Millions of dams fragment and degrade Earth’s riparian landscapes. This chapter examines linkages between dams, rivers, and the environment and is subdivided into three sections, including riparian impacts of dams, dam removal, and reservoir sediment management strategies. The latter is crucial to sustain downstream fluvial environments and water resource infrastructure. Trapping of fluvial sediments in upstream reservoirs results in downstream degradation of riparian environments by channel bed incision and terrestrialization of aquatic habitat. In North America and western Europe dam removal for environmental restoration is occurring at a brisk pace, but in Southeast Asia, South America, southeast Europe, and parts of Africa dam construction for hydropower is rapidly occurring. Dam removal is an emerging science with great potential to improve downstream riparian ecosystems. It is essential that government agencies develop strategies to sustainably manage reservoirs so that fluvial sediments can be reactivated and transported to downstream riparian and deltaic environments to offset subsidence and sea level rise.

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.