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Water conservation initiatives of the Royal Botanic Gardens Melbourne
Volume 6 Number 2 - July 2009
The availability of water for urban landscapes is under increasing threat, whether from regulation, social-political views, population demand or the impacts of climate change. Most Australian cities have imposed severe water restrictions at some stage within the last decade. Melbourne is currently on stringent restrictions and approaching critical water shortages after a decade of unprecedented below average rainfall conditions. It was through strategic planning that the Royal Botanic Gardens (RBG) Melbourne began its water management journey in 1993, well before the current water crisis now experienced in Victoria. The Gardens became recognised as a leader in urban landscape management. Public recognition of RBG Melbourne’s achievements was highlighted by the Savewater awards with the RBG winning Garden and Design Construction categories in 2003 and 2004, and reaching the finalist shortlist in 2003 (Efficiency in Government) and the Garden Management category in 2005 and 2006. RBG Melbourne was one of the first Australian botanic gardens to develop irrigation management plans to guide efficient water use and these plans have been used as a resource by other Botanic Gardens (Devin Riles pers. comm., 2008, Irrigation Specialist, Denver Botanic Gardens, USA).
The picturesque landscape of RBG Melbourne covers over 38 hectares of managed land. Over 50,000 individual plants are cultivated in the living collections representing a diverse 12,000 taxa from a variety of habitats and geographical locations around the world. Considerable benefits are provided to the community with the Gardens enjoying over 1.6 million visitors during 2007-08 which was a 14% increase from 2006-07.
RBG Melbourne’s intrinsic diversity of plants, environments, soils, landscapes and functional activities presented both stimulating challenges and opportunities for adopting appropriate strategies to improve water use efficiency.
Strategies to improve water use efficiency
Strategy 1 – Upgrade delivery infrastructure
Past landscape irrigation practices revolved around the daytime use of an inefficient manually operated hose and sprinkler system. Water losses to evaporation are highest during the day and these are exacerbated by more exposure to wind. Another significant issue was that up to 70% of the Curator’s time was estimated to be spent just on shifting sprinklers.
Following extensive hydraulic modelling and soils surveys, the installation of an automatic irrigation system (AIS) was completed during 1993-1994 at a cost of over AUD $1.3 million (US$1 million). Careful attention was given to installation techniques such as directional boring to ensure minimal disruption to the mature landscape, particularly the health of existing trees. Today the PC centrally-controlled system comprises of 18 satellite controllers, 480 stations, 6,800 sprinklers, 4 flow sensors, 16 soil moisture sensors and over 40 kilometres of pipework. In consideration of the past historical difficulties to effectively irrigate the living collections, the completion of the AIS was a very significant milestone for the Gardens.
Strategy 2 – Focus on professional development
In 1995, water management training and subsequent development of irrigation scheduling methodologies was facilitated by Burnley Campus, University of Melbourne. This training initiated an improvement in understanding soil hydrology, plant water use and climatic factors at a time when the knowledge of urban water management was very limited. Following the training there was an immediate improvement in water use efficiency of about 230%. Commitment to professional development and the practice of applied science cannot be over emphasised. For example, the total cost of the training programs in Melbourne gardens is estimated to be less than AUD$5,000, while those same employees have helped deliver water savings since that time of about AUD$1.4 million. Water management development programs are continued to ensure that employees are provided with the current scientific information and skills to inform horticultural judgement. The present reputation of RBG Melbourne as an efficient water user in the community can be primarily attributed to the early development of employee expertise in water management.
Strategy 3 - Develop research and industry partnerships
One of the core values of the Gardens is the emphasis in the development of strong relationships with other organisations for mutual benefits such as research outcomes. Applied science and industry expertise are vital foundations for continuous improvement.
University of Melbourne
Since 1995, RBG Melbourne and University of Melbourne continued on from those early training programs to develop a strong partnership in urban water management research and publication including technical presentations at various conferences. Currently, this partnership includes an industry partner - Sentek Pty Ltd an Australian manufacturer of soil moisture sensors - in a project to examine landscape water use against inputs from soil moisture data, automatic weather station and human insight through horticultural judgement. Methodologies are currently being developed to assist in the management of complex landscapes under water scarce conditions and according to soil moisture stress indicators. A paper was presented at the Irrigation Australia national conference in May 2008.
Monash University and RBG Melbourne are also engaged in a project to study rainfall interception by mature tree canopies in the urban landscape. Indicative results indicate interception losses (Xiao et al., 2000) of up to and over 60% of monthly rainfall. This is an important issue as there is some evidence that the nature of rainfall patterns in Melbourne is also changing to the extent that more rainfall will be intercepted (David Dunkerley pers. comm., 2009, Associate Professor, School of Geography and Environmental Science, Monash University) notwithstanding any further impacts from climate change. With tree canopy coverage of over 60% across its landscape, the study of rainfall interception is very pertinent as an irrigation management issue for RBG Melbourne. The quality of existing water bodies is also a very important consideration when focussing on integrating site hydrology. The Water Studies Centre, Monash University and RBG Melbourne have been working together through quality student projects to build a knowledge base on the RBG Lakes System for improving water quality, ecosystem functioning and future capacity for water storage.
RBG Melbourne has been a member of the peak industry body - Irrigation Australia (IAL) for about a decade. Since 2004, the Gardens have been the preferred host site of IAL in Melbourne for the delivery of irrigation efficiency training due to the added value of its water management experience and site diversity. Over ten workshops have been sponsored by the Gardens so far to extend the benefits of water management expertise out into the wider community.
South East Water
Since 1999, RBG Melbourne has enjoyed a strong relationship with its water authority - South East Water Limited (SEWL) through delivery of water conservation information to the community, particularly through the award-winning Water Conservation Garden. This collection was developed and is maintained by sponsorship from SEWL. Due to its track record in significant water conservation and heritage importance, RBG Melbourne has been allowed limited exemptions by SEWL from water restrictions since November 2002. SEWL regularly draw on the water management expertise of RBG Melbourne when examining urban water management in the broader sector.
Strategy 4 - Improve application efficiency
Improve sprinkler effectiveness
Interception of the sprinkler stream by foliage, branches and trunks of plants compromises effective delivery. Stream-type sprinklers are more effective and efficient than sprays in delivering water through shrubberies and were adopted widely across the landscape. Most spray-type sprinklers have been replaced with modern multi-stream types. These were found to be significantly more efficient when tested by horticultural employees. Some of the current difficulties are maintaining reasonable clearance around sprinklers through plant selection and judicious pruning to optimise sprinkler performance.
Optimising the use of rainfall
Attaining high levels of efficiency also involve making the best use of any rainfall. The use of a 10 mm effective rainfall event across RBG Melbourne results in a potential saving of 3.8 million litres of water or AUD$4,600 in today’s costs. In early 1999, improvements to flow management and pressure resulted in an increase of the effective flow rate of the irrigation from 35 L/s to 50 L/s. Although available flow rate was increased by 43%, average irrigation water use decreased by about 40-50% during 1999-2007. The generation of high flow capacity through hydraulic efficiency provides much greater flexibility in scheduling as operators can afford to delay irrigation and increase the probability of harvesting additional rainfall.
Many performance measures proposed to determine water use efficiency are best suited to production agriculture and horticulture (turf-farms, floriculture) where the end product can be measured in quantity compared to the water used. Irrigation performance for ornamental landscapes is often subjectively measured in a qualitative manner as plant aesthetics and health are regarded as paramount. RBG Melbourne adopted an irrigation management performance indicator called the Irrigation Index (Ii). This indicator accounts for climatic conditions and specific plant water use rates. It is calculated by dividing the volume of water actually applied to the site by the estimated requirement. For example, an irrigation index of 1.0 is the ‘ideal’ rating, while a result of 1.3 would possibly indicate a 30% oversupply. From 2000-2009, during severe drought conditions, irrigation indices of 1 have been consistently achieved. In more recent years an irrigation/rainfall aggregate of <900mm per annum and less than 90 litres/visitor/year have also been set as benchmark targets to cater for climate change shift and increased visitation demands. Auditing of irrigation systems is also undertaken by specially trained staff to assess efficiency. Distribution Uniformity (DU) is a measurement of sprinkler uniformity that is examined against the RBG Melbourne target to maintain all sprinkler irrigated turf areas with a Distribution Uniformity (DU) value greater than 75%.
Strategy 5 - Adopt current technology
Automatic weather station
Horticultural staff initially relied on climatic information supplied by the Melbourne Bureau of Meteorology (BOM) to guide irrigation scheduling. However this data was not representative of site conditions. In 1998, an automatic weather station (AWS) was installed in RBG Melbourne to provide climatic data to assist irrigation management, obtain records for BOM, and assist in the horticultural management of the site. A modified Penman-Monteith algorithm (FAO, 1990) calculates the evapotranspiration rate (ETo) of a standard ‘crop’ from a wide range of climatic variables such as solar radiation, air temperature, wind speed and relative humidity. Crop coefficients (Kc) (Allen et al., 1998; FAO, 1990) are required as modifying values to adjust ETo and calculate evapotranspiration of distinct plant types or landscape zones. Up to four specific landscape irrigation schedules (High X, High, Medium and Low) based on distinct landscape coefficients KL (Costello & Jones, 2000) are applied to both garden and turf areas (Connellan & Symes, 2006). It has been the Garden’s experience that weather-based irrigation scheduling can be successfully applied to maintain the health of highly diverse plant collections and landscapes.
Soil moisture sensors
Sixteen tension-based ‘Watermatic’ soil moisture sensors are installed in turf areas across the Gardens and the data is directly fed back to the irrigation control system for monitoring. This system has the ability to cease irrigation upon reaching certain set-points in soil moisture.
Up-to-date and detailed knowledge of the extraction of soil moisture from the different soil layers in the garden beds at RBG Melbourne is proving to be extremely valuable in the water management of these gardens. In a collaborative project with Sentek Pty Ltd and the University of Melbourne, landscape soil moisture is being monitored by multi-sensor capacitance type probes (EnviroSCAN®), supplied by Sentek Pty. Ltd in selected garden beds. This information is continuously relayed at frequent intervals to a host website from where it can be viewed and analysed by the project partners.
Soil moisture sensing technology assists adaptive irrigation management in providing information on actual plant water use rates, rainfall effectiveness, drainage rates and the influences of mulch, overhead tree canopy and water repellent soil on soil hydrology.
Strategy 6 – Reduce water demand
Due to physiological (C4 photosynthesis) and morphological adaptations (deeper rooting), warm-season grasses are more efficient users of water than cool-season species and can be managed to use up to 30% less water. Changing landscape turf composition from cool-season grasses to one dominated by warm-season species, either by management techniques or direct propagation, was one strategy to improve water use efficiency. A form of regulated deficit irrigation (RDI) is also applied to transition from a domination of cool-season grass to warm-season in early summer. This has been successfully managed to the extent that turf areas in the Gardens now use less water annually compared to garden beds.
Water sensitive urban design
The Water Conservation Garden and the Melbourne-indigenous flora collection developed at Long Island are key examples of proactive landscape planning to reduce water demand. Both areas are more adapted to Melbourne’s climate, including seasonal dry periods. Long Island receives no supplementary irrigation and the Water Conservation Garden is watered at about 50% of other moderately irrigated garden areas. Guilfoyles Volcano is a landmark project just in the making and will feature xerophytic plantscapes, water reuse, efficient irrigation and water quality treatment.
Strategy 7 - Diversify alternative water sources
The Gardens is currently planning the development of a stormwater harvesting system and the improvement of ornamental lake water quality through recirculation, bioremediation and wetland construction. About 50% of the funding has been provided for the construction of the AUD$2.2 million ‘Working Wetlands’ scheme through philanthropic donation, whilst the rest is being sought through government. However the projected additional annual water volumes of 70 ML will only be enough to maintain the lake quality as rates of evaporation are too high to also support irrigation demand. For water supply security, additional sources of decentralised alternative water supplies are currently being sought, particularly those that do not rely on continued patterns of average rainfall. Current projections are suggesting a potential decrease in average rainfall for the Port Philip Catchment of Melbourne (where RBG Melbourne is situated) of up to 24% less by 2070 (DSE, 2008).
Strategy 8 – Adapt to climate change
Plant selection methodologies are being applied to facilitate a transition to a landscape more suited to less water demand and greater heat tolerance over the next 50 years, whilst still maintaining the heritage style. Gardens policy has been developed and documented through the Masterplan Review and Living Collections policy. Regardless of whether alternative water sources can be identified, RBG Melbourne is still planning for the future on the basis of increasing average temperatures (up to 2.6oC by 2070) (DSE, 2008). Whilst extremes in temperatures are also a threatening process for the landscape – in late January 2009, Melbourne experienced three consecutive days over 40oC which had a very significant impact on many of our living collections. These temperature issues are very difficult to mitigate unless significant adaptation to the planting palette occurs over time. In October 2008, one employee completed a 4-week technical scholarship (funded by the Friends of RBG Melbourne) tour of Southwest USA landscapes and botanic gardens to glean insights into implementing these adaptations. Research is currently being done to try and establish comparative climates (homoclimes) with Melbourne using past long term averages and also for future projections as a guide for plant selection. One simple model that has been used is an Aridity Index (Gentilli, 1971) that only requires monthly temperature and rainfall data which are relatively available around the world. Plant selection frameworks are also being developed concurrently with climatic comparisons.
Summary - Strategies to improve water use efficiency
The adoption of these strategies resulted in progressive water savings of 50-60% from 1994-95 to 2008-09 over a decade of drought conditions.
RBG Water Conservation Webpage
RBG Melbourne Urban Landscape Water Management Research Webpage
Irrigation Australia 2008 National Conference Paper
Allen, G.R., Pereira, L.S., Raes, D. and Smith, M. 1998. FAO irrigation and drainage paper 56: crop evapotranspiration, guidelines for computing crop water requirements. Food and Agriculture Organisation of the United Nations: Rome.
Connellan, G. and Symes, P. 2006. The development and evaluation of landscape coefficients to determine plant water requirements in the urban environment. In: National Conference and Exhibition Proceedings: May, 2006, Irrigation Association of Australia: Sydney.
Costello, L.R. and Jones, K.S. 2000. Water Use Classification of Landscape Species (WUCOLS III). In: A Guide to Estimating Irrigation Water Needs of Landscape Plantings in California, Sacramento, California Department of Water Resources.
Food and Agriculture Organisation of the United Nations (FAO). 1990. Expert consultation on revision of FAO methodologies for crop water requirements. Food and Agriculture Organisation of the United Nations: Rome, Italy.
Gentilli, J. 1971. Climates of Australia and New Zealand. Elsevier Publishing.
Xiao, Q., McPherson, E.G., Ustin, S.L., Grismer, M.E. and Simpson, J.R. 2000. Winter rainfall interception by two mature open-grown trees in Davis, California. Hydrol. Process. 14: 763-784.
Victorian Government Department of Sustainability and Environment (DSE). 2008. Climate Change in Victoria: 2008 Summary, Melbourne, Victorian Government.Mr Peter Symes
Curator, Environmental Horticulture
Royal Botanic Gardens Melbourne
(Private Bag 2000)