FAQ's Stormwater and Drainage
Stormwater Drainage Assessment
These FAQs have been provided as a guide, for more in-depth information please refer to the Stormwater Drainage Assesment Executive Summary or to the full assessment.
Why is council doing this now?
The Local Government Act 2002 has brought about some significant changes to the way councils operate, with the focus being on community consultation and participation in local government and the promotion of social, economic, environmental and cultural well being of communities in the present and in the future.
One of the new challenges for Asset Managers is the Assessment of Water and Sanitary Services, as detailed in Part 7 of the Local Government Act 2002.
Because of the importance of water and sanitary services to the community, Part 7 of the Act requires territorial authorities to make assessments of;
- Water supply (drinking water);
- Wastewater services;
- Stormwater;
- Cemeteries;
- Crematoria;
- Public toilets and
- Waste disposal.
These services are vital to health and welfare. The Act therefore requires Territorial Authorities to make assessments of these services with the primary purpose to safeguard public health.
Does this assessment include wastewater/sewerage?
No, this assessment covers the Stormwater activity only.
What is a public stormwater system?
The public system provides for the collection and conveyance of stormwater from roads and from developed areas.
Typically runoff from roads, driveways and properties is collected via kerb and channel, catch pits, open drains and conveyed through a limited piped network to discharge to open drains, streams or coastal margins. Stormwater in steeper areas is generally conveyed via open drains.
What is a private stormwater system?
Private facilities collect stormwater on-site and feed it to the public stormwater system (where it exists) or directly to streams or ground soakage. This runoff is reduced where the roof water is collected for drinking water and other usage.
Where is stormwater discharged?
There are 863 discharge points (outlets) within the urban areas that discharge to the following:
- Streams
- Beach/Coast
- Open drains (numerous drains lined and unlined)
- Detention tanks/ponds
There are also a large number of rural road culverts that discharge to streams, rivers or land.
Can stormwater run-off be responsible for notifiable diseases?
The Medical Officer of Health, Mr Jonathan Jarman has confirmed that there have been no notifiable diseases that can be directly attributed to the discharge of stormwater to rivers or the coastal environmental.
All notifiable gastro-intestinal diseases have a variety of potential sources i.e. food borne, waterborne, person-to-person, contact with animals etc.
There is little evidence to suggest that public health is compromised by stormwater discharges.
According to Northland Health it is difficult to draw conclusions as to what aspect is to blame for gastro related illnesses arising from polluted stormwater.
What is council doing to plan for current and future increased capacity needs?
Council has taken a proactive approach and has scheduled hydraulic modelling to be undertaken for each urban area over the next two years. These results will be analysed and capital and renewal projects identified to remedy maintenance and capacity issues.
The urban drainage systems are planned for assessment using the SWMM model. This model allows the dynamics of the runoff process to be assessed in detail including the performance of inlets, pipes, manholes and open channels.
Information on whether the system has the capacity to carry the design flows is derived from this analysis, which involves routing both the 5 year and the 100 year storm events through the system for present development levels and maximum permitted development under the District Plan.
Modelling is complete for East Coast, and currently underway for Kaitaia, Awanui and Ahipara.
Page created/updated: 8 December 2008 at 12:25 pm
