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

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1 Study location

Tanjong Belungkor Sungai

East Johor Straits Nenas Channel Kuala Santi

Serangoon Harbour Calder Harbour

Kuala Johor Tanjong Pengelih

Changi East Finger

Singapore Straits

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Hydrodynamic Models

· Singapore Regional Model (SRM) · Eastern Singapore Local Model (ESLM) · Model (SIM)

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2 Singapore Regional Model

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SRM • detail

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3 Eastern Singapore Local Model

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Singapore Island Model

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4 bathymetry • 1

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bathymetry • 2

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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

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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

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SRModel results

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7 ESLM results

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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

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Navigation

· possible problems • 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)

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9 SHIPMA simulations

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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

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10 Surficial sediments

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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

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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

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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

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Mangroves

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14 Mangrove coast erosion

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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

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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

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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

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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

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