construction and refurbishment of earthen irrigation channel banks

Yabbies are omnivorous but primarily vegetarian, favouring rotting leaves and plantdetritus. The areas where yabbies feed are similar to carp. High levels of nutrients andorganisms are abundant in these areas.Yabbie populations are often noticed under the root zone of the plants and are evident,when water levels are reduced, by the numerous burrows in the batters of channels.In adequately compacted banks, yabbies leave small indentations in the channel banks. Inolder banks that are not well compacted yabbie burrows can extend far into thecompacted bank.Photos\yabby burrows.jpgPhoto 23-4Yabby burrows in bankWhere adjacent borrow pits or roadside drains are close to the channel, yabbies tend tomigrate through the bank as water levels fluctuate. This is more common in olderdeteriorated channels. These yabbie tunnels can form leakage paths and contribute to thedeterioration of a channel bank.Yabbie damage can be controlled by:1. Removal of Yabbies2. Habitat Manipulation23.6.1 Removal of YabbiesIn practice this is very difficult to achieve in channels.23.6.1.1 Draining of ChannelsDraining of channels will not eradicate yabbies. Yabbies will survive in theirburrows adjacent to farm dams, even if the dam is left dry for 2 or 3 years. Solong as yabbies have moist burrow available they will virtually hibernate untilconditions are satisfactory for them to return.23.6.1.2 Control with FishRedfin, brown trout and rainbow trout will all eat yabbies, but the conditions inchannels are generally not suited to trout, which require clean cool water tosurvive. Redfin, a member of the perch family, accept a less critical range ofconditions than trout, and yabbies are the preferred diet for full-grown redfin.However, the food supply in the channel must be adequate for the fish to grow toyabby eating size, and the treatment of weeds in the channel using chemicalherbicides can be fatal to fish. Emptying channels during the non-operationalperiod will also adversely impact on numbers and survival rate of fish.23.6.1.3 Chemical ControlConstruction and Refurbishment of Earthen Channel Banks August 2002 - Edition 1.0 23-30