Table 10: Risk associated with water delivery in the Lachlan catchment. Risk type Description Likelihood Consequence Risk level Mitigation Salinity Lakes Brewster and Cargelligo—often sources Likely Moderate Medium The Water Sharing Plan has a for environmental water delivery—frequently 20,000 ML Water Quality have salinity levels higher than those normally Allocation available in Wyangala found in the river due to evaporative Dam for relief of water quality processes. Released water from these sources problems. See also blue-green may increase salinity levels in the river and algae below. delivery targets. Salinity may also increase in weir pools during Continuous flows during summer low flow or no-flow periods. months. Blue-green Toxic blue-green algal blooms have occurred Likely Major High The Water Sharing Plan has a algal blooms frequently on the Lachlan, primarily on the 20,000 ML Water Quality lower river around and downstream of Lakes Allocation available in Wyangala Cargelligo and Brewster, generally starting in Dam for relief of water quality summer months and extending into the late problems. Historically the water autumn. Releases from Lake Brewster have required from Wyangala to commonly been a seeding source for these relieve algal blooms has been at blooms in the river downstream. relatively low discharges, 300 ML/d. If there are blue-green algal blooms in the Lake Brewster, the release of environmental water
Table 10: Risk associated with water delivery in the Lachlan catchment. Risk type Description Likelihood Consequence Risk level Mitigation Salinity Lakes Brewster and Cargelligo—often sources for environmental water delivery—frequently have salinity levels higher than those normally found in the river due to evaporative processes. Released water from these sources may increase salinity levels in the river and delivery targets. Likely Moderate Medium The Water Sharing Plan has a 20,000 ML Water Quality Allocation available in Wyangala Dam for relief of water quality problems. See also blue-green algae below. Salinity may also increase in weir pools during low flow or no-flow periods. Continuous flows during summer months. Blue-green algal blooms Toxic blue-green algal blooms have occurred frequently on the Lachlan, primarily on the lower river around and downstream of Lakes Cargelligo and Brewster, generally starting in summer months and extending into the late autumn. Releases from Lake Brewster have commonly been a seeding source for these blooms in the river downstream. Likely Major High The Water Sharing Plan has a 20,000 ML Water Quality Allocation available in Wyangala Dam for relief of water quality problems. Historically the water required from Wyangala to relieve algal blooms has been at relatively low discharges, ML/d. If there are blue-green algal blooms in the Lake Brewster, the release of environmental water 300