New solution for sediment management employed on Coffs Harbour bypass

TRANSPORT for NSW is utilising a new solution to protect local waterways as the Coffs Harbour bypass project progresses.

The bypass is under construction in an area with high rainfall and multiple hills and valleys, making it essential to manage water quality before it is released into the environment.

This is done by catching construction stormwater runoff and removing as much of the suspended solids, like clay and organic material, as possible.

This is usually done in sediment basins after rainfall events.

But in a first for NSW, the Coffs bypass team is also using high efficiency sediment basins that operate continuously.

Transport for NSW Snr Manager Environment and Sustainability Scott Lawrence said this allows stormwater runoff from the site to be managed in real time.

“Recent trials completed under the project’s Environmental Protection Licence showed impressive results in the reduction of total suspended solids using this system, compared to a standard construction sediment basin,” he said.

“During a major recent 480mm rainfall event in Coffs Harbour, the new basins achieved a 78 percent reduction in total suspended solids.

“These solids are things like clay, silt and plant debris, as well as heavy metals that bind to clay particles.

“They can choke the water, smother aquatic habitats, clog fish gills, reduce oxygen levels and carry pollutants, so it’s critical that as much of this can be removed as possible before water is released back into the environment.”

Mr Lawrence said the benefits of the high efficiency basins go beyond performance alone.

“Traditional sediment basin management often involves time-consuming dewatering, chemical handling, and for staff to work on and above water, and in challenging weather conditions,” Mr Lawrence said.

“The high efficiency basin system on the bypass includes auto-dosing technology, which reduces the need for manual chemical handling and for workers to be onsite during rain events.

“And they don’t need to be emptied after rainfall.

“Instead, they retain water, which can be reused for construction purposes, further supporting sustainable site practices and reducing demand on potable water.”