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