The Australian surface hydrological network has significant unregulated areas, with flows that reflect the combined effects of climate, and land use and management. There are also significant areas where water management interventions affect the flows in ways that can be beneficial, neutral or detrimental to the aquatic environment. Furthermore, the surface-water system and the broader landscape influence subsurface flows, supporting recharge and discharge of groundwater resources and, thus, the quality of both surface and subsurface resources.

Short-term and long-term changes in flows and water levels produce a range of primary and secondary effects on ecological systems. Increased low-flow and zero-flow days during droughts decrease environmentally important hydrological connectivity and increase pressure on refuge areas such as pools. Long periods of regulated flows and contraseasonal flows (e.g. high flows in dry periods to meet needs such as irrigation) disrupt the timing and nature of ecological events, such as plant growth, and fish or bird breeding. Increases in groundwater recharge above long-term values have raised groundwater levels and produced dryland salinity, whereas drainage of acid sulfate soils has acidified local waterways and caused ecological damage. Finally, although periods of flooding replenish wetlands and provide opportunities for animal breeding and plant growth, extended flooding waterlogs plants, leading to poor plant health, failed regeneration and, eventually, death. Thus, the ecological value of the state and trends of inland water flows and levels must be viewed through a variety of lenses regarding ecological consequences.

Compared with previous assessments, this assessment of the state and trends of inland water flows and levels focuses more on unregulated than on regulated flows. It is intended that this approach best represents the effects of the pressures of climate, and land use and management, without a large influence of water resources development and management intervention.

Available data

A major increase in the online availability of flow data and information on water resources assessment has occurred in Australia since 2011. The Bureau of Meteorology’s 2010 and 2012 Australian Water Resources Assessments provide detailed analyses of the water resources situation in each of the 13 national drainage divisions, and the Bureau’s 2013–14 Water in Australia report was the first in an annual series that highlights key issues related to water resources and their use at a national scale. Additionally, the Bureau’s annual National Water Accounts provide detailed information on water resource management for 10 nationally significant water regions. This includes information on Australia’s billion-dollar water market, such as volumes of water traded, extracted and managed for economic, social, cultural and environmental benefit. Many state agencies have increased online access to streamflow data in recent years, and a national repository of flow data and other information for more than 3400 sites is available at the Bureau’s Water Data Online site.

A further national source of information on surface-water resources is the Geoscience Australia – CSIRO data cube; this is a resource based on a time series of satellite data that, when integrated and calibrated with high-quality surface observations, has the potential to reveal the state of water volumes in surface storage areas and to shed light on water quality (Dekker & Hestir 2012). Remote sensing of water balance components across large areas has been found to be feasible. An analysis of remotely sensed precipitation, evapotranspiration and terrestrial water storage changes for the Lake Eyre Basin closed the water balance, with an error of around 2.1 per cent, or 6.2 mm, out of the 300 mm annual average water input through precipitation. This equated to a continental-scale average run-off of 144.7 ± 11.3 mm per year, which is comparable with the national values determined by the Bureau of Meteorology (Wang et al. 2014). The Water Observations from Space (WOfS) product is one example of application of the data cube to water resources. WOfS provides a historical summary of inundation for each grid cell across Australia, based on 27 years of Landsat images. Combining this history with local-scale information of topography and land cover could provide insight into the local ecological effects of historical inundation.

Water quality observations from space have also been investigated, looking at the use of reflected light to inform indicators such as chlorophyll, coloured dissolved organic matter, total suspended matter and the light environment of the water column. These indicators could provide estimates of important ecological factors such as trophic status and aquatic carbon content. Investigations have concluded that there is potential to use such approaches, although more in situ data are needed to support parameterisation and validation of the Earth observation–derived water quality information products (Dekker & Hestir 2012).

The Bureau of Meteorology’s Hydrologic Reference Stations and Monthly Water Update reports provide information for assessing the state and trends of water flows and levels across much of the country. The Hydrologic Reference Stations are a set of 222 long-term, high-quality flow gauging stations, all of which have no major flow-regulating structures upstream of the gauge. The gauging stations are managed by various, mostly state, water agencies. The data recorded at these stations are used to identify streamflow trends, and to analyse long-term variability and change in streamflow. Most stations—located in 10 of the 13 national drainage divisions—have data available to at least the end of December 2014.

The Monthly Water Update provides an online overview of rainfall patterns and streamflow status across Australia, updated for each month early in the following month. Updates have been produced since May 2015 and are available for 9 of the 13 national drainage divisions. Updates are not available for the North Western Plateau, Pilbara–Gascoyne or South Western Plateau because of observing network issues. The Monthly Water Update interprets the hydrological status of surface-water flows each month using provisional information from data providers. Gauging stations have been selected to best represent the spatial variation of flows across each drainage division. Data are presented as deciles to support comparison (e.g. Figures WAT12 and 13), and data for individual sites can also be viewed.

In addition to the above, the Regional Water Information online resource provides an array of options for examining the state and trends of streamflow, groundwater and major water balance components—precipitation, potential and actual evaporation, and run-off. This portal allows users to examine information at monthly and annual scales from more than 3500 gauging stations across Australia.

Triennial (i.e. every 3 years) reporting on Australia’s implementation of the Ramsar Convention on Wetlands provides a further source of information, covering wetland condition and management. The most recent report was prepared for the 12th Meeting of the Conference of the Contracting Parties, held in 2015 (Australian Government 2014). In addition to information on management planning and effectiveness, ecological value and condition, and social and cultural aspects, the most recent report stated that the condition of 59 of 65 of Australia’s Ramsar wetlands did not change.

Regional results

The Carpentaria Coast drainage division is represented in both the Monthly Water Update and the Hydrologic Reference Stations. In January 2016, more than half of the division had lower than average rainfall, with some areas reporting the lowest rainfall on record. Total rainfall across the division was 98 mm, 52 per cent lower than the 1980–2015 average of 206 mm. January rainfall was the ninth lowest in the past 117 years, and streamflows for most of the area were in the median range. Reference flow gauging stations within the division showed no significant trends for the 4 years from 2011 to 2014, with only the Wenlock River at Moreton showing a significant increasing trend in flow since 1967. Eight stations—2 in the Northern Territory and 6 in Queensland—showed significant step changes in their flow history, with the dates for these changes falling between 1970 and 1998. Annual flows for the past 4 years showed no trends towards either higher than average or lower than average values.

The Lake Eyre Basin has 5 high-quality reference flow gauges—2 in South Australia and 3 in the Northern Territory. The Monthly Water Update reports on 6 stations—5 in Queensland. Average to lower than average rainfall conditions in much of the Queensland area of the Lake Eyre Basin in mid-2015 to late 2015 produced lower than average flows in January 2016, except for the Bulloo River at Autumn Vale, which had above average flows because of some local high rainfall at the end of 2015. The region showed a small but insignificant trend towards lower than average flows in recent years, with 2 gauges reporting zero flows for 2013 and 2014.

Following periods of moderately extensive dry conditions in the northern and southern extremities of the Murray–Darling Basin during much of the period since 2012, rainfall in the 18 months leading up to 2016 was largely in the median range (decile 4–7) across the Basin. Basin streamflows in early 2016 were mostly around average in the southern and central areas, with a mix of above average and lower than average flows in some northern catchments. Stations on the Gwydir, Namoi and Macquarie rivers reported below average to very much below average flows, with the Gwydir River downstream of Copeton Dam having the lowest flow since 1980. The Copeton Dam was less than 17 per cent full at that stage, having fallen from 100 per cent full during the previous 40 months. The Basin contains 75 reference stations, with data to the end of 2013. Given the significant level of water resources development in the Basin, the stations are largely spread around the southern and eastern periphery. Of these 75, 56 had more years of below average than above average flows during 2011–13, with 28 (37 per cent) having all 3 years with below average flows.

The North East Coast drainage division covers the eastern coastal catchments of Queensland, including all those that flow to the Great Barrier Reef lagoon. The Monthly Water Update gives readings for 42 flow stations, from Pascoe River at Garraway Creek, at 12.7°S, to Logan River at Forest Home, at 28.2°S. The high-quality reference set also contains 42 stations for this division, 8 of which coincide. The tropical nature of the division and the moderate size of most of the coastal catchments mean that it is possible for adjacent catchments to have very much below average and very much above average rainfall in a given period. In early 2016, one area of the division, north of Cooktown, had above average rainfall in the previous 6–12 months, while the rest of the division had average to below average rainfall. Above average flows occurred at 16 per cent of the sites, mostly in the south, whereas average and below average flows occurred at 53 and 29 per cent of the sites, respectively, spread across most of the division. Long-term downwards flow trends are evident at 7 gauges in the Burrum, Brisbane and Logan–Albert catchments, with downwards step changes in 22 gauges across the catchment; the dates of these changes ranged from 1960 to 2007. Recent-year annual flows have not been dominated by either higher than average or lower than average values.

The North Western Plateau and Pilbara–Gascoyne divisions have insufficient river gauges or data to support either long-term, high-quality reference site trend analyses or a Monthly Water Update. Streamflow data for the De Grey River catchment showed annual flows in the past 5 years to be generally lower than in the previous decade. Streams in the Pilbara–Gascoyne have showed no consistency in annual flows in recent years, reflecting the variable nature and influence of the different rainfall pressures in the region.

Long-term and high-quality river gauging in the South Australian Gulf focuses on the less dry and more densely populated areas of the drainage division, around Adelaide. Periodic data summaries for various catchments in the Gulf are published by the South Australian Government, through its WaterConnect portal. Leading into 2016, the division saw above average rainfall in the southern half, and mainly average conditions in the north. The exception is for the end of 2015, when below average to very much below average rainfall occurred across 75 per cent of the division. Consequently, early 2016 streamflows were average to very much below average. Very much below average flows occurred at 2 sites north of Adelaide, with the Broughton River at Mooroola having its third-lowest January streamflow since 1980. Falling flow trends across 3 of the 5 long-term gauging stations aligned with more broadly observed trends across much of south-eastern and south-western Australia.

As noted previously, the combined South East Coast drainage division used in SoE 2011 is now more commonly broken into two divisions: South East Coast (New South Wales) and South East Coast (Victoria), the latter of which includes parts of the Snowy and East Gippsland catchments in New South Wales, and the South Australian areas of the Glenelg River and Millicent Coast catchments.

Similar to the North East Coast, the South East Coast (New South Wales) division covers a narrow strip of coastal catchments that extend south from the Gold Coast and Tweed River to the Towamba River. The latitudinal range of rainfall pressures—for example, through systems such as east coast lows—played out clearly on streamflow in early 2016. Flow for sites around and south of Newcastle was mostly higher than average, with the highest January flows since 1980 recorded for 3 sites. Much of this was because of the above average to very much above average rainfall falling across 62 per cent of the division. Conversely, 27 per cent of streamflow sites, all north of Newcastle, experienced below average flows. Flow trend data from long-term Hydrologic Reference Stations are largely equivocal for the division, with only 6 of the 17 stations having sufficient data to support a trend analysis, and only 1 of those (the Goulburn River at Coggan) showing a trend, which was falling. Across 2014–15, 7 of 14 sites available in the Regional Water Information service showed no trend; 5 showed a strong negative trend and 2 a weak negative trend in the medium range of flows. This was a slight degradation compared with 2013–14 conditions, when there were 9 sites with no significant trend and 5 with a strong negative trend.

Similarly, the South East Coast (Victoria) region had 10 of 19 reported sites with no significant trend in 2014–15; 3 sites had weak negative trends, and the remaining 6 sites had a strong negative trend. The latter 6 months of 2015 produced significant areas of very much below average and lowest-on-record rainfall across the western and central southern regions of Victoria, which contributed further to very low flows. The south-eastern areas of the state had mostly average conditions. The long-term, high-quality reference flow sites for this division have a range of above average and below average annual flows during the period, with 6 of 27 sites having all years above average for 2011–13, and 5 sites having all years below average. The former sites were in Gippsland and the latter near the South Australian coast, emphasising the climatological variability along the coast in the past 5 years.

One of the few wetter-than-normal areas of Australia leading into 2016 was the South West Coast. This was in stark contrast to the previous 36 months, when significant areas of the south-west experienced below average, very much below average and lowest-on-record rainfall. This region has 13 Hydrologic Reference Stations and 23 stations suitable for Monthly Water Updates, with 2 sites (Deep River at Teds Pool and Harvey River at Dingo Road) in common, meeting the differing requirements of these 2 online information products. Regional Water Information for 2014–15 reported on-flow trends for 9 sites, with the other 475 sites in the division having insufficient data to support analysis. Six of these 9 sites had a strongly significant falling trend for 2014–15, and 3 showed no trend. Early 2016 results showed above average to very much above average flows for 65 per cent of sites. Regarding of longer-term trends, 9 of 11 reference sites had significant falling trends, with 8 sites showing significant step reductions in flow from 1975 to 2000.

The Tanami–Timor Sea Coast division has 13 reference stations, with 10 in the Northern Territory. Eight of the stations show significant trends during the long term, all rising. Rainfall conditions during the latter months of 2015 ranged from very much above to very much below average across different parts of the division. Eleven flow stations normally report in the Monthly Water Update. In December 2015, 10 of these were reported to have flows exceeding average conditions, with 7 showing the highest-on-record flows for December since 1980. January 2016 conditions returned to largely average, with 7 sites having average flows, 3 below average and 1 (Daly River at Mount Nancar) very much above average.

Serious rainfall deficits affected all of Tasmania for much of 2015, with some areas in the west having the lowest 12-month rainfall on record. Four of 12 reference stations show long-term declines in flow, and declines in flow during 2015 saw the division’s 46 major water storages drop from a cumulative 46.1 to 35.6 per cent full. Streamflows for stations located mainly in the north of the state were reported in January 2016 as below average. Lowest-on-record flows occurred at 44 per cent of sites, located in the north and central east. At 7 sites, streamflows were the lowest for January since at least 1980, because of low rainfall in the previous 3 months.