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Runoff transformation performed with unit hydrographs in accordance with <br />guidance from US Bureau of Reclamation Flood Hydrology Manual (Cudworth, <br />1989) and HBRPEG (Sabo[, 2008). The Clark UH was selected for the basin <br />tributary to Havana Street since the basin was mostly urbanized. The <br />remainder of the basins utilized the Urban Unit Hydrograph presented in <br />Cudworth. <br />Channel routing elements incorporated to convey runoff through the basin to <br />the various ponds with Kinematic Wave routing method. <br />Reservoirs modeled based on stage - storage and stage - discharge relationships <br />from information in the UDFCD Irondale Gulch Outfall Systems Plan ( UDFCD, <br />2011). <br />HMS generated an inflow hydrograph to the reservoir for use in the RAS breach <br />model and subsequently the HMS breach model. <br />7.3 Dam Breach Modeling <br />A HEC -RAS model of the reservoir and spillway was developed based on surveyed <br />sections, surveyed breach geometry, original spillway geometry, estimated breach <br />development time of 45 minutes based on field observations by RMA staff (RMA, 2013), <br />and calculated inflow to the reservoir from the HMS rainfall - runoff model. This <br />analysis was initially performed in RAS because the breach algorithm in RAS is trusted <br />more than the breach algorithm in HMS and because RAS can take into account <br />tailwater affects on breach flow to account for potential submergence. The results of <br />the RAS analysis showed that the breach of this dam was not sensitive to tailwater and <br />the HMS algorithm was modeling the breach hydrograph in a similar fashion as <br />illustrated in Figure 11 below. The determination was therefore made to simulate the <br />breach in HMS for the final model to allow for easier comparisons of different sources <br />of runoff. Details of the HMS modeling are presented in Appendix G. <br />Breach parameters were determined based on observations made during the post <br />breach field investigation, video evidence of the breach in progress provided by the <br />Denver Post and on anecdotal evidence gathered from RMA staff. DSB standard breach <br />analysis spreadsheets were also used, but ultimately, the predicted parameters from <br />the empirical equations in these sheets were not used due to the actual observations <br />of the breach being more reliable. The parameters input to the HMS model to <br />simulate the breach are summarized in Table 1 below.