Construction of upgraded stormwater outfall at the Ozone Road Jetty Background The City of Greater Geelong (CoGG) is responsible for stormwater management within Barwon Heads. There is an existing 750 mm diameter stormwater outfall below the Ozone Road Jetty that can be seen at a low tide. This receives stormwater from the Clifford Parade pumping station, and gravity stormwater flows from inlets along Grove Street, Ozone Road and adjoining streets. The pumping station operates automatically in response to drainage inflows, and contains a litter trap. CoGG have identified that while the stormwater pipelines and the pumping station can accommodate storm events up to one every 100 years, the existing outfall restricts flows that occur at frequencies of greater than once every 20 years, resulting in localised flooding. For this reason they have designed a larger (1.6 m diameter) outfall that will discharge runoff from all storm events more quickly. This outfall will be parallel and 16 m north of the existing outfall, 14 m further out in the river channel, and 3.5 m east of the end of the jetty. Meeting and discussions Ross Middleton and John Nolan met with Martin Rushbrook from CoGG s Infrastructure Management and Mark Richards from the Engineering Design Unit on 18 th July. Conversations were also held with Vaughan Notting (Engineering Design) and Dianne Luscombe (Environment). All were forthcoming with information and requested documentation was provided. Response to matters or interest Will the catchment area be increased in the future? Will the stormwater volume increase? Outfall pipe diameter? Will there be a change in the peak discharge rates? Will the outfall be seen Will there be additional treatment before outfall? CoGG has given a commitment that catchment area draining into the outfall will not be increased now or in the future from that which currently occurs. This is accepted as surrounding local catchments have their own disposal points. No. 1.6 m. The concept design considered a 0.8 diameter as well as diameters up to 1.2 m. The hydraulic modelling was reviewed as part of the final detailed design by GHD. The larger pipe will reduce pipe friction losses that will enable higher flows from the pumps and greater gravity flows. The new tidal backflow valve will also be less restrictive on flows than the existing valve type. The new outfall will permit higher peak flows, and that will reduce the incidence of flooding in the Clifford - Grove Road catchment area. The top of the outfall will be lower than the existing pipeline and should not be seen as it be at the lowest astronomical tide The only water quality control is the Clifford Parade pumping station litter trap. CoGG has advised that it is not possible to install a gross pollutant trap (GPT) near the jetty due to: low pipeline grades; tidal influences and 1
would require a very deep pit CoGG has also advised that GPTs only work on flows up to 1 year ARIs. Bypasses are provided above these flows. When will construction occur? Will the bluestone wall be impacted? Will there be sand scouring? Scheduled to commence in late August with completion by December. The works will be undertaken by a Contractor and supervised by a CoGG Project Implementation Officer. GHD advise that a short section will be removed and reinstalled at the completion of the works. It did not require heritage consent however it is acknowledged that the wall is of historical significance. Because of this CoGG s contractor will be photographing and numbering the blocks and reinstatement will be completed by suitably qualified stonemasons. GHD undertook a sand movement study that identified local scour around piles during river floods. While this study did not explicitly consider scour associated with discharge through the outfall the flow velocity will be lower than that which currently occurs up to at least the 1 in 20 year storm event. What are the values of the vegetation that will be impacted? Ecology Partners identified a small area of dune vegetation along the foreshore consisting predominantly of introduced Marram Grass with scattered indigenous species (<25% cover) including Small-leaved Clematis, Seaberry Saltbush, Coast Saltbush and Hairy Spinifex. Grass extended toward the Barwon River shoreline. No native vegetation was present within the Barwon River or around the existing jetty. No threatened flora or fauna species were identified that are likely to be directly affected. Ecology Partners recommended that an EPBC Act referral be submitted as the works area extends about 3 m into the Port Phillip Bay (Western Shoreline) and Bellarine Ramsar site. An EPBC Act referral was made to the Department of the Environment and on 23/03/2016 GCoG received confirmation that the proposed works were not a controlled action. This means that no further assessment or approval was required under the EPBC Act before works could proceed. How will impacts on local ecological values be minimised during construction? Planning permit condition 4 requires a detailed Construction Environmental Management Plan (CEMP) to outline measures to ensure ecological values are protected during construction activities, such as weed management, soil stockpile locations and sediment control. This should include the following Ecology Partner recommendations: minimise soil disturbance to avoid erosion with sediment and erosion controls ensure contractors are aware of areas of ecological value place construction stockpiles and machinery away from areas supporting native vegetation/fauna habitat; 2
keep fuel and chemicals at least 50 metres from the foreshore. A copy of the CoGG endorsed CEMP is attached. How will vegetation be reinstated? How will risks to boats identify outfall location? What are the water quality implications? Planning permit condition 5 requires a Reinstatement Plan requires details of reinstatement and revegetation. As recommended it does not require the use indigenous plants as part of any landscaping/revegetation works as recommended by Ecology Partners. Three beacons will be placed as navigation markers. Extent of outfall does not go much beyond the jetty The water quality impact on the shoreline waters is likely to be less than that which currently occurs as: the flow volume will not increase the outfall is deeper and always submerged, as well as being further out the outfall is north of the jetty Will there be water quality monitoring? CoGG has given a commitment to conduct water quality monitoring at the jetty before and during construction. They are engaging ALS, a NATA accredited laboratory to undertake this work. BHA will work with stakeholders to facilitate an ongoing coastal water quality monitoring program, including the Barwon Coast Committee of Management, Corangamite CMA, DELWP, CoGG, and EPA. 11 th August 2017 Ross Middleton and John Nolan 3