A complete stormwater retention solution from Polyfabrics

The Project

Riverland Estate is a master-planned community in Warrnambool. Currently under development, the site sits on the banks of the Merri River and it is subject to Warrnambool City Council’s requirements to ensure stormwater runoff is adequately managed.

Underground storage cells would need to be installed beneath the paved surface of nearby Cassidy Esplanade, totalling 248m3 or 248,000L of underground stormwater storage.

These cells temporarily retain stormwater in the case of a 20% AEP, as well as managing any additional runoff generated by residential development before it is finally discharged into the Merri River.

How Polyfabrics addressed the challenges

The underground stormwater tanks needed to be designed to withstand the desired pavement load for light-duty asphalt pavement as per Austroads specifications.

To meet this spec, a configuration of Heavy Duty mastaTANK Double modules with a compressive strength of 340 kPa / sqm was assessed as a suitable solution.

Additionally, tank invert levels were also dropped to increase cover over the tank. This would ensure good load dispersion across the soil, reducing pressures on the tank and helping to achieve the desired strength in the long term.

The main project requirement was for 248m3 or 248,000L of water storage with a 375mm inlet. A combination of Heavy Duty mastaTANK Doubles and Arches totalling 1068 double configurations were used, providing the necessary water storage. An external pipe boot made from Geomasta HDPE Bio-Liner was used to connect the 375mm inlet pipe to the mastaTANK Arches, with 300mm outlet pipes installed inline to the mastaTANK Arches for easy maintenance access. This tank and pipe arrangement perfectly met the project requirements.

Adequate flush out points were also a critical feature, so mastaTANK Arches were implemented along the low section of the tanks to provide linear access for high flow flush outs and maintenance of the tanks.

Arch plates also provided an added advantage for the Warrnambool City Council maintenance team to inspect the tanks with remote controlled CCTV cameras.

A complete project solution from Polyfabrics

The Polyfabrics team was able to assist the contractor with a full range of products to meet different requirements across this project.

Retention tanks

A combination of heavy-duty mastaTANK Doubles and Arches totalling 1068 double configurations were wrapped with Geomasta HDPE Bio-Liner and Mastatex Non-woven Class C geotextile.

These geotextiles were used to provide the desired water storage, with an external pipe boot made from Geomasta HDPE Bio-Liner installed to connect the 375mm inlet pipe to the mastaTANK Arches.

In addition, 300mm outlet pipes were installed inline to the mastaTANK Arches for easy maintenance access.

Geomasta HDPE Bio-Liner was used to line the tanks to ensure water retention.

Well-designed pipe connections

Pipe boot flanges made from Geomasta HDPE Bio-Liners were to be used to connect all inlet, outlet, inspection, and ventilation shafts to the mastaTANK Storage system to ensure reliable leak-proof joins.

Liner protection

mastaTEX Non-Woven Class C geotextile was used to cushion the Geomasta HDPE Bio-Liner on the inside and outside of the tank lining system. The addition of a non-woven geotextile helps to protect the liner from any damage during and after installation.

An additional layer of 1mm thick HDPE liner was also installed underneath the mastaTANK Arch system to provide a rigid track for remotely operated CCTV maintenance systems.

Subgrade reinforcement

Finally, a layer of mastaGRID 3030 composite geogrid was installed over the soil cover of the tanks. Positioned under the pavement subbase, this geogrid product is ideal for assisting with load dispersion and subgrade reinforcement.