Project number: 1998-215
Project Status:
Budget expenditure: $601,379.00
Principal Investigator: Bob Creese
Organisation: NSW Department of Primary Industries
Project start/end date: 29 Jun 1999 - 30 Sep 2004


Fish habitat in coastal floodplains will continue to degrade unless practical guidelines for improvement of water quality and management of floodgates and other tidal barriers to allow passage of fish and invertebrates are developed. This is being increasingly recognised by many decision making agencies. However, landholders will not change current management practises unless as a minimum, there will be no adverse effects to their productivity. Guidelines for change must be developed in an integrated manner with a focus on land, water, agriculture and fisheries if all industry groups are to accept the changes.

Recent studies by NSW Fisheries (some funded by FRDC) show that a change in coastal floodplain and wetland habitats from freshwater to estuarine and recruitment of fish and invertebrates to these modified habitats can be achieved by increasing the degree of “leakiness” in the floodgate barriers (Gibbs et al. 1997). However, no data are available on the relationship between fish and invertebrate recruitment and the opening size or the frequency and timing of the opening of these floodgate barriers.

A second issue is the long term impact of chronic acid drainage, which does not cause major fish kills but which may have less obvious effects on the recruitment of migratory and catadromous fish such as Australian bass, striped mullet, freshwater herring, eels and school prawns. The life history, behaviour and demography of the catadromous Australian bass shows it is susceptible to such an impact (Harris 1983,1989). The Basscatch program (Harris 1989) has expanded in recent years and the population collapse through recruitment failure of Australian bass in NSW rivers such as the Hastings and Manning is partially attributed to acid drainage (Harris pers comm).

The management of floodgates and floodplains to allow passage of fish and invertebrates and the development of stable faunal communities in previously alienated habitat above the structures significantly enhances fish and invertebrate stocks. The consequent protection of fish habitats and fish and invertebrate species supports biodiversity conservation and the habitat restoration can assist in the development of management plans under the relevant Threatened Species Legislation.

Gibbs, P., McVea, T. and Louden, B. (1997). Utilisation of restored wetlands by fish and invertebrates. FRDC Project 95/150 Final Report (In Preparation).

Harris, J. H. (1983). The Australian bass, Macquaria novemaculeata. Ph. D. Thesis UNSW.

Harris, J. H. (1988). Demography of Australian bass, Macquaria novemaculeata (Perciformes, Percichthyidae), in the Sydney basin. Aust. J. Mar. Freshwater Res. 39: 355-369.

Harris, J. H. (1989). Basscatch - A co-operative fisheries project. Modern Fishing 80-83.


1. To develop guidelines for floodgate / tidal barrier specifications and management based on: (a) The relationship between recruitment of migratory and non-migratory fish and invertebrate species and the opening size of, and the frequency and timing of the opening of tidal barriers. (b) The impacts of changed hydrological conditions on watertable and water flows in associated agricultural land.
2. To assess the behaviour of catadromous fish to the tidal flows through openings in barriers and the behavioural response of recruiting juveniles to low level (chronic) concentrations of acid sulphate soil drainage water.
3. To develop and implement an extension program on the outcomes of the project, and to communicate the above guidelines to agricultural industry groups, local government and other agencies with interests in management of land and water resources in coastal floodplains using demonstration study areas and supporting literature.

Final report

Author: Bob Creese
Final Report • 2004-10-06 • 6.36 MB


Estuarine habitats, and in particular coastal floodplains and wetlands, provide essential nursery habitat for a large number of fish and prawn species, many of which are commercially and recreationally significant. Human activities on coastal land, such as those associated with grazing and intensive cropping or industrial and residential development, can have detrimental downstream effects. For fisheries production in the estuaries of northern NSW, two of these land-based activities, drainage of acid sulfate soils and the alienation of significant habitat areas, may have severe consequences.

These two issues were addressed in this research project, the findings from which will be used to restore degraded fish habitats and enhance access to them by fish, thereby improving fisheries in affected areas.  Ultimately, fishers, farmers and landholders will benefit from improved water quality in their drainage systems. The research findings will have specific implications for management of floodgates in those catchments studied and will be more generally applicable to acid sulfate soil catchments throughout NSW and Queensland.

Project products

Guide • 1.40 MB
Restoring the balance.pdf


Many coastal floodplains in Australia have an extensive network of floodgates, constructed drains and modified water courses. These are designed to mitigate the impacts of floods and large rainfall events. Floodgates prevent flood waters and tidal brackish water from inundating low areas of the floodplain. Constructed drains have converted prior wetlands into dryland farming areas. Whilst these developments have enhanced rural settlement and industries they have also caused unintended adverse impacts to fisheries, the ecology of estuaries and downstream water users.

The expanded drainage network has increased the generation and export of acidity from acid sulfate soils. Drainage systems can rapidly transfer acidity and deoxygenated water from backswamp areas to creeks and estuaries after rain. Floodgates and constructed drains have also blocked fish movement to upstream habitat areas and provide conditions that are conducive to the formation of poor water quality, particularly water with low dissolved oxygen.

These guidelines outline principles and strategies which can be employed to improve the environmental performance of coastal floodplain drainage systems, while retaining their benefits for agriculture. They have a particular focus on reducing drainage of acidity from areas with acid sulfate soils. The benefits, limitations and risks associated with management changes are described.

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