Source Documents
These are the council documents used to build the NCC calculator. If a link is broken, the document may have moved on the council website.
Nelson Tasman Land Development Manual (NTLDM) 2020
Calculation Methodology
Design event: 100-year (1% AEP)
Method: Rational Method (NTLDM)
Post-development peak flows for 10yr, 20yr, and 100yr ARI must not exceed pre-development at critical downstream locations. Uses Q = C x I x A x 2.78 (L/s). On-site tanks: lower 2/3 for reuse, upper 1/3 for detention.
Nelson and Tasman share the NTLDM. CPEng certification required for detention basins and dams. Consent notice on property title required.
Design Requirements
- 10yr, 20yr, 100yr ARI - post-dev <= pre-dev at critical downstream
- 1% AEP floodway design
- 5% AEP soakage system capacity
- Rational Method: Q = C x I x A x 2.78 (L/s)
- C values from NTLDM Table 7-4 with slope correction
- On-site tanks: 2/3 reuse (lower), 1/3 detention (upper)
- Extended detention: 24hr drawdown
- Detention basins: max 1:5 internal slope, 500mm freeboard
- CPEng certification required for detention basins/dams
- Consent notice (RMA s221) on property title
- Pipe velocity: min 0.75 m/s, max 6.0 m/s
Submission
Required Documents
- Catchment plan and hydrological analysis
- Hydraulic analysis with multiple duration events
- Detention sizing for 10yr, 20yr, 100yr ARI
- Resource consent copies
- Maintenance plan
- Lifecycle costing
- CPEng design certificate (basins/dams)
- Manufacturer's tank specifications
Contact
Last verified: April 2026 · NZ Detention Tank Calculator