sustainable sediment management and dredging seminar … · sustainable sediment management and...

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SUSTAINABLE SEDIMENT MANAGEMENT AND DREDGING SEMINAR6-8 MARCH 2019SAUSALITO, CA

Environmental Work Windows as a Management PracticeBurton Suedel

US Army Corps of Engineers • Engineer Research and Development Center

Sustainable Sediment Management and Dredging Seminar

6-8 March 2019 Sausalito, CAUNCLASSIFIED // FOR OFFICIAL USE ONLY

Chemical• Metals, PAHs, etc.

Biological• Harmful Algal Blooms

Physical• Turbidity

Environmental Stressors

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What is an Environmental Window (EW)?

EWs are time periods within which dredging is allowed Typically established using a biological metric (e.g. fish migration,

egg laying, larval development, etc.) Setting of EWs is controversial Data Gap: Lack of effects-based exposure data for suspended

sediments on species used to set EW EWs are the most frequently cited concern in the dredging program EWs impact dredging schedules and are costly

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Effects of Suspended Sediments and Sedimentation

On SAV

On FishMigration

On corals

On Fish Spawning

On T&E Species




Dredge Plume Spatial/Temporal ScalesInitial

Mixing Zone Near-Field Far-Field

sec

100s of meters 1,000s of meters

FLOW“Trace” Plume

Dredge

Time

Distance from dredge

minutes hoursmeters




Other Sources of Resuspension

Tug Plume

Plume Generated

by Bow Thruster




Applying Risk Assessment Paradigm to Manage Risk

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Exposure Assessment

Measuresof Effect

ProblemFormulation

RiskCharacterization

RiskManagement

Economic Analysis,Socio-Political,

Engineering Feasibility

Risk Assessment Paradigm




Apra Harbor Case StudyProblem Formulation

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Identify receptors (coral) Identify/map coral density/diversity Identify sources of exposure

• Dredging as source of released sediment• Background suspended solids are near zero

and there are no outfalls or other land-based sediment sources to Apra Harbor

Identify exposure mechanisms• Total sedimentation from dredging project• Maximum sedimentation rate over any 24 hour

period• Light attenuation (represented by suspended

solids time history)




Quantifying Exposure

• Quantify exposure from each risk pathway for each species in areas of concern

• Characterize risks to coral in Apra Harbor from 18 month dredging operation

• Quantify exposure:• Simulate sediment transport

and sedimentation over coral habitat – 100 scenarios modeled to bracket potential exposure

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Peak 24-hr TSS over coral

Total sedimentation for dredge cycle




Combining Exposure and Effects to Characterize Risk

1. Estimate effects via literature review of risk to coral from sediment

2. Green/Yellow/Red light indicator created for coral species using exposure and effects estimates Green – minimal damage Yellow – some damage,

recovery expected Red – Significant die-off

3. Exposure thresholds mapped from sediment transport and sedimentation model

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3) Estimated coral effects for one scenario

2) Coral thresholds identified

1) Coral thresholds evaluated from literature




Fish Larvae and Egg Exposure System (FLEES)

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FISH LARVAE AND EGG EXPOSURE SYSTEM (FLEES)Developed to expose early life history stages of fish, shellfish, and other species to specified concentrations

and durations of suspended sediment or sedimentation in a controlled laboratory environment.

SUSPENDED SEDIMENTCapability

01FLEES allows for the design of experiments that simulate resuspension of sediment as a result of dredging operations or other factors such as vessel traffic, freshets, or storms.

SEDIMENTATIONCapability

02FLEES can be quickly retrofitted to accommodate the design of experiments that simulate sedimentation.




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AND

SUSPENDED SEDIMENT WORST CASE SCENARIO

WHY FLEES WORKS

A data acquisition device and LabVIEW software is used to integrate turbidity sensors with solenoid valves to build a computer application that both continuously monitors and records turbidity in each aquarium while introducing sediment from the slurry tank to maintain specific NTUs.

Individuals contained for a prolonged periods, with no escape from exposure to field-collected sediment of varying concentrations.




EW Case study: Corals in Honolulu Harbor, HI

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Problem Concerns about suspended sediment and

sedimentation effects on corals are restricting dredging operations Exposure and effects-based data needed to

characterize and manage riskObjective Essayons dredging in HH to estimate exposure Investigate performance of corals exposed to

varying suspended sediment concentrations using FLEES Coordinate with HI coral experts




Methods

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Effects Study• Exposure parameters - monitoring• Exposure regime to mimic dredging

operation• Concentrations (NTU & TSS)• Coral species/type and life stages• Short- and long-term effects• Endpoints (lethal and sublethal)• Source of corals• Source of test water and sediment• NMFS coordination




Results indicate that detailed, site-specific knowledge of the dredge project, sediment type, and species life history can inform risk-based decision making regarding dredging effects on sensitive habitats

Exposure and effects-based data can reduce uncertainty in assessing risk associated with perturbations due to dredging

Combination of exposure and effects data can be effectively used to assess risk to species occupying sensitive habitats

Structured science-based approach can effectively assess risk to sensitive habitats for appropriately managing risk to these species

Summary

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Environmental Windows Case Studies

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The window applicable to Oakland Harbor dredging in the programmatic LTMS Biological Opinion is based on presence of salmonids, but given that the harbor is not connected to any tributaries and where it is situated in the Bay, it is reasonable to assume that salmon are not likely present SPN could consider pursuing a standalone Biological Opinion for

Oakland harbor to seek a dredging window that is less restrictive POC: Stephen Willis

Dredging Window Case Study #1 (SPN)

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Under current programmatic LTMS EFH consultation eelgrass surveys are required to satisfy indirect effects of dredging and light monitoring for direct effects of dredging when within 250m of eelgrass beds Multiple surveys have been performed both in-bay and coastal.

Reports indicate that no net-loss of eelgrass occurred due to dredging and that there is no appreciable difference in light availability to eelgrass beds when dredging is occurring within 250m of the beds SPN is planning on coordinating with NMFS to remove at least the

light monitoring provision POC: Chris Eng

Dredging Window Case Study #2 (SPN)

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Success Story Elimination of monitoring requirement for Caulerpa and grunion POC: Jim Fields

Dredging Window Case Study #3 (SPL)

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Discussion Points

What is the main basis for restricting dredging operations in your district?

What are ways in which we can overcome those restrictions?

sustainable sediment management and dredging seminar … · sustainable sediment management and...

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