Source Documents
These are the council documents used to build the RLC calculator. If a link is broken, the document may have moved on the council website.
RITS + BoPRC Stormwater Management Guidelines (2012)
Calculation Methodology
Design event: 10-year (10% AEP)
Method: RITS + BoPRC Guidelines
Permissible discharge equals pre-development 1-hour peak. Storage volume calculated as V = 1.5 x Q x D. Water quality volume based on 90th percentile rainfall (33mm). Extended detention volume for erosion control with 24-hour drawdown.
BoPRC 2012 Guidelines apply. If stream is not stable, multiply 2yr volume by 1.2. Stream erosion control required when catchment imperviousness exceeds 3%.
Design Requirements
- RITS adopted as Code of Practice
- Permissible discharge = pre-dev 1-hour peak
- Storage volume: V = 1.5 x Q x D
- Water Quality Volume: WQV = 0.033 x Awq
- Extended Detention: 24hr drawdown
- EDV = 1.2 x 2yr 1hr volume if stream not stable
- Stream erosion control when imperviousness > 3%
- BoPRC permitted discharge levels compliance
Submission
Required Documents
- Stormwater design per RITS/BoPRC 2012
- Pre/post development flow calculations
- WQV and EDV sizing
- Engineering plans and drawings
- Resource consent (BoPRC)
- Manufacturer's specifications
Contact
Last verified: April 2026 · NZ Detention Tank Calculator