PPS 15 Planning and Flood Risk (Revised)·Page 44·6.47
Assessment of extending existing culverts
The existence of a pre-existing culverted watercourse does not automatically permit its lengthening or upgrading to meet site discharge requirements. Each application is assessed on its individual merits.
If part of a watercourse is already culverted prior to the commencement of any development, this does not necessarily mean that it can automatically be lengthened or upgraded to meet the site discharge requirements. Each application will be assessed on its own merits.
Source — /Users/richardhill/Documents/planning-arch-project/data/documents/regional/PPS 15 - Planning and Flood Risk (Revised).pdf