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reservoir greatly increase through the open channel spillway. The documentation in the file <br />indicates that the spillway was originally designed to convey the 100 year flood ( UDFCD <br />Criteria) but further details on the design of the spillway were not readily available. <br />Early in 2013, UDFCD completed a rehabilitation of the dam which included a cut - and -cover <br />replacement of the service spillway conduit through the maximum section of the dam, <br />placement of additional riprap protection on the upstream face of the dam, and laterally <br />extending the concrete slab serving as the control section for the service spillway to provide <br />additional protection in the residual freeboard zone. Plans for this construction are <br />presented in Appendix A. The rehabilitation plans are the only known drawings for the <br />structure. Plans for the original construction of the dam are not available. <br />4.0 Failure Event <br />First notification of flooding conditions at the site came from news reports. This information <br />was relayed to John Batka, Dam Safety Engineer for the Division 1 area where the dam is <br />located. John contacted the owner's representatives and received confirmation that Havana <br />Street Dam had failed from Brad larossi (USFWS Dam Safety Engineer). <br />A conference call was held September 12th at 1900 with representatives from the USFWS, <br />RMA, and the State Engineer's Office. David Lucas, (RMA Manager) gave a report on the <br />condition of all of the dams on the RMA property which include Havana Street, Upper and <br />Lower Derby, Lake Ladora, and Lake Mary as illustrated in Figure 1. At that time David <br />indicated he felt the inflow onto the RMA was decreasing and the remaining dams were not in <br />danger of failure. He said the spillway of the Havana Street Dam activated at 06:30 a.m. that <br />morning and the reservoir filled to within 1 -ft of the crest of the dam. Failure of the spillway <br />was noted to begin at 10:30 and the dam was completely breached at 11:15 a.m. The <br />emergency spillways of Lake Mary and Lake Ladora were also activated but no damage was <br />done. The concern at that time was the railroad embankment located downstream of <br />Havana, Lake Ladora, and Lake Mary. The outflow from these dams was being stored behind <br />the embankment and if it were to breach would cause a significant amount of flooding in <br />Commerce City. This embankment has a 3 -ft diameter culvert that was releasing water, but <br />the level of the pool was not dropping. Pumps were brought in to help relieve pressure and <br />by September 14th the water began to recede. David Lucas later reported that the railroad <br />embankment was never overtopped. <br />A timeline of events prepared by RMA staff is provided in Appendix B (RMA, 2013). <br />Based on data collected from witnesses and the field investigation, the following event tree is <br />postulated as the probable sequence of events which led to the failure of the Havana Street <br />Dam: <br />04> Precipitation event in tributary basin generates significant inflows to the reservoir <br />q Reservoir fills enough to initiate discharge through the emergency spillway