EGL Ref: 9215 23 June 2022 Page 29 This report shall only be read in its entirety. File: WAI-985-000-REP-LC-0002_Rev0.docx. FIGURE 23: COLLECTION SUMP T18 AT TOE OF STORAGE 1A To manage surface water Storage 1A has an uphill diversion drain, which diverts clean water from the hills, southeast to the Ruahorehore Stream. There are three collections ponds (S3, S4 and S5) to collect run-off from the Storage 1A embankment during construction and operation as shown in Figure 22. A photo of S5 is shown in Figure 24. These ponds are sized to have a total volume (up to the spillway) equal to the runoff volume from a 10-year ARI 72-hour storm event. FIGURE 24: STORAGE 1A COLLECTION POND S5, WITH FOREBAY AND MAIN POND McMahon Contractors Ltd undertook construction of Storage 1A from 1 July 1998 to 28 May 2015. Since then, construction of the Storage 1A embankment and associated facilities has been undertaken by C&R Developments Ltd under the supervision of OGNZL.
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