The existing Sacramento River basin bypass system is the backbone of the Sacramento River Flood Control Project, as it conveys peak flood flows through the Sacramento Valley and to the Sacramento-San Joaquin River Delta. The bypass system currently includes the Sutter and Yolo bypasses and their primary control features – the Moulton, Colusa, Tisdale, Fremont, and Sacramento weirs/bypasses. The State of California is beginning to look at expanding portions of the bypass system, to increase its capacity and subsequently decrease peak flow likelihoods in mainstem rivers that run through communities in the Sacramento Valley and Delta regions. This is particularly important with the uncertainty of future flood frequencies, in part due to climate change. This study creates a pre-reconnaissance model of the Sacramento Valley flood management system to provide rapid preliminary modeling, conceptual understanding, and proof of concept regarding how critical components of this system interact during major storms to protect different parts of the Sacramento Valley, and how expansions of various elements of the system may reduce flood damage at various locations. The expansions included in the model increase the overall capacity and flexibility of the bypass system to deal with higher flood flows in a range that have a significant probability of future occurrence. In addition, the expansions reduce the cumulative flood damages expected during large floods. The software used in this study is HEC-ResFloodOpt (Hydrologic Engineering Center’s Reservoir Flood Control Optimization Program). The improvements examined include widening of the Sutter Bypass, Fremont Weir, Yolo Bypass, Sacramento Weir/Bypass, the addition of Cherokee Bypass, and several combinations of those expansions. It was found that, of all the expansions to the system, the Fremont Weir is the “bottleneck” of the Sacramento River Flood Control Project and the widening of this feature has potential to greatly reduce expected flood damages from extreme events.