SPATIAL DECISION SUPPORT SYSTEMS FOR ASSESSING WATER QUALITY RISKS IN SYDNEY’S DRINKING WATER CATCHMENT
Noonan, MJ 1, Greene, GR 1
1. Sydney Catchment Authority, Penrith, NSW, Australia
INTRODUCTION
The Sydney Catchment Authority (SCA) is a government agency established in 1999 to protect the quality
and quantity of water in the drinking water catchment and reservoirs that supply Sydney, the Illawarra, Blue
Mountains, Southern Highlands and the Shoalhaven, an area exceeding 16,000 square kilometres. The
catchment drains into 11 major dams, with the water released via a network of rivers, pipes and canals to
water filtration plants prior to distribution to customers. The catchment is a dynamic and productive area with
a population of around 120,000 people across 15 local government areas, and includes large regional
centres as well as 485,000 hectares of agricultural land supporting over one million sheep, 200,000 cattle
and other stock.
The SCA’s strategy for achieving the aim of management of the catchment to protect the quality and quantity
of water from current and future development and activities is set out in the Healthy Catchments Strategy
(HCS), which is delivered through an annual program of activities. To enable the SCA to prioritise its actions
in the HCS, spatial decision support systems have been developed to assess the potential risk from pollutant
sources. Two of these systems are the Neutral or Beneficial Effect on water quality (NorBE) Tool and the
Pollution Source Assessment Tool (PSAT).
The NorBE Tool addresses risk to water quality from future development and allows councils to undertake a
NorBE assessment for all low to medium complexity developments in the catchment, as required under the
State Environmental Planning Policy (Sydney Drinking Water Catchment) 2011 (the SEPP). The tool adopts
a risk based approach assuming that the site conditions, the actions that comprise a development, and the
way those actions are managed are appropriate indicators for a neutral or beneficial effect on water quality.
The PSAT brings together the best science and technical information, spatial data, modelling, expert
knowledge and best management practices to assess the potential risk of current pollution sources across
the catchment. It analyses the relative risk of four priority pollutants from 13 land use activities or ‘modules’ at
a drainage unit scale. The outputs of PSAT are used to prioritise the location and type of pollution sources
the SCA will target in its HCS. In the medium and long-term PSAT will show improvements in the level of risk
of pollutants as a result of management activities by the SCA and its partners.
METHODOLOGY
The Neutral or Beneficial Effect on Water Quality Assessment Tool
The NorBE Tool is a customised, web-based software application developed by the SCA. It guides the user
through a number of screens depending on the nature of the proposal, recording the decision process and
displaying the lot information through the Spatial Information Exchange Viewer screen. The tool enables the
assessment of development site conditions, and stormwater and wastewater impacts, and includes a GIS-
based effluent plume generation modelling tool (the WEM) to support the assessment and design of on-site
wastewater systems (Figure 1).
Pollution Source Assessment Tool
The PSAT is a spatial decision support system incorporating 14 modules, each addressing a key catchment
activity or potential pollutant source. The modules provide coverage of all significant pollution sources within
the catchment, enabling a set of inputs to be individually tailored for each pollution source. It ensures that the
most appropriate datasets were used, and allows a flexible modelling approach that uses more than one
method and set of inputs to characterise pollution from all sources (Figure 2). Some pollutants are of greater
concern for the water supply storages than others. The SCA focuses most of its catchment management
activities on addressing the following four priority pollutants: (1) pathogens, such as Cryptosporidium and
Giardia, (2) nitrogen, (3) phosphorus, and (4) suspended solids. The modules are being progressively
updated to incorporate new data, changes to existing information and advances in scientific modelling and
knowledge.
RESULTS
The Neutral or Beneficial Effect on Water Quality Assessment Tool
Implementation of the NorBE Tool since 1 March 2011 has resulted in greater consistency and accuracy in
NorBE assessments by councils, enhanced relationships between catchment councils and the SCA, greater
compliance with the SEPP and the Environmental Planning and Assessment Act 1979, streamlining councils’
development assessment process and reducing the number of development applications being referred to
the SCA for concurrence.
Pollution Source Assessment Tool
A comparison of the PSAT outputs from 2009 to 2011 data showed improvements in the relative risk rating
as a result of actions undertaken by the SCA and its partners. In 2009, PSAT showed very high risk ratings
for pathogens for five drainage units with sewage treatment plants (STPs). Between 2009 and 2011, the
SCA assisted councils through the Country Towns Water Supply and Sewerage Program to upgrade five
STPs to meet the requirements of NorBE. In PSAT 2011, four of the five drainage units risk ratings were
reduced to moderate or low.
CONCLUSION
The NorBE and PSAT are innovative decision support systems that have enabled the SCA to assess current
and future pollution source risks in the drinking water catchments that supply Greater Sydney. The
development and implementation of the NorBE Tool and its associated models, including the wastewater
effluent model, help deliver better water quality outcomes through accurate and consistent assessments,
resulting in a reduced water quality risk from new development occurring in the catchment. The PSAT
provides information on the relative risk of pollution sources and pollutant types to help the SCA target and
prioritise its catchment management programs for existing developments or land uses.
Figure 1: Example of a Wastewater Effluent Model Outcome Plume Generation (NorBE Tool)
Figure 2: Main Components of the Pollution Source Assessment Tool