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
About stormwater
The water cycle
The water cycle is perhaps the greatest wonder of the natural world. Powered
by the sun's energy, water evaporates, rises, moves on the wind, condenses and
falls. Landing on the forest canopy, rain splashes from leaf to leaf and runs
down tree trunks to reach the ground. Some water evaporates back into the air,
some runs off directly into streams and the rest gently soaks into the soil for use by the growing plants, which
breathe it back into the atmosphere by transpiration. Much of the water the plants don't use
slowly moves deeper into the soil, feeding streams and underground waters, which
eventually reach rivers, lakes and the sea, for the cycle to start all over
again.
The hard face of Auckland
The blue on the map shows impervious surface coverage in Auckland city in
2001 and 2002. Impervious surfaces are hard surfaces, such as roads, pavements
and roofs, where rain cannot soak into the ground and so runs off the surface.
When people roof and pave the land, water can't soak into the soil. It runs
off these hard surfaces very rapidly, so pipes are needed to rapidly carry the
resulting large volumes of stormwater to the nearest stream or beach. The result
is that streams dry up when it isn't raining and flood when it does. Pollutants
on roads and yards are also swept into our streams and onto our beaches. Far
from solving the problem of rain and the city, our heritage of efficient
stormwater pipes often make it worse in our streams and on our beaches.
Auckland City Council is doing its best to work with the natural water
cycle instead of against it. Come with us on our journey towards more
sustainable water management in the city.
By managing stormwater on our properties and in neighbourhood wetlands, we
can once again use plants, soils and natural water bodies to cope with rain in
the city in a more natural - and affordable - way.
Where rainwater goes
When rain falls onto lawns and gardens - called pervious areas - some of it
soaks into the soil. When rain falls onto hard impervious areas, it cannot soak
into the ground and so runs off the surface. It flows overland to drains,
streams and rivers, and eventually into the sea.
In a built-up urban environment like Auckland we have changed the natural
environment, covering much of it with impervious surfaces. This means less
natural soakage into the ground and much more surface runoff. Click
here to find out more.
Nearly all of the rain that falls on Auckland City becomes stormwater - the
name we have for rain that has fallen and has begun to run off, or flow across
the surface.
Where stormwater goes
When rain falls onto the roof of your home it runs along the spouting and
down into an underground drain. More water joins it from your driveway and
footpaths.
This drain is a private drain, owned by whoever owns your home. It carries
water to a stream or to a larger pipe, which collects stormwater from each
property along the way, as well as all the water that runs off the road and
footpaths.
That large pipe is part of Auckland's public stormwater network, which
collects stormwater from private property and provides drainage for public
areas, such as roads and parks.
Most of the piped stormwater network is underground - the manhole covers and
grates alongside roads lead into it - but streams and open stormwater channels,
such as the channel adjoining Portland Road in Remuera, also play an important
role in stormwater management.
Most stormwater is channelled into drains intended to protect against
flooding. At present, around 70 per cent of the rain that falls onto the city is
disposed of through our piped stormwater system. As the city continues to grow,
the increased runoff will overload some of these drains, causing increased flooding.
Stormwater flows downhill through the piped network and is eventually
discharged into the sea via our streams and rivers, or directly onto the beaches
of the Manukau and Waitemata harbours. In about one third of the city we also
rely on volcanic soils to drain away stormwater underground through soakage
pits.
Streams
Streams play an important role in the stormwater network and are also
important natural habitats in our city.
Many of the city's stormwater pipes discharge into streams. Streams are
privately owned by the landowners through whose property they flow, with five
exceptions, namely Oakley, Meola, Motions, Newmarket and Remuera creeks, which
are owned by Auckland City. More information about streams, and your stream
ownership responsibilities, is available in the Watercourse
guidelines.
To find out more about how you or your local school can monitor and look
after your own stream, look at the Waicare programme www.waicare.org.nz.
Beaches
Rain that falls on the city eventually makes its way onto our beaches after
travelling through stormwater pipes, over land or via streams. Any pollutants
that get into the stormwater system, streams or underground water will get there
too.
Underground waters
The 50-odd volcanoes around Auckland erupted into a coastal landscape of
gently rolling hills and valleys. Thick lava flowed down the valleys and
hardened into rivers of rock filling them up. Cracks and joints formed in the
cooling lava, and rainfall soaks into them. The water flows through the basalt
lava, and these water-bearing rocks are known as aquifers. The
basalts of Auckland's volcanic field are particularly valuable aquifers; they
hold a lot of water, it is generally of excellent quality and it is easily
extracted in large volumes for drinking water at Onehunga
and elsewhere for a range of industrial uses. Pictured right is a basalt lava
flow at Western Springs.
The Western Springs and Onehunga-Mt Wellington aquifers together cover 50
square kilometres of the Auckland isthmus - almost half of its total area. The large cracks in Auckland's basalt
lava flows house large supplies of rapidly moving groundwater. Generally water
in aquifers is of a high quality due to the filtering affect of the medium.
However it is still important to ensure sources of pollution do not enter
aquifers to protect them for the long term.
The district plan provides strict conditions to control pollution from
industry overs aquifers.
Soakage systems
Because volcanic rocks can drain rainwater very efficiently, in volcanic rock
areas we are encouraging property owners to develop soakage systems to dispose
of stormwater. This means directing all the run off from impervious surfaces
into a specially built soakage pit, which drains this stormwater into the
aquifers.
To prevent pollution of these underground waters, soakage systems must
include a way to filter out any contaminants and sediments. Soakage pits use
stone materials of varying sizes that trap the silt and contaminants as the
water drains through them.
Auckland City has introduced rules outlining the requirements for designing,
operating and maintaining soakage systems. Details of these requirements, and
information on choosing the best design for resource and building consents is
available in Auckland City's soakage
design manual. Find out more about Auckland City's global aquifer
study.
Sanitary and combined sewers
Stormwater is not the same as wastewater. Wastewater is all the water and
waste from our kitchens, laundries, bathrooms and toilets. It goes into a
separate drainage system, and is treated before it is released into the sea.
Across most of Auckland the stormwater network is separate from the
wastewater network, but in some older parts of the city, stormwater and
wastewater go into the same system, called the combined system.
The contents of the combined system feed into the wastewater network and into
the treatment plant before being discharged into the harbour. The wastewater network does not have the large pipes that the stormwater
network does as it was not designed to cope with large volumes of water over
short periods.
When there is heavy rain, high volumes of stormwater flowing into the
combined system can cause it to overflow into our streams and harbours, rather
than back up into our houses where it can pose flooding and health risks to
people.
Auckland City and Metrowater are carrying out a programme to manage the
problem of overflow and protect our environment by reducing wastewater spilling
into our harbours. This involves putting in new separate wastewater pipes and
encouraging property owners to maintain soakage systems to carry
stormwater away underground.
Who's responsible
Private property owners' responsibilities
If you own property in Auckland, you are responsible for managing stormwater
on that site and any private pipe within the road reserve that connects to a
public stormwater pipe.
This means you must have either a drainage system that collects stormwater
from your property and feeds it into the public stormwater network or provide
other means such as a soakage pit for on-site disposal or a
rain tank for on site re-use of the stormwater.
You are responsible for maintaining these systems:
. If you have a soakage system on your property, it is
your responsibility to keep it clear of litter, silt and other contaminants
before the water flows into it. This will make sure it keeps operating in the
long term - and, more importantly for your property and your downstream
neighbours' during heavy rain.
Click
here to find out where drains are on your land.
Streams.
You are also responsible for the maintenance of any streams that pass
through your property. You must make sure that they are kept clear so water
flows through them when it rains.
Overland flow paths. You also need to keep natural overland flow paths
free of obstruction, in order to prevent flooding of buildings and other
upstream property. No part of Auckland is entirely flat and under
centuries-old common law, all properties must accept and provide for natural
stormwater runoff that flows onto their property from higher land.
When rainfall exceeds the capacity of the stormwater system, the water will
begin to flow across the ground, and this is what is known as an overland flow
path.
Bylaws protect overland flow paths by requiring property
owners not to obstruct them with buildings, fences, retaining walls, and so on.
Home improvements.
If you are adding extensions, new buildings or
more paved areas on your property, all stormwater from them must be discharged
in a way that avoids creating problems for the existing site soakage system or
piped network, or for any downhill or adjacent neighbours. Find out how you can
detain or dispose of
stormwater on your site.
All developments must comply with the development and connection standards,
for connection to the city's stormwater assets - natural and built. Contact
Metrowater
for copies.
Other privately-owned stormwater facilities
Auckland City and the Auckland Regional
Council require stormwater treatment facilities to be installed, operated
and maintained on some large developments. Examples include Transit New
Zealand's systems for treating stormwater from the southern motorway, as well as
some systems owned and operated by Auckland City for the south-eastern arterial
route and other public facilities such as Unitec stormwater ponds.
Auckland City's responsibilities
Managing stormwater is one of Auckland City's many activities. In doing so,
Auckland City aims to meet community expectations by both protecting Auckland's
unique and valued environment and allowing for further urban growth.
While property owners must make sure stormwater is managed properly on their
land, it is Auckland City's job to make sure stormwater across the city is
carried away safely. This includes:
- operating and maintaining the public stormwater system to limit flooding
and pollution
- ensuring private property owners have suitable stormwater drainage on
their sites
- setting the rules for how land is used in Auckland
- installing stormwater management measures for
its own facilities
- developing plans for the future to make sure that as the city continues to
grow, the stormwater system - including our streams, beaches and underground
waters - functions sustainably.
Auckland City also maintains the Oakley, Meola, Motions, Newmarket and
Remuera streams, which are public watercourses.
In working towards managing stormwater in a more environmentally sustainable (and
affordable) way, Auckland City follows the laws set by central government, such
as the:
- Resource Management Act 1991
- Local Government Act 2002
- Building Act 2004
- Health Act 1956
- and also sets its own rules through district plans and bylaws.
Find out more about Auckland City's innovative
role in more sustainable stormwater management.
