Water quality

This program area will determine the effectiveness of conditions related to water quality. The program will do this by establishing an evidence base on how the riparian exclusion zones, riparian ground protection zones, road and track protocols and soil conditions adequately maintain water quality in Coastal IFOA state forests.

Monitoring waterway and wetland health

The program will determine if the Coastal IFOA conditions and protocols are effective in minimising the potential impacts of harvesting, roads, tracks and crossings on waterway and wetland health. It is important to understand the current state of knowledge in this area - including monitoring and research approaches - to ensure the program prioritises research and monitoring effort to address knowledge gaps and uncertainty.

Project WQ1: Review of the current state of knowledge for the monitoring of forestry impacts on waterway health in NSW coastal forests

Alluvium has delivered a peer-reviewed literature review on forestry impacts to waterway health and water quality in Coastal IFOA state forests. The review included research on practices and conditions in the Coastal IFOA. For example, temporary log crossings, class 1 stream riparian exclusion zones and soil and water protection in intensive harvest operations and exclusion zones for Coastal State Environmental Planning Policy wetlands.

The review found the management practices in the Coastal IFOA related to soil and water controls are consistent with best practice and standards. When major runoff events occur, the impact on water quality is typically short-term and transitory.

However, the frequency of intense rainfall and bushfires are likely to increase into the future due to predicted climate change. These predicted changes have the potential to increase the risk of impacts of timber harvesting on water quality in the future. As such, it is important that the objectives for this monitoring program reflect predicted changes in climate and monitoring is designed to investigate implication for the IFOA conditions and protocols.

Based on this review, the program will refine the objectives of the water quality monitoring plan to provide a stronger link between what is being monitored, and its relevance for values that are being managed for now and into the future. It will also adopt a risk based approach to monitoring. This approach will link timber harvesting, and the forest road network more broadly, to hydrologic and ecological impacts on waterways and wetlands. The approach will also measure catchment response in areas where harvesting and wildfire intersect. This will build a better understanding of how current forest management can be adapted to address emerging risk associated with new catchment disturbance regimes.

Project WQ2: Post-fire debris flow mapping in the Tumut and Tuross Catchments

Soils in eucalypt forests are at greater risk of erosion under high intensity rainfall conditions if vegetation cover has been impacted by disturbance events such as fire. Erosion events can increase sediment flows into waterways impacting water quality and aquatic habitat. However, the location and the volume of sediment transferred into waterways during these events is not well understood.

Following the 2019-20 wildfires, large rainfall events in 2020 provided an opportunity to advance our understanding of large episodic erosion events following fire. Further research about these events can provide options for improved forest management to protect waterway health. This is particularly important in the context of a predicted increase in the frequency of intense rainfall and bushfires due to climate change.

We engaged Jacobs to map post-fire debris flows (a form of sedimentation) in the fire-affected Tumut and Tuross catchments in southern NSW. Jacobs worked closely with the University of Melbourne and Forestry Corporation of NSW in delivering this work.

Jacobs used a model developed by the University of Melbourne (and previously used in Victoria) to assess and predict the impact of bushfire on sediment delivery into waterways. The project analysed new aerial imagery before and after the fires to measure channelised erosion in headwaters and debris flow occurrence. This is the first time that debris flows have been systematically mapped in NSW and linked to fire severity and other landscape features.

Jacobs found fire severity and terrain are key factors influencing the amount and frequency of debris flows. For instance, the frequency of debris flows increases under higher fire severity. Higher flows are also more associated with sedimentary and volcanic terrain than granite landscapes.

The report provides further discussion on plantations, agricultural land, the forest road network and areas to improve data generation and collaboration across institutions and jurisdictions.

Access to data used in the analysis will soon be available on NSW SEED and the TERN Data Discovery Portal.

Project WQ3: Monitoring class 1 drainage lines and exclusion zones

We engaged Jacobs to assess whether the exclusion zone conditions for Class 1 drainage lines as codified under the Coastal IFOA are effective in minimising the impact of harvesting activities on waterway condition.

Class 1 drainage lines are headwater flow paths found at the top of a catchment. Riparian buffers and exclusions zones are important to protect water quality around drainage lines, although the width and definitions of these exclusion zones varies across jurisdictions.

Jacobs will carry out field surveys to report on the performance of riparian exclusion zones and ground protection zones for Class 1 drainage lines. As a first step, Jacobs will propose a feasible and scientifically valid field survey methodology and assessment framework.

Jacobs has assembled a project team that includes expertise in forestry, hydrology and water quality, aquatic ecology and forest hydrology. The project team will draw on recent experience from involvement in other Coastal IFOA monitoring projects such as the review of temporary log crossings.

Jacobs will work closely with Commission, FCNSW and EPA to deliver the project. Dr. Peter Hairsine will also independently review methods and findings.

Monitoring landscape-scale trends

The Forest Monitoring Steering Committee commissioned the University of Melbourne to deliver baselines, drivers and trends for water quality and quantity in NSW forest catchments. The researchers have now delivered a final report which is available here.