Water forecasting for the future
About 230km north of Melbourne, Barmah is the gateway to the largest river red gum forest in Australia. Stretching across 66,000 hectares of wetlands from Victoria into NSW, the Barmah-Millewa Forest has enormous environmental, ecological, cultural and heritage value.
In 2003, in response to evidence of declining river health in the area, the Barmah-Millewa Forest was chosen as one of six icon sites in one of the biggest river and wetland rehabilitation projects ever undertaken in Australia – The Living Murray Program.
The sites were chosen due to their high conservation value and encompass floodplains, wetlands and forests.
They also provide compelling examples of how river management can cater for everyone’s needs— and there are often competing demands for Australia’s water.
The flow of the Murray–Darling
The water in the Murray–Darling is divided up to meet the needs of water conservation and supply (including for critical human needs), irrigation, environmental protection and enhancement. It is also managed to support protection of cultural heritage, protection of water quality, river navigation, recreation and tourism, hydro power generation and flood mitigation.
Since 1917, water in the Murray–Darling catchment has been regulated under various water sharing agreements, which have had far reaching social and economic benefits. But, over time, this has also contributed to a decline in the health of the river system.
Executive Director of River Management with the Murray–Darling Basin Authority (MDBA), David Dreverman says development of the large water storages in the Murray–Darling catchment to support extensive irrigation has changed the nature of the flow regime in the river.
“We converted the rivers from winter-spring rivers to summer-autumn flowing rivers. In that process we eliminated about two-thirds of the overbank flow events that used to exist prior to that dam and irrigation development. When we did that, we didn’t realise – we now do – the serious impacts on the health of the floodplains,” says Mr Dreverman.
The one-of-a-kind Barmah-Millewa Forest has a rich bird life and supports many threatened native plants and animals, but it needs regular and prolonged flooding to survive.
Almost a hundred years of water regulation has meant that flood events carry less water, are shorter and are less frequent. This has led to a significant reduction in native birds and fish and a big change in vegetation composition and health.
In response, environmental water is being allocated to preserve the Barmah-Millewa Forest, along with other unique Australian habitats.
Environmental water is strategically released into the system to refresh water-dependant ecosystems. It’s a carefully planned process.
This is where effective water management, the expertise of the MDBA, hydrological and floodplain modelling, and cutting edge forecasting technology combine to reinstate the Murray back to health.
“One of the aims of the Murray–Darling Basin Plan is to restore healthy river systems, at the same time as maintaining healthy irrigation industries and healthy communities. Irrigators have got to get smarter with how they use water and environmental water managers and floodplain land managers, particularly those who are managing for environmental outcomes, have to get smarter with what water is available,” says Mr Dreverman.
Such critical decisions depend on knowing how much water is in the system, where it is, where it is needed and how all that might change in the coming days or weeks.
“What we’re trying to do is make sure that we get the greatest value out of all available water that is in a river system. The better our forecasting and the more reliable that information is, the more we’re able to adjust our operations in a timely manner to make the best use of all water,” says Mr Dreverman.
A forecasting tool for water flows
To help facilitate better water management decisions, a 7-day streamflow forecast has just been launched, the product of research by CSIRO and the Bureau of Meteorology (the Bureau).
Scientists and hydrologists from both organisations, working as part of the Water Information Research and Development Alliance (WIRADA), shepherded the project from research to development to operations.
The new product, now available on the Bureau’s website, provides streamflow forecasts out to seven days for more than 100 locations around Australia.
The forecast uses real time observations from a national network of rain and river gauges, rainfall forecasts, and modelled runoff and river flow.
“When used with other tools, the 7-day streamflow forecasts help water managers optimise the economic value of river regulation and diversions by planning water releases and water extraction opportunities around forecast natural flows,” says Dasarath Jayasuriya, Assistant Director of Water Forecasting Services at the Bureau.
“The forecasts also offer environmental benefits, helping water managers deliver environmental flow requirements including high and low flow needs for rivers and wetlands.”
Dr David Robertson, a senior hydrologist with CSIRO and Project Leader of the WIRADA flood and short term streamflow forecasting project, says “there has long been a need for this forecast.”
“We now have a method of producing a forecast that is reproducible. So we have a forecast process that is routinely taking numerical weather predictions and ingesting them into a hydrological model. This makes it consistent and automated so the time it takes to produce the forecast is shorter meaning you can apply it to more catchments, more rapidly and more often.”
This added and real-time insight into how streams respond to rainfall will provide true operational value in meeting one of the MDBA’s key responsibilities to protect, restore and provide for the ecological values and ecosystem health of the Basin.
“The big benefit of this new technology will be around how you manage regulated releases, to actually create small overbank flow events that are needed from time to time to sustain a healthy river environment,” Mr Dreverman says.
Those strategic overbank flow events are life preserving for areas like the Barmah-Millewa Forest. According to Mr Dreverman, forecasting will allow the MDBA to maximise water availability and utility for all entitlement holders, including irrigators and the environment.
“The forecasts help us to manage rivers better whether it’s to conserve water for consumptive use, prevent unseasonal flooding of major forests or to support water events to enhance the health of the flood plain—it’s going to do all those things. This is another tool that helps us get smarter with how we manage water.”
Better management of the rivers equates to conserving and maximising available water, in preparation for times when demand will be greater, while rainfall and runoff may potentially be less.
Preparing for variability and change
Francis Chiew and Ian Prosser reported in CSIRO’s 2011 Water book that Australian rivers are amongst the most variable in the world, where river flows in a wet year can be more than 20 times greater than in a dry year. The 1997 to 2009 Millennium Drought resulted in unprecedented decline in runoff in the southern Murray–Darling Basin. The latest climate and hydrological modelling projections indicate that long-term average river flows in southern Australia are likely to decline by 10% to 25%.
David Dreverman adds that “We’ve been living with climate change for twenty years. We live it every day, and every year we’re seeing things we haven’t seen in the past, things that aren’t in our 114-year historical record. That means record summer inflows, record dry sequences. We’ve seen inflows half the previous lows.”
“The Millennium Drought from 1997 to 2009 gave Australia’s water managers a lot of insight into possible future hydrologic conditions. So while it can get drier, we’re a whole lot better prepared in 2015 than we were in 2006.”
Since that time, water managers, water users and state and federal governments have changed the way they think about, use and protect water for an uncertain future climate.
The research that underpins the 7-day streamflow forecast is ongoing, and the next generation of numerical weather prediction models will be operational in the coming years to generate both deterministic and ensemble rainfall forecasts.
“By using the methods to do the ensemble forecasting you will get a better estimate of the expected streamflow,” says Dr Robertson.
“And in addition, there will be a range of possibilities that may occur, so people will understand the uncertainty in the forecast. That will add a lot of value by allowing water managers to take a risk based approach to their daily decision making. Risk can be thought of as a product of consequence and likelihood – this provides the likelihood component to that assessment of risk.”
Managing water to maintain the natural variations in Australia’s streamflows requires a calculated ebb and flow. Today, those calculations are more precise than ever, as we take lessons learned in the past to build on technology that innovates for the future.