Levees in California's Central Valley currently face an unacceptable high level of risk. Many agencies are now attempting to analyze the probability of levee failure and the resulting flooding and damages. The California Department of Water Resources (DWR) is currently evaluating the flood risk associated with the approximately 1,600 miles of State Plan of Flood Control levees throughout California's Central Valley. The objective of this study is to present a methodology for determining floodplains associated with various potential levee breaches. Middle Creek and its tributaries contain 13.5 miles of levees that protect the town of Upper Lake in Northern California. According to DWR's Flood Control System Status Report, many of these levees have a high potential for failure. This study will utilize the most current topographical and survey data that is available from DWR to develop the hydraulic models. vi The modeling software used for this study includes the United States Army Corps of Engineers Hydrologic Engineering Center- River Analysis System (HEC-RAS) and FLO-2D, developed by FLO-2D Software, Inc. These softwares are used to model the one-dimensional channel flows and two-dimensional overland flood flows caused by levee breaches. The popularity of two-dimensional hydraulic models has grown substantially in recent years. These two-dimensional models have benefitted from increased computing power which has resulted in faster simulation times and lower project costs. The hydraulic models for this study were developed to be consistent with the recommendations made by the DWR Hydrology and Hydraulics Coordination Work Group, which is a team of leading hydraulic modelers in California. The results of the model simulations are presented as water surface profiles and floodplain depth and velocity maps for the 100- and 500-year flood events.