myGeobrugg
Year of installation
2021
Initial situation
The best management of slash material is at the source. However, even with the best practices, unforeseen extreme weather events can mobilise tree waste and debris into river channels which can cause significant damage to downstream assets. Historically in New Zealand forestry slash-catching barriers are built in-house with various combinations of rope, railway irons and recycled steel members which are then secured back to the bank with deadman anchors. These structures are effective at stopping small volumes of slash material but risk catastrophic failure from overload subsequently releasing a large volume of material downstream at once. Rayonier Matariki Forests wanted to be proactive and set a new protection benchmark by installing a Geobrugg 1:1 tested and engineered solution, common in Europe but a first in NZ. Although designed for an extreme weather event, the intention is that the barrier is never significantly impacted through slash management at the source and then it can then be dismantled and used at another similar location.
Description
A VX140-H4 was installed in the river channel near the boundary of the 800ha catchment. The barrier height and location were chosen to utilise the large upstream catchment area for log and debris accumulation. The location also has good access for future maintenance/clearing if required. The VX140-H4 System (140kN/m²) was selected to provide sufficient capacity for both the static and dynamic loads of debris and driftwood (slashing) events. Wire rope anchors were used to transfer the loads back into the ground and provide design redundancy should some bank erosion occur. Edge protection was also installed on the top rope to protect the structure in the event of overtopping.
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