Abstract
More than 7 million people and $580 billion in assets are exposed to hazard of flooding in California. All 58 counties have experienced at least one major flood events in the last 20 years resulting in loss of life and property damages. California’s diverse geography contributes to the states significant flood risks. In particular, California’s central valley is one of the most flood prone areas in the world. The largest flood volume in many parts of California occurs in a very short timeframe and spells disaster. Flooding resulted in loss of lives and billions of dollars in damages in general. Despite effective investments in improving flood management techniques and infrastructure flood risk remains high and could increase due to population growth, economic development and climate change. The communities along the Yuba and Feather Rivers have a long history of catastrophic flooding. Oroville and New Bullard’s Bar are two main reservoirs that manage flood runoff volumes of the Yuba-Feather basins and provide flood protection downstream along the Yuba and Feather River systems in conjunction with the flood control levee-system. However, these reservoirs may lose control in the faces of extreme storm weather conditions. This may impair the conveyance capacity of the flood control system and cause catastrophic flooding resulting damages to property and lives. The study investigates reservoir operation under extreme hydrologic conditions due to climate change with a view to inform flood management planning for the Yuba-Feather watershed. And to improve the understanding of flood protection for communities along the Yuba-Feather River and downstream through flow forecasting and coordinated operation reservoir. The study adopts and utilizes the HEC-RESSIM reservoir models for Lake Oroville and New Bullard’s Bar Reservoir systems including their headwater reservoirs and the Yuba-Feather River systems. A set of base and future climate change inflow scenarios are simulate using the HEC-RESSIM model for Yuba-Feather reservoirs and channel systems. The projections of median changes in temperature and precipitation over the course of the 21st century consist of three future periods to reflect near-century, mid-century, and end of century changes. Projected changes for the future periods of 2011-2040 (2025), 2041-2070 (2055), and 2070-2099 (2085) are compared to the historical climatological period of 1981-2010. The simulated reservoir storages, peak outflow, and downstream impacts are compared between the base condition scenario and corresponding climate change conditions to investigate how climate changes affects the level of runoff management by the reservoir operations and how it influences the downstream flood flows and protections. The study showed the estimated flood runoff is expected to increase by 6.31%, 10.05%, and 15.78% at the Oroville Reservoir on the Feather River for Near-Century (2025), Mid-Century (2055), and Late-Century (2085), while elevation changes will increase 0.49%, 0.56%, and 0.67%, respectively. Similarly, the estimated flood inflow is expected to increase at New Bullard’s Bar Reservoir by 4.30%, 12.99%, and 17.32%, for the three climate change scenarios respectively compared to the base climate condition. While the reservoir elevation will increase 0.18%, 0.53%, and 0.65%, respectively. The peak flood flows at the Feather River and Yuba River confluence junction is expected to increase by 1.10%, 1.96%, and 7.03%, respectively.