WSAA DAMS INFORMATION PACK ONE CONTENTS > 02 Summary points > 02 Dams in Australia > 06 Dams and flood mitigation > 07 Dams and drinking water quality > 08 Cost of dams > 08 Industry response to climate uncertainty > 12 Conclusion > 13 References WSAA VISION FOR URBAN WATER SERVICES CUSTOMER DRIVEN, ENRICHING LIFE The Water Services Association of Australia publishes this series of information packs on behalf of the Australian urban water industry to present the current situation on key issues of relevance to the industry. The urban water industry is striving to achieve four outcomes by the year 2030. By working together with a common goal WSAA members intend to be: > The most efficient trusted and valued service providers in Australia > A compelling voice in national policy making > A valued partner in urban and land use planning to enrich communities As well as taking a strong role in the: > Stewardship of the urban water cycle The urban water industry is committed to ensuring customers and communities have the water they need to live their lives. To achieve this we support a diversified portfolio of water sources accepting that some water sources have multiple roles. :01 ABOUT WATER SERVICES ASSOCIATION OF AUSTRALIA (WSAA) WSAA is the industry body that supports the Australian urban water industry. Its members and associate members provide water and sewage services to approximately 16 million Australians and many of Australia’s largest industrial and commercial enterprises. WSAA is always willing to innovate and seek new and smarter ways of doing things and prides itself on making decisions that are based on sound knowledge and research. SUMMARY POINTS > Over the long term, dams can provide the cheapest source of bulk water for the urban environment, and dam water is easier to treat than other sources, such as seawater desalination. However, their construction can involve significant costs, and environmental impacts. > The changing climate is affecting the role of dams in public water supply. Long-term forecasts are for less rain in southern Australia which challenges water quality and quantity :02 management in existing dams. > Most dams are built for water supply but a small number like Brisbane’s Wivenhoe Dam are built both for water storage and flood mitigation. Recent record floods resulted in high damage bills, so good dam management DAMS IN AUSTRALIA that protects life and property, is a high priority. Surface water dams have long dominated Australia’s > Dams are part of a wider ecosystem and are urban water system. The first two – Yan Yean integral to communities use for recreation, outside Melbourne and Lake Parramatta, Sydney tourism and agriculture. Collaboration, – were completed in 1857. Dam building continued particularly with land use planners, is needed steadily, accelerating after WW II. Today, there are to ensure better decision-making that protects 500 large (more than 15m high) dams. The Sydney drinking water quality and quantity. Catchment Authority has 20 supply dams and weirs that hold more water per head of population than > Dams are assets that need to be on the balance any other city in the world. Other metropolitan sheet. The ecosystem services provided by areas such as Melbourne and South East Queensland dams for public water supply can top over a (SEQ) store dam water providing for up to seven billion dollars, as is estimated to be the case years of secure supply based on historical inflows. for Melbourne’s closed catchments. Dams smooth out seasonal, annual and multi-year > Dams do not just store surface water, in parts of drought variations in inflow, to distribute water Australia dams store water from various sources supply according to daily demands. The capacity such as seawater desalination and groundwater. of dams to sustain supply is dictated by local site conditions and stream flow conditions that are > Australia is still building dams for public water affected by climate and weather. This leads to the supply, such as the recent enlargement of characterisation of dams as a ‘climate-dependent Cotter Dam in ACT. Utilities are quantifying water source’. all costs and benefits, testing climate and demand-related scenarios, and exploring all Dams generally provide the cheapest source of bulk options with communities and government early water for the urban environment. Dams are typically in the planning to ensure the most optimal solution for water supply. Fig. 1 TOTAL ANNUAL CATCHMENT INFLOW TO SCA’S HAWKESBURY – NEPEAN DAMS AND RAINFALL AT YERRANDERIE 10,000 0 9,000 500 8,000 1,000 789mm 958mm 763mm 7,000 1,500 6,000 2,000 5,000 2,500 4,000 3,000 Rainfall (mm/year) Rainfall Inflow (GL) Inflow 3,000 3,500 2,153 GL 2,000 4,000 951 GL 673 GL 1,000 4,500 0 5,000 1934 19 0 9 1914 1919 1924 1929 1939 19 4 4 19 4 9 195 4 1959 19 6 4 19 69 1974 1979 19 8 4 19 89 19 9 4 1999 2004 2009 563055 Yerranderie (Warragamba catchment) Total annual inflow to Warragamba, Wingecarribee, Nepean, Avon, Cordeaux and Cataract Dams Average for specified periods (1909-48, 1949-90, 1991-2012) 7 year moving average (rainfall) 7 year moving average (inflow) :03 Note: Graph does not include inflows to Woronora Dam and Shoalhaven transfers gravity-fed and are easier to treat than other sources, Climate risk – not enough rain such as seawater desalination. For a long time The water supply risk includes early projections of dams have met demand for water. Occasional up to 10% less rainfall across southern Australia by imbalances have been managed by temporary 2030 and 20% by 2050. They also include more extreme water restrictions. However, the role of dams in events including drought, floods and bushfires public water supply and flood mitigation has (CSIRO & BOM 2007, 2011). This is crucial for public been brought under the ‘political’ microscope water supply in Australia’s most populous areas. by the long term drying trend in the south of The south west of Australia has experienced a step Western Australia, by the Millennium Drought change in its rainfall and stream flow patterns (1997-2009), and by the record floods on the (Figure 2). The long-term drying trend evident from east coast/southeast of Australia (2010/11). the mid-1970s currently places this area and the city In rural and regional Australia dams have played a of Perth in a position where it is unlikely that any big part in building rural and regional prosperity. new dams will ever be built. Many towns around Australia are dependent on In Victoria during the Millennium Drought, stream dams for their water supplies. flow reductions into dams were four times greater The building and management of dams has reflected than the decline in rainfall (CSIRO 2010). This occurred how regularly Australia suffers from droughts and not only because of a general decline in annual floods. However, this is now being challenged by rainfall, but because reductions in autumn changes changing climate conditions and some of the meant catchments were drier at the start of winter, surrounding uncertainties, particularly the severity resulting in less efficient winter runoff from and timing of extreme weather events. catchment areas. Fig. 2 YEARLY STREAMFLOW FOR MAJOR SURFACE WATER SOURCES – IWSS 1,000 900 800 700 600 500 400 :04 300 Total Annual Inflow to Perth Dams(GL) 200 100 0 1911 1974 2010 1917 19 59 1914 19 41 1935 1953 1971 19 8 3 19 47 1932 193 8 1926 1950 195 6 1929 19 8 0 19 62 1977 19 65 1923 1992 1920 19 9 8 19 8 6 19 4 4 1995 1989 1968 2001 2007 2004 Note: A year is taken as May to April Annual Total 1911 to 1974 av (338 GL) 1975 to 2000 av (173 GL) 2001 to 2012 av (78 GL) This highlights the complex relationship between not that heavy rainfall events will become more climate, weather, rainfall and stream flow into dams. frequent as the temperature increases. The tendency The Millennium Drought reduced national GDP by for increase in intensity may be stronger for the almost 1% and the net welfare costs of mandatory larger, rarer events (current 1-in-20 year events) restrictions (invoked during the drought) amounted (Rafter and Abbs, 2009) particularly at the sub-daily to several hundred million dollars per jurisdiction timescale’ (Westra et al., 2013). per year (PC 2011). Average inflows into Australia’s major dams For further details, refer to WSAA’s paper ‘Climate Despite record rainfall on the east coast since the Change Adaptation in the Australian Urban Water Millennium Drought broke, the Climate Commission Industry’ (WSAA 2012). states that only about one-third of the rainfall debt was paid back with the 2010 and 2011 floods. Climate risk – too much rain (Steffen, Hughes & Karoly, 2013). The proportion of total rainfall from heavy falls will increase in the 21st century over many areas of the Table 1 includes information on total dam capacity globe (IPCC, 2012). A 1-in-20 year maximum daily in Australia’s major cities and the average inflows rainfall event is likely to become a 1-in-5 to 1-in-15 into those dams over time. It includes the reduction year event by the end of the 21st century in many in inflows experienced during the Millennium regions (IPCC, 2012). According to the Climate Drought on the east coast, and the long-term Commission ‘across Australia, it is more likely than drying trend in the southwest of Australia (Perth). Table. 1 DAM CAPACITY AND AVERAGE INFLOWS Location Total dam capacity (GL) Average inflows/yr (GL) :05 Adelaide 197 (Mount Lofty Ranges dams) Mount Lofty Ranges dams 1892-1990 (177) 1997-2007 (113) South Australians also rely