EVSC20004 Lecture Notes - Lecture 2: Wind Wave, Gippsland Lakes, Milford Sound
18 May 2018
School
Department
Course
Professor
LECTURE 2: ESTUARIES – PHYSICAL CHARACTERISTICS
• Estuary: body of water partially surrounded by land, where fresh water from a river mixes with ocean
water
• 22 of the worlds largest 32 cities on estuaries
• Delta: area of sediment deposition as a river flows to the ocean
• Need to have an estuary to have a delta
Classification of Estuaries
• Degree of mixing of water (effect on biota - not just level of salinity, but also fluctuations and changes
in parameters)
o Highly stratified (salt wedge) – distinct layer of fresh water on top of salt water
▪ Estuary deep, high river flow, fluvial sediments
o Moderately stratified (partially mixed)
▪ Majority of estuaries, shallow, tides overcome fluvial flow - less influence from river,
stronger flood at depth, stronger ebb at surface
o Non-stratified (well mixed, vertically homogenous)
▪ Tides fully overcome flow, shallow and wide, lateral differentiation of salinity
o Negatively stratified – arid areas, high evaporation
• Hydrodynamics: patterns of water movement
o Rivers, tides, waves - all influential, mix of influences most of the time, not usually
dominated
o Australia: usually wave-dominated (southern coast) or tide-dominated (northern coasts)
▪ Wave Dominated Estuary – barriers, tidal delta, coarse sands
▪ Tide Dominated Estuary – mudflats, sandbars, meandering, salt marsh
▪ River Dominated Estuary
• Geologic Origin
o Drowned river mouth: Sydney Harbour
o Fjords: Milford Sound
o Bar-Built: Gippsland Lakes
o Tectonic: San Fran Bay
Estuarine Processes
• Movement of water:
Waves
Tides
Rivers
• Storm
generated
• Swell
(mature
wind
waves)
• Driven by moon,
sun & rotation of
Earth
• Changes in bulge of
water on surface of
Earth
• Discharge is
volume of
water which
passes
through
cross-section
of river
Sediment
• Sediments: important in terms of biota
o Estuaries are sinks of sediments carried downstream or in from the ocean
o Evolutionary trend is for estuaries to infill with sediments
• Sediment Transport: patterns of movement of sediment around estuaries
o In a wave dominated estuary: waves provide majority of energy into the system
o Tide-dominated estuary: lots of tidal current, more energy in middle of the estuary
Origins & Hydrodynamics
Document Summary
Tide dominated estuary mudflats, sandbars, meandering, salt marsh. Origins & hydrodynamics: geologic origin, drowned river mouth: sydney harbour, fjords: milford sound, bar-built: gippsland lakes, tectonic: san fran bay. Swell (mature wind waves: driven by moon, sun & rotation of. Earth: changes in bulge of water on surface of. Earth: discharge is volume of water which passes through cross-section of river. Sediments: important in terms of biota: estuaries are sinks of sediments carried downstream or in from the ocean, evolutionary trend is for estuaries to infill with sediments. Sediment transport: patterns of movement of sediment around estuaries.
