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.

This chapter reviews fundamental fluvial processes and concepts to provide a basis for subsequent chapters oriented toward understanding environmental impacts of lowland river management. The goal of this chapter is to review relevant fluvial processes from a drainage basin perspective, including headwater, transfer, and deposition zones. Human impacts across headwater landscapes, especially improper agricultural and mining practices, causes upstream land degradation that can drive downstream fluvial adjustment with adverse consequences to riparian environments. Several regional land degradation case studies are briefly introduced to provide a link with downstream impacts. Characteristics of alluvial river channel patterns are reviewed to afford a perspective for considering several modes of fluvial adjustment to upstream impacts and hydraulic engineering of lowland rivers, which provides a segue to Chapter 3.

Having systematically reviewed a comprehensive range of management measures across a wide range of rivers this chapter provides an overview of lessons learned to inform future management strategies. Key lessons are elucidated that relates to (i) urban flood management, (ii) the role of floodplain sedimentology in the design of effective hydraulic infrastructure (iii), the unintended geomorphic consequences of hydraulic engineering (iv), the palimpsest of floodplain management (v), dam removal and reservoir management and (vi), linkages between geodiversity and biodiversity. These lessons pertain to three main fluvial environments, including fluvial adjustment of channels, embanked floodplains, and flood basins and deltas. The study concludes by discussing reasons for concern and reasons for optimism as regards future management of lowland river environments.

This chapter singularly focuses on the impacts of dikes (levees), including their design, management, and influence on hydrologic and fluvial sedimentary processes. Floodplain embankment commonly removes ~75% of the natural floodplain from annual flood pulse dynamics. Flood control by embankment fundamentally alters fluvial processes between, along, and beyond dikes. Over longer timescales dikes result in a unique floodplain environment characterized by distinctive morphologic, hydrologic, and sedimentary features that do not exist on natural floodplains. Dike breach ponds are distinctive hydrologic features along dikes that provide valuable ecosystem services. Embanked floodplains trap flood deposits that results in thicker and somewhat coarser flood deposits, which buries natural wetlands and infills floodplain lakes. This results in a channel belt ‘perched’ above low-lying flood basins, which increases the risk of avulsion. The chapter closes by integrating concepts related to channel engineering (Chapter 5) and floodplain embankment to arrive at an evolutionary model for engineered rivers, which provides a segue to flood basin management (Chapter 7).

This chapter examines modern approaches to river management as an alternative to traditional hard engineering that disconnected rivers from floodplains and degraded river environments. A range of measures are systematically reviewed to both reduce flood risk and improve river environments. The key measures reviewed includes meander bend reconnection, flood water retention, dike setback, groyne lowering, sediment diversion structures, and sediment replenishment. The latter approach is utilized along sediment starved rivers because of being fragmented by upstream dams (Chapter 4). Collectively, new measures are being adapted to an international range of rivers, and particularly along the Rhine River in accord with the EU Water Framework Directive. The tragedy of wetland loss at the Mississippi delta is examined with regards to coastal restoration, and in particular sediment diversion structures aligned with historic subdelta geomorphology and natural sedimentary processes. Integrated river basin management utilizes multiple approaches, including soft and hard engineering, with stakeholders having an important role in shaping the direction of river management.