Vulnerable estuaries

We have created a dataset that identifies 101 vulnerable estuaries, including intermittently closed and open lakes and lagoons (ICOLLs). The dataset:

• identifies areas of environmental value at a landscape scale
• supports and guides decision making on the extent and type of land-use change an area can sustain
• helps protect and restore our ecological or natural assets.

Uses and values

It is important to maintain and/or restore the water quality and ecological condition of vulnerable estuaries so they remain suitable for use by local communities and industries. The estuaries are:

• used for outdoor recreation such as swimming, water skiing, boating and fishing
• valued for their natural beauty, ecology and biodiversity
• managed with interventions to restore water quality and ecological health
• of high ecological value, as recognised in existing legislation
• important for industries such as fishing and aquaculture.

Why estuaries are vulnerable

The vulnerability arises from physical characteristics of an estuary and its surrounding catchment area. These characteristics can determine where and how pollutants are transported and retained in an estuary. These include:

• catchment area
• estuary surface area
• estuary volume
• estuary depth
• estuary entrance opening and closing regimes.

These characteristics combine to influence the water in an estuary. For example, water levels can increase and sediments shift with tidal flushing. The extent and rate of this flushing is dependent on whether the estuary entrance is open or closed to the sea. Similarly, the retention of pollutants from run-off will increase in an estuary that has a closed entrance channel.

ICOLLs with a small catchment-to-estuary surface area ratio are more likely to have limited connection to the sea and will be more susceptible to a build-up of land-based pollutants.

How we created the dataset

Data on estuary characteristics such as catchment area, catchment total nitrogen load, catchment runoff volume, estuary area, volume and depth, entrance state (open or closing regimes), water level and tidal exchange volumes were sourced from the Assessing the condition of estuaries and coastal lake ecosystems in NSW: State of the catchments 2010 technical report series conducted under the NSW Natural Resources Monitoring Evaluation and Reporting Program 2010–15.

These data were used to calculate:

• tidal flushing
• dilution
• retention
• freshwater residence time
• vertical stratification
• coastal exchange
• a range of indices based on the size and shape of the estuary, including an assimilation factor.

The calculated measures were then used as inputs to 6 well-established vulnerability assessment methods based on studying the effect of many variables occurring at the same time (multivariate statistics) and grading that uses a technique based on experience (heuristic grading). An estuary identified as vulnerable in more than 4 of 6 assessment methods was considered vulnerable to land-based pollutants.

Geospatial data of the vulnerable estuaries was developed by extracting the water boundary of each estuary from the Estuaries dataset, available on the NSW Government Sharing and Enabling Environmental Data in NSW (SEED) data portal. The water boundary was defined based on whether an area was discernible in the 1:25,000 topographic map series available from the Land and Property Management Authority.

Key attributes of the dataset

The dataset has 4 key attributes:

1. ‘NTHSTH_ID’ is a unique identifier for the 184 main estuaries in New South Wales that were defined under the NSW Natural Resources Monitoring Evaluation and Reporting Strategy 2010–15.
2. ‘EstuaryNam’ is the name of the estuary.
3. ‘ROYCLASS’ corresponds to a classification system of estuaries based on morphology.
4. ‘TYPE’ corresponds to a classification system of estuaries based on response to land-use inputs.

_{* Classification of the estuary according to the Roy et al. 2001.
** Classification of the estuary according to Assessing the condition of estuaries and coastal lake ecosystems in NSW: State of the catchments 2010 technical report series.}