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NUMERICAL MODELLING OF RELEASED DREDGED SEDIMENT

DISPERSION FROM PANDOP HARBOUR (NEW CALEDONIA)

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NUMERICAL MODELLING OF RELEASED DREDGED

SEDIMENT DISPERSION FROM PANDOP HARBOUR

(NEW CALEDONIA)

16/10/2019

NUMERICAL MODELLING OF RELEASED DREDGED SEDIMENT

DISPERSION FROM PANDOP HARBOUR (NEW CALEDONIA)

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ORDER OF THE PRESENTATION

1. STUDY CONTEXT 2. NUMERICAL MODEL DESCRIPTION 3. HYPOTHESIS AND MODELLING STRATEGY 4. RESULTS

NUMERICAL MODELLING OF RELEASED DREDGED SEDIMENT

DISPERSION FROM PANDOP HARBOUR (NEW CALEDONIA)

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STUDY CONTEXT

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NUMERICAL MODELLING OF RELEASED DREDGED SEDIMENT

DISPERSION FROM PANDOP HARBOUR (NEW CALEDONIA)

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• NORTHERN PROVINCE OF NEW CALEDONIA
• DREDGING OPERATIONS IN ORDER TO MAINTAIN THE HARBOR

ACTIVITIES

• AIMS :
• CHARACTERIZE THE OCEANO-CLIMATIC CONDITIONS

IMPACTING THE STUDY SITE

• EVALUATE THE RELEASED DREDGED SEDIMENT

DISPERSION IN ORDER TO DEFINE A DISPOSAL ZONE THAT GIVES THE BEST COMPROMISE BETWEEN A RELATIVELY CLOSE DISPOSAL AREA AND A LOW IMPACT ON THE CORAL REEF

• STUDY THE CUMULATIVE IMPACT OF SUCCESSIVE

DISPOSALS BY MEANS OF LONG-TERM SIMULATIONS

GENERAL CONTEXT

STUDY SITE DESCRIPTION AND GOALS OF THE STUDY

Disposal zone

NUMERICAL MODELLING OF RELEASED DREDGED SEDIMENT

DISPERSION FROM PANDOP HARBOUR (NEW CALEDONIA)

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• OFFSHORE WAVE CONDITIONS WERE STUDIED FROM A WW3 NUMERICAL MODEL

FROM IFREMER OVER A 28 YEARS PERIOD FROM 1990 TO 2018.

• HS LOWER THAN 1,5M FOR 23% OF THE TIME, LOWER THAN 2M FOR 55% OF THE

TIME AND LOWER THAN 3M FOR 92% OF THE TIME.

• SEA STATES BELOW 3.0 M USUALLY HAVE PEAK PERIODS OF THE ORDER OF 9 TO 14 S.

OCEANO-CLIMATIC CONTEXT

GENERAL WAVE CONDITIONS

• MORE RARELY, SOME SEA STATES CAN REACH SIGNIFICANT

HEIGHTS OF MORE THAN 6M AND LONG PERIODS UP TO

20S.

• WAVES PREFERENTIALLY ORIGINATE FROM SOUTH-EAST

(135°N) TO SOUTH-SOUTH-WEST (210°N).

NUMERICAL MODELLING OF RELEASED DREDGED SEDIMENT

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• TWO YEARS MEASUREMENTS (2001-2002) : MEAN VELOCITY : 5,7 M/S
• WIND VELOCITIES ARE BELOW 5,5 M/S (10 KT) DURING 26% OF THE TIME AND BELOW

10,5 M/S (21 KT) DURING 79% OF THE TIME

• TWO MAIN SEASONS :
• HOT SEASON CHARACTERIZED BY THE PASSAGE OF DEPRESSIONS AND TROPICAL

CYCLONES AND A WIND REGIME FROM SOUTH-EAST TO EAST (SOUTH-EAST TRADE WIND)

• COOL SEASON CHARACTERIZED BY WIND FROM EAST-SOUTH-EAST SECTOR, BUT

ALSO COLD FRONTS ACCOMPANIED BY ABUNDANT RAINFALL AND WEST SECTOR WINDS THAT CAN BLOW IN STORM (SHOTS FROM WEST).

WIND CLIMATE

OCEANO-CLIMATIC CONTEXT

NUMERICAL MODELLING OF RELEASED DREDGED SEDIMENT

DISPERSION FROM PANDOP HARBOUR (NEW CALEDONIA)

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• CURRENT CIRCULATIONS EXTRACTED FROM THE MERCATOR MODEL

(CMEMS)

• THESE VELOCITIES ARE RECUPERATED OVER A 10 YEARS PERIOD (2007-

2016) FOR SEVERAL DEPTHS (SURFACE, 100M, 400M AND 1000M)

• STRONG SEASONAL VARIABILITY
• CURRENT HETEROGENEITY IN THE WATER COLUMN

OFFSHORE GENERAL CURRENT

Hot season Cool season

OCEANO-CLIMATIC CONTEXT

NUMERICAL MODELLING OF RELEASED DREDGED SEDIMENT

DISPERSION FROM PANDOP HARBOUR (NEW CALEDONIA)

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NUMERICAL MODEL DESCRIPTION

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NUMERICAL MODELLING OF RELEASED DREDGED SEDIMENT

DISPERSION FROM PANDOP HARBOUR (NEW CALEDONIA)

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NUMERICAL MODEL DESCRIPTION

MESH AND FORCINGS

• 41 200 NODES
• MESH SIZE OF ABOUT 1000M OFF THE LAGOON TO 500M IN

THE LAGOON, 100M AT THE REEF AND 50M AROUND THE DISPOSAL ZONE

• SEVERAL SOURCES OF BATHYMETRIC DATA :
• GEBCO
• ZONECO
• SHOM MAPS
• VERTICAL MESH COMPOSED OF 10 PLANES (FIXED AND SIGMA

PLANES) REFINED IN THE UPPER PART OF THE WATER COLUMN.

NUMERICAL MODELLING OF RELEASED DREDGED SEDIMENT

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• GLOBAL OCEANIC TIDE MODEL TPXO
• TO IMPOSE VELOCITY PROFILES RELATED TO THE

MERCATOR MODEL AT THE BOUNDARIES, A SPECIFIC

MODULE HAS BEEN DEVELOPED. THE VELOCITIES ARE IMPOSED TO THE DIFFERENT BOUNDARIES AT THE DIFFERENT LAYERS.

NUMERICAL MODEL DESCRIPTION

MESH AND FORCINGS

NUMERICAL MODELLING OF RELEASED DREDGED SEDIMENT

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• WATER LEVEL COMPARISON WITH THE SHOM PREDICTION AT PAAGOUMÈNE (NORTH PART OF THE MODEL)
• WATER LEVEL AND VELOCITY COMPARISON WITH ADCP MEASUREMENTS AT THE DUROC INLET (SOUTH PART OF THE MODEL)

CALIBRATION AND VALIDATION

Water level at Paagoumène Velocities at Duroc

Differences Biais MAE RMAE ARMAE ARMAE (Sutherland) r Water Level (Paagoumène)

• 0,01

0,04 0,04

• 0,01

Excellent 0,98 Water Level (Duroc) 0,005 0,03 0,03 0,04 Excellent 0,99 Velocities (Duroc) 0,05 0,10 0,43 0,007 Excellent 0,91

NUMERICAL MODEL DESCRIPTION

NUMERICAL MODELLING OF RELEASED DREDGED SEDIMENT

DISPERSION FROM PANDOP HARBOUR (NEW CALEDONIA)

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HYPOTHESIS AND MODELLING STRATEGY

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NUMERICAL MODELLING OF RELEASED DREDGED SEDIMENT

DISPERSION FROM PANDOP HARBOUR (NEW CALEDONIA)

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HYPOTHESIS

DISPOSAL REPRESENTATION

HYPOTHESIS ON SEDIMENT:

• TYPE OF SEDIMENT : MUD
• FALL VELOCITY : 0,1 MM/S (LINKED DO THE GRAIN SIZE BY THE STOKES LAW)(NEGLECTING

FLOCCULATION EFFECTS)

• DEPENDING ON THE CURRENT VELOCITIES, 5% FOR CALM CONDITIONS AND 10% FOR AGITATED

CONDITIONS OF THE DUMPED SEDIMENTS ARE INJECTED AT THE SURFACE AND ALSO AT THE PYCNOCLINE (LAYER OF DENSITY CHANGE).

• THE CONVECTIVE DESCENT OF THE MAJORITY OF THE DUMPED SEDIMENT IS NOT REPRESENTED IN

THE MODEL.

• THE CRITICAL SHEAR STRESS FOR DEPOSITION AND EROSION WERE ADAPTED LINKED TO THE STATE

OF ART.

• NO SEDIMENTS ARE CONSIDERED AT THE BOTTOM AT THE BEGINNING OF THE SIMULATION.

NUMERICAL MODELLING OF RELEASED DREDGED SEDIMENT

DISPERSION FROM PANDOP HARBOUR (NEW CALEDONIA)

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HYPOTHESIS

LENGTH : 15 DAYS

• SCENARIO 1 - CALM CONDITIONS: WEAK WIND (1 – 5 M/S), LOW SEA STATE (0,5 M) FROM

SOUTH AND WEAK GENERAL CURRENT OF 0,2 M/S FROM NORTH-WEST TO SOUTH-EAST.

• SCENARIO 2 - AGITATED CONDITIONS OF THE COOL SEASON: WAVES OF 1,8M FROM SOUTH,

WIND TIME SERIES OF TRADE WIND AND WESTERLY SEA BREEZES.

• SCENARIO 3 - AGITATED CONDITIONS OF THE HOT SEASON: WAVES OF 1,8M FROM SOUTH,

STRONG SOUTH-EAST TRADE WIND AND A STRONG GENERAL CURRENT OF 0,4 M/S FROM

NORTH-WEST TO SOUTH-EAST.

SCENARIOS

NUMERICAL MODELLING OF RELEASED DREDGED SEDIMENT

DISPERSION FROM PANDOP HARBOUR (NEW CALEDONIA)

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RESULTS

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NUMERICAL MODELLING OF RELEASED DREDGED SEDIMENT

DISPERSION FROM PANDOP HARBOUR (NEW CALEDONIA)

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RESULTS

• THE CURRENTS AROUND THE DISPOSAL ZONE

ARE RELATIVELY LOW (< 0.3 M/S).

• A GYRE CAN BE OBSERVED AROUND THE

DUMPING ZONE GENERATED BY THE GLOBAL CIRCULATION IMPACTING THE BAY AND THE TWO INLETS. THE VELOCITIES OF THE GYRE ARE LINKED TO THE GLOBAL CIRCULATION.

FLOOD TIDE EBB TIDE

CALM CONDITIONS :

• WEAK WIND (1 – 5 M/S)
• LOW SEA STATE (0,5 M) FROM SOUTH
• GENERAL CURRENT OF 0,2 M/S FROM

NORTH-WEST TO SOUTH-EAST

SCENARIO 1

NUMERICAL MODELLING OF RELEASED DREDGED SEDIMENT

DISPERSION FROM PANDOP HARBOUR (NEW CALEDONIA)

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SCENARIO 1

• DUE TO DEPTH AND QUANTITIES OF SEDIMENT DUMPED, THE

SEDIMENT CONCENTRATIONS ARE WEAK.

• DUE TO THE LOW VELOCITIES, SEDIMENT TRANSPORT IS LIMITED, THE

SEDIMENTS FALL IN THE WATER COLUMN AND STAY CLOSE TO THE DISPOSAL SITE.

• AFTER A DUMPING, THE SEDIMENT CONCENTRATION IN THE DISPOSAL

ZONE DECREASES QUICKLY.

CALM CONDITIONS :

• WEAK WIND (1 – 5 M/S)
• LOW SEA STATE (0,5 M) FROM SOUTH
• GENERAL CURRENT OF 0,2 M/S FROM

NORTH-WEST TO SOUTH-EAST

RESULTS

NUMERICAL MODELLING OF RELEASED DREDGED SEDIMENT

DISPERSION FROM PANDOP HARBOUR (NEW CALEDONIA)

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SCENARIO 2

AGITATED CONDITIONS OF THE COOL SEASON :

• WIND TIME SERIES OF SOUTH-SOUTH-EAST TRADE WIND AND

WESTERLY SEA BREEZES

• WAVES OF 1,8M FROM SOUTH
• DUE TO DEPTH AND QUANTITIES OF SEDIMENT DUMPED, THE

SEDIMENT CONCENTRATIONS ARE WEAK.

• DUE TO THE LOW VELOCITIES, SEDIMENT TRANSPORT IS LIMITED, THE

SEDIMENTS FALL IN THE WATER COLUMN AND STAY CLOSE TO THE DISPOSAL SITE.

• AFTER A DUMPING, THE SEDIMENT CONCENTRATION IN THE DISPOSAL

ZONE DECREASES QUICKLY.

• THE SEDIMENT PLUME IS MOSTLY PROPAGATED TO THE NORTH-

NORTH-WEST DUE TO SOUTH-SOUTH-EAST WINDS AND TO THE NORTH-EAST DUE TO SOUTH-WEST WINDS.

RESULTS

NUMERICAL MODELLING OF RELEASED DREDGED SEDIMENT

DISPERSION FROM PANDOP HARBOUR (NEW CALEDONIA)

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SCENARIO 3

AGITATED CONDITIONS OF THE HOT SEASON :

• STRONG SOUTH-EAST TRADE WIND
• WAVES OF 1,8M FROM SOUTH
• GENERAL CURRENT OF 0,4 M/S FROM

NORTH-WEST TO SOUTH-EAST

FLOOD TIDE EBB TIDE

• THE CURRENTS AROUND THE DISPOSAL ZONE

ARE RELATIVELY LOW (< 0.3 M/S).

• A GYRE CAN BE OBSERVED AROUND THE

DUMPING ZONE GENERATED BY THE GLOBAL CIRCULATION IMPACTING THE BAY AND THE TWO INLETS. THE VELOCITIES OF THE GYRE ARE LINKED TO THE GLOBAL CIRCULATION.

RESULTS

NUMERICAL MODELLING OF RELEASED DREDGED SEDIMENT

DISPERSION FROM PANDOP HARBOUR (NEW CALEDONIA)

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SCENARIO 3

• DUE TO DEPTH AND QUANTITIES OF SEDIMENT DUMPED, THE

SEDIMENT CONCENTRATIONS ARE WEAK.

• DUE TO THE LOW VELOCITIES, SEDIMENT TRANSPORT IS LIMITED, THE

SEDIMENTS FALL IN THE WATER COLUMN AND STAY CLOSE TO THE DISPOSAL SITE.

• AFTER A DUMPING, THE SEDIMENT CONCENTRATION IN THE DISPOSAL

ZONE DECREASES QUICKLY.

• THE SEDIMENT PLUME IS MOSTLY PROPAGATED TO THE NORTH-

NORTH-WEST DUE TO SOUTH-SOUTH-EAST WINDS. AGITATED CONDITIONS OF THE HOT SEASON :

• STRONG SOUTH-EAST TRADE WIND
• WAVES OF 1,8M FROM SOUTH
• GENERAL CURRENT OF 0,4 M/S FROM

NORTH-WEST TO SOUTH-EAST

RESULTS

NUMERICAL MODELLING OF RELEASED DREDGED SEDIMENT

DISPERSION FROM PANDOP HARBOUR (NEW CALEDONIA)

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• THE FIGURE SHOWS FOR EACH CONDITION THE MAXIMAL SEDIMENT CONCENTRATION FOR DEPTH LESS THAN 100M.

IMPACT

COMPARISON FOR THE DIFFERENT CONDITIONS

• THE IMPACT THRESHOLD FOR THE REEF IS CONSIDERED REGARDING TO THE STATE OF ART. INDEED, THE REEF IS CONSIDERED AS IMPACTED FOR SEDIMENT

CONCENTRATIONS HIGHER THAN 10 MG/L (FOR DEPTH LESS THAN 100M).

INITIALISATION

RESULTS

Maximal concentrations for depth < 100m

• THE SCENARIO 3 FOR AGITATED

CONDITIONS OF THE HOT SEASON IS THE WORST ONE WITH CONCENTRATIONS AT THE REEF OF ABOUT 0,13 MG/L. THE MAXIMAL CONCENTRATION AT THE REEF FOR THE CALM SCENARIO IS ABOUT 0,075 MG/L AND 0,02 MG/L FOR THE COOL SEASON SIMULATION.

NUMERICAL MODELLING OF RELEASED DREDGED SEDIMENT

DISPERSION FROM PANDOP HARBOUR (NEW CALEDONIA)

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• THE SCENARIO 3 FOR AGITATED CONDITIONS OF THE HOT SEASON IS THE WORST

ONE WITH CONCENTRATIONS AT THE REEF OF ABOUT 0,13 MG/L. FOR THE SECOND DISPOSAL SITE, THE MAXIMAL SEDIMENT CONCENTRATION AT THE REEF IS ABOUT 0,085 MG/L WHICH IS TWICE AS LOW AS FOR THE CLOSEST SITE.

COMPARISON OF THE TWO DISPOSAL SITES

SCENARIO 3 FOR THE TWO DISPOSAL SITES :

RESULTS

Maximal concentrations for depth < 100m

Distance of

NUMERICAL MODELLING OF RELEASED DREDGED SEDIMENT

DISPERSION FROM PANDOP HARBOUR (NEW CALEDONIA)

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• A 3D HYDROSEDIMENTARY MODEL HAS BEEN DEVELOPED TO REPRODUCE THE DIFFERENT HYDRODYNAMIC PROCESSES

ON THE NORTH-WEST PART OF NEW CALEDONIA.

• FOR THE DIFFERENT MODELLED OCEANO-CLIMATIC CONDITIONS, THE SUSPENDED SEDIMENT CONCENTRATIONS AT THE

REEF CAUSED BY THE DUMPING ARE RELATIVELY LOW AND DO NOT IMPACT THE CORAL REEF.

• A SECOND DISPOSAL SITE HAS ALSO BEEN STUDIED LEADING TO A DIMINUTION OF THE IMPACT BUT A COST RISE (RISE OF

THE DISTANCE WITH THE HARBOUR AND NEED OF A SUPPLEMENTARY DREDGE TO KEEP THE SAME WORK RATE).

• LONG TERM SIMULATIONS OF ONE MONTH HAS ALSO BEEN CARRIED OUT TO OBSERVE THE CUMULATIVE IMPACT OF

SUCCESSIVE DISPOSALS. THIS WORK SHOWED THAT THE CUMULATIVE IMPACT OF SUCCESSIVE DUMPING IS NEGLIGIBLE.

• TO CONCLUDE, THE DUMPING IMPACTS ARE TEMPORARY AND PUNCTUAL.

CONCLUSION THANKS FOR YOUR

ATTENTION

NUMERICAL MODELLING OF RELEASED DREDGED SEDIMENT

DISPERSION FROM PANDOP HARBOUR (NEW CALEDONIA)

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ANNEXE :

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NUMERICAL MODELLING OF RELEASED DREDGED SEDIMENT

DISPERSION FROM PANDOP HARBOUR (NEW CALEDONIA)

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SCENARIO 3

• DUE TO THE LOW VELOCITIES, SEDIMENT TRANSPORT IS LIMITED, THE SEDIMENTS FALL IN THE WATER COLUMN AND STAY CLOSE TO THE DISPOSAL

SITE.

AGITATED CONDITIONS OF THE HOT SEASON :

• STRONG SOUTH-EAST TRADE WIND
• WAVES OF 1,8M FROM SOUTH
• GENERAL CURRENT OF 0,4 M/S FROM

NORTH-WEST TO SOUTH-EAST

RESULTS

NUMERICAL MODELLING OF RELEASED DREDGED SEDIMENT

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• WATER LEVEL AND CURRENT MEASUREMENTS IN

JUNE AND AUGUST 2001

MODEL VALIDATION

Duroc Inlet Ronfleur Inlet Gatope Inlet

WATER LEVEL AT THE DUROC INLET

BIAIS (m) MAE (m) RMAE r² (correlation coefficient) August 2001 0,005 0,03 0,03 0,99 June 2001

• 0,01

0,04 0,04 0,99

NUMERICAL MODELLING OF RELEASED DREDGED SEDIMENT

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• THE FRICTION IS COMPUTED WITH THE

MANNING LAW AND THE FRICTION

COEFFICIENTS ARE ASSIGNED DEPENDING ON THE BOTTOM TYPE :

• 0,02 M-1/3S FOR THE OCEAN,
• 0,024 M-1/3S FOR THE SANDY PART OF

THE LAGOON,

• 0,035 M-1/3S FOR THE MUDDY PART OF

THE LAGOON,

• 0,083 M-1/3S FOR THE REEF.

FRICTION

MANNING LAW

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RÉSULTATS DE MODÉLISATION

SCENARIO 1

CALM CONDITIONS :

• WEAK WIND (1 – 5 M/S)
• LOW SEA STATE (0,5 M) FROM SOUTH
• GENERAL CURRENT OF 0,2 M/S FROM

NORTH-WEST TO SOUTH-EAST

• DUE TO DEPTH AND QUANTITIES OF SEDIMENT DUMPED, THE

SEDIMENT CONCENTRATION ARE WEAK.

• CONCENTRATIONS LOWER THAN 0,01 MG/L ARE NOT REPRESENTED.
• DUE TO THE LOW VELOCITIES, SEDIMENT TRANSPORT IS LIMITED, THE

SEDIMENTS FALL IN THE WATER COLUMN AND STAY CLOSE TO THE DISPOSAL SITE

• AFTER A DUMPING, THE SEDIMENT CONCENTRATION IN THE DISPOSAL

ZONE DECREASES QUICKLY

Suspended sediment maximal concentration

NUMERICAL MODELLING OF RELEASED DREDGED SEDIMENT

DISPERSION FROM PANDOP HARBOUR (NEW CALEDONIA)

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SCENARIO 2

RÉSULTATS DE MODÉLISATION

• DUE TO DEPTH AND QUANTITIES OF SEDIMENT DUMPED, THE

SEDIMENT CONCENTRATION ARE WEAK.

• CONCENTRATIONS LOWER THAN 0,01 MG/L ARE NOT REPRESENTED.
• DUE TO THE LOW VELOCITIES, SEDIMENT TRANSPORT IS LIMITED, THE

SEDIMENTS FALL IN THE WATER COLUMN AND STAY CLOSE TO THE DISPOSAL SITE

• AFTER A DUMPING, THE SEDIMENT CONCENTRATION IN THE DISPOSAL

ZONE DECREASES QUICKLY

AGITATED CONDITIONS OF THE COOL SEASON :

• WIND TIME SERIES OF TRADE WIND AND WESTERLY SEA

BREEZES

• WAVES OF 1,8M FROM SOUTH

Suspended sediment maximal concentration

NUMERICAL MODELLING OF RELEASED DREDGED SEDIMENT

DISPERSION FROM PANDOP HARBOUR (NEW CALEDONIA)

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SCÉNARIO 3

RÉSULTATS DE MODÉLISATION

• DUE TO DEPTH AND QUANTITIES OF SEDIMENT DUMPED, THE

SEDIMENT CONCENTRATION ARE WEAK.

• CONCENTRATIONS LOWER THAN 0,01 MG/L ARE NOT REPRESENTED.
• DUE TO THE LOW VELOCITIES, SEDIMENT TRANSPORT IS LIMITED, THE

SEDIMENTS FALL IN THE WATER COLUMN AND STAY CLOSE TO THE DISPOSAL SITE.

• AFTER A DUMPING, THE SEDIMENT CONCENTRATION IN THE DISPOSAL

ZONE DECREASES QUICKLY.

• THE SEDIMENT PLUME IS MOSTLY PROPAGATED TO THE NORTH-NORTH-

WEST DUE TO SOUTH-SOUTH-EAST WINDS. AGITATED CONDITIONS OF THE HOT SEASON :

• STRONG SOUTH-EAST TRADE WIND
• WAVES OF 1,8M FROM SOUTH
• GENERAL CURRENT OF 0,4 M/S FROM

NORTH-WEST TO SOUTH-EAST

Suspended sediment maximal concentration

NUMERICAL MODELLING OF RELEASED DREDGED SEDIMENT

DISPERSION FROM PANDOP HARBOUR (NEW CALEDONIA)

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• BIBLIOGRAPHIE SUR LE SUJET VASTE ET COMPLEXE :
• LES SEUILS PROPOSÉS DANS LA BIBLIOGRAPHIE DÉPENDENT FORTEMENT DES SITES ÉTUDIÉS.
• PAR CONSÉQUENT, LES SEUILS UTILISÉS DANS LE PROJET KONIAMBO SERONT ÉGALEMENT UTILISÉS DANS LE CADRE DE

CETTE ÉTUDE.

• LES RÉCIFS SERONT ALORS CONSIDÉRÉS COMME IMPACTÉS LORSQUE LES CONCENTRATIONS EN MES SERONT SUPÉRIEURES

À 10MG/L AU NIVEAU DES PROFONDEURS INFÉRIEURES À 100M.

• DE PLUS, LE DÉPÔT MAXIMUM PERMETTANT DE NE PAS IMPACTER LES CORAUX EST DE 1 MG/CM2/D.

SEUILS D'IMPACT DES RÉCIFS