City of Greater Geelong: Eastern Park Stormwater Harvesting & Reuse
Posted under: The innovative project involved diverting stormwater that was being untreated into Corio Bay through a treatment process out into a lake system. The recycled stormwater replaces 30 million litres of mains drinking water required for watering the Historic Geelong Botanic Gardens and watering the many trees around Central Geelong. The innovative design has introduced a functional and aesthetically pleasing community asset with 600m of walking paths, 35,000 indigenous plant species and new home for flora and fauna to flourish. In addition, an entire residential catchment’s stormwater is now being treated, removing litter, sediment and nutrients from entering the Bay.
Description
The primary objective was to secure alternative water supplies to drought proof the historic and Heritage listed Geelong Botanic Gardens and to conserve valuable drinking water within the City of Geelong. This site is listed in Geelongs “Top 5 Water Users” and was purposely targeted to invewstigate a more sustainable option.
Established over a century and a half ago the Geelong Botanic Gardens has a fasinating history and recognised heritage value, Eastern Park and Geelong Botanic Gardens are listed on the Victorian Heritage REgister. Trees in the Botanic Gardens and Eastern Park are some of the finest examples in Victoria. 36 trees are listed on the National Trust of Australia (Victoria) Register of Significant Trees.
The bigger challenge as to build the enormous engineered infrastrucutre requried that would be sympathetic to this unique enviroment, receiv Heritage Victoria approval and have other functional benefits for the community.
Eastern Park is extremenly popular for locals and tourists receiving millions of visits per year. Given the importance of the plants and the volume of people whom frequented the Gardens he quality of water the porject was reqried to produce was very high. Infrastrucutre needed to be designed that would remove any public health risk whilst also removing nutrients, hydrocarbons and sediment form the water.
We looked at several locations for the water storage that would be sympathetic to the environment and community whilst hydraulically still functioning as efficiently as possible. Interestingly, our research found that up until 1925 our preferred location was the exact site in Eastern ark where a lake was until it was filled in to create a cricket field. The location was called Bunce’s Lake after the curactor that pioneered the devleopment of Eastern Park.
Because the Park is so widely used we implemented an extensive communications plan to prepare the public for the project. We invested in engaging an artist to create an impression of what the completed project might look like. The project has matched and exceeded our engineered intentions and is continuing to blend into the landscape whilst receiving widespread acclaim
Eastern Park’s rich heritage, cultural and natural values have been considered in the planning, design and implementation of the project. The finished project resembles a natural body of water and was located on the lower cricket oval.
Stormwater from a 40Ha residential catchment has been diverted from an 1100mm pipe into a SPEL stormceptor gross pollutant trap via 200m of diversion pipe. The GPT has been custom engineered to prevent bypass of litter in a large rain event protecting the water storage. Water continues to flow through the second stage of treatment, a rock filled sediment pond, over a rock constructed weir and into an open water body that holds about 4 million litres. Any water not drawn off for use is treated in the storage then overflows into a bypass back into the stormwater network.
The storage has a 500mm thick site won clay liner that is covered with a heavy grade Geosynthetic Clay Liner. The project budget prohibited the use of perfect clay to be imported from off site so we worked with what we had which was very close to specification except for the plasticity rating. To ensure the storage would last the test of time we invested in a Geosynthetic Clay Liner (GCL) to cover the floor of the storage and sediment pond.
The previous site was completely covered with the enviromental weed, Kikuyu and surrounded by large River Redgums. 35,000 wetland plants propagated offsite form indigenous seed and genetic remnant vegetation growing within 30km of Eastern Park were planted in and around the system. The water then flows by gravity into a 5.5m deep well and drawn up via a 7.5Kw Grundfos pump through 2 media filters, and ultraviolet light unit and up to storage buffer tanks ready for use.
Innovative features of the project
The core purpose of the system was to replace the irrigation requirements of Eastern Park but the use of tank’s or engineered style dams would not be appropriate in this important park. We designed the storage to hold a maximum of 2.2m deep of water but modelled it to only draw off the top meter. This would ensure the site remained visually as attractive as possible without expanses of muddy weed infested banks in drier times. In an emergency we have constructed the pump well deep enough to draw off all the water.
Our limited budget also meant we could not afford to cart spoil generated from the excavation offsite. Our solution proved to be a huge win for everyone. The sporting oval directly beside our excavation had always received complaints from cricketer’s that its slope was too great for competitive use. With the spoil we rebuilt this oval to have a greatly reduced slope and smoother surface. In addition this kept many trucks off the local roads pleasing the residents of the area and decreasing this construction’s carbon footprint.
Benefit to the community of the project or service;
The system was designed to blend into the environment and the project team are very proud to not have removed a single tree during its construction. The project offers enormous water security, environmental and financial benefits to Council for replacing the irrigation source of the Gardens but the community have received an enormous asset for recreational use also. 600m of walking paths encircle the wetland and link back up to the Eastern Park walking path. Families and people exercising are constantly adding this loop to their visit to the Park. Once the 35,000 plants mature the site will truly look like it has always been there. Families of ducks have moved in and somehow fish have been seen flipping on the surface. The treatment shed has been created with a veranda and pitched roof to be in better keeping with the environment and will double as an interpretive centre for those wishing to understand how the system works.
Costs / Benefits
Of all the alternative water or power projects Council have investigated this one has the most attractive triple bottom line assessment. The project has an 8 year payback period based off Council’s investment and the rapidly rising cost of mains potable water in Geelong. Financially this project is attractive but most importantly the prime objective of drought proofing Eastern Park and conserving mains drinking water for better purposes has been met. Participation by the thousands of user’s of Eastern Park will not be restricted by a drought or water restrictions again This part of the Park has been transformed visually which will improve passive recreation for those interested in the aesthetic appeal of the wetland or the value of the introduced flora and fauna.
The capital costs for this project were $930,000. $515,000 Council, $415,000 Australian Government
General
Through innovation, initiative and a motivation for a sustainable outcome this project has not only met its objective of creating an alternative water source for irrigation but also created an improved environmental and social outcome for the area.
A brand new habitat for flora and fauna has been created on this site which was previously an unattractive flat mown paddock. As the site matures we envisage bird life and indigenous flora to flourish.
We hope other Councils will learn from what has been achieved at this site and what is possible with minimal capital outlay to secure an alternative water supply. From a financial perspective, with the rapidly increasingly mains water costs projects like this will are looking very attractive.