Simple Estuarine Response Model

indicators

model description

forcings

case studies

Case studies

Introduction

Case study estuaries serve two purposes. Firstly, they provide an assessment of the model performance in five quite different estuaries. The estuaries chosen include lagoons, tidal and salt-wedge estuaries from a variety of climate zones. In fact, a broad range of estuarine parameters are evident in the case study estuaries. Secondly, the case study estuaries provide examples of the application of the SERM model to specific estuaries, and the interpretation of model results.

The case study estuaries are:

Brunswick River, NSW
Huon River, TAS
Maroochy River, QLD
Port Phillip Bay, VIC
Wilson Inlet, WA

Case study results can be viewed at the SERM interface using the Case study tab. For each indicator listed, three sets of statistics are given. The top colourbar, labelled obs, gives the statistics for the observed data. The second colourbar, labelled focused, gives the statistics determined from simulations using estuarine parameter values given below, and tailored as closely as possible to each estuary (e.g. Depth = 2.3 m for Brunswick River). The third colourbar, labelled serm, gives the statistics using the standard SERM parameters ranges.

Compare serm to obs. to assess the serm outputs against the observed data. Mismatches are due both to limitations in the model and to the coarse sampling of estuarine parameters in the standard SERM database.

Compare serm to focused to assess the effects of replacing the "true" values for estuarine parameters with the nearest values available in the SERM database.

Compare focused to obs. to assess the coupled physical-biological model against observed data. Remember that focused still requires a very coarse representation of estuarine circulation, so mismatches may be attributed either to the ecological model, or the simple circulation model.

Brunswick River

General description

The Brunswick River is a tidal estuary in northern NSW.

Estuarine parameters

Estuary type	Thin Tidal
Depth	2.3 m [SERM range: shallow (1-3 m)]
Fresh water replacement time	Annual mean river flow is about 1.4 m³ s^-1. This flow would deliver a volume equal to the estuary volume in about 9 days. [SERM range: short (4-20 days)]
Tidal range	1.5m tidal range at mouth [SERM range low (1-3 m)]
Climate zone	mostly summer rainfall
Point source loads	Sewage treatment plants contribute about 8.4 tonnes N per year. This is equivalent to an areal load of about 48 mg N m^-2 day^-1. [SERM range: high (20-100 mg N m^-2 d^-1)]
Inflow colour (CDOM)	1.0 m^-1. [SERM range: medium (0.5-2 m^-1)]
Catchment clearance	50% cleared [SERM range high (20-100 %)]

Model performance

A comparison of the model performance against observed data is available from the SERM interface case studies page.

Acknowledgements

We are grateful to Angus Ferguson and Jennita Gay, University of Southern Cross for making available an extensive data set, and Byron Shire Council for their interest in this project.

Huon Estuary

General description

Huon Estuary is a long, thin saltwedge estuary in south eastern Tasmania.

Estuarine parameters

Estuary type	Saltwedge 40 km long, 500 m wide
Depth	10 m [SERM range: deep ( m)]
Fresh water replacement time	Annual mean river flow from the variety of rivers that run into Port Phillip Bay take approximately 10 years to fill an equivalent volume to the estuary. [SERM range: long (100-500 days)].
Tidal range	Tidal range at mouth 1m. [SERM range: low 1-3 m].
Climate zone	uniform rainfall
Point source loads	Sewage treatment plants contribute about 29 tonnes N per year, and aquaculture 140 tonnes N per year . This is equivalent to an areal load of about 6.46 mg N m^-2 day^-1. [SERM range: low ( mg N m^-2 d^-1)]
Inflow colour (CDOM)	10.0 m^-1. [SERM range: high ( m^-1)]
Catchment clearance	0% cleared [SERM range low (2 - 5 %)]

Model performance

The model did an excellent job of predicting chl a.

A comparison of the model performance against observed data is available from the SERM interface case studies page.

Acknowledgements

The data came from the CSIRO Huon Estuary Study.

Maroochy River

General description

Maroochy River is a tidal estuary just north of Brisbane

Estuarine parameters

Estuary type	Wide Tidal
Depth	2.5 m [SERM range: shallow (1-3 m)]
Fresh water replacement time	The annual mean river flow is about 1.8 m³ s^-1. This flow would deliver a volume equal to the estuary volume in about 74 days. [SERM range: medium ( days)]
Tidal range	1.5 m at mouth [SERM range: low (1-3 m)]
Climate zone	dominant summer rainfall
Point source loads	Sewage treatment plants contribute about 110 tonnes N per year. This is equivalent to an areal load of about 64 mg N m^-2 d^-1. It should be noted that in reality most of the sewage load enters the estuary nearer to the mouth, whereas the model puts all loads into the head of the estuary. [SERM range: high (20-100 mg N m^-2 d^-1)]
Inflow colour (CDOM)	1.0 m^-1. [SERM range: medium (0.5-2 m^-1)]
Catchment clearance	50% cleared [SERM range high (20-100 %)]

Model performance

The model predicts almost continuous algal blooms through the year, and a very high annual mean chl a. While algal blooms do appear to periodically be a problem, they are certainly not continuous. The SERM model may fail to capture important physical and chemical processes which limit phytoplankton growth. In particular, the model does not capture the resuspension of sediment, which reduces light availability to phytoplankton, and therefore growth rates. The loss terms for phytoplankton, such as sinking and grazing may also be underpredicted.

A comparison of the model performance against observed data is available from the SERM interface case studies page.

Acknowledgements

We are grateful to Jonathon Hodge, QLD EPA, for the provision of data and a detail map of the Maroochy River Bathymetry.

Port Phillip Bay

General description

Port Phillip Bay is a very large coastal embayment or lagoon, around which the city of Melbourne is built.

Estuarine parameters

Estuary type	Lagoon
Depth	13.5 m [SERM range: deep (m)]
Fresh water replacement time	Annual mean river flow from the variety of rivers that run into Port Phillip Bay take approximately 10 years to fill an equivalent volume to the estuary. [SERM range: long (100-500 days)].
Oceanic flushing time	Flushing time of about 300 days, based on long term salinity balance. [SERM range: long (100-500 days)].
Climate zone	mostly winter rainfall
Point source loads	Sewage treatment plants contribute about 3,147 tonnes N per year. This is equivalent to an areal load of about 4.47 mg N m^-2 day^-1.[SERM range: low ( mg N m^-2 d^-1)]
Inflow colour (CDOM)	1.0 m^-1. [SERM range: medium (0.5-2 m^-1)]
Catchment clearance	50% cleared [SERM range high (20-100 %)]

Model performance

A comparison of the model performance against observed data is available from the SERM interface case studies page.

Acknowledgements

The data came from the Port Phillip Bay Environmental Study, conducted by CSIRO and a large number of partners.

Wilson Inlet

General description

Wilson Inlet is a coastal lagoon on the south coast of WA. A notable feature is that the opening periodically closes, and is re-opened each year.

Estuarine parameters

Estuary type	Lagoon
Depth	1.8 m [SERM range: shallow (1-3 m)]
Fresh water replacement time	Annual mean river flow is about 3 m³ s^-1 (1994-98). This flow would deliver a volume equal to the estuary volume in about 330 days. [SERM range: long (100-500 days)].
Oceanic flushing time	Flushing time of about 200 days, based on long term salinity balance. However, this estuary is alternately closed and open on a seasonal basis, and so in reality has widely varying flushing regimes. [SERM range: long (100-500 days)].
Climate zone	dominant winter rainfall
Point source loads	Sewage treatment plants contribute about 8.4 tonnes N per year. This is equivalent to an areal load of about 48 mg N m^-2 day^-1. [SERM range: high (20-100 mg N m^-2 d^-1)]
Inflow colour (CDOM)	1.0 m^-1. [SERM range: medium (0.5-2 m^-1)]
Catchment clearance	50% cleared [SERM range high (20-100 %)]

Model performance

The model captures the annual statistics of chl a, TN etc. The periodic opening and closing of the lagoon entrance, which is not represented in the SERM model, results in yearly phytoplankton events that are not well captured.

A comparison of the model performance against observed data is available from the SERM interface case studies page.

Acknowledgements

We are grateful to Dave Fredericks, Australian Geological Survey Organisation for data. We also obtained data from:

Thompson, P. and L. Twomey. The Phytoplankton ecology of Wilson Inlet.

Donohue, R. B., B. N. Jakowyna and S. W. Nelson. Nitrogen and phosporus in tributary inflows to Wilson Inlet, Western Australia.

SERM was developed as part of the Estuarine Health Theme
of the National Land and Water Resources Audit.