Bangalow Park Wetland

The storm water wetland in the park at time of writing in June 2013 is about eight months old, after construction in September 2012.

“Construction” means it’s theoretically an artificial wetland, but wetland designers use the term ‘constructed wetland’ to describe these systems.

Although they develop into naturalized wetlands over time, they need to be tightly designed initially and given engineering-type controls of pipes and weirs, usually with some kind of lined floor, to ensure the water flows in the correct way.

Most of our natural wetlands have been lost through agriculture or urban development, so these water treatment wetlands are often sited on areas that have permeable soils that would normally leak so much water that wetlands plants wouldn’t survive. So it was with the Bangalow system, which needed a clay bed beneath.

History

The project began about ten years ago when Bangalow Landcare partnered with Council engineer Dirk Wymer and Bangalow stalwart and filmmaker Terry Bleakley to apply for funding for a wetland to treat Bangalow’s stormwater.

That application was unsuccessful but the idea was born. Then four years ago Rous Water and Sustainable Futures in partnership with the Widjabul people secured funding from the NSW Environmental Trust to do four natural resource projects linked with indigenous culture.

The larger project was called “Reconnecting to Country”. A public meeting was held in Bangalow to look at what could be done in our area for one of the projects.

A number of ideas were considered, including planting more rain forest. However, the wetland was chosen for further investigation because many people liked the general idea of a wetland, the site was heavily weed-infested, it would provide a big benefit in treating polluted storm water from the main street, and it was thought there would be major biodiversity gains. In particular, birds, frogs, platypus, water dragons and other aquatic critters would be favored.

A lot of hurdles had to be overcome. Part of the site, thought previously to be Council land, was found to be privately owned, and the owner Michael Herrmann very generously donated the land. A lot of people contributed along the way, particularly the Wetland Working Group of community members. Bangalow Landcare members wrote most of the documents needed for approvals.

Extensive community consultation with meetings, newspaper stories and site inspections addressed questions and concerns around flooding, mosquitoes and other issues. The maximum depth is 300mm, except in the Western arm outlet zone which is deeper but fenced. It’s been found in operation that this deeper water is not needed, and it’s planned to place soil to make it shallower.

Council engineer James Flockton proved to be a proactive officer and secured further funding. Rous Water’s Anthony Acret provided a lot of the driving force. Sustainable Futures staff gave substantial energy particularly in the early stages.

Construction

It all came together in August 2012 when Council Works staff rolled onto the site, removed the extensive Blue Taro and camphor laurel infestations, and built the wetland to the professional design undertaken by engineering firm Geolink, and reviewed by the Working Group.

Clay from Council’s Myocum quarry was used to provide the lined floor to prevent leakage, and topsoil was spread for planting. Construction took about six weeks and was well handled by Council. Access to the park was improved with small bridges and walkways.

The system was planted by Bangalow Landcare who have committed to operating and maintaining the wetland until handover to Byron ShireCouncil.

In June 2013 most of the wetland is covered in native aquatic plants, and full coverage with design performance is expected by the spring. Two species of frogs have moved in, and ducks, Ibis and woodland birds feed on worms and insects in and around the wetland. One aspect of the vision is to see a platypus in the wetland gathering nesting material.

How it works

A design feature of treatment wetlands is to detain and treat wet weather flows. The pipe outlets are designed to restrict flows out of the system and allow slow flow along the plant beds. There are three wetland cells – an inlet cell, and two ‘arms’ – each of which coveys and treats water which flows eventually to the creek.

Runoff comes into the central inlet cell via storm water pipes, fills this cell and overflows to the other two arms of the wetland, then slowly filters through the vegetation to outlet pipes.

This wetland will treat the many smaller flows up to about 10mm of rain on the catchment, which at the moment consists of the main road from the Police Station to the Servo and all the houses south of it – probably about six hectares. Extensive research has shown that it’s these smaller flows that wash off the pollutants that collect between rainfall events and carry the majority of storm water pollutants.

Previous research on the Sportsfields Wetland (another Bangalow Landcare project) indicates the runoff contains sediments, nutrients and bacteria, some heavy metals such as zinc, and loads of grease and oil off the main road. The wetlands treat all these pollutants, and prevent them from going into the creek.

The wetland plants can tolerate elevated water levels for durations of about two weeks, while spillways allow discharge in extreme events.

The wetland in the park has been under full flood from the creek three times this year.

The major treatment function of the wetland is to address polluted runoff by managing volume variations so a steady flow can be treated, and providing a dense bed of aquatic plants as a substrate for microbial populations that do the main work of breaking down pollutants.

The next stage of the work will be placement of a pipe to bring the ‘first-flush’ flows from the main street shopping district down through the park to the wetland. Another smaller soil filter-type wetland has also been designed for the park to be built when funds are available.