Nattai and Cattai River Catchments Case Study using eWater Source
Case study focusing on the Nattai and Cattai river catchments in the Hawkesbury- Nepean basin, using eWater software to simulate in detail the movement of water and contaminants from areas of mixed land-use in a range of climatic conditions. This ‘road-test’ challenges the software to see if it can model runoff patterns at small scale. The aim is to provide detail on the variable source areas during very wet or moderately wet weather, and the influences of landscape, land-use and management factors on runoff and
Published on: Mar 3, 2016
Transcripts - Nattai and Cattai River Catchments Case Study using eWater Source
eWater CRC is working on local water-management issues in partnership
projects with organisations in NSW, at their request.
Focusing on the Nattai and Cattai river catchments in the Hawkesbury-
Nepean basin, the project teams are applying eWater software to simulate
in detail the movement of water and contaminants from areas of mixed
land-use in a range of climatic conditions.
This ‘road-test’ challenges the software
to see if it can model runoff patterns at
small scale. The aim is to provide detail
on the variable source areas during very
wet or moderately wet weather, and the
infl uences of landscape, land-use and
land management factors on runoff and
ABOUT THE FOCUS CATCHMENT
The Hawkesbury-Nepean catchment, which covers
an area of some 22,000 km2, supplies drinking
water for Sydney’s 4 million people, providing over
95% of Sydney’s water supply. More than half of
the catchment area is bushland.
The Nattai sub-catchment, south-west of Sydney
near Mittagong and Bowral in the Hawkesbury-
Nepean region, is the site for one detailed trial of
the software. Annual rainfall is 1200-800 mm, and
over two-thirds of the catchment is covered by
natural forest or woodland. The urban development,
part of the ‘southern highlands’, is mostly in the
Contamination sources include sewage (from
one treatment plant, sewer overfl ows and septic
tanks in the catchment), as well as moderately
heavy grazing pressure from mixed livestock
(cattle, sheep, horses and alpacas), though there is
generally good groundcover in the pastured areas.
Work is also commencing at a further trial site, the
Cattai sub-catchment, north-north-west of Sydney,
near Blacktown, Windsor and Penrith.
This eWater application is seeking to demonstrate
the functionality and capability of the CRC’s
software, so that partner organisations can
compare it to other commercial software that is
currently in use.
Only one of eWater CRC’s next-generation software
tools is on trial here: the catchment modelling
framework ‘WaterCAST’, which models movement
of runoff and contaminants across and out of a
FOCUS CATCHMENT and eWater CRC
and eWater CRC
SOURCES OF CONTAMINANTS AND RUNOFF
Several of the characteristics of the Nattai catchment can
infl uence the risks to a drinking-water catchment, and are of
interest for this trial. For example:
• Sewage contamination;
• Septic tanks;
• Urban development, particularly with different degrees of
• Sediment transport in runoff;
• Farm dams which can act as pollution detention basins;
• Steep forested areas which can be signifi cant sources of
sediment and nutrients in large events.
HOW eWATER IS HELPING
Using the considerable quantity of data available for Nattai
catchment, the eWater team has begun work to meet these
challenges to the catchment modelling software.
The model works with a range of climate and spatial data
relevant to subdivisions of a catchment. Rainfall data have
been collected from records held by Sydney Catchment
Authority and the Bureau of Meteorology. Subcatchments
are further divided into functional units that enable this
software tool to work with variable yields of contaminants,
and an initial set of functional units has been selected on
the basis of major land-use categories. It is intended to test
whether further refi nements of these units based on soil,
land-capability or differences in management practices will
improve the model sensitivity.
The software will be working with detailed data in the
Nattai catchment, including: digital elevation data at 25 m
spacing; mapping of land-use and land-capability, soil types,
impervious paved areas, distribution of farm dams and
unsewered residences, and rainfall variability; and a pollutant
hillslope hazard index for total phosphorus, total nitrogen,
pathogens and sediment.
This application will give partner organisations in NSW,
especially Sydney Catchment Authority, a sound basis for
comparing eWater’s ‘WaterCAST’ catchment modelling
framework against other software currently in use.
The application will also further develop the tool’s
functionality and precision simulation, which will be of value
in other situations elsewhere.
All eWater tools demonstrated in focus catchments are part
of our integrated modelling suite.
These eWater partner organisations are
involved in this project:
Sydney Catchment Authority
SKM Pty Ltd
NSW Department of Water and Energy
NSW Focus Catchments Coordinator:
Penny Knights, Sydney Catchment Authority