In this chapter we examine the impact of main-stem hydraulic engineering on large alluvial rivers, which are primarily developed for flood control and navigation. The lower Mississippi and Rhine Rivers provide interesting comparisons and serve as primary case studies. Each major type of hydraulic engineering is systematically examined, including channel cut-offs, groynes, and revetments, among others. Following, each channel engineering measure is reviewed from the perspective of erosional and depositional processes that degrade river environments. An overarching theme is the importance of sedimentology in augmenting or reducing the influence of hydraulic engineering. An important narrative is the unintended geomorphic and environmental consequences of channel engineering, which requires new management strategies within several decades. While rivers rapidly respond to emplacement of hydraulic infrastructure, because each river basin consists of a unique combination of physical controls and human influences, implementing channel engineering along lowland rivers is ultimately a large experiment that requires many decades to unfold.