Singapore Land Reclamation Goal of Modelling Study
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Singapore Land Reclamation modelling approach & results Dr. Tony Minns WL | Delft Hydraulics prepared for CEDA•NL clubavond 24 januari 2006 Goal of modelling study · Determine impacts on: • Hydrodynamics • Navigation • Sediment transport & morphology • Ecology (aquaculture) • Drainage & flooding 2 1 Study location Tanjong Belungkor Sungai Johor East Johor Straits Nenas Channel Pulau Tekong Pulau Ubin Kuala Santi Serangoon Harbour Calder Harbour Kuala Johor Tanjong Pengelih Changi East Finger Singapore Straits 3 Hydrodynamic Models · Singapore Regional Model (SRM) · Eastern Singapore Local Model (ESLM) · Singapore Island Model (SIM) 4 2 Singapore Regional Model 5 SRM • detail 6 3 Eastern Singapore Local Model 7 Singapore Island Model 8 4 bathymetry • 1 9 bathymetry • 2 10 5 Model resolution MODEL No. of gridpoints Grid size per layer SRM 38,500 200 – 300m around Pulau Tekong up to 15,000m near boundaries ESLM 100,000 down to 25m in areas of interest SIM 31000 in outer grid Pulau Tekong: 100 m 38000 in inner grid Johor Straits: 25 •100m Singapore Straits: 300• 500m Outer model: < 1000m11 Hydrodynamics around Singapore · tidal boundaries • Andaman Sea (semi•diurnal) • 12 hours 25 minutes • South China Sea (diurnal) • 24 hours 50 minutes • Java Sea · Sea•level differences (monsoonal) • December – January – South China Sea level 35 cm > Andaman Sea – residual flow 15 – 20 cm/s towards west • July – August – South China Sea level 5 cm < Andaman Sea – residual flow 5 cm/s towards east 12 6 Calibration of SRM Tidal Avg. Avg. phase constituent amplitude error error (cm) (minutes) M2 0.8 3.1 S2 0.6 5.6 K1 1.6 12.4 O1 0.7 12.9 13 SRModel results 14 7 ESLM results 15 Reclamation Profiles profile 0 profile 1 profile 2 profile 3 16 8 Hydrodynamics · Water levels • only very minor changes • small phase changes · Velocities • general increase in velocities in vicinity of reclamations 17 Navigation · possible problems • Changi East Finger – increase in current velocity of existing eddies • small eddy formation on western side of Pulau Tekong · Increased velocities do not cause problems with respect to guidelines for required width of shipping channels (including 2•way traffic) 18 9 SHIPMA simulations 19 Sediment transport & morphology · Cohesive sediments throughout • generally stiff to hard clays (or dense silty sands) overlain by recent deposits of soft clay or sand (in Calder Harbour) • estuary appears to be stable at the moment 20 10 Surficial sediments 21 Cross section – Calder Harbour Type 1A: very high plasticity soft clay Type 1B: intermediate plasticity medium stiff fluvial clay Type 1B: very high plasticity medium to very stiff clay Type 1C: sand Type 2A: firm to hard silty clay/clayey silt (residual soil) 22 11 Impacts – erosion & scour · increased velocities may lead to erosion of soft top•layers, but only down to the hard underlying layer • top•layer thickness is variable throughout the area • erosion of top•layer could take decades • depth of scour hole related to thickness of soft top•layer 23 Example of surface erosion Consolidated mud from IJmuiden harbour, The Netherlands (30kPa) 24 12 Example of mass erosion Mud from Kembs reservoir, France (125 Pa) 25 Potential mass erosion · isolated locations of potential mass erosion were identified • extra precautions taken on site to quickly complete sandkey foundation • sandkey & stone revetment successfully completed without further problems on site 26 13 Impacts – turbidity · increased erosion of soft clay layer may increase turbidity levels depending on erosion rate • lower limit of erosion rate – concentration increase would not be measurable at all • upper limit of erosion rate – concentration increase will only last about one year – probably not practically measurable – most realistic estimation is increase in concentration in the order of 1 mg/l, from about 40 mg/l to about 41 mg/l 27 Mangroves 28 14 Mangrove coast erosion 29 Mangroves • impacts · no changes to tidal inundation frequency, tidal amplitudes, sea•levels, concentrations of nutrients, runoff characteristics & freshwater inputs · no effect on the health of mangrove swamps that are currently ‘thriving’ · most serious impacts due to (external) effects from land clearance, blockage of natural drainage patterns, increased sediment runoff 30 15 Water quality · tidal volumes decrease due to reclamation of shallow areas · ‘clean’ water from Singapore Straits reaches further upstream · reduction in residence times • nutrients, organic matter, faecal bacteria, etc. washed out more quickly into Singapore Straits • slight reduction of salinity gradient 31 Aquaculture · Conditions for aquaculture likely to improve after reclamation due to improved water quality · expansion of existing floating facilities should not occur in areas of potential increased velocities 32 16 Johor River · average freshwater discharges • July: 40 m3/s • December: 120 m3/s • 100 yr return period: 1035 m3/s · Reclamation works will have negligible impact on water levels in Sungai Johor and other river basins 33 17.