Mt Wellington Watercourse Classification
The Auckland Unitary Plan has new rules for developments near streams and rivers to protect natural watercourses.
A commercial landowner planned to expand their premises but there was an open channel along the boundary that Council had previously deemed to be a natural stream. With new definitions for streams and watercourses it was important the channel was correctly classified as it had potential impacts on the proposed building expansion.
Our site visit mapped the drainage network within the small catchment before we reviewed how this network had changed and developed as the catchment was urbanised since the 1940's.
At first glance the boundary channel appeared to be a perennial stream, however its channel was clearly artificial. A review of historic aerial photos quickly determined there had originally been a meandering channel through the catchment that was firstly straightened with a constructed channel then piped before being replaced with a very large box culvert. The boundary channel had begun as an open field drain along a fence line to help drain farm paddocks and over time had been enlarged and partly piped.
The boundary channel had previously been classified by Council as a natural stream using definitions that have been superseded. A review of historic maps showed these definitions had been interpreted incorrectly so although resource consent had originally been given on the assumption the channel was a natural stream it was clear the channel was not a natural stream and the development controls should not apply.
The original meandering channel now replaced by a box culvert remained the original stream channel despite it being heavily modified over the past 75 years. Our watercourse assessment and historic research confirmed the classification of the channel and uncovered how the earlier assessment was in error.