The change from natural landforms and vegetative cover to impervious surfaces has two major effects on stormwater:
> Water quantity (urban hydrology)
> Water quality.
This is achieved primarily by reducing stormwater flows and contaminants at source.
Most common approach is use of detention tanks to temporarily detain runoff and meet one or more of the above objectives:
o flow control, for example by throttling the peak discharge
o water quality control, for example by filtering out sediment that may contain contaminants
o volume control by water re-use
Specific site characteristics so far as they relate to management of stormwater:
· Auckland Council GIS overlays - particularly relating to aquifers, streams and Significant Ecological Areas.
· Nature and size of the development.
· Topography and catchment – site fall
· Residential zoning and existing land use
· Existing stormwater infrastructure, location, capacity.
· Flooding and OLFP (· E36 - Natural hazards and flooding)
· Receiving environments – Streams (E1 – Water quality and integrated management)
· Controls - Stormwater management area control - Stream ecology, erosion and water quality. (E10 – Stormwater management area – Flow 1 and Flow 2.)
· Knowledge gaps
From this information look at constraints for development.
Auckland Unitary Plan should be used to define land uses, maximum impervious areas and other planning constraints. Precinct chapters can also include specific stormwater requirements where these have already been defined.
The AUP requires the avoidance, as far as practicable, or otherwise, the minimising or mitigation of adverse effects of stormwater runoff from greenfield developments.
Stormwater management involves careful application of site design principles, construction practices, and maintenance operations to prevent sediment and other contaminants from entering surface water, groundwater, or our coastal environments.