EGL Ref: 8983 23 June 2022 Page 7 WAI-985-000-REP-LC-0004_Rev0.docx This report shall only be read in its entirety. 2.4. Dam Safety Reviews An essential part of modern dam safety management is the regular review of the performance and safety of a dam. Two types of reviews are recommended by the NZDSG. They are discussed below. 2.4.1. Intermediate Dam Safety Review Intermediate Dam Safety Reviews (IDSR) are recommended to be conducted annually and are normally conducted by the Design Engineer. The Annual Structural Integrity Report prepared by EGL annually meets the expectations for an IDSR. 2.4.2. Comprehensive Dam Safety Reviews The 2015 NZDSG recommend that a Comprehensive Dam Safety Review (CDSR) be undertaken every 5 years for a High PIC dam. The CDSR must be undertaken by an independent, experienced, and qualified reviewer to meet the requirements of the NZDSG. The CDSR must include a comprehensive independent review of the design, construction, operation and performance of the dam and all the systems and procedures that affect dam safety and compare against current dam safety guidelines, standards and industry practice. To ensure full compliance with the 2015 NZDSG Tony Pickford was engaged by OGNZL to undertake a CDSR. Mr Pickford is a very experienced dam engineer and has undertaken CDSRs for most of the largest dams in New Zealand. He undertook a site inspection in March 2020, interviewed OGNZL staff with responsibilities for dam safety, interviewed the Designer and reviewed all relevant documents. A CDSR report was provided on 12 June 2020 (Ref. 11). Risk assessments are also undertaken as part of comprehensive reviews and a Failure Modes and Effects Analysis workshop was undertaken for the Storage 2 and 1A in August 2018 with a report outlining potential failure modes and mitigations produced (Ref. 12). 3.0 PERFORMANCE TO DATE The latest annual reports cover the period 1 April 2020 to 31 March 2021 (Ref. 8 and Ref. 9). The pore pressures measured by the piezometers, subsurface drain flow measurements and deformations confirm that the performance of the embankments are within design expectations and meet the conditions of the resource consents. Stability analyses are undertaken annually using the as-built geometry and measured pore pressures. These analyses show that calculated factors of safety exceed the criteria required by the NZDSG, indicating satisfactory performance. Assessments of earthquake deformation also meet the performance criteria recommended by the NZDSG.
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