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Fort Morgan Farms,LLC Delta Reservoir—West Cell Preliminary and East Cell Conceptual Design April 16,2021 elevation of 4607 feet is 4,562.15 AF. The design for West Cell is shown in Figure 1 in Appendix 1. The inflow spillway is 200 feet long and the outflow spillway is 170 feet long. Restricting the area available for flow to enter the reservoir causes the velocity and water surface elevation to rise through the spillway. To address this, fuse plugs were designed at both the inflow and outflow spillways to collapse when the upstream water surface elevations reach 4607 feet. The fuse plugs were included to prevent flows from smaller magnitude flood events from entering the reservoir, but they also provide the additional benefit of adding 355 AF to the existing storage to provide a total potential of 4,562.15 AF. It is not recommended to store water at the total potential storage for sustained periods as it may cause stress on the fuse plugs. During the 1-PAC storm event, the maximum flow through the inflow spillway reaches about 5500 cfs and 5500 cfs through the outflow spillway. The inflow spillway was designed to convey sufficient flows so as to not impact the existing floodplain elevation. Hydrographs of the inflow and outflow spillways are presented in Figure 6 in Appendix 1. East Cell Design The East Cell is located immediately east or downstream of the West Cell. It was designed to capture spill flows from the West Cell, and overflows from the SPR during the 1-PAC flood and prevent encroachment from smaller magnitude floods (roughly less than 25-year storm) in SPR. The berms around East Cell were designed to prevent overtopping of the crest during 1-PAC flood. The East Cell berm was designed to be minimum 30 feet wide at the top with embankment slopes down each side at 3H:1 V, and the berm top elevation range between 4606.0 and 4609.0 feet elevation to prevent CLPR channel flows from overtopping the berm and to allow for flows to enter/exit through the opening on the SPR side of the cell. The outflow spillway along the southeast of the reservoir has a crest length of approximately 2,500 feet and is proposed to match existing ground. The maximum storage at the spillway crest elevation of approximately 4602 feet is 6,441 AF. The design for East Cell is shown in Figure 2 in Appendix 1. During the 1-PAC storm event, the maximum flow through the outflow spillway reaches about 4500 cfs. The outflow spillway was designed to convey sufficient flows so as to not impact the existing floodplain elevation. Hydrograph of the outflow spillway is presented in Figure 6 in Appendix 1. Bank Stability Design Bank stability was evaluated at critical areas located along northwestern face of the storage area adjacent to the CLPR, the inside bank where flows from CLPR enter the storage area, and the spillway where flows exit the storage area. The bank stability assessment was performed using the Hydraulic Toolbox (version 4.4) created by the Federal Highways Administration (FHWA). To meet stability requirements, riprap was selected to armor critical areas of the embankment fill along the spillway crests and fill revetment adjacent to the CLPR and SPR. The riprap will be underlain by a granular filter to prevent the failure of riprap due to potential for fine particles bleeding through riprap voids. The riprap design was accomplished using the methods described in Chapter 8 of the Urban Storm Drainage Criteria Manual (USDCM) Volume 1 (Urban Drainage Flood Control District, 2016). To transport approximately 5500 cfs, reinforced concrete was selected to line the inside crest and the embankment of the inflow and outflow spillways for the West Cell. Reinforced concrete protects the inside embankment of the inflow spillway from the increased velocity F M F_Tech Memo-20210416.docx Galloway&Company, Inc. Page 5 of 7