4
Data availability UMG TSF hydrogeological conceptualisation
4.1
Site geomorphology and climate
The Mount Morgan mine area is characterised by rugged, deeply incised terrains developed on competent bedrock units, with prominent ridgelines, escarpments and incised drainage features that reflect long term the landscape evolution. This natural geomorphological setting has been modified by more than a century of mining activity, resulting in a complex legacy of landforms comprising open pits, steep gullies, waste rock dumps, tailings storage facilities and altered drainage pathways. The proposed TSF is located within a natural topographic basin, with ground elevations across the footprint varying significantly. The lowest point of the proposed TSF footprint occurs at approximately 322 m AHD, while the surrounding ridgeline rises to elevations of up to approximately 405 m AHD. The Mount Morgan mine site is located within the Dee River catchment, with the Dee River forming the principal regional drainage feature and the primary receiving water downstream of the mine site (refer to Figure 4.1). The Dee River flows perennially south to southeast past the eastern margin of the mine lease before joining the Don and Dawson river systems, and is characterised by highly seasonal flow conditions, with short duration runoff events during the wet season and extended periods of little surface flow during the dry season. Several ephemeral tributaries and mine‑affected drainage lines intersect the site, including Mundic Creek, Linda Creek, Arnolds Gully, Nelsons Gully, and Shepherds drainage, which historically conveyed runoff and shallow subsurface flow toward the Dee River [2] [3]. West of the Mount Morgan mine, local gullies and drainage lines generally flow westward before joining Turner Creek, which then flows to the north-northwest. Relevant to the UMG TSF hydrogeological conceptualisation are Paddy Creek and Spring Creek, ephemeral watercourses that drain the upper catchments immediately west of the proposed TSF area and merge with Turner Creek. These creeks are deeply incised into the sandstone units of the Razorback Beds, progressively exposing underlying stratigraphic units, with Paleozoic bedrock outcropping in both channels. The creek beds are also characterised by later erosional incisions. No specific information charactering Turner Creek flow is available although the information available in the Queensland Globe [4], indicates this creek to be intermittent suggesting creek flow occurring mainly following rainfall events. The proposed TSF is located within Upper Mundic Gully, which represents a historic drainage line largely ephemeral and controlled by rainfall events. The lower reach of this gully, immediately west of the OCP has been substantially modified by historic mining activities, including the placement of the Western spoil dump, which has effectively dammed the original watercourse and altered natural drainage patterns. As a result, runoff generated within the gully is no longer conveyed downstream via its pre‑mining alignment and instead accumulates upstream of the spoil dump during intense rainfall events. To manage these conditions, diversion infrastructure (an underground tunnel) has been constructed to direct runoff from the Upper Mundic Gully catchment toward Dam 8.
Project No PS213278 Mount Morgan Mine - Upper Mundic Gully TSF Seepage Management Plan Heritage Minerals
WSP May 2026 Page 8
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