The Sand Bypass System
The Gold Coast Seaway (or Southport Seaway as it is sometimes known) boasts the world’s first permanent sand bypassing system and stands as one of the country’s most significant engineering feats from the 80s. Read about the History of the Seaway.
What is the Sand Bypass System?
The unique and innovative system consists of a steel framed jetty, constructed 500 metres out to sea and 250 metres south of the southern training wall. Ten jet pumps, suspended from the jetty at 30 metre intervals from the seaward end, are submerged to 11 metres below mean sea level.
How does it work?
Water to operate the sand bypass system is taken from the Broadwater via twin low pressure, high volume turbine pumps to the control building where twin high pressure centrifugal pumps boost the water pressure to that required for activation of the ket pumps. Sand on the seabed in the vicinity of the operating pumps is forced into the system in a water/sand mix and returned to the shore through the gravity fed flume. Here it is discharged into a conical shaped concrete hopper where excess water is decanted back to the ocean while concentrated sand slurry is pumped by a variable speed centrifugal pump through an underground pipeline, under the seaway entrance to discharge onto the southern ocean beach on South Stradbroke Island.
The system may be operated with a varying number of selected jet pumps to give optimum performance. Computer control and monitoring ensures maximum economy and efficiency of the operation. Pumping operations are normally conducted at night during off-peak power periods. Read about how we’re improving the operational efficiency of the Sandbypass system.
Why is it necessary?
The Southport Bar was incredibly dangerous until 1986 when the Gold Coast Seaway was constructed. Predominant southeasterly winds, the significant northern drift of sand and wave climate combined to move an estimated 500,000 cubic metres of sand along the south-east Queensland coast each year. Over time the Nerang River mouth moved northward by up to 60 metres each year, causing land erosion and changing sandbanks at the bar and adjoining Broadwater. The sand bypass system was provided for in the design of the Gold Coast Seaway as it was recognised that the breakwaters would not be effective for long without a solution to the littoral drift problem. The large-capacity fixed-sand bypassing system is an integral part of the design of the seaway.
Benefits of the Sand By-Pass System
The system currently delivers 500,000 cubic metres of sand from the spit to South Stradbroke Island each year. Today, the Gold Coast Seaway facilitates safe transit between the Broadwater and the ocean for recreational and commercial vessels. An improvement in water quality due to increased tidal exchange has enhanced biodiversity in the Broadwater. The Broadwater also has a greater capacity for flood relief. New clearance provides a minimum depth of 4.6 metres at low tide. The sand bypassing system, ongoing dredging and construction of Wave Break Island have ensured that the entrance to the Broadwater was stabilised without detriment to surrounding beaches.