This chapter explains the aims of patient positioning and the complications that can arise from incorrectly positioning patients as well as the physiological changes different positions can cause. The correct positioning and alignment of limbs for surgical procedures is vital, and all perioperative practitioners should understand their role and responsibility for safe patient positioning, and the rationale for it. Safe patient positioning is always a multidisciplinary team effort, whereby all members of the perioperative team should be present in the operating theatre at the crucial moment.

This chapter examines the dynamics of meandering rivers, including the initiation of meandering in straight channels; the development of bar units; and the relation of these units to pools, riffles, and point bars. It reviews theories of pool-riffle development and maintenance; flow through meander bends, including the influence of channel curvature and the point bar on flow structure; and the relation of the spatial pattern of shear stress in curved channels to patterns of erosion and deposition, to the development of bar unit topography, and to patterns of bank erosion. Mechanisms of bank erosion are introduced, emphasizing that bank erosion occurs in different types of rivers. Modes of planform deformation on meandering rivers are explored, as well as the factors that influence planform migration dynamics in meandering rivers. The discussion includes a basic introduction to numerical models of meandering rivers and attempts to integrate models of flow and sediment transport in curved channels with models capable of simulating bank erosion and lateral migration of meandering rivers. The chapter also briefly discusses meandering of mixed bedrock-alluvial rivers.

This chapter examines the characteristics and dynamics of river floodplains. The view of the floodplain as an integral part of the river system is developed, including the role of overbank flows and lateral movement of channels across floodplains in floodplain dynamics. Major depositional mechanisms on floodplains, including lateral accretion and vertical accretion, are reviewed along with erosional processes that can affect certain types of floodplains, resulting in localized scour or catastrophic stripping, in relation to distinct planform types. Characteristic sedimentological assemblages are introduced in relation to distinct planform types, including meandering, braided, wandering gravel-bed, and anastomosing rivers. Three-dimensional alluvial architecture of floodplains is highlighted and examples provided of how this architecture can be used to interpret floodplain alluviation history and changes in the depositional dynamics of river/floodplain systems over time. The chapter also examines the classification of floodplain types in relation to fluvial energy regimes and the factors controlling spatial variations in floodplain extent and volume.