by Simon Tilleard
ICEM’s Simon Tilleard travels to the Mekong Delta with his father, visiting a unique project his father managed 13 years ago to prevent river erosion from destroying communities. This environmentally sensitive approach is proving effective and could provide a model for river bank protection today.
“It’s working!” my father exclaimed on a recent trip to the Mekong delta where 13 years ago he designed bank protection works for the My Thuan Bridge.
The bridge links the rice basket of the Mekong Delta to Ho Chi Minh, Vietnam’s largest city. At the time the bridge was Australia’s largest foreign aid investment ever.
The bank protection design was radical. The design aimed to stop erosion more than 500m upstream of the bridge. Rather than the standard concreting of the top segment of the bank where the erosion was obvious, the design instead incorporated a series of pile grovnes to slow the river flow velocity, encourage sedimentation and reduce the cause of the erosion from at the base of the bank and the bed of the channel. This was designed to treat the cause of the erosion – not the symptom.
Fifteen years ago my father sat drinking tea in the tropical heat with a man whose house was next in line for the river’s inevitable erosion. From a maximum rate of over 20m a year retreat during the 1960 and 70s the erosion had slowed to a still formidable six metres a year.
The man smiled and slyly joked “I have waited 20 years for a riverfront house, when the river destroys my house then I will just have to go to the back of the queue again”. But the old man is still grinning, drinking his tea and enjoying his river view.
Climate change is unlikely to affect the unique design because the design addresses the root problem. Recent modelling by ICEM for the USAID Mekong ARCC project showed that with SLR and increasing floods the maximum flood depth in an average year at the location will be up to 0.4m higher – high enough to nearly overtop the existing bank.
“No problem” my father claimed “the beauty of this design is that it will withstand the added pressures of climate change because it fixes the root cause of the erosion rather than just putting a concrete cap on top.”
We’ll have to come back to the My Thuan bridge in 2050 and find out if he is right.
Simon Tilleard is ICEM’s Water Resources Engineer. Simon has experience in hydrological modelling and analysis, hydraulic modelling and analysis, water quality modelling, and waterway rehabilitation/erosion control design.
Before and after pictures of the river bank at My Thuan – from 1996 and 2013. The river bank remains at the same location as in 1996, showing the efficacy of the environmentally sensitive river bank protection method.
Environmentally sensitive river bank erosion control
The banks of the Mekong River erode because of natural processes land and river uses and climate change. Infrastructure and livelihoods become threatened.
The usual response to Mekong erosion is concrete revetment. This has a profound environmental impact at the land-water interface with a reduced ability for the environment to adapt to variations (such as climate change). These methods are also prone to structural failure by scour when environmental conditions change
AusAid took a different approach in 2001 for erosion control works upstream of the My Thuan bridge
In 1996 erosion upstream of the bridge site was severe – but as Simon and his father verified – the erosion is now controlled at this same location. In 1996, bank retreat upstream of the bridge was up to 35 m per year before the works.
The erosion control system design and construction involved 12 lines of 100 submerged piles extending 100 m out from the river bank. This slows the flow against the bank over 2 km of river. Following construction, the works were monitored by velocity measurement, satellite comparisons and diver inspections in 2002, 2003 and 2004. The water velocity measurements post construction confirmed that the groynes were successful in reducing velocity near the bank. The Tilleards’ recent observation confirms that works have successfully arrested bank retreat while maintaining “natural” bank conditions.