Greater Wellington Regional Council is to extract gravel and realign the Waikanae River channel next to the El Rancho campsite in Waikanae to manage flood risks in the area caused by a build-up of gravel on the riverbed.
Surveys have found that, following the 2016 widening of the river channel as part of the construction of the new State Highway 1 bridge for Mackays to Peka Peka Expressway, the level of the river-bed has risen by an average 1 metre over 12 months.
“This is due to the accumulation of gravel and other material flowing down the river, which has heightened the risk of flooding and must be removed,” says Greater Wellington Manager, Flood Protection, Graeme Campbell.
“We will extract gravel and other material from the river-bed next to the El Rancho campsite. This will enable us to maintain the river-bed levels and re-align the river channel, both of which are key to managing the river’s flow and level. A small rock-line will also be constructed upstream of the mouth of the Muaupoko Stream”
Work is expected to be in two phases and is due for completion by Friday 31 May 2019 ahead of the trout spawning season.
“We’re conscious of maintaining the right habitat for spawning, and we’ll ensure that fish disturbed by the gravel extraction and realignment activity will be able to escape downstream,” says Mr Campbell.
About 3,000 cubic metres of gravel and accumulated material will be extracted over five days from the dry part of the channel. The realignment of the river channel will be undertaken over eight days, of which three days will involve operations in the flowing water channel.
Greater Wellington plans to use a 20-tonne excavator or front-end loader for removing gravel and accumulated material from the river channel. The extracted material will be loaded directly into dump or road trucks. A small dozer will complete the river alignment work.
“We’re conscious of leaving a light environmental footprint, so any trail and exposed area used by the heavy vehicles during the work programme will be restored after completion of the project,” says Mr Campbell.
The cost of the project is estimated to be around $80,000 being split between NZTA, the M2PP Alliance and Greater Wellington.