Porewa Stream - Cyclone Gabrielle
Emergency Installation
In December of 2021 the Porewa Stream broke out from its bed and eroded several acres of land. Once the flood waters had receded and the stream returned to its channel, the area was filled, and trees and vegetation were planted to attempt to reinforce the bank. However before any vegetation could begin to take hold, a second flood occurred in May 2022, completely destroying the repairs and vegetation, and partially eroding the filled area. Concrete walls, blocks, and groynes placed previously were of some aid, but were again levelled by flooding within 12 hours. Many of the 2-tonne concrete blocks were rolled 50-100m down the stream.
After spending large amounts of time and capital on what were effectively temporary repairs. 150 two-tonne Rock Bags were specified and procured, as they are well-established as a highly effective and eco-friendly product. In the days before Tropical Cyclone Gabrielle struck, the bags were delivered, filled, and placed, utilising river run from on site. Being an emergency installation, the bags were placed on a shallow stop bank using the “pancake” method for the greatest coverage.
Although the scale is not comparable with the likes of the Esk Valley, the amount of water in the Porewa Stream was similar to the December 2021 flood, and without the rock bags, the damage incurred would also have been substantial (as evidenced by previous floods). Although only installed hastily on a pile of loose river run, the Fortifier Rock Bags prevented erosion, containing the stream during a large flood. Without them, the recently planted willow trees and other vegetation would again have been wiped out. Post-flood, there were no works, repairs or cleanup required.
The Porewa installation was a resounding success. After multiple costly floods, causing significant damage, a simple installation of Rock Bags was sufficient to prevent any damage to a vulnerable recovering riverbank during Tropical Cyclone Gabrielle.
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