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
What Auckland City is doing
Visions and priorities
Our vision for Auckland City is for a unique and valued natural environment
with:
- clean and unpolluted water, land and air
- preserved and improved green and open spaces
Visions and priorities for stormwater and the natural environment are spelled
out in Focus on the Future
2004-2014, and the stormwater asset management
plan.
Environmental monitoring
Safeswim - bathing beach water quality
Auckland City together with North Shore City and Rodney District monitor
beach water quality at the region's most popular bathing beaches. Key aims are
to protect public health and gather ongoing information for the councils' active
stormwater and wastewater management and pollution control programmes.
Click here to find out
more, or call 0800 SAFESWIM.
Wai Care - communities monitoring streams
Wai Care is a community based water quality monitoring and action programme
that is supported by the Auckland City, Auckland Regional, North Shore, Manukau,
Waitakere and Rodney District councils. Community groups and schools are
resourced and supported to monitor a stream or water body of their choice on a
regular basis. This means that along with learning about all the interactions
that occur within the environment, the groups can build up a picture of the
health of their stream. Using this information, they can then plan appropriate
actions to restore or enhance their local stream environment.
A key concept of the programme is learning about, and looking after, the
effects that land uses have on stormwater, ground water, stream water or salt
water.
Stormwater and receiving environment
monitoring
As well as its bathing beach monitoring, Auckland City has an active
environmental research programme aimed at identifying and better managing the
environmental effects of stormwater runoff on the streams and beaches it flows
into (receiving environments).
The city monitors stormwater pollutants including metals in
both dissolved and particle form (copper, zinc, lead), fluoride, nutrients
(nitrogen in its many forms as well as available phosphorus), enterococci
(bacteria that indicate the possible presence of other bacteria and viruses
which cause infectious diseases like 'tummy bugs'), suspended sediments and
petroleum hydrocarbons and other contaminants from internal combustion engines.
These pollutants can harm stream life, cause illness to bathers and people
eating shellfish. As they accumulate over time in the estuaries where the
stormwater deposits them, they also harm coastal creatures that are important to
our marine food web and the health of our coastal waters and fisheries.
All councils in the Auckland region are at present investigating the effects
of stormwater and wastewater discharges on our natural environment in order to
obtain resource consents. Find out more about Auckland City's
extensive recent monitoring programmes.
Ongoing long term monitoring will be maintained for stream flow, bathing
beaches and groundwater, and as required, specific monitoring will also be done
for issues of environmental and community interest.
Auckland City is also developing coastal strategies for public land it
administers along the coastline.
State of the environment monitoring and
reporting
Aucklanders take great pride in and enjoyment from our beaches, parks and
heritage sites. However these are under constant pressure from natural events
such as flooding as well as our growing population. In order to maintain and
improve the quality of our environment, we need to understand these pressures
and the environmental response to them. The state of the environment
report allows us to do this. Essentially a score card, the report helps us see
where action is needed to protect our environment.
The state of the environment
report is
produced every three years, with updates in the interim years. Find out more
about Auckland City's environmental policy here.
Education
Our vision for Auckland City is for a representation and communications
process for public information that:
- is open, honest, culturally appropriate and undertaken with integrity
- ensures effective communication with the community
Stormwater poses significant management issues for Auckland City residents
and ratepayers. In order to make the important decisions the city faces, people
need to know more about our existing built and natural stormwater
infrastructure, as well as options for more sustainable management in the
future.
Current education programmes on these issues include:
If there is enough interest, possible future education programmes could also
cover:
- detailed training for engineers on how to work with the on-site and
soakage manuals
- how the council and the public can better manage flood-prone areas
- how site contractors can better control erosion and sediment runoff on
small building sites (contact the Auckland Regional Council
for
information about erosion and sediment control training on large earthworks
sites)
- how to manage private watercourses, including stream bank planting with
natives
- consequences and prevention of water pollution from every day activities
such as car washing and house painting
Contact us if you are interested in finding out more about stormwater
education.
Consultation
Auckland City and Metrowater are working together to
finalise
network resource consent applications
for our stormwater and wastewater network. The consents will set the direction
for the city's drainage network for the next 35 years.
We want you to have your say on the future of the network.
We will consult with you on this issue as part of the council's
draft
long-term council community plan
process, which takes place from 19 April to 19 May 2006. The
outcome of this process will set the direction for our network resource consent
applications.
Click here to find out more about Auckland City and Metrowater's network
resource consent applications and how you can have your say.
Stormwater innovations
The
mix of an ageing stormwater system, the demand for infill development to meet
population growth and limited capital expenditure, mean that Auckland City needs
to 'think outside the square' in order to develop economical solutions to
flooding and contamination problems. We have sought new technologies to
improve our knowledge of the stormwater system performance and its effects on
streams, beaches and aquifers.
Some of Auckland City's innovative stormwater programmes are:
Water sensitive urban design
Future growth in Auckland City will be catered for by a mix of building up
and extending site coverage. Because increased site coverage increases
stormwater volumes and more people generate more contaminants in the runoff,
Auckland City is adopting and encouraging the wider use of water sensitive urban
design. This aims at more ecologically sustainable development that uses,
conserves and enhances the community's resources so that ecological processes,
on which life depends, are maintained and the total quality of life now and in
the future can be increased.
Auckland City encourages water sensitive measures that:
- protect or enhance water quality and preserve natural habitat and
ecosystems
- mimic natural drainage regimes, including groundwater recharge where
appropriate
- enable 'greener' forms of development
- reduce the amount and form of hard infrastructure and impervious surfaces
- reduce the concentration of stormwater and its potential to cause erosion
- encourage using construction materials that do not leach zinc and copper
into stormwater
- reduce the discharge of contaminants to sensitive fresh or marine
receiving waters
- improve visual and physical amenity values.
A mix of on-site and community stormwater devices can reduce the need for
major public expenditure on stormwater services, help keep streams in a natural
state and reduce the harmful effects of the conventional approach of discharging
stormwater to streams and beaches.
Impervious area mapping
In order to design stormwater systems, Auckland City needs information on peak
stormwater runoff volumes. These volumes are dictated to a large degree by the
extent of impervious areas such as roofs, paving, roads and so on (pervious
areas like gardens and lawns can soak-up some of the rain). The stormwater
infrastructure in different parts of the city is then designed to carry runoff
volumes that equate to the permitted impervious coverage of the sites.
If people extend the impervious areas on their site, the infrastructure's
design volumes can be exceeded, causing all sorts of
problems. The extent of these problems means we need accurate information on
the amount of impervious area on every property.
Because this work is so new, we have researched the available
technologies and developed our own impervious area mapping system. Based on colour
aerial photography, the sophisticated system uses image processing software to
quantify impervious areas, supplemented by manual digitising of some areas to
provide the required definition. The statistics are embedded in a geographic information system (GIS), and results are published as both maps and
statistical spreadsheets. In 2001 this technology attracted the Australian Stormwater Industry
Association's merit award for stormwater management.
Auckland City needs to know the exact extent of impervious areas in order to:
- correlate impervious areas with flooding and pollution problems
- check compliance with permitted site impervious area controls; for
example, in residential areas, the impervious limit is 60 per cent, and this
determines the capacity of the public stormwater network
- provide data to input into catchment hydrological and hydraulic models.
Business zones allow the entire site to be impervious except for required
landscaping, so most of the permeable land is on residential properties.
Catchments with less than 10 per cent of their areas available for more development
include the CBD, Freemans, Stanley and Herne Bays, Westmere, Pt Chevalier,
Parnell and Waterview. Those with more than 20 per cent of the catchment area available
for development include Mt Wellington, Southdown, Glen Innes and Orakei.
More information about impervious area mapping is available in conference
papers.
On-site stormwater management
A good example of at-source stormwater control is Auckland City's on-site
stormwater management programme, developed mainly for infill and re-development
areas. Developers are permitted to exceed the normal site impervious area
coverage limit of 60 per cent, provided that they install an on-site device to control
stormwater runoff and intercept contaminants. In areas using the public
stormwater system, developers can
choose from a variety of devices to limit both runoff quantity and quality. The peak
stormwater runoff quantity must be limited to the equivalent from 60 per cent impervious
site coverage.
For a development of 10-20 dwelling units, the capital cost of the required
stormwater management devices is around $1,000 per unit. This is a modest figure
compared with the financial gain to the developer from being able to secure the
additional site coverage. More information is available in conference
papers.
The on-site stormwater management manual covers all aspects of device sizing, design,
operation, maintenance and permitting. As part of the programme, demonstration
devices are being constructed at two new community centres.
In November 2003 the on-site devices programme received a high commendation in the Australian Stormwater Industry Association's National
Excellence Awards for stormwater management. Based on best overseas practice,
the programme's innovations
include:
- 'win-win' outcomes:
- win to developer: for a minimal outlay, allows 33 per cent more dwelling area
(up to 80 per cent impervious area coverage, instead of the normal 60 per cent maximum)
- win to Auckland City: large saving in capital expenditure on infrastructural
upgrading
- win to downstream neighbours: reduced potential for flooding
- win to the environment: pollutants trapped at source.
- internal change management - an accompanying programme (more information
is available in conference
papers) helped gain buy-in by Auckland City staff to both the
on-site technology and the new management processes to ensure that:
- people and management processes are aligned and focused
- processes reliably deliver what is expected
- people are fully competent and continuously learning.
Integrated catchment studies
Flooding problems in the past were addressed one by one, with Auckland City
engaging consultants on an 'as-needed' basis to prepare catchment management
plans. But variable results from different methods and modelling software made
it difficult to assess priorities for capital expenditure in
one catchment versus another.
In 2001 Auckland City embarked on a five-year programme of city-wide integrated catchment studies (ICS), designed to develop a better
understanding of the city's stormwater, wastewater and natural drainage systems.
The studies will help find the best way to develop and manage these systems to provide cost-effective ways of combating flooding and environmental
degradation. Among the aims are:
- gathering information about the state of the drainage networks
- infiltration and inflow control and sewer separation
- treating stormwater and reducing overflows of wastewater
- changing people's behaviour through education
- encouraging on-site management and use of stormwater
- waste minimisation and reducing pollutants in
stormwater.
The integrated
catchment study looks at the systems already in place for stormwater and, by
using sophisticated computer modelling, works out the best options for managing
stormwater in the future. It is identifying where and how water quality can be
improved, where larger pipes are needed, or where we can rely more heavily on
soakage systems. Extensive databases are compiled on the stormwater, wastewater
and combined drainage systems and their associated receiving environments,
including the aquifer systems.
The city has been divided into five major catchments, each with the following research
stages:
- review existing data and identify additional data needs
- collect data on stormwater assets (pipes, manhole lids, outfalls)
- monitor rainfall, stormwater flows, stormwater quality and receiving
environments
- analyse the catchment by modelling stormwater flow and quality,
discharge models and modelling stormwater flow down urban streams and its
dispersion in the estuaries and harbours
- develop options for improved management based on life cycle costs and
environment, cultural and social benefits
- prepare stormwater network management plans.
The information will be used to prioritise the capital works needed for flood
alleviation and stormwater pollution control. This will help to support the
region-wide process of investigating and consenting stormwater and wastewater
discharges, including decisions about:
- where and how best to invest in the development of stormwater and
wastewater networks
- the need for and cost of larger stormwater pipes
- resolving existing flooding problems by enabling high flows to more
effectively use flood plains, overland flow paths and watercourses
- reducing wastewater overflows during heavy rain
- the need to treat stormwater to remove pollutants
- managing the future growth of the city so as to minimise adverse
environmental effects.
More information about the integrated catchment study is available in conference
papers.
Global aquifer study
The global aquifer study project is part of Auckland City's integrated
catchment studies. A significant part of the city's stormwater drainage
system uses the underlying volcanic basalt rock for the disposal of stormwater -
the volcanic lava flows cover approximately 39 per cent of the area of Auckland City.
The rock is highly fissured and fractured, with lava tubes in places, and
stormwater can be disposed into this highly permeable rock via boreholes,
soakholes and soakage tunnels. The stormwater then becomes part of the
groundwater system and flows toward either the Manukau or the Waitemata harbours
flanking the isthmus.
To better understand this groundwater system, a programme of investigation
drilling was undertaken which, together with existing information has lead to a
significant step forward in understanding the nature, extent and behaviour of
groundwater flow in the Auckland basalt aquifers. A computer groundwater model
is being built to model the behaviour of the groundwater under various
conditions, with results due by the end of 2004.
The model focuses on the role of soakage capacity, groundwater levels and
flows in the aquifers. Before more stormwater can be disposed of into these
underground waters, we need to know that this will not worsen flooding and
pollution. The model will look at:
- the potential for the basalt aquifers to accept more stormwater runoff
- movement of water between the aquifers and underground drainage networks
- groundwater flows into receiving environments (streams and beaches)
including entry into and movement through the aquifer of pollutants.
Water and sanitary services assessments
Under the 2002 Local Government Act, local authorities are required to
undertake assessments of the water and sanitary services in their area of
jurisdiction. These must cover:
- water services - water supply, wastewater and stormwater
- sanitary services - public toilets, cemeteries, crematoria and solid waste
disposal.
The aim is to assess if any of the services pose a risk to public health, for
example, a wastewater assessment must address whether any reticulated sewage
system is performing satisfactorily; or where wastewater treatment and disposal
is by on-site systems, it must address the risks of any contamination.
Although these assessments do not need to be completed until June 2005, Auckland
City chose to take a lead and initiate assessments for the Hauraki Gulf Islands under its jurisdiction in June 2003.
Find out more here.
Preparation of water and sanitary services assessments for Auckland Isthmus
began in July 2004.
Catchpit filter testing
Water running along a road kerb and channel enters the stormwater system
through a steel grill, under which sits a catchpit - a concrete box with a half
siphon outlet designed to trap litter and sediment before the stormwater enters
the piped system. The efficiency of the catchpit at trapping this material declines
between cleaning intervals, so a catchpit filter in the form of a nylon mesh
filter bag was invented. This hangs inside the catchpit to trap litter and
sediments washed off the road in wet weather.
Before spending money on a pilot programme of several hundred catchpit filter
units, Auckland City set up a field observation programme, followed by a laboratory
testing programme, to identify which products would meet a satisfactory
performance target.
Four manufacturers submitted catchpit filter units for field testing
programme. Each unit was installed in a city street and observed for five months
for ease of fitting, ability to retain sediment, maintenance needs,
rigidity/strength, ability to pass stormwater flows and the effects of litter
and leaves.
On the basis of the field results, two manufacturers' units were laboratory
tested at Auckland University and compared with a catchpit without the filter
unit, to quantify their sediment capture performance at a range of flow rates
and sediment concentrations. Auckland City catchpits remove up to 20 per cent of
fine suspended sediment. More information is available in conference
papers.
Email this page
Format to print