ICI investigates Muri flooding options

Tuesday May 28, 2019 Written by Published in Environment
Koka Lagoon Cruise manager Serena Hunter surveys the enormous area of gouged land that was previously a carpark after flooding last year. 19052719 Koka Lagoon Cruise manager Serena Hunter surveys the enormous area of gouged land that was previously a carpark after flooding last year. 19052719

A study is underway in Rarotonga to develop options to manage flooding impacts in the Muri catchment area and sediment runoff into the lagoon.

Infrastructure Cook Islands (ICI) has engaged Tonkin & Taylor International Ltd to undertake the project, which is being undertaken in parallel with the Mei Te Vai Ki Te Vai project to improve the water quality of the lagoons in Rarotonga and Aitutaki.

At a workshop at the Muri Beach Club Hotel on Thursday around 45 participants heard that the intense and long-term rainfall in Rarotonga on the night of April 9 last year was classed as a one in 10 to 50 year event.

When primary pathways for the resulting floodwaters to reach the lagoon were blocked or unable to cope with the volume, the water took secondary pathways and gouged away significant volumes of land.

This was most noticeable in the Muri area when it flowed across the sports field and the Koka Lagoon Cruises’ carpark a few hundred metres away.

ICI said “options to deal with flooding will look at engineering solutions which provide primary systems of pipes, drains and treatment pathways for rainfall events, and secondary systems of overland flow paths for larger rainfall events, which align with natural flow paths and publicly accessible land where possible”.

“Options to reduce sediment carried by storm water flows before entering Muri Lagoon will be based on applying an integrated catchment management approach that includes conveying stormwater to the lagoon in a controlled and protected manner, and treating sediment in stormwater before it reaches the lagoon.”

Reducing the amount of loose soil generated from works on private land before it reaches the lagoon - for example, construction works, agriculture and filling in of wetlands - is also critical, ICI said.

ICI said once a preferred option is identified, detailed design will be undertaken.

 - Lawrance Bailey

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