Legislative Assembly for the ACT: 2021 Week 11 Hansard (Thursday, 11 November 2021) . . Page.. 3447 ..
(1) With the diversion of only small flows along the Village Creek for Healthy Waterways Phase 1, eg, YA20, how will that be upscaled in Healthy Waterways Phase 2 and subsequent phases, so as to have a significant impact on reducing pollutants for both the low flows and higher flows.
(2) What modifications were made to the Gross Pollutant Traps audited as part of Healthy Waterways Phase 1 around 2014.
(3) Has a subsequent Gross Pollutant Traps audit been undertaken; if so, what were the results and has any action been taken.
Mr Rattenbury: The answer to the member’s question is as follows:
(1) YA020 was designed to divert a portion of storm flows from the adjacent drain. It receives inputs from all stormflows but, with a fixed inlet pipe size, the proportion of storm flows bypassing the asset increases as flows through the drain increase.
Large water sensitive urban design assets placed low down in catchments (i.e. like YA020) cannot process all the stormflows passing down the major stormwater trunks, so are designed to allow some flows to bypass them.
This design results in the greatest amount of pollution mitigation for the investment in a water quality asset because there are flows regularly entering and being filtered by the assets. Water quality assets can also be placed higher up in catchments along smaller stormwater channels where they can process all or most of the stormflows. Pollution mitigation by such assets is more expensive (considering the amount of pollution mitigated per year per $ of assets) because further up in catchments the assets are processing stormwater less frequently.
For Lake Tuggeranong, which is receiving significant loads of pollution in stormflows that stimulate algal blooms, it is likely that some water quality assets will need to be placed in the upper catchment to clean stormflows to an acceptable standard. This is being investigated as a part of planning activities for Stage 2 of Healthy Waterways. The Healthy Waterways team is also investigating other kinds of infrastructure that can encourage infiltration of stormwaters into catchment soils where it then gets cleansed, as occurs in a natural catchment. The combination of water quality assets, infiltration infrastructure and other initiatives like public education and improved management of public green spaces by Government are likely to be required to keep our lakes clean and healthy.
(2) There were some minor improvements made after the last GPT Audit, including the removal of some baskets for safety reasons and the cleaning of trash racks and GPTs.
(3) Another GPT audit is currently being conducted, but it was suspended with COVID work restrictions. When this is complete a review will be conducted of work required to address any issues raised.
Parks and reserves—Fadden Hills Pond (Question No 446)
Ms Lawder asked the Minister for Water, Energy and Emissions Reduction, upon notice, on 17 September 2021 (redirected to the Minister for Transport and City Services):