Delivering Green Space Benefits: Irrigation planning implications

Geoff ConnellanG&M Connellan Consultants

geoff.connellan@bigpond.com

Website: www.geoffconnellan.com.au

What is special about green space?

I. The nature and range of services to be provided

II. Quality and/or standard of services

III.Reliability of service delivery/supply

Green SpacePotential Landscape Outcomes or

Services Provided

Exercise – Organised sport & walking Microclimate modification (UHI) Contact with nature Habitat protection Biodiversity preservation Aesthetics

MESSAGE

Quality Green Space = Liveable Cities

Water/Irrigation has a critical role.

Some Challenges for Green Space

Lack of security of water supply

Low water quality

Footprint of WSUD systems

Maintenance of WSUD systems

High cost of potable water

Cost of recycled water – capital and operating

What is role of irrigation?

Provides critical green space in urban environments where vegetation

growing under natural (rainfall only) conditions cannot deliver the required

services.

Main Applications - Health

Exercise – Active and passive

Microclimate modification, extreme temperature reduction including Urban Heat Island (UHI)

Exercise/Recreation - Green Space

Active Recreation Passive Recreation

Obesity a major health issue

Without irrigation many sites do not deliver positive services during low

rainfall/drought

To deliver Health Benefits from Green Space

(1) Spaces for Exercise

1.Attractive – Healthy, high quality plants

2.Usable and safe – Surface functional

3. Access – 300 to 400 m

4. Area – e.g. 3.0 ha per 1000 residents 5. Reliable – Independent of climate

variations such as drought

Urban areas and cities can be hot!

The Urban Heat Island (UHI) Effect

Feb. temps 2009

Av. Deaths 2004-2009

Extra Deaths in 2009 heat wave

Reference: Rod Dedman, Vic. Depart of Health.Alternative water supplies for health and wellbeing.

Deaths from excess urban heat

To deliver Health Benefits from Green Space

(2) Spaces for Heat Moderation

1.Full coverage of vegetation – high Leaf Area Index (LAI)

2. Healthy vegetation with high ET rate.

3. Trees are powerful microclimate modifiers

Role of Trees – Environmental modification

Crop Coefficient: E.g. Strong healthy growth (Kc 0.8), not

Survival (Kc 0.4)

To achieve cooling

ETo – Evapotranspiration

Energy partition – Latent Heat

ETo

Lower air temperature

Message: Irrigation is often required to achieve microclimate cooling.

Microclimate Cooling

High Crop Coefficients (Kc) required

Security of Water Supply

Strategies

•Work with constraints (e.g. limited volumes or times, reduced pressure) of supply from reticulation mains

•Water source independent of climate conditions (e.g. recycled or desalination)

•Storage size to meet risks

•Integrated approach

Stormwater Harvesting – Meeting irrigation demand

Storage

Storage Sizing and Reliability of Supply

Increasing storage

capacity & $s

Increasing reliability of supply %

Diminishing returns

Storage Sizing and Reliability of Supply

Increasing storage

capacity &$s

Increasing reliability of supply

Use potable water to provide

security of supply during

drought

%

80

60

100

Storage Sizing for Reliability of Supply

Balancing increasing cost of storage and value of the benefits and/or potable water savings delivered by the system.

*Important to note that the value of the services will be greatest at the time that the supply is likely to fail.

Is 75% or 80% reliability adequate?

Water Quality

What are the risks?

1. Chemical

2. Physical

3. Biological

Key Water Quality Parameters

Chemical pH (Acid/Basic) Dissolved elements E.g. Sodium Heavy metals E.g. Mercury, Zinc

PhysicalSuspended solids – irrigation blockages

Microbiological – Human health & Plant health

Viruses, Bacteria - Pathogens • Human: e.g E. coli

• Plant: Phytophthora spp.

Irrigation Water Quality Parameters

Parameter Unit

Acidity/Basic pH

Salinity Electro Conductivity (EC)

Total Dissolved Solids (TDS)

dS/m

mg/L; ppm

Sodium Adsorption Ratio (SAR) SAR units

Total Suspended Solids (TSS) mg/L

EG. Sodium, Chloride, Phosphorous, Nitrogen .

e.g. Sodium mg/L

Biological/Biochemical Oxygen Demand (BOD) (5day)

Dissolved oxygen mg/L

Message: Define Water Quality Criteria

Risk of Blockage of Drip Emitter

Water Parameter

Unit Low Risk High Risk

Acid/alkaline pH < 7.0 > 8.0

Suspended solids(TSS)

mg/L < 50 100

Salinity TDS/EC

mg/L < 500 2000

Iron, Bicarbonates

Source: Harris (2006) DPI, Qld.

Stormwater StoragesWhat are the risks?

1. Human health

2. System effectiveness and functioning

Strategies to minimise the risks

a) System design (e.g. treatment systems)

b) Water quality standards

c) Regular monitoring

Water Quality Considerations

• Characteristics of catchment – Urban or industrial. Hydrocarbons, Oil spills, Chemical spills, Plant health chemicals

• Frequency of testing of stormwater E.g. 2 weeks

• Time for some tests e.g. pathogen to be done may be 2 weeks. Well after the event.

Efficient Use of Water

1. Water Use Efficiency (WUE)and

2. Irrigation Efficiency (IE)

Efficiency- Essential component of Green Space

Irrigation

How do you encourage or foster efficiency?

•Irrigation design standards.

E.g. IAL Urban Best Management PracticeIn-house Irrigation standards

* Specify regular performance evaluation.

Message: Strongly endorsed irrigation standards

OVERALL IRRIGATION EFFICIENCY

APPLICATION EFFICIENCY

SCHEDULING/WATER

MGT. EFFICIENCY

Message: Both need to be high to achieve High Overall Efficiency

Irrigation Efficiency

Green Space Messages

1.Define site outcomes and servicesE.g. Exercise? Cooling?

2. Secure water source to deliver benefits during low rainfall/drought.

3. Set water quality standards for sustainable use.Monitor both (a) water and (b) soil.

Green Space Messages

4. WSUD systems need monitoring and maintenance. Resource provision.

5. Apply design, installation and management standards that promote efficiency.

6. Irrigation zoning to allow separate watering of areas with different demand. E.g. Trees separate to grass/lawn.

Keep trees healthy.

Green Space (Irrigation)

Health

Community Wellbeing