Issues and design considerations when negotiating fish passage at everyday road causeways

Most older Australian road causeways were constructed prior to the implementation of fish passage policy and legislation and act as low-head weirs. These structures reduce fish passage, particularly upstream migrations, and negatively impact upon the distribution of native fish populations, particularly within catchments where multiple causeway structures exist. These structures can also contribute negative impacts on river morphology placing further stress on native fish populations. Age, engineering standards and increased traffic demand mean that many of these structures now require major maintenance work or complete replacement. Prior to undertaking causeway maintenance or replacement works, legislation within some jurisdictions requires asset owners to obtain approval from fisheries regulators. The approval process provides an opportunity to implement best practice fish passage techniques to ensure that the upgraded or replacement structure will provide an effective, long-lasting level of fish passage. Achieving an effective, long-lasting level of fish passage can be a difficult task for regulators because fish passage requirements are just one of many competing objectives that asset owners must meet. Within New South Wales (NSW), the ability to achieve effective, long-lasting fish passage outcomes at causeways has proved to be a challenge, particularly where budgets are constrained, or where causeways are now acting as bed control structures that are stabilising upstream habitat. To highlight the challenges associated with achieving positive outcomes for fish passage and to show what has and has not worked regarding causeway fish passage options, including rock ramp fishways, we will detail the recent design consultation process that occurred for the Sawyers Gully causeway upgrade project in northern NSW, and detail a cross-section of previously attempted causeway remediation designs. We will conclude by detailing the final agreed design of the Sawyers Gully causeway upgrade project that meets fish passage criteria, and also the economic, social, and environmental objectives