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Baseline survey of Tamar Estuary shoreline banks

Sheehan, MC and Ellison, JC 2007 , Baseline survey of Tamar Estuary shoreline banks.

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As part of an interdisciplinary study investigating the potential impacts of the widescale
eradication of Spartina anglica (Rice Grass), an intertidal surveying program
has been established to enable the assessment of the morphology and stability of
Spartina marshes throughout the Tamar Estuary, Tasmania. Erosional scarps have
developed in the past few years, on the outer margins of marshes and in high water
banks, indicating that sediment banks are retreating. This gives downstream
consequences of increased turbidity in the water column, and perhaps re-deposition of
sediment elsewhere.
The primary objective of this report is to provide baseline data and to facilitate the
continuation of the Tamar Estuary intertidal surveying program, which will provide
an understanding of the medium and long term process acting on intertidal banks, and
allow for the timely implementation of appropriate management strategies.
This report provides details of the methodology used in this baseline survey as well as
maps to assist in the location of survey benchmarks for future maintenance and resurveying.
Baseline survey profiles are also detailed to show the type of information
that can be obtained. General comments and recommendations on major findings are
briefly discussed.
Results show that two main marsh morphologies exist within the Tamar Estuary,
differentiated from each other by edge type and the extent of vertical development.
Outer margins of marshes in the upper estuary are most susceptible to erosional
processes. Retreat of the outer edge of Spartina marshes has accelerated in the past 17
years, most likely resulting from an increase in recreational boating in the Tamar
Estuary and possible changes in climatic conditions such as increased incidences of
extreme weather events.
Erosion of high water banks both landward of Spartina marshes and where marshes
are absent is also of concern. Erosion of these landforms is likely to be contributed to
by, if not caused by non-marine erosional processes such as groundwater ‘sapping’.
Detailed geomorphologic assessment of these landforms and associate erosional
processes is required to enable appropriate future management.
Cross-sectional profiles facilitate the assessment of the long-term stability of marshes.
It is recommended that the profiles be re-measured every five years to allow
quantification of long term change in marsh morphology and stability, to provide to
appropriate management objectives.

Item Type: Report (Technical Report)
Authors/Creators:Sheehan, MC and Ellison, JC
Publisher: University of Tasmania
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