The expansion of Hamersley Iron’s mining operations in Yandicoogina at the south east junction between Yandicoogina and Weeli Wolli Creek required a flood study which RPS was commissioned to undertake.
The northern edge of the orebody backs onto Yandicoogina Creek and the southern edge backs onto Weeli Wolli Creek so the peak flood levels in these creeks adjacent to the orebody were modelled. The flood modelling results were then used to determine pit flood protection requirements necessary to protect the pit from potential inundation during a large rainfall event. The modelling results took into consideration the proposed mine infrastructure such as road crossings, flood levees and an overland conveyor bridge crossing. From the modelling results, the inclusion of the proposed mine infrastructure into the model did not have a significant impact on the peak flood levels.
The second component of the project was to determine the optimum bridge opening width for the proposed overland conveyor bridge crossing for Yandicoogina Creek. The proposed overland conveyor bridge currently spaned 350 m from the abutments which was unnecessarily long. Flood modelling simulated the impacts of various bridge opening options on the peak flood levels, streamflow velocities and potential scour characteristics in the Creek. The recommended bridge opening option was a 260 m opening which produced minimal afflux and creek bed scour. This opening was 90 m smaller than the original proposed bridge opening, yet did not greatly affect the peak flood levels, streamflow velocities and bed scour characteristics.
In addition, erosion protection was designed for the main Yandicoogina access road. The mine access road crossed Phil’s Creek and needed to be designed to withstand a large storm event. The access road was recommended to be constructed in concrete and have sufficient rock armouring.