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l <br />Western Sugar Reclamation Land Development Project <br />Flood Analysis <br />Results for this scenario are summarized in Table 2 which indicates that only minimal <br />headcutting and erosion will occur before the pit tailwater elevation meets that of the floodplain <br />elevation whereby headcutting and erosion will not occur. <br />Table 2. WinDAM B Results Summary for 100 - foot -Wide Berm — Considering Pit <br />Tailwater <br />Parameter <br />Case <br />Weakest i <br />Time to <br />Headcut to <br />River <br />(hrs) <br />Best N/A 10 20 * 20 15 <br />Strongest----- - - - - -- -- - - - - -- ----- - - - - -- -- - - - - -- ---- - - - - -- <br />V. PIT FILL TIME <br />Tract C pit fill time is based on a combination of groundwater inflow rate with no pumping plus <br />flood flow — due to overbank flow from a 100 -yr flood - into the pit. This information is <br />presented in the Appendix. <br />Note that the calculations were based on average groundwater inflow and ultimate pit volume <br />(for conservatism). If a detailed reservoir routing were performed that considers inflow and pit <br />volume at various time increments, the pit fill time would be less. <br />VI. FLOOD WARNING TIME <br />The Colorado Flood Threat Portal ( http : / /www.coloradotloodthreat.com/ issued by the Colorado <br />Water Conservation Board (CWCB) includes a daily statewide flood threat bulletin and map, 7- <br />15 day flood threat outlook, and statewide 24 -hr precipitation map. <br />Should a large flood be imminent, appropriate flood threats will be issued by CWCB. As an <br />example, should a storm similar to the 1947 thunderstorm discussed above occur, there would be <br />approximately 5 — 7 days (June 17 — June 23) to issue a flood threat as the flood hydrograph <br />begins rising (around June 17th). In addition, from June 8 — 16, there is an antecedent flood <br />p9. 10 <br />Time to <br />Max Headcut <br />Max <br />Max <br />Max <br />Length at Top <br />Headcut <br />Headcut <br />Headcut <br />of Berm <br />Width <br />Depth <br />(hrs) <br />(ft) <br />(ft) <br />(ft) <br />Best N/A 10 20 * 20 15 <br />Strongest----- - - - - -- -- - - - - -- ----- - - - - -- -- - - - - -- ---- - - - - -- <br />V. PIT FILL TIME <br />Tract C pit fill time is based on a combination of groundwater inflow rate with no pumping plus <br />flood flow — due to overbank flow from a 100 -yr flood - into the pit. This information is <br />presented in the Appendix. <br />Note that the calculations were based on average groundwater inflow and ultimate pit volume <br />(for conservatism). If a detailed reservoir routing were performed that considers inflow and pit <br />volume at various time increments, the pit fill time would be less. <br />VI. FLOOD WARNING TIME <br />The Colorado Flood Threat Portal ( http : / /www.coloradotloodthreat.com/ issued by the Colorado <br />Water Conservation Board (CWCB) includes a daily statewide flood threat bulletin and map, 7- <br />15 day flood threat outlook, and statewide 24 -hr precipitation map. <br />Should a large flood be imminent, appropriate flood threats will be issued by CWCB. As an <br />example, should a storm similar to the 1947 thunderstorm discussed above occur, there would be <br />approximately 5 — 7 days (June 17 — June 23) to issue a flood threat as the flood hydrograph <br />begins rising (around June 17th). In addition, from June 8 — 16, there is an antecedent flood <br />p9. 10 <br />