During the 2019/2020 bushfire season approximately 320,000 ha in the Warragamba Catchment burnt. Following the “Black Summer” bushfires, a widespread severe storm event occurred and posed a raw water quality risk to Warragamba Dam from erosion and run off.
Soil Conservation Service (SCS) was engaged by WaterNSW to undertake a post-fire catchment investigation to identify areas of high risk to raw water quality, implement erosion mitigation works at a pilot site and undertake a monitoring program. The outcomes of the catchment investigation, erosion mitigation works, and monitoring program aimed to establish a knowledge-based approach that could be applied to future bushfire responses.
The investigation phase highlighted challenges with rapid on-ground response, gaps in bushfire response preparedness and knowledge, and the suitability of existing erosion control methods to the Warragamba Catchment's topographical and wilderness context. Key learnings from the erosion mitigation works included access considerations, material availability in a post-natural disaster context and labour skill/availability. The monitoring program identified the importance of response timeframes, natural recovery, intervention disturbance and the value of a ‘do nothing’ approach.
Watercourse condition improved across all sites, the erosion mitigation/sediment capture structures successfully captured 11.2 T of sediment and rates of sediment capture slowed over time indicating the intervention site was progressively stabilising.
This project highlighted the need for a consolidation of national knowledge surrounding post-fire response in drinking water catchments. The erosion mitigation works highlighted the applicability of interventions in different catchment contexts, scale limitations of interventions and when a ‘do nothing’ approach is applicable.