Fish, fisheries and fish passage

Fish passage barriers:

What slope makes a structure a barrier to fish?

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DPIRD Fisheries’ policy is a slope of no steeper than 1 in 20 in freshwater areas of the mid to upper catchment. In tidal or lower catchment areas it’s 1 in 30. Anything steeper can block fish passage, especially where several structures are in a row. Many hand-built rock weirs and leaky weirs on farms are a real problem for fish, as they’re often much steeper, closer to 1 in 10 or even 1 in 5.

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If fish can get past a steep structure when it's drowned out in high flows, is that enough?

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A drowned-out structure no longer acts as a slope barrier, but it isn't a reliable fix. In high flows, velocities can be too fast for fish to move upstream anyway. Barriers also add up: a fish that gets past one structure in a bankfull flow it may have to wait for the next bankfull to pass the next one. DPIRD Fisheries aims for 1 in 20 because it works in all flow conditions and is backed by a lot of research.

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Aren't some barriers useful for keeping out invasive fish?

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Yes, and DPIRD Fisheries takes this into account. Threatened stocky galaxias, for example, survive only above waterfalls that trout can't climb. DPIRD Fisheries is also working the removal of a weir and are considering  carp movement as a result of the project. We take a merit-based approach to consider all the aspects we can for the best outcome.  Where natives and pest fish share a system, opening up fish passage generally helps the natives, especially if habitat is improved to suit them (natives tend to prefer more flow, carp slower water).  

Choosing a crossing:

What's the best type of crossing for my site?

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It depends on the waterway class and how sensitive the fish habitat is. In order of preference:

1. Bridges. Fish don't know they're there, and they last a long time.

2. Box culverts. They should span the full channel width and must not be perched.

3. Bed-level crossings (fords). The surface follows the natural bed level.

Pipe culverts are being phased out except where fish passage needs are minimal. Causeways are no longer accepted.

Put the crossing on a straight section, away from bends, riffles and good riparian vegetation. One well-placed crossing is better than several.

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Bridges are expensive. Are there cheaper options?

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Farm bridges rarely need to carry heavy trucks, so they can be much cheaper than road bridges. We've seen log-sill bridges built from hardwood on the property, and bridges made from reinforced shipping containers. If a bridge truly isn't practical, a well-built bed-level crossing is often a good, low-cost alternative.

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Bed-level crossings aren't in the 2013 guidelines. Will they be added?

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They are in the guidelines, under a different name: "fords".

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Do I need approval to excavate the bed for a bed-level crossing or concrete mats?

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Yes. You'll usually need either a DPIRD Fisheries permit or a DCCEEW Water approval (see the next section).

Approvals:

What approvals do I need to build a crossing?

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If your site is in key fish habitat, talk to DPIRD Fisheries. Building a crossing counts as dredging and reclamation under Part 7 of the Fisheries Management Act, so a permit is usually needed. If a DPIRD Fisheries permit isn't required, the works usually fall under DCCEEW Water. It's normally one or the other, not both, and the two agencies have similar requirements. A phone call to your local DPIRD Fisheries manager, Local Land Services or Soil Conservation Service is a good first step.

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What information should I have ready?

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• How big your waterway is.

• What habitat is present (gravel beds, snags, aquatic plants such as cumbungi or phragmites).

• Any major barriers upstream or downstream, such as a waterfall.

• Photos looking upstream and downstream, and of the left and right banks.

• A first idea of the crossing you have in mind.

• How you've minimised impact, including where you've located the crossing.

The DPIRD Fisheries permit application form lists these requirements in full.

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I have an existing crossing built decades ago. Can I do maintenance on it?

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DPIRD Fisheries’ general approach is if that structure is at the end of its life, it should be replaced with a suitable crossing that has fish passage. If the maintenance is minor and doesn’t repair or substantially increase the functional life of the structure, we encourage fish passage to be included where possible and begin to educate that when the crossing is completely replace, a new design will be needed.  

Causeways:

Why are causeways no longer accepted?

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Causeways are designed to spread water in a thin sheet across the road surface, which fish can't swim against. Over time, sediment builds up on the upstream side and a drop forms on the downstream side, so the causeway becomes perched. That drop also scours under the structure.

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Causeways are still listed in the 2013 guidelines. Will the guidelines be updated?

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The guidelines date from 2013 and still list causeways, but DPIRD Fisheries practice has changed since then and causeways are no longer accepted. A review of the 2013 guidelines is in the pipeline.  

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‍Are there plans to remove or fix existing causeways?

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Under the Fisheries Management Act, new structures must include fish passage, and existing ones may need fish passage retrofitted.  DPIRD Fisheries helps councils upgrade structures, find funding, or retrofit fish passage. Options include cutting out the centre of a causeway to fit box culverts, or building a rock ramp at a 1 in 20 or 1 in 30 grade. For example, DPIRD Fisheries is working with National Parks to retrofit box culverts into a causeway at Wadbilliga.

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Are bridges with long causeway approaches a problem?

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Yes. On floodplains, long causeway approaches either side of a bridge can still affect the creek and block lateral fish movement in floods. Design the whole crossing with the flood in mind, not just the main channel.

Prioritising barriers across NSW:

NSW has about 5,000 barriers and fixes are expensive. How are they prioritised?

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DPIRD Fisheries works with councils to rank their structures. Larger, lower rivers come first, with a more case-by-case approach in smaller upper creeks. DPIRD Fisheries also looks at how much key fish habitat each fix would open up. If one causeway frees up 3 km and another 20 km, the 20 km one is targeted. The NSW Fish Passage Strategy sets out the statewide approach.

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Does Warragamba Dam have a fishway?

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No, a dam that size would probably need a fish lift rather than a fishway.

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How much do modern fish screens cost?

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Costs vary by site and design, so no single figure was available on the day. The main benefit for irrigators is much lower maintenance than traditional trash racks. The Fish Screens Australia FAQs cover costs in more detail.

Eels:

How big are elvers?

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Very small. Glass eels arriving on the East Australian Current are smaller still. Elvers heading up our rivers are generally less than about 10 cm long.

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Do eels reach waterways in and around Sydney?

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Yes, eels travel up Sydney's waterways. There are ‘famous’ eels in Centennial Park, which travel through Botany Bay, up stormwater channels and waterways that lead to the park’s ponds. There is an amazing ABC Catalyst episode on the Australia’s eel migration.  

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Can eels get up waterfalls?

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Eels are remarkable climbers and can climb obstacles like waterfalls. When conditions are wet enough they can move overland around obstacles. A participant added that short-finned and longfin eels can climb waterfalls and weirs. Even so, every barrier uses up energy they need for their long migration.

Riparian vegetation:

‍Is anyone still planting willows along waterways?

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Some people still do, mostly weeping willows. Willows change a waterway's hydrology and the food available to fish, and most willow species are declared Weeds of National Significance. Native riparian plants are a better choice. Your local Landcare group, Local Land Services or ARRC can advise on suitable species.