Land Use and Land Cover Impact on Probable Maximum Flood and Sedimentation for Artificial Reservoirs: Case Study in the Western United States

Abstract

Unanticipated peak inflows that can exceed the inflow design flood (IDF) for spillways and result in possible storage loss in reservoirs from increased sedimentation rates lead to a greater risk for downstream floods. Probable maximum precipitation (PMP) and probable maximum flood (PMF) are mostly used to determine IDF. Any possible change of PMP and PMF resulting from future land use and land cover (LULC) change therefore requires a methodical investigation. However, the consequential sediment yield resulting from altered precipitation and flow patterns into the reservoir has not been addressed in literature. Thus, this study aims to determine the combined impact of a modified PMP on PMF and sediment yield for an artificial reservoir. The Owyhee Dam of the Owyhee River watershed (ORW) in Oregon is selected as a case study area for understanding the impact of LULC change on PMF and sedimentation rates. Variable infiltration capacity (VIC) is used for simulating streamflow (PMF) and the revised universal soil loss equation (RUSLE) to estimate sediment yield over ORW as a result of change in precipitation intensity and LULC. Scenarios that represent pre-Owyhee Dam (pre-dam) and post-Owyhee Dam (post-dam; nonirrigation, control) are used to simulate PMF’s and consequential sediment yield. Peak PMF result for pre-dam scenarios increased by 26 (1%) and