- Title
- Tidal dynamics and oscillations within coastal lakes
- Creator
- Hart, Roseanne M.; Power, Hannah E.; Hanslow, David J.
- Relation
- Australasian Coasts and Ports 2017 Conference . Australasian Coasts and Ports 2017: Working With Nature (Cairns, Qld 20-23 June, 2017) p. 572-578
- Publisher
- Engineers Australia
- Resource Type
- conference paper
- Date
- 2017
- Description
- The large coastal lake systems along the SE Australian coast are characterised by extensive areas of low elevation, much of which has been heavily developed. Reduced tide ranges and mild wave climates (relative to the open coast) in combination with modest flood extremes have fostered development in relatively close proximity to current mean sea levels. As such, this development is highly vulnerable to sea-level rise (SLR). In several of these systems, changes to tidal processes, including increases in the principal tidal constituents, have been observed and are thought to be associated with long term morphodynamic adjustment to entrance training. Relationships between coastal lake morphology and tidal planes and tidal ranges have been well documented; however, there are still tidal features within coastal lakes that remain unquantified and require further investigation. Fortnightly oscillations of mean water level, often termed 'Spring Tidal Pumping', have been found to be linked to interactions between inlet morphology and tidal circulation. In addition to these fortnightly and other annual oscillations, inlet morphology has a significant influence on the water level variation within coastal lakes. This has been observed over a short period of time in Lake Illawarra, for example, where the lake to ocean tidal ratio observed at Cudgeree Bay has increased from 0.01 in 2007 to 0.07 in 2010 following the completion of inlet training walls in 2008. This paper investigates variation in water levels between the ocean and lake in both Lake Macquarie and Lake Illawarra. Variations in both high and low water levels are compared with mean water levels and a full harmonic analysis is undertaken to explore the behaviour of various tidal constituents over time. Water levels within Lake Macquarie are shown to be mildly influenced by the El Niño/La Niña cycle, with minimum, mean, and maximum water levels increasing steadily within the lake. The impact of training walls and dredging can be clearly seen in both lakes, with an increase in water level range following the installation of training walls at Lake Illawarra. This increase in water level range corresponds with an increase in the amplitude of diurnal and semi-diurnal constituents and a more recent increase in the Msf fortnightly cycle. There has also been a steady increase in the diurnal and semi diurnal constituent amplitudes in Lake Macquarie, but a decrease in amplitude of the fortnightly Msf harmonic after intensive dredging works in the early 2000s. Our results suggest there is a direct relationship between entrance morphology and amplitude of tidal constituents within coastal lakes and this sensitivity to change should be considered when modelling inundation and SLR. More accurate estimates of the present and future amplitudes of tidal constituents are required to prevent over- or under-estimating the effects of future SLR along the NSW coast.
- Subject
- tides; sea-level rise; coastal risk; coastal lakes; tidal harmonics
- Identifier
- http://hdl.handle.net/1959.13/1396171
- Identifier
- uon:34010
- Identifier
- ISBN:9781922107916
- Language
- eng
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