Landscape Design Guidelines for Water Conservation
5.0 Glossary of terms
Aquifer
Permeable layers of underground rock, or sand that hold or transmit ground water below the water table.
Catchment
An area of land drained by a waterway and its tributaries.
Condensation
The conversion of water from a vapour to a liquid.
Deep infiltration
Infiltration of stormwater to deep soil layers and aquifers.
Depression storage
Proportion of water that collects in minor depressions on the catchment surface during the initial stages of stormwater runoff.
Drainage catchment
The area of land contributing stormwater runoff to the point under consideration.
Erosion Wearing away of the lands by running water, glaciers, wind, and waves.
Evaporation
Process by which liquid water is converted into water vapour.
Evaporation rate
The quantity of water, expressed in terms of depth of liquid water, which is evaporated from a given surface per unit of time. It is usually expressed in millimetres per day, month, or year.
Evapotranspiration
Combination of evaporation from free water surfaces and transpiration of water from plant surfaces to the atmosphere.
Field capacity
The soil condition that results when macropores are empty of water and micropores are full of water. This state usually occurs 24 to 48 hours after rain or irrigation. Sand holds very little water at field capacity because it has few micropores. Clays and organic soils hold significantly greater quantities of water because they have more micropores.
Hydraulics
The study of the physical effects of the passage of water.
Hydrologic cycle
The natural pathway water follows as it changes between liquid, solid, and gaseous states.
Hydrology
The science of studying rainfall and the distribution of water over the land.
Hydro-zone Areas within a site of differing soil moisture, evaporation rate and exposure to the local weather conditions.
Hydro-zoning
Landscape design that locates plants according to hydro-zones.
Impervious
The ability to repel water, or not let water infiltrate.
Infiltration
Movement of water through the soil surface into the soil.
Infiltration rate
The rate at which infiltration takes place expressed in depth of water per unit time, usually in millimetres per hour.
24
Landscape Design Guidelines for Water Conservation
25
Interception
The process by which precipitation is caught and held by foliage, twigs, and branches of trees, shrubs, and other vegetation, and lost by evaporation, never reaching the surface of the ground. Interception equals the precipitation on the vegetation minus streamflow and through fall.
Irrigation
The controlled application of water to plant roots to supply water requirements not satisfied by rainfall.
Irrigation efficiency
The percentage of water applied that can be accounted for in soil moisture increase for consumptive use.
Losses
The temporary retention of rainwater through interception, surface storage and infiltration.
Macropore
Larger soil pores, generally having a minimum diameter between 30 and 100 micrometers, from which water drains readily by gravity.
Micropore
Relatively small soil pore, generally found within structural aggregates and having a diameter less than 30 micrometers. Micropores hold most of the water that can be used by plants.
Percolation The movement of water, under pressure, through the gaps in rock or soil. It does not include movement through large openings such as caves.
Pores
The gaps that exist between soil particles. They include macropores and micropores.
Precipitation Precipitation is the discharge of water out of the atmosphere onto a land or water surface. It is the common process by which atmospheric water becomes surface, or subsurface water. Precipitation includes rainfall, snow, hail, and sleet, and is therefore a more general
term than rainfall.
Rhizobia
Bacteria of the genus Rhizobium capable of forming nitrogen fixing nodules on the roots of leguminous plants.
Runoff
Portion of rainfall, melted snow or irrigation water that flows across the ground surface and is eventually returned to streams. Runoff can pick up pollutants from air or land and carry them to receiving waters.
Shallow infiltration Infiltration to topsoil and sub soil layers.
Sheet flow
Flow that occurs overland in places where there are no defined channels, the floodwater spreads out over a large area at a uniform depth. This is also referred to as overland flow.
Soil aggregate
Unit of soil structure generally less than 10mm in diameter and formed by natural forces and substances derived from root exudates and microbial products that cement smaller particles into larger units.
Subsoil The layer or bed of earth beneath the topsoil.
Swale A wide shallow depression in the ground to form a channel for storm water drainage.
Top soil
The upper part of the soil profile that is relatively rich in humus, which is technically known as the A-horizon of the soil profile.
Water logging
The soil condition that results when all of the pores have been filled with water.
Landscape Design Guidelines for Water Conservation
Wilting point
The soil condition that results when the soil dries out to the point where plants can not extract any remaining water. Soil holds onto water via capillary forces; as more water is removed, these forces become larger, making it increasingly difficult for plants to extract water. Plant leaves and stems wilt when the plant can no longer extract water.
Worm casts Excreted masses of mineral soil often mixed with smaller bits of digested plant residues.
26
Landscape Design Guidelines for Water Conservation
Bibliography
BCC 2004a, Water for today and tomorrow – a proposed integrated water management strategy for Brisbane, prepared by
Brisbane Water, Brisbane City Council, Brisbane
BCC 2004b, Water Sensitive Urban Design Engineering Guidelines, prepared by Water Resources Branch, Brisbane City
Council, Brisbane
Bluescope Steel Ltd (undated), Bluescope Water – Rainwater Tanks – Queensland Product Catalogue, accessed 13.03.2006,
http://www.bluescopewater.com.au/qldpricecl.htm
Commonwealth Bureau of Meteorology (BoM) 2004, Climate Averages for Australian Sites, accessed 06.05.2004, http://www.
bom.gov.au/climate/averages/tables/cw_040223.shtml
Cunliffe, DA 1998, Guidance on the use of rainwater tanks, National Environmental Health Forum: Adelaide, accessed
06.03.2006, http://www.eng.warwick.ac.uk/ircsa/factsheets/Cunliffe.pdf
Gold Coast Water 2002, Your Garden Guide, Gold Coast City Council Publications Unit, Nerang
Handreck, K and Black, N 1989, Growing media for ornamental plants and turf, revised edition, NSW University Press,
Kensington
Handreck, K 1986, When should I water? Division of Soils, CSIRO, Melbourne
Harris, R, Clark, J and Matheny N 2004, Arboriculture: Integrated Management of Landscape Trees, Shrubs and Vines,
Prentice Hall, New Jersey
Lines-Kelly, R and North Coast Soil Management Working Party 2000, Soil sense: Soil management for NSW north coast
farmers, 2nd edition, prepared by R Lines-Kelly and North Coast Soil Management Working Party for NSW Department of
Agriculture
Pacey, A and Cullis, A 1989, Rainwater harvesting: The collection of rainfall and run-off in rural areas, Intermediate Technology
Publications, London
Pilgrim, D (ed) 1987, Australian Rainfall and Runoff – A Guide to Flood Estimation, The Institution of Engineers, Australia
Rain Bird Corporation 2003, Irrigation for a growing world, accessed 13.05.2004, http://www.rainbird.com/pdf/iuow/iuow_
whitepapers.pdf
Ranade, R, Srinivasan, R and Suresh Babu, S 2003, A water harvesting manual for urban areas, Centre for Science and
Environment, New Delhi
Vickers A 2001, Handbook of water use and conservation, Water Plow Press, Massachusetts
WSUD Sydney 2003, The water sensitive planning guide for the Sydney region, accessed: 07.04.2004, http://www.wsud.org/
planning.htm
27
Landscape Design Guidelines for Water Conservation
Appendix 1: Acceptable soil
amelioration measures
Acceptable soil amelioration measures to improve infiltration of existing soils shall include,
where appropriate:
• scarification of crusted topsoil layers using a harrow or similar equipment
• aeration of topsoil layers using a chisel plough
• deep ripping of subsoil layers using a non-inversion plough
• using hand tools only, such as hoes and forks, within the critical root zones of existing trees
and other vegetation nominated for retention
• applications of gypsum, at the rates recommended by a soil test, to sodic clay topsoils and
subsoils
• installing a 50mm layer of lucerne hay between the topsoil and mulch layers
• adding worms and worm eggs to the topsoil as recommended by a vermiculturalist
• applying soil rhizobia in solution to the topsoil as recommended by the manufacturer
• inoculating plants with Mycorrhizal fungi at the recommended rate
• incorporating soil wetters, crystals and wettable foams at the recommended rates.
28
Landscape Design Guidelines for Water Conservation
Appendix 2: Determining site
hydro-zones
The hydro-zoning approach involves both observing the existing conditions and predicting the impacts of proposed buildings
and other items on the site’s microclimate(s). With this information, a plan of the site’s likely hydro-zones can be prepared and
suitable plant species matched to these zones. As a general guide, the following site factors should be considered:
1. Site evaporation (sun and wind exposure)
Determine areas of high, mid and low evaporation throughout the site by assessing the site’s:
• mid-summer solar exposure (including areas exposed to western sun, areas of deep shade, partial shade and full midday
sun exposure)
• exposure to drying cold westerly winds, hot northerly winds, and sea breezes.
2. Surface drainage and runoff
Determine:
• source of water flowing onto the site
• drainage patterns
• areas of concentrated runoff
• floodplain
• areas of sheet flow.
3. Soil water characteristics
Where applicable, undertake soil testing to Australian Standards (or NATA certified) to determine:
• depth, structure and texture of existing soils and subsoils
• field capacity, wilting point and available soil water
• infiltration and drainage rates
• hydrophobic soil conditions.
4. Vegetation
Identify existing species and record their condition, exposure and soil moisture.
5. Wet areas
Evaluate the site for existing ground and surface water storages of a temporary or permanent nature. On large sites these
may include:
• lakes
• swales
• puddles
• ponds
• percolation basins and beds
• billabongs
• dams
• ephemeral pools
• springs
• soaks.
On urban lot scale development sites these may include:
• source of water flowing onto the site
• drainage patterns.
Table A2.1 provides an example of how hydro-zones are determined and may be used to assist designers in predicting
hydro-zone types.
29
Landscape Design Guidelines for Water Conservation
Table A2.1: Predicted hydro-zones work sheet
Instructions:
1) Write the location of the garden bed or turf area
2) Tick the conditions predicted for each location for both the dry season and the wet season
3) Add up the number of ticks under the ‘Dry conditions’, ‘Damp conditions’ and ‘Wet conditions’ columns to get a score for
each zone. Write down the scores as shown below.
4) Compare the scores for each condition – choose plants for the zone or zones with the highest scores.
Predicted Conditions
No wind
3
3
Wet season prediction (Dec-Feb)
Example only:
North-west Corner
between Smith
Road and building
3
Dry season prediction (July to Oct)
3
SCORE: 1
3
SCORE: 3
3
3
Waterclogged
/ boggy soil
Full shade
Cool, humid
air
Wet conditions
Damp soil
surface
Light, cool /
moist winds
Dappled
shade
Humid air
Damp conditions
Dry soil
surface
Full sun
Dry air
Dry conditions
Strong, hot /
dry wind
Dry conditions
Results
Example only:
Choose plants that
enjoy damp to wet
conditions.
SCORE: 4
Wet season prediction (Dec - Feb)
Dry season prediction (July to Oct)
SCORE:
SCORE:
SCORE:
Wet season prediction (Dec - Feb)
Dry season prediction (July to Oct)
SCORE:
SCORE:
SCORE:
30
Landscape Design Guidelines for Water Conservation
Predicted Conditions
Wet season prediction (Dec-Feb)
Dry season prediction (July to Oct)
SCORE: 1
SCORE: 3
SCORE: 4
Wet season prediction (Dec - Feb)
Dry season prediction (July to Oct)
SCORE:
SCORE:
SCORE:
Wet season prediction (Dec - Feb)
Dry season prediction (July to Oct)
SCORE:
31
SCORE:
SCORE:
Waterclogged
/ boggy soil
No wind
Full shade
Cool, humid
air
Dappled
shade
Humid air
Dry soil
surface
Stron, hot /
dry wind
Full sun
Dry air
Dry conditions
Wet conditions
Damp soil
surface
Damp conditions
Light, cool /
moist winds
Dry conditions
Results
Landscape Design Guidelines for Water Conservation
Appendix 3: Estimating percentage
of plant water needs provided by
rainfall
REFERENCES
Designers should refer to the following publications when determining plant water
requirements:
Harris, R, Clark, J and Matheny N 2004, Arboriculture: Integrated Management of
Landscape Trees, Shrubs and Vines, Prentice Hall, New Jersey, pp 324-427.
Handreck, K and Black, N 1989, Growing Media for Ornamental Plants and Turf, NSW
University Press, Sydney, Chapter 22
Commonwealth Bureau of Meteorology (BoM) 2003, Climate Averages for Brisbane,
http://www.bom.gov.au/climate/averages/tables/cw_040223.shtml
METHODS
Understanding local rainfall and estimating water requirements are important factors in the
design approach to conserving water use in landscapes.
As identified in the design standards (Section 4), if direct rainfall infiltration to soils
provides 50% to 100% of the plants’ (including turf) water needs, designers can proceed
with irrigation design. If rainfall alone provides 100% of the plants’ (including turf) water
needs, irrigation design will not be required.
The following two steps outline the method for determining a landscape’s water
requirements. Step 1 shows how to estimate the plant and turf water volumes needed
(expressed as landscape evaporation, or (ETL ) . Step 2 outlines how to estimate rainfall
infiltration quantities.
Designers are required to:
1. Estimate the volumes of water required to maintain plants (including turf) at acceptable
levels of growth and appearance throughout the year. 2. Compare these values with the volume provided by direct rainfall infiltration.
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Landscape Design Guidelines for Water Conservation
STEP 1 - ESTIMATE VOLUME OF WATER REQUIRED BY PLANTS AND TURF
Water use by vegetation, or landscape evapotranspiration rate (ETL ) , is estimated by multiplying a generalised or reference
evapotranspiration rate (ETo ) by the following three coefficients:
1. Species coefficient (KC ) – assesses the plant species used in terms of their water needs. Water loving plants will have high
KC values whereas drought tolerant species will have low KC values.
2. Hydro-zone coefficient (Kh ) – accounts for the site microclimate. Sites that are exposed to sun and wind with no shade
from buildings will have high Kh values. Low Kh values will be found in sheltered sites, for example, where walled gardens are
located between buildings. Average values Kh would be for sites in full sun.
3. Density coefficient (Kd ) – assesses the density of the leaf surface area in a landscape. High Kd values would be found in
mixed plantings of tall and/ or tiered foliage. Low Kd values are for less than 60% of the surface covered in vegetation.
Landscape evapotranspiration (ETL ) can be estimated using the following formula:
ETL
=
ETo
x
Kc
x
x
Kh
Kd
Values for reference evapotranspiration rate (ETo ) are obtained from the Bureau of Meteorology evapotranspiration maps
using average areal actual data. Values for KC , Kh and Kd are shown in Table A3.1 below.
Vegetation type
Species factor (Kc )
Hydro-zone factor (Kh )
Density factor (K d)
High
Avg
Low
High
Avg
Low
High
Avg
Low
Trees
0.9
0.6
0.2
1.4
1.0
0.5
1.2
1.0
0.5
Shrubs
Ground covers
Mixed (trees, shrubs and ground covers)
Turf
0.7
0.7
1.0
0.5
0.5
0.6
0.2
0.2
0.2
1.3
1.2
1.4
1.0
1.0
1.0
0.5
0.5
0.5
1.1
1.1
1.3
1.0
1.0
1.1
0.5
0.5
0.6
0.8
0.7
0.6
1.2
1.0
0.8
1.4
1.0
0.6
Source: page 324 of Harris, R, Clark, J and Matheny N 2004, Arboriculture: Integrated Management of Landscape Trees,
Shrubs and Vines, Prentice Hall, New Jersey
Note that the ETL values estimated will be expressed in millimetres. To obtain a volume, expressed in litres, the values
obtained are multiplied by the square metre area of the planted or turfed space.
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Landscape Design Guidelines for Water Conservation
STEP 2 - ESTIMATE THE RAINWATER INFILTRATION VOLUMES
The volume of rainfall infiltration for a garden bed or turfed area can be estimated by multiplying the median monthly rainfall
(obtained from Table A3.2 below) by an ‘infiltration factor’ (obtained from Table A3.3 below) that accounts for soil type by
the area, measured in square metres. That is:
Rainwater
infiltration rate
=
Median monthly
rainfall
x
Infiltration factor
x
Area
Table A3.2: Monthly rainfall data for Brisbane
Month
Jan
Median rainfall per
month (mm)
127.4
Feb
Mar
119.8 124.4
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Total Annual
53.3
72.3
35.6
40
33.8
33
73.5
73.9
107
1138.4
Source: http://www.bom.gov.au/climate/averages/tables/cw_040223.shtml
Table A3.3: Infiltration factors for varying soil types
Soil type
Infiltration
Factor
Pervious garden - Sand (0% impervious)
0.50
Semi-impervious garden - Loam
Upper limit infiltration (10-20% impervious)
Lower limit infiltration (35-50 % impervious)
0.42
0.35
Impervious garden - Clay (75-100% impervious)
0.15
Source: Adapted from Figure 2
Please note that the values in Table A3.3 are based on overseas tropical area research and have been applied to Brisbane
conditions. The values are conservative and factored to overestimate the infiltration volumes.
34
Landscape Design Guidelines for Water Conservation
Appendix 4: Estimating a site's
stormwater harvest capacity
The capacity of a site to collect runoff can be determined through the following four step methodology.
STEP 1 - OBTAIN MONTHLY RAINFALL DATA FROM THE BUREAU OF METEOROLOGY
(BoM) FOR BRISBANE
Rainfall data should be obtained from the pluviograph station(s) closest to the site. The data shown in Table A4.1 was
obtained from the BoM’s pluviograph station at the Brisbane Airport. For the purposes of this guideline, these values will be
suitable for all development within Brisbane City.
Table A4.1: Monthly rainfall data for Brisbane
Month
Jan
Median rainfall per
month (mm)
127.4
Feb
Mar
119.8 124.4
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Total Annual
53.3
72.3
35.6
40
33.8
33
73.5
73.9
107
1138.4
Source: http://www.bom.gov.au/climate/averages/tables/cw_040223.shtml
The monthly median values provided by the BoM are used as they represent the most common value as opposed to the
mean which can be misleading due to the inclusion of lower/higher values.
Note that the values in Table A4.1 are based on the 1929 to 2000 observations and will be greater than the median values
over the last few years.
STEP 2 - ASSESS THE SITE FOR IMPERVIOUS AREAS THAT COULD ACT AS STORMWATER
HARVESTING SURFACES (TYPICALLY ROOF, DRIVEWAY PATHS, AND CAR PARKS)
Calculate the total area in square metres for each surface type. Unless pumps are incorporated, harvest surfaces levels should
be above the areas to be irrigated.
STEP 3 - DETERMINE THE VOLUMETRIC RUNOFF COEFFICIENT FOR EACH SURFACE TYPE
The 'volumetric' runoff coefficient is the factor that accounts for the fact that all the rainfall falling on a catchment cannot
be collected. Some rainfall will be lost from the catchment by evaporation and retention on the surface itself. Table A4.2
provides volumetric runoff coefficients for various surfaces (note: these are based on conditions in the UK, as no Australian
coefficients are available).
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Landscape Design Guidelines for Water Conservation
Table A4.2: Volumetric runoff coefficients for various surfaces
Type of catchment
Coefficients
Roof catchments
• Tiles
• Corrugated metal sheets
0.8 – 0.9
0.7 – 0.9
Ground surface coverings
• Concrete
• Brick pavement
0.6 – 0.8
0.5 – 0.6
Untreated ground catchments
• Soil on slopes less than 10%
• Rocky natural catchments
0.0 – 0.3
0.2 – 0.5
Source: Pacey, A and Cullis, A 1989, Rainwater Harvesting: The collection of rainfall and
run-off in rural areas, Intermediate Technology Publications, London, p. 55
STEP 4 - CALCULATE THE HARVESTABLE VOLUMES OF STORMWATER FOR EACH
SURFACE TYPE
Potential
stormwater
harvest volume
=
Median rainfall
value
x
Harvest area
x
Runoff
coeffecient
36
Landscape Design Guidelines for Water Conservation
Appendix 5: Sizing of water tanks and
cisterns
The size of a tank or combination of tanks can be established by following the following three step procedure.
STEP 1 - DETERMINE THE DAILY VOLUME REQUIRED
The daily volume of water required can be calculated by dividing the annual volume calculated in Appendix 4 by 365 days
per year.
STEP 2 - DETERMINE TOTAL TANK STORAGE REQUIRED
The total tank storage required can be determined by using the roof area and volume of water required per day to read off
the appropriate value shown in Table A5.1 below. For example, if 100 litres per day harvested from a roof area of 200sqm is
required, a storage capacity of 7000 litres will be needed. Table A5.1: Tank storage requirements
Tank size (kL)
Roof area (sqmm2)
Volume required
(L/day)
100
150
200
300
400
100
2
7
7
19
16
14
14
14
-
47
39
34
31
200
400
3423
-
-
500
600
Table adapted from Appendix A of Cunliffe, DA 1998, Guidance on the use of rainwater tanks, National Environmental
Health Forum, Adelaide. Tank sizes are based on an annual rainfall of 1200mm per year (Brisbane’s median rainfall 1138.4mm per year).
STEP 3 - DETERMINE TANK(S) SIZES REQUIRED
The size and capacity of the tank or tanks can be determined using Tables A5.2 and A5.3 below. These tables have been
provided for initial guidance only and water tank suppliers should be contacted to provide more detail. The tables do not
provide information on below ground storage systems.
Following on from the example in step 2 above, to meet an overall storage capacity of 7000 litres, two 1200 diameter by
1850 high tanks (2100 litres each) and one 1530 diameter by 1850 high tank (3400 litres) could be selected.
37
Landscape Design Guidelines for Water Conservation
Table A5.2: Water tank dimensions – round type
Dimensions (mm)
Nominal Capacity
(L)
Capacity to
AS3500
Diameter
Height
1200
2100
3300
3400
4500
5400
6700
8600
22600
23000
1100
1964
3000
3000
4130
4915
6150
7850
20 580
21340
1030
1220
1670
1530
1770
1930
2160
2440
3950
3430
1540
1850
1540
1850
1850
1850
1850
1850
1850
1850
Source: http://www.bluescopewater.com.au/qldpricecl.htm
Table A5.3: Water tank dimensions – ‘slimline’ type
Dimensions (mm)
Nominal Capacity
(L)
Capacity to
AS3500
Width
Length
Height
1200
2200
2900
3400
3490
4100
5430
1000
2000
2500
3000
3160
3700
5000
850
850
850
850
850
850
1150
1100
1900
2400
2800
2400
2800
2800
1540
1540
1540
1540
1850
1850
1850
Source: http://www.bluescopewater.com.au/qldpricecl.htm
38
Brisbane City Council
Information
GPO Box 1434
Brisbane Qld 4001
Printed on recycled paper
N2007-01685
© Brisbane City Council 2007
For more information
visit www.brisbane.qld.gov.au
or call (07) 3403 8888