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Fort Morgan Farms, LLC <br /> Delta Reservoir—West Cell Preliminary and East Cell Conceptual Design <br /> April 16,2021 <br /> Existing(Pre-Project) Conditions 2D Hydraulic Model <br /> The pre-project conditions 2D hydraulic model simulates flows through a composite surface <br /> created from LiDAR collected in 2018 for the USGS 3D Elevation Program, and ground <br /> survey collected by AW in 2019. This model served as the basis for comparison with post- <br /> project design model. <br /> Proposed(Post-Project) Conditions 2D Hydraulic Model <br /> The 2D hydraulic model of the proposed design modifies the existing condition with the Delta <br /> West and East Storage designs. The proposed design surface was incorporated into the <br /> existing condition 2D hydraulic model to assist in the design of the spillway, berm and erosion <br /> protection. The 2D hydraulic model for the proposed conditions includes an inflow spillway <br /> with gates at each spillway designed to open at an upstream water surface elevation of 4607 <br /> feet (NAVD 88) to simulate fuse plugs. Compared to the existing conditions, the water <br /> surface elevations in 2D model decrease for the proposed conditions. <br /> Preliminary/Conceptual Design <br /> The proposed design was developed considering the impacts on Poudre River and South <br /> Platte River floodways while meeting the water storage needs. The proposed storage cells <br /> are located between cross-sections 7477 and 1235 on CLPR and between cross-sections <br /> 1403473 and 1398191 on SPR in 1 D models. Storage cells are bisected by cross sections <br /> 6758 thru 1235 on CLPR and cross sections 1402708 thru 1399218 on SPR. <br /> The proposed design was evaluated fundamentally on the basis that it does not increase (0.0 <br /> feet) the water surface elevation of the floodway to meet the regulatory standards of Weld <br /> County and FEMA while increasing the potential storage capacity. The details for the <br /> proposed design are included in Figure 1 and Figure 2 in Appendix 1. <br /> The preliminary/conceptual design was developed to reduce the amount of erosion protection <br /> needed for the 1-PAC flood. Allowing flows from the 1-PAC storm event while preventing <br /> smaller, more frequent flows from entering the storage cells was also considered during the <br /> design. <br /> West Cell Design <br /> An inflow weir or spillway for the West Cell was developed to divert CLPR flows through a <br /> constrained area into the cell during the 1-PAC flood and prevent encroachment from smaller <br /> magnitude floods (roughly less than 25-year storm), and prevent flows from overtopping the <br /> berm crest during the period where the reservoir is filling up. The West Cell berm was <br /> designed to be minimum 30 feet wide at the top with embankment slopes down each side at <br /> 3HAV, and minimum 4608.5 feet elevation to prevent overtopping and divert flows. <br /> The inflow spillway is located on the Northwest side of the reservoir and the outflow spillway <br /> is located on the Northeast side. Fuse plugs are proposed at each spillway to prevent water <br /> from more frequent storm events (about 25-year storm) from entering through the spillways <br /> while providing additional potential storage. The maximum storage at the spillway crest <br /> elevation of 4602 feet is 4,207.15 AF. The maximum potential storage at the fuse plug top <br /> F M F_Tech Memo-20210416.docx <br /> Galloway&Company, Inc. Page 4 of 7 <br />