Part 5 – Wastewater Drainage
5.6 Pipeline Minimum Grade Guideline
Section 5.3 “Calculation of Flows” does not lend itself to determining the grade applicable to pipelines draining upper parts of a catchment. Council experience is that the minimum gradients shown in the following table provide satisfactory flow conditions for 150NB Pipe in both general soils and peat soils (those with greater than 300 mm of peat between 0.5 and 4.0 m depth of the natural ground surface).
Where the depth of soil exceeds 2.0 metres then specific design is required.
| Houses | Population | General Minimum Grade | Peat Soil Grades | |
| 3–4* | 7–10 | 1:100 | 1.0% | 1:60 |
| 5–8 | 12–20 | 1:120 | 0.83% | 1:80 |
| 9–18 | 22–45 | 1:150 | 0.67% | 1:80 |
| More than 18 | 45 and above | 1:200 | 0.50% | 1:80 |
*see also the requirements for service connections Section 5.13
Advice Note: A 1:180 grade to the last lot is acceptable, for existing urban areas with less than 18 houses. Flatter grades will need specific approval from the Development Engineer to assess future maintenance impacts of any proposals.
