Publication (Technical report): Fish passage and fishways in New South Wales: a status report

Publication Type:	Technical report / Consultancy
Publication Name:	Fish passage and fishways in New South Wales: a status report

Reference Information

Throncroft, G. and Harris, J.H (2000) Fish passage and fishways in New South Wales: a status report. Technical Report 1/2000, CRCFE, Canberra.

Optional Information

Attached document(s):

- Fish Passage.pdf

ISBN:
957704887

Other information:

PDF report attached below.

Fish Passage and Fishways in
New South Wales: A Status Report

Garry Thorncraft and John H. Harris

FACT SHEET

In New South Wales, over 4000 weirs and dams have been built across inland and coastal rivers. They may be as apparently innocuous as low-level regulators used to divert water, or as large and permanent as the Yarrawonga Weir, but they all have the potential to block the movements of fish.

Fish passage - that is, the directed movement of fish past a point in a stream - can also be blocked by factors that affect fish behaviour, such as release of unnaturally cold water from a dam, or changes in the cycles of river flows that stimulate and guide migrating fish.

Various fish species migrate up-river from the sea at some stage of their lives; others swim down-river to the sea; and still others need to move from place to place within a river. When the movements are blocked the populations of these fish species are affected and they decline in numbers, sometimes becoming locally extinct. Of the 55 species of native freshwater fish living in New South Wales, 32 have now been shown to be migratory, requiring free passage to sustain their populations. The same principle applies, to some degree, to all freshwater fish species.

Only a few Australian fish species jump like salmon in the Northern Hemisphere. Australian fish use differing swimming tactics to pass obstacles. Several are even capable of climbing wet vertical surfaces.

The distance over which fish have to swim under stress to negotiate a physical barrier is important to fish passage. At many barriers with sloping downstream faces, fish may be able to ascend part-way up, only to become exhausted and be washed back downstream. To allow fish past barriers, fishways can be built.

Fishways

Fishways are structures that allow fish to pass barriers. The first 44 fishways in New SouthWales were constructed between 1913 and 1985,but they did not perform effectively, usually because of design failures. Since research into fish behaviour and fishways began in the state in 1985, 27 fishways have been built, using designs that are more reliable. Seven broad categories of fishways have been used or are being planned in New South Wales: the pool type (including vertical-slot), Denil, lock, trap-and-transport, rock-ramp, bypass, and eel fishways.

An effective fishway successfully transmits at least 95% of all fish species and individuals attempting to negotiate the barrier, and operates in at least 95% of the range of flow conditions experienced at that site.

A critical requirement of fishway design is that fish attempting to migrate must be able to find the fishway entrance and enter without delay. Then they need to be able to ascend through the fishway, exit in an area where they will not be swept back downstream, and continue with their upstream movement. These requirements usually need to be met over the full daily and seasonal cycles.

The seven types of fishways

Pool-type fishways consist of a series of inter-connected pools bypassing an obstruction. In the vertical-slot design, the fish swim through a series of vertical slots linking pools (‘cells’) along a sloping channel. The slots extend over the full depth of the channel, so both top- and bottom-swimming species can use them. This design is suitable for weirs up to 6 m in height.

Denil fishways have a series of internal, upstream-sloping ‘U’-shaped baffles along a sloping channel, with large resting pools for every 1 m of vertical rise. This design can be used in steeper channels than vertical-slot designs. It can be prefabricated and installed in many existing, ineffective pool-type fishway channels.

Lock fishways attract fish through an entrance similar to that of a pool-type fishway. Instead of swimming up a channel, fish accumulate in a holding area at the base of the lock. This holding area is then sealed and filled with water to reach the level of the water upstream of the barrier. Fish are then able to swim out of the lock. The Deelder fish lock is a variation of the lock fishway for use on low barriers and in restoring ineffective fishways.

Trap-and-transport fishways attract and trap fish below a barrier and then physically transport them over it. The initial trapping is commonly done in a short section of pool-type fishway, and the fish may then be transported by pumps, or in hoppers carried by road, rail or cables. This design is currently under consideration for use in New South Wales.

Rock-ramp fishways are simple fishways designed to mimic conditions in stream riffles. They may be less inexpensive than other designs. Large rocks are carefully placed to form a series of transverse small pools and falls, of 100-150 mm, at about
2 m intervals. They are generally built on a slope of 20:1. This design can also be built over only part of the width of the stream, with a return leg to bring the entrance close to the weir wall. Assessment of rock-ramp fishways in New South Wales has shown that small and juvenile migrating fish species are able to ascend during low flows, although larger fish may require higher flows to provide passage.

Bypass fishways are successful in Europe and are under consideration for New South Wales. They are low-gradient earthen or rocky channels that mimic the structure of natural streams, and are often described as ‘nature-like’ fishways.

Another specialised type of fishway is the elver pass - generally a small-diameter pipe or channel lined with some material such as coarse brushes, which provide migrating juvenile eels with a damp, complex surface through which to wriggle.

Assigning priorities

With so many barriers for fish to overcome in New South Wales rivers, the question is where to start. A scheme has been devised for assigning priority to each barrier, based on 11 factors: (i) the relative size of the whole stream system; (ii) the location of the barrier in the system relative to the migratory needs of local fish; (iii) whether threatened species are present; (iv) the amount of upstream habitat that would become accessible when a fishway is installed; (v) other artificial and natural barriers downstream of the site; (vi) the proportion of the whole catchment of the particular stream which lies upstream of the site; (vii) the frequency with which high flows create effective drownout conditions at the site, so that head loss and velocity are minimal and fish can swim over the barrier; (viii) the barrier type and structure; (ix) whether there is an ineffective fishway on the barrier; (x) the likely cost of building a fishway; (xi) the level of financial and other support for a fishway from landholders, local government, industry, community groups, etc.

Regulatory responsibility

The state department, NSW Fisheries, is committed to restoring fish passage. The department has regulatory responsibility for protecting fisheries resources and providing fish passage, and, under the NSW Fisheries Management Act 1994, may require a fishway to be built around any new in-stream barrier. The State Fishways Program has been created to link the engineering expertise of state government agencies such as the NSW Department of Land and Water Conservation with the fish-biology expertise of NSW Fisheries, to build successful fishways.

For more details, and diagrams of the fishways, read Fish Passage and Fishways in New South Wales: A Status Report by Garry Thorncraft & John H. Harris, technical report no. 1/2000 published by the CRC for Freshwater Ecology, May 2000.

Please order technical Reports from:

Murray-Darling Freshwater Research Centre
PO Box 921
Albury NSW 2640

Phone: 02 6058 2300
Fax: 02 6043 1626
Email: enquiries@mdfrc.canberra.edu.au
Australia http://freshwater.canberra.edu.au

Search classifications

Administration