WATER LEVELS AND SALINITY - Love Our Lakes · Hydrodynamics of Gippsland Lakes 3 MAIN CHARACTERISTICS • Largest coastal estuarine lagoon system in Australia • Surface area of

WATER LEVELS AND SALINITY WHAT DRIVES THE HYDRODYNAMICS OF THE GIPPSLAND LAKES ?

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


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

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


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)


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.


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


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


HYDRODYNAMIC MODEL (YAFEI ZHU)


WATER LEVELS AT METUNG

Tide at Metung Jetty


• MHW Neap 0.02 m




WATER LEVELS IN LAKE WELLINGTON

Tide at Bull Bay


• MHW Neap <0.01 m




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


RIVER INFLOWS 2010/11/12


SALINITY AND TEMPERATURE






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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WATER LEVELS AND SALINITY - Love Our Lakes · Hydrodynamics of Gippsland Lakes 3 MAIN CHARACTERISTICS • Largest coastal estuarine lagoon system in Australia • Surface area of