Vulnerable estuaries

Vulnerable estuaries are susceptible to land-based pollutants such as urban stormwater or agricultural runoff and need a higher level of management to protect and maintain them.

Aerial view of Narrabeen Beach and Lagoon

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.

Excerpt of attribute table for shapefile identifying 6 estuaries in the north-eastern region of NSW that are vulnerable to land-use change

6 Belongil Creek 4B Creek
7 Tallow Creek 4B Lagoon
8 Broken Head Creek 4B Lagoon
10 Salty Lagoon 4C Lagoon
12 Jerusalem Creek 3B Lagoon
14 Lake Arragan 4B Lake

* 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

The academic citation for the dataset and this webpage is:

Dela-Cruz J and Scanes P 2021, Vulnerable estuaries and ICOLLs, Department of Planning and Environment, Parramatta.

  • DLWC 2000, Vulnerability Assessment of Estuaries in Eurobodalla and Bega Valley Shires, prepared for Eurobodalla and Bega Valley Shire Councils by the NSW Department of Land and Water Conservation, Sydney/South Coast Region.
  • Ferreira JG 2000, Development of an estuarine quality index based on key physical and biogeochemical features, Ocean & Coastal Management 43 (1), pp 99–122.
  • Ferreira JG, Bricker SB and Simas TC 2006, Application and sensitivity testing of a eutrophication assessment method on coastal systems in the United States and European Union, Journal of Environmental Management 82(4), pp 433-45.
  • Haines PE, Tomlinson RB and Thom BG 2006, Morphometric assessment of intermittently open/closed coastal lagoons in New South Wales, Australia, Estuarine, Coastal and Shelf Science 67(1–2), pp 321–332.
  • Roper T, Creese B, Scanes P, Stephens K, Williams R, Dela-Cruz J, Coade G, Coates B and Fraser M 2011, Assessing the condition of estuaries and coastal lake ecosystems in NSW, Monitoring, evaluation and reporting program. Technical report series, Office of Environment and Heritage, Sydney.
  • Roy PS, Williams RJ, Jones AR, Yassini I, Gibbs PJ, Coates B, West RJ, Scanes PR, Hudson JP and Nichol S 2001, Structure and function of south-east Australian estuaries, Estuarine, Coastal and Shelf Science 53, pp 351–384.