In any consideration of environmental flows and blackwater it’s important to understand that floodplains and wetlands produce most of the durable carbon in the river system - wood, twigs, grass, and leaves (litter). Floods wash this material into the river where it provides a physical habitat and energy source for bacteria, fungi and invertebrates for many months and years. Invertebrates like snails eat the fungi and bacteria that grow on the plant material or eat the decaying plant material itself. This is very important to the riverine food web and river health. It would appear the millennium drought resulted in an extraordinary build-up of litter and caused both an increase in occurrence and severity of black water events over recent years.
1. The assessment of the role of environmental water management in preventing or causing ‘blackwater’ events.
A fully implemented Basin Plan with its planned environmental flows is the best chance of reducing the severest of black water events for Victoria’s northern rivers. Environmental flows, by replacing minor flooding events lost since river regulation will regularly reduce the accumulation of organic matter ensuring the impacts of blackwater are reduced at times of medium and majors flooding.
We caution that the Murray Darling Basin Plan’s ‘SDL Adjustment Mechanism’, which, allows environmental water entitlements to be offset with alternative measures that achieve “equivalent ecological outcomes”, such as re-engineering wetlands so they can be artificially flooded with less water has the potential to cause localised blackwater events. This re-engineering we suspect does not in all cases ensure the connectivity of flows, out of, and back into the river channel which are essential not only for river health but also to avoid the risks of localised blackwater events.
2. How environmental water and environmental water managers interact with, and utilise, management tools such as carryover and whether the carryover of environmental water impacts on the availability of water for irrigators.
Environmental water is held and supplied by water managers under the same rules and regulations as all other water entitlement holders. As with most water entitlement holders the carryover facility is an important management tool. The environmental water holder generally uses this facility differently to most other users in that environmental carryover water is often required very early in the season, a time when opening allocations are low. This early use of stored entitlements has the ability to free up storages space for the traditional high inflow spring period for the befit of all entitlement holders.
3. Consider what barriers exist to the more efficient use of environmental water and how these may be addressed.
The greatest barrier to the efficient use of environmental water is clearly the resistance of the Victorian government to realistically address constraints management strategy. The current strategy restricts flows in the Goulburn River to “in channel” at the expense of environmental outcomes and will inevitably lead to further severe black water events.
These constraint strategy restrictions will almost certainly rule out any ability of water managers to “shandy down” blackwater events.
4. Assess fees and charges applied to environmental water and whether these differ from those imposed on other water users
Where applicable charges applied to environmental water do not differ from other water users.
EFN believes the implementation of the Basin Plan as agreed and intended is critical to the ongoing health of our rivers. This health includes water quality, export of salt from catchments and a more natural occurrence of blackwater and algae events, critical also to all water users.
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