Management and Assessment of Dredged Material Disposal Near ...
Management and Assessment of Dredged Material Disposal Near a South Florida Sensitive Coral Environment
Christopher J. McArthur, P.E. Member ASCE COPRI U.S. Environmental Protection Agency Region 4 – Atlanta, GA
Jack Stamates NOAA Atlantic Oceanographic and Meteorological Laboratory – Miami, FL
Dredging 2012 Conference: Dredging in the 21st Century Dredging 2012 Conference: Dredging in the 21st Century San Diego, CA October 2012 San Diego, CA October 2012
History •
In the early 1990’s EPA was requested to designate 3 ODMDS in Southeast Florida
Palm Beach ODMDS
– Support maintenance activities of existing channels – Support deepening/widening of Port of Miami
•
Concern for potential impact to South Florida’s Coral Reefs
Port Everglades ODMDS
– Corals are highly sensitive to its surrounding environment. – It is part of the only living coral barrier reef in the continental United States and is the third largest coral barrier reef system in the world. – Southeast Florida counties derive $6 billion annually from reef‐ oriented tourism and fisheries.
Miami ODMDS
Source: Southeast Florida Coral Reef Initiative
Dredging 2012 Conference: Dredging in the 21st Century Dredging 2012 Conference: Dredging in the 21st Century San Diego, CA October 2012 San Diego, CA October 2012
Unknowns • Direction of transport of disposal plumes and frequency of reef directed currents – Located on the continental slope at the edge of the Florida Current. – Florida Current spin‐off eddies were believe to occur as frequently as twice per week.
• Concentration of disposal plumes at reefs – Reefs are located within 2.5 km of the sites. – Models predicted maximum concentration at reefs in the range of 6 to 10 mg/l.
• Acceptable levels of exposure (concentration, duration, frequency) to suspended sediments due to dredged material disposal.
Dredging 2012 Conference: Dredging in the 21st Century Dredging 2012 Conference: Dredging in the 21st Century San Diego, CA October 2012 San Diego, CA October 2012
Interim Protective Measures (Environmental Windows) • Established by interagency group: EPA, USACE, NOAA, Florida, Port of Miami • Restrict disposal during onshore current events to minimize disposal plume transport towards the reefs. • Requires real‐time monitoring of currents at the disposal site and application of current velocity criteria. • Dredging contractor must be ready to cease operations with little advance notice and unknown duration. • Utilized for the 1995‐2005 Deepening Project Dredging 2012 Conference: Dredging in the 21st Century Dredging 2012 Conference: Dredging in the 21st Century San Diego, CA October 2012 San Diego, CA October 2012
Real-time current measurement system
Dredging 2012 Conference: Dredging in the 21st Century Dredging 2012 Conference: Dredging in the 21st Century San Diego, CA October 2012 San Diego, CA October 2012
Long‐term Approach 1. Establish baseline conditions at reefs to establish guidelines for acceptable suspended sediment concentrations. 2. Track and measure suspended sediment disposal plumes to determine suspended sediment concentration in plumes. 3. Monitor corals for sub‐lethal impacts during disposal project. 4. Determine the frequency of plumes reaching the reef. Dredging 2012 Conference: Dredging in the 21st Century Dredging 2012 Conference: Dredging in the 21st Century San Diego, CA October 2012 San Diego, CA October 2012
1. Exposure Guidelines • Intensity – High suspended solids concentrations place stress on corals – Elevations in SSC due to disposal plumes should not exceed the highest concentrations that naturally occur
• Duration – Elevated SSC may cause an adverse impact if the corals are exposed to elevated concentrations for a sufficient amount of time – Elevations in SSC due to disposal plumes should not exceed the length of the naturally occurring events of equal magnitude
• Frequency – Corals can tolerate occasional heavy sediment concentrations if given sufficient opportunity to recover – Elevations in SSC due to disposal plumes should not occur more frequently than the natural occurrence of similar events (magnitude & duration)
Dredging 2012 Conference: Dredging in the 21st Century Dredging 2012 Conference: Dredging in the 21st Century San Diego, CA October 2012 San Diego, CA October 2012
Measurement of ambient suspended sediment concentrations and physical processes
Optical sensors
Wave &
Acoustic sensors Dredging 2012 Conference: Dredging in the 21st Century Dredging 2012 Conference: Dredging in the 21st Century San Diego, CA October 2012 San Diego, CA October 2012
Winter SSC Frequency Distribution 16
Frequency of Occurence (%)
14 12
14 mg/l (99th percentile)
10
8 mg/l (95th percentile)
8 6 4 2 0 0
2
4
6
8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42
Suspended Solids Concentration (mg/l)
Dredging 2012 Conference: Dredging in the 21st Century Dredging 2012 Conference: Dredging in the 21st Century San Diego, CA October 2012 San Diego, CA October 2012
18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Duration above Threshold Concentration (minutes) Dredging 2012 Conference: Dredging in the 21st Century Dredging 2012 Conference: Dredging in the 21st Century San Diego, CA October 2012 San Diego, CA October 2012
1200
1140
1080
1020
960
900
840
780
720
660
600
540
480
420
360
300
240
180
120
60
Summer Fall Winter
0
Allowable Occurences per Week
Duration and Frequency Guidelines
2. Plume Measurements • Utilized calibrated optical turbidity probes suspended 5 and 10 meters below a tracking drogue. • Measured currents and backscatter acoustically from the surface to track the plume.
Dredging 2012 Conference: Dredging in the 21st Century Dredging 2012 Conference: Dredging in the 21st Century San Diego, CA October 2012 San Diego, CA October 2012
Plume Concentrations
120
35
Depth = 5 meters Depth = 10 meters
80
30
25
20
60
15
Turbidity (NTU)
Suspended Sediment Concentration (mg/l)
100
40 10
20 5
0
0 00:10
00:20
00:30
00:40
00:50
01:00
Time from Disposal (hours:minutes)
• Plume concentrations appear to be highly variable from load to load. • Surface plume concentrations appeared to reach background within 30 minutes. Dredging 2012 Conference: Dredging in the 21st Century Dredging 2012 Conference: Dredging in the 21st Century San Diego, CA October 2012 San Diego, CA October 2012
3. Monitor Corals for Sublethal Effects • Objective: Determine if dredged material disposal is inducing a stress response in hermatypic corals on nearby coral reefs. • Utilizes Coral Molecular Bioassay developed by Georgia Institute of Technology. – Montastrea faveolata
• Monitoring multiple stations (5 colonies at each) and a reference. Dredging 2012 Conference: Dredging in the 21st Century Dredging 2012 Conference: Dredging in the 21st Century San Diego, CA October 2012 San Diego, CA October 2012
Sublethal Effects •
Significant gene expression events occurred in June and October of 2005.
Colonies were photographed and marked for monitoring.
– The June event preceded the start of dredging – The October event occurred just following passage of a couple of named storms, including Rita, a major turbidity event. – June and October (2005) had the highest recorded precipitation during the period • Salinities 100 - 125 >125 - 150 >150 - 200 >200
270
90 0%
225
5%
10%
15%
20%
25%
135
180
Currents are dominated by the Florida Current with strong north northeasterly flows
• The longest onshore current event lasted 23 hours. • The probability of an onshore current event of any duration immediately following a disposal event is less than 2 percent (123 events). • The probability of onshore currents lasting for 5 hours or more immediately following a disposal event is less than 0.5 percent (19 events). Dredging 2012 Conference: Dredging in the 21st Century Dredging 2012 Conference: Dredging in the 21st Century San Diego, CA October 2012 San Diego, CA October 2012
Potential for Plume Transport to Nearshore Reefs • Streakline Analysis – One dimensional and assumes spatially homogeneous currents. – Less than 1% probability plume will reach reef within 5 hours. – Less than 3.5% probability plume will reach reef within 10 hours.
• Plume Visitation Frequency – 2 dimensional and spatially varying currents. – Contours represent the frequency that a disposal plume will visit the 0.04 km2 grid cell during the five hour travel time.
Dredging 2012 Conference: Dredging in the 21st Century Dredging 2012 Conference: Dredging in the 21st Century San Diego, CA October 2012 San Diego, CA October 2012
Study Conclusions • Guideline Development and Plume Measurements • Background suspended sediment concentrations are highly seasonal. • Disposal plume concentrations are low and infrequent in comparison to those caused by meteorological events.
• Sublethal effects are small in comparison to background levels of stress corals are experiencing. • Shoreward directed currents are infrequent and the likelihood of plumes reaching the reefs is very small.
Dredging 2012 Conference: Dredging in the 21st Century Dredging 2012 Conference: Dredging in the 21st Century San Diego, CA October 2012 San Diego, CA October 2012
Results •
•
In 2008 the Environmental Windows in place since 1995 were lifted. Miami Harbor Phase III Deepening can move forward without the need for the costly real‐time monitoring system and associated risks of project suspension. Port of Miami
Dredging 2012 Conference: Dredging in the 21st Century Dredging 2012 Conference: Dredging in the 21st Century San Diego, CA October 2012 San Diego, CA October 2012
Dredging and Port Construction Around Coral Reefs PIANC Report No 108 (2010) •
Facilitate interaction between the project proponent, regulators and stakeholders • Environmental Impact Statement • Disposal Site Management and Monitoring Plans
•
Technical mitigation measures • Environmental windows
•
Baseline surveys • Background turbidity levels and/or light levels • Shoreline and physical processes (currents, waves)
•
Predictive numerical modeling • Model validation and calibration
•
Receptor tolerance levels • Based on site specific data supplemented by relevant literature values • Should take into account both the magnitude and duration of the loading
•
Habitat monitoring during the dredging project Dredging 2012 Conference: Dredging in the 21st Century Dredging 2012 Conference: Dredging in the 21st Century San Diego, CA October 2012 San Diego, CA October 2012
Thank You
[email protected] http://www.epa.gov/region4/water/oceans/
Questions?
Dredging 2012 Conference: Dredging in the 21st Century Dredging 2012 Conference: Dredging in the 21st Century San Diego, CA October 2012 San Diego, CA October 2012
Christopher J. McArthur, P.E. Member ASCE COPRI U.S. Environmental Protection Agency Region 4 – Atlanta, GA
Jack Stamates NOAA Atlantic Oceanographic and Meteorological Laboratory – Miami, FL
Dredging 2012 Conference: Dredging in the 21st Century Dredging 2012 Conference: Dredging in the 21st Century San Diego, CA October 2012 San Diego, CA October 2012
History •
In the early 1990’s EPA was requested to designate 3 ODMDS in Southeast Florida
Palm Beach ODMDS
– Support maintenance activities of existing channels – Support deepening/widening of Port of Miami
•
Concern for potential impact to South Florida’s Coral Reefs
Port Everglades ODMDS
– Corals are highly sensitive to its surrounding environment. – It is part of the only living coral barrier reef in the continental United States and is the third largest coral barrier reef system in the world. – Southeast Florida counties derive $6 billion annually from reef‐ oriented tourism and fisheries.
Miami ODMDS
Source: Southeast Florida Coral Reef Initiative
Dredging 2012 Conference: Dredging in the 21st Century Dredging 2012 Conference: Dredging in the 21st Century San Diego, CA October 2012 San Diego, CA October 2012
Unknowns • Direction of transport of disposal plumes and frequency of reef directed currents – Located on the continental slope at the edge of the Florida Current. – Florida Current spin‐off eddies were believe to occur as frequently as twice per week.
• Concentration of disposal plumes at reefs – Reefs are located within 2.5 km of the sites. – Models predicted maximum concentration at reefs in the range of 6 to 10 mg/l.
• Acceptable levels of exposure (concentration, duration, frequency) to suspended sediments due to dredged material disposal.
Dredging 2012 Conference: Dredging in the 21st Century Dredging 2012 Conference: Dredging in the 21st Century San Diego, CA October 2012 San Diego, CA October 2012
Interim Protective Measures (Environmental Windows) • Established by interagency group: EPA, USACE, NOAA, Florida, Port of Miami • Restrict disposal during onshore current events to minimize disposal plume transport towards the reefs. • Requires real‐time monitoring of currents at the disposal site and application of current velocity criteria. • Dredging contractor must be ready to cease operations with little advance notice and unknown duration. • Utilized for the 1995‐2005 Deepening Project Dredging 2012 Conference: Dredging in the 21st Century Dredging 2012 Conference: Dredging in the 21st Century San Diego, CA October 2012 San Diego, CA October 2012
Real-time current measurement system
Dredging 2012 Conference: Dredging in the 21st Century Dredging 2012 Conference: Dredging in the 21st Century San Diego, CA October 2012 San Diego, CA October 2012
Long‐term Approach 1. Establish baseline conditions at reefs to establish guidelines for acceptable suspended sediment concentrations. 2. Track and measure suspended sediment disposal plumes to determine suspended sediment concentration in plumes. 3. Monitor corals for sub‐lethal impacts during disposal project. 4. Determine the frequency of plumes reaching the reef. Dredging 2012 Conference: Dredging in the 21st Century Dredging 2012 Conference: Dredging in the 21st Century San Diego, CA October 2012 San Diego, CA October 2012
1. Exposure Guidelines • Intensity – High suspended solids concentrations place stress on corals – Elevations in SSC due to disposal plumes should not exceed the highest concentrations that naturally occur
• Duration – Elevated SSC may cause an adverse impact if the corals are exposed to elevated concentrations for a sufficient amount of time – Elevations in SSC due to disposal plumes should not exceed the length of the naturally occurring events of equal magnitude
• Frequency – Corals can tolerate occasional heavy sediment concentrations if given sufficient opportunity to recover – Elevations in SSC due to disposal plumes should not occur more frequently than the natural occurrence of similar events (magnitude & duration)
Dredging 2012 Conference: Dredging in the 21st Century Dredging 2012 Conference: Dredging in the 21st Century San Diego, CA October 2012 San Diego, CA October 2012
Measurement of ambient suspended sediment concentrations and physical processes
Optical sensors
Wave &
Acoustic sensors Dredging 2012 Conference: Dredging in the 21st Century Dredging 2012 Conference: Dredging in the 21st Century San Diego, CA October 2012 San Diego, CA October 2012
Winter SSC Frequency Distribution 16
Frequency of Occurence (%)
14 12
14 mg/l (99th percentile)
10
8 mg/l (95th percentile)
8 6 4 2 0 0
2
4
6
8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42
Suspended Solids Concentration (mg/l)
Dredging 2012 Conference: Dredging in the 21st Century Dredging 2012 Conference: Dredging in the 21st Century San Diego, CA October 2012 San Diego, CA October 2012
18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Duration above Threshold Concentration (minutes) Dredging 2012 Conference: Dredging in the 21st Century Dredging 2012 Conference: Dredging in the 21st Century San Diego, CA October 2012 San Diego, CA October 2012
1200
1140
1080
1020
960
900
840
780
720
660
600
540
480
420
360
300
240
180
120
60
Summer Fall Winter
0
Allowable Occurences per Week
Duration and Frequency Guidelines
2. Plume Measurements • Utilized calibrated optical turbidity probes suspended 5 and 10 meters below a tracking drogue. • Measured currents and backscatter acoustically from the surface to track the plume.
Dredging 2012 Conference: Dredging in the 21st Century Dredging 2012 Conference: Dredging in the 21st Century San Diego, CA October 2012 San Diego, CA October 2012
Plume Concentrations
120
35
Depth = 5 meters Depth = 10 meters
80
30
25
20
60
15
Turbidity (NTU)
Suspended Sediment Concentration (mg/l)
100
40 10
20 5
0
0 00:10
00:20
00:30
00:40
00:50
01:00
Time from Disposal (hours:minutes)
• Plume concentrations appear to be highly variable from load to load. • Surface plume concentrations appeared to reach background within 30 minutes. Dredging 2012 Conference: Dredging in the 21st Century Dredging 2012 Conference: Dredging in the 21st Century San Diego, CA October 2012 San Diego, CA October 2012
3. Monitor Corals for Sublethal Effects • Objective: Determine if dredged material disposal is inducing a stress response in hermatypic corals on nearby coral reefs. • Utilizes Coral Molecular Bioassay developed by Georgia Institute of Technology. – Montastrea faveolata
• Monitoring multiple stations (5 colonies at each) and a reference. Dredging 2012 Conference: Dredging in the 21st Century Dredging 2012 Conference: Dredging in the 21st Century San Diego, CA October 2012 San Diego, CA October 2012
Sublethal Effects •
Significant gene expression events occurred in June and October of 2005.
Colonies were photographed and marked for monitoring.
– The June event preceded the start of dredging – The October event occurred just following passage of a couple of named storms, including Rita, a major turbidity event. – June and October (2005) had the highest recorded precipitation during the period • Salinities 100 - 125 >125 - 150 >150 - 200 >200
270
90 0%
225
5%
10%
15%
20%
25%
135
180
Currents are dominated by the Florida Current with strong north northeasterly flows
• The longest onshore current event lasted 23 hours. • The probability of an onshore current event of any duration immediately following a disposal event is less than 2 percent (123 events). • The probability of onshore currents lasting for 5 hours or more immediately following a disposal event is less than 0.5 percent (19 events). Dredging 2012 Conference: Dredging in the 21st Century Dredging 2012 Conference: Dredging in the 21st Century San Diego, CA October 2012 San Diego, CA October 2012
Potential for Plume Transport to Nearshore Reefs • Streakline Analysis – One dimensional and assumes spatially homogeneous currents. – Less than 1% probability plume will reach reef within 5 hours. – Less than 3.5% probability plume will reach reef within 10 hours.
• Plume Visitation Frequency – 2 dimensional and spatially varying currents. – Contours represent the frequency that a disposal plume will visit the 0.04 km2 grid cell during the five hour travel time.
Dredging 2012 Conference: Dredging in the 21st Century Dredging 2012 Conference: Dredging in the 21st Century San Diego, CA October 2012 San Diego, CA October 2012
Study Conclusions • Guideline Development and Plume Measurements • Background suspended sediment concentrations are highly seasonal. • Disposal plume concentrations are low and infrequent in comparison to those caused by meteorological events.
• Sublethal effects are small in comparison to background levels of stress corals are experiencing. • Shoreward directed currents are infrequent and the likelihood of plumes reaching the reefs is very small.
Dredging 2012 Conference: Dredging in the 21st Century Dredging 2012 Conference: Dredging in the 21st Century San Diego, CA October 2012 San Diego, CA October 2012
Results •
•
In 2008 the Environmental Windows in place since 1995 were lifted. Miami Harbor Phase III Deepening can move forward without the need for the costly real‐time monitoring system and associated risks of project suspension. Port of Miami
Dredging 2012 Conference: Dredging in the 21st Century Dredging 2012 Conference: Dredging in the 21st Century San Diego, CA October 2012 San Diego, CA October 2012
Dredging and Port Construction Around Coral Reefs PIANC Report No 108 (2010) •
Facilitate interaction between the project proponent, regulators and stakeholders • Environmental Impact Statement • Disposal Site Management and Monitoring Plans
•
Technical mitigation measures • Environmental windows
•
Baseline surveys • Background turbidity levels and/or light levels • Shoreline and physical processes (currents, waves)
•
Predictive numerical modeling • Model validation and calibration
•
Receptor tolerance levels • Based on site specific data supplemented by relevant literature values • Should take into account both the magnitude and duration of the loading
•
Habitat monitoring during the dredging project Dredging 2012 Conference: Dredging in the 21st Century Dredging 2012 Conference: Dredging in the 21st Century San Diego, CA October 2012 San Diego, CA October 2012
Thank You
[email protected] http://www.epa.gov/region4/water/oceans/
Questions?
Dredging 2012 Conference: Dredging in the 21st Century Dredging 2012 Conference: Dredging in the 21st Century San Diego, CA October 2012 San Diego, CA October 2012
