| |
|
|
|
Systems and TechniquesHint: If you wish to search for information in this section of the website, simply click on 'edit' then 'find' and type what you are looking for. 1
Sustainable
Development
Water
management can only be efficient in terms of satisfying human needs and
respecting environmental limitations if it is integrated with the management of
other resources and all human activity. Ecosystems are the building blocks
which determine: o
the prevailing
water quality and ecology o
ecological
sustainability o
biodiversity
(both in terms of the flora and fauna associated with particular habitats, and
the internal diversity of flora and fauna comprising the ecosystem) o
the environmental values and uses ascribed to waterways
by the community. A definition for Ecological Sustainable Development adopted by the
National Strategy for Ecologically Sustainable Development (1992), sets out the
parameters: “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.” Using ESD principles in the application of catchment management to
limit stormwater pollution in cities requires a thorough understanding of
natural biodiversity pre-development, and the potential impacts
post-development. The selection of
strategies to limit pollution impacts of stormwater runoff can only proceed
with community support, as it requires the commitment of behaviour as well as
action. The National
Strategy for Ecologically Sustainable Development (NSESD) provides an effective
basis for addressing sustainability issues at the catchment level. Specific objectives are: · to develop water
management policies which are based on an integrated approach to the
development and management of water resources [including catchment management,
public participation, water allocations to maintain aquatic and riparian
(streamside) environments, and nutrient management]; and · to develop and implement
the most effective mix of water resource management mechanisms (including
pricing, regulation, monitoring, institutional arrangements and property
rights). Coastal Development Urban, industrial, port development, tourism, and
other uses have been responsible for significant degradation in the coastal
strip in many areas around National Census statistics show that the coastal zone
supports about 80 per cent of the Australian population, with about 96% of
those people living in coastal cities and large towns. Although around 70 per cent of In an estuarine environment, the water quality impacts will be dependent
on the type of estuary and the location within the estuary. The well-flushed drowned river estuaries are
generally least susceptible to urban stormwater pollution, with coastal lakes
being most susceptible due to the absence of tides. The areas within drowned river valley and
barrier estuaries that tend to be most susceptible to pollution occur at the
tidal limit on the tributary watercourses.
At these locations, the tidal excursion (the longitudinal movement of
water) is generally small, often resulting in a long residence time for
pollutants. This can stimulate algal
growth and result in depressed oxygen concentrations (eg Onkaparinga Estuary
Task Force 1991). Biodiversity As a generalisation, poor stormwater quality has often been found to
result in a reduced diversity of aquatic fauna and flora, and dominance by less
desirable species (Whiting and Clifford 1983; Garie
and McIntosh 1986, Hogg and Norris 1991, Lenat and Crawford 1994). Table – Potential Impacts of Reduced Water Quality on Aquatic Ecosystems
Source: after Hellawell (1986), Mason (1991)
and Underwood and Chapman (1995) To ensure that urban stormwater management is consistent
with the conservation of biological diversity it is necessary to take into
account: 1.
the
need to minimise the effect that barriers to water flow have on the migration
and reproduction of aquatic fauna and dependent floodplain ecosystems; 2.
the
impacts of artificial river flows and the lowered water temperatures downstream
of large storages on the breeding of aquatic species; 3.
the
importance of natural flow regimes and habitat complexity for aquatic and
riparian ecosystems and the need to minimise the impacts of habitat alteration
in river improvement projects; 4.
the
need to minimise the adverse impacts of the use of artesian water on the
biological diversity of naturally dry areas; 5.
the need to improve management of water allocations to ensure the
maintenance of in-stream and floodplain biological diversity. 2
Flood
Effects
2.1
Inundation
Flooding generally causes
extensive pollution impacts to receiving waters due to high organic loads,
erosion of river and stream banks, discharges from flooded sewers, and litter
and rubbish caught in flow paths. It is
not realistic to attempt to manage water quality during flood events. In cases where properties are affected due to
urbanisation, flood mitigation procedures have generally been engineered, or
the properties are resumed for other purposes.
2.2
Nuisance
Flooding
Flooding which does not
affect property, but causes inundation of service corridors, parklands, etc can
also be highly polluted. Management
systems should be in place to control both water quantity and water quality. Effective planning of flow
paths across urban development can reduce floodwater velocities, and minimise
pollution from erosion and sediment.
Directing these flows to detention and retention systems can eliminate
adverse impacts. Safety of people caught
within flooded catchments, risk management considerations and emergency
response become competing factors with water quality and quantity control. 2.3
Flow
Variations
Changes to stormwater
runoff volume result from increases in impervious surfaces. This leads to higher peak flow rates in
streams. It increases stream bank
erosion and the magnitude and frequency of in-stream habitat disturbances,
causing the loss of species unsuited to such conditions. Up to 70% of the
impervious area in urban catchments has a transport related function, of which
40-50% is associated with roads. The
transport sector is clearly responsible for a large proportion of the peak flow
impacts in urban areas. How this
responsibility is distributed between industry, private residents, and local,
state and federal authorities, is an issue that is increasingly significant as
stormwater management issues become more prominent. The minimisation of runoff
volume is essential following urbanisation. The management of increased runoff
volume does, however, hold the key to managing flooding and water quality
impacts on the aquatic environment. This
applies particularly to minimising the runoff from frequent storm events eg. turbidity effects on water quality and accompanying
nutrients and remobilisation of temporally detained contaminants together with
sewage overflows. The optimum solution
for managing this increased volume of runoff is to encourage infiltration,
storage and reuse. 3
Water
Quality Management
Philosophical Approach to applying
Water Quality Guidelines The major policy objective
adopted by the NWQMS (ANZECC & ARMCANZ 1994) is “to achieve sustainable use
of the nation’s water resources by protecting and enhancing their quality while
maintaining economic and social development”. The NWQMS is part of the COAG
(Council of Australian Governments) Water Resources framework (1994). To achieve this, a
three-tiered approach to water quality management (national, state or
territory, and regional or catchment) is required. In practice, each jurisdiction uses its own
water quality planning, environmental policy and regulatory tools. Examples include at the national level NWQMS
at the state level state and territory water and land resources management
Acts, environment protection Acts, and regional plans. Long-term management of
any water resource requires a collective vision of society’s desired outcomes
for these waters, and a good scientific understanding of the impact human
activities have on them. An appropriate
set of management aims includes: o
A clear set of
environmental values o
A good level of
understanding of links between human activity and environmental quality o
Appropriate
water quality objectives o
Effective
management frameworks, including explicit goals for management, cooperative
(agreed level of protection to be attained), regulatory (impact assessment),
feed-back and auditing mechanisms To ensure that water quality
guidelines are implemented, involves : o
Sustainable use
and sharing of responsibility within an integrated catchment management
framework including integrated water quality assessment o
Cooperative best
practice management focused on attainment of environmental quality goals and
compliance o
Tailoring
guidelines to local conditions, acknowledging a wide range of ecosystem types o
Looking beyond
water quality, to environmental quality o
Focus on
guidelines, trigger values and targets Management Interventions
1.
Community benefits A well designed and integrated stormwater system can
provide the following community benefits: Remove excess water and minimise
flooding of property and the impacts of flooding community facilities Protect downstream water bodies
from the contamination in urban runoff Provide aesthetic values within
the urban landscape Provide recreational facilities
on water bodies Provide nature conservation
habitat in urban areas for birds and other valued species Provide a community education
resource in the role of water in the landscape and in our society Provide recreational corridors
and paths along drainage lines Provide second class water for
other uses There is clearly a
planning as well as a management dimension to achieving community
benefits. Pollution and Water Minimisation at Source. The main approaches to
source minimisation are: o
Planning of
appropriate land uses to ensure development is consistent with the capability
of the land o
Controls over
construction sites and land development to minimise soil loss during this phase o
Careful location
of sewer surcharge points to minimise impacts and reduction of discharges o
Minimising the area
of impervious surface o
Public education
o
Street sweeping,
litter trapping and pit cleaning Interception
of contaminants as they flow downstream.
The main approaches to interception are: ·
Vegetated floodways ·
Gross Pollutant
Traps ·
Buffer zones
between development and receiving waters ·
Oil and trash
booms ·
Bio-retention
and infiltration systems ·
Water pollution
control ponds ·
Wetlands ·
Retarding basins ·
Detention basins ·
Flood plain
protection and utilisation ·
Urban lakes Management
of Receiving Waters to Minimise Impacts. The main approaches to management of receiving waters
are: ·
Zoning of
water-based uses ·
Monitoring and
closing of water activities when quality is unsatisfactory ·
Zoning and
treatment of foreshores to encourage appropriate uses ·
In-lake treatments ·
Maintenance of
healthy ecosystems. Generic impacts of
stormwater quality on ecosystems: ·
Reduction in
light penetration by sediments, reducing macrophyte
photosynthesis, lowering predator visibility and clogging gills of fish and
macro-invertebrates ·
Sedimentation of
substrates and pools ·
Stimulation of
primary productivity by nutrients, increasing macrophyte,
algae and cyanobacteria growth rates.
(the decay of this biomass can depress oxygen levels) ·
Depression of
oxygen levels by oxygen demanding substances ·
Bioaccumulation
of chronic impacts of toxicants (pollutants) ·
A change in
trophic status of the watercourse as the primary energy source changes from
organic matter to dissolved nutrients, changing the macro-invertebrate
assemblages from shredders to scrapers. 4
Visual
Water Quality
The most obvious aspect of the pollution problem to the general
public is visual water quality. The appearance of a water body will influence
public and political opinion. This will influence the need for immediate
action, the apportioning of responsibility, and the availability of funds. Outbreaks of blue-green algae, mountains of foam, significant fish
kills, highly coloured water and oil slicks are examples of visual problems
that receive comments in the media. These problems may not be the most serious
aspects of pollution taking place, as lakes that have died from acidification
(acid rain) are crystal clear yet are biologically dead. There are two principal forms of visual water quality: surface
debris (inorganic, organic and oils) and clarity (sediment and colour). Although floating inorganic debris and
litter, such as steel drums, car tyres, bottles, aluminium cans and foam boxes,
raise community concerns, they only cause minor direct chemical water quality
pollution. The accumulation on the shoreline of the chemical components of such
debris and litter will influence the usefulness of the water body. Litter and debris can cause the destruction
of natural habitats, reduce the visual amenity, damage vegetation, harm wildlife
and reduce public safety. The presence of obvious colour also raises public concern. Organic debris, such as leaves, timber,
paper, cardboard and food will in the short term provide visual pollution only.
Eventually this organic material decays, releasing nutrients. It forms rich
organic sediment that can affect the water body causing algal blooms. Temperature increases can
also occur following urbanisation.
Impervious areas act as efficient heat collectors, with stormwater
runoff experiencing temperature rises of between 5 and 10 degrees
centigrade. A further increase in
temperature can occur if the riparian vegetation shading the watercourse is
reduced or removed. This temperature
increase can have a negative impact on fish fauna and macro-invertebrates, by
slowing growth rates. 4.1
Contaminants
& Nutrient Control
The contaminants in
stormwater are usually grouped according to their water quality impacts as
follows: ·
Suspended solids ·
Nutrients
(primary nitrogen and phosphorous) ·
BOD and COD
(biological and chemical oxygen demanding materials) ·
Microganisms ·
Toxic organics ·
Trace organics ·
Toxic trace
metals ·
Oils and
surfactants ·
Litter o
4.2
Suspended solids
Suspended solids can be
organic – derived primarily from sewage, or inorganic – derived from surface runoff. 4.3
Suspended solids reduce light penetration in water,
affecting the growth of aquatic plants.
When silts and clays settle, they may smother bottom dwelling organisms
and disrupt their habitats. Since
metals, phosphorous and various organics are adsorbed and transported with
these particles, sediment deposits may lead to a slow release of toxins and
nutrients. Suspended solids - dust,
soils and sediment cause turbidity. The
absorbed pollutants can then be released to the environment, as well as causing
problems through siltation.
4.4
Nutrients
Nutrients come from sewage
overflows, industrial discharges, animal waste, fertilisers, domestic
detergents and septic tank seepage.
Nutrients such as nitrogen and phosphorous promote rapid growth of
aquatic plants, including toxic and non-toxic algae. Excessive nutrients cause a variety of problems and are generally
indicated by raised levels of nitrogen and phosphorus in a water body. The
problems caused relate to the change in the biological balance, that frequently
involves an explosive growth of algae and other plants in the water body. This
excessive growth results in: ·
the production, during the day, and the
consumption, during the night, of a large amount of oxygen by the plants. This
wide variation can cause fish & marine organisms to die; ·
the biological smothering of other plant forms; and ·
the deposition and formation of organic
sediment. The most effective management of nutrients once in the stormwater
system is to settle out the silt and clay particles that have the nutrients
attached to their surface. Up to 85% of
phosphorus and 70 - 80% of nitrogen content can be isolated as particulate
matter. Although sediment traps collect
some clay sized particles, the majority are settled on the matrix of surfaces
found in water pollution control ponds and constructed wetlands. These surfaces form a basis for microbial
activity and are referred to as thin film bio-reactors. 4.5
Oxygen Demanding Materials
Sources of oxygen
demanding materials are biodegradable organic debris, such as decomposing food
and garden wastes and the organic material contained in sewage. BOD and COD - biological and chemical oxygen
depleting substances can cause water-borne diseases and present serious health
risks. The biological and chemical
oxygen demand of sewage, (BOD and COD) are high. If oxygen levels become too low, fish will
die. 4.6
Micro-organisms
Bacteria and viruses
found in soil and decaying vegetation, and faecal bacteria from sewer
overflows, septic tank seepage and animal waste are common contaminants in
stormwater. Pathogenic and
micro-organisms, including bacteria, viruses and faecal coliforms
cause water-borne diseases and present serious health risks. They can cause
water-borne diseases such as cholera, typhoid, infectious hepatitis and a range
of gastrointestinal diseases. 4.7
Toxic Organics
These include garden
pesticides, industrial chemicals and landfill leachate. They may cause long -term ecological damage
and danger to human health. Organochlorine pesticides, herbicides and insecticides have
varying damaging impacts on ecological and human health - some can be bioaccumulative and persistent in the environment. 4.8
Toxic Trace Metals
These include lead,
zinc, chromium and copper from motor vehicles, pavement degradation and water
pipe and roof corrosion toxins such as ammonia, hydrogen sulphide and heavy
metals (mercury, cadmium, copper, lead, zinc) and industrial chemicals from a
number of sources including sewage overflows, illegal dumping and accidental
spillages, landfill leachate and agricultural practices. Heavy metals are urban stormwater pollutants
with severe impacts on aquatic life. 4.9
Oils and surfactants
Petroleum
products such as oil and grease flushed from road surfaces and surfactants from
detergents used for washing vehicles in the street are common sources of toxic
pollutants. Rubber and hydrocarbon
derivatives, as well as surfactants from detergents that are flushed from
roadways, are common sources of toxic pollutants. 4.10
Litter
This includes
paper, plastics, glass, metal and other packaging materials from paved areas
through urban catchments. It includes
organic waste matter, which can make up a large proportion of the litter
volume, depending upon the catchment characteristics.
4.11
Algal
Blooms
An algal bloom is caused
by “the rapid excessive growth of algae, generally caused by high nutrient
levels and favourable conditions”.
Blooms can result in deoxygenation of the water mass when large masses
of algae die and decompose, leading to the death of aquatic plants and animals.
Algae are a natural
component of aquatic environments, and even when they are abundant,
it is not necessarily a problem. Often a
proliferation of microscopic algae can have beneficial effects on fisheries and
aquaculture industries such as oyster or mussel farms by increasing the amount
of food available. However, when algal
blooms increase in intensity and frequency, the results can cause community
concern, health problems, and in some cases can be catastrophic to the
environment. Internationally most
strategies to address problems of algal blooms in freshwaters require reduction
in the loads of phosphorous entering the river.
Planning must be on a catchment basis and consider pollutant loads from
the various existing land uses and any proposed land uses in the whole
catchment. Algal blooms upset the
delicate natural balance of plant and animal ecosystems in a waterway or
wetland. They can degrade recreation,
conservation and scenic values, and interfere with economic uses such as fisheries
and tourism. Weed that washes ashore and
forms rotting piles on beaches can cause offensive smells and become a health
problem for nearby residents as well as a nuisance to beach goers. An over-abundance of algae can choke a body
of water such as a river, clog irrigation pipes, and block out the light to
other plants, such as seagrasses.
Excessive algal growth can eventually kill seagrass beds. When an algal bloom dies the process of decay
can use up all the available oxygen in the water, effectively suffocating other
aquatic life. This can kill fish, crabs
and other animals, especially those that are attached or sedentary. Some species of algae produce toxins. 5
Source
Controls
Managing stormwater at the source is an important part of urban
stormwater management, as it minimises the transport of problems downstream,
reduces the need for structural management practices and can reduce the demand
for potable water. Source control falls into two main categories: ·
quantity control - minimising the amount of stormwater from a site ·
quality control -
minimising the concentration of pollutants in stormwater. To encourage quantity control, management techniques can be
implemented by preparing or amending environmental planning instruments. These
can require the use of rainwater tanks or other storage facilities to reuse
stormwater from roofs for non-potable purposes. Overflows could be directed to
an infiltration system. These facilities are not expected to reduce any
requirements for stormwater detention (e.g. on-site detention) as the
facilities may be full at the commencement of a storm event. Planning
instruments can also be amended or prepared to require water-sensitive urban
design principles (Whelans et al 1994) to be adopted
for proposed development areas. For new developments, the actual level of
appropriate source control will be dependent on the nature of the development. Source control for stormwater quality management relies heavily on
public education and the provision of facilities for disposing of oils and
hazardous chemicals. The maintenance of structural source control practices is
considered essential to the success of these management practices. This issue needs to be addressed as an
integral part of the structural practice. 5.1
Diffuse
Pollution
Source control measures
are concerned with minimising the generation of pollutants on surfaces before
they get into contact with stormwater.
This is to be achieved though changing community behaviour within a
catchment that generate pollutants and the preparation of appropriate
development and planning controls to minimise future impacts. Source control techniques can be categorised
into: ·
Non-structural
source control: techniques that aim to change human behaviour to reduce the
amount of pollutants that enter stormwater systems (pollution prevention) ·
Structural
source control: techniques that aim to reduce the quantity and improve the
quality of stormwater at or near its source by using infrastructure or natural
physical resources. Source control education
techniques concentrate on educating the public about issues such as: ·
appropriate
application of fertilisers, herbicides and pesticides to domestic gardens; ·
appropriate car
washing techniques, minimising the amount of water used and undertaking washing
on pervious surfaces where possible; ·
appropriate
disposal of grass clippings and other organic matter obtained during garden
maintenance; ·
removal of pet
droppings, particularly from impervious surfaces; ·
appropriate management of oil and other household chemicals,
including disposal in an authorised facility. Education activities can
include labelling drainage pits, to indicate the receiving waters, to increase
awareness of the destination of pollutants.
Dog-owners, for example, play a key role: the EPA of NSW estimates the
amount of dog faeces washing into Structural source controls
include a range of
devices, including wire baskets in sumps and kerb inlet pits,
filtration screens, gross pollutant traps, sand filters, swales etc. 5.2
Point
Source Impacts
Point source impacts often
come from industrial, commercial and agricultural activities. Illegal dumping of waste or production
discharge of chemicals, contaminated wash-down water or civil and building work
activities are some of the point source contaminants that can enter the
stormwater system. Often it is necessary
to conduct catchment audits to identify continuing and repeat pollution
discharges. 5.3
Sewer
Overflows
The
effect of sewer overflows on our receiving waters is generally limited to storm
events, but when pollution does occur, it is an environmental and public health
problem. Through environment protection
regulation, sewerage utilities are being forced to act to reduce sewer
overflows, and eventually eliminate them, with much of the regulatory action
being driven by public opinion and the media.
The sewer overflow problem is a complex combination of factors, which
often has as its primary cause, an aging pipe work system together with design
overflow points which were engineered to give relief at times of peak flow
i.e., they were designed discharge points.
The wet weather peak flow problem is generally caused by stormwater/groundwater
penetrating the sewerage pipe system via illegal connections, surface runoff
into sewer gullies, and cracked and broken pipes. The combination of sewer effluent plus stormwater, chokes the system - the volume of water exceeds
capacity, causing the designed overflow relief points to discharge to receiving
waters. Studies in the Sydney area have shown that up to 6,000 overflow points
exist that are capable of discharging raw sewage into the stormwater system. Treatment of sewer
overflows can be done in one of two basic ways, either structural or
non-structural. Non-structural management of the storm sewer overflows means
controlling and managing the sewer hydraulics and redirecting flows in order to
minimise the impact of storms on the sewerage system. This involves a detailed understanding of the
sewer network, catchment characteristics, receiving water quality and
sensitivity and urban use patterns. The
non-structural approaches will yield significant reductions in the storm sewer
overflow events but would be unlikely to completely solve the problem. However, considering the cost of investment
in the sewer network and additional structural control systems, improved
control of the sewerage system has a high potential return on investment. Structural
solutions rely in part on the construction of facilities to cope with and/or
treat the sewer overflow event. These
solutions can range from simple detention basins, temporary storage, advanced
physical and chemical treatment facilities, and removing and treating sewage
locally for re-cycled water use (sewer mining). 6
Service
Infrastructure Impacts
6.1
Multiple
Use Corridors (MUC)
The provision of drainage
must also be integrated with the provision of other important facilities such
as water supply, sewerage, electricity, communication cabling and roads. Thus urban development must be undertaken in
a holistic manner taking account of the various interactions and ensuring that
these are all done in sympathy with the local physical environment. Councils in most cities of
Creating multiple
corridors that provide both stormwater management and ecological function is a
challenge, and is the key to the successful implementation of Water Sensitive
Urban Design (WSUD). Developing a “particular
sense of place” in a MUC is important in making these areas attractive and
inviting to the public. The community
will be more inclined to make use of and respect these areas if they can foster
a sense of local ownership and personal linkage with the area. Substantial benefits may
accrue where facilities are planned and managed to accommodate a number of
functions such as stormwater drainage and flow control, recreation, wildlife
habitats etc. Infrastructure Provision Effective infrastructure
provision and cost recovery requires: ·
early
identification of floodplains and drainage corridors at the planning stage ·
coordinated
planning and management for growth and development ·
clear definition
and allocation of responsibility ·
comprehensive
cost analysis for the short and long term ·
evaluating and
maximising the multiple use benefits of the infrastructure, and ·
appropriate
pricing policies Potential benefits of such
an approach include: ·
a reduction in
drainage infrastructure provision capital costs ·
lower cost open
space and recreational facilities compared with non-drainage corridor areas ·
access to a low
cost water supply source ·
increased real
estate market values enabling a greater return on investment though sale of
land and enhanced rating base ·
opportunities to
commercially exploit the recreational values of corridors and waterways An ecologically-based
stormwater planning and management approach aims to recognise components of
urban drainage systems as ecosystems in their own right. This approach recognises
that some natural ecosystems have been irreversibly modified. 6.2
Road
Run-off
Motorways are particularly
subject to littering, loss of materials in transit and the concentrated
residues of combustion and vehicle wear.
Runoff is also heavily laden with detritus, particularly where wood-chip
and leaf litter mulches are used on steep slopes. Water quality from roads
can be directly related to road construction and maintenance activities, and
vehicle movement and wear. Potential
pollutants include gross pollutants and litter, sediment and suspended solids,
toxic organics, nutrients, heavy metals, and hydrocarbons. Suspended sediment is the
next most obvious pollutant, as most people can easily distinguish between
clear and turbid water. From an
ecological perspective, sediment and suspended solids are also the most
significant of all the road runoff pollutants.
Sediment interferes with the respiration and feeding of aquatic plants
and animals. Many other potential
pollutants such as nutrients, heavy metals and organic substances, are adsorbed
to, and travel with, sediments.
Sediments and suspended solids are also particularly important because
they are manageable – simple technologies now exist to control and trap
sediments. Heavy metals of concern in
road runoff include cadmium, chromium, copper, nickel, lead and zinc. The concentrations of metals found in road
runoff, especially from heavily trafficked areas, are commonly far in excess of
current ANZECC (1992) guidelines for the protection of fresh and marine
waters. However, the majority of metals
sourced from roads are in particulate form, and are unavailable to
organisms. Elevated levels of
nutrients such as phosphorous and nitrogen are also found in road runoff and
can contribute to the accelerated growth of nuisance aquatic plants and cause a
reduction in the levels of dissolved oxygen.
Nutrification is a principal cause of algal
blooms, and the nutrients contained in road runoff can add to the total
nutrient load of the waterway. Nutrients
are usually associated with fine suspended sediment in the runoff. 7 Community Perceptions
7.1
Water
Quality
It is apparent that the water
quality of urban streams and rivers does not meet the community’ environmental
values. Although knowledge
and awareness of the stormwater issue is variable across cities, there is a
clear need for further education in urban communities. 7.2
Water
Quantity
It is recognised that the
community's main concern is that their homes are not flooded causing damage to
property. Minor localised flooding is
readily accepted as long as it is for short-term duration. The community understands that engineers have
developed a variety of structural techniques to manage flooding, and hence
there is now greater emphasis on pollution impacts on the natural
environment. Flash flooding and damage
which is experienced in areas previously thought to be flood free (eg. Regulation
The responsibility for
providing and managing the urban stormwater drainage system mainly rests with
local government authorities. A range of
government agencies and statutory authorities is involved in waterway and
catchment management. In some states,
catchment management trusts or catchment management boards have been
established to prepare management plans and to bring a range of community
inputs to the process. Increasingly,
external issues and decisions relating to resource management must incorporate
national and state level considerations that are beyond a local authority’s
powers. State and Territory
government authorities have overall responsibility for land and water use
planning and management within their jurisdictions. Planning, development and regulatory controls
and institutional arrangements are already in place. In some states, legislation covering total or
integrated catchment management structures and processes addresses problems of
fragmenting administrative responsibility across natural resource management
areas. Through the
Intergovernmental Agreement on the Environment, State and Territory governments
have undertaken to include national considerations such as ESD and
international undertakings relating to protecting wetlands and endangered
species, etc, in their planning activities. It is suggested that the
roles of each tier of government, the community and the private sector are: Federal Government ·
Setting national
strategy ·
Initiating and
funding research required at a national level ·
Monitoring
performance at a national level ·
Funding major
programs ·
Developing codes
of practice and guidelines ·
Identifying and
funding training requirements ·
Coordination ·
Providing
education material ·
Promoting the
development of universal systems that facilitate communication and coordination State Government ·
Establishing
land use planning controls at state level ·
Setting state
strategy and through their catchment agencies, local strategies ·
Identifying
priorities ·
Providing
support through state agencies and reallocating responsibilities between
agencies where necessary to facilitate integrated management of catchments ·
Monitoring
performance of state agencies and local government ·
Allocating and
accounting for funds ·
Providing
appropriate structures to develop and implement local plans (e.g. catchment
management authorities) ·
Ensuring that
all state agencies operating comply with the state strategy ·
Providing
education material and field officers ·
Monitor and
report on the condition of the state’s catchments Local Government ·
Identify local
priorities ·
Amend and
administer local planning ordinances to reflect local strategic plan ·
Initiate and
support local pollution control by-laws ·
Support
educational activities ·
Show leadership
in their own works programs and actions Pricing
In
many urban areas, drainage is the highest cost component of the hydraulic
infrastructure. Some current engineered
practices are not the most cost effective, either short or long term, when
externalities are taken into account. In
February 1994, the Council of Australian Governments (COAG) agreed to implement
a strategic framework for important water reforms in The
water reform framework sets out requirements with respect to: ·
wastewater
management and water quality ·
water related
research, and ·
public consultation and education. Competition and Innovation in Urban
Water Supplies
The
increasing focus on treatment and reuse of stormwater and wastewater is
encouraged. It brings with it a
potential not only for greater development opportunities but also for improved
environmental outcomes, increased urban amenity and quality of life. The goals
of this framework are to: ·
encourage
innovative practices in provision of water services, whilst recognising the
need to retain economies of scale in infrastructure to ensure net public
benefit; ·
provide a level
of certainty for private investment in the water services market by specifying
the regulatory framework (health, environment, financial, etc) in which
potential new entrants will operate; ·
facilitate
competition in water services; but also ·
ensure there is a transparent, sustainable and equitable
approach to the pricing of water and wastewater services whilst still ensuring
reliability and consistency in the quality and safety of water services. This
leads the way forward, for innovation in stormwater storage and reuse as a
supplement to existing water services, and the potential to eliminate the need
for future new water supply dams which carry huge penalties in infrastructure
costs, and environmental river management. Natural Resource Management
Natural Resource Management
(NRM) is built around Environmentally Sustainable Development (ESD), community
empowerment, integrated management, targeted investment, accountability and
minimising bureaucracy. It is
fundamental however, that environmental value of receiving waters (and their
ecosystems) should be assessed before defining management policies for urban
catchments. In recognition of the need
to manage water quality sustainably ANZECC and
ARMCANZ have developed the National Water Quality Management Strategy (NWQMS).
The policy objective of the NWQMS is “to achieve sustainable use of the
nation’s water resources by protection and enhancing their quality while
maintaining economic and social development.” This objective is being pursued
through application of policies, a process for water quality management and a
set of national technical guidelines providing guidance on many aspects of the
water cycle. For further details see http://www.affa.gov.au/nwqms.
One of the most relevant
NWQMS guidelines documents is the Australian Guidelines for Urban
Stormwater Management. Integrated planning
through Regional Catchment Strategies/Catchment Management Plans,
can represent the first integrated natural resource management planning
approach. This provides a detailed investment strategy that directs the
activities of catchment management service providers funded by State and local
revenue. One method that enables
this to be achieved (eg. in The regional management
planning process provides a mechanism for ensuring that all funding for natural
resource management, including that provided by State and Commonwealth
Governments and the locally collected resources are directed at the key areas
of the catchment strategy. This avoids
dissipating resources through fragmented structures and piecemeal investment in
uncoordinated small-scale projects. This
is critical to developing ownership by local communities of their natural
resource management problems and solutions.
It generates greater community awareness and willingness to become
involved in decision-making. It
galvanises the concept that everyone, both urban and rural people, lives in a
catchment and is both affected by and affects the condition of the
catchment. It particularly brings urban
communities into the catchment management framework, where traditionally they
have not been active players. Developing regional
strategies for natural resource management that are based on
government-community partnerships has become widely recognised as an essential
first step toward integrating and coordinating investment and activity in
natural resource management. A regional
natural resource management strategy provides direction on NRM and planning through
input from key stakeholders and experts.
It identifies priority natural resource issues for the region and sets
goals to direct action (prioritisation process). A regional approach, however, helps
governments and communities understand natural resource problems in a wider
context, in line with the way in which natural systems operate.
|
7.2.1
|
Although urban stormwater
and treated wastewater are recognised increasingly as important economic
resources they are not yet widely used to augment supplies in expanding urban
areas. Recent research and demonstration
projects have shown that stormwater and treated wastewater can be exploited in
a cost effective and environmentally sensitive manner for new urban
developments. In this context:
Many cities in
Typically, the SMP must:
·
Identify the
existing and future values of a catchment
·
Specify
stormwater management objectives to protect these values
·
Identify the
range of land use constraints
·
Identify the
range of corridor or drainage measures related to attenuation of flow,
interception of pollutants, provision of open space and recreation,
conservation areas, urban stormwater reuse requirements and retention of the
natural values of urban streams.
·
Detail a suite
of non-structural and structural management practices to address these problems
and issues which have been agreed between all stormwater managers within a
catchment
A SMP is a framework for
action – ESD is the focus. It is important that the stormwater management
plans:
·
Encourage
community involvement in stormwater management
·
Encourage the
preservation of valuable existing elements of the water environment
·
Maximise the
control of stormwater runoff at the source
·
Identify and
prioritise an appropriate mix of cost-effective stormwater management practices
to suit the particular requirements of a catchment
·
Link to
Council’s management planning processes, and
·
Incorporate
monitoring procedures to allow for feedback and improvement of the plan
Community Management Programs
Waterwatch is a national community waterway monitoring and
environmental education program currently operating in every State and
Territory. Waterwatch
promotes water quality monitoring to create an ownership ethic for catchment
wide land and water management by the Australian people. Through its State and Territory programs, which
include ACT Waterwatch, Streamwatch
NSW, Waterwatch SA, Ribbons of Blue WA, Waterwatch
Waterwatch was initiated by the Federal
Government in 1992 in recognition of a growing concern for water quality by the
Australian people, triggered by major issues such as rising salinity and blooms
of blue-green algae in our waterways. In
the wake of these significant impacts, the Australian community, with the
support of both Commonwealth and State Governments, has developed a strong
impetus to explore and address the issue of catchment degradation.
The goal of Waterwatch
The objectives of Waterwatch are
to work with all levels of government, industry and the community to achieve:
·
Awareness
and understanding of the importance of healthy waterways and the relationship
to land uses within the catchment
·
Communities
monitoring their local waterways
·
Community
involvement in planning and action to address waterway and catchment issues
·
Effective
partnerships between all sectors of the community working towards healthy
waterways, and
·
Financial
and institutional support for the Waterwatch
Australia network.
As a result of growing community participation, the program
has achieved the following outcomes:
·
Developed
a network of more than 1800 groups regularly monitoring at 4000 sites across
·
Involves
50,000 participants in the Waterwatch program
·
National
guidelines and protocols for community monitoring adopted in every State and
Territory; and
·
Created
108 part-time regional Waterwatch coordinators funded
through the Natural Heritage Trust and 24 regional Waterwatch
coordinators funded through external funds operating in 227 catchments across
The Bushcare
program, the largest NHT program, aims to reverse the long-term decline in the
quality and extent of
Bushcare
groups are generally closely linked to catchment management groups, and work in
the areas of repair and maintenance of riparian vegetation, and in the
restoration of degraded sites which impact upon the waterway environment. Bushcare programs
are included in the stormwater planning process where they enhance water
quality objectives in urban environments.
Catchment Management Committees/Boards
Local CMC's have developed out of the community's
concerns about environmental degradation to natural waterways due to urban
impacts. They mainly offer advice and
recommendations to government. CMC's receive
limited funding to carry out and coordinate local community based programs in
education, streambank repair, litter reduction
campaigns etc. The strengthening of this
process has occurred with the formation of Catchment Boards in different
States. Some Boards have been given regulatory
powers, authority and funding. (as in
Urban stormwater involves
such conflicting interests as preservation of property rights versus preserving
natural bushland or streams, recreational values of waterways versus control of
litter and contaminants from upstream and funding of downstream flood control
measures by charges on more remote upstream properties. Community involvement is essential for
appropriate management and to resolve conflicts. Local government response and action is
critical.
The work of 'Clean-up
Local innovative projects
proposed by community groups, can also encourage action by overall catchment
bodies. Adjacent local government areas
have joined with State or regional bodies in tackling specific waterways issues
with special purpose community advisory bodies.
Community education and involvement in stormwater management requires
coordination between groups of local councils in catchment organisations,
regional, State, Territory and Commonwealth agencies.
In order to achieve
sustainability, we need to have a comprehensive understanding of the dynamics
of a system. This is no easy task. Natural ecosystems are complex. The cumulative effect of people and their
activities are equally complex and perhaps less predictable.
There is tremendous
potential to utilise electronic information systems such as GIS technology to
organise, present and analyse the data that is relevant to understanding the
dynamics of catchment systems. This is a
potentially complex undertaking, but
At the beginning of the
planning process there are many criteria to determine the suitability of
on-site management tools. These criteria
can be classified into:
These factors all have
spatial dimensions that can be presented in maps. With a Geographic Information System (GIS),
spatial factors can be analysed, transformed and presented. Depending on the location, each factor has a
different importance. GIS helps to
identify the decisive factors for the planning process.
Most councils
in
Providing
effective structural stormwater management strategies within existing urban
areas is generally expensive and often difficult due to site constraints. The potential for various processes and
levels of treatment to be implemented are conditioned by the features of the
site. These considerations include:
·
Regulatory
requirements
·
Effectiveness of
the stormwater treatment train to achieve desired pollutant reduction
·
Capital costs
·
Operations and
maintenance costs
·
Public
acceptance (eg aesthetics, safety)
·
Ability to
satisfy multiple objectives (eg. habitat, recreation)
·
Capability of
mitigating other effects of urbanisation (i.e. including runoff volumes or peak
flows)
·
Incidental
environmental impacts, and
·
Compatibility
with site constraint:
- space limitations
- topography
- geology
- soils
- groundwater
- aquatic or riparian habitats
- services or other obstructions
- climatic conditions
- community perceptions
Generally, stormwater treatment trains are not
intended to treat all catchment runoff.
The common goal is to provide effective treatment up to a certain flow
level.
The retrofitting of stormwater management systems is
a major financial issue for urban Australian cities, and most of the debate in
this area is deflected to the responsibility and funding of infrastructure to
achieve environmental improvement.
The primary goal of monitoring is to characterise the prevailing
water quality and ecological conditions in a stormwater system and receiving
water bodies, test compliance with water quality objectives and assessment of
development and management actions. Impact assessment requires good data before
and after the development actions. Long term monitoring including flow
measurements is primarily undertaken under dry weather conditions (which occur
most of the time) and at regular intervals. It is also important to measure
water quality and flow under high rainfall conditions. Such measures enable
estimates of the loading of pollutants derived from stormwater and inputs on
downstream water bodies such as lakes and estuaries. Flow velocity should also be noted. The results can be related to the ambient
water quality criteria contained in ANZECC /ARMCANZ (a) (2000). A combination of physical/chemical and
biological monitoring is advantageous, as the macroinvertebrates
commonly used in biological monitoring respond to long-term water quality
conditions, while physical/chemical monitoring reflects instantaneous
conditions. Continuous monitoring using water quality probes will also provide
useful data. Further details on
monitoring are provided in ANZECC /ARMCANZ (b) (2000).
The opportunity to carry
out water quality monitoring pre-development is often limited due to existing
land uses. Most urban land development
classed as Green Field Development is on land used previously for agriculture. Often the catchment characteristics have been
impacted upon, and if there is urbanisation further up the catchment,
considerable water quality problems may exist already. One of the issues in managing and planning
new areas, is to accept the incoming water quality problems, and to treat it
plus the proposed development impacts, so that the final discharge water
quality is improved downstream.
Pre-development monitoring is essential to understand the extent of the
catchment problems.
Pre-development monitoring
aims to provide information about the hydrological and water quality
conditions, and is often used in calibrating water quality models. Storm event based water quality monitoring
should also be undertaken (usually collected by automatic sampler) so as to
access pollution concentration variations during the passage of an event, to
derive an estimate of average event mean concentration from the catchment.
Mathematical models can
also be used to address the problem of urban stormwater quality and its impacts
on receiving waters. Deterministic
models though, can only give a rough estimate of the stormwater pollution. This is the consequence of an uncertainty of
the rain and the pollution input.
Catchment Management Boards & Committees are well placed
to play a role in the monitoring and auditing process and consequently to
enhance community involvement and awareness.
Where
it is not possible to definitely determine the relationship between pollutant
loadings and water quality impacts, an ongoing monitoring program with review
to assess performance should be incorporated within the stormwater drainage
strategy.
For
each of the outcomes of stormwater management (flood protection, environmental
protection and public health), total abatement and damage costs of alternative
stormwater management programs can be compared.
Total abatement costs are the costs needed to achieve a given level of
performance. As a target level of
abatement is raised, the abatement cost will rise. Total damage costs are the costs incurred at
given levels of abatement. For example,
the costs from property damages are higher if abatement expenditure is limited
to the control of a 1 in 20 year flood, rather than a 1 in 50 year flood. Hence, as abatement expenditure is increased,
damage costs are decreased. The
objective of a stormwater management plan will be to minimise the sum of
abatement and damage costs (Thomas et al,
1996).
The Bureau provides a range of services and products aimed at supporting
an ICM/TCM approach through the provision of basic hydro-meteorological and
hydrological data and information, including:
·
Provision of
relevant national meteorological observation networks;
·
Provision of
flood warning and forecasting services at the catchment scale;
·
Provision of
hydrometeorological advisory services at national and catchment scales;
·
Provision of
water resources assessment services at international and national scales;
·
Provision of the
meteorological component of specific ARMCANZ ‑ initiated programs; and
·
Liaison with the
World Meteorological Organisation and UNESCO in their
role as UN specialised agencies for operational hydrology and hydrological
research and education.
In
all major cities the link between poor stormwater management and waterway
contamination has attracted strong condemnation from the community. In several, the public is regularly
confronted by public health warnings about waterways and beaches impacted by
effluent overflows after high rainfall events.
In the past, risk management and legal liability have only appeared to
be targeted at threats from flooding rather than deteriorating coastal water
quality. For example, the
However,
in this context, several corporatised water
authorities have tended to narrow their view of core business and their role in
source control. An approach emphasising
business asset management and risk analysis accounting measures has prevailed.
The 1998
A
similar analysis may be applied to the objectives of water quality and
environmental protection. However, the
natural dimensions of each are different.
For flooding the appropriate measurement is target flood frequency. For water quality it is the physical,
biological and chemical parameters.
These may be expressed either as a limit, average, load or
concentration. There is no generally
accepted measurement of landscape or ecological quality.
There
are several tools available for environmental valuation. The NSW EPA has developed a bibliographic
reference tool, named ENVALUE that quantifies use values as a function of water
quality.
The states, local
government and the private sector are becoming increasingly aware of their
exposure on liability for stormwater mismanagement and approvals, brought about
by changing legislative interpretation within the courts and wider
interpretation on the issues of standing for community groups.
Accountability
The United Nations
recognises the need for a unifying integrated approach in Agenda 21. Chapter 18 states:
"Water
is needed for all aspects of life. The general objective is to make certain
that adequate supplies of water of good quality are maintained... while
preserving the hydrological, biological and chemical functions of ecosystems.
The
scarcity, destruction and pollution of fresh water resources, along with the
progressive encroachment of incompatible activities, demand integrated resource
planning and management. Such integration must cover all types of interrelated
freshwater bodies including... surface and groundwater and water quantity and
quality aspects. The multi-sectoral nature of water resources development in
the context of socio-economic development must be recognised, as well as the
multi-interest utilisation of water... integrated water resources management,
including the integration of land and water related aspects should be carried
out at the level of catchment basin or sub-basin.”
Monitoring of catchment management programs will be required
to assess their effectiveness.
Information generated as part of this assessment could be highly useful
for State of
The monitoring of catchments also provides opportunities for
cooperation and coordination between agencies or projects. For example, the State of
Catchment Audits can be prepared, following completion of
fieldwork data collection. A report
(audit) summarising the findings of the data collection and fieldwork
activities should be undertaken, which highlights the key stormwater management
issues, their location, nature and severity. Plans can be prepared noting the
location of the management issues in each sub-catchment, which could also be
noted on a geographical information system. An assessment of the relative
importance of problem sources can be made, to assist with allocating priorities
for management.
The NSW Healthy Rivers Commission has developed the concept
of a 'statement of joint intent' to ensure different government agencies commit
to agreed goals and strategies. The
following mechanisms are recommended:
·
Agreed actions in the Joint Statement of Intent should
be specified in terms of auditable processes and procedures, to the extent
necessary to provide for meaningful accountabilities for each signatory.
·
The accountability for each state agency’s
responsibility under the Statement should be publicly acknowledged by their
Chief Executive Officers, and regional accountability should be ensured by
inclusion in the annual performance reporting.
·
Council undertakings as part of the reporting statement, should be widely publicised in the local media to
provide local communities opportunities to ‘audit’ their own local Council’s
performance in relation to its specified plans.
·
An independent ‘quality assurance’ mechanism should be
put in place to ensure that action taken by all signatories truly reflects the
commitment made as part of the Statement.
Community/Government Partnerships
Community /Government
Partnerships involve commitments to consult and work together for improved
environmental and resource management outcomes.
Commitments to a community/government partnership approach does not
absolve governments from their responsibilities to make such decisions and implement
the relevant actions – that is, to fulfil their obligations in respect of the
partnership. For consultation to
contribute effectively to government decision-making, the types of decisions
that are to be made following the consultation should be specified in
advance. Once the consultation process
has been exhausted those decisions must actually be made. ‘Consultation’ which becomes an endless
search for a consensus view, is simply a means of avoiding the inevitable
decision-making and thus results in postponement of increasingly urgent
action.
A partnership in catchment
planning to date has concentrated on biophysical needs and issues with little
acknowledgement or use of ‘social boundaries’.
Whilst this approach was appropriate for the introduction of catchment
management, the end result has been a failure to incorporate and get ownership
from the entire catchment community. By
not catering for the specific needs and requirements of the catchment community
a large percentage of the biophysical research has fallen on deaf ears or
community members who have been unable to afford the desired changes to
management.
Community Participation
There is no single community
participation model, as each project will bring a unique combination of geography,
community profile and resource issues into play.
Some methods of encouraging
community participation include:
Generally in
|
|
The preparation of catchment
management and stormwater management plans includes identifying Indigenous
sites and social traditions, where they link to water management. This process involves participation and
consultation with Indigenous communities and often brings with it an enrichment and better understanding of natural resource
issues pre development.
Stakeholders in stormwater
management plans may often hold conflicting objectives and this may disrupt the
planning process. Successful stormwater
management must respond to this issue.
Where there are competing community
interests or real or perceived alternative solutions, there can be strong
objections, and often the threat of litigation.
Stormwater managers should set in motion a process of consultation with
stakeholders, which may involve education and information material being
distributed so any debate can proceed with participants involved being better
informed. It may be necessary that this
process be carried out by independent parties, as part of the objective resolution
strategy. As with all conflicts, all
parties need to be prepared to understand the alternative point of view. When resolution must be determined by a
court, there are 'Environment Courts' in each state which can hear all parties
claims, and bring down a verdict.
Managing Water Quality
Before
urbanisation, most leaves, rotting vegetation, animal droppings, sticks, dust
and sand, stayed more or less where they fell.
It is only because of the introduction of extensive sealed surfaces that
this material enters waterways to the extent that it does. Urbanisation has irrevocably changed the
ecology of waterways. Organic material
is released in unprecedented quantities to accumulate and break down on the
beds of rivers or on the bottom of harbours, where it consumes available oxygen
and creates a stagnant environment.
Sediments washed off construction sites and other unsealed surfaces are
discharged into these same waterways, causing siltation
and gradually changing contours and affecting the local currents required to
sustain a healthy environment. Litter,
whether it enters the stormwater system intentionally or not, has high visual
impact and contributes to the debris in waterways that places wildlife at risk. Such pollution is not merely visually or
aesthetically unacceptable. It
ultimately affects all life, whether through health risk to humans or danger to
wildlife through destruction of food sources or habitat.
There
is a potential interaction between the hydrological (stream flow)
characteristics, and geomorphological, water quality,
aquatic habitat and riparian vegetation of a watercourse. These interactions
can also be extended to include human health, recreation and aesthetic
considerations. Managing only one aspect
of a stormwater system is therefore unlikely to address all of these
considerations. As noted by Riley (1995), stormwater management must consider
the hydrological, geomorphological, ecological, soil,
land use and cultural characteristics of a catchment and its watercourse
network. Failure to understand these interactions may result in the
implementation of well-intentioned management techniques that have a greater
environmental impact than that associated with unmitigated stormwater runoff.
In
the management of water quality the general approach as outlined in ANZECC
(2000) is usually as follows:
·
Define the
receiving waters to be protected, which may include, for example:
-
downstream
section of river;
-
lake;
-
estuary;
-
marine environment.
·
Define the
Environmental Values of the receiving waters, which may include, for example:
-
protection and
maintenance of aquatic ecosystems;
-
recreation,
either passive or active;
-
water supply for
irrigation or stock;
-
domestic water supply.
·
For each of the
defined Environmental Values define Water Quality Objectives. These are usually taken from available Water
Quality Guidelines (ANZECC).
·
ANZECC (2000)
stresses the importance of taking local conditions (and data) into account when
applying the guidelines, for example:
-
The ecological
character of systems changes considerably from ephemeral watercourses in the
headwaters of a catchment down to the confluence with estuarine water. Adopting a single value for nutrients and
many other determinants and applying them along the entire length of a system
is clearly difficult.
-
Occasionally
naturally high concentrations of heavy metals occur in all streams.
-
The guidelines
discuss indicative nutrient levels (not presented as criteria for lakes and
rivers).
Most
landscapes in
Salinity
Salinity
is a form of land degradation that is an expression of major water imbalance in
a catchment. It is caused when salts
stored in the soil profile are mobilised and brought nearer the surface by
rising water tables. The principal cause
of rising water tables is the replacement of native woody vegetation with
introduced crops and pastures, which use water at a lower rate. This results in “leaking” of surplus rainfall
water into ground water systems, causing water tables to rise. As water tables rise, they also bring up
dissolved salts from lower in the soil profile.
In
certain parts of the landscape, the water table is close enough to the surface
for evaporation to occur. The water
evaporates, but the salts are left in the soil and with time the concentration
of salt in the upper soil profile can reach toxic levels. The initial impacts are often to the
productivity and health of crops and pastures, followed by substitution with
salt tolerant species of little commercial benefit. However, the effects of dryland
salinity reach far beyond the dryland agricultural
sector, with significant impacts to regional and urban infrastructure, water
supplies, and biodiversity in aquatic and terrestrial ecosystems.
Acid Sulphate Soils
Nationally
there is an estimated 40,000 km2 of coastal acid sulphate soils,
containing well over one billion tonnes of sulphide compounds (pyrite). In coastal catchments, mangrove swamps and
some sands contain acid sulphate soils.
In an undisturbed state, acid sulphate soils are harmless and are known
as Potential Acid Sulphate Soils (PASS).
However, when drained and exposed to air, PASS soils become Actual Acid
Sulphate Soils (ASS) and sulphuric acid is produced in large quantities. After
rain, particularly following prolonged dry periods, this acid is mobilised
along with other toxins such as heavy metals.
Toxic slugs are formed which enter the estuarine environments and travel
to the sea.
Acid
sulphate soils occur throughout
Acid sulphate soils are a naturally occurring problem, which can
be exacerbated by development disturbing and exposing the acidic layers. It derives from the oxidation of pyrite to
sulphuric acid with the pH dropping as low as 2 or 3 (pH=7 is neutral), which
corrodes steel and concrete, and dissolves aluminium, forming free aluminium
which is toxic to vegetation and aquatic life. Acid sulphate soils typically
generate from the drainage of sulphidic clays that
accumulate in tidal swamps (wetlands) and the subsequent oxidation of the
soil. Fish die when the pH of the water
body is 4 or less, with the production of iron and aluminium and low dissolved
oxygen levels, resulting from the oxidation of ferrous iron to ferrihydrate.
The
most effective means of preventing acid production and runoff in catchments,
which contain PASS, is to leave the soil undisturbed. Unless substantial capital is available to
effectively treat or safely remove and dispose of pyritic sediments, the cost
of disturbing a PASS site must be weighed against future environmental, social
and economic costs.
Remediation
plans sponsored by government or other agencies generally include some
structural changes to existing catchment drainage or flooding regimes,
treatment processes and most importantly, voluntary community action. Successful remediation plans will probably
include all these elements and to some extent depend on the level of community
goodwill (cultivated by education) and financial imperatives (or incentives). There is an urgent need to trial and
demonstrate options available to governments and communities to deal with sites
affected by acid sulphate soils runoff.
Within
the realm of current knowledge, reversal of environmental degradation in
catchments caused by acid runoff remains problematic. Effective management of acid runoff on-site
may lead to the reduction or neutralisation of acid flow into an estuarine
system and result in some minimisation of environmental degradation caused by
the amount and concentration of acid and heavy metals in the system. However the reversal of environmental
degradation of a particular site may not be possible in many cases. Once pyritic sediments are exposed to air
they compact as a result of the acidification process. Original soil levels are lowered over
substantial areas and any attempts to curb oxidation by re-flooding may have a
substantial impact on current land use.
Changing
current land use of ASS sites within a catchment may offer some solution to the
problem. However, adequate compensation
would be required for landholders to take land out of production or drastically
change the type of land use activity.
A
National Strategy for the Management of Coastal Acid Sulphate Soils has been put
in place. It was developed by a National Working Party with representatives
from relevant Ministerial Councils and establishes 4 principle objectives:
Identify
and define Coastal Acid Sulphate Soils (ASS) in
Avoid
disturbance of coastal ASS
Mitigate
impacts when ASS disturbance is unavoidable
Rehabilitate
disturbed ASS and acid drainage.
The
National Strategy provides a framework whereby the problem of coastal acid
sulphate soils can be addressed in an integrated and coordinated manner. It clearly defines the roles and
responsibilities of the various stakeholders, including all levels of
government and community catchment groups.
Vegetation
Natural
vegetation provides the protection and cover for soils and the bio-diversity of
life, which inhabits the eco-system.
Removal or changes to vegetation affects the natural balance, and one of
the many impacts is upon water.
Vegetation reduces run-off and promotes absorption and
infiltration. Vegetation takes up water
and stabilises groundwater levels.
Natural vegetated areas have a catchment run-off coefficient of about
10%. Dense urban areas have a run-off
coefficient of about 90%.
With
urbanisation and the need to design for sustainable environments, vegetation
must be introduced together with other means, to try and emulate
pre-development conditions.
Urban
runoff can encourage the growth of exotic weeds in urban bushland. Nutrients
are transported by stormwater into the bushland, where exotic weed growth is
encouraged, as native vegetation generally requires low nutrient
concentrations. Weed seeds (propagules) can also be
transported from residential areas by stormwater, with the higher moisture
content at the outlets to drains further encouraging weed establishment (Riley
and Banks 1995).
Riparian
zones are vegetated buffer strips bordering water courses. They play a number of important roles in the
water environment.
Shading:
Riparian
vegetation reduces water temperatures and light penetration, particularly in
upland streams. This vegetation maintains the in-stream biological productivity
of the watercourse and the shading can provide camouflage for prey and
predators.
Energy
input:
Leaves and other organic debris provide a major
source of organic carbon and nutrients to support aquatic ecosystems, also
primarily in upland streams. Debris from native vegetation is preferred by
native aquatic fauna over that from exotic vegetation, and avoids the potential
detrimental effects from some introduced species.
Organic debris:
Logs and other coarse organic debris from native
vegetation provide an important habitat for fish and invertebrates, and assist
with the retention of organic matter in the watercourse (by the creation of
organic debris dams) for a sufficient period to enable it to be used by aquatic
fauna. The habitat value is greatest when the bed (substrate) of the
watercourse is sand or mud. Logs from most exotic species have different decay
process to native species, and do not provide the same suitable habitat for aquatic
fauna.
Without
a well-managed riparian zone excessive sediment enters the stream from overland
flow or bank failure. This sediment
clogs the streambed, smothering native flora, and destroying the egg laying
sites of native fish. Good management of
the riparian zone is essential. While it
may be the single most important determinant of river system health, it can
become a ‘band-aid’ solution if good land use management is not practiced
upslope.
|
|
River Management
The
primary goal of river management is to maximise the environmental, social and
ecological benefits provided by rivers through the maintenance, protection or
enhancement of:
·
Biodiversity to ensure the viability and integrity of all elements in the
aquatic system
·
Productive capacity and sustainability of hydrological systems
·
Long-term multiple social and economic benefits of river and catchment
use to meet the needs of societies
·
Natural and cultural heritage values of rivers and landscapes
Local
catchment strategies and town planning include measures to protect areas along
watercourses from development which may damage the streamside environment as a
visual, conservation, ecological and recreation resource including:
·
The setting aside of land adjacent to watercourses as foreshore reserves
for public open space, landscape interests, conservation and public access
·
The control of stock to safeguard stream banks from erosion
·
The retention and planting of vegetation adjacent to streams to improve
amenity, filter drainage waters and control erosion
·
The general prohibition of houses and leach drains within 100m of a
stream or river
·
The control of drainage and stormwater runoff into streams and
watercourses
·
The control of the application of fertilisers and pesticides with a zero
discharge of nutrients and other pollutants adjacent to watercourses
The
retention of vegetated buffer zones along permanent waterways is necessary to
prevent adjacent land uses from degrading water quality by means of polluted
surface runoff.
Flow Velocity Impacts on Receiving
Waters
Urban
development increases the surface run-off flows, which in turn, affects the
in-stream velocities. The increased
magnitude and frequency of these flow peaks causes severe stream channel
erosion and increased flooding downstream.
The most commonly observed effects on receiving waters of this change to
hydrology are the physical degeneration of natural stream channels. Decreases in diversity and numbers of aquatic
stream biota are also commonly observed.
The
higher frequency of peak flows causes the stream to cut a deeper and wider
channel destroying the in-stream aquatic habitat. The eroded sediments are deposited downstream
in slower moving reaches of the stream or at the entrance to lakes or
estuaries, destroying aquatic habitat in these areas by smothering the benthos,
filling wetlands with sediment, etc.
The
retention period of wetlands in the watercourses are also drastically changed,
experiencing high flows for short periods during and after rainfall, followed
by a period of much reduced or no flow, because of the reduction of interflow.
The
most common practice is to use detention basins to slow down the
post-development flow so that basin outflow does not exceed pre-development
flow for the design storm, however experience with these facilities shows that
while they reduce downstream flooding, they are not effective at reducing the
erosion in stream channels.
·
drowned river valleys: estuaries with
open mouths and full tidal range,
·
barrier estuaries: estuaries behind coastal sand barriers with an entrance
channel, through which tides are attenuated.
·
saline coastal lakes: lakes (or lagoons) behind coastal sand barriers with
ephemeral channels that are scoured during infrequent storm events, and are
non-tidal.
These estuary classifications are based on their early,
or ‘youthful’ development stage, prior to the commencement of significant
infilling by sediment from tributary watercourses.
Coastal rivers tend to be much smaller than their inland counterparts,
and are arguably even less able to accommodate the many requirements being
imposed on them. Movement of population
from the main urban centres to rural coastal catchments has resulted in
extensive land uptake in often sensitive and fragile coastal environments. To date, coastal rivers have not received the
level of attention commensurate with the significance of these pressures.
Poor water quality and sediment loads are the most serious known
pollution issues affecting
A major threat to this diverse and valuable environment comes from
excessive sediment, nutrient and gross pollutants. Most of these polluting
materials come from human activities within the catchments, which supply
surface runoff and underground water to these estuaries. Water coming from areas of soil and
vegetation disturbance, from paved surfaces and from underground waste sites
can carry pollutants to the estuaries. The construction of stormwater drainage
systems allows pollutants to be carried efficiently from the catchment to the
estuary.
Primary responsibility for the management of land-sourced pollution is
with State and Local government. The
Commonwealth has a particular interest because of the linkages between marine
systems in inshore and offshore waters and
Coastal lakes, which have limited ocean water discharge, have been
particularly affected by urban and rural runoff. Significant losses of saltmarsh
and mangroves around urban areas, caused by land reclamations and drainage are
affecting fish and other sea life, which use the mangroves as nurseries and
feeding grounds.
Some initiatives are now being proposed or undertaken on a small scale
with urban stormwater reclamation in new housing developments primarily in
|
|
Estuarine Aquatic Habitats
There are broad similarities in the functions of estuarine habitats when
compared to freshwater habitats, although their form varies considerably from
freshwater systems. The principal estuarine habitats are the mud flats and sand
flats in the sub-tidal and intertidal zones, and the plants which develop on
these flats (Morisey 1995).
Seagrass beds:
Seagrass beds (or meadows) occur in shallow sub-tidal areas. They provide
an important habitat for juvenile fish and invertebrates (particularly prawns
and crabs). The seagrass blades (leaves) provide a host surface for epiphytes
(algae and protozoans) and epizoa (rotifers, small encrusting animals), which
are an important food source for a number of fish species. The seagrass blades
are a direct food source for sea urchins and some crustaceans, although their
primary role in the food chain relates to the decay of organic matter
(detritus). This detritus is decomposed by bacteria, which provide a food
source for zooplankton. The zooplankton is a food supply for invertebrates
(including crustaceans, shellfish and worms) and some fish species, with other
fish species preying on the invertebrates. In turn, the invertebrates and fish
are prey for seabirds. Seagrass beds
also play an important role in stabilising the bottom sediments in an estuary,
reducing turbidity levels.
Significant losses of saltmarsh
and mangroves have occurred near urban areas through reclamations, drainage and
other developments. This affects fish
and other sea life, which use these as nurseries and feeding grounds.
Wetlands
can be defined as land where the water surface is near the ground surface for
long enough to maintain related vegetation and periodic saturation of the soil
(Reed et al 1995). Waterplants,
or macrophytes, are the main building block of
wetlands and, subsequently, are an essential part of a healthy aquatic
ecosystem. Macrophytes, particularly
emergent and submerged species, facilitate a number of biological processes
that enhance water quality. This is
achieved by: addition of oxygen to the water via submerge plants; provision of
surfaces for biofilms to form on, at and below the
surface where nutrients are trapped; removal of suspended solids from the water
column by attracting them to the surfaces of the plants; and by providing
habitat for micro-organisms, invertebrates, fish and birds.
In 1989, Environment Australia established the National Wetlands Program
in response to growing concern for wetland conservation. It was also in recognition of the need to act
more strategically and cooperatively with State and Territory Governments in
implementing Australia’s obligations under the Convention on Wetlands (Ramsar, Iran, 1971) and related international treaties such
as the Japan-Australia and China-Australia Migratory Bird Agreements (JAMBA and
CAMBA respectively).
The goal of the National Wetlands Program is to promote the conservation,
repair and wise use of wetlands across
The objectives of the National Wetlands Program are, through working with
all levels of government, industry and the community, to:
·retain, restore
and raise the awareness of the ecological, cultural, economic and social values
of wetlands;
·develop and
implement best practice in the management and wise use of
·ensure a sound
information basis for the conservation, repair and ecologically sustainable use
of wetlands which is available and useable for informed and innovative
community participation in their management and wise use; and
implement the Ramsar Convention and its Strategic Plan 1997-2002, the
Commonwealth Wetlands Policy, the Japan-Australia and China-Australia Migratory
Bird Agreements, the Asia-Pacific Migratory Waterbird Strategy 1996-2000, and
its accompanying Shorebird Action Plan.
There
are vast areas of underground aquifer water basins across
An
aquifer is a permeable geological formation consisting of rock or sediment
which can contain and convey groundwater.
Recharge of aquifers occurs naturally as rainwater infiltrates through
overlying soil layers or via soil-water pathways below streams and lakes.
Protection
of water quality in these storages is of primary importance, as contamination
has occurred due to agricultural chemicals, pesticides and hydrocarbons. Natural aquifers do have the natural ability
to purify water due to the micro-organisms which can only survive in that
unique environment.
As catchments are
urbanised, the frequency and severity of flooding increases because of
increased runoff from roads, roofs and other sealed surfaces when compared with
the more pervious surfaces, which were previously in the catchment. Faster runoff occurs via gutters, drains,
pipes, etc when compared with the slower runoff generally achieved in a less
developed catchment.
These changes can have a number of effects on the stream flow
regime, which may include:
increased
frequency of runoff events (floods) in a watercourse
increased
volume, peak flow, velocity, bed shear stress and rate of water level rise and
fall during floods
increased
frequency of floodplain inundation
increased
flows in ephemeral streams
decreased
groundwater flow due to decreasing rainfall infiltration
decreased baseflows caused by lower groundwater discharges, unless
compensated by flows from excess garden watering (and similar sources) (Codner et al 1988, O’Loughlin et
al 1992, Jollife 1995).
Loss of natural flood storage
areas is inevitable as floodplains are filled, channels straightened, etc. We need to retain and reuse as much
stormwater as possible while maintaining the flows that are necessary for the
ecological integrity of the rivers, streams, lakes and groundwater systems into
which our urban stormwater flows.
The quantity of stormwater
runoff from Australian cities is about equal to the amount of high quality
imported water they use so there is potential for expanded collection, storage
and reuse of stormwater for non-drinking purposes. Urban stormwater is generally not of a high
quality but with varying degrees of treatment it can be used for: toilet
flushing, hot water systems, lawns and paying fields; car washing; irrigation
of parks and gardens and possibly vegetable crops; fire extinguishing systems
and supply to hydrants; artificial lakes and wetlands for recreation;
industrial cooling towers; and aquifer recharge.
However, the flood
management strategies set by Australian authorities are now being complemented
by water conservation and water quality considerations, which can change the
way engineers design for flood management, whilst meeting the flood regulations
and guidelines.
Another way to reduce down
stream flooding is for local councils to regulate stormwater discharges from
new developments by instituting a scheme of transferable stormwater discharge
rights. This would allow developers to
sell (or purchase) the right to discharge stormwater so that flood discharge
from the catchment can be limited. If feasible, it would result in an overall
decrease in the cost of complying with an On-Site Detention (OSD) policy aimed
at limiting downstream discharges and it would also force the cost of
preventative measures onto those responsible for generating excessive amounts
of flood runoff.
In
the advance in computational computers and the
refinements in dynamic flow models, to allow specific flood modelling of
floodplains. Ten years ago, models
contained an upper limit 10,000 computational points; today models containing a
million or more computational points are feasible.
In addition significant
advances have been made in the areas of modelling of hydraulic structures,
stability, and
ability to handle wetting and drying during the course of
the simulations. These advances have
allowed consideration of details of topographical structures as small as 300mm.
With the ability to model
more precisely, community attitudes are changing. This is reflected in the rise in class
actions against council and approving authorities. Councils are acting more cautiously and are
setting more stringent acceptance standards for developments and works in
floodplains.
There are standard
hydraulic structures used in flood control, including channels with given
roughness characteristics, gates, weirs and surface storage. Recently, increased attention has been given
to flow control methods at the source such as reuse and recycling schemes to
reduce water output (Water Sensitive Urban Design Principles).
The traditional approach to
‘improving’ a natural urban waterway (creek or overland flow path) is to increase
its capacity, which generally involves excavation, filling and grass or
concrete lining. This results in the
almost total destruction of habitats necessary to maintain a diverse aquatic
ecosystem.
The alteration of physical freshwater habitats can occur by either
direct human intervention or indirectly by altered channel morphology caused by
changes to the stream flow regime or sedimentation. Channel ‘improvement’ works undertaken to
increase the hydraulic capacity of a watercourse, generally result in the
creation of a uniform channel geometry.
Pool and riffle zones, organic debris and aquatic flora may be removed
and a uniform substrate created. As a
consequence, flow distribution and velocity characteristics are likely to be
less variable within a reach. This can result in a reduced abundance and
diversity of aquatic fauna and flora (e.g. Schoof
1980, Shields et al 1994). The
removal of trees to undertake the excavation and increased capacity, removes a
factor in creating bank stability and a habitat for aquatic biota including
fish through reduced flow velocities compared to artificial channels. Leaf litter serves as an energy source within
the ecosystem. Temperature rises from
lack of shade and increased sunlight changes and destroys the original
biodiversity of the waterway.
Flood mitigation works such as levees with outlet gates or road
embankments across estuaries with small bridge (or culvert) waterways can
significantly alter the tidal regime and/or the salinity. This can have a
negative impact on mangroves, saltmarsh and seagrass
habitats upstream of these barriers. Further, seagrass generally grows in low
current areas and increased tidal or freshwater flow rates downstream of these
bridges or gates may reduce the extent of any seagrass beds. If drains are installed through mangrove
wetlands or saltmarsh, the altered tidal conditions
may also have a negative impact on these habitats.
The design of natural channels involves the creation of channels
with the attributes of natural watercourses. These attributes include:
a
meandering plan form
a main
channel with a floodplain (principally in middle and lower reaches)
a series
of pools and riffle zones (rapids)
riparian and floodplain
vegetation.
Many of the overall considerations for stream restoration apply to
natural channel design. Guidelines on
natural channel design are provided by OMNR (1994), with the design steps
outlined as follows:
Define objectives for design:
Identify the objectives to be met for the design. Multiple objectives regarding
conveying flood flows, aquatic habitat, recreation, aesthetics and maintenance
may exist.
Define existing conditions:
The existing flow, sediment loading, channel, valley and catchment conditions
can be obtained or calculated.
Define the expected
conditions: The expected flow, sediment loading and channel slope conditions
can be calculated
Identify inconsistencies: Any
inconsistencies between the existing and expected conditions are identified and
resolved.
Design parameters: The design
parameters for the channel for unconstrained design conditions are developed to
satisfy the objectives.
Identify constraints:
Constraints to the channels design are to be identified, which may include
property boundaries, roads and services.
Identify compromises:
Compromises may be required between the optimum design conditions and the site
constraints.
Develop design: The design of
the channel systems is undertaken, based on creating a channel in dynamic
equilibrium with appropriate habitat features.
Evaluate design: The
resulting design is compared to the optimum design and the extent of any
discrepancies identified and evaluated for acceptability.
Retention Basins
On-site retention reduces
the need for high cost infrastructure further down the catchment. Its feasibility depends on soil, groundwater,
topography and climate. Retention basins
can be considered to be buffer storage.
This may take the form of existing in-line storage using oversized
pipes, minor tanks or basins, or major storage facilities.
Flood flow retention can be
linked to other water management objectives. Integrated stormwater and
pollution control is needed to balance environmental, social, economic and
technical objectives. (For example, a
comprehensive approach developed in some urban areas aims to maintain the
quality of urban stormwater runoff and enable a range of secondary uses
including passive and active recreation, landscape features and flood
management). The physical measures used
for environmental protection include:
-
Establishment of
urban lakes, primarily as biological treatment systems
-
Construction of
water pollution control ponds and wetlands to act as physical and biological
treatment systems
-
Construction of
major and minor gross pollutant traps on stormwater channels to intercept
trash, debris and coarse sediments
-
Construction of
temporary ‘off-line’ sediment detention ponds as part of land development works
to intercept and treat stormwater from development sites before it is
discharged into the stormwater system
-
Retention of
natural creeks augmented by retardation basin in preference to the construction
of trunk stormwater pipe systems and concrete-lined drains (but it is not
always possible to exclude the latter).
Flood retention storage can
be incorporated into systems also designed for water quality control. Additionally, most authorities require
temporary pollution control measures during construction and land development,
which involves retention of run-off with high loads of suspended solids.
Dry Retardation Basins
Dry retardation basins have
either short or extended detention times.
Those with short detention times aim to reduce peak storm flows from
urbanised areas. Dry retardation basins
are only marginally effective in improving water quality because the residence
time (often less than two hours) may be too short to remove or moderate
physical and chemical pollutants. Dry
retardation basins usually fill only during very large storms, they lack
permanent water to maintain a biological community for treatment, and
infrequent flushing flows may resuspend previously deposited sediments.
The control of the quantity
and quality of stormwater can be undertaken in an integrated manner to minimise
the physical and chemical changes to the water environment. Traditionally, retarding basins have been
located in the middle reaches of a catchment, where watercourses are perennial
and aquatic ecosystems are reasonably well developed. This can result on a relatively large impact
on the aquatic environment, as flows and water quality upstream of the
management control are not mitigated and the impacts on the aquatic environment
are relatively significant. The focus
for these controls has often been the protection of a significant downstream
receiving water bodies such as lakes or rivers.
An alternative approach
involves the installation of more numerous integrated controls in the upper
reaches of water -courses, where flows are generally ephemeral and aquatic
ecosystems are less well developed. This
maximises the length of protected watercourse and minimises any environmental
impacts. This approach recognises the value of the aquatic ecosystem throughout
the catchment. Construction and maintenance
costs are, however, expected to be higher for this arrangement.
The integration approach of
stormwater controls can be achieved by separate or combined quantity and
quality controls. A sustainable strategy
could combine the concept of an extended detention and flood detention storage
to reduce velocities through the basin, to give an outcome of minimising the
potential for sediment scouring and macrophyte damage
in the receiving water body.
Regional Detention Basins: These
are typically designed into a residential development scheme, and ensure that
the overall discharge from the scheme is held at pre-development levels, or
even reduced to lower levels. Such
basins can also be retro-fitted within existing urban areas, or even into
bushland settings.
To achieve flood control,
detention basins are often used to reduce the post development flow so that
basin outflow does not exceed pre-development flow for the design storm. In addition, experience in the
There
are two reasons for this:
1. The longer time of flow at the lower rate. The stream may be subjected to erosive flows
at a lower flow rate but for longer periods of time.
2. Where post-development runoff is smaller than the
basin outlet capacity very little flow attenuation takes place. With the increased frequency of peak flows in
general, and the fact that most detention basins do not regulate flows smaller
than the 10-year pre-development flow, this means that most storms will pass
through the structure unregulated subjecting the down stream channel to erosive
velocities on a more frequent basis.
Wet
detention basins (ponds), with a permanent pool of water,
have been designed to detain stormwater with a subsequent gradual discharge at
some predetermined rate and time after a storm has passed. Recently, in Florida USA, stormwater reuse
has been incorporated into the design of wet detention systems being
constructed. This reduces the volume of
stormwater discharged downstream, thereby decreasing the loss of a potentially
valuable freshwater resource.
By
reusing the detained stormwater instead of discharging it, the treatment
efficiency of the stormwater detention pond is increased, resulting in
decreased pollutant loading and concentrations delivered to downstream
waters. The pond helps improve water
quality by sediment removal, uptake of nutrients from aquatic plants, chemical
transformation and runoff water reuse.
The
detained water can be used within the catchment to:
-
irrigate open
areas
-
recharge
groundwater
-
supplement water
used for cooling & industrial
purposes
-
supplement
domestic hot water and toilet flushing water
-
enhance and
create wetlands
-
supply water for
agricultural users
A reuse pond thus helps
stimulate a natural, pre-development hydrologic balance, while preventing the
direct discharge of untreated stormwater runoff. Reuse of stormwater for irrigation also
provides a significant economic benefit.
In long established urban
areas the drainage system may well have ‘evolved’ rather than have been planned
for the extent of existing or future development. When most of the future development will be
the infilling of the existing urban area, problems are likely with the
increasing load on the stormwater drainage system. The problems are generally over and above
existing problems from overloading of the drainage system, i.e. localised
flooding. One option available to
Council to prevent further drainage problems as a result of future development
is the adoption of an on-site stormwater detention (OSD) policy.
OSD applies the philosophies
of total catchment management by which the adverse impacts of development can
be dealt with immediately and at their source.
The advantage of OSD is that the storage is constructed at the same time
as the development, providing immediate protection to downstream neighbours,
and is generally funded by individual developers.
Best practice in on-site
detention involves:
·
High early
detention: a method of maximising outflow at the onset of storms in order to
conserve storage capacity.
·
Screened
outlets: to closely control flow rate and capture litter, debris and sediment.
·
Frequency-staged
storage: this employs all available storage opportunities such as lawns and
gardens, depressions in public open spaces, open and covered pavements such as
car parks, but in a staged fashion, so that each storage
comes into operation only when the preceding one is full.
·
Tailwater compensation: a
method of controlling discharge when the bed of a storage
lies below the water surface in the receiving drain.
·
Pump discharge
regulation: a method for controlling pumpage from
basement tanks.
·
Quality
enhancement through separation and treatment of first flushes.
The ongoing maintenance,
access de-silting and surveillance of OSD systems on private property are
acknowledged problems of OSD. Many
structures have been found to have no access to carry out important maintenance
and surveillance requirements.
On-site-detention, which
includes components of groundwater recharge, reuse storage and temporary flood
storage can largely eliminate spills, reduce potable water consumption, release
reservoir storage for environmental flow, naturalise storm discharge and
preserve both the structure and habitat values of streams. The process of screening and settling of
suspended solids in runoff before its release captures litter for disposal and
retains sediment and detritus for use within the property.
The benefits of OSD are:
·
it can be funded
immediately (i.e. by the developer) and does not require any capital outlay for
council;
·
it protects downstream properties from increase in
flooding resulting from new developments.
Thus it protects councils against claims for damage arising from
increased runoff from new developments or redevelopments;
·
public land for
larger detention basins may not be available adjacent to existing trunk
drainage systems;
·
the cost of
upgrading existing drainage systems is often beyond the financial means of
councils;
·
the OSD system
tackles the problem at its source, before the increased flows enter a council’s
drainage system;
·
some water quality improvements will also result from
some deposition of coarse particles and the trapping of litter on
outlet-protecting screens within OSD storages.
The disadvantages of OSD
are:
·
Regulations,
criteria and design methods adopted by councils are often too simplistic (and
can therefore be unfair to developers)
·
Under some
hydrological conditions, storages located in the lower parts of catchments can
increase flow rates downstream due to delayed hydrographs.
·
Maintenance is a
major problem, and OSD places a large administrative burden on councils and a
possibly onerous duty on property owners.
·
OSD provides
little scope for stormwater pollution reduction, especially for dissolved
pollutants, and those attached to fine sediment particles.
On-site stormwater detention
systems were conceived to address the difficulty of coping with piecemeal
developments and re-developments when it was technically and financially
difficult to enlarge the capacities of established stormwater drainage systems. The OSD solution is to make those who are
responsible for the increased runoff, and who are the beneficiaries of the
change, to provide storages to maintain the status quo.
Restraining flow to stop
erosion of stream banks and channels is often necessary, where natural slopes
give rise to increased flow velocity. In
nature, stream stability tends to stabilise when the energy flow forces are
dissipated. Eg.
pools and riffles.
In engineered channels or streams which are subject to increased flows,
or in cases where the channels are restricted and directed under culverts or
into pipes, it is often necessary to reduce the increased velocity by
constructing energy dissipators to stop erosion and
scouring of the banks.
Dissipators can take many forms, both ‘natural’ (large rocks and
boulders) and ‘engineered’ (concrete blocks and timber bollards), however the
placement of the flow splitters must be such that it does not direct side flows
into the channel banks, causing scour.
Flow channalisation
in floodways can be used to reduce pollutants as well
as to manage flood flow, if the engineered (or natural) floodway is
vegetated. Vegetation is normally grass,
however better environmental outcomes can be obtained if the vegetation
includes trees and shrubs as well as grass.
This mixed vegetation can keep flow velocities low, which can assist in
the pollutant removal and filtering action.
These floodways may require ‘Check dams’ or
barriers across the line of flow, to reduce water velocity, and prevent erosion
of the floodway. Floodway slopes must be
limited to prevent scouring and instability.
Vegetated floodways can enhance open space public land, and multi use
corridors, and should be designed as an integral aspect of urban planning and
catchment management.
The application of water
sensitive planning and management principles involves the:
·
Incorporation of
water resources issues early in the land use planning process
·
Addressing water
resource management at the catchment or subcatchment
level
·
Wherever
possible, using the natural contours to incorporate and enhance functions of
the natural stormwater system
·
Maximising local
on-site storage and stormwater re-use, and utilising natural runoff channels
·
Use of
vegetation in stormwater management to promote filtering and slowing runoff to
maximise settling of particulate-bound pollutants, and infiltration.
The Water Sensitive Urban
Design (WSUD) philosophy has now been adopted in many
The maxim “Think globally,
act locally” is usually understood to refer to worldwide environmental values
being achieved through positive, affordable action taken by local
communities. This fusion of ecologically
sound practice with economic viability is central to the concept of sustainable
development (WCED, 1990). A microcosmic
interpretation of the maxim can be that “global” refers to city infrastructure
and “local” may be identified with individual dwellings or commercial/public
buildings or groups of such buildings that, collectively, comprise the
city.
While this interpretation of “global” may be used to develop practices
which are ecologically sustainable in the full range of utilities found in a
metropolis (transport, power, sewerage, and gas) our focus here is on the
services which provide water and the disposal and reuse of stormwater. Water sensitive urban development (WSUD) is a
local solution to the global problems created by reliance on conveyance and centralised storage/discharge of water in cities.
WSUD source control includes water conservation and stormwater
retention strategies employed at the urban allotment or cluster to reduce
infrastructure costs and environmental degradation of aquatic environments. The
principles of the WSUD approach have been incorporated in a number of
demonstration projects to foster greater understanding of the benefits and
consequences of this technology. For example, Figtree Place Development,
WSUD aims to bring stormwater
management out of pipes in the ground and to make the entire stormwater
treatment network part of the urban fabric through the use of multiple use
corridors and Best Management Practice (BMP) treatment trains. Vegetated swales,
filter strips, extended detention basins and constructed wetlands are all part
of fully functioning stormwater treatment systems and may also serve other
uses. A multidisciplinary approach to
the design of WSUD infrastructure is essential and can maximise the multiple
benefits of this type of approach.
For example, landscape
architects and urban artists can create designs and features that provide
considerable visual amenity. Ecologists
can select of a range of natural wetland species that enhance pollutant removal
and provide an important ecological function in the built environment.
Planners can incorporate
multiple use corridors into urban areas where they provide regional focal
points for the community. The community
can play a role in defining the types of passive recreational pursuits and
water features that are most attractive.
Of course engineers also play a vital role in WSUD. Engineers must provide designs that function
effectively as stormwater management systems and perform their traditional
function of ensuring minimal risk of flooding, disease or damage to public and
private property with the added requirement for protecting receiving
ecosystems.
WSUD grew out of a recognition of the linkages between the type of stormwater
disposal systems and the quality of downstream ecosystems. It provides for the establishment of links
between stormwater management, catchment management and regional natural
resource management. Regional natural resource management approaches can be
linked to catchment management networks and strategies and fed into planning by
individual councils in the catchment and then into their operational and works
programs and forward budget allocations
WSUD provides sustainable
stormwater management where hydraulic design criteria are combined with ecological , biological, economic, social and aesthetic
considerations.
The hydrological cycle is a complex interaction of rainfall,
evaporation, evapo-transpiration, overland flow and
groundwater flow. In temperate non-urban
catchments with low-medium permeability soil, runoff primarily occurs from
‘source areas’ (Dunne et al 1975). These are areas with relatively high soil
moisture located in valleys and can increase in extent with rainfall. The
extent is related to topography, soil and vegetation characteristics and evapo-transpiration. Due to the dependence of runoff on
soil moisture and the extent of source areas, the runoff characteristics from
these non-urban catchments can be highly variable. Further, many upland streams
can be ephemeral during summer, when evapo-transpiration
rates are relatively high.
Catchments with sandy, high permeability soils can have minimal
surface runoff, with rainfall infiltrating to groundwater. Following periods of
prolonged rainfall, groundwater levels can rise, potentially flooding low lying
areas. The soil, topography and
vegetation characteristics also influence the volume of runoff and the runoff
rate from the catchment, and relatively low runoff rates can occur from flat
catchments. The presence of vegetation influences evapo-transpiration
rates and groundwater characteristics.
Urbanisation changes the run-off, permeability and vegetated cover, which changes the catchment
characteristics. Managing these changes
in a sustainable manner is the basis of planning using WSUD principles.
Total Water Cycle Based
Management (TWCBM) is defined as ‘the integrated use and management of surface
water and groundwater across the landscape to secure a range of social,
economic and environmental benefits' (Lawrence et al, 1999) Surface water
includes treated wastewater and stormwater discharges.
Best practice stormwater
management plans are often integrated into the TWCBM approach. Stormwater management plans must take into
account the interdependency of natural and human factors within a catchment
area. Decisions on what to do in one
part of a catchment must be based on knowledge of the consequences for the rest
of the system.
Current policies in
Natural processes, which
control runoff are in constant change. Typically, streams change course, natural
erosion occurs, and vegetation and soil permeability change with the
seasons. When humans alter the land within
a catchment, the changes to the natural processes accelerate, creating a need
for constructed stormwater management systems.
However, if policies are adopted to encourage WSUD and many such
projects are completed then substantial urban infrastructure cost savings to
the community may materialise. Water utilities faced with the decision to expand headworks,
water distribution and stormwater infrastructure to meet the needs of extra
population, must make a comparison between:
·
the lifecycle
cost of new and existing infrastructure required to satisfy the (conventional)
additional water supply demand and additional stormwater load, and,
·
the lifecycle cost of new practices which decrease
potable water consumption and stormwater load, and encourages water reuse and
environmental sustainability.
A comparative analysis of economic externalities such
as environmental and social consequences of traditional and WSUD systems is
very important. Of all land use changes that affect an area’s hydrological
cycle, urbanisation is the most important.
However, other land use changes within a catchment such as agriculture,
forestry and mining also alter the hydrological cycle and create a need for
stormwater management. Pollution and
run-off volumes create impacts that require catchment repair strategies. These costs should be included in the
economic modelling for future water cycle management.
The ‘treatment train’
approach to integrated stormwater management improves the overall performance
of a water quality treatment system, leading to a strategy that can overcome
site related factors. Generally, the
more BMP's incorporated into the system, the better
the performance and the more likely it is that water sensitive design
objectives will be achieved. This
strategy also provides a catchment-wide approach to stormwater management. It is important to recognise however, that BMP's fail if inappropriately used, incorrectly located
within the treatment train,
misunderstood in their implementation in a staged program, or are
not maintained. A common problem in many
stormwater management strategies is the issue of maintenance and rehabilitation
of stormwater pollution control facilities.
The life cycle of stormwater management options are often not taken into
consideration when assessing the merits of individual management measures.
The selection of BMP's is likely to vary largely from site to site. No two environments are exactly the same, so
no hard and fast prescriptive assessment can be applied. The most appropriate BMP's
must be determined after assessing the characteristics of individual
elements. This must not deter designers
and managers with the willingness to work, to find appropriate solutions.
Systems
In most situations, a number
of water quality management measures may be implemented in series forming a stormwater
pollution management system, ideally based on the philosophy of:
The common elements in a
stormwater treatment train may be summarised as follows:
·
community
awareness (education)
·
land use
planning and regulation
·
permissible
discharge (and licensing)
·
street cleaning
·
sewer overflow
management
·
isolation of
high pollutant source areas
·
construction
site management
·
landfill
management
·
litter traps
·
on-site
detention/retention applications
·
stormwater
infiltration
·
stormwater
re-use
·
buffer zones
·
gross pollutant
traps
·
swale systems
·
detention basins
·
ponds and
wetlands
·
gross pollutant
traps
·
catch basins
·
floating booms
·
ponds and
wetlands
·
receiving water
management
Within
these processes, there are generally 3 levels of treatment:
·
Primary
-
Screening of gross pollutants
-
Sedimentation of coarse particles
·
Secondary
-
Sedimentation of fine particulates
-
Filtration
·
Tertiary
-
Enhanced sedimentation and filtration
-
Biological uptake
-
Absorption on to sediments
In
most circumstances, a treatment train approach is appropriate to optimise
pollutant removal. The types of primary,
secondary and tertiary treatment systems are described in Chapters 6, 7 and 8.
Stormwater management practices for
land development and similar projects should be implemented by the developer in
accordance with a stormwater management scheme based
on ecologically sustainable development principles. The scheme should be
prepared by the developer or builder and should be consistent with any stormwater management plan which applies to the development
site that has been prepared by a council or a group of councils. Land developers and builders are generally
responsible for ensuring that their development does not result in any
significant exacerbation of existing stormwater
management problem. These developments
should only occur in areas where a land capability assessment has indicated that
stormwater management practices are capable of
achieving this objective. Further,
developers should be encouraged to improve existing stormwater
systems (e.g. degraded creeks). Natural water bodies such as wetlands and
creeks should not be used for stormwater treatment
purposes.
Development using WSUD principles can create improved systems that can
be more attractive to prospective purchasers, increase the value of adjacent
land, and may avoid expensive new infrastructure. The value of land adjacent to
stormwater treatment measures such as water quality
control ponds and constructed wetlands is usually higher than for land adjacent
to a conventional drain. Water-sensitive
urban design principles should be adopted for developments, and stormwater management should be integrated with total water
cycle management. A strong emphasis should be placed on stormwater
source control within developments. The multiple use
of stormwater systems should also be encouraged. For projects requiring a development
application, conceptual stormwater management schemes
(for long-term stormwater management and re-use) and
soil and water management schemes (for construction activities) should be
prepared. Final schemes would be submitted with the building application or
subdivision plans. The soil and water management scheme should be compatible
with the stormwater management scheme. When only a
building application is required, the soil and water management scheme should
be submitted with this application.
One of the benefits of
taking a WSUD approach to stormwater management is the linkage with landscape
design to create better natural resource planning, urban streetscape, and
better urban parklands. On large
developments and green field estate development, the integration of sound
engineering principles with landscape design can not only provide more
efficient water management, pollution management, and cost savings, but
increased property values due the visual amenity of landscaped parkland
surrounding water management ponds and wetlands.
With the improved design
of water systems in the urban environment, further potential opportunities are
available for innovation with water engineering and art. Instead of piping and hiding drainage
infrastructure, water quality and quantity controls can be introduced in a
creative manner to enhance urban spaces.
Where fountains and water flow systems allow for human body contact, the
stormwater may have to be pre-treated in order to meet health regulations.
Primary Controls for Pollution
Management
Historically, stormwater
management has focussed on end-of-pipe and structural solutions, such as gross
pollutant traps and artificial drainage channels for flow control. In best management practice, however, there
is a move towards finding solutions closer to the pollution source and an
integration of structural and non-structural solutions. Despite this shift, the use of structural
in-line controls is still prevalent, and may be the only effective solution in
some retrofit applications.
The community generally,
regards litter in stormwater as an ugly constituent. Many also mistakenly believe that litter may
not need to be taken too seriously because it mainly comprises benign materials
which we use, without hesitation, every day. (reference:
EPA NSW Study of Community Attitudes 1999)
Similarly the vegetation
making up between 50% and 80% of the non-particulate solids in runoff is looked
on as an essentially natural material that belongs in the landscape and, by
extension, in the drainage system. Some sediments, too, are seen to be of little import because
streams actually require a sediment load to maintain their proper
morphology. The reality is
otherwise. The litter stream, for
example, includes millions of cigarette butts, which persist for years, being accidentally
ingested by aquatic animals and being, of course, rich in the carcinogens they
are created to capture. Polystrene, too, is both persistent and indigestible and
tends to lodge in gills and obstruct the guts of susceptible species. Hypodermic syringes are increasingly found
and the glass bottle, usually in fragments, is a hazardous feature of bottom muds in every water body.
Drink cans made of aluminium
are chemically reactive, highly toxic in some phases, and may degrade in the
low pH of anerobic zones. A high proportion of all litter sinks to the
bed where it binds the surface or becomes embedded in sediments to disrupt the
activity of benthic organisms and bottom feeders. Organics degrade, either aerobically or anerobically, causing oxygen depletion or producing gases,
odours and soluble compounds. This organic litter is called putrescible
litter. Leaf litter is not at all
natural in the quantities which reach urban drainage systems. Under natural processes the vast majority of
such material remains in the detritus layer on the forest floor, holding runoff
for slow release and gradually decaying to return nutrients to the soil. In the urban setting the tree and shrub
category is often as dense as it might have been prior to European settlement
but drops its detritus onto roofs, paved areas and manicured lawns which see it
efficiently washed into drainage systems in the slightest runoff events. The fate of this material is as discussed
above for putrescible litter.
The aesthetic effect of
litter and detritus has a profound influence upon the value people attach to their
waterways and could, alone, justify the removal of these materials from
stormwater but the case for serious underlying water quality impact by these
materials is even stronger.
Litter is unsightly, environmentally damaging and can cause blockages
to stormwater management systems.
Plastics take over 100 years or longer depending upon the type of
plastic, to decompose and can cause problems not only within the stormwater
system but to aquatic life and birds in the coastal and marine
environment. Litter and debris can also
have significant economic impacts in tourism areas and in marine engines
through their intakes. The bulk of
marine litter comes from stormwater.
Methods of reducing gross
pollutant impacts include:
·
Preventative
measures (education and awareness) including drain labelling, working with
manufacturers to reduce packaging and encouraging recycling
·
Containment of
gross pollutants (street cleaning)
·
Capture of gross
pollutants in the drainage system prior to release into receiving waters
·
Bio-retention of
pollutants (mainly applicable to nutrients and heavy metals)
·
Remedial
clean-up methods
Results from monitoring
programs suggest that, although large amounts of gross pollutants are
transported from urban catchments to receiving waters via the stormwater
system, technologies are available to capture these pollutants from within the
drainage network. However, trapping
gross pollutants from within urban waterways can be expensive. With the large areas associated with urban
centres in
Despite education,
awareness and street cleaning programs, large amounts of gross pollutants are
reaching and degrading receiving waters.
A catchment study
(SIA Source Control Workshop, Merrylands 2000) showed that
previous estimates of the number of litter items moving through the stormwater
systems are too small by orders of magnitude, and that organic material and
sediment is consistently the main component of gross pollutant loads.
The results from the
Source Control monitoring program indicated that about three quarters of gross
pollutants are organic material (mainly leaves and twigs). This was observed consistently across
different land-use types. However,
despite the large amounts of organic gross pollutants transported by
stormwater, they are not a major source of nutrients (Total Phosphorous and
Total Nitrogen). The results indicate
that nutrient loads transported by organic gross pollutants are about two
orders of magnitude lower than the diffuse loads generated from other
sources. Nevertheless, because of their
large amounts, organic gross pollutants must be taken into account in the
design of gross pollutant traps, especially where they are likely to impose
physical impacts such as pipe blockages or habitat smothering.
Higher amounts of litter
(mainly paper and plastics from pedestrians and motorists) are transported from
commercial and light-industrial areas than from residential areas. This suggests that commercial and light
industrial areas should be targeted for reduction strategies.
Only 20 percent of the
litter and less than 10 percent of the organic material transported by the flow
in urban waterways are transported as floating material. This means that floating gross pollutant traps
can, at best, only capture small fractions of the gross pollutants being
transported. There is a need to design
trapping systems that include capture of gross pollutants being transported
within the flow.
Outcomes from event
monitoring programs indicate that gross pollutant concentrations generally peak
before the peak of the storm hydrograph (first flush effect, where the
stormwater flow initially collects surface pollutant load). However, most of
the gross pollutant load is transported during peak discharges. As such, to capture the maximum amount of
gross pollutants, trapping systems could be designed to treat high
discharges. This result would suggest
that ‘first flush’ trapping systems (designed to direct the small initial
portion of runoff into a treatment chamber and allow the remainder of the flow
to by-pass the trap) will not treat the flow when most of the gross pollutants
are transported and therefore would miss significant quantities of material,
particularly for large storms.
Although gross pollutant
loads and concentrations vary considerably during runoff events, the
composition of the gross pollutants remains relatively consistent. This suggests that organic and litter
materials are transported in similar ways through drainage networks during
runoff events. It is therefore not
possible to capture exclusively one component of gross pollutants by only
treating one part of the storm hydrograph (e.g. capturing most of the litter by
removing the first part of the runoff is not possible).
Litter items mostly enter
the drainage network from commercial areas, mainly due to the actions of
pedestrians and motorists in the catchments, which contributed large quantities
of plastic and paper items (especially food and drink items) and very high
numbers of cigarette related items (approximately 35% of the total number of
items).
For stormwater management
to be effective, BMP's must be applied throughout the
catchment. Nonetheless, the increase in
pollutant loads from urban areas is typically so large that, even with the use
of BMP's, it is unlikely that pollutant loads will be
reduced to pre-development conditions.
Results suggest, that appropriately designed and properly sited BMP's can provide some mitigation of stormwater impacts on
stream communities. However, the
resulting communities differ greatly from those in undeveloped catchments and
reflect a fundamental alteration in stream biotic diversity (Jones et al, 1996). Before a particular BMP or series of BMP's can be determined, consideration of the catchment
area, objectives for the receiving waters, soil and groundwater requirements
have to be made and the preferred practice adopted that best fits with these
constraints.
Runoff Pollutant Loads – the first flush flow, has higher concentrations
of stormwater pollutants that characteristically occur during the early part of
the storm. Concentrations lessen as the
runoff continues. Concentration peak and
decay functions vary from site to site depending on landuse,
the pollutants of interest, and the characteristics of the drainage basin, such
as the amount of imperviousness, type of stormwater conveyance system, and the
length.
Increasing building
densities through urban consolidation lead to increased impervious areas which
threaten the capacity of systems and increase the risks of overflows as well as
reduce water quality by the loss of "treatment" associated with the
porosity of natural surfaces. Studies in
the
It
is difficult to assess pollution levels in stormwater as normal or typical as
they vary so much due to great differences in pollutant availability, rainfall
intensity and duration. Sydney and
Melbourne studies carried out by CDS Technologies by monitoring their Gross
Pollutant Traps, show first flush pollution may be three times that during the
peak flow, but because peak flow volumes are so high the largest quantities of
pollutants are transported with the peak flow.
Gross pollutant traps are
designed to trap litter, debris and coarse sediments in drains. They are often large concrete
structures. They sometimes incorporate a
weir, and upstream swales may be provided along the stream bank. These accommodate flows and impound water
during heavy rainfall. These structures
are used in
GPT’s
range from quite simple screens, which might be used for a single inlet pit, to
structures which straddle channels and may have a twenty metre footprint. They are
designed to remove coarse materials from the mid-range rainfall events
accounting for the majority of total runoff, generally by using screening,
stilling (stalling flow), settlement, flotation and
flow separation techniques in various combinations. Some also tend to catch quite fine particles
by filtration through the coarser material already retained.
The principle design
requirements of these devices are:
·
Selecting the
desirable sediment and litter capture sizes for particular catchment
characteristics.
·
Selecting the
storm frequency to be fully accommodated
·
Devising a
maintenance schedule to limit chemical and biochemical activity between
services
·
Providing ease,
frequency and safety of maintenance
·
Sizing the trap
to suit catchment size
·
Providing
monitoring data for pollutant loading estimation and storage sizing
·
Site location
considerations for selecting exposed or enclosed traps
·
Aesthetic
acceptability
·
Installation and
operating costs
There are two principle
types of GPT’s: Those that hold their
pollutant load in the ‘dry’ state, and those that hold it ‘wet’. ‘Dry’ traps are generally cheaper to maintain
because of the cheaper costs for litter disposal (removal to landfill). ‘Wet’ traps are generally efficiently cleaned
using eductor suction equipment, but the wet waste is toxic, and many
authorities require it to be treated or disposed under environmental safeguards
required for liquid waste. ‘Wet’ traps
which are not regularly maintained, can add to the pollutant load due to
biochemical reactions between pollutants (being dissolved and in suspension)
held in the collection chamber, washing out of the trap in the next storm flow
event.
In
· Canberra University/Willings – large concrete steel stilling bas