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Estuaries Summary

A reflection of catchment activity

• Dynamic, important systems that link freshwater and inshore marine waters
• Highly productive and diverse habitats providing fisheries, recreation and amenity
• Australia has 36 700 km of coastline and over 1000 estuaries
• Eighty-three percent of Australia's 19.4 million people live in coastal Australia

Estuary condition

• Near-pristine - 50%
• Largely unmodified - 22%
• Modified - 19%
• Extensively modified - 9%

Processes that shape estuaries and their management

• 17% of estuaries are wave-dominated 'true' estuaries - characterised by relatively high wave energy at the mouth and moderate river energy
• 11% are tide-dominated 'true' estuaries - characterised by relatively strong tidal energy throughout the estuary and moderate river energy
• 10% are wave-dominated deltas - characterised by moderate wave energy at the mouth and high river energy
• 9% are tide-dominated deltas - characterised by moderate to high tide energy throughout the delta and high river energy
• 5% are strand plains, coastal lakes and lagoons - characterised by relatively low wave energy and low to negligible river energy
• 35% are tidal creeks and flats - characterised by moderate tide energy and low to negligible river energy

Key issues

• Establishing and maintaining protective management for near-pristine estuaries
• Including estuarine management targets within catchment management planning processes
• Implementing a clearer delineation of institutional and lead agency responsibilities for estuarine management at State and national levels
• Developing an Australia-wide estuarine specific policy and management initiative that builds on the strong industry and community commitment for improved estuarine managementl
• Providing information, training and support for local government and community-based management

Introduction

The estuary assessment collated information on 979 estuaries and was undertaken to:

• assess the condition of Australian estuaries;
• develop a process-based understanding of estuaries and their diversity across Australia; and
• contribute to an information base that can underpin and inform estuarine management.

What is an estuary?

The estuaries included in this assessment were selected according to management interest rather than strict scientific definitions.

Estuaries come in all shapes and sizes, each unique to their location and climate. Estuaries are also known as harbours, bays, sounds, marshes, wetlands, inlets, coastal lakes, deltas and lagoons.

For the purposes of the estuary assessment, an estuary was broadly described as a semi-enclosed coastal water body where:

• salt from the open sea mixes with freshwater draining from the land; or
• marine and fluvial sediments occur together.

From a strictly geomorphic perspective, an estuary is a discrete type of coastal waterway. They are defined as

... the seaward limit of a drowned valley, which receives sediment from both river and marine sources and is influenced by wave, tide and river processes.
Heap et al. 2001

Only about 26% of the Australian coastal waterways included in this assessment are 'true estuaries' in terms of the geomorphic definition.

Estuaries are the report card of the catchment

Over 40% of Australian estuaries have small catchments (<15 km²). The majority of estuaries in near-pristine and largely unmodified condition have unmodified catchments, which are either protected public lands or geographically remote.

A closer investigation of the more modified estuaries reveals that most of these have larger, more developed catchments, often with intensive development on and around their floodplains. These estuaries are generally near population centres and receive increased loads of sediment and nutrient from agricultural and urbanised catchments. Many of these estuaries suffer from the effects of severe environmental damage such as chronic algal blooms.

A strong correlation exists between catchment land use and estuarine condition. Through an improved understanding of the impacts of land use on the health of estuaries we are able to target and improve practices. Land use and catchment management in the context of estuarine and river condition will ensure more integrated and cost-effective management, building on the knowledge of cause and effect gained through monitoring river and estuarine condition.

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