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12 November 2021
Peter Mellor Heritage Minerals Pty Ltd
Hydrological assessment of PMF for the Sandstone Gully Tailings Storage Facility
Dear Peter,
1.
Introduction
1.1 Background GHD were requested to provide Probable Maximum Precipitation (PMP) and Probable Maximum Flood (PMF) results for the Sandstone Gully (SSG) Tailings Storage Facility (TSF), a part of the Heritage Minerals mine site, near Mount Morgan in Queensland.
1.2
Purpose
The purpose of this letter is to report the PMP and PMF values determined for the SSG TSF based on the prevailing guidelines.
2.
Hydrological assessment
2.1 Hydrologic model and PMP inputs The XP-RAFTS (RAFTS) hydrological model was used to estimate peak flow rates and associated runoff hydrographs. RAFTS is an interactive runoff and stream routing program that uses catchment losses to calculate streamflow hydrographs resulting from rainfall events and/or other forms of inflow to channel networks. It is capable of modelling rural and urban sub-catchments, and is an accepted model used to quantify flood flows from catchments as specified in the ARR (2019) guidelines. For GSDM estimates, spatial variation was accounted by utilising PMP ellipse and overlaying it on top the catchment. For GTSMR, the PMP input factors were sourced from standard nation-wide gridded data and averaged for the catchment area. These factors are presented in Table 1.
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