WASP: A planning and policy tool for sustainable urban irrigation This article by Bhakti Devi featured in the Irrigation Australia Journal, Winter 2009, Volume 24, No. 2. With urban areas across Australia feeling the effects of drought in the last few years, the response of many water utilities has been to implement water restrictions for urban green spaces, including domestic gardens, sporting ovals and grounds and other public open spaces. While restrictions do conserve water resources, this is at the cost of the quantity and quality of the urban green space and the associated social, economic and environmental benefits. Without a tool or framework for analysing existing urban irrigation demand and determining the water saving potential of various categories of urban green spaces, it is likely that water restrictions continue to be the preferred policy option for saving water.

1. WASP: A PLANNING AND POLICY
TOOL FOR SUSTAINABLE
URBAN IRRIGATION
Bhakti Lata Devi, Manager Water
Strategy, City of Sydney
With urban areas across Australia
feeling the effects of drought in the
last few years, the response of many
water utilities has been to implement
water restrictions for urban green
spaces, including domestic gardens,
sporting ovals and grounds and
other public open spaces. While
restrictions do conserve water
resources, this is at the cost of the
quantity and quality of the urban
green space and the associated
social, economic and environmental
benefits. Without a tool or framework
for analysing existing urban irrigation
demand and determining the water
saving potential of various Figure 1: Break down of urban irrigation demand.
categories of urban green spaces, it
is likely that water restrictions
continue to be the preferred policy Irrigation demand – not easy to day to specific sites. Macro-
option for saving water. management implies managing
determine
aggregate water demand of urban
Australian urban water utilities do Unlike indoor water demand, green spaces through promotion and
have a tool for analysing the indoor irrigation demand to maintain facilitation of water use efficiency,
water demand and this is used to gardens and public open spaces is use of alternative water sources and
help quantify baseline demand for complex. Apart from depending on behavioural change amongst urban
water by each indoor end use and to the technical efficiency of the irrigators. This may be achieved by
estimate and quantify the water watering device and human
saving potential that exists with each implementing well-informed and
behaviour, it is a function of well-targeted policies and programs.
end use. Predicting the volume of
biophysical factors that include the In recent years, various tools,
water that can be saved by
water–atmosphere–soil-plant gadgets and calculators have
implementing such a program
interaction which, in turn, is dictated appeared on the market for
provides the necessary confidence for
by weather factors, particularly scheduling irrigation in public parks
investing in a policy or program for
rainfall, evaporation, wind speed, and gardens. These are being trialled
saving potable water or reducing
humidity and radiation, together by urban water utilities, although the
water demand or both.
with characteristics of the soil and rationale for trialling them is often
Because there is no similar tool for
garden plants. Any attempt to unclear. It seems that the technically-
urban irrigation demand, water
analyse urban irrigation demand minded water managers of the
utilities have to rely on guesswork,
therefore must integrate modelling of utilities believe that that tools,
which results in lack of confidence in
this interaction as part of the demand gadgets and calculators can help with
investing in any long-term programs
analyses. macro-management of urban
to target reduction in urban irrigation
demand. This means it is easier for a To put the management of irrigation demand.
utility to achieve tangible water aggregate urban irrigation demand in However, macro-management
savings by enforcing water perspective, the difference between requires policies and programs that
restrictions. The drawback is that micro-management of irrigation sites facilitate sustainable ways of
historical annual water consumption and macro-management of aggregate irrigating urban landscapes.
for urban water systems show that urban irrigation demand should be Improving water use efficiency of
water demand invariably springs back recognised. Micro-management irrigation devices with micro-
to previous high levels as soon as entails managing the frequency and management tools is therefore just
water restrictions are lifted. amount of irrigation delivered each one of the many ways of reducing
28 IRRIGATION AUSTRALIA

2. CRCIF
irrigation demand and conserving water. Other alternatives
include using alternative sources of water, designing low-
water using landscapes and xeriscapes, and promoting
garden practices that reduce water consumption by plants.
A focus on micro-management tools for improving
irrigation efficiency could lead to other options for
sustainable irrigation to be overlooked.
As a way forward from current policy position of water
restrictions that treat all urban green spaces to be the same
to a more rational policies, a decision-making tool called
WASP has been developed for macro-management of urban
irrigation demand through a PhD research under the
auspices of CRC for Irrigation Futures and University of
Western Sydney. This decision making tool was designed
to analyse urban irrigation demand to facilitate
development of sustainable urban irrigation policies and
programs.
What’s WASP?
The name comes from the acronym for Water-
Atmosphere-Soil-Plant, the interaction of which
underpins the tool. It also is an acronym for ‘water saving
potential’, which the tool is ultimately designed to map
and quantify for urban green spaces. WASP is a decision-
making tool developed for macro-management of water
demand by irrigation of urban green spaces.
Developing Baseline Data for Urban Irrigation
Demand. WASP applies end-use modelling or end-use
analysis that utilities across the world have successfully
applied to understanding the energy and indoor water
demand of an urban region. This approach builds up a
picture of demand by breaking down the demand into its
individual elements that together make up total demand.
To build an urban irrigation demand picture of a region,
the region is first broken down into zones that share
similar types of soil and climate (Figure 1). Individual soil-
climate zones are then separated into different kinds of
landscapes or green spaces that contribute to the irrigation
demand within the soil-climate zone. This is done because
water demand is influenced not only by the type of urban
landscape but also the purpose of the green space. Hence
within a soil climate zone, recreational green spaces like
golf courses and soccer fields would have different levels of
water demand compared to non-recreational parks and
domestic gardens in the same climatic and soil type zones.
The irrigation demand for each type of green space is then
modelled by taking account of the individual planting
types that constitute the particular landscape type.
This baseline data must be compiled before policies and
programs for sustainable urban irrigation can be
developed. This is because it provides a reference against
which the policy can be evaluated. It also establishes a
framework for collecting future information necessary to
evaluate the program, in addition to developing future
demand projections.
Irrigation budgets and benchmarks for urban green
spaces. Figure 2 shows two basic modules that have been
integrated to make up WASP and how their outputs can
inform the development of policies and programs focused
on promoting sustainable urban irrigation.
Module-1 of WASP simulates the biophysical
water–atmosphere–soil-plant interaction by determining a
daily water balance for the effective root zone of the plant
so the depth of irrigation water that needs to be applied
for a given soil condition and the planting type/s that
Continued on page 32
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3. CRCIF
Continued from page 29
compose the green space can be
estimated. Running a daily water
balance for 100 years of daily weather
data, WASP Module-1 estimates a
monthly irrigation budget or
benchmark for various types of urban
green spaces in a given soil-climate
zone.
Inputs required include weather
parameters, soil properties and
landscape characteristics. Taking
these inputs, Module-1, estimates the
required daily water application for
every day of 100 years for which
weather data have been inputted into
the model. The watering requirement
is expressed in depth (mm) of water,
which allows it to be used as a
benchmark or budget. Performance Figure 2: WASP and its two modules; their inputs and outputs.
between landscapes of the equivalent
type in a given soil climate zone can
Mapping the water-saving potential This output includes an estimation
also be compared. For a given soil-
of urban green spaces of potential water savings relative to
climate zone, Module-1 outputs the
the distribution of landscaped
monthly median values as monthly Module-2 of WASP maps and
properties within each landscape type
irrigation budgets or benchmark estimates the water saving potential
into low, moderate and high water
values for: of the landscapes and classifies them
saving potential. An additional
• landscapes mainly composed of into landscapes with high, moderate
output of Module-2 is a map showing
high, moderate and low water using and low water saving potential. This
the location and distribution of
plants requires historical metered water
properties with their water saving
• the microclimate to which the consumption data of the landscaped
potential.
landscape is exposed (i.e., full sun, properties to be entered and aerial
The quantified water saving
part shade, full shade) photographs of the properties linked
potential from different landscape
• the ratio of turf to shrubs in a to a Geographical Information
types can be fed into models that
landscape. System (GIS).
perform the cost benefit analysis of
Assumptions about effective root The module first estimates the
the programs and policies for
zone depth, soil properties, landscape irrigation component out of the total
sustainable urban irrigation to help
coefficient, and maximum allowable water use from the metered
prioritise the programs, based on the
depletion that are made to estimate consumption data of individual
return for investment by each of the
required irrigation application rate properties for each billing period
initiatives.
can be revised and modified if more (quarterly or monthly as convenient).
The map of the location and
accurate data becomes available. Using the area of landscape, it
distribution of properties by their
The monthly irrigation benchmark converts kilolitres of irrigation water
water saving potential can provide
values produced by WASP Module-1 applied by individual properties
clues about where the programs and
can be used by water utilities to during the billing period to
policies need to be specifically
communicate to urban irrigators the millimetres actual irrigation applied.
targeted to maximise the return on
irrigation budgets for their landscape The area of individual landscape is
the investment made in the form of
on a monthly or quarterly basis, estimated by digitising the green
water savings. It may also serve as the
matched to billing frequency. These zones in the GIS linked aerial
basis for water utilities to encourage
budgets can help water users compare photographs of individual landscaped
home gardeners to use different
their actual water consumption, as properties. Millimetres of actual
plants in landscaping their gardens.
shown on the water bill with the irrigation water applied are then
compared with the irrigation budget Both modules of WASP can also be
budget, with the benchmark provided
for the billing period and the used in tandem to study the impact
by the utility. With this information
landscape type, its layout and micro- of various policy scenarios, thereby
they can tell whether they are
realising the maximum water saving climate, to estimate the water saving helping to prioritise and rank the
potential for their garden type, and potential for each billing period. The policy options by their impact.
can adjust irrigation use to set goals water saving potential of individual
for water savings. Providing the water properties is classified as low, Conclusion
users with information that enables moderate and high and is used to WASP is a decision-making tool that
them to measure their own produce a thematic map of the helps to systematically and
performance against a benchmark property using GIS software, and by scientifically analyse and (macro)
can be seen as first step in moving producing a map of the landscaped manage urban irrigation demand. It
towards a community-based properties in the urban region, by helps take ‘guesswork’ out of the
voluntary approach to sustainable their individual water saving analysis and (macro) management of
urban irrigation. potential. urban irrigation.
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