

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Identification of Environmental Effects

Physical Change

Potential Environmental Effect• Release of particulate matter• Reduced light penetration• Release of nutrients • Release of toxic chemicals• Release of organic matter• User conflicts

• Dredging equipment presence• Removal of sediment• Placement of sediment• Altered topography/ bathymetry• Sedimentation induced by dredging• Sedimentation induced by disposal• Re-suspension of sediment matrix into water column• Rock blasting

• Re-suspension of sediment matrix into water column

Examples of impactBehavioural / physiological responses to increased suspended solids

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From Effects to Management Practices

Physical Change

• Release of particulate matter

• Re-suspension of sediment matrix into water column

Number Management Practice

M1 Select appropriate contracting approach and contract format

M2 Select the contractor based on best value or use pre-qualification to limit the bidders to qualified bidders.

M3 Use performance specifications (instead of method specifications) to allow operator flexibility

M4 Prepare project and site specific environmental and construction monitoring program.

M5 Use Adaptive Management approach during construction

P1 Reduce Dredging Requirements (i.e., horizontal and vertical extents)

P2 Optimise / increase dredging design for environmental benefit.

P3 Make changes to physical system to reduce sedimentation into project area

P4 Reduce or eliminate the need to dredge through using natural recovery and capping/cover options

P5 Sustainable placement of dredged material within the same sediment system

P6 Use of dredged material

P7 Optimise the design, location and configuration of the aquatic placement site

P8 Select appropriate placement option.

P9 Use clean dredged material for caps /covers over unsuitable sediment

P10 Habitat and species protection measures: impact minimisation

P11 Habitat enhancement options: enhance habitat development

E1 Use appropriate type and size of dredging equipment for the project.

E2 Select most appropriate type and size of mechanical dredger

E3 Select most appropriate type and size of bucket- ladder dredger.

E4 Select most appropriate type and size of hydraulic dredger

E5 Select most appropriate type and capacity of dredged material transportation method

E6 Select most appropriate type and size of haul / transport barge

E7 Select most appropriate type and size of barge offloading equipment

E8 Select most appropriate type of hydraulic pipeline

E9 Use special environmental equipment

E10 Use hydrodynamic dredging

E13 Modify existing equipment, if necessary, to make it (more) fit for purpose.

E14 Apply degassing systems to hydraulic dredging system

E18 Apply Green valve or Environmental Valve

E19 Filter overflow effluent from transport barges to improve the water quality into receiving waters.

E20 Inspect and maintain equipment in good working condition

I1 Tidal operations: flood/ebb and spring/ neap

I2 River Discharge dependent operations

I3 Time based operations: days / weeks/ day-night / weekdays-weekends.

I4 Seasonal restricted operations (Environmental Windows).

I5 Wind direction related operations.

I6 No access / No activity areas

I7 No bed contact zones

I8 No effect zones / Impact avoidance zones.

I9 Buffer zones

Dr1 Modify rate of operations

Dr2 Modify rate of excavation of mechanical dredgers.

Dr3 Modify mode of excavation for mechanical dredgers.

Dr4 Modify rate of excavation for hydraulic dredgers.

Dr5 Modify mode of excavation for hydraulic dredgers.

Dr6 Modify mode and speed of ‘mechanical’ transportation (e.g., barges)

Dr7 Bed-levelling or ploughing to reduce over-dredging, in combination with other dredgers

Dr8 Reduce or eliminate overflow during hydraulic loading at hoppers or transport barges

Dr9 Reduce or eliminate use of ‘lean mixture overboard’ pumping.

Dr10 No barge overfilling, when loading by mechanical dredgers

Dr11 Re-circulate process water from hopper or barge during loading.

Dr12 Rinse grab / bucket of mechanical excavator before lowering in water

Dr13 Use spill plate/apron during offloading

Pl1 Apply optimal sediment deposition method

Pl2 Hopper/ barge bottom door placement

Pl3 Rainbowing / sidecasting / spraying

Pl4 Direct hydraulic pipeline placement

Pl5 Use of baffle plates in pipeline outflow

Pl6 Use of tremie pipe

Pl7 Use of diffuser

Pl8 Use of Spreader

Pl9 Optimise rate/ concentration of mixture.

Pl10 Re-circulate hydraulic transport water from placement site back to hydraulic dredger

Pl11 Return placement site effluent to dredging site

Pl12 Optimize layout of storage basin.

Pl13 Optimise dimensions and location of overflow weir (i.e. waterbox)

Pl14 Optimise location of inflow point (i.e. hydraulic discharge end)

Pl15 Add a separate siltation pond to the disposal site

Pl16 Use additives / flocculants

C4 Use silt curtains to reduce loss of sediment from dredging operations.

C5 Use sheet pile walls to contain suspended sediments within enclosed area

C6 Use bubble curtain to limit spread of re-suspended sediments

C7 Dredger within enclosed compartment (e.g., caissons) to limit spread of re-suspended sediments.

C14 Use fish or marine mammal guiding systems.

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BMP selection process

Project Description and Conceptual Design

EnvironmentalCharacterisation

Final Project Design

Project Construction

Monitoring

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Assessment of Impact and Risk

Risk acceptable?

MP Selection

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BMP Evaluation Matrix

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Definition of Best Management Practice

“A practice, or combination of practices, that is determined after problem assessment, examination of alternative practices, and appropriate stakeholder participation to be an effective, practicable (including technological, economic, social and institutional considerations) means of preventing, or reducing the potential environmental impacts associated with dredging related operations.”

PIANC Envicom 13

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Recommendations

• Each dredging project has to be assessed on its own.• A comprehensive description of the project and an

exhaustive examination of the environment may be necessary.

• Consider all management practices on an equal basis. • Do not institutionalize management practices, but invest

in the development of new and better alternatives.

• Be open. Communication at all stages is essential. It is no guarantee for success, but it’s prerequsite.

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Active Working Group membersConsultants:Christine Adnitt - UK Haskoning LtdStefan Bolam – UK CEFASCaroline Fletcher – UK HR Wallingford LTDPhilip Spadaro – USA Blasland, Bouck & Lee, Inc.Thomas S. Wang – USA Anchor Environmental, LLC

Research:Raul Castro – Spain AZTI Fisheries & Food Technological InstitutePeter Whitehead – UK ABP Marine Environmental Research Ltd

Contractors:Wouter Dirks – Netherlands Van Oord DredgingGerard van Raalte – Netherlands Hydronamics = Boskalis Dredging Makoto Fujino – Japan TOA CorporationFrederik Mink - Belgium EuDA

Authorities:Koenraad Mergaert – Belgium Ministry of the Flemish CommunityDouglas Clarke – USA U.S. Army Engineer Research and Development CenterAndré van Hassent – Netherlands Port of RotterdamAxel Netzband - Germany Hamburg Port Authority