Groynes, Training Walls, and Sand Bypass System

My Coastal Processes and Management class went on a field trip to the Gold Coast to look at sand movement. We started out at Point Danger right on the border of Queensland(QLD) and New South Wales (NSW). The Tweed River is just over the border in NSW. The long rock structures at the mouth of the river are called training walls. They are designed to improve navigability of the river entrance by keeping the sand from moving across the river mouth and making it impassable. They also narrow the channel to increase the velocity to keep the sand out of the way. The first training walls were built in about 1900 and are now back inland and new ones which we see now were built in 1962. In looking at the pictures, the land on the far side of the river and training walls is further out than on the near side. This is caused by longshore drift (LSD). LSD is the movement along Australia's east coast caused by prevailing winds out of the southeast. These winds and LSD are also part of the East Australian Current (EAC). For those of you who have seen Disney's Finding Nemo, the EAC is what Marlin goes along (remember the turtles) to find Nemo. Anyways, the LSD moves sand northward along the coast. The net movement is about 500,000 cubic meters per year, the highest in the world. Back to the Tweed River, remember that NSW is south of QLD and that LSD moves sand northward. NSW built the training walls which started trapping the sand causing a deficit along QLD beaches and with cyclones and normal beach movement buildings started falling into the water because the sand was moving northward and there was none to replace it. As we moved north to our next stop at Currumbin Beach we looked at the groynes, rock walls used to help retain sand, that were built to keep the Surf Life Saving Club building from being washed away. Since 1985 all the high rises that are built in the area, the sand from the basements all has to go to the beach as part of the beach nourishment program. When we stopped at Surfers Paradise for lunch I looked around at all the buildings and they must have had a lot of sand added to the beach! We then carried on to near the Nerang River to talk to a man who helped design the submerged breakwater and artificial reef to protect the Gold Coast Highway. Building started in 1999 of the artificial reef and then sand bagging to keep the 1 million cubic meters of sand pumped in, called beach nourishment. When I say sand bagging, don't think of the 50 pound bags you can carry. Try 300 tons per bag. The whole project cost around 8 billion Australian dollars. Our last stop was at the Southport Spit Sand Bypass System station. This system was set up around the entrance to the Gold Coast Broadwater, known as the Gold Coast Seaway. Training walls similar to the ones at the Tweed River were build, but this time the Queenslanders were thinking and had seen the problems caused by the Tweed. The Sand Bypass system was also built at the same time in 1986. Considered to be one of Australia's most significant coastal engineering projects, pumping some 500,000 cubic meters(give or take) about 1 1/2 km from the south side of the training walls to the north side to keep that LSD sand movement going. This is the world's first permanent sand bypassing system. A jetty or pier sticks out with a pump every 30 m. The pumps aren't run all at once. Each day measurements are taken to decide which one or ones are used and they are run each night between 9pm and 7am and on the weekends from 9pm Friday to 7 am Monday, using off-peak electricity times. The system moves about 600 cubic meters per hour. In the picture of the machine that takes out all of the non-sand objects, I talk about body parts. No joke. A man drowned down shore from the pumps and part of his body was found in the machine. Sad but true. Anyways, now back to the Tweed River. You may have noticed that there was a long pier near those training walls too. Well, after the system at the Gold Coast Seaway was built pressure was put on NSW to do something. In 2000 the Sand bypass system was completed at the Tweed River. Overall it was a very interesting and enlightening trip. Who knew the Aussie beaches were so complex?

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Looking back now on the first half of the semester I think it’s very interesting how I'm taking 4 classes from 3 different schools and they are all so interrelated. Things I learn in one are backed up in another. Maybe I really was right when I designed my major! :-)

Cheers! Megan