EGL Ref: 9216 22 June 2022 Page 3 File: WAI-983-080-REP-GT-0013_Rev0.docx This report shall only be read in its entirety. in discharges of tailings and water into the downstream area. The receiving catchment is the Ohinemuri River and its tributaries (including the Ruahorehore Stream). The Ohinemuri River flows along the southern side of Waihi township and along State Highway 2 (SH2) to the west through the Karangahake Gorge, past Paeroa township and into the Waihou River which flows into the Firth of Thames. 3.0 OBJECTIVES AND SCOPE The results from the dam breach assessments are used to assess the consequences of dam breach events, including the Population at Risk (PAR), Potential Loss of Life, and damage to the infrastructure, environment, and community. They are the basis for assessing the PIC which sets: 1) the dam design criteria. 2) requirements for construction and operation; and 3) dam safety management including emergency planning. Storage 3 is in a rural area, approximately 3.0 km southeast of Waihi township. The area downstream of Storage 3 comprises rural, residential, recreational, and commercial land, e.g. the Waihi and Paeroa townships and the Karangahake Gorge Historical Walkway. Therefore, the assessment requires a level of detail that is appropriate to determine which assets and stakeholders could be impacted by a breach. Detailed and quantitative TDBAs are required for the Waihi Operation site. 4.0 INFORMATION REQUIREMENTS Information that is required for a comprehensive dam breach assessment for Storage 3 includes: • Identification of downstream receptors, including population, infrastructure at risk, environmental and cultural values. • Latest survey and design information for Storage 3 and the adjacent Storage 1A and Storage 2. • Water balance modelling and water management requirements to estimate the future stored water volumes in Storage 3. • Hydrologic information on the catchments of Storage 3 and the Ohinemuri River and its tributaries. • Information on the tailings properties. • Liquefaction assessments of the tailings. • Lidar survey of the project site and the area along the dam breach flow path. 5.0 POTENTIAL FAILURE MODES AND DAM FAILURE SCENARIOS A potential failure mode is a hypothetical failure mechanism which is developed considering the physical characteristics of the dam structure and its foundation, subsurface drainage conditions, surface water management, operation, maintenance, and surveillance. Potential failure modes can and do vary during the lifecycle of the TSF. A TSF that is appropriately designed and operated considers all potential failure modes and includes measures in design, construction, operation and closure which provide resilience and robustness against each,
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