Rainfall Erosion Analysis: WA-based Mineral Sands Mine

Rain Consulting was engaged by Image Resources to assess the design and performance of a proposed sump, located at a mine site in the Wheatbelt region of Western Australia. The assessment utilised industry-standard RORB and TUFLOW modelling to test whether the sump could safely manage rainfall from a major storm (2% AEP, or a 1-in-50-year event). The project aimed to prevent erosion and runoff issues that had impacted the site in past years, supporting mine compliance and site safety.

Above & Beyond Strategies

Significant rainfall events in 2021 and 2022 caused runoff and downstream issues from a portion of the mine site. While previous works helped, they didn’t fully solve the problem. The requirement was to design and verify a sump that would provide enough capacity and resilience in future major storm events, especially considering the erodible sand and fines at the site.

Rain delivered the following solutions.

• Used RORB for hydrologic modelling to define critical storm events, peak flows, and required storage volume.
• Applied high-resolution LiDAR data and GIS for catchment delineation and pre-/post-mine site comparison.
• Constructed TUFLOW 2D models for three scenarios: pre-mine, post-mine (no sump), and post-mine with sump (with and without an eastern cutoff wall).
• Analysed the impacts of each scenario on flow paths, flood depths, and downstream discharge to the nearby Brand Highway.
• Assessed sump freeboard and runoff capture under worst-case storm conditions.
• Tested the effect of additional design features (like an eastern cutoff wall) on sump efficiency and erosion risk.
• Provided operational advice for ongoing sump maintenance, sediment removal, and inspection after storm events.
• Delivered clear summary maps and figures showing changes in flow and flood depth for each scenario.

Rain confirmed the proposed sump has ample capacity after a major event. Flows across the Brand Highway are reduced by over 80% compared to pre-mine conditions, significantly decreasing downstream flood risk.

Rain’s recommendations support robust operation and maintenance to ensure long-term sump performance.