This paper discusses the design evolution of constructed watercourse diversions in coal mines located in the Bowen Basin, Queensland. A series of Australian Coal Association Research Program (ACARP) funded research projects spanning 15 years has evaluated the performance of watercourse diversions in coal mines and developed design and monitoring criteria based on characteristics of regional stream systems and replication of the natural stream processes.
An assessment comparing the performance of sixty diversions based on the ACARP design criteria (post 2000) and those older diversions built prior to the criteria was undertaken using a diversion evaluation framework modelled on the Monitoring, Evaluation, Improvement and Reporting (MERI) Framework adopted in the natural resource management industry. Through the passage of this project this MERI framework was refined and updated to identify criteria for successful constructed watercourse diversion operation and relinquishment.
The evaluation of diversions found five factors consistently limited the performance of most diversions including; sediment supply and transport, vegetation condition, occurrence of major flood flow events in early years of diversion establishment, overland flow drainage and diversion transitions. This highlighted the need to revise the design criteria to address the identified limitations and reduce impacts to adjoining waterways.
A review of best practice constructed watercourse diversion design and associated tools resulted in a refined design standard for watercourse diversions in Central Queensland. This includes an update of the hydraulic and geomorphic criteria developed in 2002, an alluvial channel design to explicitly consider sediment supply as well as a threshold design that determines the level of establishment of vegetation required post construction to increase resilience during flood events.
Throughout the ACARP research, interviews with representatives from the mining industry and Department of Natural Resources and Mines were conducted to understand the different perceptions of diversion construction and the impact on the environment, diversion operation and their relinquishment. Changes in these perceptions over the past 15 years will also be explored alongside industry plans for the future.