WATERING OF STREET TREES: THEORY AND PRACTICE For Presentation at Irrigation Australia 2008 Conference Tuesday 20 May 2008

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1 WATERING OF STREET TREES: THEORY AND PRACTICE For Presentation at Irrigation Australia 2008 Conference Tuesday 20 May 2008 Geoff Connellan G & M Connellan Consulting, Lower Plenty, Vic. Ian Shears Team Leader Tree Planning, Parks and Urban Design, City of Melbourne

2 Street Trees in City of Melbourne Value of Street Trees The City of Melbourne manages approximately 55,000 trees including approximately 18,000 street trees. The total value of Melbourne s trees is estimated to be over $550 million.

3 Melbourne s Tree Assets Tree stress is a major issue

4 Tree Stress Sources of stress Pest and disease Compaction Root damage Air pollution Age Low soil moisture

5 Factors Contributing to Low Soil Moisture Tree Stress 1) 10 years of drought 2) Reduced supplementary- Water restrictions 3) Reduced rainfall effectiveness hydrophobic soils 4) Reduced uptake of water by trees as a result of damage to tree root systems through construction works e.g. paths, service trenches

6 City of Melbourne Water Policies

7 Tree Water Management Strategy Strategies a. Changing water sources b. Improved efficiency of irrigation c. Reduction in the amount of irrigated landscape

8 The No Potable Water 2012 Target Five strategic focus areas are being developed: (1) Landscape change (2) Improved irrigation efficiencies

9 The No Potable Water 2012 Target (3) Management of use developing sustainable carrying capacity for parks whilst ensuring ongoing community use and enjoyment (4) Alternative sources (5) Offsets balancing water use in parks against savings elsewhere

10 Tree Watering Options Experience with the following methods: 1) Sprays on centre medians and nature strips 2) Shallow buried drip (up to 150 mm deep) 3) Drip under mulch 4) Subsurface drip

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12 Watering Method and Root Zone Layer

13 Innovations in Tree Watering a. Surface water storage devices b. Drainage pipe and aggregate c. Traffic barrier storages with drip d. Watering forks e. Water injection f. Wetting agents g. Water absorbing gels

14 Innovations in Tree Watering

15 Water Injection

16 Tree Watering Options Traffic Barriers Refill Systems Traffic barriers hold approximately 440 litres of water

17 Shallow Drip Watering for Street Trees

18 Response to Water Restrictions - Drip 100 kilometres of dripper lines that had been installed 2006/2007 An additional 40 kilometres of subsurface (shallow) dripper piping has been installed in early 2008

19 Fawkner Park Extensive Drip Watering

20 Emergency drip watering

21 There is a risk of root damage Need time for recovery and root development Installing drip on mature trees

22 Response to Water Restrictions Tree Health The health of some of the older Elm trees has improved with the rollout of the drip lines and the move away from surface turf irrigation. However this improvement has been apparent in the second summer after installation.

23 Tree Watering The Challenge Challenges include: a) Tree roots contained within median and street structures b) Tree root distribution highly variable c) Access to root systems often limited d) Tree roots in competition with turf roots e) Significant roots located deep within the soil profile

24 f) Canopy interception of rainfall can be significant g) Compacted soils (low infiltration rates) - particularly on nature strips h) Root disturbance and damage e.g. excavation reduce the effectiveness of parts of tree root systems i) Already be stressed due to pests, disease, damage or environmental pressures

25 Tree Watering Trial - Royal Pde Aim Assessment of drip watering, tree watering well products and other watering options that will allow effective watering of mature trees in street and boulevard situations. Trial began July 2007

26 Tree Watering Trial The watering well products used were Hunter Root Zone Watering System (75 mm diam. and 300 mm long) and Rain Bird RWS Root Watering System (100 mm diam. and 300 mm long).

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28 Watering Wells

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31 Many roots close to surface Poor lateral distribution of water

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34 The Watering Trench

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36 Delivers >100 litres per day

37 Why the watering trench? Lateral distribution of water Simple construction Relatively large volumes of water can be delivered Readily supplied from existing irrigation system

38 SUMMARY The recent drought conditions have caused much stress to the City of Melbourne trees Significant water reduction, in excess of 60%, in water use in parks, gardens and open space, have been achieved Extensive shallow buried drip systems have been installed on significant trees in parks and boulevards. These systems have been successful in applying emergency watering to trees

39 SUMMARY The new watering trench technique is to be installed in high profile avenue and boulevard tree sites in Royal Parade, St Kilda Road and Birrarung Mar Soil moisture monitoring is continuing to be used to inform on water management.

40 SUMMARY These strategies together with tanker watering, water barriers, soil water injection, mulching and modification of irrigation schedules have meant that the City has been able to keep nearly all the significant trees in a healthy condition and most other trees in acceptable condition.