US Army Corps of Engineers Omaha District Yellowtail

US Army Corps of Engineers Omaha District Yellowtail Flood Pool Reallocation Study Travis D. Yonts Water Resource Engineer U. S. Army Corps of Engineers Omaha, Nebraska Bighorn River System Issues Group July 29, 2008 1

US Army Corps of Engineers Omaha District Presentation Overview • Project background • Computer simulation efforts – What has been done to this point? • What’s next? • Questions 2

US Army Corps of Engineers Omaha District Project Objective • Evaluate the change in flood reduction benefits due to reallocation of flood control storage to joint use storage for Yellowtail Dam and Bighorn Lake. 3

BIGHORN LAKE STORAGE ALLOCATION US Army Corps of Engineers Dam Crest Omaha District Elev. 3660. 0 Surcharge - 52, 829 Acre-Feet 3657 (1, 328, 360 AF) Exclusive Flood Control - 258, 331 Acre - Feet 3640 (1, 070, 029 Acre - Feet) Joint Use - 240, 342 Acre - Feet 3614 (829, 687 Acre - Feet) Active Conservation - 336, 103 Acre - Feet Top of Conservation Elev. 3547. 00 (493, 584 Acre - Feet) Inactive Conservation - 477, 576 Acre - Feet Top of Dead Elev. 3296. 50 (16, 008 Acre - Feet) Dead - 16, 008 Acre - Feet 4

US Army Corps of Engineers PROPOSED STORAGE ALLOCATION Dam Crest Omaha District Elev. 3660. 0 Surcharge - 52, 829 Acre-Feet 3657 (1, 328, 360 AF) Exclusive Flood Control - 190, 846 Acre - Feet 3645 (1, 137, 514 Acre - Feet) Joint Use - 307, 827 Acre - Feet 3614 (829, 687 Acre - Feet) Active Conservation - 336, 103 Acre - Feet Top of Conservation Elev. 3547. 00 (493, 584 Acre - Feet) Inactive Conservation - 477, 576 Acre - Feet Top of Dead Elev. 3296. 50 (16, 008 Acre - Feet) Dead - 16, 008 Acre - Feet 5

US Army Corps of Engineers Omaha District HEC-Res. Sim (Reservoir Evaluation System-Simulation) • • Single or multiple reservoir systems Flood control Hydropower Water supply (M&I, irrigation, etc) Diversions Navigation Flow targets (max & min) POR or event simulation 6

US Army Corps of Engineers Omaha District • • • Data Requirements Daily stream flow 1967 -2007 Daily reservoir inflow, outflow, storage Daily precipitation, evaporation Elevation-area-capacity relationships Spillway & outlet rating curves Downstream discharge-damage functions Reservoir operating criteria/storage zones Project design floods Local flow calculations 7

US Army Corps of Engineers Yellowtail Downstream Control Points Omaha District Sidney Miles City Bighorn hor n. R ive r to s w lo Big Billings Yel r ive R e n St. Xavier Bighorn Lake 8

US Army Corps of Engineers Omaha District Example Res. Sim Outputs • Reservoir elevation • Reservoir releases • Flows at downstream control points 9

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US Army Corps of Engineers Omaha District What’s next? • Continue Res. Sim model calibration. • Perform baseline Res. Sim simulation. – Current conditions • Perform proposed Res. Sim simulation. – Include 5 ft pool raise 12

US Army Corps of Engineers Omaha District What’s next? • Develop analytical relationships for baseline and proposed simulations. – Pool probability, pool duration – Flow frequency, flow duration – Compute net flood benefits • Determine impact of pool raise on project design flood. • Evaluate change in flood reduction benefits. 13

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