This paper describes the Department of Corrections Flood Protection Improvements at Rimutaka Prison.
The Department of Corrections (Corrections) in collaboration with the New Zealand Defence Force (NZDF) commissioned the construction of a stormwater channel to divert an unnamed stream channel around the perimeter of the Rimutaka Prison facility and through land owned by NZDF. Corrections’ primary driver was to prevent reoccurrence of flooding damage within the prison, while NZDF’s key driver was the potential for environmental enhancement and restoration of the area. With the two different drivers, the project required strong collaboration between all parties to be successful.
The project consisted of 1,200m of new stormwater channel with part of the channel consisting of an environmental channel with several wetland areas and a weir to attenuate flows to restrict the downstream water volumes received to pre channel flows. The channel was designed to screen debris arriving at the prison and to provide a 100 ARI level of protection. In addition, an NZDF driver was to increase water quality and provide a natural habitat for fish species. The channel was located across both NZDF and Corrections land, between an operational prison site, an active live-firing military range complex and demolitions range that is used for training with explosives, and also for emergency disposal of explosive items discovered in the community, such as old ‘souvenir’ munitions or improvised explosive devices. Access to both sites is strictly controlled for safety and security reasons.
During construction the $2.8M project encountered several unforeseen factors including; poor ground conditions, bomb squad call outs, adverse weather, variation disputes and a police arrest. Both Corrections and NZDF required specific site protocols to be followed at all times, making the already dynamic project truly unique.