Soil and water resources

Project SW1: Baselines, drivers and trends for forest water catchments

The Forest Monitoring Steering Committee commissioned the University of Melbourne to deliver baselines, drivers and trends for water quality and quantity in the NSW Regional Forest Agreement (RFA) areas.

Following this work, the University of Melbourne was asked to extend this analysis to other forested catchments in NSW. In doing so, the researchers applied novel statistical approaches to identify the flow responses to climate variability to identify any impacts from catchment disturbance, specifically fire.

The researchers have now delivered final reports for the baselines analysis in the RFA regions and the extended state-wide analysis.

The findings

The full findings and analysis are available in the final report for RFA regions and extension final report for state-wide analysis.

In summary:

• Annual flows have decreased in forested catchments over the last 35 years, with most significant decreases in the RFA region in south coast forests.
• One third of coastal forest catchments had 10% to 20% flow decrease relative to the long-term average, with similar findings for almost half of the catchments outside of the RFA areas.
• In RFA regions, flow reductions were generally smaller for catchments with a higher mean annual flow, greater area of national park, greater accumulated area harvested, or greater accumulated area burnt.
• Outside of the RFA regions, catchments with higher mean annual flow and catchments with a greater percentage of area used for grazing experienced greater percentage decline in flow.
• At the catchment scale, historical changes in flow are generally more heavily affected by hydro-climatic drivers than fire events, although some impacts on streamflow due to fire events were observed.
• There were mixed and inconclusive results across water quality indicators.

The approach

The researchers:

• Identified key indicators of water quantity and quality in across all tenures.
• Established a conceptual framework for analysing baselines/trends and opportunities for future monitoring of proposed key indicators across all tenures.
• Developed historic baselines for the indicators of water quality and quantity across all tenures.
• Proposed additional baselines for the indicators for which there is no current data.
• Analysed trends in the indicators of water quality and quantity across all tenures.
• Applied statistical analysis to identify potential drivers for water quality and quantity trends including climate and catchment disturbance (fire).

Papers and reports

Soil and water resources - forest water catchments:

• Final report – Long-term trends of water quality and quantity in NSW RFA regions (University of Melbourne, September 2021)
• Final report – Extension – State-wide long-term trends of water quality and quantity for forested catchments (University of Melbourne, June 2022)
• Literature and data review report

Published papers

Researchers funded under the NSW Forest Monitoring and Improvement Program have published articles on this project in the peer-reviewed journals.

How does wildfire and climate variability affect streamflow in forested catchments? A regional study in eastern Australia
The researchers compared the influence of wildfire and climate forested catchment stream flows over multiple years. They found wildfire showed less impact on streamflow than climate over longer time periods. The results highlight the role of climate on water resources in forested catchments and the need to consider changing climatic conditions at the catchment scale.
Access the paper at Science Direct - Journal of Hydrology
Full citation: Guo D, Saft M, Hou X, Webb J A, Hairsine P B, Western A W (2023) ‘How does wildfire and climate variability affect streamflow in forested catchments? A regional study in eastern Australia’, Journal of Hydrology, volume 625 (Part A), 129979.

Region-scale decline in streamflow across New South Wales catchments
The researchers examined temporal trends for over 35 years of streamflow records across 163 catchments in New South Wales. They found indication of an overall drying pattern and the trends suggest that flow declines are generally greater than expected with the given rainfall and are likely due to region-scale processes such as groundwater and vegetation dynamics.
Access the paper at Taylor & Francis Online – Australasian Journal of Water Resources
Full citation: Guo D, Hou X, Saft M, Webb J A, Hairsine P B, & Western A (2024) ‘Region-scale decline in streamflow across New South Wales catchments’, Australasian Journal of Water Resources, 1–15.

Data

The report, methods and project data for RFA regions can be found on the NSW SEED. Data also can be visualised and interacted with through the Spatial Collaboration Portal.

The project data for NSW will soon be uploaded to NSW SEED portal.

Project SW2: Baselines, trends and drivers for soil stability and health in forest catchments

The Forest Monitoring Steering Committee commissioned a consortium between the NSW Department of Planning, Industry and Environment and the University of Sydney to deliver baselines, drivers and trends for soil stability and health in forest catchments across the NSW Regional Forest Agreement areas.

The researchers have now delivered a final report.

The findings

In summary:

• Modelling reveals soil organic carbon has declined slightly over the last three decades. However, significant fluctuations occurred in this period likely driven by climatic conditions.
• Climate change is predicted to contribute to a decline in soil organic carbon condition over most of the area covered by the NSW Regional Forest Agreements, particularly the southern alps.
• Areas subject to increased ground disturbance from land use activity (particularly in forests in which grazing is permitted) have lower concentrations of soil organic carbon than less disturbed areas.
• Wildfires have a major influence on soil organic carbon concentrations and more frequent wildfires may result in continuous decline of soil health.

The researchers reported critical data gaps relating to soil health due to a lack of sustained monitoring. They recommended that a long-term soil health monitoring program is needed to support management of forest soils. In addition, the researchers suggested forest managers should implement appropriate soil carbon-enhancing strategies to at least maintain current levels, if not increase them, to assist in meeting net carbon emission targets and mitigate climate change.

The full findings and analysis are available in the final report.

The approach

The researchers:

• Designed a conceptual framework to evaluate soil health and stability.
• Collated and evaluated existing soil data from NSW forests in relation to presence, age, geographical coverage, parameters measured, repetition, and accuracy.
• Estimate the current status of soil indicators for which there is sufficient data for analysis.
• Identified potential drivers of change and threats to soil health.
• Determined trends for soil health and stability (including by spatial analysis).
• Proposed a soil monitoring program to address data gaps, inform soil and land management and maintain or improve the condition of forest soils.

Papers and reports

• Soil baselines - Literature review - Soil health and stability monitoring in forests (NSW DPIE, February 2021)
• Soil baselines - Final report - Determining baselines, drivers and trends of soil health and stability in NSW forests – RFA regions (DPIE and University of Sydney, October 2021)

Data

The report, methods and project data can be found on the NSW SEED. Data also can be visualised and interacted with through the Spatial Collaboration Portal.

Project SW3: Evaluating forest road network to protect forest waterways

Forest roads provide important access for the community, for example emergency management, recreation and timber harvesting. However, poor road design and maintenance can cause soil erosion and impact water quality and aquatic biodiversity.

The Forest Monitoring Steering Committee appointed Alluvium to develop a cost-effective method to evaluate the effectiveness of forest road networks in maintaining water quality.

Modelling framework

Alluvium have delivered a risk-based model to enable a consistent and cost-effective approach to assess the NSW forest road network. The model can be used to improve the allocation of resources and to continually improve road design and management through time.

A final report explains the model and method, including field assessment protocols.

The excel based model is available here and on NSW SEED.

The approach

The modelling framework is based on published research in forest road impacts on sediment delivery across different tenures and road types in NSW. The modelling considers two processes: erosion on roads and associated drainage infrastructure and the probability that eroded sediment will reach a stream.

Overall, users of the risk-based model move through a five-step process. The risk assessment uses two key outputs from this project: the state-wide sediment delivery potential model (the state-wide model), and the local scale sediment delivery potential model (the local model). The state-wide and local models use the best available scientific understanding of the processes that the drive erosion of road surfaces, runoff generation and the downslope transport of runoff and sediment to waterways.

The model was tested in the field with NSW land managers. Further field data, including erosion responses should be collected by NSW land agencies to improve the model over time. This will help ensure that field assessments and monitoring activities provide value beyond the local setting where the data is collected.

NSW agencies, land managers and Dr Peter Hairsine provided technical review and feedback throughout the project and on the final model and report.

Reports and datasets

• Soil and water resources – road network - Discussion paper (September 2020)
• Soil and water resources – road network - Final report (November 2022)
• Soil and water resources – road network - Model