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CARRIAGE HILLS NO. 2 DAM, Dam Failure Forensic Investigation Report Page 35 February 27, 2015 was estimated to be about 4 feet above the bottom of the reservoir, so if the outlet works existed it was set above the bottom. We saw no evidence of the outlet works during our inspection of the breach, so it either did not exist or it was washed downstream by the breach flood. 8.1.3 Combined Overtopping and Internal Erosion: Reference 1 recommends considering a combination of possible failure mechanisms. In the case of the Carriage Hills No. 2 Dam failure, it seems likely that the low area of the dam crest at the breach location corresponded to the outlet conduit location. Crest settlement may have occurred in the past due to failure of the CMP conduit. The low area likely caused concentration of overtopping flows, which may have accelerated the process of scour and headcutting of the embankment at this location. As the headcut formed, it would shorten the seepage path along the outlet conduit and increased the potential for internal erosion. In this manner overtopping erosion at the low area of the dam crest and internal erosion along the conduit may have combined to cause the failure of the Carriage Hills No.2 Dam. 8.1.4 Poor Maintenance & Repair: The Carriage Hills No. 2 Dam’s spillway was inadequate to pass flows from the Sept. 2013 flooding. The spillway as surveyed on Sept 26, 2013, did not conform to the approved C‐1195 construction plans. We estimated the capacity of the existing spillway to be 213 cfs. The capacity on the C‐1195 plans was reported as 377 cfs. Based on our file review, the SEO cited problems with willows obstructing the spillway and inadequate spillway size as far back the 1980’s. In 1991 the DSB required the Town to remove obstructions from the spillway and provide a minimum of 3 feet of freeboard. In 2002, the DSB required the Town to restore the spillway to the conditions shown on the C‐1195 plans or hire an engineer to provide an alternative design, which was not done. It appears the Town did little to maintain or repair the Carriage Hills dams. In 2008 the DSB cited the safety problems associated with the improperly abandoned CMP outlet conduit and required the owner to prepare plans and specification to rehabilitate the outlet works. To our knowledge the owner made no progress on repairing the outlet works prior to the failure. The low area of the dam crest was likely associated with the abandoned outlet conduit and appears to have contributed to the dam failure. 8.2 Emergency Response: There was miscommunication when the DSB understood from Town staff that residents along Fish Creek were being evacuated on Thursday morning, Sept. 12, 2013, as the dams were overtopping. In reality the Town verified afterwards (e‐mail, Feb. 27, 2015) that a notification of minor flooding was issued at 03:43 hrs on Sept. 12, 2013, but a full evacuation notice did not occur until 18:12 hrs on Sept. 13, 2013, after the dam failure. It also appears no emergency action was taken to save the dams after they began overtopping. The photos taken on the morning of Sept. 12th suggest that an excavator or backhoe may have been able to access the spillways and do emergency clearing and excavation to safely pass the floods. However, the Town’s staff were likely overwhelmed by the catastrophic nature of the historic flood. 8.3 Possible Downstream Damage Resulting from the Carriage Hills No. 2 Dam Failure Mr. Bonza, homeowner at 1551 Fish Creek Road, provided an eyewitness account and videos of Fish Creek flooding on Sept. 12‐13, 2013 (see Section 5 for details). His house is located along Fish Creek immediately upstream of Country Club Road and approximately 2700 ft downstream of the Carriage Hills No. 2 Dam. Based on his account, Fish Creek at this location experienced its maximum flood stage around 22:20 hrs on Sept. 12th when it flooded his walkout basement with about a 1 foot depth of water. Mr. Bonza believes this surge in Fish