Christchurch City Council

Source Documents

These are the council documents used to build the CCC calculator. If a link is broken, the document may have moved on the council website.

📄

Onsite Stormwater Mitigation Guide (June 2021) + IDS Part 5

PDF Primary Source

🌐

CCC Stormwater Information Page

Council website - may contain updated links if documents above have moved.

Calculation Methodology

Retention

None - detention only

Method

Rate per 100m2 of NEW impervious area. Small sites (under 1,000m2): 5.0m3/100m2, 15mm orifice. Medium sites (1,001-5,000m2): 5.7m3/100m2, 20mm orifice. Attenuate for 20%, 10%, 2% AEP.

Design Requirements

• Attenuate post-dev to pre-dev for 20%, 10%, 2% AEP
• Small site: 5.0 m3/100m2 above-ground, 15mm orifice
• Medium site: 5.7 m3/100m2, 20mm orifice
• Min 50% of total impervious draining to tank
• First flush treatment if over 150m2 new hardstand
• Sites over 5,000m2: site-specific engineered design required

Submission