Indicator 4.1d: Management of the risks to water quantity from forests (2025)

• All states and territories have regulatory instruments to manage the impact of forest management activities on water yields.
• Forest hydrology research has been used to inform forest management practices and water resource planning, particularly in regions where water supply catchments overlap with commercial wood harvesting operations.
• Water quantity from forests is affected by bushfires, climate change, and forest management activities for wood production in native forests and plantations. Best practice activities for managing the risk to water quantity from forests are applied to Australia’s public forests available for wood production.

Water quantity, including streamflow, is strongly linked to forest cover and forest management activities (Harper et al. 2019). In general, forested catchments provide water supplies with a lower risk of variation in water quantity than do catchments with other (non-forest) land uses. As a result, large areas of forested land provide reliable and clean supplies of drinking water for human consumption, for irrigation and industrial uses as well as providing benefits for environmental and cultural values.

The quantity of water available in streams and rivers flowing from forested catchments depends on the combination of rainfall, water interception and use by the forest vegetation, run-off, and entry to groundwater systems. Rainfall varies seasonally and across longer periods, while the amount of water used by a forest stand depends on its age, tree density, species composition and growth rate.

The scale, timing, and intensity of forest management activities such as wood harvesting, thinning of regrowth forest and prescribed fire, can impact on water yields from forested catchments. For example, intensive harvesting in a large proportion of a forested catchment would change the forest age-class structure significantly, and this could affect the water balance of the catchment. However, most water supply catchments are sufficiently large, and the proportion affected from year to year by forest disturbance is relatively small, so effects on water supply are typically not significant.

Major bushfire events can influence water yields by changing the age-class structure of forests, as stand age and leaf area are major determinants of forest water use. Run-off can be high immediately after bushfire, and then low from the subsequent regrowth of forest stands, before increasing again as stands mature. The magnitude of these changes depends on the proportion of a catchment that is forested, soil types that are present, the proportion of forest that is burnt, and the severity of the fire. Much smaller effects are likely in mixed-species native forest catchments subject to non-stand-replacing fires.

Careful planning and implementation of best practices during forest management activities are essential to minimise potential risks to water quantity. Best practice activities such as the following are applied in the management of Australia’s public forests available for wood production:

• dispersing wood harvesting and similar activities across the landscape to reduce impacts on individual catchments
• adopting silvicultural techniques appropriate to a particular catchment and associated values
• establishing riparian exclusion and buffer zones and maintaining vegetated buffer strips along waterways
• distributing plantation age classes across the landscape and estate to minimise impacts on individual catchments
• undertaking prescribed burning during milder seasonal conditions to encourage a mosaic of burnt and unburnt area, particularly in sensitive areas such as riparian zones
• timely regeneration of forests after wood harvesting
• identifying vulnerable areas, such as wetlands, karst, waterbodies, streambeds, streambanks, major water storages, and avoiding disturbance in these high-risk areas
• conducting regular audits of all forest management activities to ensure compliance with licences, codes of practice and operational procedures.

Various legally binding and non-legally binding instruments specify measures to manage streamflow and water quantity. Legally binding instruments include legislation, regulations and licences, and non-legally binding instruments include some codes of practice, guidelines and forest management plans.

A list of instruments relating to the protection of water quantity is provided in Table 4.1d-1 of the Supporting Information for Indicator 4.1d.

Australian Capital Territory

Regulatory instruments relating to the protection of water quantity include the Planning Act 2023, Water Resources Act 2007, and the Environment Protection Act 1997, however, they do not specifically cover forest management activities. The Water Resources Act 2007 requires licenses for water extraction from surface water and groundwater sources. In the Australian Capital Territory (ACT), the conduct of logging operations requires an Environmental Authorisation (EA) from the Environmental Protection Authority (EPA), and this EA stipulates conditions related to the protection of water resources. The ACT EPA enforces these conditions by conducting compliance audits every two years, either through an inspection or a desktop assessment.

Wood harvesting in the ACT is limited to plantation forests. The protection of water quantity in plantation forests is addressed in the Strategic Plantation Management Plan 2017-2022 (updated 2025). The Plan specifies the dispersion of different age class plantations throughout catchments to limit the risk of water quantity variations.

The ACT Water Resource Plan 2019, which is an element of the Commonwealth Basin Plan 2012, regulates water use in the Murray-Darling Basin, including setting a baseline diversion limit for water associated with forest management activities in the ACT.

New South Wales

Regulatory instruments relating to the protection of water quantity include the Forestry Act 2012 requiring forestry operations on Crown-timber land to ensure the preservation of water catchment capabilities, and the Plantations and Reafforestation Act 1999 and the Plantations and Reafforestation (Code) Regulation 2001 regulating water usage associated with plantation forestry.

Maintaining appropriate water yield and flow within forested catchments is among the core objectives of the New South Wales Regional Forest Agreements implemented through the Integrated Forestry Operations Approvals (made under the Forestry Act 2012). Under the conditions of the Integrated Forestry Operations Approvals, wood harvesting operations in public multiple-use native forests are required to be dispersed in space and time; this mitigates environmental impacts, including potential effects on water quantity. Forestry Corporation of New South Wales has implemented a strategic zoning system across State forests, known as Forest Management Zoning, to guide specific management objectives. These zones help protect riparian areas, distribute harvesting activities, and minimise disturbance in environmentally sensitive or high-risk locations.

The Private Native Forestry Codes of Practice (2022) sets standards for activities in private native forests that indirectly support the maintenance of streamflow and water yield by protecting riparian zones and setting tree removal limits.

Northern Territory

The Water Act 1992 and Water Regulations 1992 are the primary legal instruments that address water resources in the Northern Territory; however, they do not specifically cover forest management activities. The Water Act 1992 requires licenses for water extraction for development activities.

Queensland

Water supply from forested catchments is generally not a limiting factor in Queensland. The Forestry Act 1959, Vegetation Management Act 1999, and the Code of practice for native forest timber production on Queensland’s State forest estate 2020, govern water use and management in forested landscapes. Native forest wood harvesting operations are generally dispersed and occur over only a small proportion of any regulated catchment. Selective harvesting practices used in these forests have only a limited impact on canopy cover, and thus on water use by the forest. As a result, native forest wood harvesting operations do not have significant impacts on water flows at the catchment scale.

South Australia

The Landscape South Australia Act 2019 requires commercial plantations in designated forestry areas to undertake formal risk assessments regarding impact on water quantity. Under the Act, the South Australia Regional Landscape Boards develop Water Allocation Plans (WAPs) for each prescribed water resource area. Once a WAP is in place, plantation managers can apply for a water licence to use water in a particular catchment. This water licensing system applies only to ‘designated forestry areas’, where commercial forestry is a major land use, such as the Lower Limestone Coast, Hills and Fleurieu, and Kangaroo Island. New commercial plantations in these areas can only be approved if sufficient water is available within the extraction limits. In ‘non-designated forestry areas’, such as the Eastern and Western Mount Lofty Ranges, commercial plantations require a Water Affecting Activity permit and a designated offset location.

Tasmania

The Water Management Act 1999, Water Management Regulations 2019, Environmental Management and Pollution Control Act 1994, Forest Practices Act 1985, and Forest Practices Code (2020) are in place to ensure the sustainable use of water resources, including during forest management activities.

The Forest Practices Code restricts clearfelling to no more than 5% of the area of any town water supply catchment in any given year. Clearfelling of native forest is prohibited in areas with vulnerable karst soils within two kilometres of a town water supply intake, unless authorised by the Chief Forest Practices Officer, who will normally apply strict prescriptions on forest harvest. In other situations, clearfelling in native forest is generally not permitted within 50 metres of a bank of a Class 1, 2 or 3 watercourse, or within 10 metres of a Class 4 watercourse, for a distance of two kilometres upstream from a town water supply intake; however, some exceptions apply in the case of Class 4 streams. Similar but slightly less stringent controls apply to plantations.

Victoria

Instruments to protect water in Victoria include the Water Act 1989, the Catchment and Land Protection Act 1994, Sustainable Water Strategies, and the Code of Practice for Timber Production 2014.

The Water Act 1989 provides a legal framework that protects rights to water and entitlements for all Victorians. It provides for the integrated management of all elements of the terrestrial phase of the water cycle and to promote the orderly, equitable and efficient use of water resources.

The Catchment and Land Protection Act 1994 includes provision to declare a catchment as a special area classified ‘Special Water Supply Catchment Area’. While it does not explicitly address forest management activities, the Act provides the legislative framework within which activities must be considered as part of broader catchment management.

The Water Act 1989 and the Catchment and Land Protection Act 1994 were amended in 2019 to align with the Victorian Government's long-term water strategy, Water for Victoria; and to recognise Traditional Owners and Aboriginal Victorians in water and catchment management. Water for Victoria outlines commitments to periodically assess risks to water availability, including those linked to land use change activities.

Sustainable Water Strategies provide for the strategic planning of the use of water resources in Victoria’s regions – including identifying threats to the reliability of supply and quality of water, and are required to be prepared for different regions of Victoria consistent with the Water Act 1989. There are three current regional Sustainable Water Strategies across Victoria

The Code of Practice for Timber Production 2014 (amended 2022) includes explicit prescriptions and environmental safeguards for timber harvesting in Victoria, including requirements related to water quality. It mandates the use of buffers and filter strips in high-risk areas and Special Water Supply Catchment Areas to maintain water quality and waterway health.

Western Australia

Water resource protection and management in Western Australia is governed through the Rights in Water and Irrigation Act 1914, Environmental Protection Act 1986, and the Conservation and Land Management Act 1984. The implementation of these legislative frameworks is supported by the Forest Management Plan 2024-2033 in the south-west forest region, which recognises the importance of forested catchments in regulating water availability.

The Forest Management Plan 2024-2033 aligns with broader catchment management objectives and provides recommendations to alleviate challenges such as the impacts of changing climate on forested catchments. Recommended management practices include thinning of densely stocked regrowth stands of jarrah (Eucalyptus marginata), karri (E. diversicolor), and wandoo (E. wandoo) forests to reduce physiological stress and improve forest resilience to a drying climate.

Native forest wood harvesting

Small changes in a landscape's hydrology may occur when forests are harvested and regrown, including fluctuations in annual water yields (Vertessy et al. 2001). Knowledge of the effects of forest management activities on water quantity is well developed, particularly in New South Wales, South Australia, Victoria and Western Australia. To assess such impacts, several long-term catchment studies have been established.

Karuah Catchment

The Karuah Catchment Study, initiated in the 1970s, investigates the impacts of forest management activities on water yield within Chichester State Forest in New South Wales. It comprises eight paired catchments, allowing for comparative analysis of different management regimes (Webb et al. 2012).

Tantawangalo Creek

The Tantawangalo Creek Catchment Study, initiated in 1985, was designed to evaluate the effect of different wood harvesting intensities and regimes on forest hydrology in mixed-species eucalypt forests in south-eastern New South Wales (Lane and Mackay 2001).

Coranderrk

The Coranderrk Paired Catchment Study, initiated in 1956 and located in the Yarra Ranges, east of Melbourne, is Australia's longest-running forest hydrology experiment. The study evaluates the long-term impacts of wood harvesting and forest regeneration on water yield in mixed-species eucalypt and mountain ash (Eucalyptus regnans) forests (Bren et al. 2010).

Yambulla

The Yambulla experiment, established in 1977 in dry sclerophyll eucalypt forests within Yambulla State Forest, New South Wales, investigates the hydrological impacts of intensive wood harvesting and subsequent mixed-species eucalypt forest regeneration, as well as wildfires, on water yield and streamflow.

The above studies indicate that for mixed-species eucalypt forests, water yield typically increases immediately after harvest. It then decreases for several years, with high water usage by vigorously growing regenerating forests before returning to pre-harvest levels. Although a longer-term decline in water yield was occasionally observed, such a reduction was usually temporary and varied with the forest regeneration dynamics, species composition, and basal area structure (Bren et al. 2010; Webb et al. 2012; Bren et al. 2013; Webb and Jarrett 2013). These findings have been important in informing forest management practices and water resource planning, particularly in regions where water supply catchments overlap with commercial wood harvesting operations.

Plantations

Water use by commercial forest plantations has occasionally caused community concern when substantial areas of new plantations are established in an area, particularly during periods of drought (Ryan 2013).

These concerns are often linked to the potential reduction in streamflow. Increasing the proportion of catchment area occupied by plantations tends to decrease water yield compared to unforested controls (Zhang et al. 2011; 2012). For instance, plantations of shining gum (E. nitens) in Tasmania and blue gum (E. globulus) in South Australia use between 500 and 1,100 mm per year (Benyon and Doody 2014, Roberts et al. 2015), highlighting the substantial water demand of some species. However, forest plantations in Australia generally occupy only a small percentage of the catchments in which they occur (Downham and Gavran 2017), and hence their overall impact is expected to be small.

The Green Triangle Forests Groundwater Monitoring examines the relationship between management practices in commercial plantations and groundwater resources, with declines in groundwater levels in the region linked to these plantations. The Department for Environment and Water maintains an extensive groundwater monitoring network across South Australia, including in areas with intensive forestry operations. This network tracks groundwater levels and salinity trends, providing data essential for assessing the impacts of various land uses, including plantations (Lawson et al. 2023).

Bushfires

Bushfires can affect water yields in forested catchments, although the extent of the impact varies by forest type and fire severity. Fire affects evapotranspiration rates and hence water balance. It may be expected that forest water use through evapotranspiration decreases immediately after fire with the loss of vegetation, however, observations of this in mountain ash (E. regnans) dominated forests are inconclusive (e.g. Langdon 1976; Kuczera 1987; Feikema et al. 2013). Hydrologic assumptions about the impact of bushfires in alpine or mountain ash forests continue to be investigated (e.g. DELWP 2022; Inbar et al. 2022; Benyon et al. 2023).

Climate change

With an increasingly variable climate, there is a growing interest to better understand the spatio-temporal dynamics and drivers of forest hydrology and the impacts on catchments (Nolan et al. 2015; Metzen et al. 2019).

Climate change continues to exacerbate water quantity related issues, for example, declining rainfall in Western Australia has increased the risk of drinking water supply scarcity and drought-related forest dieback. Water use by forests is a major component of the water balance in south-west Western Australia catchments. ‘Ecological thinning’ is currently being undertaken in south-west Western Australia public native forests to increase water availability for the remaining forest vegetation and to increase groundwater infiltration and streamflow (Harper et al. 2019; Li et al. 2020; Burrows et al. 2022; CPC 2023).

As wildfires become more frequent and severe, there are concerns regarding their impacts on water yield from forested catchments. Khaledy et al. (2022) found that wildfire regime has a highly variable influence on annual streamflow across the Australian temperate zones and the variation of streamflow also varied with hydroclimate particularly precipitation. This study also highlights that quantifying the impact of wildfires on water yield at the appropriate scale is important for determining the risk of water resources to changing fire regimes and climate.

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Benyon R, Inbar A, Sheridan GJ, Lyell CS, Lane PNJ (2023). Variable self-thinning explains hydrological responses to stand replacement in even-aged forests. Journal of Hydrology 618: 129157. doi.org/10.1016/j.jhydrol.2023.129157

Bren L, Jeyasingham J, Davey S (2013). Impacts of native forest harvesting on flows into the Murray–Darling Basin system. Australian Forestry 76:91–100.

Bren L, Lane P, Hepworth G (2010). Longer-term water use of native eucalyptus forest after logging and regeneration: The Coranderrk experiment. Journal of Hydrology 384:52–64.

Burrows N, Baker P, Harper R, Silberstein R (2022). A report on silvicultural guidelines for the 2024–2033 Forest Management Plan to the Western Australian Department of Biodiversity, Conservation and Attractions. Western Australian Department of Biodiversity, Conservation and Attractions, Perth.

CPC (Conservation and Parks Commission) (2023). Forest Management Plan 2024–2033. Conservation and Parks Commission, Perth.

DELWP (Department of Environment, Land, Water and Planning) (2022). Major Event Review of the 2019-20 bushfires Victorian Regional Forest Agreements. Department of Environment, Land, Water and Planning, Victoria.

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