WATER LEVELS AND SALINITY - Love Our Lakes · Hydrodynamics of Gippsland Lakes 3 MAIN...
Transcript of WATER LEVELS AND SALINITY - Love Our Lakes · Hydrodynamics of Gippsland Lakes 3 MAIN...
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WATER LEVELS AND SALINITY WHAT DRIVES THE HYDRODYNAMICS OF THE GIPPSLAND LAKES ?
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2 Hydrodynamics of Gippsland Lakes
BACKGROUND
CONNNECTION WITH THE GIPPSLAND LAKES
• Mid 1970s-early 1980s Student field trips in “Environmental Fluid Mechanics”
• Mid 1980s-2000 numerous hydrodynamic and coastal process studies for Esso (including full re-evaluation of design storm conditions in the region)
• 1998 – Co-supervisor of a student project on modelling sediment transport in LE
• 1999-2004 – Peer Reviewer for the Gippsland Lakes Flood Study
• 2001 – Peer Reviewer of the hydrodynamic modelling for CSIRO’s GLES
• 2005 – Water Technology study into the effects of a 2nd Entrance at Ocean Grange
• 2006-2007 – Water Technology study into Climate Change and Sea Level Rise for Gippsland Coastal Board (jointly with Ethos NRM), on-going SLR studies
• 2011- Co-supervisor of the hydrodynamic modelling component of a PhD study into modelling the Ecology of the Gippsland Lakes
• 2012- Water Technology detailed Coastal Hazard Assessment for the Gippsland Lakes
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3 Hydrodynamics of Gippsland Lakes
MAIN CHARACTERISTICS
• Largest coastal estuarine lagoon system in Australia
• Surface area of about 360 km2
• Inflows from 6 major rivers with total catchment area of over 20,000 km2
• 3 main interconnected lakes with inter-connecting channels
• Open to Bass Strait via an artificial entrance at Lakes Entrance
Lakes Entrance
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4 <<Name of presentation to go here>>
BATHYMETRY
3m
5m
5-7m
2m
7m
1-2m 8-10m
1-2m 5-10m 3m
2-3m 5m
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5 Hydrodynamics of Gippsland Lakes
LAKE FORCING
MAIN MECAHNISMS DRIVING THE HYDRODYAMINCS OF THE LAKES
External Forcing
• River inflows (Thomson, Latrobe, Avon/Perry, Mitchell, Nicholson, Tambo)
• Ocean water levels: - astronomical tidal variations - non-tidal meteorological effects (storm surges, coastal trapped waves)
Internal Processes
• Density currents (salinity intrusion, reduced vertical mixing, enhanced sedimentation)
• Rainfall (typically: 600mm on Lakes, and up to 1,200 mm on the upper catchment)
• Evaporation (typically 1,200 mm)
• Atmospheric pressure (inverse barometer effect)
• Wind: - wind-driven currents - waves (enhances vertical mixing and sediment re-suspension in shallow areas) - wind set-up (up to 0.5m or more) and “seiching” (0.25 - 1.5 hours)
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6 Hydrodynamics of Gippsland Lakes
CONCEPTUAL MODEL (CSIRO)
Conceptual model of salinity within Gippsland Lakes .Numbers denote typical salinity concentration (ppt) & colours show salinity variation WEBSTER, I. T., PARSLOW, J. S., GRAYSON, R. B., MOLLOY, R. P., ANDREWARTHA, J., SAKOV, P., TAN, K. S., WALKER, S. J. & WALLACE, B. B. 2001. Assessing Options for Improving Water Quality and Ecological Function Gippsland Lakes Environmental Study CSIRO.
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7 Hydrodynamics of Gippsland Lakes
RIVER INFLOWS
Catchments
• Latrobe 4,671 km2
• Thomson 3,772 km2
• Avon/Perry 2,644 km2
• Mitchell 4,864 km2
• Tambo/Nicholson 4,202 km2
Flood Levels L.Well L.Ent
• 100 year 2.2 m 1.8 m
• 50 year 2.0 m 1.6 m
• 20 year 1.7 m 1.3 m
1998, 2007 approx 20 year
2011, 2012 somewhat less
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8 Hydrodynamics of Gippsland Lakes
OCEAN WATER LEVELS
Tide at LE Training Walls (GPorts)
• MHW Spring 0.4 m
• MHW Neap 0.2 m
• Spring Tidal Range 0.8 m
• Neap Tidal Range 0.4 m
Storm Surge (CSIRO, 2007)
• 100 year 0.76 m
• 50 year 0.75 m
• 20 year 0.62 m
Storm Tide (CSIRO, 2007)
• 100 year 1.04 m
• 50 year 0.98 m
• 20 year 0.89 m
Sea Level Rise 0.8 m by 2100
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9 Hydrodynamics of Gippsland Lakes
HYDRODYNAMIC MODEL (YAFEI ZHU)
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10 Hydrodynamics of Gippsland Lakes
WATER LEVELS AT METUNG
Tide at Metung Jetty
• MHW Spring 0.06 m
• MHW Neap 0.02 m
• Spring Tidal Range 0.10 m
• Neap Tidal Range 0.05 m
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11 Hydrodynamics of Gippsland Lakes
WATER LEVELS IN LAKE WELLINGTON
Tide at Bull Bay
• MHW Spring 0.01 m
• MHW Neap <0.01 m
• Spring Tidal Range 0.02 m
• Neap Tidal Range 0.01 m
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12 Hydrodynamics of Gippsland Lakes
WATER LEVELS
SUMMARY
• Rapid attenuation of the tide through the Entrance and Reeve Channel
• Tidal range in main body of Lake King and Lake Victoria approximately 1/10 that in Bass Strait
• Further attenuation of the tide through McLennans Strait
• Tidal range in Lake Wellington reduced to about 1/40 that in Bass Strait
• There is little attenuation of longer duration storm surges
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13 Hydrodynamics of Gippsland Lakes
RIVER INFLOWS 2010/11/12
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14 Hydrodynamics of Gippsland Lakes
SALINITY AND TEMPERATURE
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15 Hydrodynamics of Gippsland Lakes
SALINITY AND TEMPERATURE
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16 Hydrodynamics of Gippsland Lakes
SALINITY AND TEMPERATURE
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17 Hydrodynamics of Gippsland Lakes
WATER LEVELS AND SALINITY
CONCLUSIONS
• Tide does not play a significant role on mixing within the main bodies of the Lakes
• Storm surges (at 5 to 20 times the tidal range in the Lakes) have a relatively much greater effect on mixing
• Fresh water inflows (or lack of them) play a significant role in the flow of water through the Lakes system and are the main driver affecting the salinity of the Lakes
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18 Hydrodynamics of Gippsland Lakes