Stormwater
Introduction |
About stormwater |
Solving stormwater problems |
Growth and stormwater |
What Auckland City is doing |
Stormwater projects near you |
Stormwater assets |
Stormwater guidelines and other documents |
Educational information
Solving stormwater problems
Playing
your part in looking after Auckland's waters
Auckland is a growing city. With the population expected to increase
dramatically in the next 50 years, we must plan carefully to manage this growth.
One area that will need particular attention is how we deal with stormwater, if
we are to minimise flooding and pollution in our city's streams, underground
waters and beaches, and maintain affordable infrastructure.
While Auckland City is responsible for some streams in Auckland, most pass
through private land and are known as private watercourses. It is the responsibility
of property owners to look after these streams to prevent flooding, erosion and
pollution.
This information will help you understand what stormwater is, how it
contributes to flooding and pollution, and what we can each do to minimise
stormwater's harmful and expensive effects on our natural and built
environments. We also look at Auckland City's role in managing stormwater and
what the management options are for the future.
Flooding
When it rains heavily a lot of stormwater has to be disposed of in a short
period of time. New stormwater systems are designed to cope with the volumes of
water that can be expected from a one-in-ten-year rainfall event. In fact some
pipes are so large you could drive a car through them.
Not all the pipes in our stormwater system have this capacity. Parts of the
system are gradually being upgraded, with problem
areas given priority.
However, in extreme weather the rain can be so heavy the piped system simply
doesn't have room for all of the stormwater. The pipes are designed to then
spill over onto our roads and parks, and the water must find its own overland
flow path to the sea. Always leave these overland flow paths clear, or the
water may flood your property or someone else's.
Common complaints
If a
stream runs through your property, the problems you may face include:
- flooding
- bank erosion and instability
- build-up of silt
- litter and rubbish in the stream
- vegetation blocking the stream
- pollution.
What you can do
While a certain amount of flooding during heavy rain is natural in streams,
careful maintenance should prevent serious problems with flooding and erosion.
Simple maintenance activities include:
- watching for any changes that might be happening to the stream bed or
banks
- keeping the stream clear of obstructions
- removing litter and rubbish
- watching out for pollution from upstream
- removing plants that block flow
- keeping clear any secondary overland flow paths that stormwater or stream
flow takes during floods
- keeping the banks planted to avoid erosion.
Click here
to find out more about some of the silly things people do without realising they
will cause flooding, erosion or pollution.
Detailed information about maintaining streams is in the Watercourse
guidelines produced by Auckland City and Metrowater.
Contact us if you want to carry
out any activity of any kind in or near a waterway so we can advise about how to
prevent any flooding or erosion that may easily result.
If you are buying, leasing or renting a property, you can find out if it is
in a flooding zone by inspecting maps held in Auckland City's offices or asking
for a LIM
(Land Information Memorandum). The maps and LIMS indicate flooded areas based on
a mix of historical information and computer modelling. Contact
us for more information.
If you are building a new house in a flood prone area, the Building Act
requires the minimum floor level to be high enough not to be flooded in the 1 in
50 year return period storm. Traditionally this is taken to mean at least 500mm
above the 50-year flood height. In some very flood-prone areas, development may
be more restricted or should even be avoided altogether.
Who to call
If your property becomes flooded but neither life nor property are
threatened:
- first, try to find the cause of the flooding. Common causes include
gutters full of leaves, blocked or broken downpipes or stormwater pipes,
broken connections to public stormwater system or blocked soakholes or
catchpit entries. The property owner is responsible for fixing these
problems
- if the flooding is from a source uphill or upstream beyond your property, contact
us.
In the event of serious flooding, where life or property are
threatened, call 111 and ask for the Fire Service.
If you are having new or worsened flooding because of increased runoff from
improvements such as buildings or driveways on an adjoining property, ask the
owner to control the stormwater runoff to reduce or avoid this nuisance. You are
obliged to accept stormwater runoff from uphill properties which would naturally
discharge runoff onto your own and at a rate that reflects the original state of
the property. Private stormwater issues need to be resolved between the parties
concerned, but if a nuisance is being created, Auckland City may be able to
direct some form of solution.
Tree roots can cause flooding by blocking stormwater pipes. If the tree is on
your land, you are liable for the costs of clearing the pipe. If the tree is on
a neighbouring property, you need to reach mutual agreement with the land owner
about the future of the tree. If it is on council land, contact
us to talk over the matter.
Auckland City's commitment to reduce flooding
Auckland City has a 2005 milestone of being on track to achieve protection
from flooding of 85 per cent of 1999 flood-prone habitable areas. To reduce
flooding, we are monitoring rainfall patterns, developing flood hazard maps,
carrying out flood alleviation works, improving our progress monitoring and
looking at other options to improve the stormwater network's performance. Find
out more.
Between 2000 and 2003, we protected 190 habitable floors and properties, and
a further 100 will be protected by 2005/06 when the Motions Creek project is
finished. Completing currently listed projects will see an additional 263
properties protected over the following 5-7 years. The total 20-year
expenditure on flood alleviation is predicted to be $256 million.
Erosion
Stream bank erosion
Stream bank erosion and subsidence are natural processes, but the increased
stormwater flows from more intensive development of the city can accelerate
them. Auckland City's on-site stormwater measures aim
to help landowners reduce these and other adverse effects on streams.
Contact us for advice about any
stabilisation works, as you may need approval from Auckland City or the Auckland
Regional Council.
Planting your stream banks
Stream bank planting can stabilise banks by slowing flows, and also help to
improve habitat for fish and the stream insects they eat. More serious erosion
may need works such as gabion baskets.
- A stream bank planting guide is available in the watercourse
guidelines. Contact
us for advice if you need more help - we have expert staff who can
advise about suitable plants. Other detailed information about maintaining streams
is also included in the document.
- Find out more about common erosion problems and
how to avoid them.
Silt run-off from building sites
If you are building during winter, remember to keep mud on your site. The water quality and marine life in Auckland's harbours is harmed by
silt-laden runoff from exposed ground on building sites - it is a significant
pollutant during the wet season and in summer storms. Find out more here.
Pollution
In the past, the main problem with stormwater was flooding. Now stormwater is
known to be one of the main causes of water pollution in the world.
On its journey to the sea stormwater can get dirty, picking up litter,
fertiliser, plant materials and animal excrement. It also carries away
contaminants such as petrol and oil, lead and other metals, left behind on our
busy city roads. In fact it is estimated that 55 per cent of stormwater
pollution is from roads and road use by vehicles.
Stormwater runs through a separate piped system from wastewater (including sewage),
and doesn't pass through the same treatment plant before being discharged into
the sea.
Only rain should go down the drain
Don't put anything down a stormwater grate that you wouldn't want to either
drink or swim in - rainfall runoff goes into our city's streams and underground
waters, and onto our beaches.
Everyone in Auckland city, whether we own property or not, shares
responsibility for making sure stormwater is as clean as possible.
How you can help
- dispose of litter carefully
- clear away animal droppings
- sweep paths rather than hosing them
- dispose of chemicals such as oil, paint and detergent properly and not
into the stormwater system
- wash your car on the lawn so used water soaks into the ground or use a
commercial car wash facility, which drains its water into the wastewater
system
- keep your car tuned and fix oil leaks
- use public transport whenever possible to keep the number of cars on the
city's roads to a minimum
- reduce the amount of fertiliser you use on your lawns
- minimise the amount of impervious surfaces around your home
- discharge stormwater from impervious surfaces, such as paths and driveways
into gardens, lawns and rainwater planters
- reuse rainwater for washing clothes, flushing the toilet and watering the
garden
- empty your swimming pool into the sanitary sewer via your gully trap or
stop dosing for two weeks before emptying it into the stormwater system.
- protect and maintain vegetation near the banks of streams.
To report a pollutant you have just seen entering a stormwater system, or in
a stream or on a beach, call the Auckland
Regional Council's 24-hour pollution hotline.
What Auckland City is doing
Auckland City has devices for treating stormwater to reduce the level of
pollutants. These include:
- catch pits with silt traps
- road sweeping
- litter traps, for example in Oakley Creek
- detention ponds, for example in Waiatarua Basin, which hold stormwater for
a period, allowing sediments and pollutants to settle, before it is released
into the sea
- mechanical filtration systems at Central Park in Penrose.
Auckland City's has a 2005 milestone of removing 27 per cent of
the suspended sediments in 70 per cent of stormwater catchments. The aim is to
protect the city's streams and coastal environments from the gradual build-up of
pollutants commonly transported in stormwater that can harm freshwater and
marine food webs.
Who to call or where to find out more
|
| Flooding |
If the flooding is from a source uphill or upstream beyond
your property, contact us. In
the event of serious flooding, call 111 and ask for the Fire Service. |
|
| Pollution of a stream or beach |
To report a pollutant you have just seen entering a
stormwater system, or in a stream or on a beach, call the Auckland
Regional Council's 24-hour pollution hotline. |
|
| Rusty or tainted tap water or a cut in supply |
Contact Metrowater
for information about your local water supply, or Watercare
Services Ltd about regional water supply infrastructure. |
|
| Sewage overflow or pump station failure |
Contact Metrowater
for information about sewage services, or Watercare
Services Ltd about the Manukau sewage treatment plant. |
|
| Managing stormwater to allow more intensive use of your
land |
Find out more about how to build on-site stormwater devices
here. |
|
| Where drains are on your land |
Find out more about the drainage maps available from
Auckland City here. |
|
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