Site characterisation is understanding how a particular site will respond to a rainfall event and the possible effects arising from stormwater runoff. This includes:
- Hydrological parameters (e.g. site coverage, soil type, groundwater, rainfall intensity, topography etc)
- Constraints (e.g. services, space availability, proximity to buildings etc)
- Contaminant generation (e.g. site use, likely contaminants, typical concentrations, annual loading etc)
Guidance on site characterisation
Waterways, Wetlands and Drainage Guide (WWDG)
Waterways, Wetland and Drainage Guide provides the most comprehensive guidance for site characterisation, covering all of the key parameters. Part B, Chapter 6 sets out the methodology for doing this.
Stormwater Management Devices in the Auckland Region (GD01)
For site characterisation, refer to Section B1.4 (and in particular Table 6), for an outline of the characterisation process. The Auckland data sources can be substituted with the Canterbury specific ones below.
Stormwater Treatment Standard for State Highway Infrastructure (NZTA)
This treatment standard includes guidance on the site characterisation process and requirements (Section 5.2).
Runoff – rational method for small sites
The New Zealand Building Code (E1 Surface Water) provides a verification method for the estimation of surface water runoff (section 2). This is a simplistic method suitable for small sites.
Canterbury Maps GIS data
The Canterbury Maps website provides data on depth to groundwater, soil characteristics, and other information needed for site characterisation. Examples of useful maps are given below, but it is easy to also prepare custom maps.
- Piezometric Contours
- Geological data from GNS Science
- Coastal confined gravel aquifer system
- Spring locations
Local guidance should always be used where available, but there are two main options for areas where local standards are not available:
- NIWA’s high intensity rainfall design system (HIRDS)
- NZTA’s treatment standard has a nationally applicable method for determination of water quality depth (Section 6.3 – but local methods should be used where available)
S-Map online is produced by Landcare Research and has interactive soil maps. Of particular use for stormwater are:
- Soil drainage
- Depth to hard soil/gravel/rock