Surface-water and groundwater conditions have varied considerably since 2011, largely in response to climate. Changes to flows and water levels are described in detail in the Inland water report. The Inland water report describes how short-term and long-term changes to flows and water levels affect ecological systems in a range of ways. 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 irrigation needs) disrupt the timing and nature of ecological events, such as plant growth, and fish or bird breeding. Other significant impacts on native fish arising from altered flows include barriers to migration and altered water quality (e.g. temperature, turbidity, dissolved oxygen).
River regulation and water resource development have a negative impact on some waterbird populations. This pressure is particularly prevalent in the Murray–Darling Basin of south-eastern Australia. The impact of this pressure varies across functional groups, but has recently been shown to be a significant issue for colonial nesting waterbirds (egrets, herons, ibis and spoonbills) in the Basin (Reid et al. 2013).
Overallocation of water resources is not confined to the south-east. Issues have been identified in northern Australia associated with the Tindall Limestone Aquifer underlying the Katherine–Daly Basin, and with the aquifer that sustains Howard Springs and other peri-urban water bodies in the broader Darwin area. Rivers across the south-west of Western Australia are under considerable pressure from climate change, as well as pressures associated with a growing population, including increased demand for water. Rainfall is now around 16 per cent below the long-term average in this part of Western Australia, and reduction of run-off into rivers and streams of up to 50 per cent has been recorded. The reduced run-off has resulted in a general decline in flows, causing reductions in the duration of continuous flow and increases in the period of disconnection (many systems are naturally seasonal). Drying of river pools has also been recorded in some areas.
Changed hydrology can also have beneficial effects in areas that have previously been significantly altered for agriculture. For instance, much of the bird diversity in agricultural landscapes is dependent on dams and waterways remaining hydrated. Creating and protecting habitat around waterways also creates habitat for a range of mammals and frogs. The Australian Association of Bush Regenerators (AABR) is a private organisation promoting the effective management of natural areas based on sound ecological principles. AABR reported (Barrett & Davidson 1999, Barrett 2000):
- a 3 per cent increase in diversity of woodland-dependent birds for each additional farm dam present where adequate tree and shrub cover provided habitat
- a 14 per cent increase in waterbird diversity if dense, shrubby vegetation; shallow areas; islands or dead trees for roosting; or stock-excluding fences were added.