Grosvenor Project EIS

The Grosvenor Project involves the development of an underground coal mine located near the central Queensland township of Moranbah. The Longwall mining method will be adopted for the Project which will result in subsidence troughs up to 2.7m deep, 6km long and 300m wide over the mining area. Alluvium completed the Surface Water Impact Assessment as part of the Environment Impact Statement (EIS), which received approval from Queensland’s Department of Environment and Resource Management (DERM) in September 2011.

Work undertaken for the Surface Water component of the EIS included geomorphic assessment of watercourses across the site, determination of their environmental values and baseline condition monitoring. Predictions of geomorphic response following longwall mining related subsidence were then made, informed by sediment transport projections and hydraulic modelling of pre and post subsidence scenarios. The assessment methodology followed that developed in the Isaac River Cumulative Impact Assessment of Mine Developments, which has since been adopted by DERM as an industry guideline (Watercourse Subsidence – Central Queensland Mining Industry v1.0, Draft, 2011). Where risks were identified, mitigation and management strategies were proposed including soft engineering solutions such pile fields for bank protection and bed gradient control.

The extent of pre-subsidence and post-subsidence ponding on the floodplain was mapped and quantified to determine the impacts to overland flow and also to assist with ecology assessments. The impact of the Project on downstream users was quantified for the 100 year and 1000 year ARI flood events by comparison of flood hydrographs pre and post development.