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Floodplain Development Permit Package,July 2019 <br /> 3.4. DISCUSSION AND CONCLUSIONS <br /> Both models show a reduction in the BFE through the excavation area and a rise in BFE through the spoil <br /> area.These differences are reported highest in the 1-D model, likely due to lack of accommodation of the <br /> design topography in existing cross section locations and the breakdown of 1-D modeling assumptions in <br /> the dynamic nature of a river confluence.The 1-D model was not altered, as adding cross sections affect <br /> the existing condition hydraulic results. The project 2-D model is more appropriate for characterizing <br /> complex flow paths exhibited during high-flow events at the confluence of two rivers and has updated <br /> bathymetry to support this effort.The project 2-D model more accurately depicts the flow routing through <br /> the project and between the two rivers through higher resolution topography and hydraulic <br /> computations. The stage differences reported by the 2-D model show a max rise of 0.33 ft at XS 5853, <br /> at the upstream end of the spoil location.The BFE shows a max decrease of-0.77 ft at XS 3839, near the <br /> upstream end of the excavation reach. These reported changes are lower and attenuate more quickly <br /> than the 1-D results due to the ability to accurately route flow through the dynamic nature of this river <br /> confluence and the lack of need for 1-D modeling assumptions to accommodate these complexities. <br /> 4. WORKS CITED <br /> CDM Smith (2016). Middle South Platte River Restoration Master Plan. Denver, CO. <br /> Colorado Water Conservation Board (CWCB) (2017a). Colorado Hazard Mapping Program, Hydraulic <br /> Analysis Technical Support Data Notebook for the Big Thompson Watershed(HUC-810190006). CHAMP <br /> Y1 Hydro TSDN - Big Thompson. rile/37e8176f-ffau .w� <br /> ele2eb4ec41E <br /> Colorado Water Conservation Board (CWCB) (2017b). Colorado Hazard Mapping Program, Hydraulic <br /> Analysis Technical Support Data Notebook for the South Platte River. CHAMP Hydrology TSDN, <br /> http://coloradohazardmapping.com/File/7668a8d4-9065-4951-95aO-2d35668282? <br /> Colorado Water Conservation Board (CWCB) (2017c). Colorado Hazard Mapping Program,Y1-BigT- <br /> Hydra Models: BTR_1A.PRJ 1/File/6c2f2ffc-e2b6-4328-acdc- <br /> 16b3f11aaf9e <br /> Federal Emergency Management Agency (2013). Post-Flood DEM FINAL, October 16, 2013. <br /> Federal Emergency Management Agency(2014). Post-Flood Reflight DEM FINAL. October 1, 2014. <br /> n«ps://geUQd La.CU.Kuv/, <br /> U.S. Army Corps of Engineers, Hydrologic Engineering Center(2016). HEC-RAS, River Analysis System, 2D <br /> User's Manual, Version 5.0. Davis, CA <br /> Headwaters Corporation 7 of 7 <br />