How the Gold Coast's new backpass pipeline will work
Though the wider surfing community has heard little about it, Gold Coast City Council (GCCC) is currently building a project that has the potential to improve surf conditions at the northern end of the coast.
It also has the potential to affect other, good quality waves on the same stretch of coast.
The project is called the Surfers Paradise Sand Backpass Pipeline Project, and it will serve two purposes, one of which is to alleviate erosion on the beaches between Surfers Paradise and The Spit, focussing on the Narrowneck stretch. To do this, a portion of the sand that's currently pumped across the Southport Seaway to South Stradbroke Island, will be pumped southwards, back down the coast towards Surfers Paradise.
To achieve this, 6.3 km of permanent pipe will be laid underground from the Seaway to Surfers, which will connect to flexible above ground piping that can divert outlflow to different stretches of beach.
To fully understand the dynamics of the project we've got to wind the clock back to 1986 when the Southport Seaway was built. The primary purpose of the Seaway was to stabilise the mouth of the Nerang River which was moving north at a rate of 50m per year, and this was done by bulding two rockwalls. The project also required sand to be pumped from the southern rockwall, underneath the Seaway to an outflow pipe on the northern side.
Historically, approximately 500,000 cubic metres of sand is pumped across to South Stradbroke Island each year.
However, since the Seaway was built, coastal engineers from GCCC and Griffith Centre for Coastal Management have noticed two things happening in the area. The first is that beaches along the northern end of the Gold Coast have been eroding, and the second is that the shoreline at South Straddie has been accreting.
The purpose of the Backpass Pipeline Project is to balance the two. When it's operational, the pipeline will be able to divert 120,000 cubic metres - or almost one-quarter - of the annual sand allowance that reaches South Straddie.
The change in sand flow has the potential to alter surf quality, but since the GCCC's Surf Management Plan was established, surfing amenity is factored into each coastal project. To that end, the council contracted Professor Andy Short to investigate changes in coastal processes, and Professor Short also presented his findings to the World Surfing Reserve Local Stewardship Committee, as representatives of the broader local surfing community.
Considering the quality of the surf at South South Straddie, surfers will be particularly sensitive to changes on that side of the Seaway. When asked, Professor Short told Swellnet he could foresee no issues regarding surf quality.
"TOS won't change. It's a product of the ebb tide delta and swell lines refracting around that to form peaks."
"The shoreline will be monitored every few weeks," said Professor Short, "as will the sandbank situation, and those findings will be used to make decisions on how much sand will be pumped, and where it will end up."
Wherever the sand ends up, whether it be Surfers Paradise, Narrowneck, or the Spit, the outflow pipe will release the sand on the beach with excess sand dispersing through the swash zone within days. Most backpass pumping will happen during the winter months so as not to interfere with beachgoers.
Stage 1 of the project is almost complete, however Stage 2, which involves switching the pipeline on, won't be finished until 2022.
Taking Professor Short's findings at face value, surfers have no need to worry about a reduction in quality at South Straddie, but what happens to the sandbanks on the south side is unknown. What is known is that, in terms of quality, the northern end of the Gold Coast is coming off a low base.