- Title
- Hydrodynamics, geomorphology and vegetation of estuarine wetlands in the Hunter, Australia: implications for migratory shorebord high tide roost availability
- Creator
- Howe, Alice
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2008
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- This thesis examines the ecogeomorphological drivers for estuarine wetland distribution in the lower Hunter, NSW, Australia. Particular emphasis was on the availability of high tide roost habitat for migratory shorebirds and the effect of tidal manipulation on roost availability. The Hunter estuary is a wetland of international importance for migratory shorebirds and the availability of high tide roost habitat has been identified as a factor in the declining numbers of shorebirds utilising the estuary. These roosts typically comprise saltmarsh, shallow tidal pools and river training walls. The methodology used to explore relationships between high tide roost habitat, estuarine vegetation distribution and tidal hydrodynamics was a combination of literature review, field data collection, laboratory experiments, statistical analysis and numerical hydrodynamic simulation. Field data collection included topographic, vegetation and soil surveys; velocity, water quality and water level profiling; and high precision measurements of substrate shallow subsidence and vertical accretion. Laboratory studies examined the effects of estuarine vegetation on flow resistance. Research focused primarily on Area E of Kooragang Island, which provides important shorebird habitat and was subject to tidal manipulation in 1995. Other research sites comprised the three major high tide roosts in the estuary: Kooragang Dykes, Stockton Sandspit and Windeyers Reach. Habitat availability at these roosts was calculated under various tidal planes. The analysis indicates that habitat is limited and under threat from rising sea levels, erosion, mangrove encroachment and urban development. Mangrove surface elevation was strongly correlated with estuary water level, while saltmarsh surface elevation was moderately correlated with rainfall. The rapid response of mangrove surface elevation to changes in mean water level provides a mechanism for landward migration into saltmarsh, which reduces available shorebird habitat. An elevation deficit was found for all estuarine communities studies in the Hunter, indicating that surface elevation is unable to match current increases in estuary water level. Future sea level rise scenarios and development proposals that increase estuary water levels are predicted to exacerbate this elevation deficit, and lead to further mangrove expansion. This study quantified the elevation range, tidal range and hydroperiod of saltmarsh and mangrove habitats in the Hunter estuary. These findings define hydraulic parameters for exclusion of mangrove from wetland rehabilitation projects in southeast Australia that aim to create or rehabilitate saltmarsh, such as those designed to optimise shorebird roost habitat. Results indicate that, due to the rainfall deficit that occurs in much of Australia, it is possible to create and maintain saltmarsh at lower elevations in the tidal frame than would occur under natural tidal conditions. This can be achieved, without encroachment by mangrove, by restricting tidal flows sufficiently to maintain a maximum tidal range off less than approximately 0.3 m. This finding greatly expands the area available for potential saltmarsh creation and rehabilitation within highly urbanised estuaries. It is not a substitute, however, for conservation of remnant saltmarsh or establishment of buffer zones, where possible, to allow landward migration of estuarine communities at sites that are not conducive to tidal manipulation.
- Subject
- hydrodynamics; geomorphology; vegetation; estuarine wetlands; Australia; migratory shorebirds; high tide
- Identifier
- http://hdl.handle.net/1959.13/1312529
- Identifier
- uon:22419
- Rights
- Copyright 2008 Alice Howe
- Language
- eng
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