1 S TUDY CONTEXT 3 N UMERICAL MODELLING OF RELEASED DREDGED SEDIMENT - PowerPoint PPT Presentation

N UMERICAL MODELLING OF RELEASED DREDGED SEDIMENT DISPERSION FROM P ANDOP HARBOUR (N EW C ALEDONIA ) N UMERICAL MODELLING OF RELEASED DREDGED SEDIMENT DISPERSION FROM P ANDOP HARBOUR (N EW C ALEDONIA ) 16/10/2019 1

N UMERICAL MODELLING OF RELEASED DREDGED SEDIMENT DISPERSION FROM P ANDOP HARBOUR (N EW C ALEDONIA ) O RDER OF THE PRESENTATION 1. S TUDY CONTEXT 2. N UMERICAL MODEL DESCRIPTION 3. H YPOTHESIS AND MODELLING STRATEGY 4. R ESULTS 2

N UMERICAL MODELLING OF RELEASED DREDGED SEDIMENT DISPERSION FROM P ANDOP HARBOUR (N EW C ALEDONIA ) 1 S TUDY CONTEXT 3

N UMERICAL MODELLING OF RELEASED DREDGED SEDIMENT G ENERAL CONTEXT DISPERSION FROM P ANDOP HARBOUR (N EW C ALEDONIA ) S TUDY SITE DESCRIPTION AND GOALS OF THE STUDY  N ORTHERN P ROVINCE OF N EW C ALEDONIA  D REDGING OPERATIONS IN ORDER TO MAINTAIN THE HARBOR ACTIVITIES  A IMS :  C HARACTERIZE THE OCEANO - CLIMATIC CONDITIONS Disposal zone IMPACTING THE STUDY SITE  E VALUATE 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  S TUDY THE CUMULATIVE IMPACT OF SUCCESSIVE DISPOSALS BY MEANS OF LONG - TERM SIMULATIONS 4

N UMERICAL MODELLING OF RELEASED DREDGED SEDIMENT O CEANO - CLIMATIC CONTEXT DISPERSION FROM P ANDOP HARBOUR (N EW C ALEDONIA ) G ENERAL WAVE CONDITIONS  O FFSHORE WAVE CONDITIONS WERE STUDIED FROM A WW3 NUMERICAL MODEL FROM IFREMER OVER A 28 YEARS PERIOD FROM 1990 TO 2018.  H S LOWER THAN 1,5 M FOR 23% OF THE TIME , LOWER THAN 2 M FOR 55% OF THE TIME AND LOWER THAN 3 M FOR 92% OF THE TIME .  S EA STATES BELOW 3.0 M USUALLY HAVE PEAK PERIODS OF THE ORDER OF 9 TO 14 S .  M ORE RARELY , SOME SEA STATES CAN REACH SIGNIFICANT HEIGHTS OF MORE THAN 6 M AND LONG PERIODS UP TO 20 S .  W AVES PREFERENTIALLY ORIGINATE FROM S OUTH -E AST (135°N) TO S OUTH -S OUTH -W EST (210°N). 5

N UMERICAL MODELLING OF RELEASED DREDGED SEDIMENT O CEANO - CLIMATIC CONTEXT DISPERSION FROM P ANDOP HARBOUR (N EW C ALEDONIA ) W IND CLIMATE  T WO 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  T WO MAIN SEASONS :  HOT SEASON CHARACTERIZED BY THE PASSAGE OF DEPRESSIONS AND TROPICAL CYCLONES AND A WIND REGIME FROM S OUTH -E AST TO E AST ( SOUTH - EAST TRADE WIND )  C OOL SEASON CHARACTERIZED BY WIND FROM E AST -S OUTH -E AST SECTOR , BUT ALSO COLD FRONTS ACCOMPANIED BY ABUNDANT RAINFALL AND W EST SECTOR WINDS THAT CAN BLOW IN STORM ( SHOTS FROM W EST ). 6

N UMERICAL MODELLING OF RELEASED DREDGED SEDIMENT O CEANO - CLIMATIC CONTEXT DISPERSION FROM P ANDOP HARBOUR (N EW C ALEDONIA ) O FFSHORE GENERAL CURRENT Cool season Hot season  C URRENT CIRCULATIONS EXTRACTED FROM THE M ERCATOR MODEL (CMEMS)  T HESE VELOCITIES ARE RECUPERATED OVER A 10 YEARS PERIOD (2007- 2016) FOR SEVERAL DEPTHS ( SURFACE , 100 M , 400 M AND 1000 M )  S TRONG SEASONAL VARIABILITY  C URRENT HETEROGENEITY IN THE WATER COLUMN 7

N UMERICAL MODELLING OF RELEASED DREDGED SEDIMENT DISPERSION FROM P ANDOP HARBOUR (N EW C ALEDONIA ) 2 N UMERICAL MODEL DESCRIPTION 8

N UMERICAL MODELLING OF RELEASED DREDGED SEDIMENT N UMERICAL MODEL DESCRIPTION DISPERSION FROM P ANDOP HARBOUR (N EW C ALEDONIA ) M ESH AND FORCINGS  41 200 NODES  M ESH SIZE OF ABOUT 1000 M OFF THE LAGOON TO 500 M IN THE LAGOON , 100 M AT THE REEF AND 50 M AROUND THE DISPOSAL ZONE  S EVERAL SOURCES OF BATHYMETRIC DATA :  G EBCO  ZONECO  SHOM MAPS  V ERTICAL MESH COMPOSED OF 10 PLANES ( FIXED AND SIGMA PLANES ) REFINED IN THE UPPER PART OF THE WATER COLUMN . 9

N UMERICAL MODELLING OF RELEASED DREDGED SEDIMENT N UMERICAL MODEL DESCRIPTION DISPERSION FROM P ANDOP HARBOUR (N EW C ALEDONIA ) M ESH AND FORCINGS  G LOBAL OCEANIC TIDE MODEL TPXO  T O IMPOSE VELOCITY PROFILES RELATED TO THE M ERCATOR MODEL AT THE BOUNDARIES , A SPECIFIC MODULE HAS BEEN DEVELOPED . T HE VELOCITIES ARE IMPOSED TO THE DIFFERENT BOUNDARIES AT THE DIFFERENT LAYERS . 10

N UMERICAL MODELLING OF RELEASED DREDGED SEDIMENT N UMERICAL MODEL DESCRIPTION DISPERSION FROM P ANDOP HARBOUR (N EW C ALEDONIA ) C ALIBRATION AND VALIDATION  W ATER LEVEL COMPARISON WITH THE SHOM PREDICTION AT P AAGOUMÈNE (N ORTH PART OF THE MODEL )  W ATER LEVEL AND VELOCITY COMPARISON WITH A D CP MEASUREMENTS AT THE D UROC I NLET (S OUTH PART OF THE MODEL ) 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 Water level at Paagoumène Velocities at Duroc 11

N UMERICAL MODELLING OF RELEASED DREDGED SEDIMENT DISPERSION FROM P ANDOP HARBOUR (N EW C ALEDONIA ) 3 H YPOTHESIS AND MODELLING STRATEGY 12

N UMERICAL MODELLING OF RELEASED DREDGED SEDIMENT H YPOTHESIS DISPERSION FROM P ANDOP HARBOUR (N EW C ALEDONIA ) D ISPOSAL REPRESENTATION H YPOTHESIS ON SEDIMENT :  T YPE OF SEDIMENT : MUD  F ALL VELOCITY : 0,1 MM / S ( LINKED DO THE GRAIN SIZE BY THE S TOKES L AW )( NEGLECTING FLOCCULATION EFFECTS )  D EPENDING 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 ).  T HE CONVECTIVE DESCENT OF THE MAJORITY OF THE DUMPED SEDIMENT IS NOT REPRESENTED IN THE MODEL .  T HE CRITICAL SHEAR STRESS FOR DEPOSITION AND EROSION WERE ADAPTED LINKED TO THE STATE OF ART .  N O SEDIMENTS ARE CONSIDERED AT THE BOTTOM AT THE BEGINNING OF THE SIMULATION . 13

N UMERICAL MODELLING OF RELEASED DREDGED SEDIMENT H YPOTHESIS DISPERSION FROM P ANDOP HARBOUR (N EW C ALEDONIA ) S CENARIOS L ENGTH : 15 DAYS  S CENARIO 1 - C ALM CONDITIONS : WEAK WIND (1 – 5 M / S ), LOW SEA STATE (0,5 M ) FROM S OUTH AND WEAK GENERAL CURRENT OF 0,2 M / S FROM N ORTH -W EST TO S OUTH -E AST .  S CENARIO 2 - A GITATED CONDITIONS OF THE COOL SEASON : WAVES OF 1,8 M FROM S OUTH , WIND TIME SERIES OF TRADE WIND AND WESTERLY SEA BREEZES .  S CENARIO 3 - A GITATED CONDITIONS OF THE HOT SEASON : WAVES OF 1,8 M FROM S OUTH , STRONG SOUTH - EAST TRADE WIND AND A STRONG GENERAL CURRENT OF 0,4 M / S FROM N ORTH -W EST TO S OUTH -E AST . 14

N UMERICAL MODELLING OF RELEASED DREDGED SEDIMENT DISPERSION FROM P ANDOP HARBOUR (N EW C ALEDONIA ) 4 R ESULTS 15

N UMERICAL MODELLING OF RELEASED DREDGED SEDIMENT R ESULTS DISPERSION FROM P ANDOP HARBOUR (N EW C ALEDONIA ) S CENARIO 1 C ALM CONDITIONS :  WEAK WIND (1 – 5 M / S )  LOW SEA STATE (0,5 M ) FROM S OUTH  GENERAL CURRENT OF 0,2 M / S FROM N ORTH -W EST TO S OUTH -E AST  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 . T HE VELOCITIES OF THE GYRE ARE LINKED TO THE GLOBAL CIRCULATION . F LOOD TIDE E BB TIDE 16

N UMERICAL MODELLING OF RELEASED DREDGED SEDIMENT R ESULTS DISPERSION FROM P ANDOP HARBOUR (N EW C ALEDONIA ) S CENARIO 1 C ALM CONDITIONS :  WEAK WIND (1 – 5 M / S )  LOW SEA STATE (0,5 M ) FROM S OUTH  GENERAL CURRENT OF 0,2 M / S FROM N ORTH -W EST TO S OUTH -E AST  D UE 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 .  A FTER A DUMPING , THE SEDIMENT CONCENTRATION IN THE DISPOSAL ZONE DECREASES QUICKLY . 17

N UMERICAL MODELLING OF RELEASED DREDGED SEDIMENT R ESULTS DISPERSION FROM P ANDOP HARBOUR (N EW C ALEDONIA ) S CENARIO 2 A GITATED CONDITIONS OF THE COOL SEASON :  W IND TIME SERIES OF S OUTH -S OUTH -E AST TRADE WIND AND WESTERLY SEA BREEZES  W AVES OF 1,8 M FROM S OUTH  D UE TO DEPTH AND QUANTITIES OF SEDIMENT DUMPED , THE SEDIMENT CONCENTRATIONS ARE WEAK .  D UE TO THE LOW VELOCITIES , SEDIMENT TRANSPORT IS LIMITED , THE SEDIMENTS FALL IN THE WATER COLUMN AND STAY CLOSE TO THE DISPOSAL SITE .  A FTER A DUMPING , THE SEDIMENT CONCENTRATION IN THE DISPOSAL ZONE DECREASES QUICKLY .  T HE SEDIMENT PLUME IS MOSTLY PROPAGATED TO THE N ORTH - N ORTH -W EST DUE TO S OUTH -S OUTH -E AST WINDS AND TO THE N ORTH -E AST DUE TO S OUTH -W EST WINDS . 18

N UMERICAL MODELLING OF RELEASED DREDGED SEDIMENT R ESULTS DISPERSION FROM P ANDOP HARBOUR (N EW C ALEDONIA ) S CENARIO 3 A GITATED CONDITIONS OF THE HOT SEASON :  STRONG SOUTH - EAST TRADE WIND  WAVES OF 1,8 M FROM S OUTH  GENERAL CURRENT OF 0,4 M / S FROM N ORTH -W EST TO S OUTH -E AST  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 . T HE VELOCITIES OF THE GYRE ARE F LOOD TIDE E BB TIDE LINKED TO THE GLOBAL CIRCULATION . 19